These notes are focused on definitions, facts, processes, examples and likely exam points.
1. Nutrition
Nutrition is the process by which living organisms obtain food and use it for energy, growth, repair and other life activities.
Food contains:
Carbohydrates
Proteins
Fats
Vitamins
Minerals
Roughage
Water
Main types of nutrition
There are two major modes of nutrition:
Autotrophic nutrition
Heterotrophic nutrition.
2. Autotrophic Nutrition
Autotrophs are organisms that can prepare their own food from simple inorganic substances.
Examples
Green plants
Algae
Green plants are also called producers because they produce their own food.
Requirements for autotrophic nutrition
Carbon dioxide (CO₂)
Water (H₂O)
Sunlight
Chlorophyll
3. Photosynthesis
Photosynthesis is the process by which green plants prepare food from carbon dioxide and water in the presence of sunlight and chlorophyll.
Word equation
Carbon dioxide + Water → Glucose + Oxygen
In the presence of sunlight and chlorophyll.
Chemical equation
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂
Important points
Photosynthesis mainly occurs in the leaves.
Chlorophyll absorbs light energy.
Carbon dioxide enters the leaf through stomata.
Water is absorbed from the soil through the roots.
Oxygen is released into the atmosphere.
Glucose is produced as food.
Excess glucose may be stored as starch.
4. Role of Leaves in Photosynthesis
Leaves are the main organs of photosynthesis because they contain chlorophyll.
Stomata
Stomata are tiny pores, generally present on the lower surface of leaves.
Functions:
Allow carbon dioxide to enter.
Allow oxygen to leave.
Help in exchange of gases.
Also participate in water-vapour loss through transpiration.
5. Requirements for Photosynthesis
Requirement |Source/Role
Carbon dioxide|Obtained from atmosphere
Water|Absorbed from soil by roots
Sunlight|Provides energy
Chlorophyll|Absorbs light energy
Easy memory trick: C-W-S-C
Carbon dioxide + Water + Sunlight + Chlorophyll
6. Factors Affecting Photosynthesis
The rate of photosynthesis is affected by several factors.
Light intensity: Increasing light intensity generally increases the rate of photosynthesis up to a certain limit.
Carbon dioxide: Availability of carbon dioxide affects the rate of photosynthesis.
Water: Adequate water is necessary for photosynthesis.
Temperature: Temperature affects the reactions involved in photosynthesis.
Nature of light: Different wavelengths of light are not equally effective in photosynthesis. Blue and red regions of visible light are particularly effective.
8. Heterotrophic Nutrition
Heterotrophs are organisms that cannot prepare their own food and depend on other organisms for food.
Examples:
Humans
Animals
Fungi
Many non-green plants
Types of heterotrophic nutrition
Herbivorous nutrition
Carnivorous nutrition
Omnivorous nutrition
Saprophytic nutrition
Parasitic nutrition
Insectivorous nutrition
Symbiotic nutrition
9. Herbivores
Herbivores are animals that mainly eat plants or plant products.
Examples
Cow
Goat
Deer
Elephant
Camel
Exam point: Herbivores are also called plant eaters.
10. Carnivores
Carnivores are animals that mainly eat other animals.
Examples
Lion
Tiger
Jackal
Hawk
Snake
Frog
Exam point: Carnivores are also called meat eaters.
11. Omnivores
Omnivores eat both plant and animal food.
Examples
Humans
Crow
Dog
Ant
Sparrow
Mynah
Memory:
Omni = all → Omnivores eat both plant and animal food.
12. Saprophytic Nutrition
Saprophytes obtain food from dead and decaying organic matter.
Examples
Mushrooms
Bread mould
Some bacteria
Some fungi
How do saprophytes obtain food?
They secrete digestive juices onto dead organic matter. The organic matter is broken down into soluble substances, which are then absorbed.
Key point:
Saprophytes play an important role in decomposition.
13. Parasitic Nutrition
A parasite obtains food from the body of another living organism called the host.
Examples
Cuscuta
Mistletoe
Certain fungi
Some bacteria
Host
The organism from which a parasite obtains food is called the host.
Cuscuta
Cuscuta is a well-known parasitic plant. It depends on a host plant for nutrition.
14. Insectivorous Nutrition
Some green plants prepare their own food through photosynthesis but obtain nitrogenous nutrients from insects.
