Teacher's notes and answers to questions in the book - Hodder Plus ...

WJEC GCSE Additional Science Teacher’s Notes
The sampled area represents 1000/1 000 000 (1/1000) of the whole beach. Therefore, the
number of cockles on the whole beach will be 293 x 1000 = 293 000
5. Look at the environments in Figure 7.5. Suggest a reason why scientists would need to use a bigger
sample area in woodland than in the saltmarsh.
The saltmarsh is a much more homogenous habitat. A sample taken from anywhere is likely to
be similar to any other area. In the woodland there is much more diversity within the habitat
and samples from (e.g.) open areas may be significantly different from those in the midst of
tree cover.
PRACTICAL Counting daisies (page 68)
Suggest any possible disadvantages of the method used to place the quadrat randomly.
It is not really random. It is perfectly possible to look behind you and there is a choice of place
to stand. A better method would be to divide the area into a marked grid of squares, with each
square the size of the quadrat used. Allocate each square a number and use a random number
generator to decide which squares to sample. Throwing over the shoulder is less scientifically
random but much quicker and easier to do.
_How can we find out about the distribution of_______
organisms (pages 68–70)
PRACTICAL What effect does trampling have on plants
(page 70)
For Questions 1, 2 and 4 the answers will depend upon results obtained.
For Question 3 the answer will depend upon the site chosen, but light intensity is a likely factor.
_How can we measure an animal population that moves
around (pages 71–72)
Question
6. Dave wanted to estimate the population of woodlice in his garden. He searched around and collected
100 woodlice. He marked each of them with a spot of white paint on its back, and released them (see
Figure 7.10). A week later he went into his garden and collected another 100 woodlice. Four of those
were marked ones that he had captured before. Using the equation given earlier in this section,
calculate the size of the woodlouse population in Dave’s garden.
100 100
10000
N 2500 woodlice
4 4
Discussion point
How good do you think Dave’s experimental method was Could he have improved it in any way
White paint is quite bright and could make the marked woodlice more noticeable to predators,
and more likely to be found when he took his second sample. A darker colour would have been
better.
20