Biology 2 Marks Questions

Primary and secondary productivity:

	Primary productivity	Secondary productivity
1	Rate of amount of production of organic matter by producers over a period of time.	Rate of amount of production of organic matter by consumers over a period of time.
2	It is due to photosynthesis.	It is due to herbivory and predation.

Food chain and Food web:

	Food chain	Food web
1	Food chain is single pathway of energy transfer from upper to lower.	Food web is made of several interconnecting pathways.
2	One individual occupies one trophic level at a time.	One individual occupies many trophic level at a time.
3	It decreases stability of the ecological system and less adaptive.	It increases stability of the ecological system and more adaptive.

Production and decomposition:

	Production	Decomposition
1	It is the rate of producing organic matter (food) by producers	It is the process of breaking down of complex organic matter or biomass from the body of dead plants and animals with the help of decomposers into organic raw materials.
2	It depends on the photosynthetic capacity of the producers.	It occurs with the help of decomposers.
3	Sunlight is required by plants for primary production	Sunlight is not required for decomposition by decomposers.

It is defined as the amount of organic matter or biomass produced by producers per unit area over a period of time. Primary productivity of an ecosystem depends on the variety of environmental factors such as light, temperature, water, precipitation, etc. It also depends on the availability of nutrients and the availability of plants to carry out photosynthesis.

Grazing food chain and detritus food chain:

	Grazing food chain	Detritus food chain
1	In this food chain, energy is derived from the Sun.	In this food chain, energy comes from organic matter (or detritus) generated in trophic levels of the grazing food chain.
2	It begins with producers, present at the first trophic level.	It begins with detritus such as dead bodies of animals or fallen leaves, which are then eaten by decomposers or detritivores.
3	This food chain is usually large.	It is usually smaller as compared to the grazing food chain.

Litter and detritus:

	Litter	Detritus
1	Litter contains all kinds of waste materials above the surface of the earth.	Detritus contains dead animals and plants below and above the surface of the earth.
2	It contains both biodegradable as well as non-biodegradable wastes.	It contains only biodegradable wastes.

Upright and inverted pyramid:

	Upright pyramid	Inverted pyramid
1	The pyramid of energy is always upright.	The pyramid of biomass and the pyramid of numbers can be inverted.
2	The number and biomass of organisms in the producer level of an ecosystem is the highest, which keeps on decreasing at each trophic level in a food chain.	The number and biomass of organisms in the producer level of an ecosystem is the lowest, which keeps on increasing at each tropic level. Light is not required for decomposition by decomposers.

The trophic level represents a functional level, not a species as such. A given species may occupy more than one trophic level in the same ecosystem at the same time; for example, a sparrow is a primary consumer when it eats seeds, fruits, peas, and a secondary consumer when it eats insects and worms.

Koel is a parasitic bird (which has lost the instinct to make its own nest to lay eggs) has evolved the technique of layings eggs in the nest of a crow, Its eggs bear resemblences to those of crow.

DFC - Dead and decaying organic matter/Dead remains of plants and animals.GFC - Living green plants/producers.

Productivity is rate of biomass production.
GPP - R = NPP.
NPP - is biomass available to consumers for secondary productivity.

Pyramid of energy is always upright, can never be inverted, because when energy flows from a particular trophic level to the next trophic level, some energy is always lost as heat at each step. Each bar in the energy Pyramid indicate the amount of energy present at each trophic level in a given time or annually per unit area.

Aquatic ecosystem - Grazing Food Chain/GFC.
Terrestrial ecosystem - Detritus Food Chain/DFC.
Difference : GFC begins with phytoplanktons/producers whereas DFC begins with dead organisms/detritus.

Detrivore feeds on dead plants and animals/detritus.Example: Earthworm/Nematodes.
Decomposer breaks down complex (organic) matter in (inorganic) matter.
Example: Fungus/Bacteria.

The secondary productivity indicates the rate at which food energy is assimilated at the trophic level of consumers, Light, oxygen, temperature, nitrogen.

Gradual decrease of energy at successive trophic levels.Decrease in light/ nutrients/ oxygen.

Ecosystem services are the products of ecosystem processes. Healthy forest ecosystem provides the following ecosystem services:

1. Purification of air and water.
2. Cycling of nutrients.
3. Generation of fertile soil.
4. Provision of habitat to wildlife.

Carbon is returned to the atmosphere by:

1. Respiration of all living organisms.
2. Burning of fossil fuels.
3. Decomposition of organic matter.
4. Forest fires.

1. Solar input.
2. Day length.
3. Cycle of temperature.
4. Other climatic factors.

1. A food chain is formed because of interdependence of organisms for food.
2. Starting from the producers (plants), which alone capture solar energy, the energy passes on to other consumers.
3. When the organisms die, the decomposers start acting on them and the detritus food chain starts.

Detritus is rich in nitrogen and sugars. For oxidation of nitrogen and sugars oxygen is required by a class of aerobic microbes.

