AS & A Level Biology - 9700 Paper 5 2019 Summer Zone 2

(a) Some students wanted to determine the reaction time of a sample of people aged from 5–80 years.

The students found three different methods of testing reaction time, as described in Fig. 1.1.



(i) The students decided that Method 2 was the most suitable to use for testing subjects aged from 5–80 years.

Suggest two reasons why Method 2 is the most suitable.
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(ii) State the independent variable and the dependent variable in Method 2.

independent variable ......................................................................................................................................................
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dependent variable .........................................................................................................................................................
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(iii) Describe how the students could investigate the reaction time of a sample of people aged from 5–80 years, using Method 2.

Your description should be set out in a logical order and be detailed enough to let another person follow it.

Details of Method 2, as described on page 2, are not required.

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(b) The students found some results on the internet for a reaction time test, as shown in Fig. 1.2.

The error bars show ± 1 standard deviation (s).



(i) The percentage change in mean reaction time for males between the ages of 5 years and 10 years is 47%.

Calculate the percentage change in mean reaction time for females between the ages of 5 years and 10 years. Show your working and give your answer to the nearest whole number.

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(ii) State two conclusions about the trends shown by the results in Fig. 1.2.

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(iii) State a suitable statistical test that the students could use to find out if the difference in reaction times between males and females of the same age was significant.

Give a reason for your answer.

name of test ...........................................................................................................................................................

reason ..................................................................................................................................................................
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(iv) Suggest a null hypothesis for the test that you have chosen in (iii).

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Sperm production in humans is controlled by the hormones FSH and LH. These hormones are released from the pituitary gland in males to maintain a constant concentration in the blood.

Research has shown that sperm production in humans has decreased during the last 75 years. This research has highlighted concern about the fertility of future generations.

(a) Assessments of fertility are carried out on diluted semen samples. The samples are checked for number of sperm per mm$^3$, motility and abnormal structure.

Fig. 2.1 shows sperm in one part of a haemocytometer grid used for counting sperm. The microscope illumination causes the sperm heads to fluoresce.



Fig. 2.1

The semen sample shown in Fig. 2.1 was diluted by a factor of 100.

(i) Describe a method by which the number of sperm present in this diluted sample could be estimated. ..............................................................................................................................
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(ii) Describe how you could estimate the number of sperm per mm$^3$ in the original, undiluted semen sample. ..............................................................................................................................
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(iii) Suggest why this method of counting sperm may not represent the actual number of sperm in the original, undiluted semen. ..............................................................................................................................
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(b) Hormone imbalances can result in reduced sperm production and immobile sperm, leading to infertility.

A study was carried out on 120 men with different causes of infertility.

All the subjects were non-smokers, did not drink alcohol and did not take any medication for 6 months before the study.

The concentrations of the hormones FSH and LH were measured in each man.

Semen samples were collected and tested within 2 hours of collection. The number of sperm per mm$^3$ were estimated and the motility of the sperm assessed.

(i) Identify two variables that have been standardised in this study.
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Fig. 2.2 shows the concentration of FSH and LH in four test groups. In one test group, the men are fertile and in the other three groups, the men show different types of infertility.



Fig. 2.2

(ii) State the reason for including the hormone concentrations of fertile men in Fig. 2.2. ..............................................................................................................................
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(iii) State one conclusion about the effect of FSH and LH on infertility in men that is consistent with the results of this investigation. ..............................................................................................................................
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(c) Semen samples may also be tested for viability of sperm. Viability is the proportion of live sperm present in semen samples.
Viability of sperm can be tested using a chemical which stains living cells a different colour to dead cells.

Suggest a method, using this stain and a haemocytometer, that could be used to test the viability of sperm in a semen sample. ..............................................................................................................................
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