Organisms in the environment

population

population

a group of individuals of the same species living in the same place at a certain time.

community

all the different species in a habitat

habitat

the place where an organism lives

ecosystem

the whole integrated mixture of biotic and abiotic components living in a particular habitat.

biotic factors

living components of an ecosystem

eg. producers or consumers

abiotic factors

• non-living components of an ecosystem

• the physical and chemical components that contribute to the growth of living organisms in their habitat.

eg. temperature

explain how quadrats are used to estimate population size

1. place a quadrat on the ground at a random point within the first sample area.

2. count the organisminside the quadrat.

3. repeat - putting the quadrat in different areas

4. calculate the mean number of organisms per quadrat within the first sample area.

5. repeat experiment in second sample area.

6. compare the two means.

how to calculate the mean number of organisms in a sample area

mean =

total no. of organisms/no. of quadrats

biodiversity

• describes the range and variety of living organisms within an ecosystem.

• the distribution of each species within an area.

• population size within an area.

abiotic factor - temperature

• extreme heat

• plants adapted to reduce water loss (transpiration)

• animals seek shade

abiotic factor - light

• bright sunlight/deep shade

• different species of plant sound in sunny/shady parts of woodland

abiotic factor - pH

• lakes with low pH often lack fish populations.

• plants tolerate varying levels of acidity/alkalinity in the soil

abiotic factor - water

• rainfall, moisture in soil, humidity

• water needed for all ecosystems: varies from swamps to deserts.

abiotic factors - mineral ions

• eutrophication (high levels of nutrients) to low levels

• pollution of water sources from sewage.

abiotic factors - salinity (saltiness)

• seawater or fresh water rivers (non-salty!)

• marine life can’t live in freshwater (and vice versa)

abiotic factors - gases (oxygen and carbon dioxide)

• normal levels (aerobic) to low levels.

• low levels of oxygen in polluted rivers - organisms adapt to survive here.

abiotic factor - sandy

• sandy (large particles) to clay (small particles)

• sandy soil loose, doesn’t hold water and low in nutrients.

• clay soil firm but may become waterlogged.

biotic factors - food availability

eg. more berries = blackbird population increases (because there’s enough food for all of them to survive and reproduce)

biotic factors - number of predators

number of predators decreases, number of prey increases (because not as many prey are being eaten.)

biotic factors - competition

organisms compete with other species (and their own) for the same resources