4.1 Photosynthesis: Biology Practice Questions AQA GCSE
Figure 1 shows some of the products and reactants involved in photosynthesis. Draw lines to show the following: Which substances are the reactants of photosynthesis and which chemical formulae are used to represent these reactants. Which substances are the products of photosynthesis and which chemical formulae are used to represent these products.
A line to join reactants to carbon dioxide and water; A line to join products to oxygen and glucose; A line to join carbon dioxide to CO2 and water to H2O; A line to join oxygen to O2 and glucose to C6H12O6.
Stage 1 ofthe method described in part(b)refers to 'de-starching'the plants. Describe how a plant may be de-starched and explain the purpose of de-starching in stage 1.
A plant may be de-starched by... Placing it in the dark / preventing it from photosynthesising for 48 hours / a few days; The purpose of de-starching is... Any two from the following: To remove starch before the investigation begins / ensure plants start the investigation with no starch content in the leaves; It acts as a control variable / ensures valid results; (This shows that) starch present at the end of the investigation is produced during the investigation / 24 hour period.
Which of the following statements could explain the result identified in the previous question? A. Glucose produced in photosynthesis has been stored as starch in the leaf B. The plant has been carrying out transpiration so the leaves lack starch C. Starch has been made in the leaf during the process of respiration D. Glucose is stored as starch to be used protein synthesis
A. Glucose produced in photosynthesis has been stored as starch in the leaf
Plan an investigation to show how the rate of photosynthesis in pond plants is affected by changes in light intensity. You should include detail of the independent, dependent and control variables in your investigation.
An investigation into how light intensity affects the rate of photosynthesis could be carried out as follows: Any six from the following: Independent variable: change in light intensity; Dependent variable: the rate of photosynthesis; Control variable: the species / age / size of pondweed OR the temperature of the water OR availability of CO2; Set up apparatus with lamp a measured distance from pondweed (in beaker) / accept a correctly labelled diagram; Light intensity is inversely proportional to the square of the distance between lamp and plant; Measure the number of bubbles / volume of gas produced in a set time period; Repeat to ensure results are reliable / reproducible / identify anomalies / calculate mean of results.
Farmers wish to make as much profit as they can from their crops. What do farmers need to consider before making decisions about the best growing conditions for their plants?
Any two of the following: The cost of lighting / heating / providing conditions to enhance growth; The effect of providing conditions on profits / idea of limiting waste - e.g. too much of one factor would be wasteful; Example from Figure 2 e.g. increasing the carbon dioxide concentration above 400 ppm would be wasteful; The farmer may also choose to invest in fertilisers / minerals / pest control / weed killers; Eutrophication / leaching of fertilisers into the environment is a risk that should be considered OR the effect of pest control and weed killers on biodiversity / other species.
Figure 4 shows the changes in carbon dioxide uptake and release over a 24 hour period in a tomato plant. Explain what the graph shows at 7:30 and 19:30.
At 7:30 and 19:30... The rate of photosynthesis is equal to the rate of respiration; The plant is releasing the same amount of carbon dioxide as it is absorbing.
Explain how autotrophs are different from heterotrophs.
Autotrophs are different from heterotrophs because... Any one from the following: Autotrophs make their own food through photosynthesis whereas heterotrophs obtain their nutrition through consumption of other organisms; Autotrophs are producers where as heterotrophs are consumers.
Water is usually not considered a limiting factor of photosynthesis. Which statement explains why? A. Global warming means there are lots of floods and so there is plenty of water. B. If water availability is low, plants close their stomata to stop transpiration, meaning that photosynthesis is limited by carbon dioxide. C. Water cannot be measured using a measuring cylinder. D. Water is not needed for photosynthesis, only for respiration.
B. If water availability is low, plants close their stomata to stop transpiration, meaning that photosynthesis is limited by carbon dioxide.
Starch is a polymer of glucose which is stored in the roots of many plants. Explain as fully as you can, why it is advantageous to the plants to store carbohydrates as starch rather than as sugar.
Carbohydrates are better stored as starch than sugars because... Any three marks from the following: Starch is insoluble; (Therefore) it will not affect the concentration of the water in the roots OR water will not be taken in by osmosis; (Because it is insoluble) starch will remain in the cells of the roots / will not leave the cells of the roots; Glucose / simple sugars are soluble; (Therefore) they will diffuse out of the cell.
