Plants & Photosynthesis (WJEC GCSE Science (Double Award): Biology): Flashcards
Exam code: 3430
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- FrontPhotosynthesis
Define photosynthesis.
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Cards in this collection (60)
Define photosynthesis.
The process in which green plants use chlorophyll to absorb light energy and convert carbon dioxide and water into glucose, releasing oxygen as a by-product.
State the word equation for photosynthesis.
carbon dioxide + water → glucose + oxygen
This reaction requires light energy and chlorophyll.
Define chlorophyll.
The green pigment found inside chloroplasts that absorbs light energy for photosynthesis.
Which gas is produced as a by-product of photosynthesis?
Oxygen.
Name the two raw materials required for photosynthesis.
Carbon dioxide
Water
＿＿＿＿＿＿＿＿ is the green pigment inside chloroplasts that absorbs light energy.
Chlorophyll is the green pigment inside chloroplasts that absorbs light energy.
State four uses plant cells make of the glucose produced in photosynthesis.
Respired to release energy
Converted to starch for storage
Used to make cellulose for cell walls
Used to make proteins and oils
Why do plants convert glucose into starch for storage?
Starch is insoluble, so it can be stored without affecting the water balance of the cell by osmosis.
What is glucose converted into to build plant cell walls?
Cellulose.
Glucose is converted to ＿＿＿＿＿＿＿＿ for storage in plant cells.
Glucose is converted to starch for storage in plant cells.
In which part of the plant cell does photosynthesis take place?
The chloroplasts, which contain chlorophyll.
True or False?
Photosynthesis and respiration are opposite processes.
True.
Photosynthesis uses carbon dioxide and water to make glucose and oxygen. Respiration uses glucose and oxygen and produces carbon dioxide and water.
True or False?
Plants do not respire because they photosynthesise.
False.
Plants respire all the time. Some of the glucose they make in photosynthesis is used in respiration to release energy.
Why is photosynthesis important to organisms other than plants?
It produces the glucose at the base of almost every food chain, and releases the oxygen that other organisms need for aerobic respiration.
What are the reactions of photosynthesis catalysed by?
Enzymes.
Name the three environmental factors that affect the rate of photosynthesis.
Temperature
Carbon dioxide concentration
Light intensity
Explain why increasing temperature increases the rate of photosynthesis.
Molecules gain more kinetic energy, so there are more successful collisions between the reactants per second.
Explain why the rate of photosynthesis falls sharply at very high temperatures.
The enzymes that catalyse photosynthesis denature.
The complementary shape of their active sites is lost, so the reactions can no longer be catalysed.
Explain why increasing light intensity increases the rate of photosynthesis.
Chlorophyll can absorb more light energy to power the reactions of photosynthesis.
Explain why increasing carbon dioxide concentration increases the rate of photosynthesis.
Carbon dioxide is one of the raw materials for photosynthesis, so more of it allows the reaction to proceed faster.
At very high temperatures the enzymes controlling photosynthesis ＿＿＿＿＿＿＿＿, so the rate falls sharply.
At very high temperatures the enzymes controlling photosynthesis denature, so the rate falls sharply.
Describe the shape of a graph of light intensity against rate of photosynthesis.
The rate increases as light intensity rises.
It then levels off when another factor, such as temperature or carbon dioxide, prevents any further increase.
True or False?
Increasing light intensity will always increase the rate of photosynthesis.
False.
The rate increases only until another factor becomes the one holding it back, at which point the graph levels off.
Define limiting factor. (Higher Tier Only)
An environmental factor that limits the rate of a reaction when it is in short supply.
Name the three limiting factors of photosynthesis. (Higher Tier Only)
Temperature
Light intensity
Carbon dioxide concentration
How can you tell from a graph which factor is limiting the rate of photosynthesis? (Higher Tier Only)
Where the line is sloping upwards, the factor on the x axis is limiting.
Where the line has levelled off, some other factor has become limiting.
A ＿＿＿＿＿＿＿＿ factor is one that limits the rate of a reaction when it is in short supply. (Higher Tier Only)
A limiting factor is one that limits the rate of a reaction when it is in short supply.
True or False?
Water is considered a limiting factor of photosynthesis. (Higher Tier Only)
False.
Although water is needed for photosynthesis, it is not treated as a limiting factor. If water is that scarce, the plant closes its stomata and carbon dioxide intake becomes limiting instead.
A greenhouse grower keeps light and carbon dioxide high but the rate still plateaus. Suggest why. (Higher Tier Only)
Temperature has become the limiting factor. Raising it, up to the optimum, would allow the rate to increase further.
Why is a perfect set of conditions for photosynthesis rare in nature? (Higher Tier Only)
At least one environmental factor is almost always in short supply, so the rate is nearly always limited by something.
Why is sodium hydroxide used in photosynthesis investigations?
It absorbs carbon dioxide from the air, so it can be used to show that carbon dioxide is needed for photosynthesis.
How is sodium hydroxide used to show carbon dioxide is needed?
Destarch two plants by keeping them in the dark.
