Question 1
1
Isoprene is a chemical synthesized and emitted in large amounts by some plant species, especially oak (Quercus sp.) and poplar (Populus sp.) trees. It has been suggested that isoprene increases the tolerance of plants to high temperatures, which can cause a decrease in photosynthesis rates. Black poplar (Populus nigra) plants were subjected to two raised temperatures and to drought. Measurements of photosynthesis and isoprene emission were made during a 35-day-long drought stress (drought period) and 3 and 15 days after re-watering stressed plants (recovery period). The rate of photosynthesis was recorded as the carbon dioxide taken up per unit of leaf area per second.
18 marks
Question 1(a)
1(a)
Suggest one method other than measuring \(\mathrm{CO}_{2}\) uptake by which the rate of photosynthesis could have been measured in these experiments.
Easypractical1 marks
Answer
oxygen production/release; (not count bubbles) production/increase/change/ measurement of biomass;
Question 1(b)
1(b)
Suggest why heat treatment may reduce photosynthesis rates.
Mediumshort_answer2 marks
Answer
high/higher than optimum temperatures denature enzymes (of Calvin cycle); ribulose bisphosphate carboxylase/rubisco stops working/does not bind substrate; wilting / withering / loss of water / decrease in turgor / increased transpiration; closure/reduced aperture of stomata; lower \(\mathrm{CO}_{2}\) level inside leaf / reduced \(\mathrm{CO}_{2}\) diffusion/uptake into leaf;
Question 1(c)
1(c)
Outline the effect of drought and of re-watering on the rate of photosynthesis.
Mediumdata_response1 marks
Answer
rate decreases/drops (to zero) with drought and increases when re-watered/ recovering
Question 1(d)
1(d)
Describe the isoprene emissions during the drought and recovery periods at \(25^{\circ} \mathrm{C}\).
Mediumdata_response2 marks
Answer
slight decrease/constant initially then falls / falls increasingly rapidly /decreases exponentially (in drought/up to Day 35); increases almost to original level/ but doesn't reach original level / rapidly at first then less rapidly / increases then reaches plateau (during recovery/after Day 35);
Question 1(e)
1(e)
Compare the effect of the two temperatures on the emission of isoprene. The effect of isoprene on photosynthesis was assessed in detached oak leaves that were supplied either water (control) or fosmidomycin dissolved in water. Fosmidomycin inhibits the emission of isoprene without affecting photosynthesis. The measurements were taken at 30^ C, but at three points in the experiment the leaves were subjected to heat treatment of 46^ C (indicated on the graph by the arrows). The rate of photosynthesis was measured as uptake of CO_2 in µ mol m^-2 s^-1.
Mediumdata_response2 marks
Answer
higher/greater (emission) at 35^ C than 25^ C during both drought and recovery; both at (approximately) same level at end of drought period/at 35 days; both increase during recovery but not to original level; less/little difference in emission between temperatures during recovery/after watering / converse;
Question 1(f)
1(f)
State the effect of heat treatment on the rate of photosynthesis.
Easydata_response1 marks
Answer
decreases (rate of photosynthesis);
Question 1(i)
1(i)
State the difference in percentage recovery of photosynthesis 1 hour after heat treatment between the \(22 \mu \mathrm{Ldm}^{-3}\) isoprene treatment and the \(0 \mu \mathrm{Ldm}^{-3}\) isoprene treatment.
Easydata_response1 marks
Answer
26 (\%) (Allow a range of 25 % to 27 % )
Question 1(j)
1(j)
Explain the evidence provided by the data in the bar chart for the hypothesis that isoprene improves plants' tolerance to high temperatures.
Mediumdata_response2 marks
Answer
faster recovery with isoprene than without/than with water treatment; recovery faster/better/improved with higher isoprene concentration (than lower); after both time periods / after 24 hours and 1 hour;
Question 1(k)
1(k)
Suggest two reasons for some plant species synthesizing and emitting isoprene, but not other plant species such as common beans.
