Edexcel IGCSE Biology E Nutrition Questions

Tobacco mosaic virus infects plant cells.
The photograph shows some of the virus particles.

The photograph shows the leaves of a plant infected by tobacco mosaic virus.

Plants cells infected with the virus stop making chloroplasts.

Explain why plants that are infected with the virus grow more slowly than uninfected plants.

The diagram shows a single-celled organism called Chlorella that lives in fresh water. Chlorella has a chloroplast and can photosynthesise.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Plants to the rescue

Since the early 20th century, the concentration of carbon dioxide in the atmosphere has increased rapidly. This has further increased in recent years due to more cars and the increased demand for electricity for homes and industry.

Scientists have found that plants play a critical part in removing this excess carbon dioxide from the atmosphere. Using computer models, the scientists concluded that photosynthesis has increased by 30 per cent.

The scientists measured carbonyl sulfide found in ice cores and air samples. In addition to carbon dioxide, plants take in carbonyl sulfide gas during their natural carbon cycle, and this is frequently used as a measure of photosynthesis on a global scale. Terrestrial plants are removing about 29 per cent of carbon dioxide emissions that would otherwise contribute to an increase in the atmospheric carbon dioxide concentration.

A carbon sink is an ecosystem, such as a forest, that absorbs more carbon dioxide than it releases. The size of the carbon sink depends on the rate of photosynthesis but also on the levels of deforestation and respiration. The model the scientists used showed that the role of photosynthesis in producing a carbon sink in land plants is larger than estimated in most other models.

Other scientists are less confident about using carbonyl sulfide as a measure of photosynthesis. Plant absorption of carbonyl sulfide can vary depending upon the amount of light the plants receive. Therefore, the measure of global photosynthesis could be overestimated.

Regardless of the rate at which photosynthesis has increased, scientists agree that excess carbon dioxide is boosting the growth of plants. Trees are becoming leafier, and there is more wood. The wood is where most of the carbon is stored in the plant.

In experimental research, scientists exposed plants to double the normal concentration of carbon dioxide found in the atmosphere. Under these increased carbon dioxide conditions, the composition of the leaf tissues changed. This made the leaves tougher for herbivores to eat and made it harder for insect larvae to grow.

Scientists have also observed that when plants are exposed to increasing levels of carbon dioxide, the size of the stomatal pores on a leaf increases.

Explain why increasing carbon dioxide concentration can increase photosynthesis in plants.

The diagram shows a single-celled organism called Chlorella that lives in fresh water. Chlorella has a chloroplast and can photosynthesise.

Complete the balanced chemical symbol equation for photosynthesis.
...... +...... ⟶ ......$+6 \mathrm{O}_{2}$

The diagram shows a section through a leaf with different parts labelled P to U .

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Antitranspirants

Antitranspirants are substances applied to plants to reduce water loss. There are three types of antitranspirant, film-forming compounds, stomatal regulators and reflective compounds.

The first type of antitranspirant contains film-forming compounds. These compounds are oils or waxes that are mixed with water to form an emulsion. This emulsion is then sprayed onto the leaves of plants. The emulsion forms a physical barrier that covers the stomata. The film is designed to prevent water loss but allow gas exchange. Scientists have found that the film-forming antitranspirant is effective in increasing yield and increasing photosynthesis in drought conditions. The increased leaf turgor in plants sprayed with film, compared to control plants, shows that the film decreases water loss and maintains turgor in drought conditions.

Film-forming antitranspirants are used in horticulture to reduce water stress. This can occur during storage, transport and planting of container grown plants. Application of the antitranspirant before transplanting, helps the plant survive until the root system is established. The film-forming compounds are used to reduce drying out in rolled turf and in transporting flowering plants and trees with root balls.

The second type of antitranspirants are stomatal regulators that reduce the size of the stomatal pore. Stomatal pores affect diffusion as well as transpiration. Therefore, photosynthesis and growth may change when stomatal regulators are applied to leaf surfaces. If the stomatal pores close completely this will stop photosynthesis. However, if stomatal openings are only reduced in size, transpiration will be reduced but some photosynthesis will continue.

The third type of antitranspirants are reflective compounds. These work by adding a white coating to leaves. This changes the amount of light that is reflected by the leaf surface. The coating is only applied to the upper surface of leaves so does not block the stomatal pores. Coating a leaf with a reflective chemical can reduce leaf temperature, transpiration rate and also increase the efficiency of water use. Experiments show that transpiration rate can be reduced by up to 30% and leaf temperature reduced from $40^{\circ} \mathrm{C}$ to $30^{\circ} \mathrm{C}$ after a coating of reflective compound is applied to leaf surfaces.

