Required Practical: Photosynthesis Rate Flashcards

All 7 cards in this deck

What are the steps to investigate the effect of light intensity on the rate of photosynthesis using pondweed?
e.g. lamp at 10, 20 and 30 cm

1. Put pondweed in a boiling tube of sodium hydrogencarbonate solution, lamp 10 cm away.
2. Count the oxygen bubbles released in 1 minute; repeat and take a mean.
3. Repeat at 20 cm and 30 cm, keeping temperature and the pondweed the same.

In the pondweed light intensity investigation, which variables must be controlled?

Temperature, carbon dioxide supply (same sodium hydrogencarbonate solution), the same mass/length of pondweed and the same time period.

What are the steps to calculate a rate of photosynthesis from a bubble count?
e.g. 90 bubbles counted in 3 minutes

1. Divide bubbles by time: $90 \div 3 = 30$
2. State with the unit: 30 bubbles per minute
3. Convert if needed: $30 \times 60 = 1800$ bubbles per hour

Why is a heat shield, such as a glass tank of water, placed between the lamp and the pondweed?

It absorbs heat from the lamp so the temperature of the water stays constant.

How should an anomalous result be treated when working out the mean rate of photosynthesis from repeat readings?

Leave it out of the calculation — find the mean of the remaining repeat values.

Give one possible cause of an anomalous result in a pondweed photosynthesis investigation.

The scale was misread, air was trapped in the apparatus, the lamp was moved, or the temperature changed.

What makes a suitable scale and axis label when plotting rate of photosynthesis against temperature?

Equal intervals with the points filling at least half the grid, and the axis labelled with the quantity and unit, e.g. 'rate of photosynthesis in cm³/hour'.