Ecosystem

Productivity is the rate of biomass production.

Net primary productivity is the Gross primary productivity (GPP) minus respiration losses (R). Gross primary productivity is the rate of production of organic matter during photosynthesis. Secondary productivity is the rate of formation of new organic matter by consumers.

Decomposition is the process of breaking down of complex organic matter into inorganic substance. Detritus includes dead remains of plants and animals including fecal matter and acts as the raw material for decomposition.

Degradation of humus by activity of microbes leading to release of inorganic nutrients is called Mineralisation.

Accumulation of the dark coloured amorphous substance called humus, is called humification.

Primary consumers in a food chain are the herbivores.

Energy flow is unidirectional. First plants capture solar energy and then, food is transferred from the producers to decomposers.

Pyramid of energy is always upright. It 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.

The transfer of energy follows 10 per cent law - only 10 per cent of the energy is transferred to each trophic level from the lower trophic level.

The primary source of energy in an ecosystem is solar energy. Gross primary productivity in an ecosystem refers to the rate at which organic matter is produced during photosynthesis. Therefore, while the first statement is correct, the second one is incorrect because it mistakenly defines net primary productivity instead of gross primary productivity.

Ramdeo Misra is known as the father of Ecology in India.

Sun is the only source of energy for all ecosystems on Earth, except for deep sea-hydro-thermal ecosystem.

The energy flow is unidirectional from the sun to producers and then to consumers.

Ecosystems are not exempted from the second law of thermodynamics. They need a constant supply of energy to synthesise the molecules they require to counteract the universal tendency towards increasing disorderliness.

The rate of biomass production, known as productivity, is typically expressed in units such as $\mathrm{gm}^{-2} \mathrm{yr}^{-1}$ or $\left(\mathrm{KCal} \mathrm{m}^{-2}\right) \mathrm{yr}^{-1}$. These measurements allow for the comparison of productivity across various ecosystems.

According to the given pyramid of energy, if T$_4$ is equivalent to 1000 J, then according to the 10 percent law, which states that only 10 percent of energy is transferred to each trophic level from the lower trophic level, the value at T$_1$ is 10,00,000 J.

$\begin{aligned} & T_1=10,00,000 \mathrm{~J} \\ & T_2=\frac{10}{100} \times 10,00,000=1,00,000 \mathrm{~J} \\ & T_3=\frac{10}{100} \times 100000=10,000 \mathrm{~J} \\ & T_4=\frac{10}{100} \times 10000=1000 \mathrm{~J} \end{aligned}$

The correct answer is Option C: It accommodates a food web. Here's why:

Ecological pyramids are a visual representation of the trophic levels in an ecosystem, depicting the flow of energy and biomass. However, they have limitations in accurately representing the complexities of real-world ecosystems.

Let's analyze each option:

Option A: Saprophytes are not given any place in ecological pyramids

This is a valid limitation. Saprophytes, organisms that decompose dead organic matter, play a crucial role in nutrient cycling but are often not included in traditional ecological pyramids.

Option B: It assumes a simple food chain, that almost never exists in nature

This is another valid limitation. Most ecosystems have intricate food webs, with organisms feeding on multiple trophic levels. Ecological pyramids struggle to capture these complex interrelationships.

Option C: It accommodates a food web

This is incorrect. Ecological pyramids are fundamentally based on simple food chains, not food webs. The complex interactions of a food web, where organisms occupy multiple trophic levels simultaneously, are difficult to represent using a pyramid.

Option D: It does not take into account the same species belonging to two or more trophic levels

This is another valid limitation. For example, a species like an omnivore might consume both producers and herbivores, making it difficult to categorize them in a single trophic level.

In summary, ecological pyramids are useful tools for visualizing energy flow and biomass distribution within an ecosystem. However, they are simplified models that cannot fully capture the complexity of real-world food webs and ecological relationships.

NPP at first trophic level would be the GPP for second trophic level. NPP at second trophic level would be GPP for third trophic level. Therefore, $100 x\left(\mathrm{kcal} / \mathrm{~m}^2 / \mathrm{yr}\right)$ would be GPP at second trophic level and $100 x \times 10 \%\left(\mathrm{kcal} / \mathrm{~m}^2 / \mathrm{yr}\right)$ i.e., $10 x\left(\mathrm{kcal} / \mathrm{m}^2 / \mathrm{yr}\right)$ energy would be GPP at third trophic level.

The correct answer is :

Option D : (A)-(IV), (B)-(III), (C)-(I), (D)-(II)

Explanation :

(A) Hydrarch succession - (IV) Phytoplankton to mesic conditions. Hydrarch succession occurs in wet or aquatic areas, starting from an aquatic stage like phytoplankton and gradually moving towards mesic conditions, where the environment is neither too wet nor too dry.

(B) Xerarch succession - (III) Lichens to mesic conditions. Xerarch succession occurs in dry areas, such as deserts or rocks, and typically begins with organisms like lichens, gradually moving towards mesic conditions.

