photosynthesis

Question 1

what is light energy absorbed by?

Answer 1

chlorophyll

Question 2

what kingdoms does photosynthesis occur in?

Answer 2

plants, and some bacteria/protoctista too

Question 3

2.19 word equation for photosynthesis?

Answer 3

carbon dioxide + water —> glucose + oxygen

Question 4

2.19 balanced chemical equation for photosynthesis?

Answer 4

6CO2 + 6H2O —> C6H12O6 + 6O2

Question 5

2.22 what are nitrates (NO3 -) used for in plants?

Answer 5

they’re required to make amino acids (and so proteins), and nucleic acids (DNA and RNA)

Question 6

2.22 what is magnesium (Mg) used for in plants?

Answer 6

required to make chlorophyll

Question 7

what are phosphates (PO4 3-) used for in plants?

Answer 7

required to make nucleic acids (DNA and RNA); is part of cell membrane

Question 8

symptoms of nitrates deficiency in plants?

Answer 8

stunted growth

Question 9

symptoms of magnesium deficiency in plants?

Answer 9

yellow leaves

Question 10

symptoms of phosphates deficiency in plants?

Answer 10

poor root growth; purple younger leaves

Question 11

what is the limiting factor?

Answer 11

the factor which is in shortest supply

Question 12

2.20 what are the factors affecting photosynthesis?

Answer 12

1. the availability of the substrates for the reaction - carbon dioxide & water
2. energy available to allow the reaction to occur - light intensity
3. kinetic energy available to move substrate and enzyme molecules - increasing temperature increases kinetic energy

Question 13

2.21 what are the adaptations of the upper epidermis?

Answer 13

it’s transparent, allowing light to penetrate to the mesophyll

Question 14

2.21 how is the leaf specialised for photosynthesis?

Answer 14

-large surface area, thin, to maximise absorption of sunlight by photosynthetic cells
-this also increases number of stomata, so CO2 can diffuse quicker

Question 15

2.21 what are palisade cells like?

Answer 15

-long, thin, tightly packed
-contain large numbers of chloroplasts
-this maximises absorption of sunlight energy
-palisade mesophyll is main site of photosynthesis

Question 16

2.21 what do stomata do

Answer 16

-allow gases to diffuse into air spaces of leaf
-this provides a short diffusion distance for CO2

Question 17

what’s the xylem

Answer 17

-transports water (absorbed in roots) to leaves
-this then provides short distance for water to diffuse into photosynthesising cells

Question 18

what’s the phloem vessels do

Answer 18

transport sugars made in photosynthesis to other parts of the plant

Question 19

2.20 understand how varying carbon dioxide concentration affects the rate of photosynthesis

Answer 19

• adding more CO2: reaction happens faster, as more molecules to collide w enzymes
• however, reach point when adding more CO2 has no effect - there’s a lack of energy

Question 20

2.20 understand how varying light intensity affects the rate of photosynthesis

Answer 20

• by adding brighter light we inc rate of photosynthesis, as more energy for reaction to occur
• this doesn’t last forever, as at high light intensities a different factor is limiting (and so graph levels off)

Question 21

2.20 understand how varying temperature affects the rate of photosynthesis

Answer 21

• inc temp speeds up reaction
• enzymes & substrates have more KE & collide more often
• however, at high temps rate of photosynthesis decreases & reaction stops
• this bc enzymes carrying out stages of photosynthesis have been denatured

Question 22

2.23 practical: investigate photosynthesis, showing the production of starch and the requirements of light, carbon dioxide and chlorophyll (testing leaf for starch)

Answer 22

1. take leaf that’s been destarched by placing in dark for 24 hrs
2. leave it to photosynthesise outside for a day
3. heat leaf in boiling water for 1 min (boiled w Bunsen burner) (this kills the tissue & breaks down cell walls)
4. turn off Bunsen burner
5. transfer leaf to test tube containing ethanol & place in the hot water for 5-10 mins - boil in ethanol (removes chlorophyll so colour change from iodine seen more clearly)
6. rinse the leaf in cold water (to soften leaf tissue after being in ethanol)
7. spread leaf out on white tile & cover in iodine solution
8. only parts of leaf that produce starch will turn blue/black

Question 23

2.23 practical: why do you need to destarch the leaf before/at the beginning of the practical?

Answer 23

ensures that any starch already present in leaves will be used up which means any starch in leaf you test was produced from glucose made in photosynthesis during experiment (won’t affect results of experiment)

Question 24

2.23 practical: how can you vary the experiment to show the different conditions needed for photosynthesis?

Answer 24

• light required: 1 leaf covered w foil (or part of leaf covered); only the leaves (parts of leaf) exposed to light will produce starch & turn black
• chlorophyll required: a variegated leaf, in which white parts of leaf lacks chlorophyll, is used & starch only produced in green areas
• CO2 required: 1 leaf of plant enclosed in conical flask containing soda lime to absorb CO2, compared to 1 in flask w/o soda lime. only leaf w CO2 produces starch.

Question 25

2.23 why do you drop the leaf in boiling water in the start of the practical?

Answer 25

bc it kills the tissue & breaks down cell walls in the leaf

Question 26

2.23 practical: why do you boil the leaf in hot ethanol?

Answer 26

bc it removes the chlorophyll so the colour change from the iodine can be seen clearly

Question 27

2.23 practical: investigate photosynthesis, showing the evolution of oxygen from a water plant

Answer 27

• length of pondweed Elodea put in beaker of water
• no. of bubbles released from stalk in 1 min counted
• distance of lamp can be moved to vary light intensity, or differing masses of sodium bicarbonate to vary the CO2 conc.

Question 28

2.23 practical: how can the elodea practical be improved?

Answer 28

• putting Elodea into boiling tube of water, and this can then be placed in a beaker, w a thermometer, to act as water bath - reduces temp change
• collecting gas in inverted measuring cylinder & measure vol. of oxygen evolved per unit time
• adding fixed mass of sodium bicarbonate to water, to provide higher (constant) conc. of CO2