B2.4 Organisms and their

environment

B2.4 Organisms and their environment

Living organisms form communities, and we need to

understand the relationships within and between these

communities. These relationships are affected by external

influences.

Candidates should use their skills, knowledge and

understanding to:

■ suggest reasons for the distribution of living

organisms in a particular habitat

■ evaluate methods used to collect environmental

data, and consider the validity of the method and the

reproducibility of the data as evidence for

environmental change.

Key terms

Habitat

Temperature

Nutrients

Quantitative

Random sampling

Quadrats

Transect

B2.4.1 Distribution of organisms

a) Physical factors that may affect organisms are:

■ temperature

■ availability of nutrients

■ amount of light

■ availability of water

■ availability of oxygen and carbon dioxide.

These factors will affect where and how many

organisms will grow

How many daisies?

We can study the distribution of an organism using a quadrat or a

transect.

b) Quantitative data on the distribution of organisms can be obtained

by:

■ random sampling with

quadrats

■ sampling along a transect.

22/ 10

2.2

2.8 x 5400

15120

area of strips / length of transects /

number of transects

(ii) numbers of larders observed likely to be lower than

actual

do not accept squirrels share larders or squirrels have

more than one larder

since unlikely that all could be spotted if 5 m away or

old larders or

squirrels moved on / died

since squirrels are mobile and could be

missed / counted twice

(no)

the bars show the range of the number of

squirrel larders in the different types of

woodland

although spruce woodlands have the larger

ranges, some spruce woodlands will have

very low numbers of larders

competition for light because potamogeton plants taller

competition for nutrients taller plants may have longer

roots

descriptions of:

measuring tape or similar quadrat

method of estimating cover (inside quadrat)