Photosynthesis questions

It involves the diffusion of protons from a region of high concentrations to low through a partially permeable membrane.

The movement of protons as they flow down their concentration gradient releases energy, which is used in the attachment of a phosphate group to ADP to produce ATP.

Made up of a series of electron carriers, each with progressively lower energy levels. As high energy electrons move from one carrier in the chain to another, energy is released.

Used to pump protons across a membrane, creating a concentration gradient which is maintained due to the impermeability of the membrane to H+ ions.

The process by which light energy from the sun is used to build complex organic molecules such as glucose.

Organisms that can photosynthesise to produce their own food.

Organisms that obtain their complex organic molecules by eating other heterotrophic or autotrophic organisms.

Chloroplasts

The network of membranes within a chloroplast provides a large surface area, to maximise the absorption of light.

The membranes form flattened sacs called thylakoids, which are stacked to form grana or granum.

Joined by channels called Lamellae.

The stroma and it's the site of many chemical reactions

Pigment molecules which absorb specific wavelengths/colours of light and reflect others. Different pigments therefore absorb and reflect at different wavelengths, giving way to different colours.

The primary pigment in photosynthesis is chlorophyll, which absorbs mainly red/blue light and reflects green. The high presence of chlorophyll in a plant is responsible for its green appearance.

The different combination of pigments responsible for the different colours of leaves e.g. Chlorophyll B, Xanthophyll and Carotenoids

A light harvesting system formed from the accessory and primary pigments (Chlorophyll A) embedded in the thylakoid membranes.

To absorb light energy of different wavelengths and transfer this energy quickly and efficiently to the reaction centres.

The site where the reactions involving photosynthesis takes place. Chlorophyll A is also located in the reaction centre.

The Antennae complex and reaction centre are collectively known as a Photosystem.

" 1. Light dependant stage 2. Light independent stage (Calvin cycle) "

Energy from sunlight is absorbed and used to form ATP. Hydrogen from water is used to reduce co-enzyme NADP to reduced NADP.

Hydrogen from reduced NADP and carbon dioxide is used to build organic molecules such as glucose. ATP supplies the required energy.

2 photosystems are involved in non-cyclic phosphorylation, PS2 followed by PS1. The light absorbed from the sun excites electrons at the reaction centres of the photosystems. The excited electrons are released from the reaction centre of PS2 and are passed to an electron transport chain, where ATP is produced by chemiosmosis. Excited electrons are released from the reaction centre at PS1, passed to another electron transport chain, and ATP is produced again by chemiosmosis.

Water molecules broken down through photolysis.

Replaced by electrons that have just travelled along the first electron transport chain after being released from PS2.

700nm

690nm

They are accepted, along with a hydrogen ion by co-enzyme NADP, forming reduced NADP. This helps in the production of glucose in the Calvin cycle.

Water molecules are split into hydrogen ions, electrons and oxygen gas, using energy from the sun. The electrons released replace the electrons lost from the reaction centre of PS2, which is why water is a raw material for photosynthesis. Oxygen gas is released as a waste product.

The electrons leaving the electron transport chain after PS1 can be returned to PS1, instead of being used to form reduced NADP. This means PS1 can still lead to the production of ATP without any electrons being supplied by PS2. However, in this instance, reduced NADP is not produced.

The production of organic molecules in a series of reactions known as the Calvin cycle.

Takes place in the stroma of chloroplasts.

The products from the light dependant stage of photosynthesis: 1. ATP 2. Reduced NADP 3. Carbon dioxide.

By diffusion from the atmosphere, through the stomata and makes its way to the stroma of chloroplasts.

1. Carbon dioxide combines with a 5-carbon molecule known a ribulose bisphosphate (RuBP). The carbon in carbon dioxide is now fixed – incorporated within an organic molecule. This reaction is catalysed by the enzyme Rubisco . 2. An unstable 6 carbon intermediate is formed which is immediately broken down forming 2 lots of 3-carbon glycerate-3-phosphate, also known as GP molecules. 3. Each GP molecule is converted into another 3-carbon molecule, known as Triose phosphate (TP), using a hydrogen atom from NADP and energy supplied by ATP, both supplied from the light dependant stage of photosynthesis. Reduced NADP and ATP provide energy and phosphate groups. 1 of the phosphate groups from ATP is used to turn GP into TP.

All together 6 carbons have been formed (2 TP molecules). 5 of these carbons are used to regenerate RuBP and the remaining carbon is used to produce carbohydrates. The Calvin cycle therefore would need 6 turns to produce glucose, which is a 6-carbon sugar.

A carbohydrate which is the starting point for the synthesis of other biological molecules such as carbohydrates, lipids and proteins etc…

It’s competitively inhibited by oxygen.

" 1. Light intensity 2. Carbon dioxide concentration 3. Temperature "

Light is required as an energy source and for photolysis. As it increases, ATP and reduced NADP are produced at a higher rate, which increases the production of glucose.

Carbon dioxide is required as a source of carbon, so if all other conditions are met, increasing the carbon dioxide concentration increases the rate of carbon fixation in the Calvin cycle, and therefore the rate of TP production.

Affects the rate of enzyme-controlled reactions. As temperature increases, so does the rate of the enzyme activity until the enzyme becomes denatured. An example is carbon fixation catalysed by the enzyme Rubisco in the Calvin cycle.

For water potential to become low enough to limit the rate of photosynthesis, the plant will have already closed its stomata and ceased photosynthesis.

Reducing light intensity decreases the rate of the light dependant stage of photosynthesis, meaning less ATP and reduced NADP are produced. Because these are raw materials used in the Calvin cycle to convert GP into TP, the concentration of GP will increase, and TP decrease in the absence of sufficient light. The concentration of RuBP will also decrease because it’s the TP which is used to regenerate it. The reverse will happen if light intensity is increased.

As carbon dioxide is an essential substrate of the Calvin cycle, low concentrations will lead to reduced concentrations of GP produced, as there is less carbon to be fixed, and therefore TP. The concentration of RuBP will increase as it continues to be produced by the TP, however it’s not being used up as fast in the reactions with a limited number of carbon dioxide molecules.

All the reactions in the Calvin cycle are catalysed by enzymes e.g. rubisco in carbon fixation. At lower temperatures enzymes and substrate molecules have less kinetic energy leading to fewer successful collisions and a reduced rate of reaction. Decreasing temperature therefore results in lower concentrations of GP, TP and RuBP produced. The same effect will be seen at very high temperatures as the enzyme denatures.