photosynthesis questions

Question 1

Where precisely in a cell does the Calvin cycle take place?

Answer 1

stroma

Question 2

Explain the decrease in the amount of GP after the carbon dioxide concentration was reduced.

Answer 2

(Less) RuBP combines with carbon dioxide;

Question 3

The scientist carried out a similar experiment but increased the carbon dioxide concentration from 1% to 2%. The relative amounts of GP and RuBP remained the same.
Suggest two reasons why.

Answer 3

1)Temperature is a limiting factor/below optimum;
2) Light is a limiting factor/below optimum;
3)Limited by RuBP (available/produced);
4)Accept: RuBP will always give 2 GP (at high CO ). 2
Limited by enzyme

Question 4

(c) Some bacteria use hydrogen sulfide, H S, to produce organic compounds. 2
The hydrogen sulfide has a similar role to that of water in photosynthesis.
A simple equation for this process in bacteria is shown below:
hydrogen sulfide + carbon dioxide → glucose + sulfur + water
Suggest what the hydrogen sulfide is used for in these bacteria.

Answer 4

provides hydrogen / protons/H and electrons/e
for reduction and source of electrons for chlorophyll /etc

Question 5

Crops use light energy to produce photosynthetic products.
Describe how crop plants use light energy during the light-dependent reaction.

Answer 5

(a) 1.
Excites electrons / electrons removed (from chlorophyll);

2. Electrons move along carriers/electron transfer chain releasing energy;
3. Energy used to join ADP and Pi to form ATP;
4. Photolysis of water produces protons, electrons and oxygen;

Question 6

After harvesting, the remains of crop plants are often ploughed into the soil.
Explain how microorganisms in the soil produce a source of nitrates from these remains.

Answer 6

1)Protein/amino acids/DNA into ammonium compounds / ammonia;
2. By saprobionts;
Accept: saprophytes.
3. Ammonium/ammonia into nitrite;
4. Nitrite into nitrate;
5. By nitrifying bacteria/microorganisms;

Question 7

explain why scientists measured the rate of production of o2 in the investigation

Answer 7

1)oxygen produced in ldr
2)the faster o2 produced the faster the ldr

Question 8

purpose of a no air sealing grease conditions

Answer 8

no grease means stomata are open allows normal co2 uptake

Question 9

purpose of lower surface being covered in air sealing grease that prevents gas exchange condition

Answer 9

seals stomata stopping co2 uptake

Question 10

both lower surface and upper surface in air sealing grease conditions

Answer 10

shows sealing is effective stops all co2 uptake

Question 11

what would happen in treatment one

Answer 11

Mean rate of) carbon dioxide uptake was constant and fell after the light turned off;

Uptake fell from 4.5 to 0 / uptake started to fall at 60 minutes and reached lowest at 80 minutes / uptake fell over period of 20 minutes;

Question 12

stomata closes when light is off why this an advantage

Answer 12

water is lost through stomata
closure reduces water loss
maintains water constant of cells

Question 13

in treatment one and two the uptake of co2 falls to 0 when light is off

Answer 13

Carbon dioxide uptake) through the upper surface of the leaf / through cuticle

Question 14

measurements student takes when determining rate of photosynthesis

Answer 14

o2 production /conc and time

Question 15

other than temp and ph give tw factors which should be kept constant during this investigation

Answer 15

intensity of light
time
co2 conc

Question 16

The student did not use a buffer to maintain the pH of the solution.
Explain what would happen to the pH of the solution during this investigation.

Answer 16

ph inc
as more co2 removed for photosynthesis

Question 17

Suggest and explain why the rate of photosynthesis was low between 525 nm and 575 nm wavelengths of light.

Answer 17

less absorption
for ldr
represents green light

Question 18

7 ii)Explain why CO uptake is a measure of net productivity.

Answer 18

Shows (gross) photosynthesis

Question 19

how the shade plant is better adapted than the sun plant to growing at low light intensities.

Answer 19

(Shade plant) has lower (rate of) respiration / respiratory losses / less CO2 released at 0 light intensity / in dark;

Greater (net) productivity / less sugars / glucose used / more sugars / glucose available;

Question 20

During the light-independent reaction of photosynthesis, carbon dioxide is converted into organic substances. Describe how.

Answer 20

1)co2 combines w rubp
2)produces 2 gp
3)gp reduced to tp
4)using reduced nadp
5)using energy from atp
6)tp converted to glucose/hexose

Question 21

What measurements would the scientists have made in order to calculate the rate of carbon dioxide production?

Answer 21

volume of carbon dioxide given off
(Fromknown)area/perm /m
In a known / set time

Question 22

(d) The scientists calculated the mean rate of carbon dioxide production of the leaves using measurements of carbon dioxide release in the dark.
Explain why they did not use measurements taken in the light.

