Enzymes

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)

Cow’s milk contains a mixture of nutrients, including protein, fat, sugar, vitamins, and minerals.

The main sugar in milk is a carbohydrate called lactose.

Which chemical elements are present in carbohydrates?

Describe how to test a sample of milk for protein.

Some people drink a milk alternative produced from plants, such as soy and rice, instead of milk produced by animals.

The table shows nutritional information for different milk products.

The recommended daily amount of calcium for a child is 1400 mg.

Calculate the mass of cow’s milk that would contain 1400 mg of calcium.

Discuss whether soy milk or rice milk is a suitable replacement for cow’s milk in the diet of children.

Which structure is the nucleus?

Which structure is not found in human white blood cells?

Which molecule is the storage carbohydrate in the root cell?

The actual width of the cell from P to Q is 125 μ m.

Determine the magnification of the diagram.

[1 mm = 1000 μ m]

The diagram shows a pea flower with structures labelled X and Y.

Give the names of structures X and Y.

Explain how two structures, present in the diagram, show how the flower is pollinated.

A scientist uses this method to compare the carbohydrates present in ungerminated and germinating pea seeds.

• carry out an iodine test and a Benedict’s test on ungerminated seeds

• soak another set of seeds in water and allow them to germinate in unsealed jars

• after three days, carry out an iodine test and a Benedict’s test on the germinating seeds

The table shows the scientist’s results.

State which carbohydrates the scientist identified in the ungerminated seeds and the germinating seeds.

ungerminated seeds

germinating seeds

Explain the difference in the carbohydrate composition of the ungerminated seeds and the germinating seeds.

Explain why the jars used in the investigation are not sealed.

Plant and animal cells have some features in common and some differences.

Which of these structures is not found in animal cells?

Which of these substances is a carbohydrate stored in plant cells?

The diagram shows a leaf palisade mesophyll cell.

Describe the function of the parts labelled A, B, C and D.

Explain two ways that the structure of this palisade mesophyll cell is adapted for its function.