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GCSE · Biology

B4a Photosynthesis

AQA 8464 · Calculator allowed · about 100 minutes

Total Marks

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Plants make their own food using a process called photosynthesis.

(a)Define the term 'photosynthesis'.(1)

(b)State the two raw materials (reactants) needed for photosynthesis.(2)

(c)State the two products of photosynthesis.(2)

(d)State the type of energy that is required for photosynthesis to take place.(1)

(Total for Question 1 is 6 marks)

Photosynthesis takes place inside plant cells, in a structure containing a green pigment.

(a)Name the organelle in a plant cell where most photosynthesis takes place.(1)

(b)Name the green pigment, found inside chloroplasts, that absorbs light energy for photosynthesis.(1)

(c)Give two ways that a palisade mesophyll cell is adapted for photosynthesis.(2)

(Total for Question 2 is 4 marks)

Photosynthesis and respiration are both described in terms of energy transfer.

(a)State whether photosynthesis is an exothermic or an endothermic reaction.(1)

(b)Explain what is meant by describing photosynthesis as an 'endothermic' reaction.(2)

(Total for Question 3 is 3 marks)

Photosynthesis can be represented by the following (unbalanced) symbol equation:

CO2 + H2O -> C6H12O6 + O2

(a)Balance the symbol equation above by adding the correct number in front of each formula where needed.(2)

(b)Add the correct state symbols to each substance in the balanced equation, given that the reaction occurs inside a leaf cell.(2)

(Total for Question 4 is 4 marks)

Plants use the glucose produced by photosynthesis for much more than just releasing energy.

(a)Name the process, other than converting glucose into a storage product, that plant cells mainly use glucose for, to release energy.(1)

(b)Much of a plant's glucose is converted into starch for storage. Give one reason why starch is better suited than glucose for storage in plant cells.(2)

(c)Name the insoluble carbohydrate, made from glucose, that is used to strengthen plant cell walls.(1)

(d)Explain how glucose is used, together with nitrate ions absorbed from the soil, to produce amino acids in a plant.(2)

(e)Name one other substance, used for storage in some seeds, that glucose can be converted into.(1)

(Total for Question 5 is 7 marks)

The rate of photosynthesis is affected by several environmental factors.

(a)Define the term 'limiting factor'.(1)

(b)State three factors that can limit the rate of photosynthesis.(3)

(c)Give one reason why commercial tomato growers often grow their plants in glasshouses (greenhouses) where light intensity, carbon dioxide concentration and temperature can all be controlled.(1)

(Total for Question 6 is 5 marks)

A group investigated the effect of light intensity on the rate of photosynthesis in an aquatic plant, keeping carbon dioxide concentration and temperature constant. Their results are shown in the table below.

Light intensity (arbitrary units): 0, 20, 40, 60, 80, 100
Rate of photosynthesis (arbitrary units): 0, 8, 15, 20, 20, 20

(a)Describe the relationship between light intensity and rate of photosynthesis shown by the data.(2)

(b)Explain why the rate of photosynthesis stops increasing once light intensity rises above 60 units, even though light intensity continues to increase.(2)

(c)Suggest one change to the experimental conditions that could increase the rate of photosynthesis beyond 20 units, at a light intensity of 100.(2)

(Total for Question 7 is 6 marks)

A group of students investigated the effect of light intensity on the rate of photosynthesis in pondweed. They set up a boiling tube containing a piece of pondweed in sodium hydrogencarbonate solution, placed a lamp at a measured distance from the tube, and counted the number of bubbles of gas released from the cut end of the pondweed in one minute. They repeated this at a range of distances between the lamp and the tube. (Required practical: the effect of light intensity on the rate of photosynthesis.)

(a)Identify the independent variable and the dependent variable in this investigation.(2)

(b)Name one variable, other than distance, that the students needed to control, and describe how they could control it.(2)

(c)State one hazard associated with this investigation, and a suitable control measure.(2)

(d)Counting bubbles is not always an accurate way to measure the volume of gas produced, because bubbles can vary in size. Suggest one improvement to the method that would give a more accurate measure of the rate of photosynthesis.(2)

(Total for Question 8 is 8 marks)

A different group used the same method as in Question 8, but used the relationship between distance and light intensity to analyse their results. Relative light intensity can be estimated using the equation:

relative light intensity = 1 / distance²

(a)State what happens to the relative light intensity reaching the pondweed as the distance from the lamp increases.(1)

(b)Calculate the relative light intensity, 1 / distance², for a distance of 15 cm and for a distance of 45 cm. Give each answer in standard form, with units of cm^-2.(4)

(c)Explain why using the value 1 / distance² gives a better estimate of the light intensity reaching the pondweed than simply using the distance value on its own.(2)

(Total for Question 9 is 7 marks)

A group investigated the effect of light intensity on the rate of photosynthesis of pondweed at two different carbon dioxide concentrations, keeping temperature constant. Their results are shown in the table below.

