Get the most from your plants!

Elodea is a remarkable plant, but it needs to be looked after if it is going to photosynthesise normally.

Good luck with your experiments! Remember to keep on trying.

Blackman studied photosynthesis in Elodea, and here are a few extracts from his published papers:

1. Get healthy plants

'Only the greenest and healthiest shoots were selected...'

'Many observers have noted that water-plants are very sensitive to unfavourable conditions of environment, and we have found marked depression of vigour and photosynthesis brought about by keeping plants in vessels of water in the laboratory.'

'Even plants freshly collected from a natural habitat do not always show the same uniform vigorous activity: the sickly plants give low rates of [photosynthesis] and have been excluded from our tables and figures. '

2. Understand light intensity

'The intensity of light varies as the inverse square of the distance of the lamp from the plant.' (In other words, if the lamp is distance d from the plant, plot a graph of the amount of photosynthesis against 1/d²)

3. Think about carbon dioxide

[At high carbon dioxide concentrations there] 'may be a vigorous giving-off of gas bubbles: but on analysis, the gas turns out to be mostly CO₂...'

[high levels of CO₂ depress photosynthesis (see his results supplied on the spreadsheet)...'It is a quite general phenomenon and...many vital processes are depressed by an atmosphere containing 20-25% of CO₂. '

There is more about carbon dioxide on these pages.