2g. Gas Exchange - Plants 4/28/11 8:03 AM

2. Structure and Function of Organismsg. Gas Exchange – Plants

2.39 understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis

2.40 understand that respiration continues during the day and night, but that the net exchange of carbon dioxide and oxygen depends on the intensity of light

2.41 explain how the structure of the leaf is adapted for gas exchange

2.42 describe the role of stomata in gas exchange

2.43 describe simple controlled experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator

2.39 Gas Exchange 4/28/11 8:03 AM

2.39 understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis

Ref:Pg. 34 5.3 “Photosynthesis is a chemical process”

Pg. 36 5.6 “Leaves are adapted to obtain carbon dioxide”

Pg. 44 6.1 “Respiration releases energy from food”6.2 “Respiration oxidizes sugars in stages”

1. The diagram below shows the main movement of gases in and out of two leaves.

(a) Explain how you know leaf A is photosynthesising. (1)

(b) Name ONE other substance needed by a leaf to photosynthesise. (1)

(c) What process is leaf B carrying out? (1)

2. The diagrams below show TWO different chemical processes.

(a) Fill in the blank lines on the diagrams. (2)

(b) Give ONE use for the chemical energy released in animals. (1)

3. The table below shows the results of an investigation to measure the mass of sugar in leaves at different times of the day.

(a) At what time of the day was the mass of sugar at a maximum in the leaf? Explain your answer. (2)

(b) Explain why the mass of sugar fell between 8.00 p.m. and 12 midnight. (2)

2.40 Light Intensity 4/28/11 8:03 AM

2.40 understand that respiration continues during the day and night, but that the net exchange of carbon dioxide and oxygen depends on the intensity of light

1. The diagram summarises some of the processes that take place in a plant leaf.

(a) Where in the plant cell does photosynthesis occur? (1)

(b) Name substances A and B. (2)

(c) Explain why the mass of the plant increases during the day. (3)

2. The graph shows the rates of oxygen release and uptake in some plants. The plants were placed for 12 hours in the dark followed by 12 hours in the light in a laboratory.

(a) What processes take place in the plants during the 12 hours of light? (1)

(b) Estimate the volume of oxygen taken up by the plants during the first 6 hours of darkness. (1)

3. Low light intensity is one factor that limits the yield of a crop.In Britain, many tomato growers use artificial lights to increase the yield of tomato crops.The table shows the amount of natural daylight and artificial lamplight received by a tomato crop grown in a greenhouse.

Natural daylight receivedby tomato plant

Artificial lamplight givento tomato plant

Total light energy received

Percentage increase in growth

Month Day lengthin hours

Lightenergy receivedby plantper dayin J/cm2

Hours of light given per day

Light energy receivedby plantper dayin J/cm2

by plant per dayin J/cm2

resulting from artificial light

January 8.1 239 18 492 731 206February 9.9 492 18 492 984 100March 11.9 848 12 328 1176 39April 13.9 1401 2 55 1456 4May 15.5 1786 0 0 1786 0June 16.6 1960 0 0 1960 0July 16.2 1849 0 0 1849 0August 14.7 1561 0 0 1561 0September

12.8 1064 2 55 1119 5

October 10.6 614 11 301 915 49November 8.8 288 18 492 780 171December 7.6 183 18 492 675 269

(a) Describe the pattern for the amount of light energy received from natural daylight by a tomato plant during the day. (3)

(b) A tomato plant needs 600 J of light energy per cm2 each day to grow and produce tomatoes. Use this information and data from the table to suggest an explanation for the pattern of the artificial light given to the tomato plants. (2)

4. The graph shows the mean light intensity at different times of the year in an oak wood.

(a) In which month would you expect the rate of photosynthesis in the oak trees to be greatest? (1)

(b) There are plants living on the ground in the wood. In which month would you expect their rate of growth to be fastest? Explain your answer. (3)

(c) Name two factors, other than light intensity, that would affect the rate of photosynthesis in the oak trees. (2)

2.41 Leaf Structure 4/28/11 8:03 AM

2.41 explain how the structure of the leaf is adapted for gas exchange

Ref:Pg. 34-35 5.5 “Leaf Structure is related to function”

Pg. 36 5.6 “Leaves are adapted to obtain carbon dioxide”

* Try to label the diagram without looking back at the previous diagrams

To do:Fill in the table below to link how the structure of the leaf is adapted for gas exchange.Structure FunctionStomataSpongy mesophyllAir spaces

1.

2.

3.

4.

5.

6. 7.

10.

9.

8.

1. The diagram shows the outline of a cross-section of a leaf. Name cells 1 and 2 and describe how they are involved in photosynthesis. (4)

2. The diagram shows part of a leaf.

(a) Name cells A, B and C. (3)

(b) On the diagram use (2)D to label the cells where most photosynthesis occurs.X to label the xylem.

2.42 Stomata 4/28/11 8:03 AM

2.42 describe the role of stomata in gas exchange

Ref:Pg. 41-42 5.11 “Many factors affect rate of photosynthesis – Stomata”

1. The results are shown in the table.Variety of violet Number of stomata per mm2

of leafA 150B 110C 250

Which variety would survive best in hot dry weather? Explain your answer. (3)

2. The diagram shows one of the stomata on a leaf.

Label cell A. (1)

3. A pupil painted part of a leaf with nail varnish. The nail varnish made a print of all the stomata on that part of the leaf. The varnish was peeled off when it was dry. (1)

(a) How many guard cells were there on this part of the leaf? (1)

(b) Suggest the instrument the pupil should use to see the positions of the stomata on the print. (1)

4. A pupil investigated water loss from leaves taken from the same tree. Equal masses of leaves were used in three experiments.

Experiment 1 the upper surfaces of the leaves were covered with vaseline

Experiment 2 the lower surfaces of the leaves were covered with vaseline

Experiment 3 the lower and upper surfaces of the leaves were covered with vaseline

The leaves were weighed at the start of each experiment and after 48 hours. The results are shown in the table

Experiment Mass of leaves at start (g)

Mass of leaves after 48 hours (g)

Experiment 1the upper surfaces of leaves covered with vaseline

50.0 40.8

Experiment 2the lower surfaces of leaves covered with vaseline

50.0 45.8

Experiment 3both upper and lower surfaces of leaves covered with vaseline

50.0 50.0

(a) How many grams of water were lost from the leaves covered with vaseline on the upper surfaces? (1)

(b) Why was the vaseline used? (1)

(c) Why did the leaves covered with vaseline on the upper surfaces lose more mass than the leaves covered on the lower surfaces? (1)

(d) Apart from using the same mass of leaves suggest how the pupil could have made sure that it was a fair test. (1)

2.43 Experiments 4/28/11 8:03 AM

2.43 describe simple controlled experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator

Hydrogen Carbonate IndicatorTurns yellow in CO2