9 1 the organism in the environment

A population is a group of organisms of the same species living in the same place at the same time.

A community includes all of the populations living in the same area at the same time.

An ecosystem is all of the organisms that live in an area, and their interactions with the living (biotic) and non-living (abiotic) factors in their environment.

False. Living organisms interact with both the living components (each other) and the non-living components (e.g. the temperature and rainfall) of their environment.

Abiotic factors are the non-living factors that influence ecosystems, e.g. temperature, sunlight, pH, salinity, precipitation.

Examples of abiotic factors include:

A decrease in water availability might affect a population of living organisms as follows:

Biotic factors are the living factors that affect organisms in an ecosystem, such as competition, predation and disease.

Biotic factors that could affect populations include:

False. A decrease in the size of a prey population will most likely result in a decrease in the size of a predator population. This is because there will not be enough food so predators will die, or leave.

Competition occurs when organisms fight for the same resources, e.g. food or mates

True. Competition is likely to reduce the size of a competing population. In extreme cases a less well-adapted population may die out.

Interdependence refers to the fact that organisms living in the same habitat depend on each other. A change in one species will affect other species.

Parasitism is a relationship between living organisms in which a parasite benefits from living in or on the body of a host species, while causing the host harm.

Mutualism is a relationship between living organisms in which both members of the relationship benefit in some way.

Biodiversity is the variety of living organisms found in a habitat. This includes, e.g. the number of different species, the size of each population and the differences between individuals of a species.

Sampling is used when determining the number of organisms in an area because it is easier than attempting to count all individuals. Sampling provides a representative sample from which a population size estimate can be calculated.

A quadrat is a square frame that is placed on the ground to study the organisms within.

The abundance of a species can be measured within a quadrat as follows:

Placing quadrats randomly avoids bias in an investigation, e.g. a student might choose to place all of their quadrats on bare ground because it would make counting easier, resulting in a biased sample.

True. Carrying out more quadrats will increase the sample size, meaning that the results are more likely to be a good representation of the area sampled.

An estimated population size can be calculated from quadrat data using the formula: population size = (total area ÷ area sampled) x total no. individuals counted

A belt transect is a line placed across a habitat, along which quadrat samples are taken, either continuously or at regular intervals.

A belt transect is used to investigate how the distribution of species in a habitat is affected by a particular abiotic factor, e.g. distance from a path or water source.