1
Nutrition in Plants
Learning Objectives
To know about
modes of nutrition—autotrophic and heterotrophic.
nutrition in plants—photosynthesis.
heterotrophic nutrition in plants—parasitic, saprophytic, insectivorous and
symbiotic.
All living organisms perform some basic functions to keep
themselves alive. These basic functions which allow living
organisms to live on earth are known as life processes. The
basic life processes common to all living organisms are
nutrition, respiration, excretion, growth, reproduction,
movement and response to stimuli.
You have learnt about these life processes in class VI. All living
organisms require food, which provides energy to perform
the life processes. Plants can prepare their food themselves.
Animals cannot do so and obtain food from plants or animals
that eat plants. We, human beings, also belong to this category.
Humans and animals are, thus, directly or indirectly dependent
on plants.
Food
Required to obtain energy for the growth
and proper functioning of our body.
Nutrients
• Chemical substances present in our
food which provide energy and
materials needed by the body to live
and grow.
• Seven nutrients
• Carbohydrates • Proteins
• Fats
• Vitamins
• Minerals
• Fibre
• Water
1.1 NUTRITION
The process of taking in food and its utilization by the body is
called nutrition (derived from Latin word nutrire meaning
“to nourish”). As you have learnt in class VI, food provides us
with a number of nutrients which are necessary for the proper
functioning of our body. To recall, the different nutrients
are carbohydrates, proteins, fats, vitamins and minerals. Do
you remember (i) the nutrients which provide us energy, and
(ii) the roles which the different nutrients perform in our
bodies?
Worms are an excellent source
of plant nutrition
1.2 MODES OF NUTRITION
pitcher shaped leaf
Living organisms show two modes of nutrition:
(i) they prepare their own food, and
(ii) they take in ready-made food, either from plants (fruits
and vegetables) or from animals (milk, meat and eggs).
The nutrition of the first type is called autotrophic (auto =
self, and troph = nourishment), while, the second type of
nutrition is called heterotrophic (heteros = other).
(a) Pitcher plant
1.2.1 Autotrophic Nutrition
Autotrophic nutrition is found in green plants. Green plants
prepare their own food through a process called photosynthesis.
The leaves of these plants contain a green pigment called
chlorophyll. Without chlorophyll, food cannot be prepared
by the plants.
two halves of a leaf with
spines on the margins
Green plants are called autotrophic organisms or autotrophs.
1.2.2 Heterotrophic Nutrition
All animals show heterotrophic mode of nutrition and these
organisms are called heterotrophs.
Heterotrophs are organisms that cannot manufacture their own
food and derive food from plants or animals or both.
(b) Venus flytrap
Fig. 1.1: Insectivorous plants
autotroph
herbivore
carnivore
omnivore
Fig. 1.2: Categories of animals based on their
eating habits
2
If you list all the food items that you eat during the day, you
will know how much we depend on plants and animals. Wheat,
rice, pulses (dals), vegetables and fruits are obtained from
plants. For milk, curd, cheese, eggs and meat, we depend on
animals.
Do you know that even some plants are heterotrophs as they
can eat insects? The pitcher plant and the venus flytrap are
plants which eat insects (Fig. 1.1). Such plants are called
insectivorous plants. Insectivorous plants, however, prepare
their food as an autotroph.
Based on their eating habits, animals are divided into three
categories (Fig. 1.2):
(i) Herbivores: plant eaters, like cow, buffalo, deer, sheep
and goat;
(ii) Carnivores: meat eaters, like tiger, lion and wolf;
(iii) Omnivores: eat both plants and animals, like humans,
crow and cockroach.
Do you know?
Chlorophyll gives plants their green
colour because it reflects green light
and absorbs red and blue light.
Nutrition
Autotrophic
(can prepare their own food)
Heterotrophic
(cannot prepare their own food; obtain
food from plants or from animals or
both)
Herbivores
(plant eaters)
Carnivores
(meat eaters)
Omnivores
(eat both plants and
animals)
1.3 NUTRITION IN PLANTS—PHOTOSYNTHESIS
Plants, as discussed above, are autotrophs. They prepare their
own food.
Let us find out
Key Fact
Joseph Priestley’s experiments (1771)
demonstrated that plants produce
oxygen and purify air.