1. Plants capture the solar energy and convert it into organic compounds during photosynthesis.
2. All other organisms depend on plants directly (herbivores) or indirectly (carnivores) on the plants for their energy needs.
3. So energy flows from producer to a number of consumers in a unidirectional manner and energy is neither created nor destroyed; thus the first law of thermodynamics is satisfied in the ecosystem functioning.

The reduction in population of tiger (predator) will result in an increase in deer (prey) population. The increased deer population will give more pressure on vegetation due to overgrazing. As a result, the plant population will decrease and lead to decreased deer population due to starvation, death and migration. As a result, the ecological balance will be disturbed, but in the long run these relationships stabilise the prey and predator population in a community.

The rate of succession is much faster in secondary succession as the substratum (soil) is already present as compared to primary succession where the process starts from a bare area (rock).

The producers occupy the first trophic level in terrestrial ecosystem and thus, make base of food chain. These producers (plants) are grazed upon by the grazers (herbivores) so herbivores are primary consumers. Primary carnivores prey upon herbivores and are eaten up by secondary carnivores.
This way the top carnivores are ferocious and are not eaten up by any other animal. The decomposers act on all dead animals/plants and return nutrients stored in them to the soil. These nutrients are again used up by the plants and cycle goes on. This way the grazing food chain and detritus food chains are linked up.

1. The small standing crop of the phytoplanktons-the one supports.
2. Large standing crop of zooplanktons-one which is supported.

Such a pyramid is found in aquatic ecosystem.

1. Only 1% of the incident light energy is converted by producers into chemical energy.
2. 10% energy is transferred from one trophic level to another trophic level in the food chain.
3. After a few transfers, the amount of energy at the higher trophic levels will be very less, to sustain those organisms; hence, the number of trophic levels in a food chain is limited.

Natural ecosystem These are capable of maintaining and operating themselves, without interference of man. They are further classified as:

1. Terrestrial ecosystem Forest, grassland, desert, etc.
2. Aquatic ecosystem Pond, lake, river, wetland, estuary, etc.

The rate of decomposition is regulated by climatic factors like temperature and soil moisture as they have an effect on the activities of soil microbes. The tropics with its hot and humid climatic condition provides an environment which is ideal for the microbes to speed up the process of decomposition.

Energy in an ecosystem flows from producers to primary consumers, then from primary consumers to secondary consumers and so on. There is never a back flow of energy, i.e. energy cannot come back to a trophic it has already passed. Therefore, the energy flow is unidirectional in an ecosystem.

If the rate of reproduction of phytoplanktons slows down then the net primary productivity decrease. As a result, flow of energy will also decrease in the successive trophic level.The following two factors cause reduction in phytoplankton reproduction:

1. Less water availability.
2. Less nutrient availability.

Effect of oxygen The decomposition of detritus is an energy requiring process. Most of the decomposers (bacteria and fungi) are aerobic organisms. They require oxygen for their cellular activities while acting on dead organic matter. Effect of chemical composition Decomposition rate is slower, if detritus is rich in lignin and chitin. It is quicker if detritus is rich in nitrogen and water soluble substances like sugars.

1. Succession, especially primary succession, is a very slow process taking thousands of years.
2. Both xerarch and hydrarch successions lead to a similar climax community that is mesic.

1. Stratification: It is the venical distribution of different species occupying different levels in an ecosystem, e.g. trees occupy top vertical strata or layer of a forest, shrubs the second and herbs and grasses occupy the bonom (third) layers.
2. Leaching: It is the process by which water-soluble inorganic nutrients go down into the soil horizon and get precipitated as unavailable salts.

A-Reed-swamp stage B-Submerged plant stage
C-Marsh meadow stage D-Shrub stage.

(1) and (2) are predator and prey respectively.
(3) is a primary consumer (second trophic level).
(4) is a producer (first trophic level).

It is because the biomass available to the consumer for consumption is a resultant of the primary productivity from plants.

The first pyramid of biomass corresponds to a terrestrial ecosystem. Second pyramid refers to a small standing crop of phytoplankton supporting a large standing crop of zooplankton or an aquatic ecosystem.

S.No.	Primary Succession	Secondary Succession
(i)	The ecological succession that takes place in a place, where no life existed before, is called primary succession.	The ecological that takes place in a region where life existed in the past but got wiped out completely is called secondary succession.
(ii)	It is comparatively slow as suitable soil has to be formed.	It is comparatively faster as soil or sediment is already present.

S.No.	Primary consumers	Primary carnivores
(i)	These are the animals which depend on plants for their food.	These are the animals which feed on the herbivorous animals.
(ii)	They occupy the second trophic level; they are herbivores.	They occupy the third trophic level; they are secoundary consumers.

The smallest amount of energy transferred is represented by arrow 2 and largest energy loss by arrow 3.

1. Condition of the soil.
2. Availability of water.
3. Environmental conditions.
4. Seeds/ other propagules present.

It is true that any change in the abiotic/ biotic factor will arrest a particular seral stage leading to a pre-climax condition before the climax stage is achieved. This can happen in cases of forest fires, landslide, change in soil characteristics, increase in herbivore population leading to overgrazing.

