Photosynthesis & Respiration

Respiration

Aerobic respiration is splitting respiratory substances to release CO2 as a waste product and reunite hydrogen with oxygen.

Anaerobic respiration occurs in the absence of air.

Exergonic – Releases energy, Respiration.

Endergonic– Requires energy, Active transport, and Protein synthesis.

ATP

ATP hydrolysis is the immediate source of all energy. All organisms use ATP so it is known as the Universal Energy Currency.

ATP ⇌ ADP + Pi

• It releases small amounts of energy ( 30 Kjmol) which is perfect for biological reactions.

• Glucose to CO2 uses 3000Kjmol and wastes a lot of energy as heat.

ATP is suitable for its role for 4 reasons–

1. Hydrolysis of ATP occurs very quickly.

2. Can move in and out of the mitochondria.

3. Chemically inert → does not affect other reactions.

4. Easily reformed.

• ATP consists of; Ribose, Adenine Base and 3 Phosphate groups.

• ATP is formed by condensation and Phosphorylation.

• It is used for the synthesis of biological molecules.

Chemiosmosis

• Mitochondria convert energy, they are transducers.

• They convert the energy by chemiosmosis.

• Chemiosmosis oxidises the respiratory substrate.

• Electrons are transported between protein pumps in the inner membrane.

• Energy uses to pump across the membrane to create proton gradients.

• Energy from protons pimping through gives the energy for ATP synthetase to make ATP.

1. Electrons are transferred to a chain of alternate proton pumps in the inner mitochondrial membrane.

2. These electrons are a source of energy.

3. When electrons move along the chain Redox Reactions occur.

4. The energy released from these reactions is used by the proton pumps to transfer protons to the inner membrane.

5. This generates a proton gradient.

6. H+ ions diffuse down the proton gradient through ATP synthase.

7. ATP synthase synthesizes ATP from ADP + Pi.

ATP Synthetase

• Ubquotus complex of proteins.

• Bacteria, Eukaryotes, Archaea.

• H+ move down the proton gradient, complex rotates.

• Rotation is used to produce ATP.

• It takes 3 protons to rotate the head 120 degrees to produce ATP.

Peter Michell

• Used artificial chloroplasts.

• Put them in low pH solution, very acidic, high concentration of H+ ions.

• Then put into high pH with a low concentration of H+ ions.

• Gave chloroplasts ADP + Pi.

• Made ATP immediately, No light was needed.

Photosynthesis.

• Reduction is the gain of electrons.

• 6CO2 + 6H20 → C6H12O6 + 6O2.

• Carbon dioxide + water → Glucose + Oxygen

• Carbon is reduced and becomes a carbohydrate.

Light Dependant → Uses photons of light energy, Photophosphorylation.

Light Independent → Don’t need light to occur.

• Chloroplasts are transducers turning light to ATP then ATP to triose phosphate.

• The inner membrane forms thylakoids.

• The thylakoids form discs and are called granum.

• They are suspended in a fluid called the stroma.

Absorption Spectra

• Shows absorption of light by photosynthetic pigments at different wavelengths of light. Chlorophylls absorb blue and red light.

Action Spectra

• Shows the rate of photosynthesis at different wavelengths of light.

Accessory pigments → Increase the wavelength of light so more wavelengths can be absorbed.

Peaks in the absorption spectrum indicate the photosynthetic pigments present in the organism.

Green Light is reflected as there are no pigments that are able to absorb the green light, therefore green light results in a low rate of photosynthesis.

Action spectra and absorption spectra both show photosynthesis at different wavelengths.

Light Dependent Reactions

Non-cyclic photophosphorylation

• Known as the Z-Scheme

• Light is absorbed by photosystem II and passed to the primary pigment.

• Electrons are transferred from the electron acceptor to oxidised NADP in the stroma.

• Electrons are not returned to Photosystem I as its chlorophyll has a positive charge.

• Positive charge is neutralised by the electrons from PSII, they are excited to a higher energy level, picked up by the electron acceptor and passed down.

• ELectron passage makes energy available for phosphorylation of ADP.

• Chlorophyll in PSII is left with a positive charge.

Cycloc Photophosphorylation

• PSI absorbs photons which excited electrons in the chlorophyll-a molecules in its reaction centres.

• These are emitted and picked up by an electron acceptor which passes them down a chain of electron carriers back to PSI.

• The energy released as electrons pass through the electron transport chain phosphorylates ADP to ATP.

• Electrons have flowed down from PSI to the electron acceptor back to PSI so this phosphorylation is described as Cyclic.

Hill Reaction

• Oxidised DOPIP → Reduced DOP (Blue to colourless)

• H2O → ½ O2

• Instead of NADP being reduced. DOPIP is reduced in light dependant reactions,

• Loses its blue colour.

• This can be used to measure the rate of light dependent reactions.

• Source of electrons is the photolysis of water.

Summary

• Absorption of light drives excitation of electrons from reaction centres and electron transport.

• Proton gradients generated bt electron transport drive ATP production by ATP synthesis.

• Cyclic Photophosphorylation produces ATP only.

• Non-Cyclic photophosphorylation produces ATP and NADPH, lost electrons from PSII replaced by the photolysis of water, generating oxygen.

Light Independent Reactions.

• Reduced NADP.

• Co-enzyme needed to make the enzymes work.

• Reduced NADP crucial to reduce CO2 to a carbohydrate.

• Its a reducing agent.

• Calvin Cycle

• CO2 is added to Ribulose bisphosphate, breaks down and forms glycerate-3-phosphate, which is reduced to Triose Phosphate.

1. CO2 binds to RibuloseBisphosphate and forms an unstable intermediate,

2. This breaks down to form