• where the food is prepared in the plant body.
• what are the raw materials which the plants use to prepare
their food.
sun
O2
released
• what is the chemical nature of food that is produced.
Food is prepared or synthesized only by those plants which
are green in colour. You must remember that the majority of
plants are green due to the presence of a green pigment called
chlorophyll. Chlorophyll is present in the leaves, and also in
the young green stems.
The process by which green plants prepare their own food is
called photosynthesis (photo = light; synthesis = to combine).
During this process, plants absorb the sun’s energy through
their leaves and convert it into food energy, using raw
materials from the atmosphere and soil (Fig. 1.3).
leaf (contains
chlorophyll)
CO2
sugar is
formed (food)
root (absorbs
water)
Fig. 1.3: Photosynthesis
3
Vessels
Channels for transport of water and
minerals in plants
Starch
• Presence of starch in the leaves
is used as an evidence of photosynthesis taking place.
• Its presence is tested by iodine test.
Thus, for photosynthesis, the following four things are required:
(i) Chlorophyll: It is the green pigment present in the leaves
(Fig. 1.4).
(ii) Sunlight: It is absorbed by the chlorophyll present in
the leaves.
(iii) Carbon dioxide: It is absorbed from the atmosphere by
the leaves through small pores present on the lower surface
of the leaves. These pores are called stomata (Fig. 1.5).
(iv) Water: It is taken up from the soil by the roots and
transported to the leaves through pipe-like structures called
vessels. They are present throughout the plant body.
The chlorophyll-containing cells of leaves, in the presence of
sunlight, use carbon dioxide and water to prepare food. The
food prepared is in the form of carbohydrates (sugars). These
sugars ultimately get converted into starch (another
carbohydrate). In brief, photosynthesis can be represented by
the following equation:
chlorophyll
Sunlight
6CO2
+ 6H2O ⎯⎯⎯→ C6H12O6 +
6O2
Carbon dioxide Water Chlorophyll Carbohydrate Oxygen
(from atmosphere)
(from (in the leaves)
soil)
(food)
(a) A leaf
(b) Section through a leaf
showing the presence of
chlorophyll
Fig. 1.4: Chlorophyll—the green pigment
guard cell
stomatal
opening
(a) Open
(b) Closed
Fig. 1.5: Stomata
4
From the above equation, you can see that there is an
interesting by-product of photosynthesis, oxygen. This gas is
essential for the survival of all living organisms.
1.3.1 Roles of Leaves in Photosynthesis
Synthesis of food takes place in the leaves. In other words, it
is the site of photosynthesis. All the four things (CO2, H2O,
sunlight and chlorophyll) required for the process, must reach
the leaves. Leaves possess the following two features which
make it possible:
(i) Leaves contain a green pigment, chlorophyll, in their
cells. This helps leaves to capture the sun’s energy, which
is used to prepare food from carbon dioxide and water.
(ii) There are small or tiny pores called stomata on the
surface of the leaves. Through the stomata, carbon
dioxide from the atmosphere enters the leaves. Oxygen,
a by-product of photosynthesis, and water (transpiration)
also go out of the leaves through these stomata.
Figure 1.5 shows the structure of a stomata. It has an
opening called stomatal opening in the centre. The
opening is surrounded by two kidney-shaped guard
cells.
spine
stem
What happens in plants with reduced leaves, like the desert
plants?
In desert plants, like cacti, leaves are reduced to spines. This is
done to prevent or reduce the loss of water by transpiration.
The stem in these plants becomes green to carry out
photosynthesis.
What happens to photosynthesis in plants with red, brown
or violet leaves?
Fig. 1.6: A cactus plant
Transpiration
Loss of water in vapour form through
the surface of leaves
In all such leaves, green colour is also present in addition to
red, brown, yellow and other pigments. However, the amount
of red, brown, yellow or other pigments is very high in
comparison to the green colour, and therefore, these pigments
mask the green colour. Photosynthesis does take place in all
these leaves.
You might have seen some plants which have white and green
parts in the same leaf. They are called variegated leaves.
Remember that photosynthesis will not take place in the white
portions of such leaves. Common examples are those of money
plant, croton and coleus.