Figure 2 shows a plant cell with three cellular components labelled. Identify which of the following options gives the correct name and function of P, Q and R.
D
Photosynthesis is described as an endothermic reaction because it uses energy transferred from the environment to the chloroplasts in the leaves of the plant. State where the energy comes from to drive photosynthesis.
Energy that drives photosynthesis comes from sunlight / light (energy).
Identify one molecule which can be synthesised using glucose produced in photosynthesis.
Glucose can be used to build... Any one from the following: Starch; Cellulose / cell walls; Sucrose; Amino acids / proteins; DNA / RNA / nucleotides; Fats / oils / lipids.
A typical food chain in the Pacific Ocean is: phytoplankton → zooplankton → sardines → tuna Figure 1 shows how a number of factors in the ocean change across the year. Light intensity is a major factor in controlling the number of phytoplankton. Explain why.
Light intensity is a major factor controlling the number of phytoplankton because... Phytoplankton photosynthesise / are producers; Their growth depends upon light / energy they get (for photosynthesis) OR more light means more growth.
With reference to the amount of carbon dioxide released and taken in, Figure 4 can be used to indicate how the rate of photosynthesis changes throughout the 24 hour period, assuming that the rate of respiration is constant during this time. Explain how interactions between temperature and light intensity contribute towards the changes in photosynthesis represented in Figure 4.
Limiting factors interact to produce the trend shown in Figure 4 in the following ways... Any four from the following: The rate of carbon dioxide intake increases as the temperature and light intensity increase during the day; At the peak, around 15:00, carbon dioxide intake is highest / photosynthesis is occurring at the fastest rate as light intensity and temperature are at their highest point OR light intensity and temperature are not limiting so photosynthesis / carbon dioxide intake reaches a maximum rate OWTTE; After 15:00, carbon dioxide intake decreases / the rate of photosynthesis decreases due to a decrease in light intensity and temperature OR light intensity and temperature become limiting factors so the rate of photosynthesis decreases OWTTE; Overnight, more carbon dioxide is released than taken in; (This is because) photosynthesis stops as there is no sunlight.
Identify two limiting factors of photosynthesis.
Limiting factors of photosynthesis might include: Any two of the following: Light intensity; Carbon dioxide; Chloroplasts/chlorophyll; Temperature.
Several environmental factors can affect the rate of photosynthesis, including temperature and the availability of water. Describe and explain the effects of two other factors that affect the rate of photosynthesis. You should include one or more sketch graphs in your answer.
Other factors that can affect photosynthesis are as follows: Any five of the following: Factor: Light intensity; Carbon dioxide / CO2 concentration; Effect: As light intensity increases, the rate of photosynthesis increases more rapidly at first before levelling off OR award the mark for correct trend shown on a graph; As carbon dioxide increases, the rate of photosynthesis increases more rapidly at first before levelling off OR award the mark for correct trend shown on a graph; Explanation: Light intensity is needed to drive the reaction / provide energy; Carbon dioxide is one of the reactants / raw materials used in photosynthesis; The rate of photosynthesis levels off when another factor / named factor becomes limiting.
Scientists have predicted that the weather conditions of a particular mountainous region will be influenced by global warming over the next 50 years with two potential key outcomes: 1. An increase in average summer temperatures from approximately 20 to 22 °C 2. An increase in cloud cover What effect will this change in climate have on the growth of plants in that region. A. Respiration increases, photosynthesis increases, growth increases B. Respiration decreases, photosynthesis increases, growth increases C. Respiration increases, photosynthesis decreases, growth decreases D. Respiration decreases, photosynthesis increases, growth decreases
Plant growth requires glucose from photosynthesis so the 2 processes are interlinked. If respiration rates are high, then more glucose will be used in that reaction and so less is available to form plant biomass. In this question, increased cloud cover will reduce light intensity so the rate of photosynthesis will decrease. An increase in temperature increases the rate of respiration.
Green plants and algae synthesise glucose. Energy is required for this process. Where do plants get this energy from?
Plants get their energy in the following way: Light is trapped / absorbed; By chlorophyll / chloroplasts.
Plants growing in soils lacking magnesium ions do not grow to their full potential. Suggest why this is the case.
Plants growing in soil lacking magnesium do not grow to their full potential because... Magnesium is needed to produce chlorophyll; (Chlorophyll) absorbs light energy / is needed for photosynthesis; Photosynthesis is reduced SO plants produce less glucose / have less glucose for respiration/amino acids/cellulose.
