1. How Plants Get Their Food (1)
Notice how little the leaves overlap each other. This enables them to trap the maximum amount of sunlight. the importance of this will be explained later in the presentation

2. How do plants get their food ?2
How do plants get their food ?
90.20kg soil
90.72kg soil
In the 17th Century, A Belgian physician, van Helmont, set up an
experiment in which he planted a willow sapling in a weighed
amount of soil.
The soil was watered but nothing else was added. After 5 years, the
tree had gained 74kg in weight but the soil had lost only 52g.
van Helmont concluded that the tree had made 74kg of new growth
from water alone

3. 3
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 74kg of material from just air and water?
This might seem unlikely but we now know that plants do indeed make their food from carbon dioxide from the air and water from the soil.

4. Feeding Animals get their food by eating plants, or other animals4
Animals 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
Most fungi and bacteria get their food by breaking down organic matter, such as plant and animal remains (detritus). They then absorb the soluble breakdown products.
These organisms are called detritivores.
The name ‘Photosynthesis’ is derived from ‘photo’ (light) and ‘synthesis’ (building up).
Plants synthesize their food with the aid of sunlight. (Slides 9 and 10).

5. Animals get their food …5
by eating
plants or ...
or (c) other animals
... plant
products,
Plants make their food by photosynthesis

6. Photosynthesis Green plants take in carbon dioxide (CO2) from the air6
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 to
make the sugar, glucose (C6H12O6)
When a plant is photosynthesising, it is taking in carbon dioxide and giving out oxygen.
Plants which live in ponds, streams etc. are immersed in the water they need for photosynthesis
6CO H2O = C6H12O O2
Oxygen (O2) is a by-product of this reaction

7. 6 molecules of carbon dioxide combine with 6 molecules of water 7
CO2
H2O
CO2
H2O
H2O
CO2
C6H12O6
CO2
H2O
CO2 +
H2O
CO2
H2O
6O2
This reaction is summarised by the equation
6CO2 + 6H2O = C6H12O6 + 6O2
6 molecules of carbon dioxide combine with 6 molecules of water
to make one molecule of glucose and 6 molecules of oxygen

8. Energy It takes energy to make CO2 combine with H2O9
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
Without sunlight, photosynthesis could not take place.
Without photosynthesis, plants could not survive.
Without plants, most animals would die out because, ultimately, animals depend on plants for their food.
e.g. sunlight >>>> plants >>>> herbivores >>>> carnivores

9. carbon sunlight dioxide (energy) water 9
The carbon dioxide comes from the air.
The water comes from the soil.
The energy comes from sunlight.
water

10. Chlorophyll Chlorophyll is a green coloured chemical10
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
It is not only the leaves that contain chlorophyll; any green part of a plant, leaves, leaf stalk, stem, sepals will contain chloroplasts.

11. Leaf cells with chloroplasts11
cell wall
chloroplast
nucleus
These are called palisade cells and they are present in the upper layers of a leaf where most sunlight is absorbed.
The chloroplasts are present in the cytoplasm lining the cell
cytoplasm
vacuole

12. All the reactions to combine CO2 and H2O take place in the chloroplast12
sunlight
palisade cell
of leaf
water
in the chloroplast,
carbon dioxide and
water combine to
make sugar
The water travels from the roots, through the stem and into the leaf in a system of vessels.
The carbon dioxide diffuses into the leaf through tiny pores called stomata.
carbon dioxide

13. Cell structure of a leaf13
epidermis
palisade cell ( photosynthesis)
Cell structure of a leaf
The palisade cells are in the
uppermost layers of the leaf
vessel (carries water)
The palisade layer traps most of the sunlight.
The vessel carries water from the stem to the leaf.
Carbon dioxide enters through the stoma and diffuses through the air spaces between the cells.
stoma (admits air)

14. Carbohydrates Glucose is one example of a carbohydrate14
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
The chemistry of carbohydrates is dealt with in the section ‘Chemicals of Living Cells’.