(a) Money plant
1.3.2 Importance of Photosynthesis
Imagine what will happen to life on earth in the absence of
photosynthesis!
Or
Imagine what will happen if sun does not rise at all for four
months!
In the absence of photosynthesis, life will not be possible as:
• There would be no food available. In the absence of food,
the survival of living organisms will not be possible as all
organisms are directly or indirectly dependent on food
made by plants.
(b) Croton plant
Fig. 1.7: Plants with leaves of different colours
5
S
HOT
• Oxygen, a by-product of photosynthesis, will not be
released. Living organisms will not be able to perform an
important activity of life, respiration. Without respiration,
no living organism can survive.
• Photosynthesis maintains a balance between oxygen and
carbon dioxide in the atmosphere (Fig. 1.8). This balance
will be disturbed in the absence of photosynthesis.
Classroom Discussion
What will be the effect on animals if
the number of plants on our planet is
reduced?
nt
Pho
tos
y
O2
s
he
is
Life, thus, would be impossible without photosynthesis.
plants
CO2
animal
Similarly, if the sun does not rise at all for a few months,
photosynthesis will not take place and the balance of gases
(carbon dioxide and oxygen) will also be disturbed. Thus,
existence of life would be greatly affected.
Fig. 1.8: Balance of oxygen and carbon
dioxide in the atmosphere
Activity 1.1 (demonstrate)
Aim: To show that sunlight is necessary for photosynthesis and starch is produced during
the process.
Materials required: Two potted green plants (of the same kind), iodine solution, dropper
Procedure:
• Take two potted green plants of the same kind and
label the pots as A and B.
• Keep pot A in dark (or in a black box) and pot B in
sunlight for 3–4 days.
• Test the leaves of the two pots with 2–3 drops of
iodine solution (as was done in class VI). Note
down your results.
iodine
starch
test
⎯→
⎯→
negative
result
A
(a) Pot A kept in dark
• Now, keep pot A (earlier kept in dark) in sunlight
for 3–4 days, and perform the iodine test on the
leaves.
Again note down your results.
Observations: Leaves of pot A when kept in dark
did not show blue-black colour, but those of pot B
showed blue-black colour. But when pot A was kept
in sunlight, the leaves showed blue-black colour.
Inference: Two things are proved:
• Sunlight is necessary for photosynthesis.
• Starch is produced as a result of photosynthesis.
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⎯→
⎯→
positive
result
B
(b) Pot B kept in sunlight
Fig. 1.9: Starch is produced during photosynthesis
Activity 1.2 (demonstrate)
Aim: To show that light is necessary for photosynthesis.
Materials required: A potted green plant, black
paper, paper clips, iodine solution, dropper
Procedure:
• Take a potted green plant and cover a part of
one leaf with black paper, as shown in Fig. 1.10.
• Allow the plant to carry out photosynthesis by
keeping the pot in sunlight for 3–4 hours.
• Test the leaf for formation of starch in both the
covered and uncovered portions by using iodine
solution.
Observations: When tested with iodine solution,
(i) the uncovered portion of the leaf develops blueblack colour, (ii) the covered portion of the leaf does
not develop blue-black colour. It becomes brown.
black
paper
starch
test
positive
result
negative
result
Inference: Starch is produced only in those parts
of the leaf that are exposed to sunlight. The activity,
thus, proves that sunlight is necessary for photosynthesis.
Fig. 1.10: Sunlight is necessary for photosynthesis
Activity 1.3 (demonstrate)
Aim: To show that green pigment (chlorophyll) is necessary for photosynthesis.
This activity can be performed using a variegated leaf of coleus or money plant. Perform steps 2
and 3 given in Activity 1.2.
Observations: The green portion of the leaf develops blue-black colour, when tested with iodine for
the presence of starch. The non-green portion turns brown in colour.
starch
test
⎯⎯→
⎯⎯→
negative result
positive result
Fig. 1.11: Chlorophyll is necessary for photosynthesis
Inference: Only those portions of the leaf that contained chlorophyll could perform photosynthesis.
This shows that chlorophyll is necessary for photosynthesis.
