Nutrition in Plants
Food is essential for all
living organisms and carbohydrates, proteins, fats, vitamins, and minerals are
components of food. These components of food are called nutrients and
are necessary for our body.
All living organisms
require food. Plants can synthesize food for themselves, but animals, including
humans, cannot. They get it from plants or animals that eat plants. Thus,
humans and animals are directly or indirectly dependent on plants.
Mode of Nutrition in
Plants
Plants are the only
organisms that can prepare food for themselves by using water, carbon dioxide,
and minerals. The raw materials are present in their surroundings.
The nutrients enable
living organisms to build their bodies, to grow, to repair damaged parts of
their bodies, and provide the energy to carry out life processes.
Nutrition is
the mode of taking food by an organism and its utilisation by the body. The
mode of nutrition in which organisms make food themselves from simple
substances is called autotrophic nutrition. Therefore, plants
are called autotrophs
(
auto=self; trophos=nourishment)
Animals and most other organisms take in food
prepared by plants. They are called heterotrophs (heteros=other).
Photosynthesis — Food
Making Process in Plants
Leaves are the food
factories of plants. Therefore, all the raw materials must reach the leaf.
Water and minerals present in the soil are absorbed by the roots and
transported to the leaves. Carbon dioxide from the air is taken in through the
tiny pores present on the surface of leaves. These pores are surrounded by
‘guard cells’. Such pores are called stomata.
Water and minerals are
transported to the leaves by the vessels which run like pipes throughout the
root, the stem, the branches, and the leaves. They form a continuous path or
passage for the nutrients to reach the leaf. They are called vessels.
The leaves have a green pigment called chlorophyll. It helps leaves to capture the energy of the sunlight. This energy is used to synthesise (prepare) food from carbon dioxide and water. Since the synthesis of food occurs in the presence of sunlight, it is called photosynthesis (Photo: light; synthesis : to combine).
So we find that chlorophyll, sunlight, carbon
dioxide, and water are necessary to carry out the process of photosynthesis. It
is a unique process on the earth. The solar energy is captured by the leaves
and stored in the plant in the form of food. Thus, the sun is the
ultimate source of energy for all living organisms.
In the absence of
photosynthesis, there would not be any food. The survival of almost all living
organisms directly or indirectly depends upon the food made by the plants.
Besides, oxygen, which is essential for the survival of all organisms, is
produced during photosynthesis. In the absence of photosynthesis, life would be
impossible on the earth.
During photosynthesis,
chlorophyll-containing cells of leaves in the presence of sunlight, use carbon
dioxide and water to synthesise carbohydrates. The process can be represented
in an equation:
Carbon dioxide + water sunlight →chlorophyl Carbohydrate + oxygen
Besides leaves,
photosynthesis also takes place in other green parts of the plant — in green
stems and green branches. The desert plants have scale- or spine-like leaves to
reduce the loss of water by transpiration. These plants have green stems which
carry out photosynthesis.
Synthesis of Plant Food
Other Than Carbohydrates
Plants synthesize
carbohydrates through the process of photosynthesis. The carbohydrates are made
of carbon, hydrogen, and oxygen. These are used to synthesise other components
of food such as proteins and fats. But proteins are nitrogenous substances which
contain nitrogen.
Nitrogen is present in
abundance in gaseous form in the air. However, plants cannot absorb nitrogen in
this form. Soil has certain bacteria that convert gaseous nitrogen into a
usable form and release it into the soil. These are absorbed by the plants along
with water. Also, you might have seen farmers adding fertilisers rich in
nitrogen to the soil. In this way, the plants fulfil their requirements of
nitrogen along with the other constituents. Plants can then synthesise proteins
and vitamins.
Other Modes of Nutrition
in Plants
There are some plants which do not have chlorophyll. They cannot synthesise food. How do they survive and from where do they derive nutrition? Like humans and animals, such plants depend on the food produced by other plants. They use the heterotrophic mode of nutrition.
Do you see a yellow wiry branched
structure twining around the stem and branches of a tree? This is a plant
called Cuscuta (Amarbel). It does not have chlorophyll. It
takes readymade food from the plant on which it is climbing. The plant on which
it climbs is called the host. Since it deprives the host of
valuable nutrients, Cuscuta is called the parasite.
