Friday 16 November 2018
Thursday 25 October 2018
Tuesday 7 August 2018
Saturday 28 July 2018
Monday 16 July 2018
Sunday 1 July 2018
Saturday 2 June 2018
Thursday 24 May 2018
Friday 27 April 2018
Thursday 26 April 2018
Biodiversity
BIODIVERSITY
Biodiversity is the abbreviated word for Biological diversity. This was first put forward by Norse and Mc manus. The term biodiversity was coined by W.C Rosen.
Definitions : Biologists most often define biodiversity in terms of species richness and species diversity . In 1992 United Nations earth summit in Rio de Janerio defined Biological diversity as the variability among living organisms from all sources including inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. This definition includes diversity within species, between species. This definition was adopted by United Nations convention on biological diversity. The second most commonly used definition of biodiversity is sponsored by Global biodiversity strategy “the totality of genes, species and ecosystems of a region”
Concepts of biodiversity:
i). Biodiversity is the variety of life on earth.
ii). It is generally described at three levels – Genetic diversity, species diversity and ecosystem diversity
iii) All life forms that make biodiversity, including humans are ultimately connected to all other life forms and to their physical environment.
iv). No one living element of any ecosystem can survive independently on others.
v). Connections among living and non living elements keep the environment functioning and healthy.
vi). Human impact on the environment directly or indirectly effect the functioning of other living things and by extension ourselves.
Scope of biodiversity:
i).The science of biodiversity has the potential to unify all fragmented disciplines of biology and bring together the activities of all scientists.
ii). Biodiversity is the back bone for agriculture, aquaculture, animal husbandry, forestry and a host of other applied branches of biology. Thus helping in the adequate supply of food grains and main needs for the population.
iii). Alarming changes due to intense globalization can be nullified by the deep understanding of biodiversity in all aspects.
iv). Biodiversity will offer in the coming years new sources food, medicine and other requirements.
v). Biodiversity is the resource on which all human existence depends. Biodiversity is the pillar of human development.
vi). Sustainable development can be achieved through economic, environmental, social and cultural facets of biodiversity.
Q. Write about Earth Summit.
Earth summit:
The 20th anniversary of Stockholm declaration took place in Rio de Janerio in Brazil in 1992. The UN conference on environment and development popularly known as earth summit. The assembled leaders signed the convention on climate change and the convention on biological diversity. They also endorsed the Rio declaration and the forest principles and adapted azanda 21 to plan for achieving sustainable development in the 21st century.
Earth summit 2002 (Rio +10): The world summit on sustainable development was held in Johannesberg of South Africa in 2002. Its main aim is to examine the progress made on the outcomes of the 1992 Earth summit in Rio and also reinvigorate the world’s people towards the true sustainable development.
Earth summit 2012 (Rio +20): The UN general assembly in December 2009 agreed to hold a new earth summit in 2012. This summit held in Brazil and will focus on the green chemistry emerging issues, sustainable development, governance and review of previous commitments.
Q. Write an essay on the levels and types of Biodiversity.
LEVELS AND TYPES OF BIODIVERSITY
Biodiversity or biological diversity is the sum total of all life on earth. It includes the vast array of life forms, then individual genetic makeup, their life processes and their interrelation ship in communities and ecosystems.
Biodiversity is commonly studied at three different levels. i). Genetic diversity, ii). Species diversity and iii). Ecossystem diversity. These three levels of Biodiversity form an intricate web.
i). Genetic diversity:
Genetic diversity refers to the variation of genes with in species. This covers genetic variation between distinct populations of the same species. It also covers genetic variation with in a population. Genetic diversity can be measured using a variety of DNA based techniques like Restriction fragment like polymorphism (RFLP), Polymerase chain reaction (PCR), Serial analysis gene expression (SAGE). Individuals belonging to a species share contain characteristics, but genetic variations determine the particular characteristics of individuals with in a species. The genetic makeup of an individual species is not static but it changes as a result of both external and internal factors. The main forces that determine current levels of genetic diversity within species are mutations, migration, selection and genetic drift.
ii). Species diversity:
Species diversity is related to number and relative abundance of species in a given area in a community. Species diversity is the highest in the equatorial region and gradually declines towards the Polar Regions. Species diversity is essential for the proper functioning of communities in an ecosystem. The species diversity of a region is measured on the basis of species richness (number of species in a defined area), species abundance (relative number in each species) and phylogenitic diversity (relationship between different groups of species). Greatest species richness is commonly found in relatively stable environments having high rates of productivity.
There are three perspectives of diversity at community level. They are alpha diversity, beta diversity and gamma diversity.
(a). Alpha diversity: It is the species diversity within a community or habitat. It is also defined as the variety of organisms occurring in a particular habitat. It is often called as local diversity. It is measured as the number of species within a given area. Alpha diversity comprises two components i.e, species richness and species evenness.
(b). Beta diversity: It indicates diversity between communities. It is also called differentiation diversity or turn over diversity. Species frequently change when habitat or community changes. There are differences in species composition of communities along environmental gradients.
(c). Gamma diversity: It refers to the diversity of habitat over the total land scape or geographical area. The higher diversity at community level provides stability and productivity. Gamma diversity includes both alpha and beta diversities.
[γ = α + β + Q; where Q= total number of communities; α, β are the average values of alpha and beta diversities respectively.]
iii). Ecosystem diversity: Ecosystem diversity is the highest level of biodiversity. It refers to the variation of different ecosystems such as rain forests, coral reefs. Ecosystem diversity arises due to the variation in energy flow, food chain and water cycle of different ecosystems. The enormous range of terrestrial and aquatic environments on the earth has been classified into a number of ecosystems and the examples tropical rain forests, grass lands, wet lands, coral reefs and mangroves.
All the above components of biodiversity do not work singly, but they work jointly to give rise to the manifestation of biodiversity.
Q. Describe the values of Biodiversity.
VALUES OF BIODIVERSITY
Humans derive many direct and indirect benefits from the living world. Biodiversity or biological resources is the source of food, medicines, pharmaceutical drugs, fibres, rubber and timber understanding the value of biodiversity is required for future conservation plans.
Value of Biodiversity:
The value of biodiversity is categorized basing on the benefit it provides to human society. They include (i) Cultural, social and ethical values and (ii) Aesthetic value
(i) Cultural, social and ethical values:
The cultural value of biodiversity for present and future generations is an important reason for conserving it today. Human cultures all over the globe co-evolved with their environment. So the conservation of biodiversity is essential for cultural density of a human community. Plants and animals are considered to be the symbols of national pride and cultural heritage peacock, tiger and lotus have become national icons of our country. The people should understand and appreciation of the inherent value of each and every life form that constitutes the ethical value of biodiversity.
(ii) Aesthetic value:
Nature has an aesthetic value that can be experienced by human beings when they are in natural surroundings. Nature inspires painters, architects and musicians to create works, reflecting and celebrating its beauty.
(iii) Food Security:
Biodiversity is essential requirement for the maintenance of global food supply. The main sources of human food include animals, fish and plant products. Only the conservation of biodiversity can ensure global food security for the rapidly increasing human population as well as for the animal population. To get the best balanced diet to maintain good health diversified food supply is essential.
(iv) Drugs and Medicines:
Natural flora and fauna are the major sources of pharmaceuticals (medicines) for curing ailments. The Indian system of ayurvedic medicine is dependent on plant biodiversity.
(v) Source of Genes:
Natural populations of different biological species harbour all the genes of a species irrespective of the economic value of the genes. Biodiversity protects the gene pool of a species and acts as a store house of many useful genes. The derivable genes such as resistance to pests, diseases and nematodes stress resisting gene are present in the gene pool of different biological species.
(vi). Ecosystem Services:
Ecosystem services are essential for the survival of the human beings on this planet earth. The world cannot afford to replace these services. Therefore, we must work to protect our ecosystems.
Source of these services provided by ecosystems are as follows:
(i) Air purification-Natural communities maintain proper gaseous concentrations in the atmosphere and prevent rapid climate changes of mainly by air purification.
(ii) Watershed Services-Forests regulate water flows down stream areas.
(iii) Soil formation and protection-Soil formation is promoted by biological weathering of the soil by soil organisms and the soil erosion is prohibited by grass lands and forests, which enables the soil protection.
(iv) Nutrient storage and cycling-Ecosystems perform the vital function of nutrients. Biological diversity is essential in this process.
(v) Potential pest and disease control-Source microbes and plants can act as potential pest and disease control. Which are named as biopesticides.
(vi) Pollution control-Ecosystems and ecological processes play an important in break down and absorption of many pollutants, created by humans and their activities.
(vii) Pollination-Many flowering plants rely on animals for their pollination (Ornithophily pollinating agent is birds) Chaeropteriphily pollinating agents are bats, Malacophily pollinating agents are Molluscans etc.
Q. Describe the various threats to Biodiversity.
THREATS TO BIODIVERSITY
Loss of biodiversity is a serious threat to civilization, second only to thermonuclear war in its severity all other environmental problems like pollution, global warming and ozone depletion can be overcome, but not the erosion of biodiversity or extinction of species.
The prominent threats to biodiversity which can be loss of biodiversity as follows:
1. Destruction of Habitats:- Destruction of natural habitats is the largest single cause of biodiversity loss. Tropical forests, which harbor at least 50% of the world’s biodiversity are declining at a rapid rate with current rate of deforestation 50-90% of earth’s forest inhabiting species is projected to be lost by the mid 21st century. An assessment of world life habited in tropical Asia in 1986 reported that India has already lost about 80% of its natural habitat.
2. Habitat fragmentation:- Habitat fragmentation is another serious problem that often goes unrecognized. Roads, fields, canals, power lines etc. Divide the habitat into small fragments. Fragmentation reduces biodiversity because, many species, such as bears and large cats, require large territories to subsist fragmentation divides the large populations into very small populations. These small populations are vulnerable to catastrophic events. Thus it cause loss to biodiversity.
3. Over exploitation of resources:- The overuse are over harvesting of plants, animals or natural resources threatens earth’s biodiversity. Over exploitation, such as logging, hunting or fishing reduce species number to the level of extinction. The African elephants, whose numbers have drastically declined are ruthlessly killed for their tusks.
4. Introduction of Exotic species:- The introduction of (non native species) exotic species into new areas often creates a problem and for the life of native species and causes the loss of biodiversity. The native species fast to compete with the alien species that grows abundantly. The exotic species may be pests and pathogens which causes elimination of native species. Similarly weedy invaders spread at the expense of the diverse range of indigenous undergrowth species.
