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Secondary 3 Biology Ecology Quiz
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Questions
Secondary 3 Biology Quiz - Ecology
Name: ________________________
Class: ________________________
Date: ________________________
Score: ______ / 40
Duration: 45 minutes
Total Marks: 40
Instructions:
- Answer all questions in the spaces provided.
- Write your answers in ink. Pencil may be used for diagrams and graphs.
- The number of marks for each question is shown in brackets [ ].
- You are advised to spend no more than 45 minutes on this paper.
- Show all working where applicable.
Section A: Multiple Choice Questions (10 marks)
Questions 1–10: Choose the most appropriate answer for each question. Write your answer in the space provided.
1. Which of the following best describes an ecosystem?
A. A group of organisms of the same species living in the same area
B. A community of organisms interacting with each other and their physical environment
C. The total number of individuals of a species in a given area
D. The role an organism plays in its habitat
Answer: _______________ [1]
2. Which of the following is an abiotic factor in a freshwater pond ecosystem?
A. Algae
B. Dissolved oxygen
C. Water lily
D. Mosquito larvae
Answer: _______________ [1]
3. In a food chain, which organism is always the first trophic level?
A. Herbivore
B. Carnivore
C. Producer
D. Decomposer
Answer: _______________ [1]
4. The diagram below shows a simple food web.
Grass → Grasshopper → Frog → Snake
Grass → Mouse → Snake
Grass → Rabbit → Fox
If the population of snakes decreases significantly, which of the following is most likely to occur?
A. The population of grass will decrease.
B. The population of frogs will decrease.
C. The population of mice will increase.
D. The population of foxes will increase.
Answer: _______________ [1]
5. Which of the following correctly describes the flow of energy in an ecosystem?
A. Energy is recycled within the ecosystem.
B. Energy flows in one direction and is lost as heat at each trophic level.
C. Energy increases at each successive trophic level.
D. Energy is transferred from consumers to producers.
Answer: _______________ [1]
6. A pyramid of numbers is inverted in which of the following situations?
A. A grassland with many grass plants and few herbivores
B. A single large tree supporting many insects and birds
C. A marine ecosystem with many phytoplankton and few zooplankton
D. A forest with many trees and few deer
Answer: _______________ [1]
7. Which process returns carbon dioxide to the atmosphere in the carbon cycle?
A. Photosynthesis only
B. Respiration only
C. Respiration and decomposition only
D. Respiration, decomposition, and combustion
Answer: _______________ [1]
8. The diagram below shows part of the nitrogen cycle.
Atmospheric N₂ → [X] → Nitrates → Plants → Animals
What does [X] represent?
A. Denitrification
B. Nitrogen fixation
C. Ammonification
D. Nitrification
Answer: _______________ [1]
9. Which of the following is a likely consequence of deforestation on the carbon cycle?
A. Increased rate of photosynthesis
B. Decreased atmospheric carbon dioxide levels
C. Increased release of stored carbon into the atmosphere
D. Increased absorption of carbon dioxide by soil
Answer: _______________ [1]
10. In a predator-prey relationship, what is the most likely outcome if the prey population increases sharply?
A. The predator population will decrease.
B. The predator population will remain unchanged.
C. The predator population will increase after a time lag.
D. The prey population will continue to increase indefinitely.
Answer: _______________ [1]
Section B: Structured Questions (20 marks)
Answer all questions in the spaces provided.
11. The table below shows the population sizes of four organisms in a grassland ecosystem over five years.
| Year | Grass (×1000) | Grasshoppers (×100) | Frogs | Snakes |
|---|---|---|---|---|
| 1 | 500 | 200 | 50 | 10 |
| 2 | 480 | 220 | 55 | 12 |
| 3 | 400 | 180 | 45 | 15 |
| 4 | 350 | 150 | 40 | 18 |
| 5 | 300 | 120 | 30 | 20 |
(a) Plot a line graph showing the population of grass and snakes over the five years. Use the same axes and label your lines clearly. [3]
(Graph grid space provided)
(b) Describe the relationship between the population of grass and the population of snakes over the five years. [2]
(c) Suggest a reason for the trend observed in the snake population. [1]