There are a few plants
which can trap insects and digest them. Such plants may be green or of some
other colour. The pitcher-like or jug-like structure is the modified part of
the leaf. The apex of the leaf forms a lid which can open and close the mouth
of the pitcher. Inside the pitcher, there are hair which are directed
downwards. When an insect lands in the pitcher, the lid closes and the trapped
insect gets entangled into the hair. The lid closes and the insect is trapped.
The insect is digested by the digestive juices secreted in the pitcher, and its
nutrients are absorbed. Such insect-eating plants are called insectivorous
plants.
Saprotrophs
You might have seen
packets of mushrooms sold in the vegetable market. You may have also seen
fluffy umbrella-like patches growing in moist soils or on rotting wood during
the rainy season. Let us find out what type of nutrients they need
to survive and from where they get them.
These organisms are
called fungi. They have a different mode of nutrition. They absorb
the nutrients from the bread. This mode of nutrition in which organisms take in
nutrients from dead and decaying matter is called saprotrophic
nutrition. Such organisms with saprotrophic mode of nutrition are
called saprotrophs.
Fungi also grow on
pickles, leather, clothes, and other articles that are left in hot and humid
weather for a long time. During the rainy season, they spoil many things. Ask
your parents about the menace of fungi in your house.
The fungal spores are
generally present in the air. When they land on wet and warm things, they
germinate and grow.
How Nutrients are
Replenished in the Soil
Have you seen farmers
spreading manure or fertilisers in the fields, or gardeners using them in lawns
or in pots? Do you know why this is done?
You learnt that plants
absorb minerals and nutrients from the soil. So, their amounts in the soil keep
on declining. Fertilisers and manures contain nutrients such as nitrogen,
potassium, phosphorous, etc. These nutrients need to be added from time to time
to enrich the soil. We can grow plants and keep them healthy if we can fulfil
the nutrient requirement of plants.
Usually, crop plants
absorb a lot of nitrogen, and the soil becomes deficient in nitrogen. You
learnt that though nitrogen gas is available in plenty in the air, plants
cannot use it in the manner they can use carbon dioxide. They need nitrogen in
a soluble form. The bacterium called Rhizobium can take
atmospheric nitrogen and convert it into a usable form. But Rhizobium cannot
make its own food. So it often lives in the roots of gram, peas, moong,
beans, and other legumes and provides them with nitrogen. In return, the plants
provide food and shelter to the bacteria. They, thus, have a symbiotic
relationship. This association is of great significance for the farmers. They
can reduce the use of nitrogenous fertiliser where leguminous plants are grown.
Most of the pulses (dals) are obtained from leguminous plants.
In this chapter, you
learnt that most of the plants are autotrophs. Only a few plants are parasitic
or saprotrophic. They derive nutrition from other organisms. All animals are
categorised as heterotrophs since they depend on plants and other animals for
food. Can we say that the insectivorous plants are partial heterotrophs?
What You Have Learnt
- All organisms need food and utilise
it to get energy for growth and maintenance of their body.
- Green plants synthesise food for
themselves by the process of photosynthesis. They are autotrophs.
- Plants like Cuscuta are
parasites. They take food from the host plant.
- Plants use simple chemical substances
like carbon dioxide, water, and minerals for the synthesis of food.
- Chlorophyll, water, carbon dioxide,
and sunlight are the essential requirements for photosynthesis.
- Complex chemical substances such as
carbohydrates are the products of photosynthesis.
- Solar energy is absorbed by the
chlorophylls present in leaves/plants.
- Oxygen is produced during
photosynthesis.
- Oxygen released in photosynthesis is
utilised by living organisms for their survival.
- Many fungi derive nutrition from dead
and decaying matter. They are saprotrophs.
- A few plants and all animals are dependent on others for their nutrition and are called heterotrophs.
Exercise
1. Why
do organisms take food?
2. Distinguish
between a parasite and a saprotroph.
3. How
would you test the presence of starch in leaves?
4. Give
a brief description of the process of synthesis of food in green plants.
5. Fill
in the blanks:
(a)
Green plants are called ______ since they synthesise their own food.