5. Pollution:- The environmental pollution causes the loss of biodiversity. The excessive use of pesticides in crop fields have resulted in the decline of the populations of fish eating birds and falcons. Lead poisoning is one of the major cause of mortality of many aquatic birds like ducks, swans and cranes.
6. Poaching:- Specific threats to certain animals are related to large economic benefits. Animals are very seriously affected by this poaching only for the economically important parts.
7. Global environmental changes:- The air pollution causes global warming which effects the distribution of organisms on the earth. It is estimated that the green house effect is expected to threaten 400 species of birds, 660 species of fresh water fish and tens of thousands species of invertebrates and plants.
8. Predator and pest control:- Application of predator and pest control has led to the killing of natural predators of insect pests and spread of other dangerous pests. Thus loss to biodiversity occurs.
It may be concluded that biodiversity is being destroyed mainly by human activities at alarming rates almost in all parts of the earth. If the present rate of loss of biodiversity continues, it is not surprising that many valuable species will become extinct even before they are described and named.
The main effects of loss of biodiversity are (i). Loss of valuable genes. (ii). Loss of cultural diversity. (iii). Loss of ecosystems etc;.
Q. Describe the various modes of conservation of biodiversity.
CONSERVATION OF BIODIVERSITY
The conservation of biological diversity has become a global concern due to rapid destruction of ecosystems and wild life. The most effective mechanism for conserving biodiversity is to prevent further degradation of habitats by human beings. The conservation of biodiversity is essential for the sustainable development. There are two types of conservation strategies – (i). in situ (on site) and (ii). ex situ (off site).
(i). In situ (on site) conseravation :
This is the conservation of biological diversity in their natural habitats through protection of total ecosystem. The in situ approach includes protection of a group of typical ecosystem through a net work of protected areas. The areas which provide protection to biological diversity include protected areas, biosphere reserves, sacred forests and sacred lakes.
1. Protected areas:- They are ecological bio-geographical areas where biological diversity along with natural and cultural resources is protected, maintained and managed through legal or other effective measures. The main examples for protected areas are cold desert (Ladak), hot desert (Thar), Saline swampy areas (Sundarbans). The protected areas provide benefits such as maintaining genetic diversity and viable populations. These protected areas prevent man made introduction of alien species and make it possible for the species to shift in response to environmental changes.
2. National parks:- These are the areas maintained by government and reserved for the welfare of wild life. Cultivation, grazing, foresting and habitat manipulation are not allowed in a national park. There are 92 national parks in India. The first national park in India was the Jim Crbett national park near nainital in 1936.
3. Sanctuaries:- A sanctuary is an area of land, which is reserved for the conservation of animals only. Operations such as collection of forest harvests, harvesting of timber, private owner ship of land, tilling of land etc,. are allowed, provided they donot effect the animals adversely. At present, India gas 492 wild life sanctuaries. (Eg: Nagarjuna sagar sanctuary of Guntur of A.P.)
4. Biosphere reserves:- The man and biosphere (MAB) programme of UNESCO formulated the concept of biosphere reserves in 1975. This programme meant for the conservation of ecosystems and the genetic resources contained therein. People are an integral component of an ecosystem. Biosphere reserves serves as a laboratory for sustainable development. At present there are 13 biosphere reserves in India. (Eg: Sundarbans of west Bengal; Nandadevi of Uttaranchal; Simplipal of Orissa etc.). Each biosphere reserve consists of three zones – Core, buffer and Transition zones.
Core or natural zone: It consists of an undisturbed and legally protected ecosystem. No human activity is allowed in this region.
Buffer zone: It surrounds the core area and is managed to accommodate a greater variety of resource use strategies and research and educational activities.
Transition zone: It is the outer most part of the biosphere reserve, which serves as an area of active cooperation between reserve management and local people without disturbing the ecology.
Biosphere reserve helps in restoration of degraded ecosystems and habitats. They ensure the conservation of lands scapes, ecosystems and species. They ensure culturally, socially and ecologically sustainable development. There is a regular monitoring of development and conservation progress in biosphere reserves. The biosphere reserves provide support for education and research in various ecological aspects.
5. Sacred forests and sacred lakes :- Sacred forests are forest patches around places of worship which are held in high esteem by tribal communities. They are found in several parts of India (Eg: Karnataka, Kerala etc;). Similarly, aquatic life form degradation will be inhibited in sacred lake regions.
(ii). Ex situ (off site) conseravation :
It is conservation of selected rare plants or animals in places outside their natural homes (habitats). For ex situ conservation of biodiversity, germ plasm banks or gene banks are established. There include Botanical gardens, zoos, genetic resource centers, pollen grains, seeds, seedlings, tissue culture banks. Seed gene banks are the easiest way to store germplasm of wild and cultivated plants at low temperatures in cold rooms. Storage of germplasm at ultra low temperature (at a temperature of -196 0C in liquid Nitrogen) is called Cryopreservation. There are more than 1500 Botanical gardens and arboreta. Similarly there are more than 800 zoos around the world.
There are certain draw backs to Ex situ conservation. Ex situ conservation is a supplement to in situ conservation because it cannot recreate the habitat as a whole. Natural evolution and adaptation processes are either temporarily halted or altered, when the species is introduced in an unnatural habitat. Ex situ conservation techniques are often costly.
Significance of Conservation of Biodiversity:-
The main significance of conservation of biodiversity is to provide breeders and genetic engineers with a ready source of genetic material. The plants and animals conserved in botanical gardens, zoos and aquaria can be used to restore degraded land, reintroduce species into wild and restock depleted populations.
Biodiversity is the abbreviated word for Biological diversity. This was first put forward by Norse and Mc manus. The term biodiversity was coined by W.C Rosen.
Definitions : Biologists most often define biodiversity in terms of species richness and species diversity . In 1992 United Nations earth summit in Rio de Janerio defined Biological diversity as the variability among living organisms from all sources including inter alia, terrestrial, marine and other aquatic ecosystems and the ecological complexes of which they are part. This definition includes diversity within species, between species. This definition was adopted by United Nations convention on biological diversity. The second most commonly used definition of biodiversity is sponsored by Global biodiversity strategy “the totality of genes, species and ecosystems of a region”
Concepts of biodiversity:
i). Biodiversity is the variety of life on earth.
ii). It is generally described at three levels – Genetic diversity, species diversity and ecosystem diversity
iii) All life forms that make biodiversity, including humans are ultimately connected to all other life forms and to their physical environment.
iv). No one living element of any ecosystem can survive independently on others.
v). Connections among living and non living elements keep the environment functioning and healthy.
vi). Human impact on the environment directly or indirectly effect the functioning of other living things and by extension ourselves.
Scope of biodiversity:
i).The science of biodiversity has the potential to unify all fragmented disciplines of biology and bring together the activities of all scientists.
ii). Biodiversity is the back bone for agriculture, aquaculture, animal husbandry, forestry and a host of other applied branches of biology. Thus helping in the adequate supply of food grains and main needs for the population.
iii). Alarming changes due to intense globalization can be nullified by the deep understanding of biodiversity in all aspects.
iv). Biodiversity will offer in the coming years new sources food, medicine and other requirements.
v). Biodiversity is the resource on which all human existence depends. Biodiversity is the pillar of human development.
vi). Sustainable development can be achieved through economic, environmental, social and cultural facets of biodiversity.
Q. Write about Earth Summit.
Earth summit:
The 20th anniversary of Stockholm declaration took place in Rio de Janerio in Brazil in 1992. The UN conference on environment and development popularly known as earth summit. The assembled leaders signed the convention on climate change and the convention on biological diversity. They also endorsed the Rio declaration and the forest principles and adapted azanda 21 to plan for achieving sustainable development in the 21st century.
Earth summit 2002 (Rio +10): The world summit on sustainable development was held in Johannesberg of South Africa in 2002. Its main aim is to examine the progress made on the outcomes of the 1992 Earth summit in Rio and also reinvigorate the world’s people towards the true sustainable development.
Earth summit 2012 (Rio +20): The UN general assembly in December 2009 agreed to hold a new earth summit in 2012. This summit held in Brazil and will focus on the green chemistry emerging issues, sustainable development, governance and review of previous commitments.
Q. Write an essay on the levels and types of Biodiversity.
LEVELS AND TYPES OF BIODIVERSITY
Biodiversity or biological diversity is the sum total of all life on earth. It includes the vast array of life forms, then individual genetic makeup, their life processes and their interrelation ship in communities and ecosystems.
Biodiversity is commonly studied at three different levels. i). Genetic diversity, ii). Species diversity and iii). Ecossystem diversity. These three levels of Biodiversity form an intricate web.
i). Genetic diversity:
Genetic diversity refers to the variation of genes with in species. This covers genetic variation between distinct populations of the same species. It also covers genetic variation with in a population. Genetic diversity can be measured using a variety of DNA based techniques like Restriction fragment like polymorphism (RFLP), Polymerase chain reaction (PCR), Serial analysis gene expression (SAGE). Individuals belonging to a species share contain characteristics, but genetic variations determine the particular characteristics of individuals with in a species. The genetic makeup of an individual species is not static but it changes as a result of both external and internal factors. The main forces that determine current levels of genetic diversity within species are mutations, migration, selection and genetic drift.
ii). Species diversity:
Species diversity is related to number and relative abundance of species in a given area in a community. Species diversity is the highest in the equatorial region and gradually declines towards the Polar Regions. Species diversity is essential for the proper functioning of communities in an ecosystem. The species diversity of a region is measured on the basis of species richness (number of species in a defined area), species abundance (relative number in each species) and phylogenitic diversity (relationship between different groups of species). Greatest species richness is commonly found in relatively stable environments having high rates of productivity.
There are three perspectives of diversity at community level. They are alpha diversity, beta diversity and gamma diversity.
(a). Alpha diversity: It is the species diversity within a community or habitat. It is also defined as the variety of organisms occurring in a particular habitat. It is often called as local diversity. It is measured as the number of species within a given area. Alpha diversity comprises two components i.e, species richness and species evenness.
(b). Beta diversity: It indicates diversity between communities. It is also called differentiation diversity or turn over diversity. Species frequently change when habitat or community changes. There are differences in species composition of communities along environmental gradients.
(c). Gamma diversity: It refers to the diversity of habitat over the total land scape or geographical area. The higher diversity at community level provides stability and productivity. Gamma diversity includes both alpha and beta diversities.