Hardshort_answer2 marks
Answer
different plants live in/evolved in/are adapted to different temperature regimes; (selective) advantage for plants that produce isoprene in high temperature regions; isoprene synthesis uses energy/materials/only beneficial at high temperatures; some plants do not have the enzymes/genes for making isoprene;
Question 1
1
Ozone gas in the atmosphere helps to block high-energy ultraviolet light (UV) from reaching the Earth's surface. Over the past few decades, the ozone layer has been decreasing, thus allowing through more UV. The effect of this decrease in the ozone has been studied in different plants. An early study was undertaken on patience dock plants (Rumex patientia) to test the effect of atmospheric ozone levels decreasing by 38 %. The net photosynthesis (total photosynthesis minus total respiration) and respiration of the plants were measured during seven days of exposure to UV. The rates of photosynthesis and respiration are given in rates of carbon dioxide uptake per unit area of leaf.
10 marks
Question 1(a)
1(a)
Calculate the decrease in the net photosynthesis from day 1 to day 7 in the plants exposed to UV. Workings should be shown and units given.
Mediumstructured1 marks
Answer
\(10.0-8.0=2 \mathrm{mg} \mathrm{CO}_{2} \mathrm{dm}^{-2} \mathrm{hr}^{-1}\) (units needed) Accept answers in the range of (1.9-2.1) \(\mathrm{mgCO}_{2} \mathrm{dm}^{-2} \mathrm{hr}^{-1}\) to \(2.1 \mathrm{mgCO}_{2} \mathrm{dm}^{-2} \mathrm{hr}^{-1}\). Do not accept negative values in the final answer.
Question 1(b)
1(b)
Distinguish between the results for the plants exposed to UV and the controls without UV in
0 marks
Question 1(b)(i)
1(b)(i)
net photosynthesis.
Easystructured2 marks
Answer
net photosynthesis of control is always greater than plants exposed to UV; UV causes a sharp drop in net photosynthesis (after day 3) while control rises slightly/remains the same; UV does not affect the net photosynthesis (rises slightly) between day 1 and day 3 while control drops slightly in same period;
Question 1(c)
1(c)
The rate of photosynthesis can be measured by the rate of carbon dioxide uptake. State two other ways that the rate of photosynthesis may be measured. Some recent measurements indicate a 60 % thinning of the ozone layer in some parts of the atmosphere.
Mediumstructured2 marks
Answer
production of \(\mathrm{O}_{2}\); increase/change in biomass; Accept alternate valid techniques for measuring photosynthetic rate eg starch production.
Question 1(d)
1(d)
Predict the possible effect on R. patientia plants.
Mediumstructured2 marks
Answer
(greater) decrease in (net) photosynthesis / decrease in oxygen production / less \(\mathrm{CO}_{2}\) uptake; slower growth / reduced (rate of) biomass production; (slightly) more respiration;
Question 1(e)
1(e)
Another study was undertaken to investigate the cumulative effects of different levels of UV over a six week period on net photosynthesis in soybean (Glycine max). One set of plants was in full sunlight (unshaded) and the other set received only 12 % of full sunlight ( 88 % shaded). UV was given using lamps above all of the plants. Compare the results of the unshaded and shaded plants.
Hardstructured2 marks
Answer
net photosynthesis for unshaded plants always greater than the shaded / unshaded was always more than \(10 \mathrm{mg} \mathrm{CO}_{2} \mathrm{dm}^{-2}\) while shaded was always less than 10 mg \(\mathrm{CO}_{2} \mathrm{dm}^{-2}\); (overall) both decreased with increasing UV doses/(overall) negative relationship; net photosynthesis reduced more for shaded than unshaded plants; as UV increases there was greater fluctuation in the response of unshaded plants than in shaded;
Question 1
1
Sockeye salmon (Oncorhynchus nerka) spend the first years of their lives in the freshwater lakes of Alaska before migrating to marine waters. Their first months in marine waters are spent foraging and growing near the shore line. They then move to offshore regions of the North Pacific Ocean for 2 to 3 years. The graph shows fork length frequency of juvenile O. nerka caught during their first months in marine waters in autumn 2008 and ocean age one O. nerka caught 15 months later during winter 2009 in the North Pacific Ocean.
14 marks
Question 1(e)
1(e)
Outline any correlation between total lipid content and fork length in autumn 2008 and in winter 2009. Autumn 2008: Winter 2009:
Mediumdata_response2 marks
Answer
autumn 2008: positive correlation / fork length increases as lipid content increases; winter 2009: no correlation / no overall trend; (reject "constant" or "almost same")
Question 1
1
\(R_{\mathrm{f}}\) values for photosynthetic pigments may be determined using the technique of thin-layer chromatography (TLC).
