Photosynthesis Question Flashcards
(21 cards)
What is the aim of Required Practical 6?
To investigate the effect of light intensity on the rate of photosynthesis using pondweed.
What organism is commonly used in this practical?
Pondweed.
Why is pondweed used in this photosynthesis practical?
It is easy to observe and measure the oxygen output as bubbles.
What is the independent variable (IV) in this experiment?
Light intensity (changed by adjusting the distance of the lamp).
What is the dependent variable (DV) in this experiment?
Number of bubbles produced in one minute.
What are the control variables (CVs) in this experiment?
Temperature of water, carbon dioxide concentration, pondweed used.
Describe the method used in this practical.
Place pondweed in water, shine a lamp at it, and count the bubbles produced in one minute at different distances.
Why are at least three readings taken at each distance?
To identify anomalous results and calculate a reliable mean.
What does an increase in bubbles indicate about the rate of photosynthesis?
An increase in the rate of photosynthesis.
What happens to the rate of photosynthesis as the lamp gets closer to the pondweed?
It increases due to more light energy received.
Why might the rate of photosynthesis level off at a certain point?
Because another factor (not light) becomes limiting.
What safety precautions should be taken during this practical?
Handle hot lamp carefully, avoid water on the lamp, and dispose of pondweed properly as it may be invasive.
What might you be asked to do in the photosynthesis practical exam?
Plan an investigation, explain the effect of light intensity, calculate oxygen production rate, or use the inverse square law.
Why should you leave the lamp at each distance for a few minutes before taking a measurement?
To allow the pondweed to acclimatise to the new light intensity and reach a steady rate of photosynthesis.
Why is temperature controlled in the photosynthesis practical?
Because enzymes involved in photosynthesis are affected by temperature.
How is temperature kept constant in this experiment?
A large beaker of water acts as a heat shield and a thermometer is used to monitor temperature.
Why is sodium hydrogen carbonate added to the water?
To ensure carbon dioxide is not a limiting factor by keeping it in excess.
Why should the same piece or length of pondweed be used?
To keep the amount of chlorophyll constant, as different samples may vary.
What is a source of error when counting bubbles?
Miscounting can occur if bubbles come out quickly.
How can miscounting bubbles be improved?
Record the experiment and slow down the footage to count accurately.
Why might measuring bubble volume be better than counting bubbles?
Because bubble sizes may vary, making volume measurement with a syringe more accurate.
