Photosynthesis — A survival guide
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Photosynthesis -- A survival guide
01 Pupil worksheets ? Where does the wood come from?
Where does the wood come from?
An experiment carried out by Jean Baptiste van Helmont (1580 ? 1644)
This is an extract from van Helmont's diary... "I took an earthenware pot in which I put 200 pounds of earth that had dried in a furnace. I moistened it with rain water and implanted in it a trunk of a willow tree weighing 5 pounds. 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 pounds and 3 ounces. I again dried the earth in the vessel and found it weighed almost 200 pounds (less about 2 ounces). Therefore 164 pounds of wood, bark and roots arose out of water only."
Draw a table showing the mass of the tree and soil at the beginning and end of his experiment.
? 1. What was the change in
mass of the tree? 2. What was the change
in mass of the soil? 3. What did van Helmont
conclude from his experiment? 4. Do you agree with
his conclusion? 5. What other explanations could
there be for the results he found?
02 Pupil worksheets ? Where does the wood come from?
A class was asked whether they agreed with van Helmont's conclusion. Here are some of their responses:
Some of the tree may have grown from minerals in the soil.
I agree with van Helmont. Only the water could have made this much difference.
But I think that plants make their food from sunlight...
van Helmont may not have known about the gases in the air.
03 Pupil worksheets ? Where does the wood come from?
In groups, choose one of the cards below and consider the questions and information on the card. After you have discussed the questions and information try to come up with a summary of your groups' thoughts.
"Only the water could have made this much difference..."
Think about water.
? Is water a food source? ? Would you survive on water alone? ? 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? ? What measurements could he have taken?
? 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.
But I think that plants make their food from sunlight...
What is sunlight?
? Does sunlight have mass? ? Living things are made of atoms.
Are there any atoms in sunlight? ? Could sunlight contribute to the
increase in mass of the plant? ? 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.
04 Pupil worksheets ? Where does the wood come from?
Fig 1?All minerals
Some of the tree may have grown from minerals in the 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? Look at the results of the investigation below on mung beans: Mung bean seeds were germinated and grown in two solutions ? one containing all the minerals found in soil, one with just water (no minerals). The plants were grown for the same time and in the same conditions.
? 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?
Fig 2?Water only
What gases are in the air?
? Do the gases in the air have mass? (If you compare an empty balloon and one filled with air you will soon find out.)
? How could you show that these gases have an effect on increasing the mass of a plant?
? Look at the results of an experiment that examined the growth of plants at three different concentrations of carbon dioxide. What does it tell you? Can gases in the air affect growth? Which gas is shown to have an effect in these experiments?
van Helmont may not have known about the gases in the air
Dry weight per plant (g)
Average CO2 concentration in parts per million (ppm)
05 Pupil worksheets ? The story of photosynthesis
The story of photosynthesis
Fig 3?Carbohydrate molecular structure
Take a look at how plants make their food.
We know that the food plants made from photosynthesis are called CARBOHYDRATES.
If we look at the word `CARBOHYDRATE' we can tell quite a lot about it...
Carbohydrates contain the atoms CARBON, HYDROGEN and OXYGEN.
This carbohydrate (Fig 3) is called glucose ? it is a sugary substance and you are probably very familiar with its taste if you have eaten or drunk any of the products opposite.
? 1. So, which part of the word carbohydrate means that it
contains carbon? 2. And which part of the word means that it contains
hydrogen? 3. Now, can you suggest what the letters ATE mean when
placed on the end of a chemical name? 4. Figure 3 above is a chemical picture of one carbohydrate.
Count how many carbon, hydrogen and oxygen atoms this molecule has...
06 Pupil worksheets ? The story of photosynthesis
Now, if you were a plant and you had to make this carbohydrate, what atoms are you going to need and where could you get them from?
If we had some carbon dioxide (Fig 4), could we make carbohydrates from it?
Fig 4?Carbon dioxide (CO2)
Fig 6?Water (H2O) & Sunlight
What atoms would still be missing? If we had some water as well as the carbon dioxide, what extra atom could this supply?
Fig 5?Water (H2O)
When light energy is used to split water, there is a product left over that is not needed. What is this product?
You may have come across this idea before ? it seems that photosynthesis not only results in the production of carbohydrates such as glucose, but also releases oxygen into the air ? which is a good thing as we will see later
We know that plants use sunlight energy to split water (H2O) into hydrogen and oxygen. The hydrogen is added to the carbon dioxide to make CARBOHYDRATES.
The oxygen produced from this splitting of water is released into our atmosphere.
OK ? suppose we have the carbon dioxide and some water (H2O) (Fig 5) ? we would need to split the water up to release the hydrogen from it.
We summarise this using a chemical equation:
6CO2 + 6H2O
carbon dioxide water
C6H12O6 + O2
The process of splitting water into hydrogen and oxygen is very difficult. However ? with the help of sunlight energy plants can split the water and use the hydrogen to combine with the carbon and oxygen from carbon dioxide.
07 Pupil worksheets ? Talk about...
? 1. What do these products have in common? 2. Are there any similarities and differences
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