Maris Stella High School Name: ___________________

GCE O Level Science Biology Class (Index No.): _____ ( )GEP: Topics 11 & 12 Date: ________________

Plant Nutrition & Transport1. Fig. 3 below shows an experimental set-up to investigate the uptake and loss of water by a plant.

Fig 1

a (i) Describe the changes in liquid level in tubes A and B after three hours.[2]

Tube A _______________________________________________________

Tube B _______________________________________________________

(ii) Explain clearly how you arrived at your answer for tube A. [2]

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b The dialysis tubing bag in C contains water.

(i) What will happen to the dialysis tubing in tube C after one hour?[1]

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(ii) Explain your reasoning. [1]

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c. Suggest a way to increase the rate of water uptake by the plant in tube A. Explain how your method works. [2]

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2. Figure 2 shows the fluctuations in the transpiration rate of leaves and water potential of leaf cells of cotton plants during three hours of daylight in a natural environment.

(a) Describe the relationship between the transpiration rate and water potential of cells of cotton leaves. [1]

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(b) Explain how an increase in the rate of transpiration affects the water potential of leaf cells. [2]

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(c) Explain one reason for the fluctuations in the transpiration rate shown in the graph. [2]

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An investigation was carried out to measure the rate of transpiration of cotton leaves. Several leaves were attached together by thread as shown in Figure 2.

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Figure 2

Figure 12

The leaves were weighed every thirty minutes over a period of three hours. The table shows the results of this investigation.

Time / minutes Loss in mass / mg per gram of lead30 11060 6390 22

120 21150 9180 7

(i) Explain the change in mass of the leaves over the period of investigation. [3]

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(ii) Suggest why several leaves were used in this investigation. [2]

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(e) Briefly explain how water is lost from the cells inside the leaves shown in Figure 2. [2]

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3. The following graph shows the change in concentration of oxygen and carbon dioxide in an environment with a green plant, in an enclosed area, under different light intensities.

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a. Account for the changes in the amount of gases present in the environment.

i. Oxygen [2]

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ii. Carbon dioxide [2]

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b. If light intensity is kept constant at point X for the next two months, explain your prediction of what will happen to the plant at the end of the two months? [2]

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4 Fig. 4.1 shows a picture of a leaf attached to a plant throughout the experiment.

Fig. 4.1

6 discs were cut out from regions X, Y and Z of the leaf at 10 a.m., 4 p.m. and 10 p.m. The plant may have received some treatment before the discs were cut and likewise the discs too, before their total dry weight is measured. Table 2.2 shows the steps taken in the experiment.

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leaf discs cut out at 4 p.m. leaf discs cut out at 10 p.m.

leaf discs cut out at 10 a.m.

Table 4.2

Time Treatment to plant before removing leaf discs

Treatment of leaf discs

Dry weight of leaf discs (mg)

10 a.m. exposed to sunlight killed in steam 186

4 p.m. exposed to sunlight none 209

10 p.m. kept in the dark for 6 hours none 198

(a) (i) What is the biological process that causes the change in dry weight of the leaf discs between 10 a.m. and 4 p.m.? Support your answer with reason. [2]

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(ii) What is the biological process that causes the change in dry weight of the leaf discs between 4 p.m. and 10 p.m. support your answer with reason. [2]

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(b) Why is dry weight measured instead of fresh weight? [1]

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5 Describe how the internal structure of the leaf is adapted for(a) photosynthesis

(b) gaseous exchange [7]

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Maris Stella High School Name: ___________________

GCE O Level Biology Class (Index No.): _____ ( )GEP: Topic 11&12 MS Date: ________________

Plant Nutrition & Transport Answers

1a (i) Tube A Water level will drop;Tube B Water level will increase;

(ii) The cell sap in the root hair cells have lower water potential than the water in tube A; Water moves into the roots by osmosis down the water potential gradient which decreases the level of water in tube A

1b (i) The dialysis tubing will become smaller(ii) The water potential of the water in the tubing is higher than in the roots and in the sucrose

solution. Hence, water moves into the roots and out of the dialysis tubing by osmosis down the water potential gradient.

1c Place it under the sun; to increase rate of transpiration therefore increasing the transpiration pull to move the water up the stem;

2a The higher the transpiration rate, the lower the water potential in the leaves/ The lower the transpiration rate, the higher the water potential in the leaves;

2b Transpiration involves evaporation of water from the moisture layer lining the spongy mesophyll cells; Water then diffuses out of leaves through the stomata Reduced water content in the cells/ lower water potential;

2c The fluctuations are due to environmental changes that causes the opening / closing of stomata which either affects the amount of water lost per unit time or which affect the evaporation and diffusion rate thus affecting the transpiration rate.Eg:Wind blowing: Steep diffusion gradient for water vapour / faster rate of evaporation, faster transpiration rate.Light intensity: Higher light intensity induces a larger stomata, more water vapour lostHumidity: High humidity, diffusion gradient less steep, less water lost, slower transpirationTemperature: Increase in temperature, increase in rate of evaporation, faster transpiration rate

2d (i) Initial high loss in mass, then loss in mass decreases with time; because water vapour concentration inside the leaves is higher than outside the air. Hence more water vapour diffuses out of the leaves; As diffusion gradient becomes less steep, less water lost;

(ii) To obtain replicate results so that a more accurate average can be calculated/Large sample size yield a more accurate average;

2e Water moves out of mesophyll cells by osmosis to form a layer of moisture; Water then evaporates into the intercellular air spaces, water vapour diffuses out of the leaves through the stomata;

3a (i) As light intensity increases, the concentration/ amount of oxygen produced increases; since oxygen is produced during photosynthesis.

(ii) Carbon dioxide is produced during respiration but used up during photosynthesis. As light intensity increases, rate of photosynthesis increases using more carbon dioxide, hence decreasing concentration of carbon dioxide.

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3b The plant will not grow/ increase in mass; The amount of carbon dioxide, produced during the breakdown of glucose during respiration, is used to during photosynthesis to produce glucose OR Rate of respiration is equal to that of photosynthesis (compensation point).

4ai) Photosynthesis;The light intensity increases from 10 a.m. to 4 p.m. causing an increase in the rate of photosynthesis producing more glucose to be stored as starch;

ii) Respiration; Stored starch is being converted to glucose for respiration as photosynthesis has stopped in the absence of light/rate of respiration exceeds rate of photosynthesis;

b) Dry weight is more accurate because it is not affected by the water content of the leaf discs;Which are easily affected by different environmental conditions/amount of water absorbed bythe plant;

5) Describe how the internal structure of the leaf is adapted for (a) photosynthesis and (b) gaseous exchange.

a) Mesophyll cells have chloroplasts which act as site of photosynthesis;Palisade mesophyll cells are closely packed and have greater concentration of chloroplast which allows them to absorb more light;Vascular bundles containing xylem and phloem are interspersed throughout leaf to provide easy access of water and mineral salts and efficient translocation of manufactured food out of leaf;Epidermal cells are also thin and flattened, helping channel maximum light rays into photosynthetic cell layers below at the upper surface/do not have chloroplasts to allow light rays to penetrate through to mesophyll cells beneath.

b) A thin film of moisture lines the surface of mesophyll cells which facilitates the diffusion of dissolved gases in solution and out of cell;Spongy mesophyll cells are loosely packed which creates an intercellular air space such that gaseous exchange between leaf cells and atmospheric air is optimized;Guard cells are present on epidermal layer – these create openings known as stomata when turgid and allows free diffusion of gas molecules between cells of the leaf interior and the atmosphere and vice versa;

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