U3 Photosynthesis

Question 1

What is dependent ultimately upon photosynthesis?

Answer 1

all food production

Question 2

What is photosynthesis?

Answer 2

A process in which green plants trap sunlight energy to produce carbohydrates (food)

Question 3

Chloroplast structure

Answer 3

lamella (links between grana)
stroma (fluid)
outer membrane
inner membrane
thylakoids (make up a granum)
granum (stack of thylakoids (plural=grana))
DNA

Question 4

What are the 3 fates of white light when it hits a leaf?

Answer 4

-most of it is absorbed by pigments in the leaf
light energy not absorbed can either be:
-transmitted through the leaf
-or reflected off the surface

Question 5

what do leaves contain?

Answer 5

several coloured pigments of which chlorophyll is the most important

Question 6

What do different pigments do differently?

Answer 6

absorb different wavelengths (colours) of light

Question 7

What does an action spectrum graph show?

Answer 7

the rate of photosynthesis at different wavelengths of light

Question 8

what does an absorption spectrum graph show?

Answer 8

the ability of each pigment to absorb different wavelengths of light

Question 9

what are accessory pigments?

Answer 9

Pigments that extend the range of wavelengths absorbed in photosynthesis

AND they pass the energy they capture onto chlorophyll

Question 10

Example of an accessory pigment

Answer 10

carotenoids

Question 11

what is stage 1 of photosynthesis?

Answer 11

the light reactions/photolysis

Question 12

where do the light reactions take place?

Answer 12

grana of the chloroplast

Question 13

what happens during the light reactions?

Answer 13

in the chloroplast, when light energy is absorbed by pigments, electrons in the pigment become excited and are raised to a higher energy stage

the electrons are then transferred along an electric transports chain, releasing energy

this energy is used to generate atp by atp synthesis (used later in carbon fixation)

energy is also used for photolysis in which water is split into oxygen and hydrogen

Question 14

What happens to the oxygen produced during the light reactions?

Answer 14

it is evolved (released) from the cell/leaf

it is a by-product of

Question 15

what happens to the hydrogen produced during the light reactions?

Answer 15

it is transferred to the coenzyme (hydrogen acceptor) NADP to make NADPH

The NADPH is used later in carbon fixation

Question 16

what is the second stage of photosynthesis?

Answer 16

carbon fixation where glucose is made

a series of enzyme-controlled reactions

Question 17

Steps of carbon fixation

Answer 17

1-Carbon dioxide enters the cycle and becomes attached to RuBP. This reaction is controlled by the enzyme RuBisCO

2-The carbon dioxide and RuBP combine to make 3PG

3-3PG then joins with the hydrogen from NADPH and is phosphorylated by the addition of phosphate (Pi) from ATP which supplies the energy

4-This process produces G3P

5-Some G3P is then used to regenerate RuBP (to continue the process). The remainder is used to synthesise glucose

Question 18

Fates of glucose after photosynthesis

Answer 18

Respiration (respiratory substrate)

Starch (storage carbohydrate)

Cellulose (structural carbohydrate eg cell wall)

Biosynthesis pathways-fats and oils, proteins, nucleic acids (DNA, RNA)