q1. - qclscience.weebly.com€¦ · web viewbethany wanted to compare the mass of water lost from...
TRANSCRIPT
2G Gas Exchange
Time: 58 minutes
Total marks available: 58
Total marks achieved:
Q1.
Bethany wanted to compare the mass of water lost from the upper surface and the lower surface of a leaf.
She set up an experiment using four leaves from the same species of tree. She estimated the surface area of each leaf by drawing around its outline on squared paper as shown in the diagram.
(a) Estimate the total surface area of this leaf in cm2. (2)
........................................................... cm2
(b) She applied a thin layer of petroleum jelly to the leaves as described below.
Leaf A no surface covered
Leaf B lower surface covered Leaf C upper surface coveredLeaf D upper and lower surfaces covered
She then carefully weighed the leaves and recorded their mass. She hung the leaves by their stalks from a wire as shown. She left the leaves for 6 hours and then carefully weighed them again.
Leaf C had a lower surface area of 24 cm2 and lost 0.2 g in 6 hours.Calculate the loss of mass from leaf C in g per cm2 in 1 hour.
(2)
Answer ........................................................... g per cm2 in 1 hour
(c) Identify the independent variable in this experiment.
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(d) Identify the dependent variable in this experiment.
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(e) State one variable that Bethany should control in this experiment.
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(f ) (i) Complete the table to show the order in which the leaves A to D are most likely to lose mass.
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(ii) Give an explanation for your answer.
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(3)
(Total for question = 12 marks)
Q2.
Describe the biological consequences of cigarette smoking on the human lungs.
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(5)
(Total for question = 5 marks)
Q3.
The diagram shows a model that can be used to demonstrate how the lungs inflate.
(a) Suggest which part of the human thorax is represented by(i) the balloons
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(ii) the rubber sheet
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(iii) tube A
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(iv) tube B
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(b) Describe and explain what happens to the balloons as the rubber sheet is pulled down.
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(c) Explain why the model does not fully show the mechanism of breathing in the human thorax.
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(d) Describe an experiment you could carry out to investigate the effect of exercise on breathing in humans.
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(4)
(Total for question = 13 marks)
Q4.
Ian wanted to investigate how gas exchange in a flowering plant changed with light intensity.
He set up an experiment using four tubes. Each of the tubes contained orange hydrogencarbonate indicator solution and was sealed with a cork. Ian added a fresh leaf to tubes A, B and C. Tube D had no leaf.
The tubes were then left in the following conditions:
Tube A was placed in direct sunlight.Tube B was covered with aluminium foil to prevent any light entering the tube.Tube C was covered with thin cloth which allowed some light to enter the tube.Tube D was also placed in direct sunlight.He left the tubes in the laboratory for one hour and then returned to look at the colour of theindicator solution in the tubes.
(a) Suggest a hypothesis for Ian's investigation.
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(b) Give two variables that Ian should keep constant in his investigation.
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(c) State the purpose of Tube D in the investigation.
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(d) Ian recorded his results in a table.
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(i) Explain the change in colour of the indicator in Tube A.
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(ii) Explain the change in colour of the indicator in Tube B.
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(e) Suggest why the indicator did not change colour in:
(i) Tube C
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(ii) Tube D
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(f ) Limewater is an indicator that can be used to show an increase in the level of
carbon dioxide.
Suggest why it would not be a suitable i
ndicator for use in this investigation.
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(Total for question = 12 marks)
Q5.
Caroline investigated how light affected photosynthesis by looking at changes in carbon dioxide levels.
She placed 2 cm3 of orange hydrogen carbonate indicator solution into three test tubes.
She put a leaf in two of the test tubes, which were then firmly sealed with a bung.These leaves were similar in size and were taken from the same plant. She wrapped one of the test tubes in foil to prevent light entering.
The third test tube was firmly sealed with a bung but was without a leaf.
She left the three test tubes in the conditions shown in the diagram for two hours. They were then shaken gently and the leaves were removed.
Hydrogen carbonate indicator solution is orange in normal air.
It changes colour to red as the carbon dioxide level decreases.
It changes to yellow as the carbon dioxide level increases.
The colour of the indicator solution in each test tube was recorded.
Her results are shown in the table.
(a) Explain the colour change observed in test tube C.
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(b) Explain the purpose of test tube B.
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(c) Caroline set up a fourth test tube that contained a leaf and was exposed to dim light.
After two hours the colour of the indicator solution in this test tube remained orange.
Explain why.
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(d)Caroline carried out another experiment
to investigate the effect that light intensity has on the rate of photosynthesis in a water plant.
(i) Suggest how she could change her independent variable.
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(ii) Suggest how she could measure her dependent variable.
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(iii) Suggest how she could ensure that her results were reliable.
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(2)
(Total for question = 10 marks)
Q6.
The diagram shows some structures in the human breathing system.
(a) Name structures A and B.(2)
A ..................................................................................................................................................................................................B ..................................................................................................................................................................................................