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Answer Orally (Formative Assessment)
1. Define the following:
(a) Nutrients
(b) Nutrition
(c) Autotrophic nutrition
(d) Heterotrophic nutrition
(e) Autotrophs
(f) Heterotrophs
(g) Chlorophyll
(h) Herbivores
(i) Carnivores
(j) Omnivores
(k) Photosynthesis
(l) Stomata
(m) Guard cell
(n) Variegated leaves
2. Name the four things required for photosynthesis.
3. Name the green-coloured pigment present in leaves which captures the energy of the sun.
1.4 HETEROTROPHIC NUTRITION IN PLANTS
Do you know?
So far, we have learnt about autotrophic nutrition which is
commonly found in green plants. There are, however, some
plants which cannot prepare their own food. The leaves in
these plants do not contain chlorophyll.
The world’s largest
flower bearing
plant, Rafflesia, is
a parasite.
How do these plants derive their nutrition?
Parasite
An organism that grows, feeds and lives
on or in another organism while
contributing nothing to the host.
amarbel
Fig. 1.12: Cuscuta (amarbel) on host plant
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Like humans and animals, such plants depend on the food
prepared by other plants. This is the heterotrophic mode of
nutrition.
Heterotrophic plants are of four types:
(i) Parasitic plants
(ii) Saprophytic plants
(iii) Insectivorous or carnivorous plants
(iv) Symbiotic plants
1.4.1 Parasitic Plants (Para = other;
sitic = dependent)
The non-green plants which live on other living organisms and
obtain their food from them are called parasitic plants. The
living organism from which a parasite derives its food is called
the host.
A common plant parasite is Cuscuta or dodder plant (amarbel).
This parasite produces yellow tubular structures which attach
themselves to a plant and wrap them around the stem and
branches (Fig. 1.12). Its leaves are reduced to minute scales.
Chlorophyll is not present in this plant. It absorbs readymade
food from the host plant on which it climbs, through special
structures called haustoria. The haustoria absorb food from
the host plant.
1.4.2
Saprophytic Plants (Sapro = decaying
matter; phytos = plant)
The plants which live and feed on dead and decaying organic
matter are called saprophytic plants.
Many bacteria and fungi (like mushrooms, moulds and yeast)
are saprophytic plants or saprophytes. Saprophytes, like the
parasites, lack green colour and do not carry out photosynthesis. Saprophytic fungi secrete digestive juices on the dead
and decaying matter and convert it into solution. The nutrients
are then absorbed from it.
Fungi are commonly seen during and after rains. Hot and
humid weather favours the growth of fungi.
S
HOT
Classroom Discussion
• Are we and the other animals
parasites on plants?
• Are mosquitoes and leeches that suck
our blood parasites?
Discuss with your class teacher.
Do you know?
•
•
•
•
Some fungi are used in medicine.
Fungi like mushrooms are edible.
Yeast is also a useful fungus.
Some fungi cause diseases also.
Have you ever eaten mushrooms? These days, mushrooms are
grown on a large scale, so that these can be used as food.
All mushrooms, however, are not edible. When you visit a
supermarket, you can find whitish umbrella-like structures
being sold. These are mushrooms (Fig. 1.13). These can also
be observed in nature in a forest, during rainy season, growing
on rotting wood pieces.
Also, have you noticed your unused shoes or school bags left
in hot and humid weather for a long time? You will find white
patches appearing on them. These white patches are fungi
(singular fungus).
Let us perform the Activity 1.4 to see fungi.
Fig. 1.13: Mushroom (saprophyte)
Activity 1.4 (study)
To study the growth of fungi.
1. Take a piece of bread on a glass plate and moisten it with
water.
2. Keep the glass plate in a moist warm place and cover it with a
lid of petri dish or bell jar.
(a) Fungal hyphae
3. Leave it for 2–3 days. Observe the piece of bread. You will
observe a white cottony growth on the piece of bread.
Now observe the cottony growth with a magnifying glass.
You may be able to see cotton-like threads (hyphae).
The cottony growth and the threads are of a fungus called
bread mould (Fig. 1.14).
(b) Bread mould
Fig. 1.14: Growth of fungus
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Insectivorous plants
These are both autotrophic and heterotrophic in their nutrition.
1.4.3 Insectivorous or Carnivorous Plants
Plants which eat animals, particularly insects are called
insectivorous or carnivorous plants.