Plants store some of the glucose that they produce in the form of starch. Give three other ways in which plants use glucose.
Plants use glucose in the following ways: Any three of the following: Respiration to release energy; Fats / oils for storage; Amino acids for proteins; Cellulose for cell walls.
The student sets up the same experiment as shown in part(b) but this time, puts some ice cubes into the beaker also. State what effect this may have on the rate of photosynthesis of the plant.
Putting ice cubes into the water would slow down / reduce the rate of photosynthesis in the aquatic plant.
The image in Figure 1 shows some strawberry plants growing in a greenhouse on a hot sunny day in August. Identify one limiting factor that will affect the rate of photosynthesis at this time? Explain your answer.
The factor that is most likely to be limiting at this time is... Carbon dioxide concentration; because atmospheric CO2 levels are very low (∼0.035%); OR Water; because there is no obvious irrigation system / only watering cans are used to water OR transpiration rates will be very high; AND Temperature is not limiting as it is a hot day; Light intensity is not limiting as it is a sunny day.
Figure 3 shows the effect of several different factors on the growth of tomato plants in a greenhouse. Describe and explain how temperature and light intensity, as recorded in Figure 3, affect the rate of photosynthesis of the tomato plants.
The factors that affect growth can be described as follows: For all light intensities, as temperature increases, the rate of photosynthesis increase until the optimum temperature Then the rate of photosynthesis decreases as temperature becomes too high The highest peak / optimum rate of photosynthesis occurs when light intensity is high The lowest peak / optimum is seen in low light intensity At low light intensity, the rate of photosynthesis reaches zero at 42 °C At high light intensity the rate of photosynthesis reaches zero at 49 °C Explanation The increase in photosynthesis occurs as temperature increases and becomes less of a limiting factor / enzyme activity is faster as temperature increases The decrease in photosynthesis occurs as enzymes become denatured OR stomata close so less carbon dioxide is taken in High light intensity gives the biggest peak because more light is available for photosynthesis / light is not a limiting factor Low light intensity gives the lowest peak because light is a limiting factor
Suggest why the farmer may not have achieved a rate of photosynthesis as high as the data in Figure 2 predicted.
The farmer may not have achieved a rate of photosynthesis as high as predicted because: Another factor is limiting photosynthesis; (This could include) carbon dioxide / light intensity.
With reference to Figure 3, which factors are limiting the rate of photosynthesis between points X and Y?
The following factors are limiting: Temperature; Light intensity.
A gardener used the results in Figure 4 to decide how much carbon dioxide to pump into the greenhouse. He decided to increase the atmospheric levels to 600 ppm rather than 700 ppm. Suggest why he made this decision.
The gardener made this decision because: There was no further increase in photosynthesis after 600 ppm; It would cost more to increase the levels higher than that / it would not be cost effective.
A gardener is setting up his greenhouse. He is given advice from two friends on the correct conditions for his greenhouse to grow the most vegetables. Friend X suggested that he provide plenty of water to his vegetables but should cover all the windows in black card to stop the plants getting too hot. Friend Y suggested that he provide plenty of water and open the windows of the greenhouse but did not suggest covering them. Should the farmer follow the advice of friend X or friend Y? Explain your choice.
The gardener should follow the advice of friend Y. Any one from the following: Opening the windows will keep the temperature cool; Covering the windows with black card will prevent light energy getting in OR light will be the limiting factor OR Plants need the light for photosynthesis.
A student wanted to test the effect of light intensity on the number of bubbles produced by an aquatic plant over one hour. Figure 3 shows how the student set up his investigation. Identify the gas being collected in the measuring cylinder which shows that the aquatic plant is photosynthesising.
The gas being produced by the pond plant is oxygen.
Plot the results from Table 1 onto an appropriate graph using the graph paper in Figure 2.
The graph should be plotted as follows: Sensible, linear scale; Axis labelled correctly (both X and Y); Points plotted correctly; Line chart with suitable line/curve of best fit; Units included.
The rate at which plants grow can be altered by changing the conditions in which they grow. A propagator is a container in which the temperature, light intensity and carbon dioxide concentration can be controlled. The graph in Figure 2 shows the effects of changing these factors on the growth of strawberry plants. Describe and explain the impact of increasing carbon dioxide concentration on the mean mass of strawberry plants at bright light and 20 °C.