(C) Ecological succession - (I) Gradual change in the species composition. Ecological succession is the process by which the structure of a biological community evolves over time, involving a gradual change in species composition.

(D) Secondary succession - (II) Faster and climax reached quickly. Secondary succession refers to the series of community changes that occur on a preexisting, disrupted habitat and is typically faster than primary succession with the climax being reached more quickly because it begins on soil and not bare rock.

Option A : Standing state

Explanation : "Standing state" is a term used in ecology to denote the amount of nutrients such as carbon, nitrogen, potassium, calcium, etc., present in the soil at any given time. It provides an estimate of the availability of these nutrients in the ecosystem.

On the other hand, "Standing crop" is a term used to describe the total biomass (the mass of living biological organisms) of an organism in a particular area or volume at a specific time.

"Humus" refers to the organic component of soil, formed by the decomposition of leaves and other plant material by soil microorganisms.

"Detritus" is dead particulate organic material. It typically includes the bodies or fragments of dead organisms, as well as fecal material. Detritus is typically colonized by communities of microorganisms which act to decompose it.

The correct answer is :

Option D : Keystone species

A keystone species plays a crucial role in maintaining the structure of an ecological community, affecting many other organisms in an ecosystem and helping to determine the types and numbers of various other species in the community. The absence of a keystone species can lead to a significant shift in the ecosystem and a loss of biodiversity.

Exotic species or Alien species are organisms that have been introduced into an area outside their normal distribution.

Endemic species are species that are native to, and only found in, a specific geographical area. This could be an island, a country, or even a particular habitat type. Endemic species often have unique adaptations to their specific environment and may be particularly vulnerable to changes in that environment, including the introduction of exotic species.

Let's evaluate each statement:

A. Detrivores perform fragmentation.

• This statement is true. Detrivores, such as earthworms and beetles, break down detritus (dead organic material) into smaller pieces in a process called fragmentation.

B. The humus is further degraded by some microbes during mineralization.

• This statement is true. Microbes, including bacteria and fungi, break down humus into inorganic nutrients in a process called mineralization.

C. Water-soluble inorganic nutrients go down into the soil and get precipitated by a process called leaching.

• This statement is true. Leaching refers to the process where nutrients are washed away from the soil into lower layers or into bodies of water.

D. The detritus food chain begins with living organisms.

• This statement is false. The detritus food chain begins with dead organic material or detritus, not living organisms.

E. Earthworms break down detritus into smaller particles by a process called catabolism.

• This statement is false. The process by which earthworms break down detritus into smaller particles is called fragmentation, not catabolism. Catabolism refers to the breakdown of complex molecules in living organisms to form simpler ones, along with the release of energy.

Therefore, the correct answer is :

Option D : A, B, C only.

In the equation GPP - R = NPP,

GPP stands for Gross Primary Productivity, NPP stands for Net Primary Productivity, and R represents the energy used by plants for their own metabolic processes, which is also known as Respiratory loss.

Algal bloom imparts a distinct colour to the water bodies. It causes deterioration of the water quantity and fish mortality.

(+, +) Mutualism : In this interaction, both the interacting species are benefitted.

(+, 0) Commensalism : Only one species is benefitted and the other species remains unharmed.

($-$, 0) Amensalism : Neither species is benefitted. One remains unharmed and the other is harmed.

(+, $-$) Parasitism : One species is benefitted and other is negatively effected.

Both hydrarch and xerarch succession lead to medium water condition called mesic condition. This condition is neither too dry nor too wet.

In primary succession in water, the pioneers are the small phytoplanktons, which are replaced with time by rooted-submerged plants, rooted floating angiosperms followed by free-floating plants, then reed-swamp, marsh-meadow, scrub and finally trees.

The species that invade a bare area are called pioneer species.

The individual transitional communities in an ecological succession are termed as seral stages or seral communities.

Two individuals that are competing for same resource can avoid competition by choosing different times for feeding or different foraging patterns.

Decomposition is the process by which decomposers breakdown complex organic matter into inorganic substances.

The rate of decomposition is controlled by chemical composition of detritus and climatic factors. Decomposition is slower if detritus is rich in lignin and chitin and quicker, if detritus is rich in nitrogen and water soluble substances like sugars.

Phosphorus cycle is a sedimentary cycle. Reservoir pool of phosphorus in ecosystem is the earth's crust or lithosphere. Weathering of rocks accelerate phosphorus cycle.

(Detritivores break down detritus into smaller particles) e.g. earthworm. This process is called fragmentation.

Nitrogen cycle is an example of gaseous cycle where the material involved in circulation between biotic and abiotic components of biosphere are gases. The reservoir pool is atmosphere. On the other hand, in sedimentary cycle, the reservoir pool is lithosphere and the circulating material is non-gaseous, e.g. phosphorus, sulphur, etc. The pyramid of biomass in aquatic environment, e.g. sea is inverted.