BIOLOGY M.C.Q (1 Marks)

The gradual change in the species structure of an ecological community is known as ecological succession. A climax community is the final community formed when the ecological succession becomes stable. It remains relatively unchanged until destroyed by an event such as fire or human interference. It is also known as a stable biological community.

Climax community is in a state of equilibrium.

The plants or the other autotrophic organisms which can prepare food require sunlight. In a cave, there will be very less availability of sunlight and hence primary productivity due to photosynthesis by green plants will be very low. Hence, a cave ecosystem is most unsuitable for primary productivity.

The appearance of living organisms on disturbed or damaged habitat is referred to as secondary succession.
Primary succession occurs in a barren land where no life existed before.
So, flooded land abandoned croplands and the area where organisms existed before exhibit the secondary succession.

In tropical rain forest, there is ambient temperature, good moisture and plenty of sugar in detritus. Due to this, rate of decomposition would be fast.

The total quantity of solar energy converted into chemical energy by green plant is known as gross primary production.
A portion of gross production is used by the producers for their various metabolic activities. The remainder of energy after utilization is called as net primary production.

Losses due to respiration is seen in case of carbon cycle.

In an ecosystem, the rate of production or accumulation of organic matter per unit area per unit time is called productivity.
Plants are autotrophic. They perform photosynthesis by using solar energy to synthesize their own food. Hence they are the producers in an ecosystem.
The rate at which solar energy is stored by producers is called primary productivity.

The carbon cycle involves the exchange of carbon among the biosphere, pedosphere, geosphere, hydrosphere and atmosphere of the Earth.

This final, stable community is called as climax community because, unlike communities earlier on in the successional process, it doesn’t change much in composition from year to year succession has reached its climax.

A pyramid of numbers is a graphical representation of the number of organisms per unit area at each trophic level.
It is generally upright as the maximum number of individuals occur at the producer level.

Recycling of material is carried out by decomposers. If decomposers of an ecosystem vanish recycling of materials is stopped, thereby affecting the movement materials between the biotic and the abiotic systems that forms the biogeochemical cycle.

Zooplankton are primary consumers in aquatic food chains that feed upon phytoplankton.
Therefore, they are present at the second trophic level in a lake.

Primary productivity is the amount of energy or biomass accumulation in green plants per unit area per unit time. It depends upon the availability of solar radiations, optimum temperature, soil moisture and biogenetic nutrients.
Gross primary productivity is the total organic matter synthesized by the producers in the process of photosynthesis.
Net primary productivity is the total organic matter stored by producers per unit area per unit time.
Secondary productivity is synthesis of organic matter by consumers per unit area per unit time.

The rate of production of total organic matter during photosynthesis is called the gross primary productivity. It is also equal to the amount of carbon fixed during photosynthesis by all producers in that particular ecosystem.

The pyramid of biomass is an ecological pyramid, which represents the biomass at various trophic levels.
It represents the living material produced at each level from the food obtained from the previous level.
It is upright except for the aquatic food chain, which involves planktons.

Although grazing is harmful for plants but grazing may beneficial by adding their excretion into soil, which provides essential mineral nutrition to plants.

Lichens are considered as pioneer species in primary succession on rocks because they can easily grow on rocks where other plants cannot grow. They produce oxalic acid which induced the weathering of rocks and thus soil is formed. When these lichens die they increase the soil fertility so other plants can grow and start the chain reaction.

Lichens are pioneer in succession in a new terrain and colonise bare rocks. They are the pioneers of plant kingdom. Since they are able to establish themselves on bare rocks and initiate formation of soil, they are called "farmers of nature".

Secondary succession is the sequence of changes that happens on a previously colonized but damaged habitat. The forests fires have resulted in the destruction of the habitat which was present at a time. The development of new vegetation after forest fire is an example of secondary succession.

If the carbon atoms fixed by producers already have passed through three species, the trophic level of the last species would be tertiary consumer.

Cycling of nutrients, prevention of soil erosion and pollutant absorption and reduction of the threat of global warming is an ecosystem service provided by a natural ecosystem.

Pyramid of energy is ecological pyramid, that represents the flow of energy from one trophic level to the next a lot of wastage occurs in metabolism and energy transfer. Maximum energy content is present in producers and least at top carnivore levels.

Agaricus belongs to fungi and hence are saprotrophs, while others belong to algae which are autotrophs.

The natural reservoir of phosphate is the rock which contains phosphorus in the form of phosphates when rocks are weathered, minute amounts of these phosphate dissolve in soil solution and are absorbed by the roots of the plants. Herbivores and other animals obtain this element from plants.

Decomposers depend on other organisms for food, hence they are heterotrophs. They obtain nutrients by decomposing the detritus and hence are called saprotrophs.

Primary succession can happen when bare sand is colonised by plants. Over time, the sand builds up into sand dunes, raising the ground above the height of sea level. Succession in sand dunes is sometimes called a psammosere.

A large amount of phosphate is lost in the sea by sedimentation. This is irretrievable loss.

The pyramid of biomass is more fundamental, they represent the quantitative relationships of the standing crops. In this pyramid, there is a gradual decrease in the biomass from the producers to the higher trophic levels.
In an ocean, as the producers are small organisms, their biomass is the least, and this value gradually shows an increase towards the apex of the pyramid, thus making the pyramid inverted in shape.

In terrestrial ecosystem pyramid of biomass is generally upright. The pyramid of biomass in sea or lake is generally inverted because the biomass of fishes for exceeds that of phytoplankton.

Tropical rain forests have high population density of green plants. Hence, net primary productions are maximum in such conditions.

Pyramid of energy is always upright, and can never be inverted, because when energy flows from a particular trophic level to the next, some energy is always lost as heat at each step. The base of the pyramid is broad and it narrows down at the apex.

An ecosystem is an open system because an open system is a system in which energy and nutrients are exchanged between the physical environment and living organisms.
All the ecosystems on Earth are called open systems.

The zone at the edge of a lake or ocean which is alternatively exposed to air and immersed in water is called littoral zone.