Quick questions on Photosynthesis and cellular respiration (QCE Biology Unit 1)

Word equation. Carbon dioxide + water + (light energy) → glucose + oxygen.

Word equation. Glucose + oxygen → carbon dioxide + water + energy (ATP).

When O2 is unavailable, cells regenerate NAD+ from NADH so that glycolysis can continue to make a small amount of ATP. Two pathways are examined.

ATP is the cell's energy currency. Hydrolysis of one phosphate bond releases about 30 kJ per mol, used to power active transport, biosynthesis, muscle contraction and many other processes. Cells regenerate ATP from ADP and Pi continuously using energy from respiration (or photosynthesis in chloroplasts).

Photosynthesis and aerobic respiration are inverse:

Carbon dioxide + water + (light energy) → glucose + oxygen.

6 CO2 + 6 H2O + light energy → C6H12O6 + 6 O2.

Chloroplasts of plant mesophyll cells, algae and cyanobacteria (the latter in their thylakoid membranes only).

1. Light-dependent reactions. Occur on the thylakoid membranes. Light energy excites electrons in chlorophyll, which splits water (photolysis) releasing O2, electrons and protons.

O2 is the final electron acceptor at the end of the electron transport chain, forming water. Without O2 the chain backs up, NADH cannot be reoxidised and aerobic respiration halts.

- Glucose → 2 lactic acid + 2 ATP. - Pyruvate accepts the electrons from NADH, becoming lactic acid (lactate). - Occurs in vertebrate muscle during intense exercise.

- Glucose → 2 ethanol + 2 CO2 + 2 ATP. - Pyruvate is decarboxylated to acetaldehyde, then reduced to ethanol. - The basis of brewing, wine-making and bread leavening.

Always include the 6 in front of CO2, H2O and O2 to balance carbon, hydrogen and oxygen atoms.

Glycolysis is cytosolic. The pyruvate produced is then imported into the mitochondrion.

Anaerobic respiration still uses glycolysis (the first stage of cellular respiration) but no oxygen for the later stages.