How Plants Get Their Food )

Photosynthesis Green plants take in carbon dioxide (CO 2 ) from the air They take up water (H 2 O) from the soil The plants combine the CO 2 with the H 2 O to make the sugar, glucose (C 6 H 12 O 6 ) 6CO 2 + 6H 2 O = C 6 H 12 O 6 + 6O 2 Oxygen (O 2 ) is a by-product of this reaction

C 6 H 12 O 6 CO 2 H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O H2OH2O 6O molecules of carbon dioxide combine with 6 molecules of water to make one molecule of glucose and 6 molecules of oxygen

Energy It takes energy to make CO 2 combine with H 2 O This energy comes from sunlight The energy is absorbed and used by a substance called chlorophyll

sunlight (energy) water 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 CO 2 and H 2 O take place in the chloroplast sunlight water carbon dioxide in the chloroplast, carbon dioxide and water combine to make sugar palisade cell of leaf

Cell structure of a leaf The palisade cells are in the uppermost 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 fruits other 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 1 For a plant to make glucose it needs (a) CO 2 and H 2 O (b) CO 2, H 2 O and sunlight (c) CO 2, H 2 O, sunlight and chlorophyll (d) CO 2, H 2 O, 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