Name:
Date:
Class:
How to use this worksheet. Read each passage and the data table before you answer. Choose the
best answer and write its letter on the answer line.
- Every question has a Nudge — a hint about how to think it through. It does not give the answer away. Try the question first; read the nudge if you get stuck.
- Base every answer on evidence in the passage or the table — not on memory or opinion.
- A calculator is allowed. Suggested time: 45–55 minutes, but accuracy matters more than speed.
PASSAGE 1Limiting Factors and Carrying Capacity
In any ecosystem, populations of organisms do not grow indefinitely. The maximum number of individuals of a species that an environment can support over time is called the carrying capacity. Several factors limit population growth. These are called limiting factors.
Limiting factors can be density-dependent (their effect increases as population density increases) or density-independent (their effect is unrelated to population density). Examples of density-dependent factors include competition for food or space, predation, and disease. Density-independent factors include natural disasters, extreme weather, and human activities such as habitat destruction or pollution. When a population exceeds its carrying capacity, limiting factors usually cause the population to decline until it returns to a sustainable level.
1.What is the main idea of Passage 1?
- A. Populations are limited by carrying capacity and both density-dependent and density-independent factors that prevent indefinite growth.
- B. Only natural disasters limit population growth in ecosystems.
- C. Carrying capacity always increases when more individuals are born.
- D. Human activities never affect population sizes in nature.
Nudge — A main idea must cover the whole passage, not one detail. Watch for absolute words like only, always, and never — they usually make an option too extreme to be right.
Answer:
2.According to the passage, which of the following is an example of a density-dependent limiting factor?
- A. A severe drought that affects an entire region
- B. A sudden volcanic eruption
- C. Competition for limited food resources as population size increases
- D. Habitat destruction caused by a hurricane
Nudge — Density-dependent means the effect gets worse when the population is crowded. Test each option: "Would this hurt more if there were more animals?" If crowding doesn't matter, cross it out.
Answer:
3.If a deer population greatly exceeds the carrying capacity of its habitat, what is the most likely long-term outcome according to the passage?
- A. The population will continue to grow rapidly forever.
- B. Only density-independent factors will affect the deer.
- C. The carrying capacity will immediately increase to match the new population size.
- D. Limiting factors such as food shortage and disease will cause the population to decline.
Nudge — The phrase "according to the passage" means the answer is written there. Find the last sentence of Passage 1 — it says exactly what happens when a population goes over carrying capacity.
Answer:
4.Which statement best describes the relationship between carrying capacity and limiting factors?
- A. Carrying capacity is determined by the combined effects of limiting factors in an environment.
- B. Limiting factors have no effect on carrying capacity.
- C. Carrying capacity only applies to plant populations.
- D. Limiting factors always increase carrying capacity.
Nudge — Ask which one causes the other. Limiting factors are the things that hold a population back — so do they set the ceiling, or raise it? Eliminate any option that reverses the cause and effect.
Answer:
5.According to the passage, which of the following human activities would most likely act as a density-independent limiting factor for a wildlife population?
- A. Increased hunting pressure as the animal population grows
- B. Spread of a disease that spreads more easily in crowded populations
- C. Large-scale deforestation that destroys habitat regardless of population size
- D. Competition for nesting sites among birds
Nudge — This is the opposite of Question 2. Density-independent means the factor does the same damage whether the population is large or small. Test each option: "Would this still strike just as hard if there were far fewer animals?" Keep the one where crowding makes no difference.
Answer:
PASSAGE 2 · EXPERIMENTLimiting Factors on a Fish Population
Scientists studied a small pond to understand what limits the population of a certain species of fish. They set up four large experimental tanks with similar conditions to the pond. Each tank started with the same number of fish. Over 12 weeks, they recorded the average number of fish surviving in each tank under different conditions.
Table 1. Average number of fish surviving after 12 weeks
| Tank |
Food availability |
Predators present |
Fish at week 12 |
| Tank 1 (control) | High | No | 48 |
| Tank 2 | Low | No | 19 |
| Tank 3 | High | Yes | 27 |
| Tank 4 | Low | Yes | 9 |
All tanks started with 50 fish. Temperature, water quality, and space were kept the same in every tank.