12. The diagram below shows a food web in a mangrove ecosystem.
Mangrove leaves → Crabs → Herons
Mangrove leaves → Insects → Mudskippers → Herons
Algae → Snails → Mudskippers → Herons
Algae → Small fish → Herons
(a) Identify the producer(s) in this food web. [1]
(b) Name two secondary consumers in this food web. [2]
(c) Construct a food chain from this web that contains four trophic levels. [1]
(d) Explain what would happen to the population of mudskippers if the population of herons decreased significantly. [2]
13. The diagram below shows a simplified carbon cycle.
Atmosphere (CO₂)
↑↓
Plants → Animals
↓ ↓
Fossil fuels ← Decomposers
(a) Name process X that removes carbon dioxide from the atmosphere. [1]
(b) Name two processes that return carbon dioxide to the atmosphere. [2]
(c) Explain how human activities have disrupted the carbon cycle. [2]
(d) Describe one way in which the carbon cycle helps to regulate Earth's climate. [1]
14. The diagram below shows part of the nitrogen cycle in a grassland ecosystem.
Atmospheric N₂
↓ (Process A)
Ammonia/NH₃
↓ (Process B)
Nitrites → Nitrates
↓
Plants → Animals
↓ (Death/Excretion)
Dead organic matter
↓ (Process C)
Ammonia/NH₃
(a) Name Process A. [1]
(b) Name Process B. [1]
(c) Name Process C. [1]
(d) Explain why nitrogen is important for living organisms. [2]
(e) Describe the role of nitrogen-fixing bacteria in the nitrogen cycle. [2]
15. A student investigated the effect of light intensity on the distribution of a plant species along a transect from a shaded forest edge into an open field. The results are shown in the table below.
| Distance from forest edge (m) | Light intensity (arbitrary units) | Number of plants per m² |
|---|---|---|
| 0 | 10 | 2 |
| 5 | 30 | 8 |
| 10 | 60 | 15 |
| 15 | 80 | 22 |
| 20 | 95 | 25 |
| 25 | 100 | 24 |
(a) Describe the relationship between light intensity and the number of plants per m². [2]
(b) Suggest a reason why the number of plants per m² does not increase beyond 20 m from the forest edge despite increasing light intensity. [1]
(c) Name the ecological technique the student used to collect this data. [1]
(d) Explain why it is important to record light intensity at each sampling point along the transect. [2]
Section C: Extended Response (10 marks)
Answer all questions in the spaces provided.
16. A student investigated the distribution of organisms in a school field using a quadrat sampling method. The field contained grass, dandelions, clover, and earthworms.
(a) Describe how the student should use a quadrat to obtain a reliable estimate of the population density of dandelions in the field. [3]
(b) The student recorded the following data from 10 quadrat samples:
| Quadrat | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9 | 10 |
|---|---|---|---|---|---|---|---|---|---|---|
| Dandelions | 3 | 5 | 2 | 4 | 6 | 3 | 5 | 4 | 2 | 6 |
Calculate the mean number of dandelions per quadrat. Show your working. [2]
(c) Explain why the student should take multiple quadrat samples rather than just one. [2]
(d) Suggest two abiotic factors that could affect the distribution of dandelions in the field. [2]
(e) Explain how one of the abiotic factors you named in (d) could affect the growth of dandelions. [1]
17. Read the following passage and answer the questions below.
In a tropical rainforest, a species of fig tree relies exclusively on a specific species of fig wasp for pollination. The female wasp enters the fig to lay her eggs, and in the process, pollinates the flowers inside. The wasp larvae develop inside the fig, and when they emerge, they carry pollen to other fig trees. This relationship is an example of mutualism, where both species benefit. However, deforestation has led to a decline in fig tree populations, which in turn has caused a decline in fig wasp populations.
