Photosynthesis

Question 1

Photosynthesis symbol equation

Answer 1

6CO2 + 6H2O + light energy —> C6H12O6 + 6O2

Question 2

What is a metabolic pathway?

Answer 2

A series of small reactions controlled by enzymes

Question 3

What is phosphorylation?

Answer 3

Adding phosphate to a molecule (eg. ADP + Pi —> ATP)

Question 4

Properties of ATP

Answer 4

• Releases only a small, manageable amount of energy at a time (less energy is wasted as heat)
• Small, soluble molecule (easily transported around the cell)
• Easily broken down in one step (energy can be easily released instantaneously)
• Rapidly resynthesised
• Can make other molecules more reactive by transferring one of its phosphate groups to them (phosphorylation)

Question 5

Compensation point

Answer 5

The rate of photosynthesis is equal to the rate of respiration

Question 6

Chloroplast structure (+ function)

Answer 6

• Thylakoids stacked up into grana linked by lamellae (large SA for LDR)
• Photosynthetic pigments (absorb the light energy)
• Two photosystems (absorb light energy)
• Stroma (contains enzymes for LIDR)

Question 7

The light-dependent reaction (photophosphorylation)

Answer 7

• Photosynthetic pigments (chlorophyll a) absorb light energy
• Excites an electron which leaves the chlorophyll is PSII (photoionisation)
• Electron moves down the electron transport chain, releasing energy
• Energy used to actively transport protons (H+) into thylakoid, forming an electrochemical gradient
• H+ move down their electrochemical gradient, through ATP synthase into the stroma, joining ADP + Pi —> ATP
• Electrons in PSII replaced by electrons from photolysis of water which makes H+, electrons and oxygen
• NADP is reduced to form NADPH

Question 8

The light independent reaction (Calvin Cycle)

Answer 8

• Carbon dioxide combines with RuBP catalysed by the enzyme rubisco
• Makes 2 molecules of GP
• Both GP are reduced to form 2 molecules of TRIOSE PHOSPHATE, using 2x NADPH and 2x ATP
• Most TP is regenerated to form RuBP using energy from ATP
• Some TP is converted into useful organic compounds

Question 9

How does light intensity affect rate of photosynthesis

Answer 9

The higher the light intensity, the more energy for the LDR so faster rate of photosynthesis. However, light must be the right wavelength (different pigments absorb different wavelengths)

Question 10

How does CO2 concentration affect rate of photosynthesis

Answer 10

Increasing CO2 concentration to optimum (0.4%) increases rate but any higher decreases rate as stomata close

Question 11

How does temperature affect rate of photosynthesis

Answer 11

The higher the temperature, the more KE, increasing rate but beyond optimum rate decreases as enzymes denature