1
A group of students visited a forest and observed the following: various types of trees, grasses, insects, birds, frogs, and a deer. They also noted the temperature, rainfall, and sunlight in the area.(a) Identify the biotic components from the observations.(b) Identify the abiotic components from the observations.(c) Explain how the biotic and abiotic components interact to form an ecosystem.(d) Classify this ecosystem as natural or human-made. 3marks
2
A farmer is concerned about pests damaging his crops. He decides to use a new, powerful pesticide.(a) Explain the immediate effect of the pesticide on the pests and potentially on other insects in the field.(b) Describe how this pesticide might enter the food chain.(c) What is the term for the increasing concentration of such harmful chemicals at successive trophic levels, and why is it a cause for concern for humans? 5marks
3
Assertion (A): Decomposers are essential for the recycling of nutrients in an ecosystem.Reason (R): Decomposers break down complex organic matter into simple inorganic substances which are then utilized by producers.(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. 1mark
4
A scientist is studying an aquarium. They observe fish, aquatic plants, and a few microorganisms. The aquarium is a closed system that needs regular cleaning.(a) Explain why the aquarium needs regular cleaning, unlike a natural pond.(b) Identify the producers, consumers, and decomposers that might be present in the aquarium.(c) How would the introduction of a new species of fish that eats all the existing fish affect the aquarium's ecosystem? 3marks
5
The diagram below shows a simple food chain:Grass → Grasshopper → Frog → Snake(a) Identify the producers, primary consumers, secondary consumers, and tertiary consumers in this food chain.(b) What would happen to the population of grasshoppers if all the frogs were removed from this ecosystem? Justify your answer.(c) Explain why food chains usually have only three or four trophic levels. 5marks
6
Read the following passage:"The ozone layer, located in the Earth's stratosphere, acts as a protective shield by absorbing most of the Sun's harmful ultraviolet (UV) radiation. In the 1980s, scientists observed a significant depletion of this ozone layer, primarily attributed to synthetic chemicals known as chlorofluorocarbons (CFCs). CFCs were widely used in refrigerants, aerosols, and fire extinguishers. An international agreement, the Montreal Protocol, was established in 1987 to phase out the production and consumption of ozone-depleting substances. This collective action has shown positive results, with signs of ozone layer recovery."(a) What is the primary function of the ozone layer?(b) Name the main group of chemicals responsible for ozone depletion.(c) What international agreement was made to address this issue, and what was its objective? 3marks
7
A village has a small pond that supports a variety of aquatic life, including algae, small fish, larger fish, and birds. The pond water is naturally replenished and receives nutrients from surrounding vegetation.(a) Classify this pond as a natural or human-made ecosystem.(b) Describe a possible food chain that exists in this pond.(c) Explain why this pond, unlike an artificial aquarium, does not require frequent manual cleaning. 3marks
8
Assertion (A): The flow of energy in an ecosystem is always unidirectional.Reason (R): Energy is lost as heat at each trophic level and cannot be transferred back to 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. 1mark
9
Consider a scenario where a new factory is set up near a residential area. The factory generates a lot of waste, some of which is plastic and some is organic kitchen waste from its canteen.(a) Differentiate between biodegradable and non-biodegradable waste, using examples from the factory's waste.(b) Describe two potential environmental problems caused by the disposal of the plastic waste from the factory.(c) How could the organic kitchen waste be managed in an environmentally friendly way? 5marks
10
A student is observing a food web in a grassland ecosystem, which includes grasses, insects, rabbits, foxes, and hawks.(a) Draw a possible food web showing at least three food chains.(b) If the population of rabbits drastically decreases due to a disease, predict the impact on the populations of grasses and foxes. Justify your predictions.(c) Explain the concept of trophic levels using the organisms in this grassland. 5marks
11
You are collecting waste from your home for a week and notice that some items, like fruit peels and leftover food, decompose quickly, while others, like plastic bags and glass bottles, remain intact for a very long time.(a) Based on your observations, define biodegradable and non-biodegradable substances.(b) List two environmental problems caused by the accumulation of non-biodegradable waste.(c) Suggest one method to reduce the generation of non-biodegradable waste in your household. 3marks
12
Assertion (A): Even if all the waste generated by humans were biodegradable, it could still pose environmental problems.Reason (R): A large quantity of biodegradable waste can overwhelm the decomposers, leading to pollution and resource depletion.(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. 1mark
13
