Photosynthesis

Question 1

Define phosphorylation

Answer 1

Adding phosphate to a molecule eg. ADP to ATP

Question 2

Defin photoposphorylation

Answer 2

Adding phosphate to a molecule using light

Question 3

Define photolysis

Answer 3

The splitting of a moleule using light energy

Question 4

Define hydrolysis

Answer 4

The splitting of a molecule using water eg. ATP to ADP

Question 5

Define redox reactions

Answer 5

Reactions that involve:
Reduction = gain of electrons and maybe a gain of hydrogen
Oxidation = loss of electrons and maybe a loss of hydrogen

Question 6

What is photosynthesis?

Answer 6

The process where energy from light is used to break apart water
The hydrogen from water is stored as a fuel in glucose which forms when combined with CO2. O2 is released into atmosphere

Question 7

Gibe the equation for photosynthesis

Answer 7

6CO2 + 6H20 —-> C6H12O6 + 6O2

Question 8

How is ATP made?

Answer 8

Its synthesised by the phosphorylation of ADP using energy from the breakdown of glucose in respiration

Question 9

How and where is energy stored in ATP?

Answer 9

Stored as chemical energy in the phosphate bond

Question 10

What enzyme catalyses the hydrolysis of ATP into ADP and Pi?

Answer 10

ATP synthase

Question 11

What is a coenzyme and how do they work?

Answer 11

A molecule that aids the function of an enzyme

They transfer a chemical group from one molecule to another

Question 12

Give an example of a coenzyme used in photosynthesis:

Answer 12

NADP transfers hydrogen so can either reduce or oxidise a molecule

Question 13

Where does photosynthesis take place?

Answer 13

The chloroplast of a plant cell

Question 14

What are chloroplasts?

Answer 14

Flattened organelles that contain a double membrane (chloroplast envelope)

Question 15

What are thylakoids?

Answer 15

Fluid-filled sacs found in the chloroplast that are stacked into grana

Question 16

Why do thylakoids have a large surface area?

Answer 16

So as much light energy can be absorbed as possible

Question 17

How are grana linked?

Answer 17

Llamelae

Question 18

What molecules are abundant in the thylakoids membranes?

Answer 18

ATP synthase (to produce ATP in light dependent reaction)

Question 19

What pigments do chloroplasts contain and where are they found?

Answer 19

Photosynthetic pigments – chlorophyll a, chlorophyll b, carotene
Found in thylakoid membranes and attached to proteins = photo system

Question 20

What are photosynthetic pigments?

Answer 20

Coloured substances that absorb light energy

Question 21

What wavelength does photo system 1 absorb?

Answer 21

700nm

Question 22

What wavelength does photo system 2 absorb?

Answer 22

680nm

Question 23

What is the stroma?

Answer 23

A gel-like substance surrounding the thylakoids that contains enzymes, sugars and organic acids required for light independent reaction

Question 24

Briefly describe the light dependent reaction:

Answer 24

• Requires light energy which is absorbed by photo systems
• Light energy adds a phosphate group to ADP to form ATP
• NADP converted to reduced NADP
• H2O oxidised to O2
• Occurs in thylakoids membranes

Question 25

How is ATP made in the light dependent reaction?

Answer 25

Photophosphorylation

Question 26

What is light energy needed for in light dependent reaction? X3

Answer 26

1) Making ATP from ADP and Pi = photophosphorylation 2) Making reduced NADP from NADP 3) Splitting water into protons, electrons and oxygen = photolysis

Question 27

What two types of photophosphorylation occur in light dependent reaction?

Answer 27

Cyclic and non-cyclic

Question 28

Name the products of non-cyclic photophosphorylation:

Answer 28

ATP, reduced NADP and O2

Question 29

What are electron carriers?

Answer 29

Proteins that transfer elections

Question 30

What is an electron transport chain?

Answer 30

A chain of proteins through which excited electrons flow

Question 31

Describe non-cyclic photophosphorylation:

Answer 31

- Light energy is absorbed by PSII - Light energy excites electrons in chlorophyll moving them to a higher energy level - High-energy electrons move along the electron transport chain to PSI - As electrons move along the chain, they must be replaced so light energy splits water into protons, electrons and oxygen through photolysis - Excited electrons lose energy as they move along the ETC - Energy used to pump protons INTO THE THYLAKOIDS so higher concentration inside than in the stroma = proton gradient - Protons diffuse down their concentration gradient into the stroma via enzyme ATP synthase which combines ADP + Pi to form ATP = chemiosmosis - Electrons from NADP, and a proton from stroma, are transferred to form reduced NADP

Question 32

Describe cyclic photophosphorylation:

Answer 32

- Only uses PSI - Only produces small amounts of ATP - Electrons are recycled repeatedly through PSI and not passed onto NADP

Question 33

Briefly describe the light independent reaction (Calvin Cycle):

Answer 33

- Doesn’t require light energy - ATP and reduced NADP (made in light dependent reaction) supply energy and hydrogen to make glucose and CO2 - Occurs in stroma

Question 34

Describe the Calvin cycle:

Answer 34

1. CO2 enters leaf through stomata and diffuses into the stroma Combines with ribulose bisphosphate Catalysed by RUBISCO Creates 2x GP (3C) 2. Hydrolysis of ATP provides energy to turn GP into GALP (some converted to useful organic compounds and some is put back into Calvin cycle Reduced NADP is recycled into NADP 3. Two molecules of GALP used to make a hexose sugar BUT 5 out of every 6 GALP molecules used to regenerate RuBP which uses ATP

Question 35

What biological molecules are made from GALP and GP?

Answer 35

- Carbohydrates – simple sugars made from joining 2 GALP together, polysaccharides made by joining two hexose sugars together - Lipids – made using glycerol which is synthesised from GALP and fatty acids from GP - Amino acids – some made from GP - Nucleic acids – sugar in RNA (ribose) made from GALP

Question 36

Name of experiment to investigate photosynthesis using extracts of chloroplasts:

Answer 36

Hill Reaction

Question 37

Name of redox indicator dye and colour change:

Answer 37

DCPIP turns from blue to colourless

Question 38

Describe the Hill Reaction:

Answer 38

1. Cut spinach leaves into pieces, removing tough stalks 2. Grind leaf with chilled isolation solution 3. Filter liquid through a funnel with muslin cloth and transfer to centrifuge tubes 4. Place in centrifuge at high speed for 10 minutes – chloroplast will be observable as a pellet 5. Get rid of excess liquid 6. Re-suspend pellets in fresh chilled isolation solution = chloroplast extract = store in ice 7. Set up a colorimeter with red filter and fill cuvette with chloroplast extract and distilled water 8. Set up a test tube rack a set distance from lamp 9. Put a test tube in the rack and fill with a set volume of chloroplast extract and a set volume of DCPIP – mix 10. Immediately take a sample from test tube and place into a cuvette and record absorbance using a colorimeter – continue doing every 2 mins for 10 mins 11. Repeat experiment including two controls

Question 39

What will happen to the absorbency as DCPIP becomes reduced?

Answer 39

The absorbance will decrease as DCPIP becomes reduced and loses its blue colour

Question 40

Independent variable of Hill Reaction:

Answer 40

Light reaching chloroplast samples

Question 41

Dependent variable of Hill Reaction:

Answer 41

Amount of DCPIP reduced

Question 42

Control variables for Hill Reaction: x4

Answer 42

- Chloroplast from same species of plants - Amount of buffer solution added to each tube 5cm3 - Amount of DCPIP added to each tube 10cm3 - Length of time left for

Question 43

What substance does DCPIP take the place of?

Answer 43

NADP | Acts as an electron receptog