Edexcel IGCSE Biology G Gas Exchange Questions

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.

Some people have a condition called asthma. This condition causes the person's airways to become narrow.

Explain why consuming curcumin can improve the concentration of oxygen in the blood of people who have asthma (lines 25 to 26).

The diagram shows parts of the human respiratory system with some structures labelled.

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

The photograph shows water lilies, plants that float on the surface of ponds.

Suggest why the leaves of the water lily only have stomata on their upper surface.

The diagram shows parts of the human respiratory system with some structures labelled.

A scientist compared the rate at which oxygen is used during exercise by a person who is a non-smoker with a person who is a smoker.

The rate is measured in $\mathrm{cm}^{3}$ per minute for each kilogram of body mass.
The table shows the scientist's results.

Calculate the volume of oxygen used in 30 minutes by a non-smoker with a mass of 70 kg .

volume =…… $\mathrm{cm}^{3}$

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.

Explain why reflective compounds should only be applied to the upper surface of a leaf (Lines 27 and 28).

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

The graph shows the effect of light intensity on gas exchange by Chlorella.
oxygen released by Chlorella
oxygen taken in by Chlorella

Explain why Chlorella takes in oxygen at light intensities below 10 arbitrary units.

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.

Light affects gas exchange in leaves. (Lines 19 and 20)

Describe an experiment that shows how the net gas exchange from a leaf varies with light intensity.

The diagram shows parts of the human respiratory system with some structures labelled.

Which of these is the structure labelled X ?

The diagram shows parts of the human respiratory system with some structures labelled.

Explain how contraction of the diaphragm causes air to move into the lungs.

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

Badgers and bovine tuberculosis

The bacterium Mycobacterium bovis causes the lung disease bovine tuberculosis (TB) in cattle. Infected cattle have damaged lungs, which causes gas exchange problems and makes them cough into the air. The pathogen spreads to humans if they inhale air containing the bacterium. Humans also become infected if they drink unpasteurised milk from infected cattle. Milk is usually pasteurised by heating it for a period of time at a high temperature.

Bovine TB can kill humans. In one year, 13400 people died from a total of 149000 reported cases of TB. Some of these cases were from Europe, where 103 people died from 1290 reported cases. The rest of the cases were from outside Europe.

Some farmers in the United Kingdom are concerned that badgers spread the TB pathogen to cattle.

The photograph shows a badger.

Badgers act as a reservoir for the TB pathogen and can live for several years without showing any signs of TB. Some farmers want badgers to be culled (killed) to stop the spread of bovine TB to cattle.

However, some scientists claim that only a fraction of cattle catch TB from badgers, and that culling badgers could spread the disease to new areas. This is because badger culling changes the behaviour of the badgers that survive. Normally, badgers live in social groups and will defend their territory from other badgers by being aggressive. This territorial behaviour reduces the spread of disease between groups. If badgers are culled, then their territories cannot be defended. Surviving badgers could move in to occupy the undefended territory, bringing TB with them. This could spread TB to new animals and new areas.

Some people believe that badgers should be vaccinated to stop the spread of TB. However, there is some concern that vaccination may increase the spread of TB because it might also change badger behaviour.

An investigation is needed to find out if badger vaccination can reduce TB both in badgers and in cattle.

Explain why cattle with damaged lungs have gas exchange problems (lines 2 to 3).

The diagram shows parts of the human respiratory system with some structures labelled.

A scientist compared the rate at which oxygen is used during exercise by a person who is a non-smoker with a person who is a smoker.

The rate is measured in $\mathrm{cm}^{3}$ per minute for each kilogram of body mass.
The table shows the scientist's results.

Explain the effect of cigarette smoking on the rate at which oxygen is used.

A scientist investigates the effect of exercise on breathing rate.
She measures the breathing rate in breaths per minute of two people, P and Q , every 5 minutes for 30 minutes.

This is her method.
- measure their breathing rate every 5 minutes while they exercise for 20 minutes
- measure their breathing rate every 5 minutes for a further 10 minutes while they recover from the exercise

The table shows her results.