This mode of nutrition is called insectivorous nutrition.
Examples
Pitcher plant
Sundew
Bladderwort
Why do these plants catch insects?
They generally grow in soils that are poor in nitrogen.
Important ADRE point
Insectivorous plants do not depend on insects for carbohydrates. They obtain mainly nitrogenous nutrients from them.
15. Symbiotic Nutrition
Symbiosis is a relationship in which two different organisms live together and mutually benefit each other.
Example: Lichen
Lichen consists of:
Alga
Fungus
Role of alga
The alga prepares food by photosynthesis.
Role of fungus
The fungus provides shelter and helps supply water and minerals.
Thus, both organisms benefit.
16. Nitrogen and Plant Nutrition
Plants require nitrogen mainly for making proteins and supporting growth.
Plants obtain nitrogen mainly in the form of soluble nitrogen compounds from the soil.
Nitrogen sources
Manure
Fertilizers
Crop rotation
Nitrogen-fixing bacteria
17. Rhizobium and Nitrogen Fixation
Rhizobium is a nitrogen-fixing bacterium associated with the root nodules of leguminous plants.
Examples of leguminous plants
Gram
Pea
Moong
Beans
Rhizobium converts atmospheric nitrogen into forms that can ultimately be used by plants.
Important correction for exams
Rhizobium does not make its own food. It lives in association with leguminous plants and helps them obtain usable nitrogen.
18. Replenishment of Soil Nutrients
Soil nutrients can be replenished by:
Using manure
Using fertilizers
Crop rotation
Crop rotation
Growing a cereal crop alternately with a leguminous crop helps improve soil nitrogen.
Example: Cereal crop → Leguminous crop → Cereal crop
19. Synthesis of Other Food Substances
Plants first produce carbohydrates through photosynthesis.
Plants can then use these products to synthesize:
Proteins
Fats
Other organic substances
Proteins
Proteins contain elements such as:
Nitrogen
Phosphorus
Sulphur
Plants obtain nitrogen mainly from nitrogen-containing salts in the soil.
20. Quick Revision Table
Term
Meaning
Example
Autotroph
Makes its own food
Green plants
Heterotroph
Depends on others for food
Humans
Producer
Organism that prepares its own food
Green plant
Herbivore
Eats plants
Cow
Carnivore
Eats animals
Lion
Omnivore
Eats plants and animals
Human
Saprophyte
Feeds on dead organic matter
Mushroom
Parasite
Gets food from a living host
Cuscuta
Insectivorous plant
Gets nitrogenous nutrients from insects
Pitcher plant
Symbiosis
Two organisms mutually benefit
Lichen
Rhizobium
Nitrogen-fixing bacterium
Root nodules of legumes
Stomata
Tiny pores in leaves
Leaf surface
Chlorophyll
Green pigment involved in photosynthesis
Green leaves
⭐ ADRE Most Important One-Liners
Green plants are called producers.
Autotrophs prepare their own food.
Photosynthesis occurs mainly in green leaves.
Chlorophyll absorbs light energy.
Carbon dioxide enters leaves through stomata.
Roots absorb water and minerals from the soil.
Oxygen is released during photosynthesis.
Glucose is the primary food produced during photosynthesis.
Excess glucose can be stored as starch.
Herbivores eat plants.
Carnivores eat animals.
Omnivores eat both plants and animals.
Saprophytes obtain food from dead and decaying matter.
Parasites obtain food from living hosts.
Cuscuta is a parasitic plant.
Pitcher plant is an insectivorous plant.
Insectivorous plants obtain nitrogenous nutrients from insects.
Lichen is an example of symbiosis.
Lichen consists of an alga and a fungus.
Rhizobium is associated with root nodules of leguminous plants.
Gram, pea, moong and beans are leguminous plants.
Crop rotation helps replenish soil nutrients.
Sunlight is necessary for photosynthesis.
Chlorophyll is necessary for photosynthesis.
Nitrogen is essential for protein synthesis in plants.
🎯 ADRE Exam Focus
For ADRE preparation, give special attention to:
Photosynthesis → Stomata → Chlorophyll → Modes of nutrition → Herbivores/Carnivores/Omnivores → Saprophytes → Parasites → Insectivorous plants → Symbiosis → Lichen → Rhizobium → Nitrogen fixation → Crop rotation.
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