Answer 22

(In the light) photosynthesis / in the dark no photosynthesis;
(In light,) carbon dioxide (from respiration) being used / taken up (by photosynthesis)

Question 23

Describe two ways in which the mean rate of respiration in soil under trees is different from soil not under trees.

Answer 23

In soil under trees (always) higher;
n soil under trees does not rise between 06.00 and 12.00
In soil not under trees, peaks at about 14:00-15:00

Question 24

suggest one explanation for the differences in the mean rate of respiration in soil under trees and soil not under trees between 06.00 and 12.00.

Answer 24

1. Tree roots carry out (a lot of) respiration;
2. More / there are roots under tree;

Question 25

Suggest how the rise in the mean rate of photosynthesis could lead to mean rate of respiration in soil under trees.

Answer 25

1. Photosynthesis produces sugars;
2. Sugars moved to roots;
   Do not penalise named sugars other than sucrose
3. (Sugars) are used / required for respiration;

Question 26

The experiments were carried out at a high carbon dioxide concentration. Explain why.

Answer 26

Soit/CO isnotalimitingfactor

Question 27

explain why it was important to grow the plants under the same conditions up to ten days before the experiment.

Answer 27

o any difference is due to iron (deficiency);

Question 28

(iii) The plants were left in the for 6 hours before the experiment. Explain why.

Answer 28

Amount of triose phosphate / TP will be similar / same / low (at start);

Question 29

iron deficiency results in a decrease in the uptake of carbon dioxide. Explain why.

Answer 29

Less triose phosphate converted to RuBP;
Accept: less triose phosphate so less RuBP
CO combines with RuBP;

Question 30

Rubisco activase is an enzyme found in chloroplasts. It activates the light-independent reaction of photosynthesis.
The scientists discovered that, as temperature increased from 25°C to 45°C, rubisco activase began attaching to thylakoid membranes in chloroplasts and this stopped it working.
(c) Rubisco activase stops working when it attaches to a thylakoid.
Use your knowledge of protein structure to explain why.

Answer 30

Enzyme activity reduced / (some) enzymes denatured;
2. Less photosynthesis, so fewer sugars formed;
3. Less respiration / less energy / ATP for growth;
4. Less energy for named function associated with growth
4. Eg mitosis, uptake of mineral ions

Question 31

13c in leaves at the top of trees in a forest, carbon dioxide is often the limiting factor for photosynthesis.
Use your knowledge of photosynthesis to suggest and explain one reason why.

Answer 31

Light not limiting / lots of light (as no shading);
Light-dependent reaction not limiting / fast;

Question 32

16a )Where exactly in a cell is the enzyme Rubisco found?

Answer 32

stroma

Question 33

use the information provided and your knowledge of the light-independent reaction to explain why the yield from soya bean plants is decreased at higher concentrations of oxygen. Phosphoglycolate is not used in the light-independent reaction.

Answer 33

1) less gp produced
2)less tp to form sugars
3)less rub formed

Question 34

explain why the results in tube B are similar to those in tube A.

Question 35

19b)
the scientists measured the oxygen produced by the light-dependent reaction of photosynthesis. Name two other substances produced by the light-dependent reaction

Answer 35

reduced nadp
atp

Question 36

The scientists measured the rate of photosynthesis of the seaweeds in this investigation in terms of oxygen produced.
Suggest the units they should use.

Answer 36

cm3 or ml

Question 37

this investigation was carried out in bright light. Explain why reducing the light intensity would affect the amount of oxygen released by the seaweeds.

Answer 37

(Light intensity) limiting factor;
Fewer electrons (released) from chlorophyll;
Less photolysis therefore (less) oxygen from water;

Question 38

(d) In this investigation, the scientists kept the temperature at 15 °C. A student suggested that repeating the investigation at 20 °C would not affect the amount of oxygen released by the seaweed. Evaluate this suggestion.

Question 39

23b)During photosynthesis, oil-palm trees convert carbon dioxide into organic substances. Describe how.

Answer 39

.
1(Carbon dioxide combines with ribulose bisphosphate / RuBP;
2. Produces two molecules of glycerate (3-)phosphate / GP;
3. Reduced to triose phosphate / TP;
4. Using reduced NADP;
5. Using energy from ATP;
6. Triose phosphate converted to other organic substances / named organic substances / ribulose bisphosphate;
7. In light independent reactio

Question 40

In photosynthesis, which chemicals are needed for the light-dependent reaction?

Answer 40

NADP, ADP, Pi and water;

Question 41

Describe what happens during photoionisation in the light-dependent reaction.
(1)

Answer 41

Chlorophyll absorbs light
Electron/s are lost

Question 42

Explain why the student marked the origin using a pencil rather than using ink

Answer 42

Ink and (leaf) pigments would mix

Question 43

Describe the method the student used to separate the pigments after the solution of pigments had been applied to the origin.