In short, these are insect-eating plants.
leaf tip
modified
to form a lid
These plants are usually green and prepare their own food.
Then, why do they eat insects? This is because in some areas,
the soil is deficient in nitrogen. The plants growing in such
areas need to obtain nitrogen from outside sources. This is
done by trapping and eating insects.
leaf modified
into a pitcher
Examples: Pitcher plant [Fig. 1.2(a)], Venus flytrap [Fig. 1.2(b)],
bladderwort and sundew plant.
Fig. 1.15: A pitcher-like structure in a
pitcher plant
Do you know?
Lichens are excellent indicators of air
pollution. These are sensitive primarily
to sulphur dioxide and other air pollutants and will not grow at places which
are polluted.
Insectivorous plants have developed special structures to catch
insects. In a pitcher plant, the pitcher-like structure (Fig. 1.15)
is the modified part of the leaf. The leaf tip is modified to
form a lid which can open or close the mouth of the pitcher.
Inside the pitcher, downward-pointing hair are present. Once
an insect enters the pitcher, the lid closes and the insect gets
trapped in the hair. Digestive juices secreted in the pitcher
now digest the insect.
1.4.4 Symbiotic Plants
Plants which live in association with other plants and share
shelter and nutrients are called symbiotic plants. This
association between two different plants is called symbiotic
association or relationship. Both the plants benefit from a
symbiotic association.
Examples
Fig. 1.16: Lichens
Mind Scrambler
Unscramble each of the following to
form a word or term:
(a) TAHUSIROA _________________
(b) HLCLORLPHOY ________________
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• Certain fungi live in the roots of trees. The tree provides
nutrients to the fungus. In return, the fungus provides
certain nutrients from the soil to the tree.
• In lichens (Fig. 1.16) also, symbiotic relationship is seen.
There is an association between a green alga and a nongreen fungus. The fungus provides shelter, water and
minerals to the alga. The alga, in return, provides food to
the fungus. The alga, being green, prepares food by
photosynthesis.
Answer Orally (Formative Assessment)
1. Name the four types of heterotrophic plants.
2. Define and give examples of each of the following:
(a) Parasite
(b) Host
(d) Insectivorous plants
(e) Symbiotic plants
(c) Saprophytes
DEFINITIONS
•
•
•
•
•
•
•
•
•
•
Life process: The basic functions which allow living organisms to live on earth
Nutrition: The process of taking in food and its utilization by the body
Autotrophs: Organisms which prepare their food
Photosynthesis: The process through which green plants prepare their own food
Heterotrophs: Organisms that cannot manufacture their own food and derive food from
plants or animals or both
Parasitic plants: The non-green plants which live on other living organisms and obtain their
food from them
Host: The living organism from which a parasite derives its food
Saprophytic plants: The plants which live and feed on dead and decaying organic matter
Insectivorous plants: Plants which eat animals, particularly insects
Symbiotic plants: Plants which live in association with other plants and share shelter and
nutrients
QUICK ROUNDUP
1.
2.
3.
4.
5.
Food is required to perform basic life processes.
Nutrition may be autotrophic or heterotrophic.
Green plants are autotrophic, while non-green plants and animals are heterotrophic.
Four things are required for photosynthesis—carbon dioxide, water, sunlight and chlorophyll.
Food is synthesized in the form of carbohydrates and oxygen is released as a by-product
during photosynthesis.
6. Heterotrophic plants include parasitic, saprophytic, insectivorous and symbiotic plants.
EXERCISES FOR FORMATIVE AND SUMMATIVE ASSESSMENT
A. Answer in Detail (Summative Assessment)
1. Describe the process of photosynthesis. Also give its equation.
2. Describe how non-green plants obtain their food.
3. How does a pitcher plant catch insects?
4. Give differences between the following:
(a) Parasites and Saprophytes
(b) Autotrophs and Heterotrophs
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B. Answer Briefly
1. Why do we need food?
2. Mention: (a) the role of chlorophyll in photosynthesis, and
(b) the part of the plant in which food is made.
