NCERT-Class 7-Science-Chapter-1-Nutrition in Plants

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How do plants prepare their food?

Plants prepare their food with the help of certain raw materials that they gather from their surroundings:

• Water, carbon dioxide, sunlight, minerals, chlorophyll

The process by which plants prepare their food by using these raw materials is called Photosynthesis.

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Photosynthesis :

(i) Photosynthesis is the process performed by the plants with the help of sunlight and chlorophyll by using water and nutrients from the soil and carbon dioxide from the air, in which own food is synthesized.

(ii) Chemical equations for photosynthesis.

Where is the food made in plants?

(i) Energy is transformed in process of photosynthesis. Light energy of sun is converted into chemical energy which is stored in the form of food.

(ii) Roots absorb water, minerals and salts from the soil. Stem transports these materials up to the leaves. Carbon dioxide from the air is taken inside from the stomata on the leaves.

(iii) In the leaves there are chloroplasts which contain chlorophyll, which absorbs sunlight, and helps in the conversion of carbon dioxide and water into food.

(iv) In the process of photosynthesis oxygen is given out.

(v) The green parts of the plants that have chlorophyll perform photosynthesis.

• Inhalation of Carbon Dioxide- There are tiny holes or pores present on the surface of the leaves called Stomata that take in the carbon dioxide present in the atmosphere.

• Presences of Chlorophyll in the Leaves- A substance called Chlorophyll is present in the leaves of the plants. It is a green colour pigment. The chlorophyll not only provides green colour to the leaves but also helps in the process of photosynthesis. Chlorophyll captures the sunlight and along with other raw materials prepares the food in the leaves.
• This process of photosynthesis only occurs in the daytime in the presence of Sunlight hence it is called Photosynthesis, photo means light.

Why sun is called the ultimate source of energy for all living organisms?

We know that the plants use solar energy to make their food. The herbivores animals depend upon the plants for their food. Animals (carnivores) that do not eat plants depend upon the herbivores animals. Therefore, all of the living organisms directly or indirectly receive their energy from the Sun.  [/responsivevoice]

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All living organisms are made up of tiny structures called cells. Some organisms (microscopic) contains only one cell while others plants and animals contain many cells of different kinds.

Parts of a cell:

• The Nucleus- Every cell has a nucleus present in the centre that performs various functions of the cell.
• The Cell Membrane- Every cell has an outer boundary which protects the cell called the Cell Membrane.
• The cytoplasm- Every cell has a gel-like structure present in it called the Cytoplasm.
• Cell organelles:These are membrane bound structures found within a cell in the cytoplasm. The cell organelles have special function associated with them. Different cell organelles found in the cell are:
  • Mitochondria – Produces energy for the cell
  • Endoplasmic Reticulum– Produces lipids and proteins in cell
  • Golgi apparatus– Helps in exporting materials out of cell
  • Lysosomes– Help in digestion in the cell

Can photosynthesis take place in other parts of the plant?

Yes, green stems and branches of the plants can also undergo the process of photosynthesis. For example, plants in the desert area like cactus do not have leaves but they still exist there because their stem produces the food for the plant.

Why is the process of photosynthesis important?

• There will be no food if the plants would stop conducting the photosynthesis process.
• The plants take in carbon dioxide and produce oxygen during the process of photosynthesis. Hence, without this process, it would not be possible to survive on earth as they would be no oxygen.

Production of Oxygen and Carbohydrates by the Plants

Plants use carbon dioxide and water in presence of the sunlight and chlorophyll to produce carbohydrates and oxygen. The carbohydrates thus produced by the plants are converted into starch.

Chloroplast and the Process of Photosynthesis

• Chloroplasts are special cell organelles that are found only in plant cells. They are called the food producers of the plant cells.
• The chloroplasts are surrounded by two membranes called the Inner and Outer Membrane. The inner membrane surrounds stroma and thylakoid
• The chlorophyll molecules are present on each of the thylakoids. The chloroplasts convert the sunlight into sugars that are used by the plant cells.
• Hence, chloroplasts allow the conduction of the process of photosynthesis. The chlorophyllthat can absorb the sunlight is present inside the chloroplasts.
• When the light of the sun hits the chloroplasts and the chlorophyll, the light energy is converted into chemical energy found in compounds such as ATP and NADPH.
• Then these energy molecules move into the stroma where carbon dioxide is attached to them. As a result of the molecular reactions, oxygen and glucose are created.

