Populations & CommunitiesObj: 11B

Investigate and analyze how organisms, populations, and

communities respond to external factors.

What is an organism?

• An individual living thing, such as a bacterium, protist, fungi, plant, or animal.

What is a population?

• A group of one species of organisms that live together in a certain area.

Examples:• Humans living in the city of Houston• Tree frogs living in a forest

What is a community?• A group of populations of different

species that interact with one another.

Example:• Populations of tree frogs, snakes, birds,

as well as other animals and plants all living together on a tropical island

What is an ecosystem?

• Communities in the environment• Includes abiotic (non-living) and

biotic (living) factors.

Example: the tropical island

• When a rabbit senses that a predator is near…

How do organisms respond to external factors?

It runs away or hides in a burrow

• When a skunk feels threatened…

It sprays its attacker with a foul-smelling liquid

• When an opossum is attacked…

It curls into a ball, and pretends to be dead.

• Plants that grow as vines, such as pumpkin and ivy, produce tendrils that can wrap around surfaces

• Roots of plants tend to grow toward wet soil, while the leaves grow toward light

• Predator & prey relationships• Competition among predators• Invasive species outcompete

natives• Disease

How do populations respond to external factors?

Predation

Competition

Invasive species• Asian carp were

introduced to Michigan lakes to control algae.

• Now introduced species outcompeting native fish for food.

Pythons in the Everglades in Florida

Disease

How do communities respond to external factors?

What happens to the snake population when the toad population dies out due to disease?

Volcano Explosion

Oil Spills

The Role Microorganisms

11C: Summarize the role of microorganisms in both maintaining

and disrupting the health of both organisms and ecosystems.

What is a microorganism?

• Any organism that cannot be seen without the aid of a magnifying glass or microscope

• Examples – bacteria, protists, fungi• Found in almost every habitat on Earth

How can microorganisms maintain the health of other organisms?

Mutualistic Relationships• Microorganism gains benefits such as

a warm environment to inhabit and gain nutrients

• Animal or plant may gain benefits such as protection from other microorganisms or a supply of enzymes they need but cannot produce

• Example – bacteria living in guts of termites & cows to produce enzymes to digest cellulose

• Example - Fungi & plants form relationship called mycorrhizae.

• The Fungi collect water & minerals and deliver them to plant roots

• The Plants provide the fungi with nutrients made through photosynthesis.

• Example – Plants called legumes contain bacteria of the genus Rhizobium in structures on their roots called nodes.

• The Rhizobium fixes atmospheric nitrogen so that is is available for plants to use.

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How can microorganisms disrupt the health of organisms?

Parasitic Relationships• Some microorganisms causes diseases

in a host. These microorganisms are called pathogens.

• Pathogens cause a disease by killing the host cells, releasing toxins, or interfering with the processes within the host’s body.

Lyme Disease

• Caused by at least three species of bacteria belonging to the genus Borrelia.

Tetanus

• Caused by the bacteria Clostridium tetani.

Strep Throat

• Caused by the bacteria Streptococcus pyogenes.

How do microorganisms maintain the health of ecosystems?

Mutualistic Relationships

• Microorganisms recycle nutrients. Decomposers break down organic matter of dead plants & animals.

• Some bacteria living on the ocean floor feed on oil that seeps from the ground.

How do microorganisms disrupt the health of ecosystems?

• Pathogens (microorganisms that cause disease) can kill off large numbers of a plant or animal species that is important to the health of the ecosystem.

Example

• In oak forests, many animals depend on the acorns that fall each autumn for food.

• What would happen if a pathogen infected the oak trees and prevented them from producing acorns?

Oak Wilt

Caused by the fungus Ceratocystis fagacearum.

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• Algal blooms in aquatic ecosystems such as oceans can block sunlight and cause death of plants along with organisms that eat the plants.

• Bacteria populations rise because of an increase in food supply of dead organic matter.

• Oxygen levels drop because of the bacteria population increase. Fish and other organisms then die. These areas are called dead zones.