Light intensity (arbitrary units): 0, 10, 20, 30, 40, 50
Rate of photosynthesis at low CO2 concentration (arbitrary units): 0, 5, 9, 11, 11, 11
Rate of photosynthesis at high CO2 concentration (arbitrary units): 0, 5, 9, 13, 16, 18

(a)Explain why the rate of photosynthesis is the same for both carbon dioxide concentrations at light intensities of 0 to 20 units.(2)

(b)Explain why the high carbon dioxide concentration curve reaches a higher rate of photosynthesis than the low carbon dioxide concentration curve at light intensities above 20 units.(2)

(c)The experiment was repeated for the high carbon dioxide concentration curve at a higher constant temperature, still below the optimum temperature for photosynthesis. Predict and explain the effect this would have on the maximum (plateau) rate of photosynthesis reached.(2)

(Total for Question 10 is 6 marks)

A group investigated the effect of temperature on the rate of photosynthesis of pondweed, keeping light intensity and carbon dioxide concentration constant. Their results are shown in the table below.

Temperature (degrees C): 10, 20, 30, 40, 45, 50
Rate of photosynthesis (arbitrary units): 4, 9, 15, 18, 10, 2

(a)Describe how the rate of photosynthesis changes as temperature increases from 10 to 40 degrees C.(2)

(b)Describe and explain the change in the rate of photosynthesis between 40 and 50 degrees C.(3)

(c)State the approximate optimum temperature for photosynthesis shown by this data.(1)

(Total for Question 11 is 6 marks)

A student used a gas syringe to collect the oxygen gas produced by a piece of pondweed placed under a bright lamp. In 5 minutes, the gas syringe collected 12.5 cm³ of oxygen gas.

(a)Calculate the mean rate of oxygen production, in cm³ per minute.(2)

(b)Convert this rate into mm³ per second. Show your working.(3)

(Total for Question 12 is 5 marks)

A gardener named Kwame compared the mean mass of tomatoes produced per plant under three different glasshouse conditions over one growing season.

Condition A (no additional carbon dioxide or light): 2.4 kg per plant
Condition B (additional carbon dioxide only): 3.0 kg per plant
Condition C (additional carbon dioxide and additional light): 3.9 kg per plant

(a)Calculate the percentage increase in mean mass per plant between Condition A and Condition C.(3)

(b)Suggest why Condition C produced a greater mean mass per plant than Condition B, even though both conditions included additional carbon dioxide.(2)

(Total for Question 13 is 5 marks)

Commercial glasshouse (greenhouse) growers can increase crop yields by artificially controlling carbon dioxide concentration, light intensity and temperature. However, installing and running this equipment has financial costs.

Evaluate the economic (financial) advantages and disadvantages for a commercial grower of installing carbon dioxide enrichment and supplementary lighting equipment in a glasshouse, in order to increase crop yield.

(Total for Question 14 is 6 marks)

A different grower currently produces 45 tonnes of tomatoes per year without carbon dioxide enrichment, selling them at £850 per tonne. Installing a carbon dioxide enrichment system is predicted to increase the yield to 54 tonnes per year. The system would cost £2400 per year to run (this does not include the cost of installing the equipment).

(a)Calculate the percentage increase in yield predicted for the carbon dioxide enrichment system.(2)

(b)Calculate the extra revenue (income) per year predicted from the increased yield.(2)

(c)Calculate the net financial benefit per year (the extra revenue minus the running cost) of installing the system.(2)

(d)The carbon dioxide enrichment system itself costs £15000 to install. Calculate how many years it would take for the net financial benefit to pay back this installation cost. Give your answer to 1 decimal place.(3)

(Total for Question 15 is 9 marks)

In an experiment, it was found that for every 22 g of carbon dioxide absorbed by a plant during photosynthesis, 15 g of glucose was produced (assuming none of the glucose was used for anything else during the experiment).

