photosynthesis 2.18, 2.19, 2.20, 2.21, 2.22, 2.23

Question 1

what’s the word equation for photosynthesis?

Answer 1

carbon dioxide + water > (light energy and chlorophyll) > glucose + oxygen

Question 2

what’s the balanced chemical equation for photosynthesis?

Answer 2

6CO2 + 6H20 > C6H12O6 +6O2

Question 3

what are five things that plants use from the glucose produced from photosynthesis?

Answer 3

chlorophyll
lipids (to make cell membranes etc)
amino acids
DNA
carbohydrates (cellulose, fructose, starch for storage, sucrose for transport)

Question 4

why do plants need mineral ion nitrates (NO3-)?

Answer 4

to make amino acids (proteins) and nucleic acids (DNA and RNA)

Question 5

why do plants need the mineral ion magnesium (Mg)?

Answer 5

to make chlorophyll

Question 6

why do plants need mineral ion phosphates (PO4,3-)?

Answer 6

needed to make nucleic acids (DNA and RNA) and part of cell membrane

Question 7

what three factors affect the rate of photosynthesis?

Answer 7

availability of the substances needed for reaction (carbon dioxide and water)
energy availability (light intensity)
kinetic energy available to move substrate and enzyme molecules (increasing temperature and increasing kinetic energy)

Question 8

what is the factor that is in shortest supply called?

Answer 8

limiting factor

Question 9

the effects of temperature on photosynthesis and enzymes?

Answer 9

as temperature increases speeds up the reaction
the enzyme and substrate have more kinetic energy so they move faster and there are more successful collisions
however, when the temperature meets a certain temp the shape of the active site changes the enzyme denatures and the active site is no longer complementary to the substrate
therefore rate of photosynthesis decreases and reaction stopos

Question 10

list the structure of a leaf from the top, downwards:

Answer 10

cuticle
upper epidermis
palisade mesophyll
xylem and phloem
spongy mesophyll
lower epidermis
stomata and guard cells

Question 11

how is the leaf specialised for photosynthesis?

Answer 11

large surface area and thin - maximises light absorption and increases number of stomata so carbon can diffuse quicker

Question 12

how is the upper epidermis specialised for photosynthesis?

Answer 12

transparent so light can penetrate the mesophyll

Question 13

how are the palisade cells specialised for photosynthesis?

Answer 13

long, thin and tightly packed
contain large amounts of chloroplasts, maximising the absorption of sunlight energy
palisade mesophyll is the main site of photosynthesis

Question 14

how are the stomata specialised for photosynthesis?

Answer 14

allow gases to diffuse into air spaces of the leaf providing a short diffusion distance for CO2

Question 15

practical:
photosynthesis experiment of chlorophyll and starch

Answer 15

shows that chlorophyll is needed for photosynthesis
- take a leaf that’s variegated (some bits green, some white) and destarched (place in dark for 24 hours)
- heat in boiling water for 1 minute stopping any chemical reactions and waxy cuticle
- transfer leaf to a test tube containing ethanol and place test tube in hot water, this gets rid of any chlorophyll
- to soften ethanol leaf place it in hot water and rinse leaf
- place leaf on a white tile and cover it in an iodine solution
the leaf will turn blue-black to show starch is present

Question 16

practical
rate of photosynthesis with factors that affect it

Answer 16

equipment: pondweed, a beaker of water, ruler, light source

number of bubbles released from the stalk in 1 minute is counted
distance of the light source can be varied to see the effect of changing light intensity

improvements of method:
- put pondweed in a test tube and then in a beaker with a thermometer to act as a water bath, this reduces the temperature change
- collect gas in an inverted measuring cylinder to measure the volume of oxygen evolved

Question 17

what is photosynthesis?

Answer 17

process that produces food in plants
when plants use simple molecules (CO2 and H2O) to make glucose and O2
requires light energy, which is absorbed by chlorophyll
occurs in plants and some bacteria and protoctista

Question 18

what happens if a plant is deficient in nitrates (NO3-)?

Answer 18

if deficient stunted growth

Question 19

what happens if a plant is deficient in magnesium (Mg)?

Answer 19

if deficient yellow leaves

Question 20

what happens if a plant is deficient in phosphates (PO4 3-)?

Answer 20

if deficient poor root growth, purple younger leaves

Question 21

what happens to rate of photosynthesis as you add more carbon dioxide?

Answer 21

by adding more carbon dioxide the reaction can happen faster as there are more molecules to collide with enzymes
however, there is a point where adding more CO2 has no effect as there is a lack of energy

Question 22

what happens to the rate of photosynthesis in a brighter light?

Answer 22

by adding a brighter light we increase the rate of photosynthesis as there is more energy for the reaction to occur

Question 23

how is the xylem specialised for photosynthesis?

Answer 23

the xylem transports water (absorbed in the roots) into the leaves
providing a short distance for water to diffuse into the photosynthesising cells

Question 24

how is the phloem specialised for photosynthesis?

Answer 24

phloem vessels transport sugars made in photosynthesis to other parts of the plant

Question 25

how can the photosynthesis experiment of chlorophyll and starch be adapted to show that light is required?

Answer 25

to show that light is required one leaf is covered by foil (or part of the leaf), and only the leaves exposed to light will produce starch and turn black

Question 26

how can the photosynthesis experiment of chlorophyll and starch be adapted to show that carbon dioxide is required?

Answer 26

to show that carbon dioxide is required one leaf of a plant is enclosed in a conical flask containing soda lime to absorb the carbon dioxide and this leaf is compared to another enclosed flask but without the soda lime
only the leaf that had access to carbon dioxide produces starch

Question 27

why do plants need potassium?

Answer 27

to help the enzymes needed for photosynthesis and respiration

Question 28

what happens if a plant is deficient in potassium?

Answer 28

if deficient plants will have poor flower and fruit growth and discoloured leaves