Question 1

Fill in the blanks.

(a) Plants are called as ______ because they fix carbon dioxide.
(b) In an ecosystem dominated by trees, the pyramid (of numbers) is ______ type.
(c) In aquatic ecosystems, the limiting factor for the productivity is _______.
(d) Common detritivores in our ecosystem are _______.
(e) The major reservoir of carbon on earth is _______.

Accepted Answer

(a) Plants are called as producers because they fix carbon dioxide through photosynthesis.

(b) In an ecosystem dominated by trees, the pyramid (of numbers) is inverted type because large trees are fewer in number compared to the organisms that feed on them.

(c) In aquatic ecosystems, the limiting factor for productivity is usually light or nutrients (commonly nitrogen or phosphorus).

(d) Common detritivores in our ecosystem are earthworms, fungi, and bacteria which decompose dead organic matter.

(e) The major reservoir of carbon on earth is the sedimentary rocks (like limestone) and the oceans. — Each blank corresponds to a key ecological concept:
(a) Plants fix CO2 via photosynthesis, hence called producers.
(b) Tree-dominated ecosystems have fewer trees but many herbivores, leading to an inverted pyramid of numbers.
(c) Aquatic productivity is limited by light penetration or nutrient availability.
(d) Detritivores break down dead matter; common examples include earthworms and microbes.
(e) Carbon is mostly stored in sedimentary rocks and oceans, forming the major carbon reservoir.

Question 2

Which one of the following has the largest population in a food chain?
(a) Producers
(b) Primary consumers
(c) Secondary consumers
(d) Decomposers

Accepted Answer

Producers have the largest population in a food chain because they form the base of the food chain by producing energy through photosynthesis, supporting all other trophic levels. — Producers (plants and autotrophs) convert solar energy into chemical energy and are the most abundant organisms in terms of population to sustain higher trophic levels. Consumers and decomposers depend on producers directly or indirectly, so their populations are smaller.

Question 3

The second trophic level in a lake is
(a) Phytoplankton
(b) Zooplankton
(c) Benthos
(d) Fishes

Accepted Answer

Zooplankton form the second trophic level in a lake as they are primary consumers feeding on phytoplankton (producers). — The trophic levels are:
1st level - Producers (phytoplankton)
2nd level - Primary consumers (zooplankton)
3rd level - Secondary consumers (small fishes)
4th level - Tertiary consumers (larger fishes)
Hence, zooplankton are the second trophic level.

Question 4

Secondary producers are
(a) Herbivores
(b) Producers
(c) Carnivores
(d) None of the above

Accepted Answer

Carnivores are secondary producers as they feed on herbivores (primary consumers) and occupy the secondary consumer trophic level. — Primary producers are autotrophs (plants), primary consumers are herbivores, and secondary consumers are carnivores feeding on herbivores. Hence, secondary producers refer to carnivores.

Question 5

What is the percentage of photosynthetically active radiation (PAR) in the incident solar radiation?
(a) 100%
(b) 50%
(c) 1-5%
(d) 2-10%

Accepted Answer

2-10% of the incident solar radiation is photosynthetically active radiation (PAR) which plants can use for photosynthesis. — Photosynthetically active radiation (PAR) is the portion of the light spectrum (400-700 nm) usable by plants. It constitutes about 2-10% of the total incident solar radiation reaching the earth's surface.

Question 6

Distinguish between
(a) Grazing food chain and detritus food chain
(b) Production and decomposition
(c) Upright and inverted pyramid
(d) Food chain and Food web
(e) Litter and detritus
(f) Primary and secondary productivity

Accepted Answer

(a) Grazing food chain vs Detritus food chain:
- Grazing food chain starts with living green plants (producers) and moves to herbivores and carnivores.
- Detritus food chain starts with dead organic matter (detritus) and involves decomposers and detritivores.

(b) Production vs Decomposition:
- Production is the synthesis of organic matter by autotrophs.
- Decomposition is the breakdown of organic matter into simpler inorganic substances.

(c) Upright vs Inverted pyramid:
- Upright pyramid has a broad base and narrow top (e.g., pyramid of biomass in grassland).
- Inverted pyramid has a narrow base and broad top (e.g., pyramid of numbers in tree ecosystem).

(d) Food chain vs Food web:
- Food chain is a linear sequence of organisms feeding on each other.
- Food web is a complex network of interconnected food chains.

(e) Litter vs Detritus:
- Litter is freshly fallen dead organic matter like leaves.
- Detritus is decomposed organic matter derived from litter.

(f) Primary vs Secondary productivity:
- Primary productivity is the rate of production of organic matter by autotrophs.
- Secondary productivity is the rate of production of biomass by heterotrophs (consumers). — Each pair contrasts two ecological concepts:
(a) Grazing food chain involves living plants; detritus food chain involves dead matter.
(b) Production builds organic matter; decomposition breaks it down.
(c) Pyramids represent trophic levels; their shape depends on ecosystem.
(d) Food chain is simple; food web is complex.
(e) Litter is fresh dead material; detritus is decomposed material.
(f) Primary productivity is autotrophic; secondary productivity is heterotrophic.

Question 7

Describe the components of an ecosystem.