A group of students are discussing environmental issues. One student says, "Using cloth bags instead of plastic bags is good because it reduces pollution." Another student adds, "Turning off lights when not in use also helps the environment."(a) Explain why the use of cloth bags is considered an environment-friendly practice.(b) How does switching off unnecessary lights contribute to environmental conservation?(c) Identify one other everyday activity that can be considered environment-friendly and explain its benefit. 3marks
14
A farmer uses pesticides and fertilizers liberally on his fields. These chemicals get washed into a nearby river.(a) Explain how these chemicals can enter the bodies of aquatic organisms.(b) What is the term for the process where these chemicals accumulate in organisms at different trophic levels, and what is its effect on top predators?(c) How can the excessive use of fertilizers lead to the depletion of oxygen in the river water? 5marks
15
Assertion (A): Human activities can impact the ozone layer.Reason (R): The use of chemicals like CFCs in aerosols and refrigerators leads to the breakdown of ozone molecules.(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. 1mark
16
A local authority is planning to manage the waste generated by its citizens. They are considering different methods for treating biodegradable and non-biodegradable waste separately.(a) Suggest one method for treating biodegradable waste that could benefit the community.(b) Explain why non-biodegradable waste poses a greater challenge for disposal.(c) How can public awareness campaigns help in managing the waste disposal problem? 3marks
17
A group of scientists are investigating the flow of energy in a pond ecosystem. They have identified algae as producers, small invertebrates as primary consumers, small fish as secondary consumers, and a heron as a tertiary consumer.(a) Describe the path of energy flow through these organisms.(b) If 1000 kJ of energy is available at the producer level, calculate the approximate energy available at the secondary consumer level. Show your steps.(c) Explain why the heron, at the tertiary trophic level, would have a smaller population size compared to the algae. 5marks
18
Assertion (A): All organisms in an ecosystem are interdependent.Reason (R): Producers rely on consumers for pollination and seed dispersal, while consumers rely on producers for food and shelter.(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. 1mark
19
Consider the following scenario: A forest fire destroys a large area of vegetation.(a) What would be the immediate impact on the producers in this ecosystem?(b) How would the removal of producers affect the primary consumers?(c) Explain the role of decomposers in the recovery of the ecosystem after the fire. 3marks
20
A news report states that a significant amount of plastic waste is ending up in the oceans, harming marine life.(a) Explain why plastic is considered a non-biodegradable waste.(b) Describe two ways in which plastic waste in oceans can harm marine animals.(c) Suggest two practical steps that individuals can take to reduce their use of plastic. 5marks
Answers
1
(a) Biotic components: various types of trees, grasses, insects, birds, frogs, and deer.(b) Abiotic components: temperature, rainfall, and sunlight.(c) The biotic components (living organisms) interact with each other for food, shelter, and reproduction. They also interact with the abiotic components (non-living factors) like temperature, rainfall, and sunlight, which influence their growth, survival, and activities. Together, these interacting organisms and their physical surroundings form an ecosystem.(d) This ecosystem is a natural ecosystem.
2
(a) The pesticide will kill the pests. However, it may also kill beneficial insects like pollinators (e.g., bees) or natural predators of other pests, potentially disrupting the field's ecosystem.(b) When the pesticide is applied, it can be absorbed by the plants. When herbivores (e.g., insects that feed on the crop) eat these plants, they ingest the pesticide. Then, when carnivores eat these herbivores, the pesticide is transferred to them. This transfer continues up the food chain.(c) This phenomenon is known as biological magnification. It is a cause for concern for humans because as apex predators, humans are at the top of many food chains. Therefore, they accumulate the highest concentration of these harmful chemicals, which can lead to severe health problems.
3
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
4
(a) Unlike a natural pond, an aquarium is a small, enclosed system. The waste produced by the organisms accumulates, and the limited volume of water cannot dilute or process it efficiently. Natural ponds have larger volumes, more diverse decomposer populations, and continuous water flow, which help in natural waste management.(b) Producers: Aquatic plants, algae. Consumers: Fish (herbivores or carnivores depending on species). Decomposers: Bacteria and fungi present in the water and substrate.(c) If a new species of fish that eats all the existing fish is introduced, it would lead to the extinction of the existing fish population. This would remove a consumer level, potentially causing an imbalance: the primary consumers might increase unchecked, or if they rely on the existing fish for another reason (e.g., grazing on algae), their populations might also decline. The ecosystem would likely collapse.