(b) The table shows the level of two gases, X and Y, in blood entering and leaving the lungs during the process of gas exchange.
gas
(i) Name the two gases.(2)
X ............................................................................................................................................................................................gas
Y ............................................................................................................................................................................................
(ii) How much of gas X enters 100 cm3 of blood, before the blood leaves the lungs?(1)
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(iii) What term is used to describe how the process of gas exchange takes place? Put a cross in the box to indicate your answer.
A active transport
B diffusion
C transpiration
D osmosis
(1)
(Total for question = 6 marks)
Q1.
(a) Many candidates failed to attempt this question. An answer within the range of 120 to 136 was awarded both marks. Candidates gained one mark for providing an answer within the range of 60 to 68, but to get the second mark they needed to multiply by 2 to take into account the fact that the leaf has two surfaces. Any indication of a wrong number being multiplied by 2 in the working was credited with one mark.(b) Very few candidates calculated the correct answer of 0.00138. Most candidates scored one mark for the answer 0.03. These candidates had divided 0.2 by 6 but then failed to divide by 24.(c) The examiners were looking for some indication of surface of leaf covered, or the place where the jelly had been applied. Answers that simply stated the amount of jelly were not credited. Many candidates are aware of what a variable is, but they are not able to recognise which is the independent. Dependent and controlled variables were named in abundance.(d) The examiners credited the word mass or weight as being indicative of the dependent variable. A variety of wrong answers were noted with the most common being 'time'.(e) Students tended to do better on this question. Temperature was the most popular correct answer, closely followed by light or species of leaf. Surface area, leaf size and mass loss were the most frequently stated incorrect answers.(f) (i) The correct sequence of A, C, B and D was seldom seen indicating that candidates struggled to interpret the information they were given. Examiners were allowed to award one mark if the wrong order appeared in the table providing A was written before D or C was written before B.
(ii) A full explanation required candidates to make reference to stomata and the fact that they are not equally distributed on the upper and lower surfaces of the leaves. They were then expected to link this to how
coverage by the jelly, effectively blocking stomata, would affect the loss in mass. Candidates struggled to gain full marks and many weak answers linked mass of jelly to mass loss.
Q2.
This question was well answered with 41% of candidates gaining full marks. This demonstrated that candidates have a good understanding of the consequences of cigarette smoking on the human lungs. Again, some candidates failed to read the question carefully and wrote about the biological consequences to the human cardiovascular system. The examiners rewarded answers that discussed emphysema, bronchitis and cancer.
Q3.
In this question students were able to recognise the parts of the human thorax represented in the model. However, those who chose bronchioles for (iv) lost credit as the only accepted answer was bronchus. In part (b), many appreciated the how an increase in volume would decrease the pressure and lead to inflation of the balloons, and many appreciated in part (c) that the model did not have ribs, muscles or pleural membranes and that there was no movement involved. Part (d) was challenging to most and a surprising number made reference to measuring heart rate. Credit was given for answers that demonstrated quantification of exercise, measuring by counting breaths per stated time period and for understanding the need to replicate for reliability.
Q4.
The term 'hypothesis' seemed unfamiliar to many candidates and, as such, their attempts to construct a sentence that explained the observations made in this investigation were disappointing. The examiners were looking for answers that showed an understanding that light intensity affected the level of carbon dioxide in the tubes. Candidates who repeated the information describing the investigation or only made reference to the colour changes gained no credit. In (b), credit was given for temperature, species of plant and volume of indicator solution. Most candidates were able to gain at least one mark showing that they have a good understanding of controlled variables.Equally pleasing were answers to (c). Candidates appreciated the role of a control to allow a valid comparison to be made between tubes A, B and C. Part(d) expected students to offer explanations for the colours seen in the tubes. The better candidates appreciated the roles of photosynthesis and respiration and how the net change in carbon dioxide is affected by light intensity.Weaker candidates described the colour changes or made reference to oxygen gas. Only the best candidates appreciated that limewater can only show an increase in carbon dioxide and, unlike hydrogencarbonate indicator, cannot show a decrease in carbon dioxide.
Q5.
This question gave a description of an experiment (described in the specification) to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator. In part(a) the majority of students gained full marks for explaining that in light a leaf will carry out photosynthesis and therefore absorb carbon dioxide. Also in (b) most could explain that tube B acted as a control to show that it is the leaf that is causing the colour change in the indicator solution. In (c) most students appreciated that in dim light photosynthesis and respiration would both occur and there would be no change in the carbon dioxide concentration in the tube. In part(d) students were asked about another experiment to investigate the effect of light intensity on photosynthesis in a water plant. Most could describe how she could change her independent variable and how she could measure her dependent variable and ensure that her results were reliable.
Q6.
Part (a) was intended to offer a gentle introduction to the paper and most candidates were able to gain two marks for correctly identifying the trachea and alveoli. Candidates did less well on item (b) with manyinterpreting the table on gases in the blood entering and leaving the lungs incorrectly. These candidates also then mismatched oxygen and carbon dioxide. Most could identify diffusion as the means of gas exchange in the lungs.
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