The impact of increasing carbon dioxide concentration on the mass of strawberry plants in bright light and at 20 °C can be described and explained as follows: Any three of the following: (The mass of strawberries) increases up to 400 ppm carbon dioxide concentration OR an increase in carbon dioxide results in an increase in mass of strawberries us to 400 ppm; Carbon dioxide is the limiting factor up to 400 ppm; (Carbon dioxide is) the raw material / substrate for photosynthesis; (The mass of strawberries) remains the same / levels off after 400 ppm carbon dioxide concentration; Above 400 ppm, another factor / temperature is the limiting factor; (This is because) temperature / 20 °C is below (plant) enzyme optimum OR enzyme activity is reduced at lower temperatures.
A group of students wanted to investigate how the rate of photosynthesis is affected by temperature. They grew some tomato plants in a greenhouse on school grounds then cut disks from the leaves of the plants in their experiments. To show the rate of photosynthesis, the students measured the rate of carbon dioxide uptake by the leaf disks. In the dark, the leaf disks did not take up any carbon dioxide, but did produce it. Explain this observation.
The leaf disks produced carbon dioxide in the dark, and did not take up any carbon dioxide because... Photosynthesis cannot occur in the dark (as there is no light) OR there is no light for photosynthesis; Carbon dioxide is produced / is a product of (aerobic) respiration; Plants respire constantly / respire during the day and night OR in the dark, plants only respire.
A student set up an investigation into the limiting factors of photosynthesis. His set up is shown in Figure 5 below. Identify the limiting factor being investigated in this practical.
The limiting factor being investigated is light intensity.
Finding the optimum conditions for photosynthesis will ensure that growth is maximised. Using Figure 4, complete the following sentences to identify which conditions gave the fastest rate of photosynthesis and therefore, the maximum growth. Optimum temperature would be __________ Optimum carbon dioxide % would be __________ Optimum light intensity would be __________
The optimum conditions would be as follows: 30 °C; 600 ppm (or above); Bright light.
Over 24 hours, the tomato plant takes in more carbon dioxide than it releases. Explain the value of this to the tomato plant.
The plant takes in more carbon dioxide than it releases because... Any two from the following: There is more photosynthesis than respiration; Carbon / glucose / carbohydrate is stored in the biomass of the plant; The plant can grow / flower / store sugars.
Using the information from Figure 1, suggest two reasons why the population of phytoplankton decreases between summer and autumn.
The population of phytoplankton decreases between summer and autumn because... Any two from the following: In the summer, temperature is higher so the rate of photosynthesis is higher OR temperature decreases / it gets colder in autumn so the rate of photosynthesis decreases; There is less light / lower light intensity in autumn (compared to summer) so less photosynthesis; Minerals / nitrates / phosphates / potassium reach their lowest levels at the end of the summer, this will limit growth (of phytoplankton) into the autumn.
An investigation was carried out to test the effect of temperature on the rate of photosynthesis of pondweed. The volume of oxygen produced per hour was measured. The results can be seen in Table 1. Calculate the mean rate of photosynthesis per hour when the temperature was 45 °C.
The rate of photosynthesis at 45 °C should be calculated as follows: (1.9 + 2.2) ÷ 2; 2.1 cm3 / hour; OR (1.9 + 14.2 + 2.2) ÷ 3 = 6.1.
A farmer growing strawberries in his greenhouse used the results in Table 1 to decide on the best temperature for his greenhouse. He decided to heat the greenhouse to 30 °C. When the farmer measured the rate of photosynthesis of his plants, he found the rate to be 11.5% slower than the data suggested. Calculate the rate of photosynthesis that the farmer actually achieved at 30 °C.
The rate of photosynthesis that the farmer achieved at 30 °C can be calculated as follows: Predicted rate = 44 cm3 / hr; 11.5 % = (44 / 100) X 11.5 = 5.06; Actual rate = 44 - 5.06; = 38.94 / 38.9 / 39 cm3 hr-1;
State where a land-based plant would obtain the reactants of photosynthesis named in part(a).
The reactants would be obtained from: (Water from) the soil; (Carbon dioxide from) the air.
Describe and explain the results shown in the graph.
The results on the graph can be explained as follows: Any four from the following: As temperature increases, so does the rate of photosynthesis, up to 30 °C; This is because an increase in temperature increases enzyme activity / kinetic energy so the rate of reaction increases; After 30 °C the rate of photosynthesis decreases; This is because an increase in temperature past the optimum temperature results in enzymes being denatured so photosynthesis cannot occur; The optimum temperature is between 30 and 35 °C.
