Biology Unit 2 Chapter 13 ko - Exchange and Transport

Root pressure moves water through the xylem. Describe what causes root pressure. (3)

Active transport of salts into the xylem; by endodermis; lowers water potential in xylem

Ions enter a root hair cell from the soil. Describe how. (3)

Active transport; Against concentration gradient; Energy required;

The diameter of the trunk decreased during the same period, reaching its minimum when the flow rate was highest. Use your knowledge of the cohesion-tension theory to suggest an explanation for this decrease. (2)

Adhesion of water molecules to walls of xylem; results in tension as water pulled up stem; pulling in walls

Suggest why she made repeat measurements. (1)

Anomalous result can be identified

(Refer to Jan 2006 paper) The diagram shows part of a leaf. The arrows show one pathway taken by water through the leaf and into the atmosphere. (Shows through cell walls.) Name the pathway shown. (1)

Apoplastic pathway

Give two differences between the structure of arteries and the structure of veins. (2)

Arteries have thicker muscular walls; Arteries have more elastic tissue

(Refer to Jan 2013 paper) The students' results are shown in the table. Explain the relationship between the number of leaves removed from the plant shoot and the mean rate of water uptake. (3)

As number of leaves are reduced there are fewer stomata; so less evaporation; so less cohesion pulling the water up

(Refer to Jan 2010 paper) The diagram shows tissue fluid and cells surrounding a capillary. Name fluid F. (Inside capillary) (1)

Blood plasma

There is a one-way flow of water over the gills of a fish whereas there is a two-way flow of air in the lungs of a mammal. Suggest one advantage to a fish of this one-way flow of water over its gills. (1)

Continuous flow of O2

Gas exchange in fish takes place in gills. Explain how two features of gills allow efficient gas exchange. (2)

Countercurrent maintains a concentration gradient; Lamellae provide a large surface area

Give two precautions the students should have taken when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot. (2)

Cut shoot under water; Ensure no air bubbles are present

The student measured the water loss in milligrams. Explain the advantage of using ten leaves when taking measurements in milligrams. (1)

Decreases chance of error

The student wanted to calculate the rate of water uptake by the shoot in cm3 per minute. What measurements did she need to make? (2)

Distance and time; Area of capillary tube

Arteries and arterioles take blood away from the heart. Explain how the structures of the walls of arteries and arterioles are related to their functions. (6)

Elastic tissue stretches under pressure; And recoils; Which evens out pressure; Muscle contracts; Which constricts vessel; To change flow; Epithelium is smooth; To reduce friction

The zoologist measured oxygen uptake per gram of body mass. Explain why he measured oxygen uptake per gram of body mass. (2)

Enables comparison; As animals differ in size

(Refer to June 2010) The diagram shows a cross-section of a blood vessel. Name layer C. (1)

Endothelium

Emphysema is a disease which affects the lungs. It causes a decrease in the number of alveoli. It may also cause the alveolar walls to become thickened. Explain why people with emphysema may need to use oxygen masks to help with their breathing. (3)

Fewer alveoli decreases the surface area; The thick wall increases the diffusion pathway; Mask increases the concentration gradient

The blood pressure decreases along the length of the capillary. What causes this decrease in pressure? (1)

Friction of capillary wall

The ends of tracheoles connect directly with the insect's muscle tissue and are filled with water. When flying, water is absorbed into the muscle tissue. Removal of water from the tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle tissue. Suggest one reason why. (1)

Gases diffuse faster in air than through water

The endodermis controls the entry of substances into the xylem. Explain how. (2)

Has a casparian strip; So water cannot move through apoplast

Describe and explain how water is exchanged between the blood and tissue fluid as blood flows along the capillary. (4)

Hydrostatic Pressure forces water out of capillary; because Hydrostatic Pressure is higher than Water Potential; Proteins remain in blood which increases Water Potential; Water Potential is now higher than Hydrostatic Pressure; So water returns by osmosis

(Refer to Jan 2006 paper) The graph shows the flow rate in the xylem in the trunk of a tree. Explain the increase in the flow rate between 1000 and 1400 hours. (2)

Increase in evaporation rate due to increase in temperature ; increased kinetic energy of water molecules

(Refer to June 2010 paper) The graph shows the rate of blood flow in different blood vessels. It also shows the total cross-sectional area of these blood vessels. The rate of blood flow decreases from the aorta to the capillaries. Use information from the graph to explain why. (1)

Increase in total cross sectional area so increase in friction

The stomata on the leaves of pine trees are found in pits below the leaf surface. Explain how this helps to reduce water loss. (2)

Increases humidity around stomata; So that the water potential gradient is reduced

Suggest an explanation for the difference in transpiration rate between conditions A and C. (Still air at 15 degrees and still air at 25 degrees) (2)

