IB BIO TOPIC 3.8 : PHOTOSYNTHESIS Flashcards
What is photosynthesis ?
Photosynthesis involves the conversion of light energy into chemical energy.
What is the white sunlight composed of ?
White light from the Sun is composed of a range of wavelengths (colours).
What is the main photosynthetic pigment.
Chlorophyll
What is visible light ?
• Visible light is a range of wavelengths (380 - 750 nm) which have different energy levels and different colours.
Outline the differences in absorption of red, blue, and green light by chlorophyll.
• Chlorophyll absorbs some wavelengths of light and transmits or reflects others.
o Red (650 -750 nm) and blue (450 - 500 nm) light
• absorbed most efficiently by chlorophyll
• their energy is used in photosynthesis.
o Green (500 -550 nm) light is transmitted or reflected by chlorophyll
• so humans see plant leaves as green
What is the use of light energy ?
The light energy is used to produce Adenosine triphosphate (ATP), and to split water molecules (photolysis) to form oxygen and hydrogen.
What is the use of ATP and hydrogen ?
ATP and hydrogen (derived from the photolysis of water) are used to fix carbon dioxide to make organic molecules.
How can one measure the rate of photosynthesis ?
The rate of photosynthesis can be measured directly by the production of oxygen or the uptake of carbon dioxide, or indirectly by the increase in biomass
How do you measure the rate with O2 production ?
• O2 production:
o Place plant in an enclosed volume of water
o monitor the change in gaseous O2 over time
o O2 is produced by the photolysis of water
o directly measures photosynthetic rate.
How do you measure the rate with CO2 uptake ?
• CO2 uptake:
o Place plant in an enclosed volume and monitor the change in gaseous CO2 over time
o CO2 is consumed during the Calvin cycle and directly measures photosynthetic rate
o Place plant in an enclosed volume containing water and bicarbonate
• monitor the change in pH of the water over time
• CO2 is consumed during the Calvin cycle
• CO2 dissociates from bicarbonate, making the water more basic (increase in pH)
• thus providing a direct measure of photosynthetic rate.
• How do you measure the rate with Biomass increase
• Biomass increase
o Measure organic content of plants before and after experiment
o organic content of plants is measured by removing water through dehydration (drying), usually in an oven.
Outline the effects of temperature on the rate of photosynthesis.
o The enzymes involved in photosynthesis have temperature ranges in which they are most effective
o The rate is therefore highest at the optimum temperature and lower at both very low and very high temperatures.
Outline the effects of Light intensity on the rate of photosynthesis.
o Visible light (especially red and blue)
o is essential for the reduction of chlorophyll during the light-dependent reactions.
Outline the effects of Carbon dioxide concentration on the rate of photosynthesis.
o CO2 is essential for the reduction of ribulose bisphosphate
o during the Calvin cycle
o for the production of carbohydrates
