Levels of Organization
The definition of ecosystem.
All the living and non-living parts of an environment, including the interactions among them?
What is a limiting factor?
Any biotic or abiotic factor that restricts the growth or size of a population.
What is a symbiotic relationship
A close relationship between two different species.
What are the three main roles organisms play in the movement of energy through an ecosystem, and what does each role do?
Producers make their own food, usually using sunlight.
Consumers obtain energy by eating other organisms.
Decomposers break down dead organisms and waste, returning nutrients to the environment.
What is the primary function of cellular respiration, and which two types of nutrients are primarily used by the body for energy?
Cellular respiration converts the chemical energy in glucose into usable energy stored in ATP. Carbohydrates and fats are primarily used for energy, while proteins are mainly used to build and repair body structures.
Explain how a species, a population, and a community are related to one another. How are they different?
A species is a group of organisms that can reproduce with one another. A population is a group of organisms of the same species living in the same area. A community includes all the different populations living in an area.
A population of deer grows until the forest can no longer provide enough food, water, and shelter for additional deer. What term describes the maximum population size the forest can support?
Carrying capacity.
Bees collect nectar from flowers to make food, while transferring pollen between flowers. Identify the type of symbiotic relationship and explain how each organism either benefits, is unaffected, or harmed.
Mutualism. The bee gets food from the nectar, and the flower benefits from pollination, which helps it reproduce.
Consider this food chain:
Grass → Grasshopper → Frog → Snake
Identify the producer, the primary consumer, and the secondary consumer. Then explain what the arrows represent.
Producer: Grass
Primary consumer: Grasshopper
Secondary consumer: Frog
The arrows show the direction energy moves, from the organism being eaten to the organism that eats it.
Plants use photosynthesis to make glucose, and both plants and animals perform cellular respiration. Explain how these two processes are connected by identifying what photosynthesis produces that cellular respiration uses.
Photosynthesis produces glucose and oxygen, which are used in cellular respiration to release usable energy in ATP. Cellular respiration produces carbon dioxide and water, which plants can use as inputs for photosynthesis.
In a pond, there are 25 frogs of the same species living together. What level of organization do these frogs represent?
A population.
Two ponds are the same size. Pond A contains 20 frogs, while Pond B contains 80 frogs. Which pond has the greater population density, and how do you know?
Pond B has the greater population density because it contains more frogs in the same amount of space. This means there are more frogs per unit of area in Pond B.
Small fish called remoras attach themselves to sharks and eat leftover food scraps. The remoras benefit, but the sharks are not significantly helped or harmed. Identify the relationship and explain why.
Commensalism. The remoras benefit by getting food, while the sharks are unaffected. It is not mutualism because both organisms do not benefit, and it is not parasitism because the shark is not harmed.
An energy pyramid contains 10,000 units of energy at the producer level. If approximately 10% of the energy is transferred to the next trophic level, how much energy reaches the primary consumers? Explain why less energy is available at higher trophic levels.
Approximately 1,000 units reach the primary consumers. Organisms use much of the energy they obtain for life processes, such as movement, growth, and cellular respiration. Much of that energy is released as heat, so only a portion is transferred to the next trophic level.
A plant takes in carbon dioxide from the atmosphere and uses it to make glucose. A rabbit eats the plant, and later the rabbit releases carbon dioxide through cellular respiration. Explain how carbon moved from an abiotic factor to a biotic factor and then back to an abiotic factor.
Carbon moved from atmospheric carbon dioxide, an abiotic factor, into the plant's glucose, a part of a living organism. The rabbit obtained that carbon by eating the plant. Cellular respiration then released some of the carbon back into the atmosphere as carbon dioxide.
A forest contains deer, rabbits, squirrels, and several species of trees. What level of organization includes all these living organisms, and why?
A community, because it includes all the different populations living in the same area.
A rabbit population grows rapidly in a meadow. Over time, the grass becomes scarce, and the rabbit population stops increasing. Explain why the population stopped growing and identify the two ecosystem concepts involved.
Limited grass availability is a limiting factor because rabbits have less food. The population has reached or is approaching the meadow's carrying capacity.
A tick attaches to a deer and feeds on its blood. Identify the type of relationship and explain how the interaction affects both organisms. Then explain why this is different from predation.
Parasitism. The tick benefits by getting food, while the deer is harmed. Unlike predation, the tick typically feeds on the deer without killing it immediately.
In a grassland food web, grass is eaten by grasshoppers and rabbits. Grasshoppers are eaten by frogs, and frogs are eaten by snakes. Rabbits are also eaten by snakes.
