photosynthesis

Question 1

Describe how the structure of a chloroplast is adapted to its function in photosynthesis (

Answer 1

Membrane/disc shape produces large SA for light absorption;
layering of membrane allows a lot of pigment;
(permeable) membrane allows diffusion of gases/carbon dioxide;
membranes provide surface for attachement of electrons;
stroma/matrix contains enzymes for LIR;

Question 2

why does the amount of gp increase in darkness

Answer 2

gp accumulates as it can not be converted to tp as it requires the products of the ldr

Question 3

what does water do

Answer 3

provies protons and electrons to replaced the ones lost after photoionisation

Question 4

The weedkiller DCMU blocks the flow of electrons along the chains of electron carriers. Describe and explain the effect this will have on the production of TP in the light-independent reaction. (3)

Answer 4

Fall in production of TP;
TP production requires ATP/reduced NADP;
produced during passage of electrons along electron transport chain

Question 5

Explain why ATP is better than glucose as an immediate energy source for cell metabolism (2)

Answer 5

Energy is available more rapidly because released in a single reaction/does not go through as many processes;
ATP releases its energy in small/manageable quantities;

Question 6

DNP is a substance which allows electron transport to take place without the production of ATP. When DNP is given to rats, their body temperatures rise. Explain why. (2)

Answer 6

Energy released as heat;

as energy is not being used to produce ATP

Question 7

Plants produce ATP in the light-dependent reaction of photosynthesis. Explain why plants cannot use this as their only source of ATP. (2)

Answer 7

Photosynthesis cannot produce ATP in dark;
Cannot be produced in cells lacking chlorophyll;
ATP cannot be transported;

Question 8

Explain the change in the concentration of radioactive GP after the light was switched off. (3)

Answer 8

No ATP made;
No reduced NADP;
GP not converted (in dark);
TP not formed (in dark);

Question 9

What is the role of chlorophyll in photosynthesis? (3)

Answer 9

Absorbs light/energy;
Loses electrons/becomes positively charged/is oxidised;
Accepts electrons from water/from OH- ;
Causes more water to dissociate/pulls equilibrium to the right;

Question 10

how is reduced nadph used

Answer 10

for the reduction of gp to tp

Question 11

Describe how light energy absorbed by chlorophyll molecules is used to synthesise ATP. (5)

Answer 11

Excitates electrons
electrons raised to higher energy level;
Electrons emitted from chlorophyll molecule;
electron transport chain;
Loss of energy by electron(s) along electron transport chain;
Energy lost by electron(s) is used to synthesise ATP;
From ADP + Pi;

Question 12

how is nadph formed

Answer 12

when electrons from the etc and protons from photolysis combine with nadp the co enzyme.

Question 13

photosynthesis generally takes place in a leaf. Describe how the leaf is adapted to allow
this process to occur effectively. (3)

Answer 13

Large surface area to collect solar energy;
transparent nature of cuticle to allow light penetration;
position of chlorophyll to trap light;
stomata to allow exchange of gases;
thin / max. surface area to volume ratio for diffusion of gases;
spongy mesophyll / air spaces for carbon dioxide store;
xylem for input of water;
phloem for removal of end products;

Question 14

what is rubp

Answer 14

carbon dioxide acceptor, forms gp

Question 15

Explain why an increase in temperature will increase the rate of photosynthesis. (3)

Answer 15

enzymes are involved;
extra kinetic energy / molecules move faster;
molecules collide more often / more enzyme - substrate complexes formed;
increased rate of diffusion of raw materials;

Question 16

Explain why the rate of CO2 uptake decreased in cloudy conditions (2)

Answer 16

Carbon dioxide taken up in photosynthesis

light limits rate of photosynthesis;

Question 17

Explain why the rate of CO2 uptake is lower at midnight than at midday (2)

Answer 17

No photosynthesis at midnight
Smaller CO2 diffusion gradient;
stomata closed

Question 18

Describe two features of an ATP molecule which make it a “biologically useful
source of energy”.

Answer 18

Releases energy when hydrolysed (immediate energy source)
Can be readily transported when needed;
Allows energy to be released in suitable amounts;

Question 19

Describe two ways in which the structure of a chloroplast differs from the structure
of this bacterial cell. (2)

Answer 19

chloroplast has (and bacterium does not)/ no cell wall;
two membranes surrounding chloroplast;
grana/thylakoids;

Question 20

The suspension of chloroplasts in blue reagent was exposed to sunlight. The blue colour disappeared. Use your knowledge of the light-dependent reactions of photosynthesis to explain why. (2)

Answer 20

chlorophyll excited

electrons from chlorophyll changes the dye colour;

Question 21

Another suspension of chloroplasts was set up as before. Small quantities of ADP and phosphate ions were added and then the tube was exposed to light. The blue colour disappeared more quickly. Explain why.