6 marks
Question 1(a)
1(a)
Outline what happens when spinach extract is spotted on a TLC plate and placed into a container of solvent.
Mediumstructured2 marks
Answer
a. solvent will move up «the TLC plate/stationary phase» b. pigments will move up «the TLC plate/stationary phase carried by solvent» c. pigments will move at different rates/separate 2 max
Question 1(b)
1(b)
Explain what the \(R_{\mathrm{f}}\) values represent in chromatography.
Easystructured3 marks
Answer
a. \(R_{\mathrm{f}}=\frac{\text { distance moved by pigment }}{\text { distance moved by solvent «front» }}\) OR distance moved by pigment relative to distance moved by solvent b. each pigment has/is represented by a specific \(R_{\mathrm{f}}\) «value» c. used to identify different pigments d. \(R_{\mathrm{f}}\) «value» depends on density/solubility/polarity of the pigment in solvent Allow "compound" or "molecule" instead of pigment 3 max
Question 1(c)
1(c)
State two photosynthetic pigments that could be identified using chromatography. 1. 2.
Easystructured1 marks
Answer
chlorophyll carotene xanthophyll Accept other valid pigments Do not accept pigments named by colour Award [1] for any two correct Award [1] for chlorophyll a AND (chlorophyll) b 1 max
Question 1
1
Chromatography is a technique used to separate the components of a mixture. The photosynthetic pigments from three organisms were separated by thin layer chromatography: spinach (Spinacia oleracea), a red alga (Porphyra) and a brown alga (Fucus).
3 marks
Question 1(a)
1(a)
Identify a pigment found in all three organisms.
Easystructured1 marks
Answer
chlorophyll a OR \(\beta\) carotene
Question 1(b)
1(b)
Compare and contrast absorption spectra and action spectra.
Mediumstructured2 marks
Answer
a. horizontal axis for both is wavelength/colour OR «for a chloroplast/cells/leaves/plants extract» they will have the same/similar shape b. an action spectrum shows the rate of photosynthesis «in chloroplasts/ cells/leaves/plants» and an absorption spectrum shows the absorption of light Marking point a. may be shown with a diagram. 2 max
Question 1(c)
1(c)
Porphyra also contains phycoerythrin, which is a red pigment.
0 marks
Question 1(c)(i)
1(c)(i)
Suggest a reason for phycoerythrin being absent from the Porphyra chromatogram.
Mediumstructured1 marks
Answer
a. the pigment didn't dissolve / was insoluble when the pigments from the algae were extracted b. the pigment was not moved by / was insoluble in the solvent used to separate the pigments
Question 1(c)(ii)
1(c)(ii)
Predict one colour of light that will be absorbed efficiently by phycoerythrin.
Easystructured1 marks
Answer
orange/yellow/green/blue/violet
Question 1
1
A variegated Pelargonium plant was grown outdoors in a plant pot. Figure 1 shows one leaf of the Pelargonium. The plant was left in the dark for 24 hours to inhibit photosynthesis. After this time, a sketch was made of the leaf to show the colours (Figure 2), then part of the leaf was covered with black card (Figure 3). Following the exposure of the plant to sunlight for six hours, the black card was removed and the leaf tested for starch (Figure 4).
2 marks
Question 1(a)
1(a)
Outline a reason for inhibiting photosynthesis for 24 hours.
Mediumstructured1 marks
Answer
to remove any starch already in the leaf OR so any starch found in the leaf was made during the experiment OR to prevent further production of starch
Question 1(b)
1(b)
0 marks
Question 1(b)(i)
1(b)(i)
Identify which two areas, W, X, Y or Z , in Figure 4 show that light is required for photosynthesis.
Mediumstructured1 marks
Answer
X AND Y Both needed
Question 1(b)(ii)
1(b)(ii)
Identify which two areas, W, X, Y or Z , in Figure 4 show that chlorophyll is required for photosynthesis.
Mediumstructured1 marks
Answer
W AND X Both needed
Question 1(b)(iii)
1(b)(iii)
Discuss briefly whether the detection of starch in this experiment was proof that photosynthesis had occurred in the leaf.
