How%20Plants%20Get%20Their%20Food%20(1) - PowerPoint PPT Presentation

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How%20Plants%20Get%20Their%20Food%20(1)

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tree had gained 74kg in weight but the soil had lost only 57g. ... But he had overlooked the fact that air was available to the plant as well as water. ... – PowerPoint PPT presentation

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Title: How%20Plants%20Get%20Their%20Food%20(1)

1
How Plants Get Their Food (1)
2
2
How do plants get their food ?
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 Helmonts experiment was effective in showing
that the plants 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
4

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

5
Animals get their food
5
Plants make their food by photosynthesis
6
Photosynthesis
6
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)
6CO2 6H2O C6H12O6 6O2
Oxygen (O2) is a by-product of this reaction
7
7
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
9

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

9
9
10
Chlorophyll
10

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

11
Leaf cells with chloroplasts
11
cell wall
chloroplast
nucleus
cytoplasm
vacuole
12
All the reactions to combine CO2 and H2O take
place in the chloroplast
12
sunlight
palisade cell of leaf
water
in the chloroplast, carbon dioxide and water
combine to make sugar
carbon dioxide
13
13
Cell structure of a leaf The palisade cells are
in the uppermost layers of the leaf
14
Carbohydrates
14

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

15
What happens to the glucose?
15

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

16
How Plants get their Food (2)
How Plants Get Their Food (2)
How plants get their food (2)
17
Other Food
17

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)

18
18
fruits
other sugars
energy
protein
GLUCOSE
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
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
19

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

21
Mineral ions
20

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)

22
Effects of fertilisers
21
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
plots
22
24
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.