Answer 21

ADP and phosphate needed to produce ATP

ADP levels are a limiting factor

Question 22

The red seaweed lives under water at a depth of 2 metres. Suggest an advantage to the red seaweed of having other pigments in addition to chlorophyll a. (2)

Answer 22

more wavelengths of light absorbed

more efficient photosynthesis can occur at these depths

Question 23

why would a scientist measure oxygen and time… in a reac

Answer 23

as o2 is produced in the ldr so, to measure the rate of psynth

Question 24

why is.. low at these wavelengths of light

Answer 24

less absorption of light more reflection, less photosynthesis as less light for ldr

Question 25

3 leaf grease treatments

Answer 25

no grease means stomata is open, 2nd- grease on lower surface seals the stomata 3- grease on both surfaces shows that sealing is effective as it stops co2

Question 26

The stomata close when the light is turned off.

Explain the advantage of this to the plant.

Answer 26

water is lost through stomata;

prevents water loss; keeps plants turgid to prevent wilting

Question 27

Treatment 2 shows that even when the lower surface of the leaf is sealed

there is still some uptake of carbon dioxide.
Suggest how this uptake of carbon dioxide continues.

Answer 27

(Carbon dioxide uptake) through the upper surface of the leaf, through the cuticle

Question 28

In both Treatment 1 and Treatment 2, the uptake of carbon dioxide falls to
zero when the light is turned off.
Explain why.

Answer 28

No use of carbon dioxide in photosynthesis (in the dark);

2. No diffusion gradient for co2 into the leaf

Question 29

DCMU is used as a weed killer. It inhibits electron transfer during photosynthesis. The addition of DCMU to tube A decreased the uptake of carbon dioxide. Explain why

Answer 29

as less atp produced during etc, less nadph produced

Question 30

  Explain why the increase in the dry mass of a plant over twelve months is less than the mass of hexose produced over the same period

Answer 30

same hexose, co2 is produced and some parts of the plant are eaten

Question 31

the ways we can increase photosynthesis

Answer 31

artificial lighting, heating a greenhouse, humidifers maybe. burning fuel eg paraffin burners to release more co2

Question 32

why is aerobic respiration only 32 percent efficient

Answer 32

due to some protons leaking across across the mitochondrial membrane during oxidative phosphorylation, atp being used to actively transport pyruvate and nadh into the matrix AND
because some energy is lost as heat

Question 33

Iron deficiency results in a decrease in the uptake of co2. iron deficiency deceases atp

Answer 33

less tp is re converted to rubp as atp is required for that. this means that less co2 can be combined with rubp.

Question 34

dcmu is used as a weed killer why does it decrease co2 uptake

Answer 34

less atp produced, less reduced nadp formed during electron transport.

Question 35

Why is it important for plants to produce atp during resp in addition to psynth

Answer 35

in the dark theres no production of atp in psynth
some tissues may be unable to photosynthesise
atp cannot be moved from cell to cell or stored
atp produced in psynth may not be sufficient
atp for active transport
atp for synthesis of glucose

Question 36

A plant grows on mountains scientists predict that temp will increase from 20-23 degrees. its also likely to become cloudier how are these changes likely to affect them

Answer 36

higher temp so higher rate of resp
growth will decrease at higher temps
photosynthesis decreases as its limited by light

Question 37

how could psynth be measured

Answer 37

oxygen uptake and time or co2 uptake and time

Question 38

iron deficiency results in a decrease in the uptake of co2 why as tp decreases

Answer 38

as less tp converted back to rubp
less co2 combines with rubp
no diff gradient maintained for co2 into leaf

Question 39

less gp so why does co2 decrease

Answer 39

less tp, less tp, less rubp reformed so less co2 can react with it no diff gradient maintainef

Question 40

energy enters most ecosystems through the ldr of psynth, Describe what happens during the ldr

Answer 40

photolysis- chlorophyll absorbs ligjht energy and electrons are moved alogn the etc releasing energy and photolysis produces protons electrons and o2, nadp is reduced by protons and electrons

Question 41

the concs of co2 in the air at diff heights above ground changes over a period of 24 hours, use your knowledge of psynth to describe these changes and explain why they occur

Answer 41

co2 has a high conc in the dark as no psynth
dark plants respire more producing a net co2 whereas in the light the plant takes in more co2

decrease in co2 means a decrease in co2 at ground level where there is fewer leaves, less psynth and less light.

Question 42

as o2 increases what happens to co2 concs

Answer 42

as it increases less of rubp can react with co2, as o acts as a competitive inhibitor and therefore blocks rubiscos active site and therefore less rubp regenerated