A student wanted to set up an investigation to show that photosynthesis requires carbon dioxide. The method they followed can be seen below: 1. De-starch 2 plants ofthe same species and size 2. Place each plant under a bell jar (bell jars A and B) 3. Put NaHCO in bell jar A with the first plant 4. Put NaOH solution in bell jarB with the second plant. 5. Place a bung with delivery tubes in the top of bell jar A and Bto allow an airflow 6. Add some soda lime to the inlettube ofjarB 7. Putthe apparatus in full sunlight and leave for 24 hours. 8. Observe the results ofthe investigation. The set up described in points 2 to 6 can be as seen in Figure 1. The independent variable in the investigation is the presence or absence of carbon dioxide. Suggest how stages 3, 4 and 6 allow the student to test the independent variable.
Stages 3, 4 and 6 allow the student to test the independent variable because... Stage 3: NaOHCO3 provides extra carbon dioxide OR ensures that carbon dioxide isn't a limiting factor; Stage 4: NaOH and limewater absorb CO2 / remove carbon dioxide from the air; Stage 6: To show how photosynthesis is affected by lack of carbon dioxide OR to show the effect of carbon dioxide on growth.
One method that can be used to show that photosynthesis has occurred is to test the leaves with iodine. Explain how this shows that photosynthesis has occurred.
Testing the leaves with iodine would show that photosynthesis has occurred because... Glucose (from photosynthesis) is stored as starch (in the leaves); The presence of starch is shown when iodine changes from brown to black.
The student carried out an investigation to find out the effect of light intensity on the rate of photosynthesis by moving the light source further and further away from the aquatic plant and counting the bubbles produced per minute at each distance. The results can be seen in Table 1 below. One of the results recorded was an anomaly. Identify which result was anomalous and explain your choice.
The anomalous result is: At 20 cm / 45 bubbles; This result doesn't follow the pattern / fit the trend OR all the other results decrease with distance apart from this one.
Explain the benefit of storing glucose as starch in the plant.
The benefit of storing glucose as starch in plants is.... Starch is insoluble / glucose is soluble; (So) storing glucose as starch means it won't affect osmosis in plant cells.
Which cellular process reacts glucose with oxygen to release energy to drive other cell processes?
The cell process which uses glucose is respiration.
A student wanted to show the starch content of a leaf. He carried outthe following procedure: 1. Take a leaffrom a photosynthesising plant 2.Boilthe leafin water 3. Place the leafin ethanolfor10 minutes 4. Wash the leafin water 5. Place the leaf on a white tile 6. Add several drops ofiodine and observe the colour change Complete the table to show what colour change the student should expect to see.
The colour change should be:
Calculate the percentage decrease in carbon dioxide uptake between 15:00 and 18:00 in Figure 4.
The decrease in carbon dioxide uptake can be calculated as follows: 22 - 17 = 5; (5 ÷ 22) X 100; = 22.7 (decrease).
In their investigation, the scientists measure the rate of carbon dioxide taken in by the leaf discs in the light. The scientists then measured the rate of carbon dioxide produced by the leaf discs when they were placed in the dark. The graph in Figure 1 shows the effect of temperature on: Carbon dioxide uptake in the light Carbon dioxide uptake in the light added to carbon dioxide production in the dark Use the information in Figure 1 to describe the effect of temperature on carbon dioxide uptake in the light.
The effect of temperature on carbon dioxide uptake in the light can be described as follows: As temperature increases, the rate of uptake of carbon dioxide/CO2 rises initially and then it falls; E.g. at 40°C, the rate of uptake was highest (820-825) / Any correct use of data taken from the graph.
Explain the effect of temperature on carbon dioxide uptake in the light when the temperature is increased from 20 °C to 35 °C and then from 45 °C to 50 °C.
The effect of temperature on the rate of carbon dioxide uptake in the light can be explained as follows: (From 20 °C to 35 °C) temperature is the limiting factor OR enzymes / substrates have more kinetic energy / are moving faster / colliding with more energy; (From 45 °C to 50 °C) enzymes / proteins are becoming denatured (so CO2 uptake is reduced).
Write out the full word equation for photosynthesis.
The equation for photosynthesis should look as follows: Left hand side: carbon dioxide and water; Arrow labelled with 'light energy'; Right hand side: glucose and oxygen.
