Two Petri dishes
Cress seeds (50 per Petri dish)
Forceps/tweezers with blunt (rounded) ends
Forceps/tweezers with pointed ends
Graph paper
Stopclock
Getting started
Birds have different shaped beaks depending on their diet. Charles Darwin noticed this when he studied Galapagos finches. His observations led him to start thinking about evolution. In this investigation, we will study how the shape of the beak may give an advantage to seed-eating birds. Work in groups of three.
Investigating
1 Place 50 cress seeds into a Petri dish.
2 Time how long it takes for one member of your group to transfer all the seeds from one dish to another using blunt (rounded) forceps/tweezers, as shown in the diagram.
3 Repeat the process, with the other two members of the group taking turns to do the picking, to give a mean time.
4 Repeat steps 2 and 3, but this time using the pointed forceps/tweezers.
5 The same three people need to repeat the test, and again a mean time can be recorded.
Thinking about
Record your results in a copy of the table below.
Name / Student 1------ / Student 2
------ / Student 3
------ / Mean
Time to transfer seeds with blunt forceps (seconds)
Time to transfer seeds with pointed forceps (seconds)
From the average results can you conclude which forceps gave the advantage when picking up the seeds?
Why do you think that these forceps gave an advantage?
Spreading the word
Look at the drawings of the birds.
A Which beak most closely resembles the fine forceps?
B Which beak most closely resembles the blunt forceps?
C Predict which beak will pick up seeds the best, and explain your decision.
D If a bird was adapted to eating seeds, what shaped beak would give an advantage?
E Can you explain how the shape of a bird’s beak may evolve over many years?
F Why did more than one person need to be timed in this experiment?
G What would you do to improve this experiment?
H How could you extend this experiment to look at different foods that birds eat?