(a) Define the term mutualism. [1]
(b) Explain why the decline in fig tree populations has led to a decline in fig wasp populations. [2]
(c) Explain how deforestation affects biodiversity in the rainforest ecosystem. [2]
(d) Suggest two conservation measures that could help protect the fig tree and fig wasp populations. [2]
(e) Explain why the relationship between the fig tree and fig wasp is described as obligate mutualism. [1]
(f) Predict what would happen to the fig wasp population if a new pollinator species were introduced that could also pollinate the fig tree. [2]
18. The diagram below shows a pyramid of biomass for a food chain in a marine ecosystem.
Sharks (0.5 kg/m²)
/
Tuna (5 kg/m²)
/
Zooplankton (25 kg/m²)
/
Phytoplankton (125 kg/m²)
(a) Define the term pyramid of biomass. [1]
(b) Explain why the pyramid of biomass decreases at each successive trophic level. [2]
(c) Calculate the percentage of biomass transferred from zooplankton to tuna. Show your working. [2]
(d) Explain why food chains rarely exceed four or five trophic levels. [2]
19. The table below shows the concentration of a pesticide (in parts per million, ppm) in four organisms in a food chain.
| Organism | Trophic Level | Pesticide concentration (ppm) |
|---|---|---|
| Algae | Producer | 0.02 |
| Small fish | Primary consumer | 0.5 |
| Large fish | Secondary consumer | 5.0 |
| Osprey | Tertiary consumer | 50.0 |
(a) Describe the trend in pesticide concentration shown in the table. [1]
(b) Explain why the pesticide concentration increases at each successive trophic level. [2]
(c) Name this biological phenomenon. [1]
(d) Explain one consequence of this phenomenon for top predators in an ecosystem. [2]
20. A farmer cleared a patch of forest to create agricultural land. After several years of farming, the soil became depleted of nutrients and the land was abandoned.
(a) Describe what is likely to happen to the abandoned land over the next 50 years in terms of ecological succession. [3]
(b) Explain why the pioneer species in primary succession are different from those in secondary succession. [2]
(c) Define the term climax community. [1]
(d) Explain how biodiversity changes during ecological succession. [2]
End of Quiz
Answers
Secondary 3 Biology Quiz - Ecology: Answer Key
Total Marks: 40
Section A: Multiple Choice Questions (10 marks)
1. B [1]
An ecosystem is defined as a community of organisms interacting with each other and their physical (abiotic) environment. Option A describes a population. Option C describes population size. Option D describes a niche.
2. B [1]
Dissolved oxygen is a non-living (abiotic) factor. Algae, water lily, and mosquito larvae are all living (biotic) components of the ecosystem.
3. C [1]
Producers (autotrophs such as plants and algae) form the first trophic level in a food chain because they convert light energy into chemical energy through photosynthesis.
4. C [1]
If snakes decrease, the predation pressure on mice will be reduced, so the mouse population is likely to increase. Frogs would also increase (not decrease), and grass would likely increase due to reduced herbivory. Foxes are not directly affected by snake numbers in this web.
5. B [1]
Energy flows in one direction through an ecosystem (from producers to consumers) and is lost as heat at each trophic level through respiration. Energy is not recycled — matter is recycled, but energy is not.
6. B [1]
An inverted pyramid of numbers occurs when a single large producer (e.g., one tree) supports many smaller consumers (e.g., insects and birds). The base of the pyramid (one tree) is smaller than the level above it (many insects).
7. D [1]
Carbon dioxide is returned to the atmosphere through respiration (by all living organisms), decomposition (by decomposers breaking down dead organic matter), and combustion (burning of fossil fuels and biomass). Photosynthesis removes CO₂ from the atmosphere.
8. B [1]
Nitrogen fixation is the process by which atmospheric nitrogen (N₂) is converted into ammonia or nitrates by nitrogen-fixing bacteria, making it available for plant uptake.
9. C [1]
Deforestation removes trees that store carbon. When trees are cut down and burned or left to decompose, the stored carbon is released into the atmosphere as CO₂. This increases atmospheric CO₂ levels.
10. C [1]
When prey population increases, there is more food available for predators. After a time lag (time needed for predators to reproduce and increase in number), the predator population will increase. The prey population will not increase indefinitely due to limiting factors such as food availability and predation.
Section B: Structured Questions (20 marks)
11.
(a) [3 marks]
Correct graph plotting:
- Axes correctly labelled: x-axis = "Year", y-axis = "Population" [1]
- Both lines plotted accurately with data points joined [1]
- Lines clearly labelled ("Grass" and "Snakes") with a key or direct labelling [1]
Expected pattern: Grass population decreases steadily from 500 to 300 (×1000). Snake population increases steadily from 10 to 20.
