5A- Photosynthesis

Question 1

Where does photosynthesis take place?

Answer 1

In the chloroplasts. Chloroplasts are flatterenrd organelles surrounded by a double membrane.

Thylakoids are stacked up in the chloroplast into to structures called grana. The grana are linked by lamellae.

Question 2

What do chloroplasts contain?

Answer 2

Photosynthetic pigments (chlorophyll A, B and Carotene)

These are coloured substances that absorb light energy.

They are found in the thylakoid membrane and are attached to proteins. This is a photosystem.

Question 3

How many photosystems are there?

Answer 3

Two.

PSI absorbs light at 700 nm and PSII absorbs light at 680 nm.

Question 4

What is the stroma?

Answer 4

The membrane surrounding the thylakoids.

It contains enzymes, sugars and organic acids.

Carbohydrates produced by photosynthesis and not used straight away are stored as starch grains in the aroma.

Question 5

What stages is photosynthesis split into?

Answer 5

The light dependent and the light independent reaction.

Question 6

What is the light dependent reaction?

Answer 6

This reaction needs light energy.

Takes place in the thylakoid membrane.

Light energy is absorbed by the CHLOROPHYLL (and other pigments) in the PS.
This energy excited the electron in the chlorophyll so its released. It’s photoionised.

Some of the energy from the released electron is used to add phosphate to ADP, forming ATP. Also some is used to form reduced NAPD by reducing NADP.

ATP transfers energy and reduced NADP transfers hydrogen to the light independent reaction.

H2O is oxidised to O2.

Question 7

What is the light independent reaction?

Answer 7

This also known as the Calvin cycle. It doesn’t use light energy directly.

It takes place in the stroma.

ATP and reduced NADP from the light dependent reaction supply the energy and hydrogen to make simple sugars from CO2.

Question 8

How is ATP made in the light dependent reaction?

Answer 8

It’s made by photophosphorylation.

Question 9

In the light dependent reaction what is the energy resulting from the photoionisation of chlorophyll used for?

Answer 9

Making ATP from ADP and Pi.

Making reduced NADP from NADP.

Splitting water into protons. (H+ ions), electrons and O2. This is photolysis.

Question 10

How many stages of photophosphorylation does the light dependent reaction have?

Answer 10

Two.

Non cyclic

And

Cyclic.

(Each process has different products).

Question 11

What does non cyclic photophosphorylation produce?

Answer 11

ATP, reduces NaDP and O2.

Question 12

What does cyclic photophosphorylation produce?

Answer 12

Only ATP.

It only uses PSI.

The electrons are passed back to PS1 via electron carriers.

Question 13

Where does the Calvin cycle take place?

Answer 13

The Calvin cycle takes place in the stroma of the chloroplasts.

Question 14

What does the light independent reaction make?

Answer 14

Triose phosphate, which can be used to make glucose and other organic substances.

Ribulose bisphosphate.

Question 15

What does the light independent reaction need to keep it going?

Answer 15

CO2

ATP

H+ Ions

Question 16

What are TP and GP converted into?

Answer 16

Useful organic substances like glucose.

Can be used to make carbohydrates, lipids and amino acids.

Carbs- heroes sugars are made by joining two TP and larger carbohydrates are made by joining become sugars together.

Lipids- Made using glycerol, which is synthesised from TP and fatty acids which are synthesised from GP.

Question 17

Why does the Calvin cycle need to turn six times?

Answer 17

Three turns of the cycle produced six molecules of TP.

Five out of six and regenerated to make RuBP.

For every three turns one TP is produced to make a hexose sugar.

Glucose takes 2 TP so needs 6 turns.

Takes 18 ATP and 12 reduces NADP.