Grade 7 Science Practice Test: Symbiosis, Competition and Predation

Both organisms benefit: the clownfish gets protection and the anemone gets a defender. In commensalism only one partner benefits.

In commensalism one organism benefits, here the bird with a place to nest, and the other is not affected.

The tick benefits and the dog is harmed but not killed. That is parasitism. A predator usually kills its prey.

When organisms need the same limited resource, they compete. Each bird species gets fewer seeds because of the other.

With fewer hares, many lynx cannot find enough food, so fewer survive and raise young. Predator numbers usually fall a little after prey numbers fall.

Without predators, more deer survive and the population grows. Large herds eat young trees and shrubs faster than they can grow back.

A limiting factor is a resource or condition that keeps a population from growing larger. In a desert, water is scarce, so it limits plant growth.

Carrying capacity is set by resources such as food, water and space. A population may rise above it for a while, but then it usually falls back.

In predation one animal, the predator, kills and eats another, the prey. The tapeworm is a parasite, and the bee and flower help each other.

Members of the same species need the same resources. In a crowded pot there is not enough light, water and nutrients for all of them.