If a disease causes the rabbit population to decrease sharply, predict one possible effect on the grass population and one possible effect on the snake population. Explain your reasoning.
Grass: May increase because fewer rabbits are eating it.
Snakes: May decrease because there are fewer rabbits available as a food source.
Reasoning: A change in one population can affect other populations through feeding relationships in the food web.
After a rainstorm, water from a pond goes into the atmosphere. Later, the water vapor forms clouds and falls back to Earth as rain. Identify the three processes described and explain how water moves between abiotic and biotic parts of an ecosystem during the water cycle.
The three processes are evaporation, condensation, and precipitation. Water also moves from abiotic factors into living organisms when plants absorb it through their roots. It can return to the atmosphere through transpiration from plants and through other processes, including evaporation from surfaces.
A disease kills most of the rabbits living in a meadow, but other species in the meadow survive. Which level of organization is directly affected, and how could this change affect the community?
The rabbit population is directly affected because its size decreases. The community could also be affected because other organisms that depend on rabbits for food may have less food available, while plants eaten by rabbits may increase.
A scientist records the population of rabbits in a meadow over five years.
Years | 1 | 2 | 3 | 4 | 5
Rabbit # | 20 | 45 | 70 | 72 | 69
Which statement best explains the change in the rabbit population between Years 3 and 5?
A. The rabbit population has reached or is approaching carrying capacity because limiting factors restrict further growth.
B. The rabbit population is increasing exponentially because the number of rabbits is greater than it was in Year 1.
C. The carrying capacity has increased because the rabbit population has decreased slightly.
D. The population density has decreased because the rabbits are reproducing more slowly than expected.
A. The rabbit population has reached or is approaching carrying capacity because limiting factors restrict further growth.
Scientists observe three interactions between organisms in a forest.
Interaction 1: A fungus grows on tree roots and helps the tree absorb water and minerals. The fungus receives sugars from the tree.
Interaction 2: Mistletoe grows on a tree and takes water and nutrients from it, weakening the tree.
Interaction 3: A bird builds a nest in a tree. The bird gains shelter, while the tree is unaffected.
Question: Identify the symbiotic relationship in each interaction and explain how the organisms are affected.
A. Mutualism, parasitism, commensalism
B. Commensalism, mutualism, parasitism
C. Parasitism, commensalism, mutualism
D. Mutualism, commensalism, parasitism
A. In Interaction 1, both the fungus and tree benefit. In Interaction 2, mistletoe benefits while the tree is harmed. In Interaction 3, the bird benefits while the tree is unaffected.
Scientists study the following food web in a meadow.
Grass → Grasshopper → Frog → Hawk
Grass → Mouse → Hawk
Grasshopper → Mouse
A drought causes the amount of grass in the meadow to decrease significantly.
Question: Which prediction is best supported by the food web, and why?
A. The hawk population will increase because less grass means less energy is lost to producers.
B. The grasshopper and mouse populations may decrease because less grass is available as a food source, which could also reduce the food available to hawks.
C. The frog population will increase because fewer grasshoppers means less competition for food.
D. The hawk population will remain unchanged because consumers can obtain energy directly from the Sun.
B. Less grass means less energy enters the food web through the producers. Grasshoppers and mice may have less food available, and frogs may also be affected if grasshopper numbers decrease. Hawks could then have fewer prey available. These changes can ripple through the food web because organisms depend on one another for energy.
Scientists study a forest ecosystem where plants use photosynthesis to make glucose. Deer eat the plants, and both plants and deer perform cellular respiration. The deer release carbon dioxide into the atmosphere, and water moves through the ecosystem by evaporation, condensation, and precipitation.
Question: Which statement best explains how matter and energy move through this ecosystem?
A. Carbon and water cycle through the ecosystem, while energy flows through organisms and some is released as heat during cellular respiration.
B. Carbon and energy are both recycled indefinitely, so organisms can reuse the same energy without additional sunlight.
C. Water and carbon enter the ecosystem only through precipitation, and cellular respiration stores energy in glucose.
D. Plants obtain their energy from soil nutrients, while animals create new matter when they digest food.
A. Carbon and water are recycled through the ecosystem. Plants take in carbon dioxide during photosynthesis, and carbon moves through food webs before returning to the environment through processes such as cellular respiration and decomposition. Water moves through the water cycle and through organisms. In contrast, energy enters mainly as sunlight, is stored as chemical energy through photosynthesis, and is transferred between organisms. During cellular respiration, usable energy is transferred to ATP, and some energy is released as heat rather than recycled.