Test: Ecosystem - 2 - NEET MCQ

Decomposers breaks the complex organic matter present in dead plants and animals into simpler form that can be reused. They acts as reducer of dead and decaying matters.

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.

Ecosystem consists of biotic component producer, consumer and decomposer. Producer fix solar energy into useable forms and decomposer breaks the complex organic matter into simpler forms but consumer do not perform specific function so non-essential.

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.

Carbon cycle is the most perfect biogeochemical cycle because carbon cycle operates globally. Carbon cycles include atmosphere, lithosphere and hydrosphere all together.

The characteristic of soils such as soil composition, grain size and aggregation determine the percolation and water holding capacity of the soil. Along with these pH and mineral composition determine the type of vegetation.

The unit of primary productivity is the weight (g^-2) or weight (kcal m^-2). The rate at which the solar energy is converted and stored by the producers per unit area over a time period is called primary productivity.

Exponential growth occurs in the population in which sufficient food and nutrients are available in sufficient amount. The rate of growth is very fast in this kinds of growth.

Exponential growth in a population occurs when:

• Food and nutrients are plentiful.
• Water is abundant.
• There is sufficient living space.

These conditions ensure that individuals can reproduce rapidly without facing resource limitations, leading to a fast and continuous increase in population size. Thus, the correct answer is C: All of these.

The species facing completion might evolve mechanisms that that promote co-existence rather than exclusion. This mechanism is called resource partitioning.

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.

In ecological succession, the individual transitional communities to inhibit an area are commonly called seral stage or seral communities that leads to climax communities.

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.

Phosphorus cycle occurs at local level in an ecosystem as it is mainly derived from soil. Carbon cycles occurs through environment and affected by different ecosystem present on earth surface. So, carbon cycle is global in nature.

Universal non-polluting source of energy is sun. All the sources of energy are directly and indirectly derived from sun including fossil fuels.

Earth crust is the reservoir of sedimentary type of nutrients like phosphorus. Atmosphere is the reservoir of gaseous types of cycle like oxygen and nitrogen along with carbon.