Hardstructured2 marks
Answer
pro (yes it could be evidence): a. starch is a product of photosynthesis con (not necessarily evidence): b. starch could be made elsewhere «in the plant» and transported to/stored in leaves OR starch could be made by another process «other than photosynthesis» OR starch is being detected although glucose is the direct product limitations of experiment: c. starch depletion may take more than 24 hours «of dark» OR starch production may take more than 6 hours «of light» OR starch should have been measured before and after OWTTE 2 max
Question 1(c)
1(c)
0 marks
Question 1(c)(i)
1(c)(i)
Using the axes, sketch the action spectrum for photosynthesis in the green area of the leaf in Figure 1.
Mediumstructured1 marks
Answer
sketch showing 2 peaks at either end of the spectrum Rate
Question 1(c)(ii)
1(c)(ii)
Predict how the action spectrum from the white areas of the leaf would differ from the green areas.
Mediumstructured1 marks
Answer
it would be a straight line/have no peaks OR no photosynthesis Accept a labelled horizontal line in the bottom third of the y-axis. Do not accept "lower line" or "lower photosynthesis"
Question 1(d)
1(d)
Suggest reasons that plants with variegated leaves are rarely found growing wild naturally.
Mediumstructured1 marks
Answer
«having the leaf partly white would be» no selective advantage/cannot compete OR natural selection would reduce the frequency of the mutation causing variegated leaves OR occur due to artificial selection Some reference to evolution or natural selection required Do not accept reference to photosynthesis alone
Question 1
1
A community living in the water of an estuary was used to investigate how climate change may affect ecological systems. The food web in this community included phytoplankton (producers), zooplankton (consumers) and saprotrophic bacteria. Small plastic mesocosms were set up with water from the estuary containing only these three groups of organisms. The mesocosms were subjected to four different temperatures and two nutrient levels (control and nutrients added) to replicate local variations of the conditions in the estuary during springtime warming. The graph shows the biomass of the community for each of the eight mesocosms at the end of the experimental period. Biomass was measured in terms of the amount of carbon present. The horizontal line indicates the initial biomass.
15 marks
Question 1(c)
1(c)
Chlorophyll concentration was used as an estimate of the photosynthetic capacity of the community. The rate of photosynthesis and mass of chlorophyll per unit volume were measured in a mesocosm at three different temperatures. Explain the effect of temperature on the rate of photosynthesis in this mesocosm.
Mediumstructured2 marks
Answer
rate of photosynthesis increases as temperature rises because: a temperature is the limiting factor for photosynthesis; b higher temperatures increase enzyme activity; c faster molecular motion/more molecular kinetic energy/more frequent enzyme-substrate collisions; d Calvin cycle/light independent reactions (of photosynthesis) speed up; 2 max
Question 1
1
An experiment on aerobic respiration was performed using a plant in a pot containing fertile soil. The apparatus was set up as shown in the diagram. Sodium hydroxide and limewater (calcium hydroxide) are both alkaline solutions. Limewater goes cloudy when carbon dioxide is bubbled into it.
0 marks
Question 1(d)
1(d)
The same apparatus was used in another experiment, but the potted plant was exposed to light. Predict with a reason the results for lime water in flask C after one hour.
Mediumstructured1 marks
Answer
no change/limewater stays clear OR because plant takes in carbon dioxide by photosynthesis; Do not accept references to oxygen produced by photosynthesis
Question 4
4
The graph shows the effect of light intensity on the rate of photosynthesis of a green plant at different \(\mathrm{CO}_{2}\) concentrations. The temperature is kept constant at \(25^{\circ} \mathrm{C}\). What is the limiting factor at × ? Chlorophyll \(\mathrm{CO}_{2}\) concentration Temperature Light intensity
Mediummcq1 marks
Answer
B
Question 5
5
The graph shows the rate of photosynthesis as light intensity increases at two different carbon dioxide ( CO_2 ) concentrations. \text { Key: }-0.40 \% \mathrm{CO}_{2} \quad \cdots \quad 0.04 \% \mathrm{CO}_{2} What are the limiting factors of photosynthesis at regions X and Y on the graph? \begin{tabular}{|c|c|c|} \hline & X & Y \\ \hline A. & CO_2 concentration & light intensity \\ \hline B. & temperature & light intensity \\ \hline C. & light intensity & CO_2 concentration \\ \hline D. & light intensity & temperature \\ \hline \end{tabular}
Mediummcq1 marks
Answer
C