Rate of photosynthesis Flashcards – AQA GCSE Combined Science: Trilogy (8464) — Biology — Higher

When is an environmental factor limiting the rate of photosynthesis?

When increasing that factor increases the photosynthetic rate under the prevailing conditions.

Which three environmental factors can limit the rate of photosynthesis?

Light intensity, carbon dioxide concentration and temperature.

Why might increasing one factor have little effect, or only a limited effect, on photosynthetic rate?

Another factor may remain or become limiting.

Why can photosynthetic rate fall at excessively high temperatures?

Enzyme activity can decline.

What three agricultural practices can reduce limitations on photosynthesis?

Supplementary lighting, carbon dioxide enrichment and temperature control.

What data can be used to assess whether a treatment improves photosynthesis or crop production?

Photosynthetic rate or crop yield data.

How can data help judge whether an agricultural treatment is worth its cost?

By comparing its measured benefit with its cost under the conditions measured.

Which three factors affect the rate of photosynthesis?

Light intensity, carbon dioxide concentration, and temperature.

How does increasing light intensity or carbon dioxide concentration affect the rate of photosynthesis?

The rate rises if that factor is limiting, until another factor becomes limiting.

How does temperature affect the rate of photosynthesis?

The rate generally rises towards an optimum temperature, then falls at higher temperatures.

How can the effect of one factor on photosynthetic rate be investigated?

Vary that factor, measure a consistent indicator of photosynthetic rate, and control other relevant conditions.

Which quantities go on the axes of a graph showing how a factor affects photosynthesis rate?

Put the factor on the horizontal axis and photosynthesis rate on the vertical axis. Label both axes with quantities and units.

How should scales be chosen for a photosynthesis rate graph?

Choose scales that cover the data and use the available space appropriately.

How should tabulated values be represented on a photosynthesis rate graph?

Plot the numerical values accurately as points, then draw an appropriate line or curve to show the pattern.

How can you find the numerical values represented by a point on a photosynthesis rate graph?

Read the point’s values from the axis scales.

What changes in rate should you look for when interpreting a photosynthesis rate graph?

Identify where the rate rises, levels off or falls as the factor changes.

What might a plateau on a photosynthesis rate graph indicate?

Another factor may be limiting, so further increases in the plotted factor do not increase the rate.

What is the role of chlorophyll in photosynthesis?

It absorbs light energy used in photosynthesis.

Under otherwise comparable conditions, why does less chlorophyll reduce the rate of photosynthesis?

Less light is absorbed, so less energy is available for photosynthesis.

When can increasing chlorophyll increase the rate of photosynthesis, and when might it not?

It can increase the rate when light absorption is limiting, but may not when another factor is limiting.

How can photosynthesis rate be estimated from changes in oxygen or carbon dioxide?

Measure the oxygen released or carbon dioxide taken up over a known time interval.

How can oxygen release from an aquatic plant be measured to estimate photosynthesis rate?

Collect the oxygen and measure its volume.

Why is counting oxygen bubbles a less precise way to measure photosynthesis rate?

Bubbles can differ in size.

How is mean photosynthesis rate calculated from a measured change?

Divide the measured change by the time taken. Use corresponding units, such as volume of oxygen per minute.

What is needed to compare measured photosynthesis rates reliably?

Use a consistent measurement method and controlled conditions.

How does light intensity vary with distance from a point source?

It is inversely proportional to the square of the distance: $I \propto \frac{1}{d^2}$.

For a point light source, how are intensities $I_1$ and $I_2$ related at distances $d_1$ and $d_2$?

$\frac{I_2}{I_1} = \left(\frac{d_1}{d_2}\right)^2$

What assumptions are needed to compare light intensities at two distances using the inverse square law?

The source is approximated as a point source, it is the same source at both distances, and background light is negligible.

Why might a plant's photosynthesis rate not change in the same proportion as the light intensity from a lamp?

Photosynthesis may be limited by another factor.