Name a piece of apparatus used to measure the volume of oxygen released by an aquatic plant.

A photosynthometer, in which the gas collected is drawn along a capillary tube so that the length of the bubble can be measured.

Why is sodium hydrogencarbonate solution added to the water around an aquatic plant in a photosynthesis experiment?

It supplies carbon dioxide at a constant and non-limiting concentration, so that the factor being investigated is the only variable.

A lamp is moved from 10 cm to 20 cm from a piece of pondweed. By what factor does the light intensity reaching the plant change?

It falls to one quarter of its original value, because doubling the distance divides the intensity by four.

Describe how the effect of wavelength on photosynthesis is investigated.

Coloured filters that transmit known wavelengths are placed between a lamp of fixed intensity and the plant, and the rate of oxygen release is measured for each filter.

OCR A-Level Biology B H422

The Developing Cell: Cell Division and Cell Differentiation

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Photosynthesis, Food Production and Management of the Environment

Investigating the factors affecting photosynthesis

3 things to know
Components 01, 02 and 03

Overview

Recall questions on measuring oxygen release, why hydrogencarbonate is added, how lamp distance changes intensity, wavelength and temperature effects, and why readings wait after a change in conditions.

What you need to know

Answer each one before you reveal it.

Your recallNot started

Key term

Why is counting bubbles a less reliable measure of photosynthesis than collecting the gas released?

Key term

How is light intensity usually varied in a photosynthesis practical, and how does intensity depend on that variable?

Key term

Why should an LED lamp or a heat shield be used when investigating light intensity?

Questions from this subtopic

Each one with the model answer underneath.

1
Name a piece of apparatus used to measure the volume of oxygen released by an aquatic plant.
Model answer
A photosynthometer, in which the gas collected is drawn along a capillary tube so that the length of the bubble can be measured.
2
Why is sodium hydrogencarbonate solution added to the water around an aquatic plant in a photosynthesis experiment?
Model answer
It supplies carbon dioxide at a constant and non-limiting concentration, so that the factor being investigated is the only variable.
3
How is light intensity usually varied in a photosynthesis practical, and how does intensity depend on that variable?
Model answer
The lamp is placed at different distances from the plant, and the intensity reaching it is inversely proportional to the square of the distance.
4
A lamp is moved from 10 cm to 20 cm from a piece of pondweed. By what factor does the light intensity reaching the plant change?
Model answer
It falls to one quarter of its original value, because doubling the distance divides the intensity by four.
5
Why should an LED lamp or a heat shield be used when investigating light intensity?
Model answer
A filament lamp warms the water as it is brought closer, so temperature would change alongside light intensity and the results could not be attributed to light alone.
6
Describe how the effect of wavelength on photosynthesis is investigated.
Model answer
Coloured filters that transmit known wavelengths are placed between a lamp of fixed intensity and the plant, and the rate of oxygen release is measured for each filter.

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