BIOLOGY 3 Marks Question

1. Primary succession in water:

• The pioneer species are phytoplanktons.
• The phytoplanktons are replaced by free-floating angiosperms.
• Then, rooted angiosperms invade sedges, grasses and finally the trees.
• At last, a stable climax forest is formed.
• An aquatic habitat is converted into mesic habitat.

2. Primary succession on rocks:

• Lichens are the pioneer species on a bare area.
• The lichen secretes some acids to dissolve rock and help in weathering and soil formation.
• Later, some small bryophytes invade and hold the small amount of soil.
• The bryophytes are succeeded by herbs, shrubs and ultimately big trees.
• At last, a stable climax forest is formed.
• The xerophytic habitat gets converted into a mesophytic one.

1. Ecological succession is the phenomenon in which the structure and composition of communities change in an orderly and sequential manner leading ultimately to the establishment of a climax community.
2. The ecological succession in a forest destroyed by a forest fire will be faster, because, there is already soil (substratum) and organic matter present; some vegetative propagules may also be present and it is secondary succession.
3. In a newly created pond, it is primary succession as there is not much of organic matter or any propagules; hence it will take a very long time.

1. Terrestrial ecosystem: Forest, grassland, desert, etc.

2. Aquatic ecosystem: Pond, lake, river, wetland, estuary, etc.

3. Man-Made ecosystem: A manmade ecosystem is an artificial biological system that is managed and sustained by people.

1. Chemical composition of detritus:

• Decomposition is faster when detritus is rich in nitrogen and water-soluble substances like sugars.
• Decomposition is slow when detritus is rich in lignin and chitin.

2. Oxygen:

• Decomposition is an oxygen-consuming process.
• Anaerobic conditions inhibit decomposition.

1. Trees.
2. Deer and rabbits.
3. Snakes and hawks.

2. As energy flows from one trophic level to the next, approximately 90% of it is lost.
3. Eventually there is not enough energy to support another level.

1. Lichen stage.
2. Moss stage.
3. Annual grass stage.
4. Perennial grass stage.
5. Shrub stage.
6. Climax community.

1. Small short lived plants (r-selection) to large long lived plants (k-selection).
2. Unstable biotic community to stable biotic community.
3. Little diversity to high degree of diversity.
4. Aquatic or dry conditions to mesic conditions.

1. Both producers and consumers die and decompose.
2. Only producers use inorganic nutrients to make organic molecules.
3. Energy does not cycle.

1. The process by which autotrophs convert inorganic materials into organic material with the help of solar energy is called photosynthesis.
2. The green pigment which traps solar energy and converts light energy into chemical energy is chlorophyll.
3. The three pigments, i.e. chlorophyll, carotenoids and xenthophylls together form a complex of pigments in the thylakoid membrane. These complexes work for the absorption of light and its transfer to a reaction centre,

These complexes are called photosynthetic unit or photosystem or pigment system.

1. Primary consumers: The consumers that feed on plants direcdy, are called primary consumers or herbivores.

2. Secondary consumers: Those animals, which ear other animals, who ear plants are called secondary consumers. These are also referred ro as primary carnivores.

3. Tertiary consumers: These are animals who feeds on secondary consumers for their nutrition. These are also referred to as secondary carnivores.

Therefore, due to this interdependence of food/energy between organisms, the chains or webs are formed in the ecosystem.

It is a graphic presentation of aquatic food chain in terms of numbers of producers and consumers at each level.

1. It never takes into account the same species belonging to two or more trophic levels.
2. It assumes a simple food chain, which never exists in nature.
3. In spite of the vital role played by saprophytes/ decomposers, they are not given any position in ecological pyramids.

1. Reed-swamp stage.
2. Submerged plant stage.
3. Marsh-meadow stage.
4. Scrub stage.

Both the hydrarch and xerarch lead to mesic conditions of forest.

1. Reduction in primary productivity. No biomass available for consumption by higher trophic levels/ heterotrophs and hence heterotrophs also die of starvation.
2. Increase in primary productivity and biomass of producers. Carnivore population will subsequently dwindle due to food shortage.
3. Increase in number of herbivores which leads to over-grazing by herbivores, finally resulting in desertification.

1. The process of harvesting chemical energy for metabolic activities by oxidising the food molecules is called respiration.
2. The most common substrate used in the process is glucose.
3. ATP or Adenosine Triphosphate is also known as energy currency of the cell.