3.8 Photosynthesis

Question 1

Photosynthesis equation

Answer 1

Carbon dioxide + water → Glucose + oxygen + water

6CO₂ + 12H₂O → C₆H12O + 6O2 + 6H₂O

Question 2

Factors that affect the rate of photosynthesis

Answer 2

Temperature, light intensity, CO₂ concentration

Question 3

How temperature affects the rate of photosynthesis

Answer 3

• Rise in temperature increases the rate of photosynthesis: greater kinetic energy
• Above certain temperature decreases the rate of photosynthesis: enzyme denatures

Question 4

How light intensity affects the rate of photosynthesis

Answer 4

* Increase in light intensity increases the rate of photosynthesis up until a certain point * Chlorophyll saturated by light

Question 5

How CO₂ concentration affects the rate of photosynthesis

Answer 5

• Increase in CO₂ concentration increases the rate of photosynthesis up until a certain point
• Enzyme responsible for carbon fixation become saturated

Question 6

Ways to measure the rate of photosynthesis

Answer 6

• Measure CO2 uptake - Change in pH of water (more alkaline)
• Measure O2 production - bubbles produced
• Measure biomass - glucose production seen by change in biomass
• Starch - by iodine staining

Question 7

Colours of visible spectrum

Answer 7

(700nm) Red Orange Yellow Green Blue Indigo Violet (400nm) Longer to shorter wavelength

Question 8

Chlorophyll

Answer 8

* The main site of light absorption * When chlorophyll absorb light, it releases electrons which are used to produce ATP

Question 9

Red, green and blue light in photosynthesis

Answer 9

• Red and blue are absorbed by chlorophyll
• Green is reflected - thus the colour of plants

Question 10

Light dependent reaction

Answer 10

• Light stimulates chlorophyll to produce electrons → produce ATP
• Light also splits water molecules into hydrogen and oxygen → hydrogen taken up by a NADP⁺ to form NADPH