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Unit 4 Mock

I'm stressing out because I don't know photosynthesis, respiration or the nitrogen/carbon cycles and inheritance confuses me.
I can explain each one to you if you like
I've done photosynthesis and respiration


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Original post by spiritless98
I can explain each one to you if you like
I've done photosynthesis and respiration


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if you have the time and really want to then I'd be grateful haha
Respiration: C6H12O6 + 6O2 6CO2 + 6H2O

Respiration = turning glucose (and other molecules) into ATP

There are two types of respiration:

Aerobic is normal respiration it occurs in the presence of oxygen

Anaerobic occurs when there is not enough oxygen available (e.g. during strenuous exercise)

Aerobic respiration has 4 main stages:

Glycolysis (cytoplasm of the cell) both aerobic and anaerobic

Link reaction (matrix of mitochondria)

Krebs cycle (matrix of mitochondria)

Oxidative phosphorylation/ETC (inner mitochondrial membrane/cristae)

Anaerobic respiration has 2 main stages:

Glycolysis (cytoplasm of the cell) both aerobic and anaerobic

Ethanol or Lactate Pathway (cytoplasm)


Glycolysis (cytoplasm)




Occurs in the cytoplasm of the cell

1 glucose is broken down into 2 pyruvate
o Glucose is big (6 carbons) and can’t fit into the mitochondria for the later stages o Pyruvate is smaller (3 carbons) and can fit in the mitochondria later

Thereisanetgainof2ATP
o 2 ATP are used and 4 ATP are made o This is the only step to use ATP

2 hydrogens are made, these reduce 2 NAD to make 2 NADH o NAD is known as a hydrogen carrier and is a coenzyme

A coenzyme carries a product from one reaction so it can be used in another reaction.
Note: glucose is almost always the respiratory substrate, but other substrates can also be used e.g. fats








The Link Reaction (AQA, OCR, Edexcel, Pre-U)

Occurs in the matrix of mitochondria

For each glucose used, 2x pyruvate enters the matrix of mitochondria (by active transport) There are reactions and the following are produced:

2CO2
2NADH
2 acetyl coenzyme A

You do not need to learn numbers of each molecule.
Coenzyme A is a coenzyme. Its job is to transport the acetyl to the Krebs cycle.

3. Krebs cycle (AQA, OCR, Edexcel, Pre-U)
Occurs in the matrix of mitochondria
The main role of the Krebs cycle in respiration is to make lots of hydrogen.

For each glucose used, 2x Acetyl Coenzyme A enter the cycle. There are reactions and the following are produced:

4CO2
6NADH 2FADH 2ATP

FAD is similar to NAD and is a hydrogen carrier and is a coenzyme.

2C (Acetyl CoA / acetate) + 4C (oxaloacetate) =====> 6C (citrate / citric acid) Citrate + little reactions ====> oxaloacetate

The regenerated oxaloacetate can combine with another ACoA


Oxidative phosphorylation (Electron transport chain)

Occurs within the inner membrane of the mitochondria cristae

1. NADH and FADH move to the cristae
o NADH and FADH release their hydrogen atom
o NAD and FAD can be reused in glycolysis, link and Krebs

The hydrogen splits up into an electron and hydrogen ion (H+)

Electrons pass along a row of molecules in the inner mitochondrial membrane

o This is called the electron transport chain

o This produces some energy 4. H+ move by active transport

o They move from the matrix, across the cristae into the intermembrane space o This creates a high concentration of H+ in the intermembrane space
o They move using energy from the electron transport chain

5. H+ then move by diffusion
o They move from the intermembrane space (high concentration of H+), across the cristae

into the matrix (low concentration of H+)
This activates ATP-synthase (enzyme) which makes lots of ATP from ADP + Pi This is called chemiosmosis

6. The final electron carrier in the ETC is oxygen

o Oxygen binds with electrons and H+ to make water





(This is from my notes, see if you understand it and if you have any specific questions ask away)












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