Before the student completed the investigation described in part(b), he made the following prediction: 'The plant in bell jar B will not photosynthesise' After the investigation was complete, the student observed the plants but noted no fundamental differences in their visible appearance. Describe another method that the student should use to show that the plant in bell jar A had photosynthesised whereas the plant in bell jar B had not.
The student could carry out the following method: Any five from the following: Remove a leaf from each plant / the plant in bell jar A and the plant in bell jar B; Boil the leaves and add iodine to each leaf; The leaf from bell jar A should turn black to show the presence of starch; Starch is present because glucose produced in photosynthesis is stored as starch in the leaves; The leaf from bell jar B should remain brown to show no starch is present; No photosynthesis means that no glucose has been made or stored as starch in the leaf.
The student evaluated his method and decided that counting bubbles is an inaccurate way of measuring the rate of photosynthesis for two reasons. 1. It does not take into account the fact that there may be bubbles of different sizes 2. Tiny bubbles may be hard to see and so may not be counted at all Suggest a more accurate method which could be used to collect information about the amount of oxygen gas produced as the aquatic plant photosynthesises.
The student could use a measuring cylinder OR gas syringe.
When selecting the plants for the investigation in part(b),the student made sure that they picked plants with the same number of leaves. Explain why this was necessary.
The student selected leaves with the same number of leaves.. Any two from the following: To ensure results were valid / comparable; It was a control variable; More leaves would mean more chlorophyll / chloroplasts; (More chloroplasts would lead to) a faster rate of / more photosynthesis.
The student carried out another investigation into the effect of soil magnesium on plant growth. In this investigation, the student set up three environments as follows: 1. One plant was grown in sterile soil, provided with distilled water and placed in bright light. 2. One plant was grown in sterile soil, provided with magnesium dissolved in distilled water and placed in bright light. Predict what the student will have observed after two weeks of growing in these conditions. Explain your prediction.
The student will have made the following observation: The plant that had been provided with water and magnesium / plant 2 will have shown a greater amount of growth (compared to the other plant / plant 1); Plant 1 will have yellow leaves; This is because... Any three from the following: Magnesium is needed for production of chlorophyll / chloroplasts; In plant 1, lack of chlorophyll results in yellow leaves; In plant 1, chlorophyll / chloroplasts are limiting factors OR in plant 2 there is more chlorophyll / chlorophyll is not a limiting factor; More chlorophyll means more light can be absorbed for photosynthesis; More photosynthesis means more glucose; More glucose means more growth / more proteins / cellulose.
The students want to maximise the rate of growth of their tomatoes. Suggest the best temperature that they should heat their greenhouse to, and give a reason for your suggestion.
The students should set their greenhouse to... Around 35 °C; Because... Any two of the following: Above this, there is little increase in rate of carbon dioxide uptake / above 40 °C there is a decrease in rate of carbon dioxide uptake; (Therefore) it would be a waste of money / too expensive / reduce profits to heat above 35 °C; Respiration rate is higher above 35 °C / reduces the effect of photosynthesis.
The graph in Figure 4 shows how the rate of photosynthesis of strawberry plants is affected by changes in three limiting factors. Identify which three limiting factors were investigated to produce this graph.
The three limiting factors that were investigated were: Carbon dioxide; Light intensity; Temperature.
Describe the trend shown by the data in Table 1.
The trend in Table 1 shows: As the distance from the lamp increases, the number of bubbles decreases.
During the summer, over a 24 hour period, the mean total amount of carbon dioxide taken in by the phytoplankton is greater than the total amount of carbon dioxide released. Explain why this is important for the phytoplankton.
This is important for the phytoplankton because... Any two from the following: The rate of photosynthesis will exceed the rate of respiration OR more glucose is produced in photosynthesis than used in respiration; (Glucose can be used) to build biomass / for growth (of phytoplankton); (Therefore) the phytoplankton will be able reproduce more.
On a summer day, the tomato plants in the greenhouse will require a greater amount of water. However, even if extra water is not provided, water is unlikely to become a limiting factor of photosynthesis. Explain how this is possible.
Water may not be a limiting factor even if not provided on a hot day because... Any four from the following: Plants use/lose most of their water through transpiration / transpiration occurs; On a hot day, stomata will close to conserve water; This results in no diffusion of carbon dioxide into the leaf; No carbon dioxide means no photosynthesis; Carbon dioxide is then the limiting factor;
