Photosynthesis and CAM

Question 1

What type of reaction is Photosynthesis?

Answer 1

Anabolic chemical reaction: forming larger molecules from smaller parts

Question 2

Role of Xylem

Answer 2

Responsible for providing water for photosynthesis

Question 3

Purpose of Photosynthesis

Answer 3

Produce glucose to be used as energy

Question 4

Where does photosynthesis take place?

Answer 4

in the chloroplasts and light energy is needed for the reaction to happen

Question 5

What are chlorophylls

Answer 5

Found in chloroplasts, they absorb light energy.

Question 6

What are chloroplasts and structure

Answer 6

> Eukaryotic cells that contain membrane-bound organelles.
They have outer and inner membranes regulating the movement of materials in and out of the organelle
-> Inner Membrane: Single thylakoids and stacks of multiple thylakoids called granum ( plural: grana)
–> Thylakoids have a thylakoid membrane in them which is surrounded by a lumen ( cytosol). Chlorophyll is inside these membrane.
amount of chlorophyll affects the rate of photosynthesis

Question 7

Inputs of Photosynthesis

Answer 7

CO2 ( taken through the stomata) and water (taken up through the roots of the plant towards the leaves via the xylem.

Question 8

Outputs of Photosynthesis

Answer 8

glucose, oxygen (O2) and water

Question 9

What is a stomata

Answer 9

> Singular: stoma
Plural : stomata
It is a pore in the epidermis of leaves that allows gas exchange and water to leave the plant. It is surrounded by guard cells

Question 10

What are guard cells?

Answer 10

They regulate the opening and closing of the pore ( stomata)

Question 11

Closing and opening of the stomata

Question 12

1st stage of photosynthesis

Answer 12

The light-dependent stage which occurs in the thylakoid membranes of chloroplasts
> Absorption of light energy by chlorophyll
> Splitting of water (photolysis)

Question 13

How does photolysis happen?

Answer 13

1. Light energy splits producing oxygen (O2) and H ions (H+) and electors
2. Oxygen (waste) release through diffusion out of the thylakoid membrane > stroma > chloroplast > atmosphere via stomata
3. Electrons released when light e stimulates chlorophyll are used by ATP synthase ( enzyme in thylakoid membrane ) to catalyze the synthesis of ATP from ADP + Pi.
4. H ions and some electrons released previously are taken up by an acceptor molecule called NADP+ which forms NADPH
5. H ions ( via NADPH) and ATP produced during the light-dependent stage are then transported to the stroma for the light-independent stage photosynthesis

Question 14

2nd stage of photosynthesis

Answer 14

The light-independent stage which occurs in the stroma of the chloroplast
> Formation of glucose from CO2
> Is the Calvin Cycle

Question 15

Calvin Cycle Steps

Answer 15

1. Begin with 5 C RuBP which is joined with CO2 from the atmosphere with the help of the enzyme RuBisCO ( RuBP carboxylase)
2. The compound breaks down into 2 x PGA. ATP is the energy source from the dependent stage. H ions carried by the loaded ‘NADPH’ are coming from the light-dependent stage.
3. PGA is converted into (PGAL) using NADPH and ATP
4. PGAL molecules then leave the chloroplast and move into the cytosol of the cell. They form glucose and regenerate RuBP
5. NADP+, ATP and Pi are produced and returned to the light-dependent stage
6. H2O is formed -> The oxygen created from breakdown of CO2 binds with some free H+ released by the NADPH

Question 16

Inputs and Outputs of Independent Stage

Answer 16

Inputs: NADPH, ATP, CO2
Outputs: Water, ADP + Pi, NADP+, 2PGAL

Question 17

Limiting factors of photosynthesis

Answer 17

> Light availability
Water Availability
Temperature
Carbon Dixoide concentration

Question 18

Limiting factors of enzyme activity

Answer 18

> Temp
pH
Concentration ( substrate and enzyme )
Inhibition (comp and non-comp)

Question 19

What are C3 plants?

Answer 19

> 85% of plants
Form 3C compound PGA during CC
—> Uses the enzyme RuBisCO to catalyse carbon fixation

Question 20

RuBisCO role

Answer 20

> Catalyses the fixation of carbon to RuBP
It is not very efficient, particularly in C3 plants.
Oxygen in a competitive inhibitor for RuBisCO= Rate of photosynthesis decreases

Question 21

What is photorespiration?

Answer 21

When oxygen is the substrate for RuBisCO, not CO2.
> Oxygen is usually removed in photosynthesis so photorespiration is not an issue

Question 22

What condition does photorespiration occur more?

Answer 22

> Hot and dry water where there is very little water
–> C3 plants close their stomata to conserve water which limits their access to CO2 and prevents getting rid of waste oxygen. RuBisCO binds to O2 instead of CO2.

Question 23

C4 Plants

Answer 23

> Use the enzyme PEP carboxylase to fix carbon dioxide and form malate (4C)
Separate the light-dependent reactions and the use of CO2 in space
Formation of malate is in mesophyll cells
and the Calvin cycle is in the bundle-sheath cell.

Question 24

CAM Plants

Answer 24

> Use the enzyme PEP carboxylase to fix carbon dioxide and form malate (4C)
Separate the light-dependent reactions and the use of carbon dioxide in time
Formation of malate (OAA) is AT NIGHT whilst Calvin cycle forms PGA is DURING THE DAY