1
What is an ecosystem? Explain the interaction between biotic and abiotic components with an example. 3marks
2
Differentiate between producers, consumers, and decomposers, providing an example for each. 3marks
3
Explain the concept of trophic levels in a food chain. Give an example of a four-step food chain and identify the trophic level of each organism. 3marks
4
Describe the flow of energy in an ecosystem, highlighting the 10% energy transfer rule at each trophic level. 3marks
5
What is a food web? How is it different from a food chain? Illustrate with an example. 2marks
6
Explain the phenomenon of biological magnification. Why are human beings most affected by it? 3marks
7
Discuss the role of decomposers in maintaining the balance of an ecosystem. What would happen if decomposers were absent? 3marks
8
Elaborate on the process of ozone formation in the Earth's upper atmosphere and its significance. 3marks
9
Explain how human activities, such as the use of synthetic chemicals, contribute to the depletion of the ozone layer. 3marks
10
What are biodegradable and non-biodegradable substances? Give examples of each. 2marks
11
Discuss the environmental problems caused by the disposal of non-biodegradable wastes. 3marks
12
How can you contribute to reducing the problem of waste disposal in your daily life? Suggest any two practical methods. 2marks
13
Explain the concept of an artificial ecosystem and provide two examples. 2marks
14
Discuss the advantages and disadvantages of using disposable items like paper cups or plastic cups. 3marks
15
Case Study: A local community is facing a severe waste management problem. They have overflowing landfills and polluted water bodies due to untreated sewage. The community is considering implementing new waste management strategies.(a) Identify two types of waste generated by households that are likely non-biodegradable. [1 mark](b) Suggest two methods for treating biodegradable waste generated by households. [2 marks](c) Explain how untreated sewage can pollute water bodies and harm aquatic life. 2marks
16
Data Interpretation: The table below shows the average energy transfer at different trophic levels in an ecosystem:
| Trophic Level | Energy Available (in Joules) |
|---|---|
| Producers | 10,000 |
| Primary Consumers | 1,000 |
| Secondary Consumers | 100 |
| Tertiary Consumers | 10 |
| (a) What percentage of energy is transferred from producers to primary consumers? [1 mark] | |
| (b) Which trophic level receives the least amount of energy? [1 mark] | |
| (c) Explain why there are generally only three or four trophic levels in most ecosystems, based on the data. [3 marks] | |
| 17. Situational Analysis: During a school project, students surveyed the waste generated in their locality for a week. They found that a significant portion of the waste was plastic packaging. | |
| (a) What are the harmful effects of excessive plastic waste on the environment? [2 marks] | |
| (b) Suggest two eco-friendly alternatives to plastic packaging for common household items. [2 marks] | |
| (c) Explain the concept of recycling and how it helps in managing plastic waste. [1 mark] | |
| 18. Application-Based: A farmer is concerned about pests damaging his crops. He is considering using chemical pesticides. | |
| (a) Explain how the use of chemical pesticides can lead to biological magnification. [3 marks] | |
| (b) Name one harmful chemical that was widely used as a refrigerant and is now banned due to its effect on the ozone layer. [1 mark] | |
| (c) What is the specific function of the ozone layer in the Earth's atmosphere? [1 mark] | |
| 19. Assertion-Reason: | |
| Assertion (A): Decomposers are essential for maintaining the fertility of the soil. | |
| Reason (R): Decomposers break down complex organic matter into simpler inorganic nutrients. | |
| (A) Both (A) and (R) are true and (R) is the correct explanation of (A). | |
| (B) Both (A) and (R) are true but (R) is not the correct explanation of (A). | |
| (C) (A) is true but (R) is false. | |
| (D) (A) is false but (R) is true. [1 mark] | |
| 20. Assertion-Reason: | |
| Assertion (A): The flow of energy in an ecosystem is unidirectional. | |
| Reason (R): Energy is lost as heat at each trophic level and cannot be reused by the previous level. | |
| (A) Both (A) and (R) are true and (R) is the correct explanation of (A). | |
| (B) Both (A) and (R) are true but (R) is not the correct explanation of (A). | |
| (C) (A) is true but (R) is false. | |
| (D) (A) is false but (R) is true. [1 mark] |
Answers
1
An ecosystem is a community of living organisms (biotic components) interacting with each other and with their non-living physical surroundings (abiotic components). For example, in a pond ecosystem, biotic components include fish, frogs, aquatic plants, and microorganisms, while abiotic components include water, sunlight, temperature, and dissolved oxygen. These components interact; for instance, fish depend on aquatic plants for food and oxygen, and plants use nutrients from the water.
