5A photosynthesis

How is ATP produced?

by the addition of inorganic phosphate (P_i) to ADP

Why is energy required?

• during anabolic reactions

• active transport

• For muscle contraction 

• In the conduction of nerve impulse

How does the electron transport chain contribute to releasing energy for the making of ATP?

the passage of electrons along the electron transport chain releases energy for the phosphorylation of ADP

Hydrolsis/Breakdown of ATP

• catalysed by the enzyme ATPase

• The ADP and inorganic phosphate produced can be recycled to make more ATP

Adaptations of the thylakoid membrane

• contains ATP synthase enzymes

• contains proteins called photosystems that contain photosynthetic pigments

function of chloroplast envelope

• encloses the chloroplast - compartmentalisation

• transport proteins present in the inner membrane control the flow of molecule

function of stroma

gel-like fluid contains enzymes that catalyse the reactions of photosynthesis

function of thylakoid membrane

• There is a space between the two thylakoid membranes known as the thylakoid space where proton gradient can be established

• contains photosystems for photosynthesis

• contains electron carriers for chemiosmosis

• it contains ATP synthase

function of grana

• create a large surface area, maximising the number of photosystems and allowing maximum light absorption

• also provide more membrane area for proteins such as electron carriers and ATP synthase enzymes

Wavelength of photosystems

• photosystem I - 700nm

• photosystem ll - 680nm

chlorophyll a pigment

reflect: blue green

absorb: blue-violet and red regions

chlorophyll b pigment

reflect: yellow green

absorb: blue-violet and red regions

B carotene pigment

reflect: orange

absorb: blue-violet region

Xanthophyll pigment

reflect: Yellow

absorb: blue-violet region

what is absorption spectrum

The amount of light at different wavelengths absorbed by a particular pigment

what is action spectrum

The changing rate of photosynthesis at different wavelengths

Non cyclic photophosphorylation

1) Light energy hits photosystem II in the thylakoid membrane

2) electrons are excited to a higher energy level

3) these electrons leave the PSll by the electron transport chain which releases energy, they are replaced by electrons from the photolysis of water

4) the energy released allows chemiosmosis to occur

• H­­⁺ ions are actively pumped from a low concentration in the stroma to a high concentration in the thylakoid space

• H­­⁺ ions diffuse back across the thylakoid membrane into the stroma via ATP synthase enzymes embedded in the membrane

• The movement of H­­⁺ ions causes the ATP synthase enzyme to catalyse the production of ATP

5) the electrons from photosystem II are passed to photosystem I

6) Light energy also hits photosystem I, exciting the electrons

7) The excited electrons from photosystem I also pass along an electron transport chain

8 - These electrons combine with hydrogen ions from the photolysis of water and the coenzyme NADP to form reduced NADP

chemiosmosis

• The energy released as electrons pass down the electron transport chain is used to produce ATP

photolysis

Light energy enables the splitting of water molecules into

• 2 hydrogen ions (2H⁺), also known as protons

• 2 electrons (2e^-)

• One atom of oxygen

cyclic photophosphorylation

• Light hits photosystem I 

• Electrons are excited to a higher energy level and leave the photosystem

• they pass along electron transport chain, releasing energy as they do so

• which provides energy to drive the process of chemiosmosis

• H­­⁺ ions are actively pumped from a low concentration in the stroma to a high concentration in the thylakoid space

• H­­⁺ ions diffuse back across the thylakoid membrane into the stroma via ATP synthase enzymes embedded in the membrane

• The movement of H­­⁺ ions cause the ATP synthase enzyme to catalyse the production of ATP

• At the end the electrons rejoin photosystem I in a complete cycle

Process of carbon fixation

• Takes place in the stroma

• Carbon dioxide is combined with (RuBP), a 5-carbon (5C) compound; this yields two molecules of (GP), which is catalysed by RUBISCO

• GP is reduced to (GALP), another 3C compound, in a reaction involving reduced NADP and ATP

• RuBP is regenerated from GALP in reactions that use ATP, five sixths of the GALP molecules are used to regenerate RuBP

Uses of products made from light independent reactions

• carbohydrates

• glycerol is made from GALP and fatty acids are made from GP which are combined to make lipids

• Some amino acids are made from GP (combined w nitrates)

• the sugar in RNA is made using GALP (combined w phosphates