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BIO BOTANY [ 5 Marks Questions ]

Ecosystem. · Tamil Nadu Board STD 12 (Tamil - English Medium). 7 questions.

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Question 15 Marks
What are the significance of plant succession?
Significance of Plant Succession
Answer
  1. Succession is a dynamic process. Hence an ecologist can access and study the serai stages of a plant community found in a particular area.
  2. The knowledge of ecological, succession helps to understand the controlled growth of one or more species in a forest.
  3. Utilizing the knowledge of succession, even dams can be protected by preventing siltation.
  4. It gives information about the techniques to be used during reforestation and afforestation.
  5. It helps in the maintenance of pastures.
  6. Plant succession helps to maintain species diversity in an ecosystem.
  7. Patterns of diversity during succession are influenced by resource availability and disturbance by various factors.
  8. Primary succession involves the colonization of habitat of an area devoid of life.
  9. Secondary succession involves the re-establishment of a plant community in disturbed area or habitat.
  10. Forests and vegetation that we come across all over the world are the result of plant succession.
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Question 25 Marks
Write in detail about Autogenic succession and Allogenic succession.
Answer
Autogenic succession
Autogenic succession occurs as a result of biotic factors. The vegetation reacts with its environment and modifies its own environment causing its own replacement by new communities. This is known as autogenic succession.
Example: In forest ecosystem, the larger trees produce broader leaves providing shade to the forest floor area. It affects the shrubs and herbs which require more light (heliophytes) but supports the shade tolerant species (sciophytes) to grow well.Allogenic succession:
Allogenic succession occurs as a result of abiotic factors. The replacement of existing community is caused by other external factors (soil erosion and leaching, etc) and not by existing organisms.
Example: In a forest ecosystem soil erosion and leaching alter the nutrient value of the soil leading to the change of vegetation in that area.
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Question 35 Marks
Differentiate Primary succession and Secondary succession
Answer
Primary succession:
  1. Developing in an barren area.
  2. Initiated due to a biological or any other external factors.
  3. No soil, while primary succession starts
  4. Pioneer species come from outside environment.
  5. It takes more time to complete.
Secondary succession:
  1. Developing in disturbed area.
  2. Starts due to external factors only.
  3. It starts where soil covers is already present.
  4. Pioneer species develop from existing environment.
  5. It takes comparatively less time to complete.
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Question 45 Marks
List the characteristics of ecological succession.
Answer
  1. It is a systematic process which causes changes in specific structure of plant community.
  2. It is resultant of changes of abiotic and biotic factors.
  3. It transforms unstable community into a stable community.
  4. Gradual progression in species diversity, total biomass, niche specialisation, and humus content of soil takes place.
  5. It progresses from simple food chain to complex food web.
  6. It modifies the lower and simple life form to the higher life forms.
  7. It creates inter-dependence of plants and animals
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Question 55 Marks
What are the strategies of eco system management?
Answer
Strategy of ecosystem management
  1. It is used to maintain biodiversity of ecosystems.
  2. It helps in indicating the damaged ecosystem (Some species indicate the health of the ecosystem: such species are called a flagship species).
  3. It is used to recognize the inevitability of ecosystem change and plan accordingly.
  4. It is one of the tools used for achieving sustainability of ecosystem through sustainable development programme (or projects).
  5. It is also helpful in identifying ecosystems which are in need of rehabilitation.
  6. It involves collaborative management with government agencies, local population, communities and NGO’s.
  7. It is used to build the capacity of local institutions and community groups to assume responsibility for long term implementation of ecosystem management activities even after, the completion of the project.
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Question 65 Marks
Give a detailed account of Biotic and abiotic components of a pond ecosystem. Abiotic components
Answer
solution A pond ecosystem consists of dissolved inorganic $\left( CO _2, O _2, Ca , N\right.$ and Phosphate) and organic substances (amino acids and humic acid) formed from the dead organic matter. The function of pond ecosystem is regulated by few factors like the amount of light, temperature, pH value of water and other climatic conditions.
Biotic components:
They constitute the producers, variety of consumers and decomposers (microorganisms).
(a) Producers: A variety of phytoplanktons like Oscillatoria, Anabaena, Eudorina, Volvox and Diatoms. Filamentous algae such as Ulothrix, Spirogyra, Cladophora and Oedogonium; floating plants Azolla, Salvia, Pistia, Wolffia and Eichhornia; sub-merged plants Potamogeton and Phragmitis; rooted floating plants Nymphaea and Nelumbo; macrophytes like Typha and Ipomoea, constitute the major producers of a pond ecosystem.
(b) Consumers: The animals represent the consumers of a pond ecosystem include zooplanktons like Paramoecium and Daphnia (primary consumers); benthos (bottom living animals) like molluscs and annelids; secondary consumers like water beetles and frogs; and tertiary consumers (carnivores) like duck, crane and some top carnivores which include large fish, hawk and man, etc.
(c) Decomposers: They are also called as microconsumers. They help to recycle the nutrients in the ecosystem. These are present in mud water and bottom of the ponds. Example: Bacteria and Fungi. Decomposers perform the process of decomposition in order to enrich the nutrients in the pond ecosystem.
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Question 75 Marks
Describe the various stages of decomposition process.
Answer
  1. Fragmentation – The breaking down of detritus into smaller particles by detritivores like bacteria, fungi and earth worm is known as fragmentation. These detritivores secrete certain substances to enhance the fragmentation process and increase the surface area of detritus particles.
  2. Catabolism – The decomposers produce some extracellular enzymes in their surroundings to break down complex organic and inorganic compounds in to simpler ones. This is called catabolism
  3. Leaching or Eluviation – The movement of decomposed, water-soluble organic and inorganic compounds from the surface to the lower layer of soil or the carrying away of the same by water is called leaching or eluviation.
  4. Humification – It is a process by which simplified detritus is changed into dark coloured amorphous substance called humus. It is highly resistant to microbial action, therefore
    decomposition is very slow. It is the reservoir of nutrients.
  5. Mineralisation – Some microbes are involved in the release of inorganic nutrients from the humus of the soil, such process is called mineralisation.
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