3. How would you test for the presence of starch in leaves?
4. What is produced as a result of photosynthesis?
5. What will happen to life on earth in the absence of photosynthesis?
C. Answer in One Word or a Few Words
C1. Name the following:
1. Type of nutrition found in fungi, lichen, amarbel and pitcher plant
2. A parasite plant with long, yellow and slender stem
3. The pores in leaves through which exchange of gases takes place
4. A plant with both autotrophic and heterotrophic mode of nutrition
5. The gas released during photosynthesis
C2. Fill
1.
2.
3.
4.
5.
6.
7.
in the blanks:
The food prepared by the plants is stored as ________________.
Presence of starch is tested with the help of ________________.
Heterotrophs derive their food from ______________________.
________________ is a parasitic plant.
In photosynthesis, sun’s energy is captured by the pigment called ________________.
Plants which obtain their food from dead and decaying matter are called ________________.
During photosynthesis, ________________ is taken in and ________________ is given out.
C3. Match the two columns:
Column A
1. Fungi
2. Amarbel
3. Pitcher plant
4. Animals
5. Plant’s food factory
(i)
(ii)
(iii)
(iv)
(v)
Column B
Leaf
Heterotrophs
Parasite
Saprophyte
Insects
C4. Multiple Choice Questions (MCQs): Choose the correct answer for each of the following:
1. Carbon dioxide is taken in from the atmosphere by the plants through
(a) roots.
(b) stems.
(c) leaves.
(d) all of these.
2. Which of the following is a saprophyte?
(a) Amarbel
(b) Lichen
(c) Mushroom
(d) None of these
3. Which of the following is/are raw materials for photosynthesis?
(a) Water
(b) Water and carbon dioxide
(c) Sunlight, water and carbon dioxide
(d) Sunlight, chlorophyll, water and carbon dioxide
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4. Which of the following is a symbiotic plant?
(a) Amarbel
(b) Lichen
5. Stomatal opening is surrounded by
(a) guard cells.
(b) stomata.
(c) Yeast
(d) Pitcher plant
(c) epidermal cells.
(d) chloroplast.
TASKS FOR FORMATIVE ASSESSMENT
A. Complete the Web Chart:
Plant
Sunlight
Water
Absorbed by
roots
Results in formation of
Food
B. Field Trip
1. Visit a nursery located in or near your locality. Ask the gardener to show you the greenhouse.
A greenhouse is a place where plants are grown by providing proper conditions of light,
water and temperature. Find out how in the greenhouse proper conditions have been provided
to grow the plants. Make a report and present in your class.
2. In the nursery locate cactus plant and money plant. Note down how are these two plants
different from each other.
3. Visit a garden, an agricultural field, and a greenhouse. Answer the following questions in
‘yes’ or ‘no’:
garden
greenhouse
(a) An agricultural field is usually smaller than a greenhouse.
(b) There are trees in a garden and a greenhouse, but not in an
agricultural field.
agricultural field
_________
_________
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(c) Temperature is controlled in a garden and a field, but not in a
greenhouse.
(d) There is a variety of flowers in a garden and a greenhouse,
but not in an agricultural field.
_________
_________
C. Seminar
Organize a seminar in the class on “Importance of plants life on planet earth”.
D. Crossword Puzzle
Solve the crossword puzzle given alongside with the help of the clues given below:
Across
1
2
1. A plant parasite (7)
5. An organism deriving food from
3
another living organism (8)
4
5
6. Green pigment present in the
plant leaves (11)
8. Process of obtaining and
6 7
utilizing food (9)
9. Organism eating both
9
plants and animals (8) 8
10. Animal which eats plants (9)
10
11. Plant which can prepare its
own food (9)
12. The process by which green
11
plants prepare their food (14)
Down
2. Two different organisms that
live together and both benefit 12
from each other (9)
3. Animal which eats flesh (9)
4. Organism feeding on dead matter (10)
7. Organism which cannot prepare its own food (11)
Surf to Know More
Visit http://www.ncagr.gov/cyber/kidswrld/plant/nutrient.htm to learn about plant nutrients.
Know the Scientist
Joseph Priestley (1733–1804), an English scientist performed a series of
experiments and showed that impure air containing carbon dioxide gets
purified if kept in contact with green mint plants (because of oxygen released
by the plants). He discovered that oxygen is produced by green plants.
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Joseph Priestley