Required Practicals (Paper 2)

Question 1

Describe a method to investigate the effect of light on the growth of seedlings

Answer 1

1. Set up three petri dishes
2. Place cotton wool in each petri dish
3. Soak the cotton wool in an equal volume of water
4. place 10 mustard seedlings in the petri dish
5. Place in a warm location to allow germination
6. Equalise the number of seedlings
7. Place petri dishes in three different locations: total darkness (dark cupboard), partial sunlight (room), total sunlight (windowsill)
8. Leave for 5 days
9. Measure the height of the seedlings every day
10. Water and equalise daily
11. Measure the length of the shoots and record the direction they grow in using labelled scientific drawing
12. CVs - type of seed, volume of water added, temperature, number of seeds
13. Repeat experiment and caluclate mean

if it says newly germinated seedlings, simply place the germinated seedlings in the petri dish

Question 2

How could the student use the maize seedlings to investigate the effect the growth response to one-sided lighting and give sample results

Answer 2

• use scissors to cut tips from some shoots and cut a hole in the box
• use forceps to handle seedling
• use ruler to measure lengths of shoots at start
• control temperature and same volume of water added to maize seedlings
• set up experiment in a dark cupboard
• use lamp and box to give one sided lighting
• leave for a few days and observe results
• repeat 3 times
• do control in total darkness without any light
• sample results: tip exposed to 1-sided light - bend to light, tip removed - vertical, control - vertical

Question 3

Why is the height of leaves the same for total and partial light exposure?

Answer 3

chlorophyll is very efficient at transporting light energy

Question 4

Describe a method to determine the population size of a species

Answer 4

• Lay two tape measures in sample area at right angles to create a grid
• Use a random number generator to generate coordinates.
• At the coordinates lay the quadrat down and count the number of individual plants of various species in the quadrat
• Repeat this process a 10 times in different areas of the sample area and calculate a mean result
• Multiply area per m² by sample area (x by 100) to find population size

The question could ask you about population change in which you would place down one quadrant of 1m², count the number of one species, calculate the whole area using tape measures and multiply the species by area

Question 5

Why may someone use more quadrants to determine a population size a species?

Answer 5

the original experiment may have not been representative

Question 6

How could students investigate the abundance of a species by measuring percentage cover?

Answer 6

Use (additional) tape measures to create a grid

Use random coordinates to establish where to place a quadrat

Estimate the % cover of each of the species if present in quadrat

Repeat process several times

Calculate mean % cover by the species

Question 7

What are some control variables for the seed experiment?

Answer 7

• keep temperature the same
• use equal numbers of seedlings in each dish
• give all dishes the same volume of water
• use seedlings of same species

Question 8

How would you measure the length of an elongated seedling?

Answer 8

Straighten seedling and measure with ruler

may use piece of thread/string and measure length of the thread/string

Question 9

What is a standard improvement to the quadrate experiment?

Answer 9

use more quadrats

as original results may have not been representative

Question 10

What is another reason why the quadrat results not be accurate other than not being representative?

Answer 10

to few quadrats used

allow sample size too small