BIOLOGY 3 Marks Question

If all herbivores are eliminated from an ecosystem, there will be no food for the carnivores. Eventually, all the carnivores would be finished because of lack of food. Absence of herbivores will also result in exponential growth in plant population. But lack of other biotic factors will stop biogeochemical cycle. This will finally finish the ecosystem.

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.

Eltonian pyramid or ecological pyramid is graphic representation of an ecological parameter such as number of individuals, biomass or energy present in various trophic levels of a food chain with producers forming the base and carnivores the top.

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

The pioneer community of xerarch is usually lichens in the temperate regions and blue green algae in tropical region, whereas phytoplanktons (diatoms, green flagellates, green algae) followed by the zooplankton in the hydrarch succession.

Humification leads to accumulation of a dark coloured amorphous substance called humus that is highly resistant to microbial action and undergoes decomposition at an extremely slow rate. Being colloidal in nature it serves as a reservoir of nutrients. The humus is further degraded by some microbes and release of inorganic nutrients occurs by the process known as mineralisation.

The decomposition of detritus is due to activities of micro-organisms. The rate of growth of microbes is affected by temperature. The pH of substratum affects the composition of microbes (acidophiles/ basophiles) which degrade the dead organic matter. If oxygen is present, aerobic degradation occurs. In the absence of oxygen anaerobiosis sets in and there will be incomplete degradation. Also, the degradation is due to activity of exoenzymes secreted by the microbes and the activity of enzyme is affected by factors such as temperature etc.

We know that just 10% of energy consumed at a trophic level is available for the next trophic level. Here; 10kg of deer’s meat means 10kg of biomass at the level of primary consumer. Out of this, 90% is utilized by the deer for its own needs. Rest 10%, i.e. just 1kg is available for the lion. Hence, it is correct to say that 10kg of deer’s meat is equivalent to 1kg of lion’s flesh.

Limitations of ecological pyramids:

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.

Aquarium is man-made ecosystem and it has its own limitations. The confined space of aquarium cannot have endless supply of inorganic materials for producers. For supporting even a small number of consumers, there is a need for a large number of producers which is not possible in a small space of aquarium. One needs to provides food for the fish in the aquarium and regular cleaning of aquarium is also necessary. This shows that an aquarium is not a complete ecosystem because it is not self-sustainable.

Oceans and atmosphere.

Decomposers are saprophagous/ saprotrophs, which feed on dead bodies of organisms and organic wastes of living organisms.
They bring about decomposition and mineralisation of the dead matter to release them back for reuse by the autotrophs.

Detritivore	Decomposer
Detritivore is an organism that breaks down the detritus into smaller particles in the process, called fragmentation, e.g. Earthworm.	Decomposer is an organism which by secreting enzymes degrades the detritus into simpler inorganic substances, e.g. Some bacteria and some fungi.

An ecosystem is a functional unit with biotic and abiotic factors interacting with one another resulting in a physical structure. Absence of any component will make an ecosystem incomplete as it will hinder the functioning of the ecosystem. Examples of such an ecosystem can be a fish tank or deep aphotic zone of the oceans where producers are absent.

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.

Gross primary productivity (GPP) is the rate of production of organic matter during photosynthesis.
GPP - Respiration losses (R) = Net primary productivity (NPP).

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.

The entire sequence of development stages of biotic succession from pioneer to a climax community is called sere.
Dominant species is that species which represent most numerous population in a seral or climax community.

Poaching (hunting) of tiger disturbs the ecological balance in ecosystem. Tigers are important predator of forest. Predator keeps prey population under control. Due to hunting of tiger its population decreases, hence the population of deer (prey) increases and interspecific competition occurs between them. Due to increase in prey population (that feeds on vegetation/ grass), vegetation destroyed rapidly which causes ecological disturbance.

The consumers may be of following types:

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.