The Organism in the environment

Question 1

Population definition

Answer 1

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

Question 2

Community definition

Answer 2

All the populations of organisms that life in an area or ecosystem

Question 3

Habitat definition

Answer 3

The place where an organism lives

Question 4

Ecosystem definition

Answer 4

All the organisms (biotic factors) and physical (abiotic) factors in a fairly self contained area, such as a lake or desert.

Question 5

Investigate the population size of an organism in two different areas using quadrants

Answer 5

• In order to measure population size or abundance of an organism, you need to calculate the number of individuals of that species in a given area.
  
  • It is rarely possible to count all the organisms of a species in an area, so the population size may be estimated.
  • This can be done by counting the number of organisms in a small part of that area and then using that number to calculate the population size in the whole habitat.
  • For organisms that don’t move that much, you can use a quadrat to measure the population size in a given area.
  • A quadrat is a square often made from wire, plastic or wood.
  • The quadrat is placed on the ground and the number of individuals of the species that lie within the quadrat are counted.
  • You need to use a quadrat large enough to contain a fair number of individuals of the species.
  • The quadrats have to be placed randomly and this can be done by throwing it behind your shoulders without looking or using measuring tapes to indicate the axes of a grid over the area.
  • Repeat the experiment so that the results are accurate.
  • The results from the quadrats are then averaged to give an average number per quadrat.
  • This technique is useful for comparing two different habitats with different physical or biological factors.
  • Or you can estimate the percentage cover of each species within a quadrat.

Question 6

Biotic factors

Answer 6

Biotic factors affect both the population sizes of organisms, as well as where they live (their distribution).

Biotic factors include the following:

1. Predation of animals and grazing of plants, by other animals will often act to reduce population sizes. Often we only realise this when the predation or grazing stops, and the animal or plant species that is no longer being eaten greatly increases in numbers. On the other hand, some species only survive in areas here there are few or or no predators.
2. Competition for limited resources, such as food or shelter for animals, or light or water for plants, keeps population in check

Question 7

Abiotic factors

Answer 7

Abiotic factors include the following:

1. Light, which is needed by plants to photosynthesise and grow. This is why plants do not grow in places such as deep caves where there is no light, and may struggle to grow in places with reduced light such as on a forest floor.
2. Temperature affects organisms because extreme temperatures may kill them by stopping their enzymes working effectively. However, some species are especially adapted to live in very cold or very hot places.
3. Water is needed by all living things so a lack of water will limit the population size of organisms, or determine which species can survive.

Question 8

Biodiversity definition

Answer 8

Biodiversity is a measure of the variety of living things in an area.

Question 9

Investigating the distribution and biodiversity of organisms

Answer 9

You can use quadrats also to sample how organisms are spread in an area, their distribution, as well as get a measure of biodiversity. Distribution is often measured is relation to a changing factor. For example, you might want to look at how the distribution of different species of plants changes between a field and the edge of a nearby pond. For this, you use a line transect, which is a line between the two areas often marked by a long measuring tape. Quadrats are placed at regular intervals along the line and the number of each species of plant is counted. The number of quadrats counted will probably be limited by the time available.

The results from the line transect shown in the diagram would probably tell you which plants need to grow in dry soil and which plants grow better in damp or waterlogged soil. You might investigate how shade from a large tree affects the distribution of plants by using a transect from the base of the tree out into full sunshine. You could also measure the effect of waves on the distribution of seaweeds or species of seashells between high tide and low tide marks.

By counting the number of different species in each quadrant along a line transect, you would also have a measure of how biodiversity changes along the transect. Or you could compare the biodiversity of two completely different areas by using results from quadrats to compare the number and types of species between the two places.