5
(a) Producers: Grass. Primary consumers: Grasshopper. Secondary consumers: Frog. Tertiary consumers: Snake.(b) If all the frogs were removed, the population of grasshoppers would likely increase significantly because their natural predator is gone. This increased grasshopper population would then consume a much larger amount of grass, potentially leading to a decrease in the grass population.(c) Food chains usually have only three or four levels because of the significant loss of energy at each trophic level. Producers capture only a small percentage of solar energy (about 1%). When this energy is transferred to primary consumers, only about 10% of it is incorporated into their biomass. This 10% rule means that very little usable energy remains for higher trophic levels, making it unsustainable to support many levels.
6
(a) The primary function of the ozone layer is to shield the Earth's surface from the Sun's harmful ultraviolet (UV) radiation.(b) The main group of chemicals responsible for ozone depletion are chlorofluorocarbons (CFCs).(c) The international agreement made to address this issue was the Montreal Protocol. Its objective was to phase out the production and consumption of ozone-depleting substances like CFCs.
7
(a) This pond is a natural ecosystem.(b) A possible food chain in this pond could be: Algae (Producers) → Small invertebrates (Primary Consumers) → Small fish (Secondary Consumers) → Larger fish (Tertiary Consumers) → Birds (Quaternary Consumers).(c) Natural ponds are large and have a complex web of decomposers (bacteria and fungi) that break down dead organic matter. They also have continuous water flow and a large volume that dilutes waste. Artificial aquariums are small, closed systems where waste accumulates quickly and the decomposer population is limited, necessitating regular cleaning.
8
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
9
(a) Biodegradable waste is material that can be broken down by biological processes (by microorganisms) into simpler substances. Examples from the factory: organic kitchen waste from the canteen. Non-biodegradable waste is material that cannot be broken down by biological processes and persists in the environment for a long time. Examples from the factory: plastic bags.(b) Two potential environmental problems caused by plastic waste are:i. Pollution: Plastic pollutes land and water bodies, harming wildlife that may ingest it or get entangled in it.ii. Persistence: Plastic takes hundreds of years to decompose, accumulating in landfills and the environment.(c) The organic kitchen waste could be managed through composting. Composting converts the organic waste into nutrient-rich manure that can be used to fertilize soil, thus recycling nutrients and reducing landfill waste.
10
(a) Possible food web:
- Grass → Grasshopper → Fox
- Grass → Rabbit → Fox
- Grass → Rabbit → Hawk
- Grass → Insect → Hawk
(b) If the population of rabbits drastically decreases: - Grasses: The population of grasses might increase initially because there are fewer herbivores (rabbits) to eat them. However, if other herbivores (like grasshoppers) increase significantly due to the lack of competition, the grass population might eventually decrease.
- Foxes: The population of foxes would likely decrease because rabbits are a primary food source for them. With fewer rabbits available, foxes would face starvation or reduced reproductive success.
(c) Trophic levels represent the steps in a food chain. - Producers (1st trophic level): Grass (plants that make their own food).
- Primary consumers (2nd trophic level): Rabbits, Grasshoppers, Insects (herbivores that eat producers).
- Secondary consumers (3rd trophic level): Foxes (carnivores that eat primary consumers like rabbits).
- Tertiary consumers (4th trophic level): Hawks (carnivores that eat secondary consumers like foxes, or primary consumers like insects).
11
(a) Biodegradable substances are those that can be decomposed or broken down into simpler natural substances by the action of living organisms like bacteria and fungi. Non-biodegradable substances are those that cannot be decomposed by natural biological processes and persist in the environment for very long periods.(b) Two environmental problems caused by the accumulation of non-biodegradable waste:i. Pollution: They contribute to land, water, and air pollution.ii. Harm to wildlife: Animals can ingest or become entangled in non-biodegradable materials, leading to injury or death.(c) One method to reduce household non-biodegradable waste is to practice the "Reduce, Reuse, Recycle" principle. For example, consciously choosing products with minimal packaging (reduce), reusing plastic containers or bags (reuse), and ensuring that recyclable items like glass and certain plastics are collected for recycling.
12
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
13
(a) Using cloth bags is environment-friendly because they are reusable and durable, reducing the need for single-use plastic bags. Plastic bags contribute to pollution, harm wildlife, and take a very long time to decompose. Cloth bags, made from natural fibers, are biodegradable and have a lower environmental impact.(b) Switching off unnecessary lights saves electricity. Electricity generation, especially from fossil fuels, contributes to air pollution, greenhouse gas emissions, and resource depletion. By saving electricity, we reduce the demand for power generation, thereby lessening these environmental impacts.(c) One other environment-friendly activity is walking or cycling for short distances instead of using a vehicle. This reduces air pollution caused by vehicle emissions, conserves fossil fuels, and also promotes personal health.