(a)Calculate the mass of glucose that would be produced from 264 g of carbon dioxide, assuming the same ratio applies. Show your working.(3)

(b)A student claims that doubling the mass of carbon dioxide supplied to a plant will always exactly double the mass of glucose produced by the plant in a given time. Evaluate this claim, using the idea of limiting factors.(2)

(c)In a real experiment using this ratio, the actual mass of glucose produced from 264 g of carbon dioxide was only 165 g, not 180 g as calculated in part (a). Suggest one reason for this difference.(2)

(Total for Question 16 is 7 marks)

A commercial grower recorded the rate of oxygen production by photosynthesis from a crop in a glasshouse with supplementary lighting, over a 24-hour period. Oxygen was produced at a constant rate of 45 cm³ per minute throughout the 12 hours of daylight (from 06:00 to 18:00), and photosynthesis did not occur during the remaining 12 hours of darkness.

(a)Calculate the total volume of oxygen produced by photosynthesis during the 12 hours of daylight. Give your answer in dm^3.(4)

(b)Suggest why the rate of oxygen production by photosynthesis would not actually stay exactly constant throughout the 12 hours of daylight in a real glasshouse without supplementary lighting.(2)

(Total for Question 17 is 6 marks)

A student named Freya investigated the effect of distance from a lamp on the rate of photosynthesis of pondweed, by counting bubbles of oxygen produced per minute. Her results are shown in the table below.

Distance from lamp (cm): 10, 20, 30, 40, 50
Bubbles of oxygen produced per minute: 58, 33, 19, 34, 8

(a)Identify the anomalous result in Freya's data, and explain why it is anomalous.(2)

(b)Suggest one improvement Freya could make to her method to obtain more reliable results.(2)

(Total for Question 18 is 4 marks)

Mark scheme · B4a Photosynthesis

Question 1

(a) B1 the process by which plants (and algae) make glucose (food), using carbon dioxide and water, with light energy, oe
(a) Answer: The process by which plants (and algae) make glucose using carbon dioxide and water, using light energy.
(b) B1 carbon dioxide
(b) B1 water
(b) Answer: Carbon dioxide and water.
(c) B1 glucose
(c) B1 oxygen
(c) Answer: Glucose and oxygen.
(d) B1 light energy cao
(d) Answer: Light energy.

Question 2

(a) B1 chloroplast cao
(a) Answer: Chloroplast.
(b) B1 chlorophyll cao
(b) Answer: Chlorophyll.
(c) B1 contains many chloroplasts, oe
(c) B1 is a tall, narrow (column-shaped) cell positioned near the top (upper surface) of the leaf, so many cells can be packed into the region that receives most light, oe
(c) Answer: Any two of: contains many chloroplasts; is a tall, narrow cell packed near the top of the leaf, where most light is absorbed.

Question 3

(a) B1 endothermic cao
(a) Answer: Endothermic.
(b) B1 energy is transferred (taken in) from the environment to the chloroplast/plant, oe
(b) B1 this light energy is transferred to (stored in) the chemical bonds of the glucose that is produced, oe
(b) Answer: Energy (light energy) is taken in from the environment, and is transferred to (stored in) the chemical bonds of the glucose produced.

Question 4

(a) M1 correctly balances at least two of the three formulae that need a coefficient (6CO2, 6H2O, 6O2), oe
(a) A1 fully balanced: 6CO2 + 6H2O -> C6H12O6 + 6O2, cao
(a) Answer: 6CO2 + 6H2O -> C6H12O6 + 6O2
(b) B1 (g) correctly used for carbon dioxide and for oxygen
(b) B1 (l) correctly used for water and (aq) correctly used for glucose
(b) Answer: 6CO2(g) + 6H2O(l) -> C6H12O6(aq) + 6O2(g)

Question 5

(a) B1 (aerobic) respiration cao
(a) Answer: (Aerobic) respiration.
(b) B1 starch is insoluble, oe
(b) B1 so it does not dissolve and draw water into the cell by osmosis (does not affect the cell's water potential), or: it is a large, compact molecule that is well suited to storage, oe
(b) Answer: Starch is insoluble, so (unlike glucose) it does not dissolve and affect the movement of water into the cell by osmosis.
(c) B1 cellulose cao
(c) Answer: Cellulose.
(d) B1 glucose is combined (reacts) with nitrate ions to produce amino acids, oe
(d) B1 these amino acids are then used to build proteins, oe
(d) Answer: Glucose is combined with nitrate ions (absorbed from the soil) to produce amino acids, which are then used to build proteins.
(e) B1 lipids (fats/oils) cao
(e) Answer: Lipids (fats or oils).

