Living Things and the Environment

Living Things and the Environment

Middle School

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Learning Objectives

• Define biotic and abiotic factors and the levels of organization in an ecosystem.

• Explain how resource availability limits population growth and determines carrying capacity.

• Analyze how competition for resources affects organism growth, reproduction, and survival.

• Interpret data to see how resource changes affect a population's health.

Key Vocabulary

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Habitat

An environment providing things an organism needs to live, grow, and successfully reproduce.

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Biotic Factor

A living or once-living part of a habitat that interacts with other organisms.

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Abiotic Factor

A nonliving physical or chemical part of a habitat, like water, light, or temperature.

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Species

A group of organisms that can mate and produce offspring that can also reproduce.

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Population

All members of a single species living together in a particular defined area.

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Community

All the different populations of various species that live and interact in the same area.

Key Vocabulary

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Ecosystem

A community of organisms and all of the nonliving factors with which they interact.

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Competition

The struggle between organisms to survive as they use the same limited resources available.

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Resource Availability

The amount of food, water, and other necessities that are accessible to the organisms.

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Limiting Factor

An environmental factor that causes a population to stop growing or decrease in its size.

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Carrying Capacity

The largest population size that a specific area can support over a long period.

Biotic and Abiotic Factors

• Biotic factors are the living parts of a habitat, like plants and animals.

• Abiotic factors are the nonliving parts, such as water, sunlight, and temperature.

• Both are essential for the survival and balance of an ecosystem.

Multiple Choice

What are biotic factors in a habitat?

• The living parts, like plants and animals

• The nonliving parts, like water and sunlight

• The temperature and climate of the area

• The amount of rainfall an area receives

Multiple Choice

Which of the following lists contains only abiotic factors?

• Sunlight, water, and temperature

• Plants, animals, and fungi

• Water, soil, and trees

• Birds, fish, and rocks

Multiple Choice

If a prolonged drought drastically reduces the amount of water in a forest, what is the most likely impact on the ecosystem?

• The biotic factors, like trees and animals, would struggle to survive.

• The abiotic factors, like sunlight and temperature, would disappear.

• The number of animals would increase due to less water.

• The ecosystem would remain balanced and unaffected.

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Levels of Ecosystem Organization

• An organism, or a single living thing, is the first level of organization.

• A population includes all members of one species living in the same area.

• A community consists of all the different populations that live and interact together.

• An ecosystem is the community plus the nonliving, abiotic environment they all share.

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Multiple Choice

Which level of ecosystem organization refers to a single living thing?

• Organism

• Population

• Community

• Ecosystem

Multiple Choice

What is the primary difference between a population and a community?

• A community includes multiple populations, while a population includes members of only one species.

• A population includes the nonliving environment, while a community includes only living things.

• A community is made of individual organisms, while a population is made of multiple communities.

• A population and a community are the same level of organization.

Multiple Choice

A scientist studies how all the different plants and animals in a forest interact with the soil, water, and sunlight. Which level of organization is being studied and why?

• A community, because it only involves different populations of living things.

• A population, because it focuses on one area.

• An ecosystem, because it includes both the living community and the nonliving environment.

• An organism, because it involves the study of living things.

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How Populations Change

• A population increases when its birth rate is higher than its death rate.

• Immigration (moving in) grows a population, while emigration (moving out) shrinks it.

• Population density measures crowding, calculated as: Number of individuals / Unit area.

Multiple Choice

What are the primary factors that determine a population's size?

• The comparison of its birth rate to its death rate.

• The number of individuals who move into the area.

• The amount of space the population occupies.

• The average age of the individuals in the population.

Multiple Choice

What is the relationship between immigration, emigration, and a population's size?

• Immigration causes a population to grow, while emigration causes it to shrink.

• Emigration causes a population to grow, while immigration causes it to shrink.

• Both immigration and emigration cause a population to grow.

• Both immigration and emigration cause a population to shrink.

Multiple Choice

A population of 100 rabbits lives in a 2-acre field. If a wildfire forces 30 of these rabbits to permanently move to a different field, what is the most likely immediate impact?

• The population density will decrease because of emigration.

• The population density will increase because of immigration.

• The birth rate will decrease to save resources.

• The death rate will increase because of the limited space.

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Limiting Factors and Carrying Capacity

• A limiting factor is anything that stops or slows population growth.

• The availability of resources like food, water, and oxygen limits populations.

• Lack of space and shelter can stop a population from growing larger.

• Carrying capacity is the largest population an area can support over time.

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Multiple Choice

What is a limiting factor?

• Anything that stops or slows population growth.

• The largest population an area can support.

• The amount of food and water in an area.

• The number of new animals born each year.

Multiple Choice

What is the relationship between limiting factors and carrying capacity?

• They determine the maximum population size an area can support.

• They only affect populations that are already very large.

• They have no effect on the number of animals in an area.

• They help populations grow much faster.

Multiple Choice

A forest fire destroys most of the plants that a deer population uses for food. What is the most likely long-term effect on the forest's carrying capacity for deer?

• The carrying capacity will decrease because there is less food available.

• The carrying capacity will increase because the deer have more space.

• The carrying capacity will not change, but the deer will stop eating.

• The carrying capacity will only decrease if the water supply is also affected.

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Competition for Resources

• Organisms with similar needs will compete for food, water, and other resources.

• The amount of available resources is what drives this intense competition among organisms.

• This competition for limited resources restricts the growth and reproduction of organisms.

• A scarce resource is the cause that limits population size and growth.

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Multiple Choice

Under which condition do organisms most often compete with one another?

• When they live in different types of habitats.

• When they require the same limited resources to survive.

• When one organism is much larger than the other.

• When they do not interact with each other in any way.

Multiple Choice

What is the primary effect of competition on a population of organisms?

• It causes the organisms to find new types of food.

• It restricts the overall growth of the population.

• It helps all organisms to grow and reproduce faster.

• It has no effect on the population size.

Multiple Choice

If a severe drought occurs in a forest, significantly reducing the available water, what is the most likely impact on the animal populations living there?

• The organisms will learn to live without water.

• Competition for water will increase, limiting population growth.

• The population size will increase due to less competition.

• Organisms will stop competing for food and other resources.

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Common Misconceptions

Misconception	Correction
An ecosystem is just a random group of animals.	An ecosystem includes the community and its interaction with the abiotic environment.
A population can grow forever.	Limiting factors restrict growth and determine an environment's carrying capacity.
Competition only happens between predators and prey.	Competition occurs when any two organisms need the same limited resource.

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Summary

• Ecosystems include interactions between living (biotic) and nonliving (abiotic) things.

• Population size changes with births, deaths, and migration due to resource availability.

• Competition and carrying capacity limit how large a population can grow.

• Analyzing population data helps us understand and predict changes in ecosystems.

Poll

On a scale of 1-4, how confident are you about the concepts covered in today's review?

• 1

• 2

• 3

• 4