[γ = α + β + Q; where Q= total number of communities; α, β are the average values of alpha and beta diversities respectively.]
iii). Ecosystem diversity: Ecosystem diversity is the highest level of biodiversity. It refers to the variation of different ecosystems such as rain forests, coral reefs. Ecosystem diversity arises due to the variation in energy flow, food chain and water cycle of different ecosystems. The enormous range of terrestrial and aquatic environments on the earth has been classified into a number of ecosystems and the examples tropical rain forests, grass lands, wet lands, coral reefs and mangroves.
All the above components of biodiversity do not work singly, but they work jointly to give rise to the manifestation of biodiversity.
Q. Describe the values of Biodiversity.
VALUES OF BIODIVERSITY
Humans derive many direct and indirect benefits from the living world. Biodiversity or biological resources is the source of food, medicines, pharmaceutical drugs, fibres, rubber and timber understanding the value of biodiversity is required for future conservation plans.
Value of Biodiversity:
The value of biodiversity is categorized basing on the benefit it provides to human society. They include (i) Cultural, social and ethical values and (ii) Aesthetic value
(i) Cultural, social and ethical values:
The cultural value of biodiversity for present and future generations is an important reason for conserving it today. Human cultures all over the globe co-evolved with their environment. So the conservation of biodiversity is essential for cultural density of a human community. Plants and animals are considered to be the symbols of national pride and cultural heritage peacock, tiger and lotus have become national icons of our country. The people should understand and appreciation of the inherent value of each and every life form that constitutes the ethical value of biodiversity.
(ii) Aesthetic value:
Nature has an aesthetic value that can be experienced by human beings when they are in natural surroundings. Nature inspires painters, architects and musicians to create works, reflecting and celebrating its beauty.
(iii) Food Security:
Biodiversity is essential requirement for the maintenance of global food supply. The main sources of human food include animals, fish and plant products. Only the conservation of biodiversity can ensure global food security for the rapidly increasing human population as well as for the animal population. To get the best balanced diet to maintain good health diversified food supply is essential.
(iv) Drugs and Medicines:
Natural flora and fauna are the major sources of pharmaceuticals (medicines) for curing ailments. The Indian system of ayurvedic medicine is dependent on plant biodiversity.
(v) Source of Genes:
Natural populations of different biological species harbour all the genes of a species irrespective of the economic value of the genes. Biodiversity protects the gene pool of a species and acts as a store house of many useful genes. The derivable genes such as resistance to pests, diseases and nematodes stress resisting gene are present in the gene pool of different biological species.
(vi). Ecosystem Services:
Ecosystem services are essential for the survival of the human beings on this planet earth. The world cannot afford to replace these services. Therefore, we must work to protect our ecosystems.
Source of these services provided by ecosystems are as follows:
(i) Air purification-Natural communities maintain proper gaseous concentrations in the atmosphere and prevent rapid climate changes of mainly by air purification.
(ii) Watershed Services-Forests regulate water flows down stream areas.
(iii) Soil formation and protection-Soil formation is promoted by biological weathering of the soil by soil organisms and the soil erosion is prohibited by grass lands and forests, which enables the soil protection.
(iv) Nutrient storage and cycling-Ecosystems perform the vital function of nutrients. Biological diversity is essential in this process.
(v) Potential pest and disease control-Source microbes and plants can act as potential pest and disease control. Which are named as biopesticides.
(vi) Pollution control-Ecosystems and ecological processes play an important in break down and absorption of many pollutants, created by humans and their activities.
(vii) Pollination-Many flowering plants rely on animals for their pollination (Ornithophily pollinating agent is birds) Chaeropteriphily pollinating agents are bats, Malacophily pollinating agents are Molluscans etc.
Q. Describe the various threats to Biodiversity.
THREATS TO BIODIVERSITY
Loss of biodiversity is a serious threat to civilization, second only to thermonuclear war in its severity all other environmental problems like pollution, global warming and ozone depletion can be overcome, but not the erosion of biodiversity or extinction of species.
The prominent threats to biodiversity which can be loss of biodiversity as follows:
1. Destruction of Habitats:- Destruction of natural habitats is the largest single cause of biodiversity loss. Tropical forests, which harbor at least 50% of the world’s biodiversity are declining at a rapid rate with current rate of deforestation 50-90% of earth’s forest inhabiting species is projected to be lost by the mid 21st century. An assessment of world life habited in tropical Asia in 1986 reported that India has already lost about 80% of its natural habitat.
2. Habitat fragmentation:- Habitat fragmentation is another serious problem that often goes unrecognized. Roads, fields, canals, power lines etc. Divide the habitat into small fragments. Fragmentation reduces biodiversity because, many species, such as bears and large cats, require large territories to subsist fragmentation divides the large populations into very small populations. These small populations are vulnerable to catastrophic events. Thus it cause loss to biodiversity.
3. Over exploitation of resources:- The overuse are over harvesting of plants, animals or natural resources threatens earth’s biodiversity. Over exploitation, such as logging, hunting or fishing reduce species number to the level of extinction. The African elephants, whose numbers have drastically declined are ruthlessly killed for their tusks.
4. Introduction of Exotic species:- The introduction of (non native species) exotic species into new areas often creates a problem and for the life of native species and causes the loss of biodiversity. The native species fast to compete with the alien species that grows abundantly. The exotic species may be pests and pathogens which causes elimination of native species. Similarly weedy invaders spread at the expense of the diverse range of indigenous undergrowth species.
5. Pollution:- The environmental pollution causes the loss of biodiversity. The excessive use of pesticides in crop fields have resulted in the decline of the populations of fish eating birds and falcons. Lead poisoning is one of the major cause of mortality of many aquatic birds like ducks, swans and cranes.
6. Poaching:- Specific threats to certain animals are related to large economic benefits. Animals are very seriously affected by this poaching only for the economically important parts.
7. Global environmental changes:- The air pollution causes global warming which effects the distribution of organisms on the earth. It is estimated that the green house effect is expected to threaten 400 species of birds, 660 species of fresh water fish and tens of thousands species of invertebrates and plants.
8. Predator and pest control:- Application of predator and pest control has led to the killing of natural predators of insect pests and spread of other dangerous pests. Thus loss to biodiversity occurs.
It may be concluded that biodiversity is being destroyed mainly by human activities at alarming rates almost in all parts of the earth. If the present rate of loss of biodiversity continues, it is not surprising that many valuable species will become extinct even before they are described and named.
The main effects of loss of biodiversity are (i). Loss of valuable genes. (ii). Loss of cultural diversity. (iii). Loss of ecosystems etc;.
Q. Describe the various modes of conservation of biodiversity.
CONSERVATION OF BIODIVERSITY
The conservation of biological diversity has become a global concern due to rapid destruction of ecosystems and wild life. The most effective mechanism for conserving biodiversity is to prevent further degradation of habitats by human beings. The conservation of biodiversity is essential for the sustainable development. There are two types of conservation strategies – (i). in situ (on site) and (ii). ex situ (off site).
(i). In situ (on site) conseravation :
This is the conservation of biological diversity in their natural habitats through protection of total ecosystem. The in situ approach includes protection of a group of typical ecosystem through a net work of protected areas. The areas which provide protection to biological diversity include protected areas, biosphere reserves, sacred forests and sacred lakes.
1. Protected areas:- They are ecological bio-geographical areas where biological diversity along with natural and cultural resources is protected, maintained and managed through legal or other effective measures. The main examples for protected areas are cold desert (Ladak), hot desert (Thar), Saline swampy areas (Sundarbans). The protected areas provide benefits such as maintaining genetic diversity and viable populations. These protected areas prevent man made introduction of alien species and make it possible for the species to shift in response to environmental changes.
2. National parks:- These are the areas maintained by government and reserved for the welfare of wild life. Cultivation, grazing, foresting and habitat manipulation are not allowed in a national park. There are 92 national parks in India. The first national park in India was the Jim Crbett national park near nainital in 1936.
3. Sanctuaries:- A sanctuary is an area of land, which is reserved for the conservation of animals only. Operations such as collection of forest harvests, harvesting of timber, private owner ship of land, tilling of land etc,. are allowed, provided they donot effect the animals adversely. At present, India gas 492 wild life sanctuaries. (Eg: Nagarjuna sagar sanctuary of Guntur of A.P.)
4. Biosphere reserves:- The man and biosphere (MAB) programme of UNESCO formulated the concept of biosphere reserves in 1975. This programme meant for the conservation of ecosystems and the genetic resources contained therein. People are an integral component of an ecosystem. Biosphere reserves serves as a laboratory for sustainable development. At present there are 13 biosphere reserves in India. (Eg: Sundarbans of west Bengal; Nandadevi of Uttaranchal; Simplipal of Orissa etc.). Each biosphere reserve consists of three zones – Core, buffer and Transition zones.
Core or natural zone: It consists of an undisturbed and legally protected ecosystem. No human activity is allowed in this region.
Buffer zone: It surrounds the core area and is managed to accommodate a greater variety of resource use strategies and research and educational activities.
Transition zone: It is the outer most part of the biosphere reserve, which serves as an area of active cooperation between reserve management and local people without disturbing the ecology.
Biosphere reserve helps in restoration of degraded ecosystems and habitats. They ensure the conservation of lands scapes, ecosystems and species. They ensure culturally, socially and ecologically sustainable development. There is a regular monitoring of development and conservation progress in biosphere reserves. The biosphere reserves provide support for education and research in various ecological aspects.
5. Sacred forests and sacred lakes :- Sacred forests are forest patches around places of worship which are held in high esteem by tribal communities. They are found in several parts of India (Eg: Karnataka, Kerala etc;). Similarly, aquatic life form degradation will be inhibited in sacred lake regions.
(ii). Ex situ (off site) conseravation :
It is conservation of selected rare plants or animals in places outside their natural homes (habitats). For ex situ conservation of biodiversity, germ plasm banks or gene banks are established. There include Botanical gardens, zoos, genetic resource centers, pollen grains, seeds, seedlings, tissue culture banks. Seed gene banks are the easiest way to store germplasm of wild and cultivated plants at low temperatures in cold rooms. Storage of germplasm at ultra low temperature (at a temperature of -196 0C in liquid Nitrogen) is called Cryopreservation. There are more than 1500 Botanical gardens and arboreta. Similarly there are more than 800 zoos around the world.
There are certain draw backs to Ex situ conservation. Ex situ conservation is a supplement to in situ conservation because it cannot recreate the habitat as a whole. Natural evolution and adaptation processes are either temporarily halted or altered, when the species is introduced in an unnatural habitat. Ex situ conservation techniques are often costly.