Question 6

(a) B1 a factor that, when in short supply, restricts (limits) the rate of a process such as photosynthesis, oe
(a) Answer: A factor that, when in short supply, restricts the rate of a process (such as photosynthesis).
(b) B1 light intensity
(b) B1 carbon dioxide concentration
(b) B1 temperature
(b) Answer: Light intensity, carbon dioxide concentration and temperature.
(c) B1 to prevent any one of these factors from becoming too low and limiting the rate of photosynthesis, keeping growth and crop yield as high as possible, oe
(c) Answer: To prevent any one factor from being too low and limiting the rate of photosynthesis, so growth and yield stay as high as possible.

Question 7

(a) B1 as light intensity increases from 0 to 60 units, the rate of photosynthesis increases, oe
(a) B1 above a light intensity of 60 units, the rate stays constant (levels off / reaches a plateau), oe
(a) Answer: The rate of photosynthesis increases as light intensity increases from 0 to 60 units, then stays constant (levels off) above 60 units.
(b) B1 above this point, light intensity is no longer the limiting factor, oe
(b) B1 another factor (e.g. carbon dioxide concentration or temperature) has become the limiting factor instead, oe
(b) Answer: Above 60 units, light intensity is no longer limiting the rate; another factor (such as carbon dioxide concentration or temperature) has become the limiting factor instead.
(c) B1 increase the carbon dioxide concentration, or increase the temperature (up to the optimum), oe
(c) B1 because this factor was now limiting the rate, so increasing it would allow the rate of photosynthesis to rise again, oe
(c) Answer: Increase the carbon dioxide concentration (or increase the temperature, up to the optimum), because one of these factors is now limiting the rate, and increasing it would allow the rate to rise further.

Question 8

(a) B1 independent variable: distance between the lamp and the pondweed (light intensity), oe
(a) B1 dependent variable: number of bubbles produced per minute (rate of oxygen/gas production), oe
(a) Answer: Independent variable: distance of the lamp from the pondweed. Dependent variable: number of bubbles (of oxygen) produced per minute.
(b) B1 named variable, e.g. carbon dioxide concentration, oe (accept temperature, or species/length of pondweed)
(b) B1 control method, e.g. using the same concentration of sodium hydrogencarbonate solution each time, oe (accept: controlling temperature with a water bath, if temperature named)
(b) Answer: Carbon dioxide concentration, controlled by using the same concentration of sodium hydrogencarbonate solution in every test.
(c) B1 hazard, e.g. electric shock from the lamp near water, or burns from a hot lamp bulb, oe
(c) B1 control measure, e.g. keep electrical connections away from water/spillages, or allow the lamp to cool before touching it, oe
(c) Answer: Hazard: electric shock from the lamp being used near water. Control measure: keep all electrical connections away from water and any spillages.
(d) B1 use a gas syringe (or an inverted, water-filled measuring cylinder/burette) to collect the gas, oe
(d) B1 so the actual volume of gas produced over a set time can be measured directly, rather than relying on counting bubbles of varying size, oe
(d) Answer: Use a gas syringe to collect the gas, so the actual volume produced over a set time can be measured directly, rather than counting bubbles of varying size.

Question 9

(a) B1 the relative light intensity decreases (gets smaller) cao
(a) Answer: It decreases.
(b) M1 method: squares the distance then takes the reciprocal (1 / d²), shown for d = 15 cm
(b) A1 d = 15 cm: 4.44 x 10^-3 cm^-2 (awrt), cao
(b) M1 method correctly applied again for d = 45 cm
(b) A1 d = 45 cm: 4.94 x 10^-4 cm^-2 (awrt), cao
(b) Answer: d = 15 cm: 4.44 x 10^-3 cm^-2. d = 45 cm: 4.94 x 10^-4 cm^-2.
(c) B1 light intensity from a lamp follows an inverse square law with distance from the source, oe
(c) B1 so 1 / distance² is proportional to the actual light intensity reaching the pondweed, whereas distance alone is not, oe
(c) Answer: Light intensity follows an inverse square law with distance, so 1 / distance² is proportional to the actual light intensity reaching the pondweed, unlike distance alone.