(b) The food synthesised by plants is stored as ______.
(c) In photosynthesis, solar energy is absorbed by the pigment called ______.
(d) During photosynthesis, plants take in ______ and release ______ gas.
6. Name
the following:
(i) A parasitic plant
with yellow, slender, and branched stem.
(ii) A plant that is partially autotrophic.
(iii) The pores through which leaves exchange gases.
7.
Tick the correct answer:
(a) Cuscuta is an example of:
(i) autotroph (ii) parasite (iii) saprotroph (iv) host
(b) The plant which traps and feeds on insects is:
(i) Cuscuta (ii) china rose (iv) pitcher plant (iv) rose
8. Match
the items given in Column I with those in Column II:
|
Column I |
Column II |
|
Chlorophyll |
Rhizobium |
|
Nitrogen |
Heterotrophs |
|
Cuscuta |
Pitcher plant |
|
Animals |
Leaf |
|
Insects |
Parasite |
Did you know?
Light is so important to
plants that their leaves grow in many patterns so as to absorb maximum
sunlight.
MCQs with Answers and Explanations
1. Which of the following are considered nutrients?
A)
Water and oxygen
B)
Carbohydrates, proteins, fats, vitamins, and minerals
C)
Glucose and starch only
D)
Carbon dioxide and sunlight
Answer: B
Explanation: Nutrients are components of food essential for the
body. Carbohydrates, proteins, fats, vitamins, and minerals are considered
nutrients.
2. What is the primary source of food for all living organisms?
A)
Animals
B)
Soil
C)
Water
D)
Plants
Answer: D
Explanation: Plants can prepare their own food and serve as the
base of the food chain. Humans and animals depend on plants directly or
indirectly.
3. Which mode of nutrition is used by plants?
A)
Heterotrophic
B)
Parasitic
C)
Autotrophic
D)
Saprotrophic
Answer: C
Explanation: Plants use autotrophic nutrition, making food from
simple substances like water and carbon dioxide.
4. What is autotrophic nutrition?
A)
Organisms obtain food by digesting other organisms
B)
Organisms prepare their own food from simple substances
C)
Organisms absorb nutrients from decaying matter
D)
Organisms live inside others and obtain food
Answer: B
Explanation: Autotrophic nutrition refers to the mode of
nutrition where organisms synthesize their own food using basic raw materials.
5. What does the term "autotroph" mean?
A)
One who depends on others for food
B)
One who synthesizes food from light
C)
Self-nourishing organism
D)
One who eats only plants
Answer: C
Explanation: “Auto” means self and “trophos” means nourishment,
so autotrophs are self-nourishing organisms.
6. Why are animals called heterotrophs?
A)
They produce their own food
B)
They depend on plants or other animals for food
C)
They absorb sunlight directly
D)
They can grow without nutrients
Answer: B
Explanation: “Hetero” means other. Animals rely on food prepared
by plants or plant-eating animals, hence they are heterotrophs.
7. Which of the following is not a function of nutrients?
A)
Provide energy
B)
Help in growth
C)
Help in digestion
D)
Repair damaged body parts
Answer: C
Explanation: Nutrients help in body-building, growth, energy
production, and repair of body parts. Digestion is a process, not a function of
nutrients themselves.
8. What raw materials do plants use to synthesize their food?
A)
Oxygen, minerals, and glucose
B)
Water, carbon dioxide, and minerals
C)
Water, oxygen, and sunlight
D)
Glucose, starch, and vitamins
Answer: B
Explanation: Plants use water, carbon dioxide, and minerals as
raw materials to synthesize food.
9. What is nutrition?
A)
Process of cooking food
B)
Process of synthesizing food by the sun
C)
Mode of taking food and its utilisation in the body
D)
Process of excretion
Answer: C
Explanation: Nutrition is the process by which organisms intake
food and utilize it for bodily functions.
10. Which organisms form the basis of food for heterotrophs?
A)
Fungi
B)
Animals
C)
Plants
D)
Bacteria
Answer: C
Explanation: Plants prepare food via photosynthesis and form the
base of the food chain for heterotrophs.