Significance of Conservation of Biodiversity:-
The main significance of conservation of biodiversity is to provide breeders and genetic engineers with a ready source of genetic material. The plants and animals conserved in botanical gardens, zoos and aquaria can be used to restore degraded land, reintroduce species into wild and restock depleted populations.
Cell wall and plasma membrane
Q. Write an essay on the Cell wall.
CELL WALL
The cells of all plants, bacteria and fungi have a rigid, protective covering outside the plasma membrane called cell wall. The presence of cell wall in plant cells distinguishes them from animal cells. Among the vascular plants only certain cells connected with the reproductive processes, are naked, all other cells have walls. The cell wall was first observed by Hooke in the year 1865 in cork cells. Originally it was thought that the cell wall was a non-living secretion of the protoplasm, but now it is known to be metabolically active and is capable of growth and at least during its growth, contains protoplasmic material.
Structure of the cell wall:
A typical plant cell has the following three parts.
1. Middle lamella, 2. Primary wall, 3. Secondary Wall.
1.Middle lamella
It is a thin amorphous cement like layer between two adjacent cells. Middle lamella is the first layer, which is deposited at the time of cytokinesis. It is optically inactive (isotropic). It is made up of calcium and magnesium pectates. In addition to these substances proteins are also present.
2.Primary wall
It is the first formed wall of the cell which is produced inner to the middle lamella. It is thin, elastic and extensible in growing cells. It is optically active (anisotropic). It grows by addition of more wall material within the existing one. Such a growth is termed as intussusception. Some cells like the parenchymatous cells and meristematic cells have only the primary wall. The primary wall consists of a loose network of cellulose microfibrils embedded in a gel like matrix or ground substances. In most of the plants the micro fibrils are made up of cellulose. The micro fibrils are oriented variously according to shape and thickness of the wall. The matrix of the primary wall in which the micro fibrils are embedded is mainly composed of water, hemicellulose, pectin and glycoprotein. Pectin is the filling material of the matrix. Hemicellulose binds the microfibrils with the matrix and the glycoproteins control the orientation of the microfibrils.
3.Secondary Wall
A thick secondary wall is laid inner to the primary wall after the cell has reached maturity. It is laid down is succession of at least three layers often named S1, S2 and S3. It grows in thickness by accretion (apposition) i.e deposition of materials over the existing structures. The central layer (S2)is usually the thickest layer. In some cells however, the number of layers may be more than three. The formation of secondary wall is not uniform in all the cells. This results in the
differentiation of various types of cells, such as parenchyma, collenchyma, fibres and tracheids.
The micro fibrils of secondary wall are compactly arranged with different orientation in different layers embedded in a matrix of pectin and hemicellulose. Substances like lignin, suberin, minerals,waxes, tannins, resins, gums, inorganic salts such as calcium carbonate, calcium oxalate, silica etc may be deposited in the secondary wall. The secondary wall is very strongly anisotropic and layering can be observed in it. Fine structure of the cell wall particularly that of the secondary wall, has been intensively studied. This study was stimulated because of its importance to the fibre, paper and other industries. Cell wall is built of a system of microscopic threads the micro fibrils, which are grouped together in larger bundles. the layering seen in the secondary wall is often the result of the different density of the micro fibrils. The secondary wall consists of two continuous interpenetrating systems one of which is the cellulose micro fibrils and the other, the continuous system of microcapillary spaces. These spaces may the filled with lignin, cutin, suberin, hemicelluloses and other organic substances and sometimes even some mineral crystals. The cellulose molecules consist of long chains of linked glucose residues. The chain molecules are arranged in bundles which are generally termed micellae. The hypothesis of the presence of micellae was proposed by Nageli. According to Frey-wyssling and Muhlethaler the thread like cellulose molecules are arranged in bundles. Each such bundle which forms an elementary fibril consists of about 36 cellulose molecules. The elementary fibril is mostly crytalline.
Plasmodesmata
The cell wall is not totally complete around the cell. It is interrupted by narrow pores carrying fine strands of cytoplasm, which interlink the contents of the cells. They are called plasmodesmata. They form a protoplasmic continuum called symplast. It consists of a canal, lined by plasma membrane. It has a simple or branched tubule known as desmotubule. Desmotubule is an extension of endoplasmic reticulum. Plasmodesmata serves as a passage for many substances to pass through. It is also believed that they have a role in the relay of stimuli.
Pits
Pits are the areas on the cell wall on which the secondary wall is not laid down. The pits of adjacent cells are opposite to each other. Each pit has a pit chamber and a pit membrane. The pit membrane consists of middle lamella and primary wall. Pit membrane has many minute pores and thus they are permeable.
Pits are of two types 1.Simple pits 2.Bordered pits. In simple pits the width of the pit chamber is uniform. There is no secondary wall in the simple pit. In bordered pit the secondary wall partly overhangs the pit. Pits help in the translocation of substances between two adjacent cells. Generally each pit has a complementary pit lying exactly opposite to it in the wall of the neighbouring cell. Such pits form a morphological and functional unit called the pit pair.
Chemical Composition
The chemical composition of cell wall varies in different kingdoms. In bacteria the cell wall is composed of peptidoglycan, in Fungi it is made up of chitin. The plant cell wall is made up of cellulose. Besides cellulose certain other chemicals such as hemicellulose, pectin, lignin, cutin, suberin, silica may also be seen deposited on the wall.
Functions of cell wall:
1. It gives definite shape to the cell.
2. It protects the internal protoplasm against injury.
3. It gives rigidity to the cell
4. It prevents the bursting of plant cells due to endosmosis.
5. The walls of xylem vessels, tracheids and sieve tubes are specialized for long distance transport.
6. In many cases, the cell wall takes part in offense and defense.
Q. Write about the Structural Organization of Plasmamembrane
Ans: Plasmamembrane is a thin layer covering the cytoplasm and separates it from the cell wall. This layer is also called as cell membrane or Plasmalemma. All biological membranes covering various cell organelles are known as cell membrane. Biologicalmembranes are having similar structure and chemical composition, like that of plasmamembrane but performing different functions.
Chemical composition of Plasmamembrane:-
Chemically Plasma membrane is made up of lipids, proteins and carbohydrates. Generally Plasma membrane is 75A0 to 150A0 in thickness but in different cells it may be of different thickness. Quantitatively proteins and lipids are more than carbohydrates in the composition of Plasma membrane.
Lipids : lipids constitute the 40% of the total chemical constituents of Plasma membrane. Four different types of lipids are present in the Plasma membrane. They are Phospholipids, Glycolipids, Sphingolipids and Sterols.
Proteins: In the construction of Plasma membrane, proteins constitute 50%. The proteins are of three types. They are Structural proteins(important component of Plasma membrane-both intrinsic and extrinsic proteins), functional proteins (mostly enzymes catalyzing different chemical reactions) and Carrier proteins (meant for the transportation of different ions and other material through the membrane).
Carbohydrates :Carbohydrates may be in smaller proportion. These Carbohydrates may be branched or unbranched chains of sugars. Glucose derived Carbohydrates generally occur in an attached condition as Glycoproteins and Glycolipids in Plasma membrane.
Ultra structure of Plasma membrane:-
Several cellbiologists attempted to understand the molecular structure of the Plasmamembrane in various ways and proposed models for the same. Some of the models are explained here.
Lipid Bilayer model:
• Proposrd by E.Gorter and F.Grendel in 1925.
• This is the first proposal stating that the Plasmamembrane might contain a lipid bilayer.
• Polar groups of each molecular layer of lipid bilayer were directed towards the outside of the bilayer
Danielli-Davson Model:
• Proposed by James Danielli and Hugh Davson
• They proposed that the Plasmamembrane consists of two layers of lipid molecules. Bimolecular leaf let – formed in such a way that the polar ends of the lipid facing outward and the hydrophobic ends are associated in the central region of the leaf let. They further stated that the polar ends of the lipid molecules as being associated with a monomolecular layer of polar globular protein molecules.
• This is known as Sandwich model as the lipid bilayer is sandwiched between two continous layers of globular proteins.
• This sandwich model is first structural interpretation to account for the physical charecteristics of the membrane.
Unitmembrane Model or Robertson’s Model:
• Proposrd by Robertson in 1957
• He found that all Biligical membranes appear to be made up of lipid layer having a thickness of 35A0 and dense band of proteins of 20A0 thickness present on either side.
• The two outer electron dense layers of proteins separated by the light middle layer of phospholipids together form a unitmembrane.
• The outer surface has mucoproteins while the inner surface proteins are non-mucoid proteins.
The Fluid Mosaic Model:
• Proposed by Singer and Nicolson in 1972.
• In this model, attention is focused on the physical state of the lipid bilayer.
• Here the lipid molecules are present in a fluid state capable of rotating and moving laterally within the membrane. The proteins occur as a mosaic of discontinuous particles that penetrate deeply into the lipid sheet.
• In a way, these protein particles resemble floating icebergs in the sea of lipids.
• Thus the Plasmamembrane is a double layer of phospholipids with their polar ends away from one another and the globular molecules of proteins and sterols scattered in between.
• Integrated proteins penetrate lipid bilayer partially or wholly and project out from both the extracellular and cytoplasmic sides of the membrane. The globular peripheral proteins are loosely attached to the membrane lipids.
Micellar Model:
• Proposed by Hilleir and Hoffman
• They suggested that the membrane have a non-lamellar pattern,consisting of globular subunits known as “micelles”.
• Accordind to this model the membrane is consisting of closely packed repeating units which are similar in structure.
• The protein components of the membrane form a monolayer on either side of the plane of lipid micelles.
Q. Describe the functions of Plasmamembrane
FUNCTIONS OF PLASMA MEMBRANE
In all cells the plasma membrane has several essential functions to perform. These include transporting nutrients into and metabolic wastes out of the cell preventing unwanted materials from entering the cell. In short, the intercellular and intra cellular transport is regulated by plasma membrane. The plasma membrane maintains the proper ionic composition pH (~7.2) and osmotic pressure of the Cytosol. To carry out all these functions, the plasma membrane contains specific transport proteins that permit the passage of certain small molecules but not others. Several of these proteins use the energy released by ATP hydrolysis to pump ions and other molecules into or out of the cell against concentration gradients. Small charged molecules such as ATP and amino acids can diffuse freely within the Cytosol but are restricted in their ability to leave or enter it across the plasma membrane. In addition to these universal functions, the plasma membrane has other important functions to perform. Enzymes bound to the plasma membrane catalyze reactions that would occur with difficulty in an aqueous environment. The plasma membranes of many types of eukaryotic cells also contain Receptor proteins that bind specific Signalling molecules like hormones, growth factors, neurotransmitters etc. leading to various cellular responses. Like the entire cell, each organelle in eukaryotic cells is bounded by a unit membrane containing a unique set of proteins essential for its proper functioning.