Question 10

(a) B1 at these light intensities, light intensity (not carbon dioxide concentration) is the limiting factor for both curves, oe
(a) B1 so increasing the carbon dioxide concentration has no effect on the rate until light intensity is no longer limiting, oe
(a) Answer: Light intensity, not carbon dioxide concentration, is the limiting factor at these light intensities for both curves, so extra carbon dioxide makes no difference until light is no longer limiting.
(b) B1 above a light intensity of 20 units, carbon dioxide concentration becomes the limiting factor for the low CO2 curve, oe
(b) B1 since the high CO2 curve has more carbon dioxide available, the rate can keep increasing to a higher value before another factor becomes limiting, oe
(b) Answer: Above 20 units, carbon dioxide becomes the limiting factor for the low-CO2 curve. With more carbon dioxide available, the high-CO2 curve can reach a higher rate before another factor limits it.
(c) B1 the maximum rate reached would be higher than before, oe
(c) B1 because temperature was below the optimum, increasing it increases the rate of the enzyme-controlled reactions of photosynthesis, allowing a higher rate to be reached provided light and carbon dioxide are not limiting, oe
(c) Answer: The maximum rate would be higher, because temperature was below the optimum, so raising it speeds up the enzyme-controlled reactions of photosynthesis (provided light and CO2 are not limiting).

Question 11

(a) B1 the rate of photosynthesis increases as temperature increases, oe
(a) B1 correctly uses data from the table to support this, e.g. from 4 units at 10 degrees C to 18 units at 40 degrees C, oe
(a) Answer: The rate of photosynthesis increases steadily as temperature rises, from 4 units at 10 degrees C to 18 units at 40 degrees C.
(b) B1 the rate decreases (falls sharply), oe
(b) B1 this is because the enzymes involved in the reactions of photosynthesis begin to denature above the optimum temperature, oe
(b) B1 the active site of the enzyme changes shape, so the substrate can no longer bind (fit), reducing the rate of the enzyme-controlled reactions, oe
(b) Answer: The rate falls sharply, because above the optimum temperature the enzymes involved in photosynthesis denature; the active site changes shape so the substrate can no longer bind, slowing the reactions.
(c) B1 40 degrees C cao (accept any value in the range 38-42 degrees C, since the exact peak is not shown by the data given)
(c) Answer: Approximately 40 degrees C.

Question 12

(a) M1 12.5 / 5, oe
(a) A1 2.5 cm³/min cao
(a) Answer: 2.5 cm³ per minute.
(b) M1 converts cm³ to mm³: 2.5 x 1000 = 2500 (mm³ per minute), oe
(b) M1 converts per minute to per second: 2500 / 60, oe
(b) A1 41.7 mm³/s (awrt), cao
(b) Answer: 41.7 mm³ per second (or 41.67 mm³/s to 2 decimal places).

Question 13

(a) M1 3.9 - 2.4 = 1.5, oe
(a) M1 (1.5 / 2.4) x 100, oe
(a) A1 62.5% cao
(a) Answer: 62.5%
(b) B1 in Condition B, light intensity may still have been limiting the rate of photosynthesis, even with extra carbon dioxide supplied, oe
(b) B1 adding extra light as well, in Condition C, removed this second limiting factor, allowing a higher rate of photosynthesis (and so more glucose for growth), oe
(b) Answer: In Condition B, light intensity may still have been limiting the rate of photosynthesis. Adding extra light too, in Condition C, removed this limiting factor, allowing a higher rate of photosynthesis and more growth.