2
Producers are organisms that produce their own food, usually through photosynthesis (e.g., green plants like grass). Consumers are organisms that obtain food by feeding on other organisms; herbivores eat plants (e.g., deer), carnivores eat animals (e.g., lion), and omnivores eat both (e.g., humans). Decomposers are organisms like bacteria and fungi that break down dead organic matter and waste products, returning nutrients to the soil (e.g., earthworms, fungi).
3
Trophic levels represent the different feeding positions in a food chain. Producers form the first trophic level, herbivores (primary consumers) the second, small carnivores (secondary consumers) the third, and larger carnivores (tertiary consumers) the fourth. Example: Grass (Producer, Trophic Level 1) → Grasshopper (Primary Consumer, Trophic Level 2) → Frog (Secondary Consumer, Trophic Level 3) → Snake (Tertiary Consumer, Trophic Level 4).
4
The flow of energy in an ecosystem begins with producers capturing solar energy. This energy is transferred to consumers at subsequent trophic levels. However, at each transfer, approximately 90% of the energy is lost as heat, used for metabolic activities, or undigested. Only about 10% of the energy from one trophic level is incorporated into the biomass of the next level, limiting the number of trophic levels.
5
A food chain is a linear sequence showing who eats whom, illustrating the flow of energy. A food web is a complex network of interconnected food chains, showing multiple feeding relationships between different organisms in an ecosystem. For example, a food web might show that a frog eats grasshoppers, but it is also eaten by snakes and birds.
6
Biological magnification is the increasing concentration of a harmful chemical substance in organisms at successively higher levels in a food chain. This occurs because non-biodegradable substances are not easily excreted or broken down. For example, if plants absorb a pesticide, it concentrates in herbivores that eat the plants, and further concentrates in carnivores that eat the herbivores. Humans, often at the top of food chains, accumulate the highest concentrations, leading to severe health problems like cancer and reproductive issues.
7
Decomposers break down dead organisms and waste products into simpler inorganic substances, releasing essential nutrients back into the soil and water. This process recycles matter and makes nutrients available for producers. In the absence of decomposers, dead organic matter would accumulate, nutrients would be locked up, and the soil would become infertile, disrupting the entire ecosystem.
8
Ozone () is formed in the Earth's stratosphere when high-energy ultraviolet (UV) radiation from the sun splits oxygen molecules () into free oxygen atoms (). These free oxygen atoms then combine with other oxygen molecules to form ozone (). The ozone layer is significant because it absorbs most of the harmful UV radiation from the sun, preventing it from reaching the Earth's surface and causing damage to living organisms.
9
The depletion of the ozone layer is primarily caused by synthetic chemicals called chlorofluorocarbons (CFCs), commonly used in refrigerants, aerosols, and fire extinguishers. When CFCs rise to the stratosphere, they are broken down by UV radiation, releasing chlorine atoms. These chlorine atoms catalytically destroy ozone molecules, leading to a decrease in the ozone layer's thickness.
10
Biodegradable substances are those that can be broken down into simpler substances by the action of biological agents like bacteria and fungi. Examples include food waste, paper, and cotton. Non-biodegradable substances are materials that cannot be broken down by biological processes and persist in the environment for very long periods. Examples include plastics, glass, and metals.
11
Non-biodegradable wastes cause several environmental problems: they accumulate in landfills, taking up valuable space and potentially leaching toxic substances into the soil and groundwater. Plastics, in particular, can persist for hundreds of years, harming wildlife through ingestion or entanglement, and contributing to microplastic pollution in oceans and rivers. They also clog drainage systems, leading to flooding.