Membrane Transport
Based on the permeability a membrane is said to be:
1. Permeable: If a substance passes readily through the membrane
2. Impermeable: If a substance does not pass through the membrane
3. Selectively permeable: If the membrane allows some of the substances to pass through but does not allow all the substances to pass through it. The permeability of a membrane depends on 1)the size of pores in the Plasma membrane. 2)The size of the substance molecules 3)The charge on the substance molecules.
All the biological membranes are selectively permeable. Its permeability properties ensure that essential molecules such as glucose, amino acids and lipids readily enter the cell, metabolic intermediates remain in the cell and waste compounds leave the cell. In short it allows the cell to maintain a constant internal environment.
Substances are transported across the membrane either by:
1. Passive Transport or 2. Active Transport
Passive Transport
Physical processes
Passive Transport of materials across the membrane requires no energy by the cell and it is unaided by the transport proteins. The physical processes through which substances get into the cell are 1.Diffusion 2.Osmosis
Diffusion
Diffusion is the movement of molecules of any substance from a region of it’s higher to a region of it’s lower concentration (down its own concentration gradient) to spread uniformly in the dispersion medium on account of their random kinetic motion.
The rate of diffusion is directly proportional to
1. The concentration of the substance
2. Temperature of the medium
3. Area of the diffusion pathway
The diffusion is inversely proportional to
1. The size of the substance molecules
2. The molecular weight of the substance molecule
3. The distance over which the molecules have to diffuse
Diffusion through Biomembranes
Gases and small hydrophobic molecules diffuse directly across the phospholipid bilayer at a rate proportional to their ability to dissolve in a liquid hydro carbon. Transport of molecules takes place along the concentration gradient and no metabolic energy is expended in this process. This can be described as ‘Downhill transport’. Diffusion through the bio membrane takes place in two ways.
1. Diffusion of fat-soluble substances through plasma membrane simply by dissolving in the lipid bilayer.
2. Diffusion of water soluble substances and ions: This takes place through pores in the membranes.
Diffusion of charged particles water soluble substances and ions such as K + Cl - and HCO3- diffuse through the pores in the membranes. An ion diffuses from the side richer in like charges to the side with an excess of opposite charges. The difference of electrical charges between the two sides of a membrance is called electro chemical gradient. The integral proteins of the membrane act as protein channels extending through the membrane. The movement of gas molecules occurs down its pressuregradient.
Osmosis
It is the special type of diffusion where the water or solvent diffuses through a selectively permeable membrane from a region of high solvent concentration to a region of low solvent concentration.
Uniporter Catalyzed Transport
The plasma membrane of most cells (animal or plant) contains several uniporters that enable amino acids, nucleosides, sugars and other small molecules to enter and leave cells down their concentration gradients. Similar to enzymes, uniporters accelerate a reaction that is thermodynamically favoured. This type of movement sometimes is referred to as facilitated transport or facilitated diffusion.
Three main features distinguish uniport transport from passive diffusion. 1. the rate of transport is far higher than predicted 2.transport is specific 3.transport occurs via a limited number of transporter proteins rather than throughout the phospholipids bilayer.
Active transport
It is vital process. It is the movement of molecules or ions against the concentration gradient. i.e the molecules or ions move from the region of lower concentration towards the region of higher concentration. The movement of molecules can be compared with the uphill movement of water. Energy is required to counteract the force of diffusion and the energy comes from ATP produced by oxidative phosphorylation or by concentration gradient of ions. Thus active transport is defined as athe energy dependent transport of molecules or ions across a semi permeable membrane against the concentration gradient. Active transport takes place with the help of carrier proteins that are present in the plasma membrane. In the plasma membrane there are a number of carrier molecules called permeases or translocases present. For each type of solute molecule there is a specific carrier molecule. It has got two binding sites; one for the transportant and other for ATP molecule. The carrier proteins bind the transportant molecule on the outer side of the plasma membrane. This results in the formation of carrier-transportant-complex. As the ATP molecule binds itself to the other binding site of the carrier protein it is hydrolysed to form ADP and energy is released. This energy brings conformational change in the carrier transportant-complex and the transportant is carried through the channel on the other side of the membrane. The carrier molecule regains its original form and repeats the precess.
There are two forces which govern the movement of ions across selectively permeable membranes, the membrane electric potential and the ion concentration gradient. ATP driven ion pumps generate and maintain ionic gradients across the plasma membrane.
Endocytosis and exocytosis
Endocytosis and exocytosis are active processes involving bulk transport of materials through membranes, either into cells (endocytosis) or out of cells (exocytosis). Endocytosis occurs by an in folding or extension of the plasma membrane to form a vesicle or vacuole or vauole. It is of two types.
1. Phagocytosis:(cell eating)-Substances are taken up in solid form. Cells involving in this process are called phagocytes and said to be phagocytic. (eg.) some white blood cells. A phagocytic vacuole is formed during the uptake.
2. Pinocytosis (cell drinking)-Substances are taken up in liquid form. Vesicles which are very small are formed during intake. Pinocytosis is often associated with amoebiod protozozns, and in certain kidney cells involved in fluid exchange. It can also occur in plant cells. Exocytosis is the reverse of endocytosis by which materials are removed from cells such as undigested remains from food vacuoles.
CELL WALL
The cells of all plants, bacteria and fungi have a rigid, protective covering outside the plasma membrane called cell wall. The presence of cell wall in plant cells distinguishes them from animal cells. Among the vascular plants only certain cells connected with the reproductive processes, are naked, all other cells have walls. The cell wall was first observed by Hooke in the year 1865 in cork cells. Originally it was thought that the cell wall was a non-living secretion of the protoplasm, but now it is known to be metabolically active and is capable of growth and at least during its growth, contains protoplasmic material.
Structure of the cell wall:
A typical plant cell has the following three parts.
1. Middle lamella, 2. Primary wall, 3. Secondary Wall.
1.Middle lamella
It is a thin amorphous cement like layer between two adjacent cells. Middle lamella is the first layer, which is deposited at the time of cytokinesis. It is optically inactive (isotropic). It is made up of calcium and magnesium pectates. In addition to these substances proteins are also present.
2.Primary wall
It is the first formed wall of the cell which is produced inner to the middle lamella. It is thin, elastic and extensible in growing cells. It is optically active (anisotropic). It grows by addition of more wall material within the existing one. Such a growth is termed as intussusception. Some cells like the parenchymatous cells and meristematic cells have only the primary wall. The primary wall consists of a loose network of cellulose microfibrils embedded in a gel like matrix or ground substances. In most of the plants the micro fibrils are made up of cellulose. The micro fibrils are oriented variously according to shape and thickness of the wall. The matrix of the primary wall in which the micro fibrils are embedded is mainly composed of water, hemicellulose, pectin and glycoprotein. Pectin is the filling material of the matrix. Hemicellulose binds the microfibrils with the matrix and the glycoproteins control the orientation of the microfibrils.
3.Secondary Wall
A thick secondary wall is laid inner to the primary wall after the cell has reached maturity. It is laid down is succession of at least three layers often named S1, S2 and S3. It grows in thickness by accretion (apposition) i.e deposition of materials over the existing structures. The central layer (S2)is usually the thickest layer. In some cells however, the number of layers may be more than three. The formation of secondary wall is not uniform in all the cells. This results in the
differentiation of various types of cells, such as parenchyma, collenchyma, fibres and tracheids.
The micro fibrils of secondary wall are compactly arranged with different orientation in different layers embedded in a matrix of pectin and hemicellulose. Substances like lignin, suberin, minerals,waxes, tannins, resins, gums, inorganic salts such as calcium carbonate, calcium oxalate, silica etc may be deposited in the secondary wall. The secondary wall is very strongly anisotropic and layering can be observed in it. Fine structure of the cell wall particularly that of the secondary wall, has been intensively studied. This study was stimulated because of its importance to the fibre, paper and other industries. Cell wall is built of a system of microscopic threads the micro fibrils, which are grouped together in larger bundles. the layering seen in the secondary wall is often the result of the different density of the micro fibrils. The secondary wall consists of two continuous interpenetrating systems one of which is the cellulose micro fibrils and the other, the continuous system of microcapillary spaces. These spaces may the filled with lignin, cutin, suberin, hemicelluloses and other organic substances and sometimes even some mineral crystals. The cellulose molecules consist of long chains of linked glucose residues. The chain molecules are arranged in bundles which are generally termed micellae. The hypothesis of the presence of micellae was proposed by Nageli. According to Frey-wyssling and Muhlethaler the thread like cellulose molecules are arranged in bundles. Each such bundle which forms an elementary fibril consists of about 36 cellulose molecules. The elementary fibril is mostly crytalline.
Plasmodesmata
The cell wall is not totally complete around the cell. It is interrupted by narrow pores carrying fine strands of cytoplasm, which interlink the contents of the cells. They are called plasmodesmata. They form a protoplasmic continuum called symplast. It consists of a canal, lined by plasma membrane. It has a simple or branched tubule known as desmotubule. Desmotubule is an extension of endoplasmic reticulum. Plasmodesmata serves as a passage for many substances to pass through. It is also believed that they have a role in the relay of stimuli.
Pits
Pits are the areas on the cell wall on which the secondary wall is not laid down. The pits of adjacent cells are opposite to each other. Each pit has a pit chamber and a pit membrane. The pit membrane consists of middle lamella and primary wall. Pit membrane has many minute pores and thus they are permeable.
Pits are of two types 1.Simple pits 2.Bordered pits. In simple pits the width of the pit chamber is uniform. There is no secondary wall in the simple pit. In bordered pit the secondary wall partly overhangs the pit. Pits help in the translocation of substances between two adjacent cells. Generally each pit has a complementary pit lying exactly opposite to it in the wall of the neighbouring cell. Such pits form a morphological and functional unit called the pit pair.
Chemical Composition
The chemical composition of cell wall varies in different kingdoms. In bacteria the cell wall is composed of peptidoglycan, in Fungi it is made up of chitin. The plant cell wall is made up of cellulose. Besides cellulose certain other chemicals such as hemicellulose, pectin, lignin, cutin, suberin, silica may also be seen deposited on the wall.
