Biology 5090/62 — May/June 2021

Cambridge O-Level · Alternative to Practical · worked solutions for every part, with the mark scheme

questions

marks

minutes

Topics Observations and Measurements · Experimental Contexts · Analysis, Conclusions and Evaluation · Planning Experiments and Investigations · Microscopy and Biological Drawing

Q127MObservations and MeasurementsExperimental ContextsAnalysis, Conclusions and EvaluationPlanning Experiments and InvestigationsFree sample

Some students investigated the growth of some seedlings.

Fig. 1.1

They had three dishes of seedlings, A, B and C, that had been growing in the same conditions for different amounts of time.

(a)

They selected three seedlings from each dish and measured their heights to the nearest millimetre. The results for dishes A and C are shown in the table.

dish	height of seedling 1 / $\text{mm}$	height of seedling 2 / $\text{mm}$	height of seedling 3 / $\text{mm}$
A	21	23	25
B
C	2	4	3

(i)

Three seedlings from dish B are shown below. Measure them and record their heights to the nearest millimetre in the table.

Fig. 1.2

(ii)

Calculate the mean height of the three seedlings from each dish to the nearest millimetre and complete the table.

(iii)

Use the data to suggest which seedlings had been growing for the longest period of time and give a reason for your answer.

______

(iv)

Suggest two reasons why a number of seeds, rather than just one seed, were placed in each Petri dish at the beginning of the investigation.

______
______

(v)

The students selected three seedlings from each dish to measure. Suggest a method the students could have used for choosing the three seedlings and state an advantage of this method.

method = ______
advantage = ______

(b)

In another investigation, some students calculated the mean heights of some seedlings as they grew. They recorded their results.

Grown for 6 days mean height $8\,\text{mm}$ .

Grown for 10 days mean height $23\,\text{mm}$ .

Grown for 12 days mean height $27\,\text{mm}$ .

Grown for 15 days mean height $32\,\text{mm}$ .

Grown for 20 days mean height $36\,\text{mm}$ .

Grown for 23 days mean height $37\,\text{mm}$ .

(i)

On the grid construct a line graph to show the relationship between time and mean height for these seedlings. Join your points with ruled lines.

Fig. 1.3

(ii)

Use the graph to describe the growth of these seedlings.

______

(iii)

Use the graph to state the time period during which the rate of growth of the seedlings was greatest.

______

(iv)

Use the data and your graph to calculate the rate of growth of the seedlings for the five days from day 15 to day 20.

rate = ______

(v)

State two variables that need to be controlled whilst growing these seedlings and explain why they need to be controlled.

variable 1 ______
variable 2 ______
explanation ______

(c)

The seeds needed water to germinate and for the seedlings to grow.

Design an investigation to determine the effect of the pH of water on the growth (mean height) of seedlings. You should use seedlings grown in Petri dishes in a laboratory.

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Q2Experimental Contexts · Microscopy and Biological Drawing · Observations and Measurements · Analysis, Conclusions and Evaluation13M

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