(b) [2 marks]
As the population of grass decreases over the five years, the population of snakes increases. [1] This is an inverse/negative relationship between the two populations. [1]
(c) [1 mark]
The snake population increases because there is less competition for prey (frogs and mice), or because the ecosystem has changed in a way that favours snakes (e.g., fewer predators of snakes, or snakes are generalist feeders that can find alternative food sources). [1]
Accept any reasonable suggestion consistent with the data.
12.
(a) [1 mark]
Mangrove leaves and algae. [1] (Both must be named for the mark.)
(b) [2 marks]
Any two of the following: crabs, mudskippers, small fish. [1 mark each]
Secondary consumers feed on primary consumers (herbivores). Crabs eat mangrove leaves (producer → primary consumer → crab is secondary). Mudskippers eat insects (primary consumer). Small fish eat algae (producer → primary consumer → small fish is secondary).
(c) [1 mark]
Mangrove leaves → Insects → Mudskippers → Herons [1]
OR: Algae → Snails → Mudskippers → Herons [1]
(d) [2 marks]
If the heron population decreases, there will be less predation pressure on mudskippers. [1] Therefore, the mudskipper population would increase. [1]
13.
(a) [1 mark]
Photosynthesis [1]
(b) [2 marks]
Any two of the following: respiration, decomposition, combustion (burning of fossil fuels). [1 mark each]
(c) [2 marks]
Human activities such as burning fossil fuels and deforestation have increased the amount of carbon dioxide released into the atmosphere. [1] This disrupts the natural balance of the carbon cycle by adding more CO₂ than can be absorbed by photosynthesis, contributing to global warming. [1]
(d) [1 mark]
The carbon cycle regulates Earth's climate by controlling the amount of CO₂ in the atmosphere. CO₂ is a greenhouse gas that traps heat. When the carbon cycle is balanced, CO₂ levels remain stable, helping to maintain a stable climate. [1]
14.
(a) [1 mark]
Nitrogen fixation [1]
(b) [1 mark]
Nitrification [1]
(c) [1 mark]
Ammonification [1]
(d) [2 marks]
Nitrogen is an essential element required for the synthesis of proteins and nucleic acids (DNA and RNA). [1] Proteins are needed for growth, repair, and enzyme function, while nucleic acids are needed for genetic information and cell division. [1]
(e) [2 marks]
Nitrogen-fixing bacteria convert atmospheric nitrogen (N₂) into ammonia (NH₃) or ammonium compounds. [1] This makes nitrogen available in a form that plants can absorb and use to make proteins, thus playing a crucial role in the nitrogen cycle. [1]
15.
(a) [2 marks]
As light intensity increases, the number of plants per m² also increases. [1] The number of plants rises from 2 per m² at 10 units of light to a maximum of 25 per m² at 95 units of light. [1]
(b) [1 mark]
Other abiotic factors may become limiting, such as water availability, soil nutrients, or temperature. Alternatively, competition between plants for space may prevent further increase. [1]
Accept any reasonable suggestion.
(c) [1 mark]
Transect sampling / line transect [1]
(d) [2 marks]
Recording light intensity at each sampling point allows the student to correlate the distribution of the plant species with light intensity. [1] This helps to determine whether light intensity is a factor influencing the distribution of the plant species along the transect. [1]
Section C: Extended Response (10 marks)
16.
(a) [3 marks]
- The student should place the quadrat randomly at several locations within the field to avoid bias. [1]
- The student should count the number of dandelions within each quadrat. [1]
- The student should calculate the mean number of dandelions per quadrat and multiply by the total area of the field divided by the area of one quadrat to estimate the total population. [1]
(b) [2 marks]
Mean = (3 + 5 + 2 + 4 + 6 + 3 + 5 + 4 + 2 + 6) / 10 [1]
Mean = 40 / 10 = 4 dandelions per quadrat [1]
(c) [2 marks]
Taking multiple samples reduces the effect of random variation and ensures the data is more representative of the entire field. [1] A single quadrat may be placed in an unusually dense or sparse area, giving an unreliable estimate. [1]
(d) [2 marks]
Any two of the following: light intensity, soil pH, soil moisture, temperature, nutrient availability, water availability. [1 mark each]
(e) [1 mark]
Example: Light intensity affects the rate of photosynthesis in dandelions. Higher light intensity increases the rate of photosynthesis, leading to faster growth and reproduction. [1]
Accept any valid explanation linked to a named abiotic factor.