Functions of cell wall:
1. It gives definite shape to the cell.
2. It protects the internal protoplasm against injury.
3. It gives rigidity to the cell
4. It prevents the bursting of plant cells due to endosmosis.
5. The walls of xylem vessels, tracheids and sieve tubes are specialized for long distance transport.
6. In many cases, the cell wall takes part in offense and defense.
Q. Write about the Structural Organization of Plasmamembrane
Ans: Plasmamembrane is a thin layer covering the cytoplasm and separates it from the cell wall. This layer is also called as cell membrane or Plasmalemma. All biological membranes covering various cell organelles are known as cell membrane. Biologicalmembranes are having similar structure and chemical composition, like that of plasmamembrane but performing different functions.
Chemical composition of Plasmamembrane:-
Chemically Plasma membrane is made up of lipids, proteins and carbohydrates. Generally Plasma membrane is 75A0 to 150A0 in thickness but in different cells it may be of different thickness. Quantitatively proteins and lipids are more than carbohydrates in the composition of Plasma membrane.
Lipids : lipids constitute the 40% of the total chemical constituents of Plasma membrane. Four different types of lipids are present in the Plasma membrane. They are Phospholipids, Glycolipids, Sphingolipids and Sterols.
Proteins: In the construction of Plasma membrane, proteins constitute 50%. The proteins are of three types. They are Structural proteins(important component of Plasma membrane-both intrinsic and extrinsic proteins), functional proteins (mostly enzymes catalyzing different chemical reactions) and Carrier proteins (meant for the transportation of different ions and other material through the membrane).
Carbohydrates :Carbohydrates may be in smaller proportion. These Carbohydrates may be branched or unbranched chains of sugars. Glucose derived Carbohydrates generally occur in an attached condition as Glycoproteins and Glycolipids in Plasma membrane.
Ultra structure of Plasma membrane:-
Several cellbiologists attempted to understand the molecular structure of the Plasmamembrane in various ways and proposed models for the same. Some of the models are explained here.
Lipid Bilayer model:
• Proposrd by E.Gorter and F.Grendel in 1925.
• This is the first proposal stating that the Plasmamembrane might contain a lipid bilayer.
• Polar groups of each molecular layer of lipid bilayer were directed towards the outside of the bilayer
Danielli-Davson Model:
• Proposed by James Danielli and Hugh Davson
• They proposed that the Plasmamembrane consists of two layers of lipid molecules. Bimolecular leaf let – formed in such a way that the polar ends of the lipid facing outward and the hydrophobic ends are associated in the central region of the leaf let. They further stated that the polar ends of the lipid molecules as being associated with a monomolecular layer of polar globular protein molecules.
• This is known as Sandwich model as the lipid bilayer is sandwiched between two continous layers of globular proteins.
• This sandwich model is first structural interpretation to account for the physical charecteristics of the membrane.
Unitmembrane Model or Robertson’s Model:
• Proposrd by Robertson in 1957
• He found that all Biligical membranes appear to be made up of lipid layer having a thickness of 35A0 and dense band of proteins of 20A0 thickness present on either side.
• The two outer electron dense layers of proteins separated by the light middle layer of phospholipids together form a unitmembrane.
• The outer surface has mucoproteins while the inner surface proteins are non-mucoid proteins.
The Fluid Mosaic Model:
• Proposed by Singer and Nicolson in 1972.
• In this model, attention is focused on the physical state of the lipid bilayer.
• Here the lipid molecules are present in a fluid state capable of rotating and moving laterally within the membrane. The proteins occur as a mosaic of discontinuous particles that penetrate deeply into the lipid sheet.
• In a way, these protein particles resemble floating icebergs in the sea of lipids.
• Thus the Plasmamembrane is a double layer of phospholipids with their polar ends away from one another and the globular molecules of proteins and sterols scattered in between.
• Integrated proteins penetrate lipid bilayer partially or wholly and project out from both the extracellular and cytoplasmic sides of the membrane. The globular peripheral proteins are loosely attached to the membrane lipids.
Micellar Model:
• Proposed by Hilleir and Hoffman
• They suggested that the membrane have a non-lamellar pattern,consisting of globular subunits known as “micelles”.
• Accordind to this model the membrane is consisting of closely packed repeating units which are similar in structure.
• The protein components of the membrane form a monolayer on either side of the plane of lipid micelles.
Q. Describe the functions of Plasmamembrane
FUNCTIONS OF PLASMA MEMBRANE
In all cells the plasma membrane has several essential functions to perform. These include transporting nutrients into and metabolic wastes out of the cell preventing unwanted materials from entering the cell. In short, the intercellular and intra cellular transport is regulated by plasma membrane. The plasma membrane maintains the proper ionic composition pH (~7.2) and osmotic pressure of the Cytosol. To carry out all these functions, the plasma membrane contains specific transport proteins that permit the passage of certain small molecules but not others. Several of these proteins use the energy released by ATP hydrolysis to pump ions and other molecules into or out of the cell against concentration gradients. Small charged molecules such as ATP and amino acids can diffuse freely within the Cytosol but are restricted in their ability to leave or enter it across the plasma membrane. In addition to these universal functions, the plasma membrane has other important functions to perform. Enzymes bound to the plasma membrane catalyze reactions that would occur with difficulty in an aqueous environment. The plasma membranes of many types of eukaryotic cells also contain Receptor proteins that bind specific Signalling molecules like hormones, growth factors, neurotransmitters etc. leading to various cellular responses. Like the entire cell, each organelle in eukaryotic cells is bounded by a unit membrane containing a unique set of proteins essential for its proper functioning.
Membrane Transport
Based on the permeability a membrane is said to be:
1. Permeable: If a substance passes readily through the membrane
2. Impermeable: If a substance does not pass through the membrane
3. Selectively permeable: If the membrane allows some of the substances to pass through but does not allow all the substances to pass through it. The permeability of a membrane depends on 1)the size of pores in the Plasma membrane. 2)The size of the substance molecules 3)The charge on the substance molecules.
All the biological membranes are selectively permeable. Its permeability properties ensure that essential molecules such as glucose, amino acids and lipids readily enter the cell, metabolic intermediates remain in the cell and waste compounds leave the cell. In short it allows the cell to maintain a constant internal environment.
Substances are transported across the membrane either by:
1. Passive Transport or 2. Active Transport
Passive Transport
Physical processes
Passive Transport of materials across the membrane requires no energy by the cell and it is unaided by the transport proteins. The physical processes through which substances get into the cell are 1.Diffusion 2.Osmosis
Diffusion
Diffusion is the movement of molecules of any substance from a region of it’s higher to a region of it’s lower concentration (down its own concentration gradient) to spread uniformly in the dispersion medium on account of their random kinetic motion.
The rate of diffusion is directly proportional to
1. The concentration of the substance
2. Temperature of the medium
3. Area of the diffusion pathway
The diffusion is inversely proportional to
1. The size of the substance molecules
2. The molecular weight of the substance molecule
3. The distance over which the molecules have to diffuse
Diffusion through Biomembranes
Gases and small hydrophobic molecules diffuse directly across the phospholipid bilayer at a rate proportional to their ability to dissolve in a liquid hydro carbon. Transport of molecules takes place along the concentration gradient and no metabolic energy is expended in this process. This can be described as ‘Downhill transport’. Diffusion through the bio membrane takes place in two ways.
1. Diffusion of fat-soluble substances through plasma membrane simply by dissolving in the lipid bilayer.
2. Diffusion of water soluble substances and ions: This takes place through pores in the membranes.
Diffusion of charged particles water soluble substances and ions such as K + Cl - and HCO3- diffuse through the pores in the membranes. An ion diffuses from the side richer in like charges to the side with an excess of opposite charges. The difference of electrical charges between the two sides of a membrance is called electro chemical gradient. The integral proteins of the membrane act as protein channels extending through the membrane. The movement of gas molecules occurs down its pressuregradient.
Osmosis
It is the special type of diffusion where the water or solvent diffuses through a selectively permeable membrane from a region of high solvent concentration to a region of low solvent concentration.
Uniporter Catalyzed Transport
The plasma membrane of most cells (animal or plant) contains several uniporters that enable amino acids, nucleosides, sugars and other small molecules to enter and leave cells down their concentration gradients. Similar to enzymes, uniporters accelerate a reaction that is thermodynamically favoured. This type of movement sometimes is referred to as facilitated transport or facilitated diffusion.
Three main features distinguish uniport transport from passive diffusion. 1. the rate of transport is far higher than predicted 2.transport is specific 3.transport occurs via a limited number of transporter proteins rather than throughout the phospholipids bilayer.
Active transport
It is vital process. It is the movement of molecules or ions against the concentration gradient. i.e the molecules or ions move from the region of lower concentration towards the region of higher concentration. The movement of molecules can be compared with the uphill movement of water. Energy is required to counteract the force of diffusion and the energy comes from ATP produced by oxidative phosphorylation or by concentration gradient of ions. Thus active transport is defined as athe energy dependent transport of molecules or ions across a semi permeable membrane against the concentration gradient. Active transport takes place with the help of carrier proteins that are present in the plasma membrane. In the plasma membrane there are a number of carrier molecules called permeases or translocases present. For each type of solute molecule there is a specific carrier molecule. It has got two binding sites; one for the transportant and other for ATP molecule. The carrier proteins bind the transportant molecule on the outer side of the plasma membrane. This results in the formation of carrier-transportant-complex. As the ATP molecule binds itself to the other binding site of the carrier protein it is hydrolysed to form ADP and energy is released. This energy brings conformational change in the carrier transportant-complex and the transportant is carried through the channel on the other side of the membrane. The carrier molecule regains its original form and repeats the precess.
There are two forces which govern the movement of ions across selectively permeable membranes, the membrane electric potential and the ion concentration gradient. ATP driven ion pumps generate and maintain ionic gradients across the plasma membrane.
Endocytosis and exocytosis
Endocytosis and exocytosis are active processes involving bulk transport of materials through membranes, either into cells (endocytosis) or out of cells (exocytosis). Endocytosis occurs by an in folding or extension of the plasma membrane to form a vesicle or vacuole or vauole. It is of two types.
1. Phagocytosis:(cell eating)-Substances are taken up in solid form. Cells involving in this process are called phagocytes and said to be phagocytic. (eg.) some white blood cells. A phagocytic vacuole is formed during the uptake.
2. Pinocytosis (cell drinking)-Substances are taken up in liquid form. Vesicles which are very small are formed during intake. Pinocytosis is often associated with amoebiod protozozns, and in certain kidney cells involved in fluid exchange. It can also occur in plant cells. Exocytosis is the reverse of endocytosis by which materials are removed from cells such as undigested remains from food vacuoles.
