How Plants Get Their Food

How do plants get their food ?

199.8 lb soil

The soil was watered but nothing else was added. After 5 years, the tree had gained 169.2 lb in weight but the soil had lost only 2 pounds. van Helmont concluded that the tree had made 169lb of new growth from water alone.

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200 lb soil

In 1649, A Belgian physician, van Helmont, set up an experiment in which he planted a willow sapling, weighing 5 lb, in 200 lb of soil.

van Helmont’s experiment was effective in showing that the plant’s food did not come from the soil.

But he had overlooked the fact that air was available to the plant as well as water.

Could it be that the plant made 169 lb of material from just air and water?

This might seem unlikely, but we now know that plants do indeed make their food using carbon dioxide from the air and water from the soil.

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FeedingAnimals get their food by eating plants, or other animals Carnivores eat animals Herbivores eat plants

Plants make their own food They combine carbon dioxide from the air with water

and dissolved salts from the soil Plants do NOT get their food from the soil

The first stage by which plants make food is called PHOTOSYNTHESIS

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by eating plants or ...

Animals get their food …

... plant products,

or (c) other animals

Plants make their food by photosynthesis

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Photosynthesis6

Green plants take in carbon dioxide (CO2) from the air

They take up water (H2O) from the soil

The plants combine the CO2 with the H2O tomake the sugar, glucose (C6H12O6)

6CO2 + 6H2O = C6H12O6 + 6O2

Oxygen (O2) is a by-product of this reaction

C6H12O6

CO2

CO2

CO2

CO2

CO2

CO2

H2O

H2O

H2O

H2O

H2O

H2O

6O2

+

6 molecules of carbon dioxide combine with 6 molecules of waterto make one molecule of glucose and 6 molecules of oxygen

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Energy

It takes energy to make CO2 combine with H2O

This energy comes from sunlight

The energy is absorbed and used by a substance called chlorophyll

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sunlight(energy)

waterwater

carbon dioxide

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Chlorophyll

Chlorophyll is a green colored chemical

It is present in the leaves of green plants

The chlorophyll in the cells is packaged into tiny structures called chloroplasts

The next slide shows a diagram of leaf cells with their chloroplasts

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Leaf cells with chloroplasts

cell wall

nucleus

chloroplast

cytoplasm vacuole

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All the reactions to combine CO2 and H2O take place in the chloroplast

sunlight

water

carbon dioxide

in the chloroplast,carbon dioxide andwater combine tomake sugar

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palisade cell of leaf

Cell structure of a leafThe palisade cells are in theuppermost layers of the leaf

epidermis

palisade cell ( photosynthesis)

vessel (carries water)

stoma (admits air)

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Carbohydrates

• Glucose is one example of a carbohydrate

• Other examples are starch, sucrose and cellulose (in cell walls)

• Carbohydrate molecules contain the elements carbon, hydrogen and oxygen

• Living organisms can easily change one carbohydrate into another

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What happens to the glucose? The glucose made by the chloroplast is either (a) used to provide energy for the chemical

processes in the cell ( by respiration)

(b)turned into sucrose and transported to other parts of the plant

(c) turned into starch and stored in the cell as starch

grains

In darkness the starch is changed back into glucose and transported out of the cell

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GLUCOSE

storage e.g. starch in potato

starch

fruitsother sugars

e.g. seed germination

energy

cytoplasm

protein

cell walls

cellulose

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