Can leaves which are red or Brown or violet in colour conduct photosynthesis?

Yes, the chlorophyll is also present in leaves that are not green in color. They are of different colours because the other colour pigments are more than the green colour pigments in such leaves.

Algae contain chlorophyll ?

Algae are green coloured organisms found in the stagnant water. They get their green color from chlorophyll. Since they have chlorophyll in them they are capable of conducting photosynthesis.

Algae

How do plants generate proteins and fats?

• Along with carbohydrates, plants can also produce proteins and fats which are formed with the help of Nitrogen.
• Nitrogen is present in large amounts in the air but plants cannot consume the nitrogen directly from the atmosphere.
• The soil often contains some bacteria that are capable of converting the nitrogen into nitrates which can be the used by the plants.
• Also, fertilizers used by farmers and gardeners contain a high amount of Nitrogen which mixes into the soil and is used by the plants. [/responsivevoice]

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Many plants do not contain any chlorophyll. Hence they are unable to prepare their food by themselves. Therefore, they rely on other plants and animals for their food.

1. Parasitic Plants- Some plants live on another plant for their nutrition. These are called parasites. The plants on which these parasitic plants survive are called the host. For Example, cuscuta is a parasitic plant.
2. Insectivorous Plants- Some plants depend upon insects for the food and thus are called Insectivorous. The leaves of these plants are modified into a pitcher like structure. The top part of the leaves acts as a lid which can open and close the pitcher. The pitcher contains hair in a downward direction which traps the insects. The pitcher on capturing the insect secretes some digestive juices which help in the digestion of the insect. For Example, Dischidia and Nepenthes
3. Saprotrophs- Some organisms survive on decaying food and organisms. This mode of nutrition is called saprotrophic nutrition and the organisms that survive because of the saprotrophic nutrition are called Saprophytes.

How do saprophytes obtain their nutrition?

• The saprophytes secrete digestive juices on the decaying and dead matter.
• These juices convert the matter into a solution.
• The saprophytes that absorb the nutrients from the solution.
• For Example, Fungi (yeast and mushrooms) are a saprophytes that can be found on stale food and pickles which are exposed to the hot and humid environment.

Symbiotic Relationship - Sometimes organisms live together to share shelter and food with each other. These are said to have a symbiotic relationship.

Examples of organisms living in a symbiotic relationship:

• Some fungi live in the roots of the trees. These fungi take food from the trees and in return help the trees in absorbing water and nutrients from the soil.
• Sometimes an organism that contains chlorophyll such as algae lives in association with a fungus (together called as Lichens). The algae provide food and nutrition to the fungus while the fungus provides water, minerals and shelter to the algae. [/responsivevoice]

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Replenishing the Soil with Nutrients

• Plants get their nutrients from the soil mainly hence there is a need to replenish the soil again with nutrients so that the plants can survive on it.
• Fertilizers and manure are often used to replenish the soil with the nutrients. They contain potassium, phosphorus and nitrogen all of which are important for the plants.
• A bacterium called Rhizobiumis present in the soil which can convert nitrogen present in it in the form that can be consumed by the plants.

The rhizobium generally lives in the roots of the plants such as peas, beans, grams and legumes and provides nitrogen to these plants. This again is an example of a symbiotic relationship. The farmers often do not need to use fertilizers while growing such crops. [/responsivevoice]

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Quick Revision

• Living organisms such as plants and animals survive on food.
• The food gives them the energy to perform several activities in their life and helps in the growth.
• All organisms take food and utilise it to get energy for the growth and maintenance of their bodies.
• Green plants synthesise their food themselves by the process of photosynthesis. They are autotrophs.
• Plants use simple chemical substances like carbon dioxide, water and minerals for the synthesis of food.
• Chlorophyll and sunlight are the essential requirements for photosynthesis.
• Complex chemical substances such as carbohydrates are the products of photosynthesis.
• Solar energy is stored in the form of food in the leaves with the help of chlorophyll.
• Oxygen is produced during photosynthesis.
• Oxygen released in photosynthesis is utilised by living organisms for their survival.
• Fungi derive nutrition from dead, decaying matter. They are saprotrophs.
• Plants like Cuscuta are parasites. They take food from the host plant.
• A few plants and all animals are dependent on others for their nutrition and are called heterotrophs. [/responsivevoice]