Edexcel SNAB A level Biology - Topic 5

Phosphorylation

Adding phosphate to a molecule

Photophosphorylation

Adding phosphate to a molecule using light

Photolysis

The splitting of a molecule using light energy

Hydrolysis

The splitting of a molecule using water

Redox reactions

Reactions that involve oxidation and reduction

Reduction

Gain of electrons and may have gained hydrogen or lost oxygen

Oxidation

Loss of electrons and may have lost hydrogen or gained oxygen

Photosynthesis

The process where energy from light is used to break apart the strong bonds in H2O molecules

Overall equation for photosynthesis

6CO2 + 6H2O + light --> C6H12O6 + 6O2

How do animals obtain glucose?

Eating plants or other animals

How do cells get their energy?

During respiration glucose is broken-down which releases energy which is used to make ATP

What does ATP do?

Carries energy around the cell to where it's needed

How is ATP made?

The phosphorylation of ADP using energy from an energy releasing reaction e.g. the breakdown of glucose in respiration.

How is energy stored in ATP?

Stored as chemical energy in the phosphate bond

What enzyme catalyses the phosphorylation of ADP?

ATP synthase

How does ATP supply energy?

- Diffuses to the part of the cell that needs energy

- Its broken down via hydrolysis back into ADP and inorganic phosphate

- Chemical energy is released from the phosphate bond and used by the cell

What enzyme catalyses breakdown of ATP to ADP?

ATPase

What happens after ATP is broken down to ADP and inorganic phosphate?

They are recycled and the process starts again

Coenzyme

A molecule that aids the function of an enzyme.

How do coenzymes work?

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

Coenzyme used is photosynthesis

NADP

Where does photosynthesis take place?

Chloroplast

Structure of chloroplast

- Flattened organelles

- Double membrane (chloroplast envelope)

- Thylakoids staked up into grana, linked by lamellae

- Photosynthetic pigments

- Photosystems

- Stroma

Function of the double membrane in chloroplast

Keeps the reactants for photosynthesis close to their reaction sites

Structure and function of thylakoids

- Fluid filled sacs

- Have a large surface area to allow as much light energy to be absorbed as possible

- Stacked into grana

What are grana linked together by?

Lamella

What are lamella?

Bits of thylakoid membrane

What is present in thylakoid membranes and why?

- Lots of ATP synthase molecules to produce ATP in the light dependent reaction of photosynthesis

- Photosynthetic pigments

What are photosynthetic pigments?

Coloured substances that absorb the light energy needed for photosynthesis

Where are photosynthesis pigments found?

Thylakoid membranes - they're attached to proteins

Photosystem

Protein and pigment

What are the two photosystems?

- Photosystem I (PSI)

- Photosystem II (PSII)

At what wavelength does PSI absorb light best?

700nm

At what wavelength does PSII absorb light best?

680nm

What surrounds the thylakoids?

Stroma

Structure and function of stroma

Contain all the enzymes, sugars and organic acids required for the light independent reaction of photo synthesis. As well as oil droplets which store non-carbohydrate organic material

2 stages of photosynthesis

- Light dependent

- Light independent (Calvin cycle)

Where does the light dependent reaction of photosynthesis take place?

Thylakoid membranes of the chloroplast

Where does the light independent reaction of photosynthesis take place?

Stroma of the chloroplasts

What happens at the thylakoid membranes in the light dependent reaction of photosynthesis?

Light energy is absorbed by photosynthetic pigments in the photosystems and converted to chemical energy

What does ATP transfer to the light independent reaction?

Energy

What does NADPH transfer to the light independent reaction?

Hydrogen

What happens to H2O in the light dependent reaction?

Oxidised to O2

What does the Calvin cycle rely on?

The products of the light dependent reaction

What is ATP and NADPH from the light dependent reaction used for in the Calvin cycle?

Used to supply the energy and hydrogen to make glucose from CO2

What are the two types of photophosphorylation?

Non-cyclic and cyclic

Stage 1 of non-cyclic photophosphorylation:

Light energy is absorbed by PSII

Light energy is absorbed by PSII...

Stage 2 of non-cyclic photophosphorylation:

The light energy excites electrons in the chlorophyll

The light energy excites electrons in the chlorophyll...

