How Plants Get Their Food )

Photosynthesis

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

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

sunlight(energy)

waterwater

carbon dioxide

Chlorophyll

Chlorophyll is a green coloured 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

Leaf cells with chloroplasts

cell wall

nucleus

chloroplast

cytoplasm vacuole

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

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)

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

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 or (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

GLUCOSE

storage e.g. starch in potato

starch

fruitsother sugars

e.g. seed germination

energy

cytoplasm

protein

cell walls

cellulose

Plants combine carbon dioxide from the air, and water from the soil to make glucose.

The energy needed for this process comes from sunlight

The sunlight is absorbed by chlorophyll contained in the chloroplasts of the leaf.

The glucose can be used for energy or to make other substances.

To make other substances, the glucose must be combined with other chemical elements such as nitrogen and potassium.

These chemical elements are present as ions in the soil and are taken up in solution by the roots.

TO SUM UP

QUESTIONS

In the questions which follow, choose the best answer from the four alternatives

Question 1For a plant to make glucose it needs

(a) CO2 and H2O

(b) CO2, H2O and sunlight

(c) CO2, H2O, sunlight and chlorophyll

(d) CO2, H2O, sunlight, chlorophyll and nitrates

Question 2

A by-product of photosynthesis is

(a) Water vapour

(b) Oxygen

(c) Carbon dioxide

(d) Nitrogen

Question 3

Chlorophyll is present only in

(a) The cytoplasm

(b) The vacuole

(c) The cell wall

(d) The chloroplasts

Question 4

The food made by photosynthesis is transported round the plant in the form of

(a) Glucose

(b) Sucrose

(c) Starch

(e) Cytoplasm