Bihar Board - Class 12 Biology - Chapter 14: Ecosystem Long Answer Question

1. What is meant by ecological succession? Describe the different stages in which succession occurs? 

Ans. Ecological succession is a community–controlled phenomenon in which the structure and composition of the community change in a systematic and orderly manner, eventually leading to the establishment of a climax community.

Stages of Succession: - 

1. Invasion: - Invasion is the arrival of propagating organs such as seeds, spores, bulbils, etc. on a bare area of primary or secondary succession. Those for which conditions are favorable germinate in a new area and some of them grow into mature plants. These new arrivals from outside are called pioneers.

2. Establishment: - The process by which migrants adjust themselves to new areas after the migration is called ecesic. It consists of three essential processes i.e., germination, growth, and reproduction. 

3. Aggregation: - The coming together of individuals of various species in an area are called aggregation. 

4. Competition: - The species which have similar requirements of nutrition are known as competitive species e.g., those with the different requirements are complementary species. 

5. Reaction: - It is the changes caused by colonizers within the habitat. The influence of vegetation on the site is referred to as a reaction until a stable community develops in that area.

2. Describe the components of an ecosystem? 

Ans. An ecosystem is a functional unit of nature consisting of biotic and abiotic factors where the living organisms interact among themselves and with the physical environment. The ecosystem consists of two components: -

1. Abiotic Components: - 

1. Inorganic substances e.g., phosphorus, Sulphur, carbon, nitrogen hydrogen, etc.

2. Organic substances e.g., carbohydrates, proteins, lipids. 

3. Climatic regime e.g., light, humidity, rainfall, temperature. 

2. Biotic Components: - 

1. Producers: - The organisms which produce food for themselves and all living organisms from inorganic raw material and solar radiation are called producers. 

2. Consumers: - These are living heterotrophic members of the ecosystem that consume the food synthesized lay producers. They are broadly classified as: 

1. Primary Consumers: - They are directly dependent on producers called herbivores. Example: - Rat, deer, cow, goat. 

2. Secondary Consumers: - The organisms that use primary consumers as their food are called carnivores. Example: - Fox cats, lions. 

3. Tertiary Consumers: - These are top carnivores that prey upon other carnivores and herbivores. Example: - Crow, man. 

3. Decomposers: - Organisms that break up the dead bodies of plants, animals, and related waste products are called decomposers. Example: - Bacteria, Fungi etc.

3. What do you mean by “productivity of an ecosystem? What types of productivity also mention the factors on which productivity of an ecosystem depends? 

Ans. Productivity of an ecosystem is the rate at which solar radiation energy is fixed by the vegetation of an ecosystem per unit area & per unit time. It is generally expressed in terms of a unit of energy (cal) produced in a unit area (m2) per unit time (year). Productivity can be of two types: - 

1. Primary Productivity: - It is defined as the amount of biomass or organic matter produced per unit area by plants during photosynthesis over a given period. Primary productivity is of following two types: - 

1. Gross primary productivity (GPP): - It refers to the total amount of food formed by the producers during photosynthesis.

2. Net primary productivity (NPP): - It refers to gross primary productivity minus loss by respiration (R).

NPP=GPP-R

2. Secondary Productivity: - Secondary productivity is the rate of storage at the consumer level. It is defined as the rate at which organic matter is synthesized by consumers over a given period.

Primary productivity is determined by: - 

1. Several environmental factors.

2. Availability of nutrients. 

3. Photosynthetic capacity of plants.

4. What is decomposition? Describe the different processes involved in decomposition?

Ans. Decomposers (bacteria, fungi) help in the breakdown of complex organic matter into simple inorganic substances like CO2, H2O, minerals. This process is called decomposition. Detritus is made up of dead plant remains such as leaves, bark, and flowers, as well as remains of dead animals along with fecal matter. The important processes involved in decomposition are: -

1. Fragmentation: - Detritivores are organisms that break down detritus into smaller particles. 

2. Leaching: - By leaching, water-soluble inorganic nutrients penetrate the soil horizon and precipitate as unavailable salts.

3. Catabolism: - The enzymes of bacteria and fungi degrade detritus into simple inorganic substances.

4. Humification: - Humification results in the accumulation of humus, a dark-colored amorphous substance. This is highly resistant to microbial action and undergoes decomposition at an extremely slower rate. 

5. Mineralization: - Some microbes further degrade the humus, resulting in the release of inorganic nutrients via the mineralization process.

5. Describe the phosphorus cycle in an ecosystem?

Ans. Phosphorus Cycle: -

1. The major reservoir of phosphorus is sedimentary rocks which are only available to basic cycle in small amounts as a result of weathering.

2. This phosphorus is weathered and later transported to the soil by wind and water, where they exist as inorganic dissolved phosphates.

3. The basic phosphorus cycle begins with dissolved phosphates which are absorbed by plants for making their issue. 

4. Plants are then eaten by animals. Decaying bacteria break the tissue of dead animals and these products return phosphates to the soil. 

5. The water-soluble phosphates are lost to the deep rudiments of the ocean through run-off. 

6. The major pathway of returning phosphorus to land is the uplifting of marine sediments. Some amount of phosphorus is returned to absorb inorganic phosphate, when they die, most of the absorbed phosphate is recycled back into ambient matter. This sort of cycling is called the biological cycle or metabolic cycle.

6. Why is the rate of decomposition affected by abiotic factors such as pH of the soil, availability of oxygen, temperature etc?

ANS. The pH of the soil affects the structure of basophilic and acidophilic microbes. The aerobic processes occur in the presence of oxygen causing complete degradation of a substance whereas anaerobic processes occur in the absence of oxygen, resulting in incomplete degradation of a substance. Microbes are unable to grow to their fullest at higher temperatures but at low or high temperatures, stress-tolerant microbes flourish.