Stage 3 of non-cyclic photophosphorylation:

The electrons move to a higher energy level

The electrons move to a higher energy level...

Stage 4 of non-cyclic photophosphorylation:

These high energy electrons move along the electron transport chain to PSI

These high energy electrons move along the electron transport chain to PSI...

Stage 5 of non-cyclic photophosphorylation:

As the excited electrons from chlorophyl leave PSII to move along the transport chain, they must be replaced

As the excited electrons from chlorophyl leave PSII to move along the transport chain, they must be replaced

Stage 6 of non-cyclic photophosphorylation:

Light energy splits water into protons (H+ ions), electrons and oxygen. (Photolysis)

Light energy splits water into protons (H+ ions), electrons and oxygen. (Photolysis)...

Stage 7 of non-cyclic photophosphorylation:

The excited electrons lose energy as they move along the electron transport chain

The excited electrons lose energy as they move along the electron transport chain...

Stage 8 of non-cyclic photophosphorylation:

This energy is used to transport protons into the thylakoids so that the thylakoid has a higher concentration of protons than the stroma. This forms a proton gradient across the membrane.

This energy is used to transport protons into the thylakoids so that the thylakoid has a higher concentration of protons than the stroma. This forms a proton gradient across the membrane...

Stage 9 of non-cyclic photophosphorylation:

Protons move down their concentration gradient, into the stroma via ATP synthase. The energy from this movement combines ADP and inorganic phosphate to form ATP

Protons move down their concentration gradient, into the stroma via ATP synthase. The energy from this movement combines ADP and inorganic phosphate to form ATP...

Stage 10 of non-cyclic photophosphorylation:

Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level

Light energy is absorbed by PSI, which excites the electrons again to an even higher energy level...

Stage 11 of non-cyclic photophosphorylation:

The electrons are transferred to NADP along with a proton (H+ ion) from the stroma, to form NADPH

Cyclic photophosphorylation

- Only uses PSI

- The electrons from the chlorophyll molecule aren't passed onto NADP, but are passed back to PSI via electron carriers

- The electrons are recycled and repeatedly flow through PSI

- Only produces small amounts of ATP

What is stage 1 of the Calvin cycle called?

Carbon fixation

Stage 1 of carbon fixation:

CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast

CO2 enters the leaf through the stomata and diffuses into the stroma of the chloroplast...

Stage 2 of carbon fixation:

Here, its combined with RuBP. This is catalysed by RuBisCo

Here, its combined with RuBP. This is catalysed by RuBisCo...

Stage 3 of carbon fixation:

This gives an unstable 6-carbon compound, which quickly breaks down into two molecules of a 3 -carbon compound called GP

What is stage 2 of the Calvin cycle called?

Reduction of GP

Stage 1 of reduction of GP:

The hydrolysis of ATP from the light dependent reaction, provides energy to turn GP into a different 3-carbon compound called GALP

The hydrolysis of ATP from the light dependent reaction, provides energy to turn GP into a different 3-carbon compound called GALP...

Stage 2 of reduction of GP:

This reaction requires H+ ions, which come from NADPH from the light dependent reaction. NADPH is recycled to NADP

This reaction requires H+ ions, which come from NADPH from the light dependent reaction. NADPH is recycled to NADP...

Stage 3 of reduction of GP:

Some GALP is converted into useful organic compounds. Some continues int the Calvin cycle to regenerate RuBP

What is stage 3 of the Calvin cycle called?

Regeneration of RuBP

Stage 1 of regeneration of RuBP:

2 molecules of GALP can be used to make a hexose sugar, but 5 out of every 6 molecules are used to regenerate RuBP

2 molecules of GALP can be used to make a hexose sugar, but 5 out of every 6 molecules are used to regenerate RuBP...

Stage 2 of regeneration of RuBP:

Regenerating RuBP uses the rest of the ATP from the light dependent reaction

What organic substances can be made from the products of the Calvin cycle?

Carbohydrates:

- Simple sugars e.g. glucose (made from 2 GALP molecules)

- Polysaccharides e.g. starch and cellulose (made from joint hexose sugars)

Lipids: Made using glycerol which is synthesised from GALP

Fatty acids: Synthesised from GP

Amino acids: Some are made from GP

Nucleic acids: Ribose sugar is made using GALP