20: Photosynthesis - Practical Flashcards
20.1: Detection of oxygen produced in photosynthesis
A Hydrilla plant is put in an inverted funnel connecting to a test tube, bathed in a beaker of dilute sodium hydrogencarbonate solution.
Explain the significance of using dilute sodium hydrogencarbonate solution.
Dilute sodium hydrogencarbonate solution provides carbon dioxide for the plant for it to carry out photosynthesis.
20.1: Detection of oxygen produced in photosynthesis
A Hydrilla plant is put in an inverted funnel connecting to a test tube, bathed in a beaker of dilute sodium hydrogencarbonate solution.
Explain the significance of using stoppers to raise the inverted funnel so that it does not touch the bottom of the beaker.
The funnel is raised for good circulation of gases and dilute sodium hydrogencarbonate solution, allowing the carbon dioxide to reach the plant for photosynthesis.
20.1: Detection of oxygen produced in photosynthesis
A Hydrilla plant is put in an inverted funnel connecting to a test tube, bathed in a beaker of dilute sodium hydrogencarbonate solution.
Explain the significance of stoppering the test tube in water instead of stoppering it above the water.
This is to make sure oxygen collected in the test tube does not escape.
20.1: Detection of oxygen produced in photosynthesis
A Hydrilla plant is put in an inverted funnel connecting to a test tube, bathed in a beaker of dilute sodium hydrogencarbonate solution.
Explain a significant assumption made in this investigation.
The rate of photosynthesis of the plant is higher than the rate of respiration, so thar there is a net oxygen production, not consumption.
20.2: Detection of starch produced in photosynthesis by iodine test
A green leaf put under bright light for several hours is picked, boiled in water, soaked in hot alcohol, washed again, and iodine solution is added to it.
What is the purpose of boiling the leaf in water?
This destroys the differentially permeable cell membrane of the leaf cells and thus allows the iodine solution to enter the leaf cells in later steps.
20.2: Detection of starch produced in photosynthesis by iodine test
A green leaf put under bright light for several hours is picked, boiled in water, soaked in hot alcohol, washed again, and iodine solution is added to it.
What is the purpose of heating the leaf in alcohol?
Alcohol dissolves and removes chlorophyll from the leaf so that any colour changes can be observed clearly on the decolourized leaf.
20.2: Detection of starch produced in photosynthesis by iodine test
A green leaf put under bright light for several hours is picked, boiled in water, soaked in hot alcohol, washed again, and iodine solution is added to it.
What is the purpose of washing the leaf in hot water again after heating in alcohol?
This step removes the alcohol on the leaf because alcohol makes the leaf brittle. Therefore, the leaf softens.
20.2: Detection of starch produced in photosynthesis by iodine test
A green leaf put under bright light for several hours is picked, boiled in water, soaked in hot alcohol, washed again, and iodine solution is added to it.
Explain the expected results and the conclusion from this investigation.
The iodine solution turns from reddish-brown to blue-black all over the leaf. This indicates that starch is present in the green leaf. Photosynthesis has taken place.
20.3: Investigation of the need for light in photosynthesis
A plant is destarched. A green leaf is chosen with parts of it masked with black paper, then exposed to bright light for a few hours. Iodine test is conducted on the leaf afterwards.
Explain the expected results and the conclusion from this investigation. (3)
In the iodine test, the iodine solution on the unmasked parts of the leaf turn from reddish-brown to blue-black,
while that on the masked part of the leaf remains reddish-brown. This shows that the unmasked parts (the parts exposed to bright light) produce starch.
Since starch is made only in the presence of light, this shows that light is needed for photosynthesis.
20.4: Investigation of the need for carbon dioxide in photosynthesis
A plant is destarched. Two green leaves on the plant, A and B, are exposed to bright light for several hours. Leaf A is enclosed with a conical flask, while leaf B is enclosed with a conical flask containing potassium hydroxide pellets.
Which leaf serves as the control set-up and the experimental set-up respectively?
Leaf A is the experimental set-up and leaf B is the control set-up, since the factor for investigation (presence of carbon dioxide) is absent in leaf B.
20.4: Investigation of the need for carbon dioxide in photosynthesis
A plant is destarched. Two green leaves on the plant, A and B, are exposed to bright light for several hours. Leaf A is enclosed with a conical flask, while leaf B is enclosed with a conical flask containing potassium hydroxide pellets.
Suggest three other substances to replace potassium hydroxide in the set-up.
Sodium hydroxide, calcium hydroxide, and soda lime, since they can all absorb carbon dioxide.
20.4: Investigation of the need for carbon dioxide in photosynthesis
A plant is destarched. Two green leaves on the plant, A and B, are exposed to bright light for several hours. Leaf A is enclosed with a conical flask, while leaf B is enclosed with a conical flask containing potassium hydroxide pellets. Iodine test is then conducted on the leaves.
Explain the expected results and the conclusion from this investigation. (3)
In the iodine test, the colour of iodine solution on leaf A turns from reddish-brown to blue-black while that on leaf B remains reddish-brown. Leaf A has been exposed to normal air. Photosynthesis has taken place in the leaf and starch is produced.
Leaf B has been exposed to air without carbon dioxide. Photosynthesis has not taken place in the leaf and no starch is produced.
Starch is made only in the presence of carbon dioxide. Carbon dioxide is needed for photosynthesis.
20.4: Investigation of the need for carbon dioxide in photosynthesis
A plant is destarched. Two green leaves on the plant, A and B, are exposed to bright light for several hours. Leaf A is enclosed with a conical flask, while leaf B is enclosed with a conical flask containing potassium hydroxide pellets.
Suggest another way to carry out the investigation without the use of conical flasks.
Use a **plastic bag **to enclose leaves A and B. Put potassium hydroxide pellets into the bag of leaf B. Seal the mouth of each bag by tying it around the leaf stalk.
20.5: Investigation of the need of chlorophyll in photosynthesis
Name a type of plant that has variegated leaves.
Coleus
20.5: Investigation of the need of chlorophyll in photosynthesis
A variegated plant is destarched and a leaf is picked to test for starch; then, the plant is exposed to bright light for several hours, and iodine test is conducted on one of the leaves.
What is the significance of destarching the plant? (2)
Destarching removes the starch in the leaves.
This ensures that any starch found at the end of the experiment is made during the experiment.