Grazing food chain:
Grass → Grasshopper → Frog → Snake → Vulture.
Detritus food chain:
Decaying plant matter → Earthworm → Bird Snake → Vulture.

GPP stands for Gross Primary Productivity. It is the rate of production of organic matter during photosynthesis in an ecosystem.
NPP stands for Net Primary Productivity. It is defined as GPP-Respiratory loss.

1. About 50%
2. < 10%
3. < 6%
4. < 6%

In this case, regrowth of forests is an example of ecological succession. After clearing of forests, the conditions become xerarch which proceeds to mesarch condition after the growth of forests.

Functional aspects of an ecosystem are:

1. Productivity.
2. Decomposition.
3. Energy flow.
4. Nutrient cycle.

Saprotrophs are those organisms, which meet their energy requirements by degrading the organic molecules.
They release enzymes which degrade/ decompose the organic matter outside their body and absorb the digested nutrients.

The three parameters used are:

1. Number of individuals in a trophic level.
2. Biomass of individuals in a trophic level.
3. Rate of flow of energy in a trophic level.

The pyramid may look inverted in a tree ecosystem where the number of consumers are numerous depending on a single producer.

1. Desert ecosystem.
2. Opuntia, Cacti and Acacia.

Primary productivity varies from ecosystem to ecosystem because it depends on the plant species inhabiting the area and their photosynthetic activity. It also depends on various environmental factors, which vary in different ecosystems.

The amount of living matter present at every trophic level at any given time, is called standing crop.

Availability of solar radiation is least in oceans; especially in deep oceans. Due to this, oceans are least productive.

1. Light.
2. Temperature.

1. Primary producer.
2. Secondary producer.
3. Secondary producer.
4. Primary producer.

S.No.	Primary Carnivores	Secondary Carnivores
(i)	These are the animals which feed on the herbivores (primary consumers).	These are the snimals, which feed on the primary carnivores (secondary consumers).
(ii)	They occupy the third trophic level; they are the secondary consumers.	They occupy the fourth trophic level; they are the tertiary consumers.

Lichens are pioneer species in primary succession on rocks. They secrete organic acids, which withers the rock and help in soil formation. Lichens by forming soil pave way for the next community, i.e. bryophytes.

Sparrow: It is a primary consumer when it feeds on grans but becomes a secondary consumer when it feeds on worms and insects.
Human: It is a primary consumer when it feeds on grains and pulses but becomes a secondary consumer when it feeds on lamb.

Crop fields and an aquarium considered as man-made ecosystems. In artificial ecosystems the biotic and abiotic components of ecosystems are maintained artificially by regular feeding and clearing of aquarium and regular irrigation and sowing of seeds in crop field ecosystem. Natural ecosystem self sustains biotic and abiotic components of an ecosystem.

Nutrients are cycles through biotic components as well as through abiotic components. The term ‘bio’ shows biotic components while ‘geo’ shows abiotic components. Hence, nutrient cycles in nature are called biogeochemical cycles.

If all the top carnivores are eliminated, then population of herbivores will become manifold. This will put the existence of green plants in danger because of overgrazing. Loss of green plants will force the herbivores to die because of starvation.

Secondary succession is faster than the primary succession because of presence of:

1. Soil for growth, which also results in quick attainment of climax.
2. Water, the environment and the seeds or other propagules which are easily available.

1. Zooplanktons.
2. Phytoplanktons.

• Such a pyramid of biomass is found in aquatic/ marine ecosystem.

In nature, the decomposer organisms like bacteria and fungi act on the dead organic matter and decompose it. Decomposition is a process of breaking down of complex organic matter into inorganic substances like CO, water and nutrients.

Reservoir in an ecosystem meets the deficit that arises due to the imbalance in the rate of influx and efflux of nutrients. The two types of nutrient cycles are:

1. Gaseous cycle.
2. Sedimentary cycle.

Apart from being a part of food chain, predators play important role in:

1. Maintaining the prey population and regulate intraspecies competition.
2. Indicating ecological disturbances as predators are small in number and highly sensitive to ecological changes owing to their excessive adaptation.

The rate of assimilation and formation of new organic matter by consumers is called secondary productivity.The factors which affect productivity in an aquatic ecosystem are:

1. Nitrogen in marine ecosystem.
2. Light, which decreases with increasing depth of water.

A system which is sustainable without relying on any external input is called a selfsustainable system. This ability of the system is called self-sustainability. Natural ecosystems are self-sustainable.

Following are the two activities which interfere with carbon cycle:

1. Clearing of forests: Reduced green cover hampers carbonification and thus interferes with carbon cycle.
2. Burning of Fossil Fuels: Burning of fossil fuels adds carbon to the atmosphere and increases the percentage of carbon dioxide in the atmosphere. It also interferes with the carbon cycle.