6.In this experiment, what is the dependent variable?
- A. Food availability and presence of predators
- B. The size of the experimental tanks
- C. The species of fish used
- D. Average number of fish surviving after 12 weeks
Nudge — The dependent variable is what the scientists measured — the result, not the setup. In a data table it is almost always the final column. What did they count at the end?
Answer:
7.Which tank serves as the control group?
- A. Tank 2
- B. Tank 3
- C. Tank 1
- D. Tank 4
Nudge — A control is the "normal" setup with nothing taken away and nothing added — the baseline everything else is compared against. Which row has plenty of food and no predators?
Answer:
8.Based on the data in Table 1, which limiting factor appears to have the strongest negative effect on fish survival when acting alone?
- A. Low food availability
- B. High food availability
- C. Presence of predators
- D. High food with predators
Nudge — "Acting alone" means only one thing changed from the control. That's Tank 2 (food only) and Tank 3 (predators only). Compare each to Tank 1's 48 — which one drops further?
Answer:
9.Which statement is best supported by comparing Tank 1 and Tank 4?
- A. Low food and predators together caused the greatest reduction in fish numbers.
- B. Predators had no effect when food was low.
- C. Food availability had no impact on survival.
- D. The control tank had the lowest survival rate.
Nudge — Read only those two rows. Note what is different between them and what happened to the fish count. Then check each option against the table — three of them say something the numbers flatly contradict.
Answer:
10.The data suggest that low food availability and the presence of predators have which type of combined effect?
- A. They cancel each other out.
- B. They appear to have a combined negative effect greater than either factor alone.
- C. Only food availability matters.
- D. Predators improve survival when food is low.
Nudge — Line up all four numbers: 48, 19, 27, 9. Each factor alone caused a drop. Is the drop when both are present bigger than either one on its own, or smaller?
Answer:
11.If the scientists wanted to test whether disease is also a limiting factor, what would be the best improvement to the experiment?
- A. Add a new tank with disease introduced while keeping other conditions the same as Tank 1.
- B. Remove all food from every tank.
- C. Use only one tank for the entire experiment.
- D. Measure only the size of the fish instead of counting them.
Nudge — To test a new factor fairly, change that one thing and hold everything else steady, so any difference must come from the new factor. Which option changes exactly one thing from the control?
Answer:
12.Based on the data, which condition would most likely allow a fish population to reach or exceed carrying capacity in a natural pond?
- A. Very low food supply and many predators
- B. High food availability and few or no predators
- C. Low food but no predators
- D. High number of predators only
Nudge — Work backwards from the data: find the row with the highest survival, then read across to see what conditions produced it. That combination is your answer.
Answer:
13.Which of the following is the best example of a density-independent limiting factor?
- A. Competition for mates among male birds
- B. Increased spread of parasites in a crowded deer population
- C. A forest fire that destroys habitat for many animals regardless of how many there are
- D. Starvation due to overgrazing by a large herbivore population
Nudge — Same test as Questions 2 and 5. Ask of each option: "Does crowding make this worse?" Three describe pressures that build as animals become more numerous; one would strike just as hard in a sparse population. That odd one out is the density-independent factor.
Answer:
14.In a food chain, energy is transferred from one trophic level to the next. Approximately what percentage of energy is typically transferred?
- A. 100%
- B. About 10%
- C. About 50%
- D. About 90%
Nudge — Think about why food chains rarely have more than four or five links: most energy is lost at each step rather than passed on. If most is lost at every level, the share that transfers must be small — rule out the large percentages.
Answer:
15.A scientist is studying how temperature affects the growth rate of bacteria. She sets up three identical cultures at different temperatures while keeping everything else the same. What is the independent variable?
- A. The growth rate of the bacteria
- B. The type of bacteria used
- C. The temperature of each culture
- D. The size of the culture containers
Nudge — The independent variable is what the scientist deliberately changes; the dependent variable is what she measures. Find the one thing that is different between the three cultures — everything else was held the same.
Answer:
16.Which of the following would most likely increase the carrying capacity of an ecosystem for a herbivore population?
