Test: Ecosystem - 2 - NEET MCQ

Primary productivity is the rate at which solar energy is converted and stored by the producers per unit area over a time period. It involves the conversion of solar energy into organic substances by photosynthetic and chemosynthetic autotrophs.

The chemical energy of food is the main source of energy required by all living organisms. This energy is transmitted to different trophic levels along the food chain. This energy flow is based on two different laws of thermodynamics:

• First law of thermodynamics, that states that energy can neither be created nor destroyed, it can only change from one form to another.
• Second law of thermodynamics, that states that as energy is transferred more and more of it is wasted.

In most of the food chain of ecosystem only 4 to 5 trophic levels are present because loss of energy at successive levels is very high. Only 10% of energy is transferred to next trophic level.

A detritus food chain begins with dead organic matter. It is made of decomposers which are heterotrophic organism fungi and bacteria.Rhizophora species is a saprophyticheterotrophs.

Food web is formed by interaction between a numbers of food chains having common members. Stability of ecosystem largely depends upon the kinds of food web exists in it for proper flow of energy.

For greater efficiency a food chain must have three to four trophic levels. At each trophic levels loss of energy is very high so very small amount of energy is left after there trophic level.

At each trophic level only ten percent of energy is transferred from one trophic level to next trophic level from producer to consumers. So, only 20J of energy is available to tertiary consumers.

Productivity is the rate of new biomass production by an individual, population, community within an ecosystem. The productivity of an ecosystem depends on several environmental factors such as light, water, temperature, precipitation, etc.

In a food chain, number of organisms reduce from producer to carnivores at each trophic levels. So, the number of carnivores will be less than the prouder which is less than 10 million.

In ecological pyramids, saprophytes do not have any place even though they play very vital role in ecosystem. This is because ecological pyramids does not take into account same species belonging to two or more trophic levels.

A constant input of solar energy is the basic requirement for any ecosystem to function and sustain. Primary production is defined as the amount of  biomass or organic matter produced per unit area over a time period by plants during photosynthesis. It is expressed in terms of weight (gm^–2 ) or energy (kcal m^–2 ). The rate of biomass production is called productivity. It is expressed in terms of gm² yr ^–1 or (kcal m^–2 ) yr ^–1 to compare the productivity of different ecosystems.

Breakdown of detritus by microbial enzymes into simple forms is called catabolism in which mass of the organisms decrease without any external reduction is size of the organisms.

If a predator is too efficient and overexploits its prey, then prey might become extinct. The predator will also become extinct for lack of food. Therefore, predators in nature are prudent.

Primary consumers obtain food from producers or autotrophs. In aquatic ecosystem phytoplankton are main prouder and zooplankton are primary consumers along with frog tadpole , snail and tortoise.

Decomposition is the process by which decomposers like bacteria and fungi break down dead organic matter, releasing nutrients back into the soil for reuse by producers. This is crucial for nutrient recycling in an ecosystem. Photosynthesis produces energy-rich compounds but does not recycle nutrients. Respiration releases energy, not nutrients. Nitrogen fixation converts atmospheric nitrogen into usable forms but is less broad in nutrient recycling compared to decomposition.