Photosynthesis and Light Dependent Reaction

Question 1

Where does photosynthesis take place?

Answer 1

In the chloroplasts of plant cells.

Question 2

What are chloroplasts?

Answer 2

Small flattened organelles found in plant cells.
They have a double membrane called the chloroplast envelope.
Thylakoids are stacked up in the chloroplast into structures called grana.
The grana are linked together by bits of thylakoid membrane called lamellae.

Question 3

What happens if something has been reduced?

Answer 3

Loss of oxygen
Gain of electrons
Gain of hydrogen
Energy taken in

Question 4

What happens if something has been oxidised?

Answer 4

Addition of oxygen
Loss of electrons
Loss of hydrogen
Energy given out

Question 5

What are coenzymes?

Answer 5

A molecule that aids the function of an enzyme.

They work by transferring a chemical group from one molecule to another.

Question 6

What is a coenzyme used in photosynthesis?

Answer 6

NADP- this transfers hydrogen from one molecule to another

Question 7

What are the two stages to photosynthesis?

Answer 7

Light dependent reaction

Light independent reaction.

Question 8

Where does the light dependent reaction take place?

Answer 8

In the thylakoid membrane of the chloroplast.

Question 9

What three things are the light energy absorbed by photosynthesis used for?

Answer 9

Making ATP from ADP and inorganic phosphate (phosphorylation).
Making reduced NADP from NADP.
Splitting water into H+ ions, electrons and oxygen (photolysis).

Question 10

What are photosynthetic pigments?

Give one example of a photosynthetic pigment.

Answer 10

Coloured substances that absorb the light energy needed for photosynthesis.
E.g Chlorophyll a/ chlorophyll b/ carotene

Question 11

NADP is a coenzyme used in photosynthesis. What chemical group does it transfer between molecules?

Answer 11

Hydrogen

Question 12

Which products of the light dependent reaction are needed in the light independent reaction?

Answer 12

ATP and reduced NADP

Question 13

What is phosphorylation?

Answer 13

The process of adding phosphate to a molecule using light.

Question 14

What is the electron transport chain?

Answer 14

A chain of proteins through which excited electrons flow.

Question 15

Name the products of the photolyis of water?

Answer 15

Protons, electrons and oxygen.

Question 16

What is the purpose of photolysis in the light dependent reaction?

Answer 16

To replace excited electrons in photosystem II.

Question 17

Excited electrons lose energy as they move along the electron transport chain. Explain how this leads to ATP synthesis.

Answer 17

This energy is used to transport protons into the thylakoid so that the thylakoid has a higher concentration of protons than the stroma.
This forms a proton gradient across the membrane.
Protons move down their concentration gradient, into the stroma, via an enzyme called ATP synthase.
The energy from this movement combines ADP and inorganic phosphate to form ATP.

Question 18

Name the photosystems involved in:

a) non cyclic photophosphorylation
b) cyclic photophosphorylation

Answer 18

a) Photosystem I and photosystem II

b) Photosystem I

Question 19

Name the products of:

a) non cyclic photophosphorylation
b) cyclic photophosphorylation

Answer 19

a) ATP, Reduced NADP and oxygen

b) ATP

Question 20

What happens in the light dependent reaction?

Answer 20

Photon of light strikes psII.
This causes it to become excited.
When excitation occurs two high energy electrons are released.
They move to an ETC and are passed down from carrier to carrier which releases a small amount of energy for the production of ATP.
These electrons replace the electrons that have been released from PSI after being struck by a photon.
Those electrons pass down an ETC.
These electrons bind to 2 H+ ions which have been created in the photolysis of water to form to reduce NADP into NADPH.
The two electrons from the water go to replace those that were lost in PSII.