Accepted Answer

An ecosystem consists of biotic and abiotic components:
- Biotic components: Producers (autotrophs), consumers (herbivores, carnivores, omnivores), and decomposers (bacteria, fungi).
- Abiotic components: Non-living physical and chemical factors like sunlight, temperature, water, air, minerals, and soil.
These components interact to form a functional unit where energy flows and nutrients cycle. — The ecosystem is a community of living organisms interacting with their physical environment. Producers synthesize food, consumers feed on producers or other consumers, and decomposers recycle nutrients. Abiotic factors influence the living organisms and ecosystem processes.

Question 8

Define ecological pyramids and describe with examples, pyramids of number and biomass.

Accepted Answer

Ecological pyramids are graphical representations showing the number of organisms, biomass, or energy at different trophic levels in an ecosystem.

Pyramid of number: Shows the number of organisms at each trophic level. For example, in a grassland ecosystem, the pyramid of number is upright because many grass plants support fewer herbivores and even fewer carnivores. In a tree ecosystem, it may be inverted because few trees support many herbivores.

Pyramid of biomass: Shows the total biomass (weight) of organisms at each trophic level. For example, in a grassland, the pyramid of biomass is upright as producers have the highest biomass. In aquatic ecosystems, it can be inverted because phytoplankton biomass is less than that of zooplankton. — Ecological pyramids help understand the structure and function of ecosystems. Number pyramids count individuals, biomass pyramids measure total mass. Their shape (upright or inverted) depends on the ecosystem type and trophic interactions.

Question 9

What is primary productivity? Give brief description of factors that affect primary productivity.

Accepted Answer

Primary productivity is the rate at which autotrophs (producers) convert solar energy into chemical energy by synthesizing organic compounds from carbon dioxide and water through photosynthesis.

Factors affecting primary productivity include:
- Light intensity and duration: More light increases photosynthesis.
- Temperature: Optimal temperature enhances enzyme activity.
- Availability of water: Essential for photosynthesis.
- Nutrient availability: Nitrogen, phosphorus, and other minerals are necessary.
- Carbon dioxide concentration: Higher CO2 can increase productivity.
- Type of vegetation and ecosystem: Different plants have different productivity rates. — Primary productivity determines the energy input into an ecosystem. Environmental factors influence photosynthetic efficiency and growth of producers, thereby affecting overall productivity.

Question 10

Define decomposition and describe the processes and products of decomposition.

Accepted Answer

Decomposition is the biological process by which organic substances are broken down into simpler inorganic substances by decomposers like bacteria and fungi.

Processes of decomposition include:
- Fragmentation: Breaking down of litter into smaller pieces by detritivores.
- Leaching: Water-soluble substances are washed out.
- Catabolism: Microbial breakdown of organic matter releasing energy.
- Humification: Formation of humus from resistant organic matter.
- Mineralization: Conversion of organic matter into inorganic nutrients like CO2, NH3, NO3-, and PO43-.

Products of decomposition include carbon dioxide, water, mineral salts, and humus which enrich the soil. — Decomposition recycles nutrients, maintaining ecosystem productivity. It involves physical, chemical, and biological processes transforming dead matter into usable forms for plants.

Question 11

Give an account of energy flow in an ecosystem.

Accepted Answer

Energy flow in an ecosystem is unidirectional and follows the path from the sun to producers and then to consumers and decomposers.

- Solar energy is captured by producers through photosynthesis and converted into chemical energy.
- Energy is transferred to primary consumers (herbivores) when they feed on producers.
- Secondary and tertiary consumers obtain energy by feeding on lower trophic levels.
- At each trophic level, energy is lost as heat due to metabolic activities (Second Law of Thermodynamics).
- Decomposers break down dead organisms, releasing nutrients back to the environment but energy flow continues to be one-way.

The efficiency of energy transfer between trophic levels is about 10%, known as the 10% law. — Energy flow is fundamental to ecosystem functioning. It is not recycled but continuously supplied by the sun. Energy loss at each level limits the number of trophic levels and biomass.

Question 12

Which of the following best defines an ecosystem?

Accepted Answer

A functional unit of nature where living organisms interact among themselves and with the surrounding physical environment — An ecosystem is defined as a functional unit of nature where living organisms (biotic components) interact among themselves and also with the surrounding physical environment (abiotic components). It includes both biotic and abiotic factors functioning together.

Question 13

Identify the correct classification of ecosystems based on their environment.

Accepted Answer

Terrestrial and Aquatic ecosystems — Ecosystems are broadly classified into terrestrial (land-based) and aquatic (water-based) ecosystems. Examples of terrestrial include forests, grasslands, deserts; aquatic include ponds, lakes, rivers, estuaries.

Question 14

In the vertical stratification of a forest ecosystem, which of the following correctly represents the order from top to bottom?

Accepted Answer

Trees → Shrubs → Herbs and Grasses — Stratification refers to vertical distribution of species in layers. In forests, trees occupy the top layer, shrubs the middle layer, and herbs and grasses the bottom layer.

Question 15

Which of the following is NOT a function of an ecosystem?

Accepted Answer

Photosynthesis only by animals — Ecosystem functions include productivity (biomass production by plants), decomposition, energy flow, and nutrient cycling. Photosynthesis is performed by autotrophs (plants, algae), not animals.

Ecosystem

Ecosystem — Study Notes

Ecosystem

12.1 Ecosystem – Structure and Function

12.2 Productivity

Practice Questions — Ecosystem

All 13 Chapters in Biology