Classification of Pteridophytes
CLASSIFICATION OF PTERIDOPHYTES
• According to the older taxonomists, vascular cryptogams in to two divisions: Pteridophyta and Spermatophyta.
• With the discovery of some fern like, seed bearing fossil plants the distinction between the two divisions Pteridophyta and Spermatophyta has been eliminated.
• All the vascular plants are placed in a single division, Tracheophyta. Now the plant kingdom includes, only three divisions – Thallophyta, Bryophyta and Tracheophyta.
• Eams divided the vascular plants or tracheophyta in to four main groups. Psilopsida, Lycopsida, Sphenopsida and Pteropsida.
a. Psilopsida includes Psilophytales and Psilotales.
b. Lycopsida includes Lycopodiales, Selaginellales, Lepidodendrales, Isoetales.
c. Sphenopsida includes Hyeniales, Sphenophyllales and Equisetales.
d. Pteropsida includes Filicineae, Gymnosperamae, Angiospermae.
• Tippo in his classification of Vascular plants gives “Tracheophyta”, the rank of phylum, which is subdivided into four subphyla: Psilopsida, Lycopsida, Sphenopsida and Pteropsida.
• In accordance with the International Code of Nomenclature Wardlaw suggested the rank of subdivisions for the four groups. According to the recommendations of ICBN, the name of the division should end in the suffix-Phyta, of a sub division in Phytina and of a class in opsida. On this basis, Smith divided the vascular cryptogams into four divisions – Psilophyta, Lepidophyta, Calamophyta and Pterophyta.
• According to Bierhorst, taxon subdivision has been deleted and redivided the division Tracheophyta into 14 classes.
• Sporne proposed the following classificatio for the vascular cryptogams. He recognised six classes in pteridophytes.
• Class A: Psilopsida
Orders: Rhyniales
Trimerophytales
Zosterophyllales
• Class B: Psilotopsida
Order: Psilotales
• Class C: Lycopsida
Orders: Protolepidodendrales
Lycopodiales
Lepidodendrales
Isoetales
Selaginellales
• Class D: Sphenopsida
Orders: Hyeniales
Sphenophyllales
Calamitales
Equisetales
• Class E: Pteropsida:
Sub-class: Primofilices
Orders: Cladoxylales
Coenopteridales
Sub-class: Eusporangiate
Orders: Marattiales
Ophioglossales
Sub-class: Osmundidae
Order: Osmundales
Sub-class: Leptosporangiatae
Order: Filicales
Marseliales
Salviniales
(f) Class F: Progymnospermopsida
Orders: Aneurophytales
Protopityales
Archaeopteridales
• According to the older taxonomists, vascular cryptogams in to two divisions: Pteridophyta and Spermatophyta.
• With the discovery of some fern like, seed bearing fossil plants the distinction between the two divisions Pteridophyta and Spermatophyta has been eliminated.
• All the vascular plants are placed in a single division, Tracheophyta. Now the plant kingdom includes, only three divisions – Thallophyta, Bryophyta and Tracheophyta.
• Eams divided the vascular plants or tracheophyta in to four main groups. Psilopsida, Lycopsida, Sphenopsida and Pteropsida.
a. Psilopsida includes Psilophytales and Psilotales.
b. Lycopsida includes Lycopodiales, Selaginellales, Lepidodendrales, Isoetales.
c. Sphenopsida includes Hyeniales, Sphenophyllales and Equisetales.
d. Pteropsida includes Filicineae, Gymnosperamae, Angiospermae.
• Tippo in his classification of Vascular plants gives “Tracheophyta”, the rank of phylum, which is subdivided into four subphyla: Psilopsida, Lycopsida, Sphenopsida and Pteropsida.
• In accordance with the International Code of Nomenclature Wardlaw suggested the rank of subdivisions for the four groups. According to the recommendations of ICBN, the name of the division should end in the suffix-Phyta, of a sub division in Phytina and of a class in opsida. On this basis, Smith divided the vascular cryptogams into four divisions – Psilophyta, Lepidophyta, Calamophyta and Pterophyta.
• According to Bierhorst, taxon subdivision has been deleted and redivided the division Tracheophyta into 14 classes.
• Sporne proposed the following classificatio for the vascular cryptogams. He recognised six classes in pteridophytes.
• Class A: Psilopsida
Orders: Rhyniales
Trimerophytales
Zosterophyllales
• Class B: Psilotopsida
Order: Psilotales
• Class C: Lycopsida
Orders: Protolepidodendrales
Lycopodiales
Lepidodendrales
Isoetales
Selaginellales
• Class D: Sphenopsida
Orders: Hyeniales
Sphenophyllales
Calamitales
Equisetales
• Class E: Pteropsida:
Sub-class: Primofilices
Orders: Cladoxylales
Coenopteridales
Sub-class: Eusporangiate
Orders: Marattiales
Ophioglossales
Sub-class: Osmundidae
Order: Osmundales
Sub-class: Leptosporangiatae
Order: Filicales
Marseliales
Salviniales
(f) Class F: Progymnospermopsida
Orders: Aneurophytales
Protopityales
Archaeopteridales
Lichens
LICHENS
Lichens are a small group of plants made up of algal and fungal components, living tigether in an intimate symbiotic relationship. Lichen is an autotrophic, thallophytic composite organism which consists of both algae and fungi. The algal component is known as phycobiont. In this symbiotic assiciation or relationship both the partners derive mutual benefit. The fungus derives food from the algal cells and inturn protects the alga from unfavourable conditions, specially from drought. Only the fungal component is involved in in sexual reproduction. The growth of lichens is very slow. Direct light, moderate or cod tempearture, moisture and pure atmosphere favours the growth of lichens. Polluted, smooky atmosphere as found in industrial area is nit favourable for the growth of lichens. Lichens arew orld wide in distribution. These are found growing in a variety of habitats from arcitic to the Antarcitic and all the regions in between. In India , Lichens are much more common in Eastern Himalayas as compared to that in the Western Himalayas. The algal component belongs to chlorophyceae or Myxophyceae (Cyanobacteria), where as the fungal component belongs to Basidiomycotina or Ascomycotina.
Types of Lichens
Lichens are classified into different types
I. On the basis of the structure of the thallus, lichens have been classified in to Three broad types
• Crustose Lichens
• Foliose Lichens
• Fruticose Lichens
II. On the basis of the type of fungal component, Lichens have been classified in to Three broad types.
• Ascilichens
• Basidiolichens
• Deuterolichens
I. On the basis of the structure of the thallus :
1. Crustose Lichens:
The thallus is thin, flat and crust like. The thalli are appressed to the substratum forming thin flat crusts. The thalli are partly or wholly embedded in tthe substrartum and cannot be removed from the substratum without injuring the thallus. Sometimes only the fruiting bodies are visible above the surface of the substratum.
Examples: Graphis, Haematomma, Verrucaria, Lecanora
2. Foliose Lichens:
These lichens are flat with leaf like and lobed thallus. They are attached to the substratum with thw help of rhizoid like rhizines.
Examples: Parmelia, Peltigera, Physica
3. Fruticose Lichens:
These are bush like having cylindrical or strap shaped branched thallus. The branches may grow errect or hang from the substratum with the help of a basal mucilage disc.
Examples: Usnea, Cladonia, Ramalina
II. On the basis of the type of fungal component:
1. Ascolichens:
The fungal component of these Lichens is a member of the class Ascomycetes.
Example: Dermatocarpon, Parmelia
2. Basidiolichens:
The fungal component of these Lichens is a member of the class Basidiomycetes.
Example: Corella, Dictyonema
3. Deuterolichens:
The fungal component of these Lichens is a member of the class Basidiomycetes.
Anatomy or Internal Structure of Lichens:
The internal organisation of lichens depends upon the type of Lichen based upon its structure.
1. Crustose Lichens :
• Anatomically there is much differentiation in Crustose Lichens.
• In transverse setcion, the lichen thallus shows cortex, an algal layer and medulla.
• The cortex is made up of fungal hyphae.
• Following cortex an algal layer madee up of algae are present.
• Medulla is the final layer made up of a loose tissue of branching hyphae.
• The lower cortex is not distinguishable.
2. Foliose Lichens:
• On the basis of distribution of algal cells among the fungal tissue, two types of foliose thalli are recognised.
• They are Homiomerous and Heteromerous type.
• Homiomerous Type: The algae are more or less uniformly distributed throughout the thallus. The algae are usually gealtinous and belongs to Cyanobacteria. The outer protective layer of he thallus is formed by the fungi.
Examples: Collema, Leptogium.
• Heteromerous Type: The algal cells form a distinct layer with in the thallus. Bulk of the thallus is made up of fungal hyphae. Thallus is differentiated into four distinct regions namely, Upper Cortex, Algal layer, Medulla and Lower Cortex. The upper cortex is made up of completely interwoven hyphae. The Algal layer or gonidial layer is consisting of loosely interwoven fungal hyphae, intermingled with algal cells of a green alga. Medulla which is the central part of the thallus comprised of loosely interwoven fungal hyphae with larger spaces between them. Lower cortex is present below the medulla madeup of densely compacted hyphae present at the lower surface of the thallus.
3. Fruticose Lichens:
• The lower cortex doesnot occur in fruticose lichens due to cylindrical structure and medulla forms the central part of the axis.
• The external layer of a lichen thallus or surface is termed the cortex. Beneath it is a layer of fungus enmeshed algal cells called the algal layer. Below the algal layer is a region of cottony, loosely woven fungal hyphae free from algal cells, the medulla.
Reproduction:
The main modes of the reproduction found in Lichens.
1. Vegetative reproduction:
Lichens reproduce vegetatively by mean sof Fragmentation, Isidia and Soredia.
2. Asexual reproduction:
Only fungal component of the Lichen can be reproduced asexually. In Ascolichens, asexual reproduction commonly takes place by ascospores and the fruiting body or fructification is known as the Ascocarp. In some Ascolichens, the fruiting body appears as a cup shaped structure commonly called apothecium. Each Ascus usually contains eight ascospores. Sometimes in some lochens ascogonium takes the shape of Perithecium. In Basidiolichens asexual reproduction takes place by means of basidiospores. In some lichens asexual reproduction is fullfilled by pycniospores or Pycnidia. These Pycniospores germinate by giving rise to hyphal branches in all directions and when any such branch comes in contact with algal cells, a lichen body is formed.
