Put the starch test steps in order.
Reveal answer
- boil leaf in water
- heat in ethanol (water bath)
- rinse in water
- add iodine
Key words: ethanol · iodine
2(e) NUTRITION · RECALL
2.23 Photosynthesis investigations
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What does destarching mean and how is it done?
Reveal answer
Removing starch from leaves by keeping the plant in the dark for about 48 hours.
Key words: dark · 48 hours
How do you show light is needed for photosynthesis?
Reveal answer
Destarch; cover part of a leaf with foil; leave in light; starch test: covered part stays orange-brown.
Key words: foil · destarch
How do you show chlorophyll is needed?
Reveal answer
Destarch a variegated leaf, put in light, starch test: only green parts turn blue-black.
Key words: variegated
How do you show CO₂ is needed?
Reveal answer
Destarch; enclose a leaf with sodium hydroxide / soda lime; control experiment without it; starch test.
Key words: sodium hydroxide · control experiment
How do you show oxygen is produced?
Reveal answer
Collect gas from pondweed in an inverted test tube; a glowing splint relights.
Key words: glowing splint
Why heat ethanol in a water bath?
Reveal answer
Ethanol is flammable, so no naked flame.
Key words: flammable
How do you vary light intensity in the pondweed experiment while controlling temperature?
Reveal answer
Move the lamp to different distances and use a heat shield or LED lamp.
Key words: distance · heat shield
What is meant by the term destarch?
Reveal answer
Remove stored starch by keeping a plant in darkness long enough for respiration to use it.
Key words: destarch
What is meant by the term control experiment?
Reveal answer
A matched set-up without the factor being tested, used for comparison.
Key words: control experiment
What is meant by the term variegated leaf?
Reveal answer
A leaf with both chlorophyll-containing and chlorophyll-deficient regions.
Key words: variegated leaf
What is meant by the term qualitative test?
Reveal answer
A test identifying presence or type rather than a precise quantity.
Key words: qualitative test
Four complementary investigations, Is oxygen produced?. Key comparison or test? Supported conclusion?
Reveal answer
Key comparison or test: Collect aquatic-plant gas; test with glowing splint. Supported conclusion: The evolved gas contains oxygen.
Key words: Is oxygen produced?
Four complementary investigations, Is light required?. Key comparison or test? Supported conclusion?
Reveal answer
Key comparison or test: Covered versus uncovered regions of a destarched leaf. Supported conclusion: Starch accumulates in illuminated tissue.
Key words: Is light required?
Four complementary investigations, Is carbon dioxide required?. Key comparison or test? Supported conclusion?
Reveal answer
Key comparison or test: CO₂ absorber versus matched control experiment (no absorber) in light. Supported conclusion: Starch accumulation depends on available carbon dioxide.
Key words: Is carbon dioxide required?
Four complementary investigations, Is chlorophyll required?. Key comparison or test? Supported conclusion?
Reveal answer
Key comparison or test: Green versus non-green regions of one variegated leaf. Supported conclusion: Starch accumulates in chlorophyll-containing tissue.
Key words: Is chlorophyll required?
True or false, and why? “Bubble count is an exact oxygen-volume measurement.”
Reveal answer
False. Bubble size varies; collect gas volume and identify the gas.
True or false, and why? “Iodine directly tests for photosynthesis.”
Reveal answer
False. Iodine tests for starch accumulated after photosynthesis.
True or false, and why? “Boiling a leaf in ethanol over a flame is acceptable.”
Reveal answer
False. Ethanol is flammable and must be heated in a water bath away from flames.
True or false, and why? “One negative leaf proves a factor is required.”
Reveal answer
False. Control experiments, replicates and checks for healthy tissue and successful destarching are needed.