How Plants Get Their Food (1). 2. 90.20kg soil. 90.72kg soil. 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.
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
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 airwas available to the plant as well as water.
Could it be that the plant made 74kg of material from just airand 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.
Animals get their food by eating plants, orother 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 NOTget their food from the soil
The first stage by which plants make food is called PHOTOSYNTHESIS
or (c) other animals
plants or ...
Plants make their food by 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)
6CO2 + 6H2O = C6H12O6 + 6O2
Oxygen (O2) is a by-product of this reaction
6 molecules of carbon dioxide combine with 6 molecules of water
to make one molecule of glucose and 6 molecules of oxygen
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
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
in the chloroplast,
carbon dioxide and
water combine to
palisade cell ( photosynthesis)
vessel (carries water)
stoma (admits air)
Cell structure of a leaf
The palisade cells are in the
uppermost layers of the leaf
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
How Plants Get Their Food (2)
How plants get their food (2)
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 proteinsplants combine glucose with compounds of nitrogen, (nitrates)
e.g. seed germination
storage e.g. starch in potato
KNO3 K+ + NO3-
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
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
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)
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
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.
In the questions which follow, choose the best
answer from the four alternatives
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
A by-product of photosynthesis is
(a) Water vapour
(c) Carbon dioxide
The plant needs to take in nitrate ions in order to make
Chlorophyll is present only in
(a) The cytoplasm
(b) The vacuole
(c) The cell wall
(d) The chloroplasts
The food made by photosynthesis is transported round the plant in the form of
Which mineral ions are needed for making protein?
(a) Magnesium ions
(b) Sulphate ions
(c) Phosphate ions
(d) Nitrate ions