Practice Paper 2 (Edexcel IGCSE Biology)

Separate: Biology Only

Decomposer bacteria are involved in the nitrogen cycle.

The bacteria release an enzyme called urease.

The diagram shows part of one strand of DNA used to make urease.

Complete the diagram by giving the missing bases on the other strand of DNA.

Separate: Biology Only

Urease acts on urine to produce ammonia.

The graph shows how pH affects the activity of urease.

(i) Which of these is the optimum pH for urease?

(ii) Explain the activity of urease at pH 8.5.

Separate: Biology Only

Describe the role of the other bacteria involved in the nitrogen cycle.

The plants in a woodland are eaten by mice and caterpillars.

The mice also eat the caterpillars.

The mice are eaten by birds called owls.

Draw a food web showing these feeding relationships.

Give the term that describes the trophic level of a caterpillar.

The woodland covered a total area of 5 km².

A scientist investigates the number of mice and owls in the woodland.

He counts the number of mice and owls on the same summer day each year for five years.

The table shows the scientist’s results.

(i) Calculate the number of mice in the total area of woodland in year 3.

(ii) Suggest why there were more mice in year 4 than in the other years.

(iii) Suggest why the number of owls was fairly constant each year.

(iv) Suggest a method you would use to estimate the number of mice in the woodland.

Farmers may add chemical fertilisers to their soil.

Explain how chemical fertilisers can increase crop yield.

These fertilisers may leak into rivers.

A scientist measures the oxygen content of water in two different locations of the same river during the month of April.

In location A he finds that the mean dissolved oxygen was 6 mg per litre and at location B he finds that the mean dissolved oxygen was 3 mg per litre.

He concludes that the use of fertiliser in the field has affected the oxygen content of the river.

Discuss his conclusion.

Some farmers use alternative substances to chemical fertilisers.

Suggest one alternative substance that a farmer may use.

A scientist uses this method to investigate the effect of water quality on the growth of fish.

• fill a pond with filtered water
• fill another pond with unfiltered water
• place the same mass of fish of the same species in each pond
• determine the increase in total mass of fish in each pond after 180 days

The graph shows the scientist’s results.

The mean rate of increase in total mass of the fish in the filtered water is 0.214kg per day.

Calculate the difference between the mean rate of increase in the total mass of the fish in filtered and unfiltered water.

Unfiltered water contains more bacteria.

Explain why unfiltered water containing more bacteria affects the growth of fish.

Give one biotic variable the scientist controlled in the investigation.

Give a method the scientist could use to control interspecific predation in the ponds.

The chromosomes found in human cells can be photographed and arranged in order to produce a karyotype.

The karyotype shown in Diagram 1 is from a normal human body cell.

Diagram 1

(i) Explain how you can identify the sex of the person from the karyotype shown in Diagram 1.

(ii) Cells can be described using the terms diploid or haploid.

Explain the difference between these two terms using the information in Diagram 1.

The karyotype shown in Diagram 2 is from a body cell of a person with a condition called Klinefelter syndrome.

This condition only affects males.

Diagram 2

(i) Describe the differences between the karyotype in Diagram 1 and the karyotype in Diagram 2.

(ii) Suggest how the karyotype in Diagram 2 may have been caused.

(iii) The frequency of Klinefelter syndrome in the United Kingdom is 1 in every 660 males.

The population of the United Kingdom is 66 million, of which 49% are male.

Calculate the total number of males in the United Kingdom with Klinefelter syndrome.

(iv) Suggest why females who are aged over 35 are more likely to give birth to a baby with the Klinefelter karyotype.

Scientists investigate the effect of salt (NaCl) concentration on the germination of maize seeds.

Batches of seeds are watered with different concentrations of salt solution.

They count the number of seeds that germinate in each batch 12 days after sowing. They then determined the percentage germination.

(i) Describe how the scientists could tell if a maize seed had germinated.

(ii) The scientists measured the germination after 12 days.

State two other abiotic variables that the scientists need to control in their investigation.

The table shows the scientists’ results.

(i) Plot a line graph to show the effect of the concentration of the salt solution on germination.

Use a ruler to join your points with straight lines.

(ii) Explain the effect of increasing the concentration of the salt solution on germination.

As plants grow, they produce roots and stems.

(i) Explain the responses of roots and stems to gravity.

(ii) Explain the responses of roots and stems to light.

The diagram shows three types of neurone.

(i) Give the names of these neurones.

(ii) Explain the role of these neurones in the withdrawal reflex of a finger from a hot object.

A teacher uses this method to estimate the speed of a nerve impulse.

• Students stand in a circle and hold hands
• Student A in the circle starts a timer and at the same time squeezes the hand of student B on his left
• When student B feels his hand being squeezed, he immediately squeezes the hand of the student on his left
• This process continues around the circle of students until student A feels his hand being squeezed and he stops the timer

(i) Explain what other measurements the teacher would need to make in order to calculate the speed of a nerve impulse.

(ii) Describe whether the teacher’s method is likely to give an accurate estimate of the speed of a nerve impulse.

The diagram shows some human excretory organs.

Name organ X and organ Z shown in the diagram.

One waste product that is excreted from the human body is urea.

Urea is made from excess proteins that can't be stored in the body.

Excess carbohydrates and lipids do not need to be excreted,

Suggest why excess carbohydrates and lipids do not need to be excreted.

Carbon dioxide is one of the substances that is excreted by the body.

Explain the importance of excreting carbon dioxide.

Another organ of excretion is the skin.

Explain how the skin is able to carry out excretion.