Crops depend on photosynthesis for growth and final yield. Therefore, it is unlikely that currently available antitranspirants would increase the yield of a crop unless the crop suffers from a low water supply or very high rates of evaporation. Spraying film-forming or stomata regulating antitranspirants on a field-grown cereal crop under drought conditions, produced a grain yield increase of 17%. Experiments also show that any effect that antitranspirants have on the minerals supplied to the leaves has little effect on plant growth.

Describe the role of one named mineral ion in plant growth.

Photosynthesis is the process green plants use to convert light energy into chemical energy.

The diagram shows the digestive system of a dog with some structures labelled. The digestive system of the dog is similar to that of a human.

The diagram shows a fetus in the uterus of a woman.

The umbilical cord transports blood from the placenta to the fetus.
This blood contains molecules from the mother that are needed by the developing fetus.

Doctors recommend that pregnant women obtain more of some dietary components than women who are not pregnant.

The table shows the recommended percentage increase of some dietary components in the diet of a woman who is pregnant compared to a woman who is not pregnant.

Explain why a woman who is pregnant requires more of each of the dietary components listed in the table.

A balanced diet should include the correct proportions of each component.

Read the passage below. Use the information in the passage and your own knowledge to answer the questions that follow.

Physic Gardens

The photograph shows a physic garden. Physic gardens are places where people grow many types of plants that produce medicinal drugs.

People have grown medicinal plants in physic gardens for thousands of years. It was estimated in 2016 that out of 30000 plant species that are known to be useful to humans, 17000 of these plant species have medicinal uses.

Medicinal plants produce a wide range of types of drugs including alkaloids, glycosides, terpenes and polyphenols.

Alkaloids are bitter-tasting, alkaline chemicals found in many different plant species. Alkaloids are often toxic in high doses so care needs to be taken when using them. Examples of alkaloids are caffeine and quinine. Caffeine, found in tea and coffee, can stimulate the adrenal glands. Quinine from the bark of the cinchona tree has been used for many centuries to kill the parasite that causes malaria.

An example of a glycoside drug is senna. This drug is extracted from the Senna plant and is used to treat constipation. The drug affects muscles in the intestine.

Terpenes are chemicals that often have strong smells. Terpenes are thought to have evolved to prevent herbivore animals from eating certain plants. An example of a plant that produces terpenes is thyme. The terpenes in thyme have an antiseptic effect which means they can be used to sterilise wounds.

Phytoestrogens are molecules found in plants such as angelica and have been used for many years to treat problems with human fertility. Examples of polyphenols are phytoestrogens, taxol and curcumin. Polyphenols have many roles within plants and many are used as medicines. Taxol is a drug extracted from yew trees and is used to prevent cell division in human body cell tumours.

Curcumin is a drug produced by the turmeric plant. Curcumin can help widen the airways to the lungs so can help people with asthma breathe.

Scientists are looking to reproduce many of these drugs artificially. They are developing genetically modified bacteria containing genes that will allow these drugs to be mass produced in fermenters.

Explain how the drug senna helps to reduce constipation (lines 14 to 15).

Pineapple juice contains a protease called bromelain.
A student uses this method to investigate the digestion of solid gelatine protein by bromelain.
- place solid gelatine protein into a test tube up to a height of 5 cm
- mix $5 \mathrm{~cm}^{3}$ pineapple juice with $1 \mathrm{~cm}^{3}$ of pH 4 buffer
- place $1 \mathrm{~cm}^{3}$ of the pineapple juice and buffer solution on top of the gelatine
- leave for one hour in a water bath set to $37^{\circ} \mathrm{C}$
- measure the height of the solid gelatine and use it to calculate the volume of gelatine that has been digested

Repeat the method three more times.
The diagram shows part of the student's method.

The table shows the student's results for the volumes of gelatine digested at pH 4 .

State what substances are produced when the gelatine protein is digested.

The diagram shows the human alimentary canal.

Which labelled structure produces bile?

The diagram shows the human alimentary canal.

Describe the role of bile in digestion.

The diagram shows the digestive system of a dog with some structures labelled. The digestive system of the dog is similar to that of a human.

Which structure contains villi?

Scientists have genetically modified soya plants so that the soya beans they produce contain less saturated fat.

The scientists produced one transgenic soya plant. Micropropagation was then used to make multiple copies of this transgenic soya plant.