17.
(a) [1 mark]
Mutualism is a type of symbiotic relationship in which both species benefit from the interaction. [1]
(b) [2 marks]
The fig wasp depends on the fig tree for reproduction (it lays eggs inside the fig) and for food (the larvae feed on fig tissue). [1] When fig tree populations decline, the wasps lose their breeding site and food source, causing their population to decline. [1]
(c) [2 marks]
Deforestation destroys the habitat of many species, leading to loss of shelter, food sources, and breeding sites. [1] This reduces species diversity and can lead to extinction of species that are unable to adapt or relocate. [1]
(d) [2 marks]
Any two of the following: establish protected areas/nature reserves, enforce laws against illegal logging, promote reforestation/afforestation, educate local communities about conservation, create wildlife corridors. [1 mark each]
(e) [1 mark]
It is obligate mutualism because both species are entirely dependent on each other for survival and reproduction — the fig tree can only be pollinated by this specific wasp, and the wasp can only reproduce in this specific fig tree. [1]
(f) [2 marks]
If a new pollinator were introduced, the fig tree would no longer be exclusively dependent on the fig wasp for pollination. [1] The fig wasp population might decline because the fig tree could survive without it, reducing the selective pressure to maintain the mutualistic relationship. Alternatively, the wasp might face competition from the new pollinator for access to figs. [1]
Accept any reasonable prediction with valid reasoning.
18.
(a) [1 mark]
A pyramid of biomass is a graphical representation showing the total mass of living organisms (biomass) at each successive trophic level in a food chain. [1]
(b) [2 marks]
Biomass decreases at each trophic level because energy is lost as heat through respiration at each level. [1] Only a small proportion (approximately 10%) of the energy/biomass at one trophic level is transferred to the next, so the total biomass decreases progressively. [1]
(c) [2 marks]
Percentage transfer = (Biomass at trophic level n+1 / Biomass at trophic level n) × 100 [1]
= (5 / 25) × 100 = 20% [1]
(d) [2 marks]
At each trophic level, a large proportion of energy is lost as heat through respiration, through uneaten parts of organisms, and through excretion. [1] By the fourth or fifth trophic level, there is insufficient energy remaining to support another level of organisms. [1]
19.
(a) [1 mark]
The pesticide concentration increases at each successive trophic level, from 0.02 ppm in algae to 50.0 ppm in the osprey. [1]
(b) [2 marks]
The pesticide is absorbed by organisms at the lowest trophic level and is not easily broken down or excreted (it is persistent). [1] As organisms at each trophic level consume large quantities of organisms from the level below, the pesticide accumulates in their tissues, leading to higher concentrations at each successive level. [1]
(c) [1 mark]
Bioaccumulation / Biomagnification [1]
(d) [2 marks]
Top predators accumulate very high concentrations of the pesticide in their bodies, which can reach toxic levels. [1] This can cause reproductive failure, weakened immune systems, behavioural changes, or death, potentially leading to population decline or extinction of the top predator species. [1]
20.
(a) [3 marks]
Pioneer species such as grasses and herbs would colonise the bare soil first. [1] Over time, shrubs and small trees would grow, followed by larger trees as the soil becomes richer in nutrients from decomposing organic matter. [1] Eventually, after many years, the land would develop into a mature forest community similar to the original forest that was cleared. [1]
(b) [2 marks]
In primary succession, the area starts with bare rock or no soil, so pioneer species such as lichens and mosses that can grow on bare rock and help form soil are needed. [1] In secondary succession, soil is already present, so pioneer species such as grasses and fast-growing herbs that can colonise existing soil are the first to appear. [1]
(c) [1 mark]
A climax community is the final, stable community that develops at the end of ecological succession, which remains relatively unchanged as long as environmental conditions remain constant. [1]
(d) [2 marks]
Biodiversity increases during the early and middle stages of succession as more species colonise the area and habitats become more complex. [1] In the climax community, biodiversity may stabilise or slightly decrease as competitive exclusion leads to dominance by a few well-adapted species, but overall species richness is higher than in the early stages. [1]
End of Answer Key