CP 10 Flashcards
What are the types of pigments found in
chloroplasts?
Primary pigment and accessory pigments.
What is the purpose of having different accessory
pigments?
To absorb a wider range of wavelengths of light.
Why is sodium hydrogen carbonate added?
To supply carbon dioxide for photosynthesis.
What does the volume of gas produced indicate?
It is assumed to be oxygen, so the volume of gas is proportional to the rate of photosynthesis
What are the controlled variables of this practical?
Light intensity (distance from lamp)
Amount of sodium hydrogen carbonate
Time allowed for gas collection
Temperature
How is the light intensity controlled?
By using different coloured filters to cover one side of the beaker close to the lamp, and covering the other side using aluminium foil.
IV DV
IV: Wavelength of Light
DV: Rate of O2 Production (Volume of Gas/Min)
PROCEDURE
● Place a 10cm piece of pondweed into large beaker of H2O.
● Cover one side of beaker with foil so light can only enter the beaker from 1 side.
● Add half a spatula of NaHCO3 to water
● Place bench lamp close to beaker with a colourless filter between the lamp and beaker. = white light control. Allow the pondweed to adjust for 5 minutes.
● Fill the capillary tubing of the photosynthometer with water.
● After a suitable time draw up any oxygen produced into the capillary tubing using the syringe. Record the volume of gas produced.
● To do this use the formula for the volume of a cylinder: pi r2 h
where r is the radius of the hole in the glass tube and h is the distance covered by the oxygen bubbles.
EVALUATION
● Leaks in the apparatus mean that some gas will escape
● Difficult to measure the total volume of O2 if it remains as separate bubbles
● Not enough NaHCO3 = CO2 becomes limiting factor
● Pondweed could die
● Light intensity too low = limiting factor
● Temp too high = limiting factor temp can increase due to the lamp as it gives off heat.
● Incomplete sealing of the tube and so some white light may get in, affecting results
Discuss ways in which you could improve your investigation to make the results more reliable.
- Longer test periods
- better ways of ensuring that no ambient light influences results
- repeating the procedure with different pieces of pondweed
- greater control of factors such as temperature, measurement of light wavelength and quantification of light intensity or plant biomass.
This investigation measured the production of oxygen in a given time to indicate the rate of photosynthesis. Give two other measurements that could have been used
The absorption of CO2 per unit time; the increase in biomass or production of carbohydrate per unit time
What assumptions were made about the gas bubbles?
We assume that the gas is oxygen and that the rate of bubble formation will be directly proportional to the rate of photosynthesis.
Evaluate the validity of these assumptions.
Oxygen will be produced by photosynthesis but there could be a small amount of carbon dioxide in the bubbles from respiration. Some of the oxygen produced will be used internally in respiration. Nitrogen may also come out of solution in the water.
The rate of respiration is likely to be constant and is unlikely to be affected by altering the wavelength of light. Providing the temperature remains constant, the assumption that any change in rate of gas production is due to changes in the rate of photosynthesis is therefore probably valid.
This investigation measured the production of oxygen in a given time to indicate the rate of
photosynthesis.
Give two other measurements that could have been used.
The absorption of CO2 per unit time; the increase in biomass or production of carbohydrate per unit time.