Question 14

Level 3 (5-6): A detailed, logically structured evaluation of both the financial advantages and disadvantages of installing carbon dioxide enrichment and supplementary lighting, leading to a clear, justified conclusion about whether it is likely to be worthwhile for a grower. Correct scientific and economic terminology is used throughout.
Level 2 (3-4): A description of some financial advantages and disadvantages of the equipment, with a simple attempt to weigh them against each other, though the reasoning or conclusion may be incomplete or one-sided.
Level 1 (1-2): Basic, isolated statements are made about the cost or benefit of controlling growing conditions, with little or no attempt to compare them or reach a justified conclusion.
Level 0 (0): No relevant content.
Indicative content:
- Installing carbon dioxide enrichment and supplementary lighting equipment has an initial (capital) cost to purchase and install.
- There are ongoing running costs, such as electricity for lighting and heating, and the cost of the carbon dioxide supplied (or fuel burned to produce it).
- Removing light intensity or carbon dioxide concentration as a limiting factor increases the rate of photosynthesis, increasing the amount of glucose produced and so increasing plant growth and crop yield.
- A higher yield means more produce to sell, increasing the grower's revenue (income).
- Supplementary lighting can also extend the growing season or allow crops to be grown earlier or out of season, when selling prices may be higher.
- However, if only one limiting factor is removed (e.g. only carbon dioxide added, while light is still limiting), the increase in yield may be smaller than expected, giving a poorer return on the investment.
- There are diminishing returns: once light and carbon dioxide are no longer limiting, another factor (e.g. temperature) may limit the rate, so increasing light and carbon dioxide further gives little extra benefit for the additional cost.
- The extra revenue from the increased yield must be compared with the running costs to calculate the net financial benefit each year.
- The initial equipment cost is only recovered (paid back) over a number of years, so the investment is more worthwhile if the equipment lasts a long time and running costs stay low relative to the extra revenue generated.
- A justified conclusion should weigh the increase in revenue from higher yield against the installation and ongoing running costs, for example concluding that the investment is worthwhile if the payback period is short compared with the expected lifetime of the equipment, or not worthwhile if running costs are high relative to the extra revenue gained.
- Credit any scientifically and economically accurate evaluation that is clearly supported by comparing the costs and financial benefits described.

Question 15

(a) M1 (54 - 45) / 45 x 100, oe
(a) A1 20% cao
(a) Answer: 20%
(b) M1 9 (tonnes) x £850, oe
(b) A1 £7650 cao
(b) Answer: £7650
(c) M1 7650 - 2400 (ft from (b)), oe
(c) A1 £5250 cao (ft from (b))
(c) Answer: £5250
(d) M1 15000 / their (c), oe
(d) M1 15000 / 5250, method correctly shown
(d) A1 2.9 years (awrt), cao (ft from (c))
(d) Answer: 2.9 years

Question 16

(a) M1 264 / 22 = 12 (scale factor), oe
(a) M1 12 x 15, method shown
(a) A1 180 g cao
(a) Answer: 180 g
(b) B1 this is not necessarily true for a real plant, oe
(b) B1 the calculation in part (a) assumes carbon dioxide is the only limiting factor; if light intensity or temperature is limiting instead, doubling the carbon dioxide supplied would not double the actual mass of glucose produced, oe
(b) Answer: Not necessarily true. The calculation assumes carbon dioxide is the only limiting factor; if light intensity or temperature is limiting instead, doubling the carbon dioxide would not double the actual mass of glucose produced.
(c) B1 light intensity or temperature may have been a limiting factor during the experiment, oe
(c) B1 so the extra carbon dioxide could not be used at the maximum possible rate, meaning less glucose than predicted was produced, oe
(c) Answer: Light intensity or temperature may have been limiting the rate of photosynthesis during the experiment, so the plant could not use all the carbon dioxide at the maximum possible rate, producing less glucose than predicted.

Question 17

(a) M1 converts 12 hours to minutes: 12 x 60 = 720 (minutes), oe
(a) M1 total volume in cm³ = 45 x 720, oe
(a) M1 45 x 720 = 32400 (cm³), oe
(a) A1 32.4 dm³ cao
(a) Answer: 32.4 dm³
(b) B1 natural light intensity changes throughout the day (e.g. rising after sunrise, then falling before sunset), oe
(b) B1 since light intensity is a limiting factor, the rate of photosynthesis (and oxygen production) would rise and fall with it, rather than staying constant, oe (accept: temperature also varies through the day and could also cause the rate to vary)
(b) Answer: Natural light intensity rises and falls through the day. Since light intensity is a limiting factor, the rate of photosynthesis (and oxygen production) would rise and fall with it, rather than staying constant.

Question 18

(a) B1 the result at 40 cm (34 bubbles per minute) is anomalous, oe
(a) B1 because it does not fit the pattern of decreasing bubble production with increasing distance shown by the rest of the data (it is higher than the neighbouring results at 30 cm and 50 cm), oe
(a) Answer: The result at 40 cm (34 bubbles per minute) is anomalous, because it is higher than the neighbouring results at 30 cm and 50 cm and does not fit the decreasing pattern shown by the rest of the data.
(b) B1 repeat each distance (e.g. three times) and calculate a mean rate, oe
(b) B1 this would allow anomalous results to be identified and excluded, and reduce the effect of random errors on the conclusion, oe
(b) Answer: Repeat each distance (e.g. three times) and calculate a mean, so anomalous results can be identified and excluded and random error is reduced.

Photosynthesis - Worksheets, Questions and Revision