respiration and photosynthesis 5a Flashcards
What is the overall equation for photosynthesis?
6CO₂ + 6H₂O → light, chlorophyll, C₆H₁₂O₆ + 6O₂
Where does photosynthesis take place?
In the chloroplasts of plant cells.
What are the two main stages of photosynthesis?
Light-dependent reaction
Light-independent reaction (Calvin cycle)
Where does the light-dependent reaction take place?
In the thylakoid membranes of the chloroplasts.
What are the main products of the light-dependent reaction?
ATP (chemical energy)
NADPH (reduced NADP)
O₂ (from photolysis of water)
What happens in photolysis?
Water is split by light into protons (H⁺), electrons, and oxygen:
H₂O → 2H⁺ + 2e⁻ + ½O₂
What happens to the electrons in the light-dependent reaction?
They are excited by light energy and passed along an electron transport chain, releasing energy used to pump H⁺ ions.
How is ATP produced in the light-dependent reaction?
By chemiosmosis – H⁺ ions move down their gradient through ATP synthase.
What is the role of NADP?
Accepts electrons and H⁺ to become reduced NADP (NADPH), used in the Calvin cycle.
Where does the light-independent reaction take place?
In the stroma of the chloroplast.
What molecule does CO₂ combine with in the Calvin cycle?
Ribulose bisphosphate (RuBP)
What enzyme catalyses the reaction between CO₂ and RuBP?
RuBisCO
What is the first stable product of carbon fixation?
Two molecules of glycerate-3-phosphate (GP)
What happens to GP in the Calvin cycle?
Reduced to triose phosphate (TP) using ATP and NADPH from the light-dependent reaction.
What is triose phosphate used for?
Some used to regenerate RuBP
Some converted to glucose, amino acids, or lipids
How many turns of the Calvin cycle are needed to make one glucose molecule?
Six turns (requires 6 CO₂)
What are the limiting factors of photosynthesis?
Light intensity
CO₂ concentration
Temperature
Water availability (indirect)
What is the compensation point in photosynthesis?
The light intensity at which the rate of photosynthesis equals the rate of respiration.
What is the overall equation for aerobic respiration?
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + energy (ATP)
What are the four stages of aerobic respiration?
Glycolysis
Link reaction
Krebs cycle
Oxidative phosphorylation
Where does glycolysis occur?
In the cytoplasm of the cell.
What are the products of glycolysis?
2 pyruvate
2 ATP (net)
2 reduced NAD (NADH)
Does glycolysis require oxygen?
No – it’s an anaerobic process.
Where does the link reaction take place?
In the mitochondrial matrix
What happens to pyruvate in the link reaction?
Decarboxylated (CO₂ removed)
Oxidised (NAD → NADH)
Forms acetyl CoA
What are the products per glucose molecule in the link reaction?
2 acetyl CoA
2 CO₂
2 NADH
Where does the Krebs cycle occur?
In the mitochondrial matrix
What are the main products of the Krebs cycle per glucose?
6 NADH
2 FADH₂
2 ATP
4 CO₂
Where does oxidative phosphorylation occur?
In the inner mitochondrial membrane
What happens in oxidative phosphorylation?
Electrons from NADH/FADH₂ passed down the electron transport chain
Energy released pumps H⁺ ions into intermembrane space
H⁺ moves back through ATP synthase, generating ATP
Oxygen is the final electron acceptor, forming H₂O
What happens to pyruvate in anaerobic respiration (animals)?
Converted to lactate using NADH (which is oxidised to NAD).
What happens to pyruvate in anaerobic respiration (yeast/plants)?
Converted to ethanol and CO₂
NADH is oxidised to regenerate NAD
Why is anaerobic respiration less efficient?
Only 2 ATP made per glucose (from glycolysis), because oxidative phosphorylation doesn’t occur.