11. What are the tiny pores on the surface of leaves called?
A)
Vessels
B)
Stomata
C)
Chloroplasts
D)
Nodes
Answer: B
Explanation: Tiny pores on leaves that take in carbon dioxide
from the air are called stomata, surrounded by guard cells.
12. Which of the following is NOT required for photosynthesis?
A)
Sunlight
B)
Carbon dioxide
C)
Oxygen
D)
Water
Answer: C
Explanation: Oxygen is a by-product of photosynthesis, not a
requirement for the process.
13. What helps the leaf capture sunlight for photosynthesis?
A)
Stomata
B)
Guard cells
C)
Chlorophyll
D)
Xylem
Answer: C
Explanation: Chlorophyll, a green pigment in leaves, captures
sunlight needed for photosynthesis.
14. How are water and minerals transported to the leaves?
A)
Through stomata
B)
Through chlorophyll
C)
Through vessels
D)
Through guard cells
Answer: C
Explanation: Vessels act like pipes, carrying water and minerals
from roots to leaves.
15. Which part of the plant is called the ‘food factory’?
A)
Roots
B)
Stem
C)
Leaves
D)
Flowers
Answer: C
Explanation: Leaves are called the food factories because
photosynthesis takes place in them.
16. What is the ultimate source of energy for all living
organisms?
A)
Oxygen
B)
Soil
C)
Sun
D)
Water
Answer: C
Explanation: The sun is the ultimate source of energy, as solar
energy drives photosynthesis.
17. Which of the following is a product of photosynthesis?
A)
Carbon dioxide
B)
Carbohydrate
C)
Water
D)
Chlorophyll
Answer: B
Explanation: Carbohydrate (glucose) and oxygen are the main
products of photosynthesis.
18. What is the role of guard cells in photosynthesis?
A)
Transport nutrients
B)
Synthesize chlorophyll
C)
Control the opening and closing of stomata
D)
Absorb sunlight
Answer: C
Explanation: Guard cells regulate the opening and closing of
stomata to allow gas exchange.
19. Which desert plant part performs photosynthesis?
A)
Spines
B)
Roots
C)
Flowers
D)
Green stems
Answer: D
Explanation: In desert plants, green stems carry out
photosynthesis as leaves are modified into spines.
20. What will happen in the absence of photosynthesis?
A)
More oxygen will be produced
B)
All life forms will flourish
C)
Life on Earth would be impossible
D)
Water will be abundant
Answer: C
Explanation: Photosynthesis is essential for producing both food
and oxygen. Without it, life would not survive.
21. Which of the following correctly represents the
photosynthesis equation?
A)
Oxygen + water → carbohydrate +
carbon dioxide
B)
Carbon dioxide + water → carbohydrate +
oxygen
C)
Carbohydrate + oxygen → carbon dioxide +
water
D)
Sunlight + oxygen → carbohydrate +
water
Answer: B
Explanation: The correct photosynthesis equation is:
Carbon dioxide + water → (sunlight +
chlorophyll) → carbohydrate + oxygen
22. In which plant parts besides leaves does photosynthesis
occur?
A)
Flowers and fruits
B)
Roots and bark
C)
Green stems and green branches
D)
Spines and thorns
Answer: C
Explanation: Green stems and green branches also contain
chlorophyll and perform photosynthesis.
23. Why can plants not use atmospheric nitrogen directly?
A)
It is too cold
B)
It is not in usable form
C)
It dissolves in water quickly
D)
It contains carbon
Answer: B
Explanation: Although nitrogen is abundant in the atmosphere,
plants cannot use it directly because it is in gaseous form and must be
converted into a usable form by soil bacteria.
24. Which component of food requires nitrogen for its synthesis?
A)
Carbohydrates
B)
Fats
C)
Proteins
D)
Vitamins
Answer: C
Explanation: Proteins are nitrogen-containing nutrients; hence,
plants need nitrogen to synthesize proteins.
25. What is the role of bacteria in soil in plant nutrition?
A)
They absorb sunlight
B)
They decompose plants
C)
They convert nitrogen into a usable form
D)
They provide oxygen to roots
Answer: C
Explanation: Certain soil bacteria convert gaseous nitrogen into
usable compounds that plants can absorb.