12
To reduce waste disposal problems, one can: (a) Practice the 3Rs: Reduce, Reuse, and Recycle. Reduce consumption of disposable items, reuse containers and bags, and recycle materials like paper, plastic, and metal. (b) Compost biodegradable kitchen waste at home or in a community compost pit, turning it into valuable fertilizer. (c) Avoid single-use plastics by opting for reusable alternatives like cloth bags, metal water bottles, and cloth napkins.
13
An artificial ecosystem is one that is created and managed by humans. These ecosystems are often designed to serve specific purposes, such as food production or aesthetic appeal, and require human intervention to maintain balance. Examples include: 1. Aquariums: designed to house aquatic life, requiring regular cleaning, feeding, and oxygenation. 2. Crop fields: managed for agriculture, involving tilling, irrigation, and the use of fertilizers and pesticides.
14
Disposable items offer convenience and hygiene benefits, as seen with disposable cups for tea or coffee. However, their widespread use generates enormous amounts of non-biodegradable waste. For example, millions of disposable plastic cups are discarded daily, contributing to landfill burden and pollution. While paper cups are biodegradable, their production requires significant resources and can lead to deforestation. Using reusable alternatives like ceramic mugs or steel tumblers is a more sustainable option.
15
(a) Two types of non-biodegradable waste generated by households are plastic bags, bottles, and packaging materials; and electronic waste like old batteries or broken electronic devices.(b) Two methods for treating biodegradable waste include: Composting, where kitchen waste is decomposed in pits or bins to produce nutrient-rich manure, and Anaerobic Digestion, where organic waste is broken down in the absence of oxygen to produce biogas (fuel) and slurry (fertilizer).(c) Untreated sewage contains harmful pathogens, organic pollutants, and excess nutrients. When discharged into water bodies, it reduces dissolved oxygen levels, harming or killing fish and other aquatic organisms. Pathogens can contaminate drinking water sources, leading to waterborne diseases in humans. Excess nutrients can cause eutrophication, leading to algal blooms that further deplete oxygen.
16
(a) The percentage of energy transferred from producers to primary consumers is approximately 10% (1000 Joules / 10,000 Joules * 100 = 10%).(b) The trophic level that receives the least amount of energy is the tertiary consumers (10 Joules).(c) There are generally only three or four trophic levels in most ecosystems because the energy transfer between levels is highly inefficient. At each step, about 90% of the energy is lost, leaving very little usable energy to support higher trophic levels. If a food chain were longer, the energy available at the top would be insufficient to sustain a viable population.
17
(a) Harmful effects of excessive plastic waste include: blockage of drains leading to floods, ingestion by animals causing internal injuries and starvation, release of toxic chemicals into soil and water as it degrades, and contribution to microplastic pollution in oceans, affecting marine ecosystems.(b) Two eco-friendly alternatives to plastic packaging are: biodegradable packaging materials made from plant-based starches or cellulose, and reusable containers made from glass, metal, or durable plastic that can be used multiple times.(c) Recycling is the process of collecting and reprocessing waste materials into new products. For plastics, it involves sorting, cleaning, melting, and reforming them into pellets or directly into new items. Recycling helps manage plastic waste by reducing the volume sent to landfills, conserving natural resources, and saving energy compared to producing virgin plastic.
18
(a) The use of chemical pesticides can lead to biological magnification as follows: Plants absorb pesticides from the soil or water. When herbivores eat these plants, the pesticides accumulate in their bodies. Carnivores that eat these herbivores ingest an even higher concentration of pesticides. This process continues up the food chain, with the highest concentration of pesticides accumulating in top predators like humans, leading to severe health issues.(b) Chlorofluorocarbons (CFCs) is one such harmful chemical.(c) The ozone layer in the Earth's stratosphere absorbs most of the harmful ultraviolet (UV) radiation from the sun, protecting life on Earth from its damaging effects, such as skin cancer and damage to DNA.
19
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
20
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
