Introduction
Unit 8 of AP Biology covers ecology, focusing on ecosystems, population dynamics, conservation biology, and biodiversity. Mastering this unit is crucial for the AP Biology exam. In this guide, we provide classified questions with detailed answers and explanations to help you understand key concepts effectively.
Topics Covered in Unit 8 AP Biology:
- Ecosystem dynamics and energy flow
- Population ecology and species interactions
- Biodiversity and conservation biology
- Climate change and human impact on ecosystems
Classified Questions with Answers
1. Question: What is the difference between a food chain and a food web?
Answer: A food chain represents a single pathway of energy flow in an ecosystem, while a food web consists of multiple interconnected food chains, showing a more complex and realistic transfer of energy.
Explanation:
- Food chains illustrate a linear energy flow (e.g., grass → rabbit → fox).
- Food webs depict interdependencies, providing ecosystem stability.
- Disruptions (e.g., species extinction) affect food webs more significantly than food chains.
2. Question: How does carrying capacity affect population size?
Answer: Carrying capacity (K) is the maximum population size an environment can support based on available resources.
Explanation:
- When population size is below K, it grows exponentially.
- As it nears K, growth slows due to limited resources.
- If exceeded, competition increases, causing a population decline.
Example: The deer population in a forest increases until food and space become limiting factors.
3. Question: What are keystone species, and why are they important?
Answer: Keystone species have a disproportionate impact on ecosystem stability and biodiversity.
Explanation:
- Their presence maintains ecological balance.
- Example: Sea otters control sea urchin populations, preventing kelp forest destruction.
- Loss of a keystone species can lead to ecosystem collapse.
4. Question: How does human activity contribute to climate change?
Answer: Human activities, such as burning fossil fuels and deforestation, increase greenhouse gases (CO2, CH4), leading to global warming and climate shifts.
Explanation:
- Deforestation reduces CO2 absorption.
- Burning fossil fuels releases excess CO2.
- Industrial emissions contribute to atmospheric pollution.
Impact: Rising temperatures, melting ice caps, and habitat destruction.
More questions
Question 1: Population Growth
A population of rabbits in a meadow grows according to the logistic growth model. If the carrying capacity (K) of the environment is 500 rabbits and the current population size (N) is 200, what is the population growth rate relative to its maximum potential growth rate (r)?
Answer:
The population growth rate relative to its maximum potential growth rate is 60% .
Explanation:
The logistic growth model is described by the equation:dtdN​=rN(1−KN​)
where:
- dtdN​ is the rate of population growth,
- r is the intrinsic growth rate,
- N is the current population size,
- K is the carrying capacity.
To determine the population growth rate relative to the maximum potential growth rate (r), we calculate the factor (1−KN​):1−KN​=1−500200​=1−0.4=0.6
Thus, the population is growing at 60% of its maximum potential growth rate because only 60% of the carrying capacity remains available for population expansion.
Question 2: Community Interactions
In a forest ecosystem, a species of bird feeds exclusively on insects found under the bark of trees. A new species of woodpecker is introduced, which also feeds on these insects. Over time, the original bird species begins feeding on insects found in the canopy instead of under the bark. This is an example of:
Answer:
Resource partitioning
Explanation:
Resource partitioning occurs when two species compete for the same resource, but over time, they evolve to use different parts of the resource or different resources altogether. In this case, the original bird species shifts its feeding behavior to avoid direct competition with the woodpecker. By moving to the canopy, the original bird reduces competition and allows both species to coexist. This is a classic example of how niche differentiation can reduce competitive exclusion.
Question 3: Ecosystem Energy Flow
In a grassland ecosystem, the net primary productivity (NPP) is measured to be 5000 kcal/m²/year, and the gross primary productivity (GPP) is 8000 kcal/m²/year. What percentage of the energy captured by producers is used for their own cellular respiration?
Answer:
37.5%
Explanation:
Net primary productivity (NPP) is calculated as:NPP=GPP−R
where R is the energy used by producers for cellular respiration.
Rearranging the equation to solve for R:R=GPP−NPP
Substituting the given values:R=8000−5000=3000kcal/m²/year
The percentage of energy used for respiration is:Percentage=(GPPR​)×100=(80003000​)×100=37.5%
Thus, 37.5% of the energy captured by producers is used for cellular respiration .
Question 4: Trophic Levels and Biomagnification
In a marine food chain, phytoplankton are consumed by zooplankton, which are eaten by small fish, which are then eaten by large predatory fish. A toxin is introduced into the ecosystem and accumulates in the bodies of organisms. Which organism would have the highest concentration of the toxin?
Answer:
Large predatory fish
Explanation:
This is an example of biomagnification , where toxins become increasingly concentrated as they move up the food chain. Organisms at higher trophic levels consume many individuals from lower trophic levels, accumulating the toxin in their bodies over time. Since large predatory fish are at the top of this food chain, they will have the highest concentration of the toxin.
Question 5: Human Impact on Ecosystems
Which of the following human activities has the greatest potential to disrupt the carbon cycle and contribute to global climate change?
Answer:
Burning fossil fuels
Explanation:
Burning fossil fuels releases large amounts of carbon dioxide (COâ‚‚) into the atmosphere, which disrupts the natural balance of the carbon cycle. COâ‚‚ is a greenhouse gas that traps heat in Earth’s atmosphere, leading to global warming and climate change. Other human activities, such as deforestation, also impact the carbon cycle, but fossil fuel combustion is the largest contributor to atmospheric COâ‚‚ levels.
Question 6: Succession
After a volcanic eruption, a barren landscape is gradually colonized by lichens and mosses, followed by grasses and shrubs, and eventually by trees. This process is an example of:
Answer:
Primary succession
Explanation:
Primary succession occurs in areas where no soil exists initially, such as after a volcanic eruption or glacial retreat. The first organisms to colonize are pioneer species like lichens and mosses, which help break down rock and form soil. Over time, more complex plants like grasses, shrubs, and trees establish themselves, leading to the development of a stable climax community.
These questions cover key concepts in Unit 8 of AP Biology and provide a deeper understanding of ecological principles. Let me know if you’d like additional practice or further clarification!
Final Boxed Answer for Reference:
- 60%
- Resource partitioning
- 37.5%
- Large predatory fish
- Burning fossil fuels
- Primary succession
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