Carrying Capacity
What term describes the maximum number of organisms of a species that an environment can support over time?
Carrying capacity
Which group of organisms is responsible for converting sunlight into chemical energy through photosynthesis?
Producers (autotrophs)
What term describes a living (biological) factor in an ecosystem that can affect population size?
Biotic factor
Which process removes carbon dioxide from the atmosphere and stores it in organic molecules?
Photosynthesis
Why is biodiversity important for the stability of an ecosystem?
Biodiversity helps ecosystems remain stable because a variety of species can perform different roles, provide resilience against changes, and ensure energy and matter flow efficiently.
Identify one biotic factor and one abiotic factor that can limit the carrying capacity of a population.
Biotic: predation, disease, competition
Abiotic: water, temperature, sunlight, space, nutrients
What happens to most of the energy as it moves from one trophic level to the next?
Most energy is lost as heat; only about 10% is transferred to the next level.
Identify one physical factor that could cause a population to decrease in an ecosystem.
Temperature change, drought, flooding, pollution, habitat loss, lack of sunlight (any one)
Identify one way photosynthesis and cellular respiration are related in the carbon cycle.
Photosynthesis removes carbon dioxide from the atmosphere, while cellular respiration returns carbon dioxide to the atmosphere.
How does the niche of an organism help reduce competition in an ecosystem?
An organism’s niche determines its role, habitat, and what it eats, so different species use different resources or occupy different areas, which reduces competition.
A population of rabbits increases rapidly, then levels off and fluctuates around 500 individuals.
What does the number 500 most likely represent?
The carrying capacity of the ecosystem
Why can food chains usually support fewer organisms at higher trophic levels?
Because energy decreases at each trophic level due to loss as heat and metabolic processes.
If the grasshopper population decreases, explain how this change could affect two other populations in the food web.
The frog population may decrease because grasshoppers are a major food source.
The bird population may decrease due to reduced food availability.
The grass population may increase because fewer grasshoppers are feeding on it.
Populations of snakes or hawks may decrease due to reduced energy moving up the food web.
Describe how carbon in atmospheric carbon dioxide can become part of an animal’s body.
Carbon dioxide is taken in by plants during photosynthesis, incorporated into organic molecules, and then passed to animals when they eat plants or other animals.
A forest loses all of its wolves. Describe the likely effect on the populations of deer, plants, and other species in the forest over time.
Deer populations increase, plants decrease due to overgrazing, and other species that depend on plants or habitat may decline.
Explain how a decrease in available food would affect the carrying capacity of a population. Include the direction of change.
The carrying capacity would decrease because fewer resources can support fewer individuals.
A farmer adds fertilizer to a field, increasing plant growth. Explain how this change could affect energy flow through the entire food web.
Increased producers capture more energy
More energy becomes available to herbivores and higher consumers
Population sizes at higher trophic levels may increase due to increased energy availability
Explain how a decrease in soil bacteria involved in the nitrogen cycle could affect plant and animal populations in an ecosystem.
Plants would have less usable nitrogen, limiting growth
Herbivores would be affected due to reduced plant populations
Higher-level consumers may also decrease as energy moves through the food web
Explain how the ocean acts as a carbon sink and how this affects the amount of carbon dioxide in the atmosphere.
The ocean absorbs large amounts of carbon dioxide from the atmosphere. This carbon can dissolve in water or be used by marine organisms for photosynthesis, reducing atmospheric carbon dioxide levels and helping regulate Earth’s climate.
Explain the difference between how energy and matter move through an ecosystem. Why does energy decrease at higher trophic levels while matter cycles?
Energy flows one-way and decreases at each trophic level due to heat loss, while matter (like carbon, nitrogen, water) is recycled and reused continuously.
A graph shows a deer population growing beyond the carrying capacity after a mild winter.
Within two years, the population sharply declines.
Using ecosystem principles, explain two reasons for this decline.
Overuse of resources leading to starvation
Increased disease or competition due to overcrowding
Habitat damage reducing future resources
A pesticide is sprayed on a farm to reduce insect pests. Over time, bird populations that feed on the insects sharply decline, even though insects briefly increase after spraying. Using your knowledge of energy flow through ecosystems, explain one reason why the bird population decreases.
The pesticide reduces insect populations long-term, decreasing the amount of energy available to birds.
Toxins accumulate in insects and are transferred to birds through feeding, disrupting energy use and survival.
Reduced energy transfer through the food web limits the ability of birds to survive and reproduce.
A wetland is drained to build housing.
Support the claim that this physical change will affect populations in the ecosystem by explaining two different population changes that are likely to occur.
Aquatic organisms will decrease or die off due to habitat loss
Bird, fish, and amphibian populations will decline due to reduced food and breeding areas
Species adapted to dry conditions may increase
Describe how carbon cycles through the biosphere, atmosphere, hydrosphere, and geosphere, including the roles of photosynthesis and cellular respiration.
Carbon dioxide in the atmosphere is taken up by plants in the biosphere through photosynthesis.
Animals in the biosphere obtain carbon by consuming plants or other animals.
Cellular respiration by organisms releases carbon dioxide back into the atmosphere.
Carbon dioxide also dissolves in the hydrosphere (oceans), where marine organisms use it for photosynthesis.
Carbon can be stored long-term in the geosphere as fossil fuels or sediments, which release carbon back to the atmosphere through volcanic activity or combustion.
A lake experiences a sudden decline in phytoplankton due to pollution. Predict how this change will affect zooplankton, fish, and decomposers, and explain why.
Zooplankton populations decline because they have less food. Fish that eat zooplankton or smaller fish also decline. Decomposers may temporarily increase due to more dead organisms, but eventually decline as overall biomass decreases. The energy flow and ecosystem stability are disrupted.