Answer 43

Level of solvent below origin/line;
Remove/stop before (solvent) reaches top/end;

Question 44

The pigments in leaves are different colours. Suggest and explain the advantage of having different coloured pigments in leaves

Answer 44

(Absorb) different/more wavelengths (of light) for photosynthesis;

Question 45

Heat stress is a condition that often occurs in plants exposed to high temperatures for a prolonged period of time. Heat stress is a major factor in limiting the rate of photosynthesis.
(a) Heat stress decreases the light-dependent reaction of photosynthesis.
Explain why this leads to a decrease in the light-independent reaction.

Answer 45

(Less/no) ATP
(Less/no) reduced NADP;

Question 46

A decrease in the activity of the enzyme rubisco would limit the rate of photosynthesis.
Explain why.

Answer 46

(Less/no) carbon dioxide (reacts) with RuBP; (Less/no) GP;

Question 47

The solution that the student used to produce the chloroplast suspension
had the same water potential as the chloroplasts.
Explain why it was important that these water potentials were the same.

Answer 47

osmosis doesn’t ocurr
chloroplast doesn’t burst

Question 48

Explain how chemicals which inhibit the decolourisation of DCPIP could slow the growth of weeds.

Answer 48

1.
2. Less / no reduced NADP produced;
3. Less / no GP reduced / converted to TP;
Less / no ATP produced;

Question 49

Other than the thermometer, explain how two features of the calorimeter shown in the diagram above would enable a valid measurement of the total heat energy released.

Answer 49

Water has high (specific) heat capacity;
Insulation/space/air reduces loss/gain of heat
Stirrer distributes heat (energy);

Question 50

Atrazine binds to proteins in the electron transfer chain in chloroplasts of weeds, reducing the transfer of electrons down the chain.
Explain how this reduces the rate of photosynthesis in weeds.

Answer 50

Reduced transfer of protons across thylakoid membrane
(So) less ATP produced;
less reduced NADP produced;
So) light-independent reaction slows

Question 51

When treated with Atrazine, weeds have been shown to give off small amounts of heat.
Suggest an explanation for this observation.

Answer 51

Idea that energy is released from high energy / excited electron/s (that were lost from chlorophyll)

Question 52

A scientist investigated the effect of inhibitors on neurones. She added a respiratory inhibitor to a neurone. The resting potential of the neurone changed from –70 mV to 0 mV.
Explain why.

Answer 52

1.less atp produced
2. No/less active transport
Electrochemical gradient not maintained

Question 53

Describe the sequence of events involved in transmission across a cholinergic synapse.
Do not include details on the breakdown of acetylcholine in your answer

Answer 53

1. Depolarisation of presynaptic membrane;
2. Calcium channels open and calcium ions enter
3. (Calcium ions cause) synaptic vesicles move to/fuse with presynaptic membrane and release acetylcholine/neurotransmitter;
4. Acetylcholine/neurotransmitter diffuses across (synaptic cleft);
   5~(Acetylcholine attaches) to receptors on the postsynaptic membran

Question 54

Dopamine is a neurotransmitter released in some synapses in the brain. The transmission of dopamine is similar to that of acetylcholine.
Dopamine stimulates the production of nerve impulses in postsynaptic neurones.
Describe how.
Do not include in your answer the events leading to the release of dopamine and the events following production of nerve impulses at postsynaptic neurones.

Answer 54

(Dopamine) diffuses across (synapse);
Attaches to receptors on postsynaptic membrane;
Ignore name/nature of receptor e.g. cholinergic
Stimulates entry of sodium ions and depolarisation/action potential;

Question 55

Morphine is a drug that has a similar structure to endorphins and can provide pain relief.
Explain how.

Answer 55

Morphine attaches to opioid receptors;
More) dopamine released (to provide pain relief);

Question 56

GABA is a neurotransmitter released in some inhibitory synapses in the brain. GABA causes negatively charged chloride ions to enter postsynaptic neurones.
Explain how this inhibits postsynaptic neurones.

Answer 56

neurone becomes more negative/hyperpolarisation/inhibitory postsynaptic potential;
More sodium ions required (to reach threshold)
For depolarisation/action potential;

Question 57

When a nerve impulse arrives at a synapse, it causes the release of neurotransmitter from vesicles in the presynaptic knob.
Describe how.

Answer 57

(Nerve impulse / depolarisation of membrane) causes Ca 2+ channel (proteins) to open;
Ca 2+ enter by (facilitated) diffusion;
Causes (synaptic) vesicles to fuse with (presynaptic) membrane

Question 58

Suggest and explain one advantage of the movement of mitochondria towards the presynaptic membrane when nerve impulses arrive at the synapse.

Answer 58

1.
2. To move vesicles / for active transport of ions / for myosin to
(Mitochondria) supply (additional) ATP / energy;
move past actin