Potometer

Question 1

How to plan an investigation into the rate of respiration of two different species of plant

Answer 1

• Pick two plant species and set up the pedometer to measure the rate of transpiration by measuring the distance The bubble has moved at regular intervals.
• Repeat the experiment 3 times to find a mean and identify anomalies
• plot a graph to compare the results with time on the X axis and distance moved by the bubble on the Y axis
• Make sure that temperature, pH, light intensity and humidity is controlled
• you can do this by having the room at a certain temperature, using a lamp for the same light intensity or using blinds
• make sure the same surface area is measured for both species by measuring using square paper and counting squares

Question 2

How to do the potometer pag to improve accuracy

Answer 2

• be sure potometer is airtight/water tight by Keeping screw clips closed to prevent entry of water while measuring
• pick out dry leaves
• cut shoot underwater and slanted
• Measure the distance air bubble travels every 10 seconds
• calculate water uptake
• maintain temperature, light intensity, humidity, and wind conditions
• Make sure to read meniscus accurately
• Keep screw clip closed to prevent entry of water while measuring

to ensure no air:
- cut stem under water
- have apparatus under water
- insert stem under water
- joints must be sealed so no air can enter apparatus as it could block xylem from obtain a continuous column of water
- do not allow the bubble to move too far so bubble does not enter xylem and same air bubble can be reused
- place open end in water so no, air new bubble is introduced
- keep shoot, still / supported to avoid breaking,
- seal water column to measure transpiration accurately and ensure validity

Question 3

How to compare rate of transpiration when leaves are different sizes

Answer 3

Account for the surface area of each type of leaf, calculate transpiration rate / mm2

Question 4

Why do we have a control experiment

Answer 4

To compare effects of any other conditions not controlled

Question 5

What is an assumption we make using the potometer

Answer 5

transpiration/water loss = water uptake and that no water is used by the plant