3. Sexual reproduction:
Sexual reproduction in Ascolichens and bsidiolichens resemble to that of Ascomycetes and Basidiomycetes members respectively. Ascolichens are the most common lichens containing male and female sex organs like spermatia and carpogonia (Ascogonia) respectively. Fertilisation if followed by the formation of ascogeenous hyphae from the basal portion of the ascogonium. The ascocarp is lined with a paliside like layer of paraphyses. During weather ascospores germinate and give rise to germtubes which on coming in contact with algal element produce the new thallus.
Lichens are a small group of plants made up of algal and fungal components, living tigether in an intimate symbiotic relationship. Lichen is an autotrophic, thallophytic composite organism which consists of both algae and fungi. The algal component is known as phycobiont. In this symbiotic assiciation or relationship both the partners derive mutual benefit. The fungus derives food from the algal cells and inturn protects the alga from unfavourable conditions, specially from drought. Only the fungal component is involved in in sexual reproduction. The growth of lichens is very slow. Direct light, moderate or cod tempearture, moisture and pure atmosphere favours the growth of lichens. Polluted, smooky atmosphere as found in industrial area is nit favourable for the growth of lichens. Lichens arew orld wide in distribution. These are found growing in a variety of habitats from arcitic to the Antarcitic and all the regions in between. In India , Lichens are much more common in Eastern Himalayas as compared to that in the Western Himalayas. The algal component belongs to chlorophyceae or Myxophyceae (Cyanobacteria), where as the fungal component belongs to Basidiomycotina or Ascomycotina.
Types of Lichens
Lichens are classified into different types
I. On the basis of the structure of the thallus, lichens have been classified in to Three broad types
• Crustose Lichens
• Foliose Lichens
• Fruticose Lichens
II. On the basis of the type of fungal component, Lichens have been classified in to Three broad types.
• Ascilichens
• Basidiolichens
• Deuterolichens
I. On the basis of the structure of the thallus :
1. Crustose Lichens:
The thallus is thin, flat and crust like. The thalli are appressed to the substratum forming thin flat crusts. The thalli are partly or wholly embedded in tthe substrartum and cannot be removed from the substratum without injuring the thallus. Sometimes only the fruiting bodies are visible above the surface of the substratum.
Examples: Graphis, Haematomma, Verrucaria, Lecanora
2. Foliose Lichens:
These lichens are flat with leaf like and lobed thallus. They are attached to the substratum with thw help of rhizoid like rhizines.
Examples: Parmelia, Peltigera, Physica
3. Fruticose Lichens:
These are bush like having cylindrical or strap shaped branched thallus. The branches may grow errect or hang from the substratum with the help of a basal mucilage disc.
Examples: Usnea, Cladonia, Ramalina
II. On the basis of the type of fungal component:
1. Ascolichens:
The fungal component of these Lichens is a member of the class Ascomycetes.
Example: Dermatocarpon, Parmelia
2. Basidiolichens:
The fungal component of these Lichens is a member of the class Basidiomycetes.
Example: Corella, Dictyonema
3. Deuterolichens:
The fungal component of these Lichens is a member of the class Basidiomycetes.
Anatomy or Internal Structure of Lichens:
The internal organisation of lichens depends upon the type of Lichen based upon its structure.
1. Crustose Lichens :
• Anatomically there is much differentiation in Crustose Lichens.
• In transverse setcion, the lichen thallus shows cortex, an algal layer and medulla.
• The cortex is made up of fungal hyphae.
• Following cortex an algal layer madee up of algae are present.
• Medulla is the final layer made up of a loose tissue of branching hyphae.
• The lower cortex is not distinguishable.
2. Foliose Lichens:
• On the basis of distribution of algal cells among the fungal tissue, two types of foliose thalli are recognised.
• They are Homiomerous and Heteromerous type.
• Homiomerous Type: The algae are more or less uniformly distributed throughout the thallus. The algae are usually gealtinous and belongs to Cyanobacteria. The outer protective layer of he thallus is formed by the fungi.
Examples: Collema, Leptogium.
• Heteromerous Type: The algal cells form a distinct layer with in the thallus. Bulk of the thallus is made up of fungal hyphae. Thallus is differentiated into four distinct regions namely, Upper Cortex, Algal layer, Medulla and Lower Cortex. The upper cortex is made up of completely interwoven hyphae. The Algal layer or gonidial layer is consisting of loosely interwoven fungal hyphae, intermingled with algal cells of a green alga. Medulla which is the central part of the thallus comprised of loosely interwoven fungal hyphae with larger spaces between them. Lower cortex is present below the medulla madeup of densely compacted hyphae present at the lower surface of the thallus.
3. Fruticose Lichens:
• The lower cortex doesnot occur in fruticose lichens due to cylindrical structure and medulla forms the central part of the axis.
• The external layer of a lichen thallus or surface is termed the cortex. Beneath it is a layer of fungus enmeshed algal cells called the algal layer. Below the algal layer is a region of cottony, loosely woven fungal hyphae free from algal cells, the medulla.
Reproduction:
The main modes of the reproduction found in Lichens.
1. Vegetative reproduction:
Lichens reproduce vegetatively by mean sof Fragmentation, Isidia and Soredia.
2. Asexual reproduction:
Only fungal component of the Lichen can be reproduced asexually. In Ascolichens, asexual reproduction commonly takes place by ascospores and the fruiting body or fructification is known as the Ascocarp. In some Ascolichens, the fruiting body appears as a cup shaped structure commonly called apothecium. Each Ascus usually contains eight ascospores. Sometimes in some lochens ascogonium takes the shape of Perithecium. In Basidiolichens asexual reproduction takes place by means of basidiospores. In some lichens asexual reproduction is fullfilled by pycniospores or Pycnidia. These Pycniospores germinate by giving rise to hyphal branches in all directions and when any such branch comes in contact with algal cells, a lichen body is formed.
3. Sexual reproduction:
Sexual reproduction in Ascolichens and bsidiolichens resemble to that of Ascomycetes and Basidiomycetes members respectively. Ascolichens are the most common lichens containing male and female sex organs like spermatia and carpogonia (Ascogonia) respectively. Fertilisation if followed by the formation of ascogeenous hyphae from the basal portion of the ascogonium. The ascocarp is lined with a paliside like layer of paraphyses. During weather ascospores germinate and give rise to germtubes which on coming in contact with algal element produce the new thallus.
Classification of Gymnosperms
1. CLASSIFICATION OF GYMNOSPERMS
It was Robert brown who first recognized Gymnosperms directly into 7 orders.
• Bentham and Hooker while classification Angiosperms placed them in between Dicots and Monocots.
• Van Teigham divided Spermatophyte into 2 divisions: The Gymnosperms and Angiosperms.
• Coulter and Chamberlain divided Gymnosperms in to Seven orders
Bennettitales, Cycadales, Cordaitales, Ginkgoales, Coniferales and Gnetales(1917).
• Chamberlain(1934) classification.
GYMNOSPERMS
Cycadophyta Coniferophyta
Cycadifilicales Cycadeoidales Cycadales Cordaitales Ginkgoales Coniferales Gnetales
• Classification of Prof. Birbalsahani
GYMNOSPERMS
STACHYSPERM PHYLLOSPERMAE
CORDAITALES GINKGOALES CONIFERALES TAXALES PTERIDOSPERM CYCADALES
• Engler and Gilg divided Gymnosperms directly in to Seven orders
Cycadofilicales , Cordaitales , Bennettitales , Ginkgooales , Coniferales and Gnetales .
• Arnold divided gymnosperms in to 3 – phyla
Cycadophyta :- Pteridospermales , Cycadeoidales , Cycadales .
Coniferophyta :- Cordaitales , Ginkgoales ,Taxales and Coniferales
• Raizada and Sahni divided Gymnosperms into Three divisions
i. Cycadophytes : Pteridospermales , Cycadeoidales , Cycadales
ii. Pentoxylales : Pentoxylales
iii. Coniferophytes : Cordaitales , Ginkgoales , Coniferales , Gnetales
• Sporne also recognised in to three classes among the gymnosperms (1966).
Gymnosperms
Cycodopsida Coniferopsida Gnetopsida
Pteridospermales Cordaitales
Bennettitales Coniferales Gnetales
Pentoxylales Taxales
Cycadales Ginkgoales
• David birhorst (1971)
Gymnosperms
Cycadopsida Coniferopsida Gnetopsida
Pteridospermales Cordaitales Ephedrales
Caytoniales Protopityales Gnetales
Cycadeoidales Ginkgoales Welwistchiales
Pentoxylales Pentoxylales
Glossopteridales Taxales
It was Robert brown who first recognized Gymnosperms directly into 7 orders.
• Bentham and Hooker while classification Angiosperms placed them in between Dicots and Monocots.
• Van Teigham divided Spermatophyte into 2 divisions: The Gymnosperms and Angiosperms.
• Coulter and Chamberlain divided Gymnosperms in to Seven orders
Bennettitales, Cycadales, Cordaitales, Ginkgoales, Coniferales and Gnetales(1917).
• Chamberlain(1934) classification.
GYMNOSPERMS
Cycadophyta Coniferophyta
Cycadifilicales Cycadeoidales Cycadales Cordaitales Ginkgoales Coniferales Gnetales
• Classification of Prof. Birbalsahani
GYMNOSPERMS
STACHYSPERM PHYLLOSPERMAE
CORDAITALES GINKGOALES CONIFERALES TAXALES PTERIDOSPERM CYCADALES
• Engler and Gilg divided Gymnosperms directly in to Seven orders
Cycadofilicales , Cordaitales , Bennettitales , Ginkgooales , Coniferales and Gnetales .
• Arnold divided gymnosperms in to 3 – phyla
Cycadophyta :- Pteridospermales , Cycadeoidales , Cycadales .
Coniferophyta :- Cordaitales , Ginkgoales ,Taxales and Coniferales
• Raizada and Sahni divided Gymnosperms into Three divisions
i. Cycadophytes : Pteridospermales , Cycadeoidales , Cycadales
ii. Pentoxylales : Pentoxylales
iii. Coniferophytes : Cordaitales , Ginkgoales , Coniferales , Gnetales
• Sporne also recognised in to three classes among the gymnosperms (1966).
Gymnosperms
Cycodopsida Coniferopsida Gnetopsida
Pteridospermales Cordaitales
Bennettitales Coniferales Gnetales
Pentoxylales Taxales
Cycadales Ginkgoales
• David birhorst (1971)
Gymnosperms
Cycadopsida Coniferopsida Gnetopsida
Pteridospermales Cordaitales Ephedrales
Caytoniales Protopityales Gnetales
Cycadeoidales Ginkgoales Welwistchiales
Pentoxylales Pentoxylales
Glossopteridales Taxales
Subscribe to:
Posts (Atom)