Increases kinetic energy; So water molecules move faster

(Refer to Jan 2012 paper) A biologist investigated the rate of water movement during the day in different parts of a tree. The results are shown in the graph. Describe how the rate of water movement in the upper branches changed over the period shown in the graph. (2)

Increases then decreases; Peak at 13.00 - 14.00 hours

The blood pressure is high at the start of the capillary. Explain how the left ventricle causes the blood to be at high pressure. (1)

It contracts

Explain how the cuticle reduces water loss. (1)

It is waxy so waterproof

Abdominal pumping is an adaptation not found in many small insects. These small insects obtain sufficient oxygen by diffusion. Explain how their small size enables gas exchange to be efficient without the need for abdominal pumping. (1)

Larger surface area to volume ratio to increase diffusion

(Refer to June 2010) A student investigated the rate of transpiration from a leafy shoot. She used a potometer to measure the rate of water uptake by the shoot. The diagram shows the potometer used by the student. Give one environmental factor that the student should have kept constant during this investigation. (1)

Light intensity

(Refer to June 2011 paper) A student investigated the rate of transpiration from privet leaves. - She obtained two sets of ten privet leaves. - She left the ten leaves in set A untreated. She covered the upper surfaces of the ten leaves in set B with grease. - She weighed each set of leaves and then tied all the leaves in each set to a separate length of thread. This is shown in the diagram. - She then weighed each set of leaves every 20 minutes over a period of 2 hours and plotted a graph of her results. Give two environmental conditions that the student should have kept constant during this investigation. (2)

Light; Humidity in air

Explain how xylem tissue is adapted for its function. (4)

Long cells with no end walls; to create continuous water columns; It is thick; To withstand tension

An arteriole is described as an organ. Explain why. (1)

Made of different tissues

Water containing dissolved oxygen flows over the gill in the opposite direction to the blood flow inside. Explain why this arrangement is important for efficient oxygen uptake. (2)

Maintains diffusion gradient; and allows diffusion to occur across the whole length of the lamellae

Describe how a potometer could be used to measure the rate of water uptake by a leafy shoot in cm3 per minute. (3)

Measure time taken; For bubble to move a given distance; Calculate cross sectional area of capillary tubing

Suggest how the student could have used his slide to find the number of stomata per cm2. (3)

Method of determining area of field of view; Count number of stomata in field of view; Repeats and calculation of mean

Abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of the insect. Explain why. (2)

More oxygen enters; So maintains a greater diffusion gradient

Give one way in which fluid F is different from tissue fluid. (1)

More proteins

Blood flow in capillaries is slow. Give the advantage of this. (1)

More time for diffusion of substances

(Refer to Jan 2011 paper) Students measured the rate of transpiration of a plant growing in a pot under different environmental conditions. Their results are shown in the table. During transpiration, water diffuses from cells to the air surrounding a leaf. Suggest an explanation for the difference in transpiration rate between conditions A and B. (Still air and moving air)(2)

Moving air removes water vapour; And increases the water potential gradient

Explain the importance of muscle fibres in the wall of an arteriole. (2)

Muscle contracts; Allowing arteriole to constrict to regulate blood flow

An arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries. (2)

Muscle contracts; Arteriole constricts

Describe the relationship between body mass and oxygen uptake. (1)

Negative correlation

Two shoots were kept in the same environmental conditions. Give one measurement that you would need to make to be able to compare water uptake by the shoots. Give a reason for your answer. (2)

Number of stomata; As larger number mean more water loss

Name a tissue that transports solutes from the leaves. (1)

Phloem

(Refer to Jan 2011 paper) Scientists investigated the rate of water movement through the xylem of a twig from a tree over 24 hours. The graph shows their results. It also shows the light intensity for the same period of time. Describe the relationship between the rate of water movement through the xylem and the light intensity. (1)

Positive correlation

The student measured the rate of water uptake three times. Suggest how the reservoir allows repeat measurements to be made. (1)

Returns bubble to the start

Explain how two adaptations of their leaves reduce water loss from xerophytes. (2)

Rolled leaves reduce surface area for evaporation; Stomata in sunken pits to reduce diffusion gradient

Describe how water is taken up by root hairs and reaches the xylem in the root. (6)

Root hair cells have lower water potential than soil; Due to uptake of ions by active transport; So water enters root hair cells by osmosis; Passes along apoplast pathway; Through water filled spaces of cell walls; And passes along symplast pathway; Through cytoplasm of cells

A capillary has a thin wall. This leads to rapid exchange of substances between the blood and tissue fluid. Explain why. (1)

Short diffusion pathway

Heat from respiration helps mammals to maintain a constant body temperature. Use this information to explain the relationship between body mass and oxygen uptake shown in the graph. (3)

Smaller animals have larger surface area to volume ratio; and so lose more heat per gram of tissue; They respire more; and oxygen is used in respiration

The results that the student obtained for the leaves in set B were different from those for set A. Suggest an explanation for this difference. (2)

