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Q pack 4
Terms in this set (18)
Describe the relationship between size and surface area to volume ratio of organisms (1 mark)
As size increases, the surface area to volume ratio decreases
The scientists calculated the ratio of surface area to mass for eggs, tadpoles, and frogs. He also determined the mean rate of oxygen uptake by tadpoles and frogs.
The scientists used units of umol g^-1 h^-1 for the rate of oxygen uptake.
Suggest why he used umol in these units
The mass of oxygen is very small so umol is the appropriate units to use. Also, it is the standard for measuring oxygen uptake.
The scientist decided to use ratio of surface area to mass, rather than the ratio of surface area to volume. He made this decision for practical reasons.
Suggest one practical advantage of measuring the masses of frog eggs, tadpoles and adults, compared with measuring their volumes.
It is easier to measure the mass of living organisms rather than volume as their shapes are not perfect (e.g. not spheres/cubes).
The figure below represents a capillary surrounded by tissue fluid. The values of the hydrostatic pressure are shown.
Use the information in the figure above to explain how tissue fluid is formed. (2 marks)
There is an overall outward pressure of 3.2 kPa which forces small molecules out of the capillary. This it what forms the tissue fluid.
The hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why. (1 mark)
Loss of fluid, so hydrostatic pressure reduces.
High blood pressure leads to an accumulation of tissue fluid. Explain how. (3 marks)
A high blood pressure equals a high hydrostatic pressure. It increases the outward pressure from the arterial end of the capillary, so more tissue fluid is formed.
The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why. (3 marks)
At the arterial end, water has left the capillary due to hydrostatic pressure. However, proteins in the blood are too large to leave the capillary. Therefore giving a higher concentration of blood proteins and thus a lower water potential.
Describe and explain the mechanism that causes forced expiration. (4 marks)
The internal intercostal muscles contract while the diaphragm muscles and external intercostal muscles relax. This causes a decrease in the volume of the thoracic cavity and so air is pushed down the pressure gradient and forcibly expired.
The people in group B were recovering from an asthma attack. Explain how an asthma attack caused the drop in the mean FEV shown in the figure below. (4 marks)
The muscle walls of the bronchioles contract, so the walls of the bronchioles secrete more mucus and the diameter of the airways are reduced. Therefore, airflow is reduced.
Organic compounds synthesised in the leaves of a plant can be transported to the plant's roots. This transport is called translocation and occurs in the phloem tissue of the plant.
(a) One theory of translocation states that organic substances are pushed from a high pressure in the leaves to a lower pressure in the roots. Describe how a high pressure is produced in the leaves. (3 marks)
As sugar enters the phloem, water potential becomes more negative. As such, water potential enters the phloem by osmosis. The increased volume of water causes and increase in pressure.
PCMBS is a substance that inhibits the uptake of sucrose by plant cells. Scientists investigated the effect of PCMBS on the rate of translocation in sugar beet. The figure below shows their results.
During their experiment, the scientists ensured that the rate of photosynthesis of their plants remained constant. Explain why this was important. (2 marks)
The rate of photosynthesis is related to the rate of sucrose production, so when the concentration of sucrose is higher the rate of translocation is higher.
The scientists concluded that some translocation must occur in the spaces in the cell walls. Explain how the information in the figure above supports this conclusion. (2 marks)
The rate of translocation does not fall to zero, but sucrose is no longer able to enter the cytoplasm of phloem cells.
Describe how oxygen in the air reaches capillaries surrounding alveoli in the lungs. Details of breathing are not required. (4 marks)
Oxygen travels down through the trachea, bronchi, and bronchioles. It travels down the pressure gradient and diffusion gradient across the alveolar epithelium to reach the blood in the capillaries.
Asthma affects bronchioles and reduces flow of air in and out of the lungs. Fibrosis does not affect bronchioles; it reduces the volume of the lungs. Which group, B or C, was the one containing people with fibrosis of their lungs? Use the information provided and evidence from the figure above to explain your answer (3 marks)
It is group B because they have a similar FEV to group A, so the bronchioles aren't affected. Instead, the total volume they breathe out is reduced.
The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. Explain the advantage of this shift. (3 marks)
Haemoglobin has a lower affinity for oxygen, so oxygen is released quicker to the muscles for rapid respiration.
Weddell seals are diving mammals that live in cold environments. A Weddell seal is shown in Figure 1.
Explain how the body shape of a Weddell seal is an adaptation to living in a cold environment. (2 marks)
The Weddell seal has a small surface area to volume ratio which reduces heat loss.
Weddell seals can remain underwater for long periods of time. Figure 2 shows the rate of blood flow to different organs of a Weddell seal before a dive and during a long dive.
Describe and explain the changes in the rate of blood flow to the different organs during a long dive. (3 marks)
The rate of blood flow for the brain remains the same but for the others, it falls. This is because the brain controls the other organs and so needs a constant supply of oxygen. The lungs are used less since the seal is not breathing and a most of the seals blood is being diverted to its muscles.
Explain why a small mammal needs a relatively high metabolic rate compared to a large mammal (3 marks)
A small mammal has a larger surface area to volume ratio than a large mammal. This means that heat is lost more easily from a small mammal. So a small mammal needs a relatively high metabolic rate in order to generate enough heat to maintain a constant body temperature.
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