Revision of Practical

Question 1:• Why are some leaves not green?

• 2 main reasons(1) Genes in the leaves reduce amount of

chlorophyll. Variegated leaf is a leaf that has 2 or more colours.

Normal leaf has 3 types of coloured pigments…

• Chlorophyll (green)Which covers

• Anthocyanins (red, purple, pink)Which covers

• Xanthophylls (yellow)

A Scientist’s Problem• This is an extract from van Helmont’s diary…

• • “I took an earthenware pot in which I put 200

kilograms of earth that had dried in an oven.• I moistened it with rain water and implanted in it a trunk of a willow tree weighing 5 kilograms. I planted it in the garden and covered the earth with an iron lid

punched with many holes to allow rain water in.• At length, after 5 years, the tree did weigh 169

kilograms and 3 grams. I again dried the earth in the vessel and found it weighed almost 200 kilograms (less 2 grams). Therefore 164 kilograms of wood,

bark and roots arose out of water only.”

A Scientist’s Problem

• What was the change in mass of the tree?

• What was the change in mass of the soil?

• What did van Helmont conclude from his experiment?

• Do you agree with his conclusion?• What other explanations could there be

for the results he found?

Group discussion

In groups of 3-4, discuss the questions that you have been given

Which is the most important ingredient that allows plants to grow?

• Water• Sunlight• Minerals• Carbon dioxide

Group 1: How critical is the role of water?

• Is water a food source? • Would you survive on water alone? Why?• Do we know how much water was added to the pot over

the five years?• What should van Helmont have done if he had wanted to

prove that all this increase in mass was from water?

• Do you think van Helmont was correct to say that water alone accounted for the growth of the willow tree? Try to summarise your thoughts using some of the points above to support your argument.

Group 2: How critical is the role of Sunlight?

• Living things are made of atoms. Are there any atoms in sunlight?

• Could sunlight contribute to the increase in mass of the plant? How does it contribute?

• Is sunlight needed for plants to grow? What role do you think it might have?

• Do you think it is correct to say that plants make their food from sunlight? Try to summarise your thoughts using some of the points above to support your argument.

Group 3: How important is soil?

• What constitutes soil? Is it mostly solid particles? What can you find in soil?

• How much did the mass of the soil decrease over the five years? Could this have contributed to the growth of the plant? How much?

• Can plants grow without soil? Can you name any alternative methods where plants can grow without soil?

Group 4: How important is CO2 to plant growth?

• What gases are in the air? • Do the gases in the air have mass? (If you

compare and empty balloon and one filled with air you will soon find out.)

• Design an experiment show that carbon dioxide has an effect on increasing the mass of a plant.

Can plants grow without minerals?Do minerals have an effect?Do you think it is correct to say that some of the tree came from minerals in the soil? How much could the minerals have contributed to growth?

Water only Water plus minerals

How does amount of CO2 affect plant growth?