- A. Introducing more predators into the ecosystem
- B. Removing all shelter from the area
- C. Decreasing the amount of water available
- D. Increasing the amount of available plant food
Nudge — Carrying capacity goes up when resources go up. Three options take something away or add a threat. Only one adds a resource — and remember a herbivore eats plants.
Answer:
17.In an experiment, a researcher notices that results vary widely between trials even though conditions seem the same. What should the researcher do first?
- A. Change the hypothesis immediately
- B. Publish the results without further testing
- C. Ignore the inconsistent results
- D. Check for errors in procedure or measurement and repeat the trials
Nudge — The key word is first. Good scientists check their own work before drawing any conclusion. Which option is the careful, cautious next step — and which three would a scientist never do?
Answer:
18.Which of the following best explains why only a small amount of energy is transferred from one trophic level to the next in a food chain?
- A. Energy is destroyed at each level.
- B. Most energy is used for metabolism and lost as heat.
- C. All energy is stored in the organism's body.
- D. Producers do not produce usable energy.
Nudge — Follow up from Question 14: if only about 10% moves up, where does the rest go? Remember that energy cannot be destroyed — so rule out any option that says it is. Think about what staying alive costs an animal.
Answer:
19.A biologist wants to test the effect of different amounts of fertilizer on plant growth. She sets up four groups of plants and gives each group a different amount of fertilizer while keeping light, water, and soil type the same. What is the dependent variable?
- A. The amount of fertilizer given to each group
- B. The amount of light the plants receive
- C. The type of soil used
- D. The growth (height or mass) of the plants
Nudge — Careful: this asks for the dependent variable, not the independent one. The fertilizer is what she changes; light and soil are held constant. So what is left — the thing she measures at the end?
Answer:
20.Which of the following human activities would most likely decrease the carrying capacity of an area for native wildlife?
- A. Large-scale removal of native vegetation for agriculture
- B. Creating protected wildlife corridors
- C. Reintroducing native predator species
- D. Reducing pollution in local rivers
Nudge — Decrease is the key word. Sort the options into "helps wildlife" and "takes something away." Three of them protect or restore the habitat. Only one strips resources out of it.
Answer:
21.In a well-designed experiment, why is it important to change only one variable at a time?
- A. To make the experiment more complicated
- B. To clearly determine which variable is responsible for the observed results
- C. To ensure all variables change together
- D. To reduce the need for a control group
Nudge — Imagine changing food and predators at once and seeing fewer fish. Could you tell which one caused it? That impossibility is exactly the reason for the rule.
Answer:
22.Which of the following is an example of a density-dependent limiting factor that can affect human populations?
- A. A major earthquake
- B. A powerful hurricane
- C. The rapid spread of an infectious disease in a crowded city
- D. A long-term drought affecting an entire country
Nudge — Density-dependent means crowding makes it worse. A natural disaster hits whether an area is packed or empty, so those are density-independent. Find the factor whose spread or intensity would actually rise as the population gets denser.
Answer:
23.According to scientific understanding, which statement about carrying capacity is most accurate?
- A. Carrying capacity is always fixed and never changes.
- B. Carrying capacity can change over time if environmental conditions change.
- C. Only animal populations have a carrying capacity.
- D. Carrying capacity only applies to very small ecosystems.
Nudge — Scan for the absolute words again: always, never, only. Three options contain one. Carrying capacity depends on resources — so what happens to it if the resources change?
Answer:
Extended Response
24. Using evidence from both Passage 1 and Table 1, explain how limiting factors determine the carrying capacity of an environment. In your answer, describe what the fish experiment shows about how two limiting factors act together, and identify which tank represents the highest carrying capacity and why.
Nudge — Plan before you write. (1) Define carrying capacity and limiting factor in your own words. (2) Quote at least two numbers from Table 1 — numbers are your evidence. (3) Compare Tank 4 against Tanks 2 and 3 to show the combined effect. (4) Finish by naming the tank with the highest carrying capacity and explaining what its conditions were.
Reflection
Which questions did you need the nudge for? What kind of question was hardest — reading the passage, reading the table, or experimental design? Name one thing to practice next.