Place one in a bell jar with sodium hydroxide and the other in a bell jar with water as a control.
Leave both in bright light for several hours, then test both leaves for starch.
What results would you expect from the sodium hydroxide experiment?
The leaf from the plant near sodium hydroxide tests negative for starch, as there was no carbon dioxide for photosynthesis.
The leaf from the plant near water tests positive for starch.
What does it mean to destarch a plant, and why is it done?
The plant is kept in the dark for a prolonged period so it uses up its starch reserves.
This removes any starch present before the investigation begins, so results are valid.
Why is a leaf tested for starch rather than for glucose?
Glucose is quickly used, converted or stored, so it is not a reliable indicator.
Starch is stored in the chloroplasts, so its presence reliably shows photosynthesis has happened.
Describe how to test a leaf for the presence of starch.
Place the leaf in boiling water to kill it and stop reactions.
Place it in hot ethanol for 5–10 minutes to remove the chlorophyll.
Rinse the leaf in water to soften it.
Spread it on a white tile and add iodine solution.
Why is the leaf placed in hot ethanol during the starch test?
To remove the chlorophyll, so the colour change with iodine can be seen clearly.
Why must a Bunsen burner be switched off before using ethanol?
Ethanol is highly flammable. A water bath should be used to heat it instead.
What result shows that photosynthesis has taken place in part of a leaf?
That area turns blue-black with iodine solution, showing starch is present.
＿＿＿＿＿＿＿＿ is used to remove chlorophyll from a leaf before the starch test.
Ethanol is used to remove chlorophyll from a leaf before the starch test.
How can gas sensors and data loggers be used to measure photosynthesis?
A plant is placed in a sealed container.
A gas sensor connected to a data logger records the concentration of oxygen and carbon dioxide continuously over a set period.
The change in concentration over time gives a measure of the rate.
What gas changes would a data logger record during photosynthesis?
Carbon dioxide concentration decreases, as it is used up
Oxygen concentration increases, as it is produced
A leaf that has been photosynthesising will turn ＿＿＿＿＿＿＿＿ when iodine solution is added.
A leaf that has been photosynthesising will turn blue-black when iodine solution is added.
True or False?
The plant kept next to water in the bell jar acts as an experimental control.
True.
Water does not absorb carbon dioxide, so that plant has everything it needs for photosynthesis and provides a comparison.
True or False?
Boiling the leaf in water kills it and stops the chemical reactions in its cells.
True.
This fixes the results at the moment the leaf was taken, so the starch pattern does not change during testing.
Why is pondweed useful for measuring the rate of photosynthesis?
The oxygen they produce forms bubbles, which can be counted or collected in a gas syringe.
Describe how to investigate the effect of light intensity.
Place Elodea pondweed in a beaker of water with sodium hydrogen carbonate added.
Place a funnel over the pondweed and an inverted, water-filled test tube over the funnel.
Set a lamp a measured distance from the plant and count the bubbles produced in 1 minute.
Repeat, then move the lamp to different distances and repeat again.
Why is sodium hydrogen carbonate added to the water?
It allows the concentration of dissolved carbon dioxide to be controlled, so it does not become a limiting factor.
Why is a glass tank of water placed between the lamp and the beaker?
It supplies dissolved carbon dioxide and keeps the supply constant, so a shortage of carbon dioxide does not slow the rate down.
State the independent and dependent variables in this investigation.
Independent variable: light intensity, changed by moving the lamp
Dependent variable: the number of bubbles produced per minute
Give three control variables for this investigation.
Any three of:
Temperature
Carbon dioxide concentration
Other light sources, e.g. classroom lights off and blinds closed
Size and type of pondweed
What results would you expect as the lamp is moved further from the plant?
Fewer bubbles are produced per minute, because there is less light energy available at lower light intensities.
How could the accuracy of this investigation be improved?
Measure the volume of gas collected in a gas syringe rather than counting bubbles, since bubbles vary in size and are easy to miscount.
How can the reliability of the results be improved?
Carry out repeats at each light intensity and calculate a mean, which also allows anomalies to be spotted.
State the hazard, risk and control measure for the lamp in this practical.
Hazard: the light bulb becomes hot
Risk: burns if the skin touches it
Control measure: avoid touching the bulb and let it cool before moving the lamp
The gas collected in the inverted test tube during this experiment is ＿＿＿＿＿＿＿＿.
The gas collected in the inverted test tube during this experiment is oxygen.
＿＿＿＿＿＿＿＿ hydrogen carbonate is added to the water to supply carbon dioxide.
Sodium hydrogen carbonate is added to the water to supply carbon dioxide.
True or False?
Moving the lamp further from the plant decreases the light intensity reaching it.
True.
Light intensity falls as distance from the source increases, so fewer bubbles are produced.
True or False?
Counting bubbles is a highly accurate way to measure oxygen production.
False.
Bubbles vary in size and are easy to miscount. Collecting the gas in a gas syringe is more accurate.
Why should classroom lights be switched off during this investigation?
So that the lamp is the only light source, meaning the light intensity reaching the plant depends only on the lamp's distance.
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