Primary 6 · Science · Systems: Photosynthesis
Systems: Photosynthesis questions for Primary 6 Science
10 questions to work through online, 2 of them written out the way the paper asks. Answer and you get the working straight away, then a score at the end. No sign-up, and you can retake it as often as you like.
- Predicting a starch test
- Purpose of a leaf in the set-up
- Raw materials and products
- Reasoning about a sealed jar
- Reading rate data
- Why the leaf is prepared
- Reasoning about a variegated leaf
- Naming the gas released
- Naming the test result
- Applying the ideas
Same picture as the question above.
| Condition | Bubbles of gas per minute |
|---|---|
| bright light, normal air | 26 |
| bright light, extra carbon dioxide | 41 |
| dim light, extra carbon dioxide | 9 |
| darkness, extra carbon dioxide | 0 |
Answers and explanations for all 10 questions
Every answer with the reasoning behind it. Worth reading after you have tried the set — or on its own, if you are a parent marking it.
After the day, each leaf in the set-up above was tested with iodine. Which result would be expected?
Answer: A turns blue-black, B does not, and only the uncovered part of C does.
A had everything and made starch. B was missing carbon dioxide, so it made none. C made starch only where light reached it.
What is the purpose of leaf A in the set-up above?
Answer: It is the control, showing that a leaf with everything does make starch.
A is in a clear bag with normal air and nothing removed. Without it, a negative result in B or C could not be blamed on the missing condition.
Which two of these are used up during photosynthesis?
Answer: A and B only
Carbon dioxide and water go in; food and oxygen come out. Reversing any of those is the commonest error on this topic.
In the set-ups above, the fish in P survived and the fish in Q died. Why?
Answer: The plant in P kept replacing the oxygen the fish used.
In a sealed jar the fish uses up the oxygen. The plant in P photosynthesises and releases oxygen, so the supply is renewed; in Q there is nothing to renew it.
Based on the table above, which conclusion is correct?
Answer: Extra carbon dioxide only helps when there is light to use it.
Extra carbon dioxide raised the rate from 26 to 41 in bright light, but gave nothing at all in darkness. Both are needed together.
Which two steps are needed before a leaf can be tested for starch?
Answer: A and B only
De-starching in the dark makes sure any starch found was made during the test. Removing the green colouring lets the blue-black of the iodine be seen.
A leaf that is green in the middle and white at the edges is tested for starch after a day in the light. What is found?
Answer: Only the green part turns blue-black.
Chlorophyll is what traps the light, and it is only in the green parts. Those make starch; the white parts cannot, so the iodine shows the pattern of the green.
A water plant in bright light gives off a steady stream of bubbles. Which gas is in the bubbles?
Answer: oxygen
The gas given off during photosynthesis is oxygen.
Iodine solution is normally yellowish-brown. On a leaf that has been photosynthesising, it changes to a distinctive colour. What colour does it turn?
Answer: blue-black
Iodine turns blue-black where starch is present.
A grower pumps extra carbon dioxide into a greenhouse and also fits bright lamps. Why do both together raise the crop more than either alone?
Answer: Photosynthesis needs both, so whichever is in shortest supply limits the rate.
Supplying more of one raw material only helps until something else runs short. Raising both at once lifts the ceiling that either alone would impose.