• 
  The distribution of an organism is affected by a number of physical factors.
• Sampling is carried out to get an idea of an organism’s distribution.
• The more samples taken, the more valid and reproducible the results.
• Quadrats are used to count the number of organisms within a square.
• Transects are used to count the number of organisms along a specific line.
• Data is analysed by calculating the mean, median and mode.
• The mean is the average of the results.
• The median is the middle value.
• The mode is the result which appears the most.

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TEST IT!

1. A group of scientists investigate how three species of plant were distributed along a certain section of a country road and took measurements every metre.

a) What apparatus did they use?

b) How did they use it?

2. For an investigation into the number of daises in a field, a class of students was asked to use a 1m² quadrat. The dimensions of the field were 4800m².

a) What would be the best way to use the quadrats?

i. Place them all where there are a lot of plants growing.

ii. Place all the quadrats in two random places.

iii. Place all the quadrats where there are at least four different species of plant.

b) The results of one student were as follows:

Calculate the:

1. mean
2. median
3. mode

3. A biologist wanted to see how a river affected the dandelion population close to it. She took a sample every metre, moving further away from the water. The table below shows her results.

a) Which of the following factors is the one most to have had an effect on the dandelion distribution?

i. the amount of light

ii. the temperature of the air

iii. the amount of moisture in the soil

b) Which result was probably taken down incorrectly?

c) What would have made the results better?

i. only using the first four measurements

ii. not using the first four measurements

iii. only taking measurements where they were a lot of dandelions

iv. also taking measurements from the other side of the river

ANSWERS

a) A transect.

b) They placed the transect along the road then counted the number of species alongside it. Then they moved the transect a metre away from the road and counted the species along this stretch. They then repeated this process as many times as necessary and recorded their results.

a) ii. Place all the quadrats in two random places.

b)

i. mean = (8 + 9 + 10 + 8 + 6 + 10 + 11 +9 + 10 + 7) 10 = 82 10 = 8.2

ii. median = 6 7 8 8 9 9 10 10 10 11 = 9

iii. mode = 6 7 8 8 9 9 10 10 10 11 = 10

a) iii. the amount of moisture in the soil

b) 6 metres

c) iv. also taking measurements from the other side of the river