The equation and what it means, why photosynthesis is endothermic, where the raw materials come from, and the five things a plant does with the glucose it makes.
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1.Give the word equation for photosynthesis.
carbon dioxide + water, in the presence of light, gives glucose + oxygen
2.Give the symbol equation for photosynthesis.
6CO2 + 6H2O gives C6H12O6 + 6O2
3.Where in a plant cell does photosynthesis happen?
In the chloroplasts, mostly in the palisade mesophyll cells near the top of the leaf.
4.What is chlorophyll and what does it do?
The green pigment inside chloroplasts. It absorbs the light needed for photosynthesis.
5.Is photosynthesis endothermic or exothermic?
Endothermic. Energy is transferred from the environment, as light, into the plant.
6.What does endothermic mean?
A reaction that takes in energy from its surroundings.
7.Where does a plant get its carbon dioxide from?
From the air. It diffuses into the leaf through the stomata.
8.Where does a plant get its water from?
From the soil. Root hair cells absorb it and the xylem carries it up to the leaves.
9.What happens to the oxygen made in photosynthesis?
Some is used by the plant for respiration. The rest diffuses out of the leaf through the stomata.
10.State five uses of the glucose made in photosynthesis.
Used in respiration, converted into starch for storage, used to make cellulose for cell walls, combined with nitrate ions to make amino acids, and converted into lipids for storage in seeds.
11.Why is glucose stored as starch rather than as glucose?
Starch is insoluble, so it does not affect the water balance of the cell by osmosis and it will not move out of the storage cells.
12.What are nitrate ions used for in a plant?
They are combined with glucose to make amino acids, which are then built into proteins.
13.What is cellulose used for?
Making and strengthening plant cell walls.
14.Which plant organ stores lipids, and why?
Seeds. Lipids store a lot of energy in a small mass, giving the seedling a supply before it can photosynthesise.
15.Describe how to test a leaf for starch.
Boil the leaf in water to kill it, boil it in ethanol to remove the chlorophyll, rinse it in water to soften it, then add iodine solution. Blue-black shows starch is present.
16.Why is the leaf boiled in ethanol?
To remove the green chlorophyll, so the colour change produced by iodine can actually be seen.
17.Why is the ethanol heated in a water bath rather than over a flame?
Ethanol is highly flammable, so heating it with a naked flame would be dangerous.
18.What does destarching a plant mean, and how is it done?
Removing the starch already stored in its leaves, by leaving the plant in the dark for a day or two.
19.Why must a plant be destarched before a photosynthesis experiment?
So that any starch found afterwards must have been made during the experiment itself.
20.How could you show that light is needed for photosynthesis?
Destarch the plant, cover part of a leaf with foil, leave it in the light, then test the leaf for starch. Only the uncovered part turns blue-black.
21.How could you show that chlorophyll is needed?
Use a variegated leaf with green and white areas. After the starch test, only the parts that were green turn blue-black.
22.How could you show that carbon dioxide is needed?
Put a destarched plant in a sealed container with soda lime, which absorbs carbon dioxide. That leaf will not produce starch.
23.What is the relationship between photosynthesis and respiration in a plant?
Photosynthesis makes glucose and oxygen and takes in carbon dioxide. Respiration does the reverse. Both happen in a plant, but photosynthesis only in the light.
24.Why do plants respire at night but not photosynthesise?
Respiration happens continuously in all living cells. Photosynthesis needs light, so it stops in the dark.
25.At what point does a plant give out no gas overall?
When the rate of photosynthesis exactly equals the rate of respiration, so the oxygen made is all used up.
26.How is a leaf adapted for photosynthesis?
Broad and flat for a large surface area, thin for a short diffusion path, packed with chloroplasts near the top, air spaces inside, and stomata to let carbon dioxide in.
27.Why do plants need magnesium ions?
To make chlorophyll. Without enough, the leaves yellow and photosynthesis slows.
28.What happens to the glucose that is not used straight away?
It is converted into insoluble starch and stored in the leaves, stem or roots until it is needed.
29.Why can a plant grow in mass even though it takes in gases and water?
The carbon in carbon dioxide is built into glucose and then into starch, cellulose and proteins, which make up most of the dry mass of the plant.
30.Why is photosynthesis important for other organisms?
It produces the glucose that starts almost every food chain, and it releases the oxygen that most organisms need for respiration.
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