26. Which plant lacks chlorophyll and survives by depending on
other plants?
A)
Rose
B)
Mushroom
C)
Cuscuta
D)
Algae
Answer: C
Explanation: Cuscuta (Amarbel) lacks chlorophyll and is a
parasite, drawing nutrition from its host plant.
27. What is the host in a parasitic relationship?
A)
Organism that traps insects
B)
Plant that absorbs sunlight
C)
Plant that provides food to a parasite
D)
Insect-eating plant
Answer: C
Explanation: In a parasitic relationship, the host is the plant
that is climbed upon and exploited for nutrients by the parasite.
28. Which of the following is a parasitic plant?
A)
Cuscuta
B)
Mushroom
C)
Venus flytrap
D)
Neem
Answer: A
Explanation: Cuscuta is a parasitic plant that obtains food from
a host plant.
29. What is the function of the lid in a pitcher plant?
A)
To collect water
B)
To trap insects inside
C)
To photosynthesize
D)
To absorb nitrogen
Answer: B
Explanation: The lid in a pitcher plant closes the pitcher once
an insect enters, trapping it for digestion.
30. What kind of nutrition do insectivorous plants exhibit?
A)
Autotrophic only
B)
Heterotrophic only
C)
Both autotrophic and heterotrophic
D)
Saprotrophic
Answer: C
Explanation: Insectivorous plants are green (autotrophic) but
also trap insects (heterotrophic) to meet nitrogen needs.
31. The nutrition in fungi is called:
A)
Heterotrophic
B)
Autotrophic
C)
Parasitic
D)
Saprotrophic
Answer: D
Explanation: Fungi use saprotrophic nutrition, absorbing
nutrients from dead and decaying matter.
32. What enables fungi to spread rapidly in damp conditions?
A)
Their roots grow fast
B)
Spores present in the air
C)
They have leaves
D)
They move towards food
Answer: B
Explanation: Fungal spores, which are present in the air,
germinate rapidly on warm and wet surfaces.
33. Which of the following is an example of a saprotroph?
A)
Cuscuta
B)
Mushroom
C)
Venus flytrap
D)
Mango
Answer: B
Explanation: Mushrooms are fungi that absorb nutrients from dead
matter, making them saprotrophs.
34. What allows fungi to grow on pickles, clothes, and leather?
A)
Acidic conditions
B)
Salty environment
C)
Hot and humid weather
D)
Sunlight and air
Answer: C
Explanation: Hot and humid weather promotes fungal growth on
organic materials like pickles, clothes, and leather.
35. Why do farmers add manure or fertilisers to the soil?
A)
To protect plants from pests
B)
To kill weeds
C)
To enrich the soil with nutrients
D)
To make soil dry
Answer: C
Explanation: Manure and fertilisers are added to replenish
nutrients like nitrogen, phosphorus, and potassium that are absorbed by plants
from the soil.
36. Which nutrient is commonly depleted from the soil by crop
plants?
A)
Carbon
B)
Oxygen
C)
Nitrogen
D)
Calcium
Answer: C
Explanation: Nitrogen is the most commonly depleted nutrient
because crop plants absorb large amounts of it for growth.
37. Which gas is abundant in the air but unusable directly by
plants?
A)
Oxygen
B)
Nitrogen
C)
Carbon dioxide
D)
Hydrogen
Answer: B
Explanation: Although nitrogen gas is abundant in the air,
plants cannot use it directly; it must be converted to a soluble form.
38. What is the role of the bacterium Rhizobium in plant
nutrition?
A)
It decomposes dead plants
B)
It traps sunlight for photosynthesis
C)
It converts atmospheric nitrogen into usable form
D)
It absorbs minerals from the soil
Answer: C
Explanation: Rhizobium helps plants by fixing nitrogen from the
atmosphere into a form that plants can use.
39. Rhizobium bacteria live in the roots of which type of
plants?
A)
Ferns
B)
Leguminous plants
C)
Trees
D)
Grasses
Answer: B
Explanation: Leguminous plants such as peas, beans, and moong
have root nodules where Rhizobium bacteria live symbiotically.