Stomata on the upper surface are covered; So there is less evaporation

Explain the change in the rate of water movement through the xylem between 06.00 and 12.00 hours. (2)

Stomata open; So transpiration increases

The aorta has many elastic fibres in its wall. An arteriole has many muscle fibres in its wall. Explain the importance of elastic fibres in the wall of the aorta. (2)

Stretches under high pressure when the ventricle contracts; Recoils under low pressure when the ventricle relaxes

Name a tissue that prevents the movement of water through the apoplast pathway. (1)

The casparian strip of the endodermis

The rate of water movement in the upper branches was different from the rate of water movement in the trunk. Describe how. (2)

The maximum rate is higher in the branches; It reaches the peak earlier in the day in the branches

The results of this investigation support the cohesion tension theory. Explain how. (2)

The movement starts in the branches; And creates tension, pulling water up from the trunk

(Refer to Jan 2010 paper) A zoologist investigated the relationship between body mass and rate of oxygen uptake in four species of mammal. The results are shown in the graph. The scale for plotting body mass is a logarithmic scale. Explain why a logarithmic scale was used to plot body mass. (1)

There is a large range of values so used so that they can fit on graph

Explain how water enters xylem from the endodermis in the root and is then transported to the leaves. (6)

There is active transport of salts into the xylem; by the endodermis; which lowers the water potential in the xylem; Water evaporates from the leaves; and this creates cohesion between water molecules; This creates a continuous water column up the plant

Efficient exchange of substances in the capillaries is linked to the rate of blood flow. Explain how. (1)

There is more time for exchange of substances

Very small organisms do not have specialised gas exchange systems. Explain how they obtain sufficient oxygen for respiration. (2)

They have a large surface area to volume ratio; and a short diffusion distance

(Refer to exam q) The photograph shows part of the gill of a fish as seen through a light microscope. It is magnified × 400. Explain how the structure of the gill makes oxygen uptake efficient. (2)

Thin epithelium; creates a short diffusion pathway

Describe and explain how water in the mesophyll cells passes out of the leaf. (3)

Through air spaces and out through stomata; by diffusion; down a diffusion gradient

A student found the number of stomata per cm2 on the lower surface of a daffodil leaf. He removed a small, thin piece of lower epidermis and mounted it on a microscope slide. He examined the slide using an optical microscope. Explain why it was important that the piece of the epidermis that the student removed was thin. (2)

To obtain fewer layers of cells; So that light that can pass through

The student cut the shoot and put it into the potometer under water. Explain why. (1)

To prevent air entering

(Refer to Jan 2013 paper) Students investigated the effect of removing leaves from a plant shoot on the rate of water uptake. Each student set up a potometer with a shoot that had eight leaves. All the shoots came from the same plant. The potometer they used is shown in the diagram. Describe how the students would have returned the air bubble to the start of the capillary tube in this investigation. (1)

Use tap to add water from resevoir

Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue. (4)

Wall one cell thick, reduces diffusion distance; Flattened cells, reduced diffusion distance; Narrow lumen, reduces flow rate so more time for diffusion; Small diameter, creates a large surface area to volume ratio

Larger organisms have specialised gas exchange systems. Explain how the countercurrent mechanism helps fish to extract oxygen from water. (3)

Water and blood flow in opposite directions; Oxygen difference maintained; so diffusion always occurs

Explain the change in mass of untreated leaves in set A shown in the graph. (3)

Water evaporates out of leaf; Via a water potential gradient; The water is then not being replaced

Use your knowledge of the cohesion-tension theory to explain how water in the xylem in the roots moves up the stem. (4)

Water evaporates out the leaves; which creates a water potential gradient; Water is drawn out of xylem; which creates tension and a pulling effect

The scientists also measured the diameter of the trunk of the tree on which the twig had been growing. The diameter was less at 12.00 than it was at 03.00 hours. Explain why the diameter was less at 12.00 hours. (2)

Water is pulled up the trunk faster; The water column is under tension; And there is adhesion between water and xylem

The student assumed that water uptake was equivalent to the rate of transpiration. Give two reasons why this might not be a valid assumption. (2)

Water is used to provide support; Water is used in photosynthesis

Kwashiorkor is a disease caused by a lack of protein in the blood. This leads to a swollen abdomen due to a build up of tissue fluid. Explain why a lack of protein in the blood causes a build up of tissue fluid. (3)

Water potential in capillary is higher; So less water is removed; by osmosis into capillary

In children, some diets may result in a low concentration of protein in fluid F. This can cause the accumulation of tissue fluid. Explain the link between a low concentration of protein in fluid F and the accumulation of tissue fluid. (3)

Water potential in capillary is higher; so less water absorbed into the blood capillary; by osmosis

A potometer measures the rate of water uptake rather than the rate of transpiration. Give two reasons why the potometer does not truly measure the rate of transpiration. (2)

Water used for support; Water used in photosynthesis