Edexcel IGCSE Biology Biology Paper 2 June 2025 question paper 4BI1/2BR

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow. Pollination in fruit trees Plants need to be pollinated to produce fruits and seeds. Some plants are self‑pollinated and others are cross‑pollinated. Self‑pollination is usually the transfer of pollen from flowers on the same tree. In fruit trees, self‑pollination also includes the transfer of pollen from another tree of the same cultivar. A cultivar is a genetically identical group of trees produced by selective breeding. Self‑pollinating plants need bees or other insects to transfer pollen. Examples of self‑pollinated fruit trees are plum, apricot and peach that have sweet‑tasting, soft fruits.

(Source: © freya‑photographer/Shutterstock) (Source: © Leena Robinson/Shutterstock) Other fruit trees require cross‑pollination and can only produce fruit by fertilisation from a different cultivar. Cross‑pollination is the transfer of pollen from one cultivar to the flower of a different cultivar. Self‑incompatibility prevents the same plant or cultivar from fertilising its own flowers. For example, the pollen from one cultivar of an apple tree will not fertilise trees of the same cultivar. Most hard fruit trees such as pear and apple require the presence of two different compatible cultivars for pollination to result in fruit production. Pollen can be transferred by wind, insects or birds. Many fruit trees are pollinated by insects. Nut trees are usually pollinated by wind. After pollination the pollen grain must germinate to lead to fertilisation. The success of pollination and fertilisation depends on favourable environmental conditions. It also requires the right pollen grain reaching the right flower, as pollen can only fertilise specific, compatible flowers. For example, pollen from a peach flower will not pollinate apple flowers.

Cross-pollinating fruit trees should be planted no more than 60 m apart. This will ensure that bees visit the trees often enough to ensure pollination. Nut trees need to be planted no more than 15 m apart. A further complication is that a few apple and pear cultivars, known as triploids, produce sterile pollen. Triploid cultivars have three sets of chromosomes within their cells. A triploid cultivar will require another cultivar for pollination, and the trees must flower at the same time.

Explain the differences between self-pollination and cross‑pollination. (lines 3 to 5 and 9 to 11)

Describe the sequence of events from pollen landing on a flower to fruit production.

Fruit trees often produce sweet-tasting fruit containing sugars.

Sugars are carbohydrates. Name the three elements in carbohydrates.

Suggest how production of sweet-tasting fruit may help spread the seeds of fruit trees. (lines 7 to 8)

Explain how self-incompatibility prevents self-fertilisation. (lines 11 to 13)

Describe how the structure of insect‑pollinated flowers helps to achieve pollination. (line 16)

Give a reason why nut trees need to be planted closer together than fruit trees. (lines 23 to 25)

Explain why triploid cultivars produce sterile pollen. (lines 26 to 29)

The diagram shows a section through an eye with some parts labelled.

Name parts W, X and Y.

Describe how structure Z changes when a person moves into a dark room.

A student uses this apparatus to investigate water loss from a plant.

This is the student’s method. step 1 measure the total mass of the flask, water, oil, cotton wool and plant step 2 leave the apparatus for 48 hours step 3 measure the new total mass of the flask, water, oil, cotton wool and plant step 4 calculate the rate of change of mass during the 48 hours Repeat steps 1–4 with the same conditions.

Name the piece of apparatus used in this investigation.

The total mass changes from 207.25 g to 204.50 g in the first 48 hours. Calculate, in grams per hour, the rate of change of mass. Give your answer to two significant figures.

rate of change of mass =_........ grams per hour

Explain why the student repeats the investigation with the same conditions.

The student then changes the conditions surrounding the plant.

Describe how the student could investigate the effect that moving air has on the change in mass.

Explain the effect that faster moving air has on the change in mass.

Describe how the student could modify the investigation to study the role of roots in the loss of water from a plant.

A group of students investigate the biodiversity in two fields, A and B. Field A is grazed by cattle and field B has no cattle.

Explain what is meant by the term biodiversity.

The students investigate the plant species in each field. They counted the number of each species in five 0.5 m × 0.5 m quadrats. They repeated this for each field. Table 1 shows their results.

Describe how the quadrats should be placed to obtain unbiased species numbers for each field.

For the most frequently occurring plant species in field B, calculate the number of plants in one square metre.

number of plants =_........

Name the species with the greatest variation in number of plants recorded in quadrats for field B.

Table 1 is repeated here.

The students conclude that grazing affects the species in field A. Using information in Table 1 and your own knowledge, discuss the students’ conclusion.

Scientists collect data to measure how successful cloning is in cattle. Table 1 shows the scientists’ data.

Calculate the percentage of embryos transferred that result in live calves being born.

Describe the stages in the production of a cloned mammal from an adult mammal.

There is some evidence that cloned cattle may have weakened immune systems. Explain why a weakened immune system can affect the health of cloned cattle.

Scientists also collected data comparing cloned cattle and a control group. Table 2 shows their results.

Comment on the effects of cloning on the growth and development of these cattle.

The diagram shows a nephron from a human kidney with some structures labelled.

Which of these is structure U?

Which process occurs between structure S and structure T?

Which structure is the collecting duct?

The table shows the concentrations of protein and glucose in blood plasma, in glomerular filtrate and in urine.

Calculate the mass of glucose in 5 dm³ of blood plasma.

[1000 cm³ = 1 dm³]

Explain why there is no protein in the urine.

Explain why there is glucose in the glomerular filtrate but no glucose in the urine.