40. What type of relationship exists between Rhizobium and
leguminous plants?
A)
Parasitic
B)
Competitive
C)
Symbiotic
D)
Saprotrophic
Answer: C
Explanation: The relationship is symbiotic because both
Rhizobium and the plant benefit — the bacteria get food and shelter, and the
plant gets usable nitrogen.
41. Which of the following is NOT true about Rhizobium bacteria?
A)
They fix atmospheric nitrogen
B)
They make their own food through photosynthesis
C)
They live in leguminous plant roots
D)
They help reduce the use of fertilisers
Answer: B
Explanation: Rhizobium cannot photosynthesise; they depend on
host plants for food.
42. Why is the Rhizobium-legume relationship beneficial for
farmers?
A)
It increases the water content in soil
B)
It eliminates pests
C)
It reduces the need for nitrogen fertilisers
D)
It improves photosynthesis
Answer: C
Explanation: Since Rhizobium fixes nitrogen naturally, farmers
don’t need to use as much nitrogen-based fertiliser.
43. From which type of plants are most pulses (dals) obtained?
A)
Parasitic plants
B)
Insectivorous plants
C)
Leguminous plants
D)
Carnivorous plants
Answer: C
Explanation: Most pulses (like moong, gram, peas) are obtained
from leguminous plants.
44. Insectivorous plants can be considered as:
A)
Complete autotrophs
B)
Complete heterotrophs
C)
Partial heterotrophs
D)
Saprotrophs
Answer: C
Explanation: Though insectivorous plants can photosynthesise,
they depend on insects for additional nutrients (like nitrogen), making them
partial heterotrophs.
45. What do all organisms require food for?
A)
Reproduction
B)
Energy for growth and maintenance
C)
Producing oxygen
D)
Photosynthesis
Answer: B
Explanation: Food provides energy for the growth and maintenance
of body functions.
46. Green plants are called autotrophs because they:
A)
Absorb oxygen from air
B)
Depend on animals for food
C)
Make their own food
D)
Trap insects for nutrients
Answer: C
Explanation: Autotrophs are organisms that can synthesise their
own food, like green plants via photosynthesis.
47. Which of the following is a parasitic plant?
A)
Mushroom
B)
Cuscuta
C)
Rose
D)
Pitcher plant
Answer: B
Explanation: Cuscuta lacks chlorophyll and depends on other
plants (hosts) for food, making it parasitic.
48. Which of these is NOT a raw material for photosynthesis?
A)
Water
B)
Chlorophyll
C)
Oxygen
D)
Carbon dioxide
Answer: C
Explanation: Oxygen is a by-product, not a raw material in
photosynthesis.
49. What is the role of chlorophyll in photosynthesis?
A)
Absorbs minerals from soil
B)
Reflects sunlight
C)
Absorbs solar energy
D)
Combines water and CO₂
Answer: C
Explanation: Chlorophyll absorbs solar energy, which is
essential for the photosynthesis process.
50. What is the main product of photosynthesis?
A)
Water
B)
Protein
C)
Carbohydrates
D)
Fat
Answer: C
Explanation: Photosynthesis produces carbohydrates, a complex
chemical used for energy storage.
51. During photosynthesis, the gas released is:
A)
Carbon dioxide
B)
Oxygen
C)
Nitrogen
D)
Hydrogen
Answer: B
Explanation: Oxygen is released as a by-product during the
process of photosynthesis.
52. Why is the oxygen released during photosynthesis important?
A)
It cools the plant
B)
It forms sugars
C)
It is needed by all living organisms to survive
D)
It helps in water absorption
Answer: C
Explanation: The oxygen produced is used in respiration by most
living organisms.
53. What is the mode of nutrition in fungi like mushrooms?
A)
Autotrophic
B)
Parasitic
C)
Saprotrophic
D)
Symbiotic
Answer: C
Explanation: Fungi feed on dead and decaying matter, which is a
saprotrophic mode of nutrition.
54. Organisms that depend on others for food are called:
A)
Autotrophs
B)
Heterotrophs
C)
Saprotrophs
D)
Chemotrophs
Answer: B
Explanation: Heterotrophs are organisms (like animals and some
plants) that depend on others for food.
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