14
(a) When fertilizers and pesticides are washed into the river, they are absorbed by aquatic plants and algae. Small aquatic organisms then consume these plants, ingesting the chemicals. These chemicals are then transferred to larger organisms that feed on the smaller ones.(b) The phenomenon is known as biological magnification (or biomagnification). In top predators, the concentration of these harmful chemicals becomes very high, leading to severe health issues, reproductive problems, and even death.(c) Excessive use of fertilizers leads to eutrophication. Fertilizers contain nutrients like nitrates and phosphates. When these enter the river, they promote the rapid growth of algae and aquatic plants (algal blooms). When these blooms die, their decomposition by bacteria consumes a large amount of dissolved oxygen in the water, leading to oxygen depletion (hypoxia), which harms or kills fish and other aquatic organisms.
15
(A) Both (A) and (R) are true and (R) is the correct explanation of (A).
16
(a) One method for treating biodegradable waste is composting. This process converts kitchen waste, yard waste, etc., into nutrient-rich manure, which can be used to improve soil fertility in local gardens or farms, reducing the need for chemical fertilizers.(b) Non-biodegradable waste poses a greater challenge for disposal because it does not break down naturally. It accumulates in landfills, takes up space, can leach harmful substances into the soil and groundwater, and persists in the environment for centuries, causing long-term pollution.(c) Public awareness campaigns can educate citizens about the importance of waste segregation at source (separating biodegradable from non-biodegradable waste), the benefits of recycling and composting, and the harmful effects of littering and improper waste disposal. This can lead to greater participation in waste management initiatives and reduce the overall burden on the local authority.
17
(a) The path of energy flow is:
- Algae (Producers) capture solar energy.
- Small invertebrates (Primary Consumers) consume algae, obtaining energy.
- Small fish (Secondary Consumers) eat the invertebrates, obtaining energy.
- Heron (Tertiary Consumer) eats the small fish, obtaining energy.
(b) Energy transfer efficiency between trophic levels is approximately 10%. - Energy at producer level (Algae) = 1000 kJ
- Energy at primary consumer level (Invertebrates) = 10% of 1000 kJ = 100 kJ
- Energy at secondary consumer level (Small fish) = 10% of 100 kJ = 10 kJ
(c) The heron, at the tertiary trophic level, would have a smaller population size compared to the algae because of the significant loss of energy at each successive trophic level (the 10% rule). There is simply not enough energy available to support a large population of top consumers.
18
(A) Both (A) and (R) are true and (R) is the correct explanation of (A). (While the statement in (R) focuses on specific interactions, the core idea of interdependence holds true for producers and consumers within an ecosystem.)
19
(a) The immediate impact on the producers (vegetation) would be their destruction. This means a loss of the primary source of food and energy for the entire ecosystem.(b) The removal of producers would lead to a drastic reduction or starvation of the primary consumers, as their food source is gone. Their population would likely decline sharply.(c) After the fire, decomposers (bacteria and fungi) would play a crucial role in the ecosystem's recovery. They would break down the dead, burnt organic matter (trees, plants) into simpler inorganic nutrients. These nutrients would then be released into the soil, enriching it and making it fertile again, which is essential for the regrowth of new producers (plants).
20
(a) Plastic is considered non-biodegradable because it is a synthetic material made from polymers that cannot be easily broken down by natural microorganisms (bacteria and fungi) present in the environment. It resists decomposition for hundreds or thousands of years.(b) Two ways plastic waste in oceans can harm marine animals:i. Ingestion: Marine animals mistake plastic items for food, leading to internal injuries, blockages in their digestive systems, starvation, and death.ii. Entanglement: Animals can get entangled in plastic debris like fishing nets, bags, or rings, which can restrict their movement, cause suffocation, drowning, or lead to starvation as they cannot hunt or escape predators.(c) Two practical steps individuals can take to reduce their use of plastic:i. Use reusable alternatives: Opt for reusable cloth bags for shopping, use metal or glass water bottles instead of single-use plastic ones, and carry reusable coffee cups.ii. Avoid single-use plastics: Refuse plastic straws, cutlery, and excessive packaging. Choose products that use less plastic packaging or are packaged in biodegradable materials.