15. What happens to the glucose?15
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
Before it is transported, glucose is converted to sucrose. Two glucose molecules combine to make a molecule of sucrose.
2C6H12O6 = C12H22O H20
glucose sucrose
It is the sucrose which is transported throughout the plant

16. How Plants get their Food (2)
Pyracantha. Some of the food made in the leaves is sent to the berries

17. Other Food Glucose and starch are carbohydrates17
Other Food
Glucose and starch are carbohydrates
Carbohydrates can be oxidised during respiration to produce energy
Plants need more than carbohydrates
They need proteins for making new cytoplasm and cells for growth
To make proteins plants combine glucose with compounds of nitrogen, (nitrates)
Carbohydrates may be
(a) oxidised to provide energy for chemical reactions.
(b) turned into starch and stored in storage organs such as potatoes and parsnips.
(c) turned into cellulose which builds the cell walls.
(d) Combined with nitrogen (from nitrates) to make amino acids , which are combined to make proteins

18. GLUCOSE 18 fruits other sugars energy protein e.g. seed germination
cytoplasm
starch
cellulose
cell walls
storage e.g. starch in potato

19. Ions
When a salt such as potassium nitrate dissolves in water it separates into two ions, a potassium ion and a nitrate ion
KNO K+ + NO3-
The potassium ion (K+) carries a positive charge. The nitrate ion (NO3-) carries a negative charge
These ions move freely and independently in the soil water and it is in this form that they are taken up by plants

20. Nitrates Nitrate ions are present in the soil, dissolved in water19
Nitrates
Nitrate ions are present in the soil, dissolved in water
The plants take up nitrate ions in the soil water
The nitrate ions are conducted through the roots to the stem and then to the leaves
In the leaves, the nitrate ions and glucose are combined to make proteins
This process is called assimilation
Proteins are needed for making the cell structures, e.g. cytoplasm, nucleus, chloroplasts.
The plant can grow only by making new cells and cell structures
Strictly speaking, it is not nitrates salts that are taken up but nitrate ions. When a salt such as potassium nitrate, is dissolved in water it splits into positively charged potassium ions and negatively charged nitrate ions.
KNO3 becomes K+ and NO3- The plant may take up either or both of these ions.

21. 20
Mineral ions
Nitrates are not the only ions that plants need to take in from the soil
They need phosphate, sulphate, iron, potassium and magnesium ions
This is the reason why farmers and gardeners add fertiliser to the soil
These fertilisers usually contain nitrates, phosphates and potassium (NPK)
Nitrates are needed for making proteins.
Phosphates are needed for DNA and for chemical reactions involving energy release.
Sulphates are needed for some proteins.
Iron is needed for certain enzyme reactions.
Magnesium is needed for making chlorophyll.

22. Effects of fertilisers21
Some of these plots have received different types of fertiliser.
Some have had only manure added to the soil.
Some had neither manure nor fertiliser for many years
These are experimental strips of wheat. Varying amounts and types of fertiliser have been added to the soil to see which give the best plant growth

23. Average yearly wheat yields from experimental plots22
The chemical fertilizer contains all the mineral ions needed by the plants. The other fertilizers are lacking in one of the essential ions. Which of these mineral ions appears to be the most important?

24. The energy needed for this process comes from sunlight 23
TO SUM UP
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.

25. QUESTIONS In the questions which follow, choose the best24
QUESTIONS
In the questions which follow, choose the best
answer from the four alternatives

26. Question 1 For a plant to make glucose it needs (a) CO2 and H2O25
For 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

27. Question 2 A by-product of photosynthesis is (a) Water vapour26
Question 2
A by-product of photosynthesis is
(a) Water vapour
(b) Oxygen
(c) Carbon dioxide
(d) Nitrogen

28. Question 3 The plant needs to take in nitrate ions in order to make27
Question 3
The plant needs to take in nitrate ions in order to make
(a) Protein
(b) Cellulose
(c) Starch
(d) Sugars

29. Question 4 Chlorophyll is present only in (a) The cytoplasm28
Question 4
Chlorophyll is present only in
(a) The cytoplasm
(b) The vacuole
(c) The cell wall
(d) The chloroplasts

30. Question 5 29
The food made by photosynthesis is transported round the plant in the form of
(a) Glucose
(b) Sucrose
(c) Starch
(e) Cytoplasm

31. Question 6 Which mineral ions are needed for making protein?30
Question 6
Which mineral ions are needed for making protein?
(a) Magnesium ions
(b) Sulphate ions
(c) Phosphate ions
(d) Nitrate ions

32. 31
Incorrect

33. 32
Correct