CBSE Notes Class 7 Science Chapter 1 Nutrition in Plants

All living organisms require food to grow, repair damaged parts of their bodies and get the energy to carry out life processes. Plants can make food themselves, but animals, including humans, cannot. Animals get ready-made food from plants or from animals that eat plants. Thus, humans and animals directly or indirectly depend on plants for food.

1.0Nutrition 

Nutrition is the process of taking and utilizing food. There are two modes of nutrition :  

• Autotrophic nutrition 
• Heterotrophic nutrition

Autotrophic Nutrition

Autotrophic nutrition : (auto-self; trophies - nourishment) 

• The mode of nutrition in which organisms make their food from simple inorganic substances is called autotrophic nutrition. 
• Therefore, green plants are called autotrophs. 
• Autotrophs prepare their food through the process of photosynthesis. 
• They are also known as producers, as they are the only source of producing food. 
• All the animals directly or indirectly depend upon plants for food.

Heterotrophic Nutrition

Heterotrophic Nutrition : (heteros-other; trophos-nourishment)

• The mode of nutrition in which organisms can not make their food is known as heterotrophic nutrition. 
• Organisms which obtain food from other organisms are called heterotrophs. 
• They obtain food from plants or animals, e.g., Animals, fungi and some bacteria.

2.0Photosynthesis

• Photosynthesis (photo-light; synthesis-to combine) is the process of synthesizing organic food (glucose) from inorganic carbon dioxide and water using solar energy captured by chlorophyll pigments. 
• During this process, oxygen is released. 
• The glucose thus formed is ultimately converted into starch, which is also a carbohydrate. 
• Photosynthesis takes place in the green parts (mostly in leaves ) of the plant because of the presence of chlorophyll pigments inside their cells. 
• Therefore, leaves are plants' food factories.

Requirements in Photosynthesis

Green plants require four things (sunlight, chlorophyll, carbon dioxide and water ) to prepare food.

• Sunlight: Sun is the natural source of sunlight, which provides solar energy to the plant. Solar energy is converted into chemical energy by plants through photosynthesis. Thus, the sun is the ultimate source of energy.
• Chlorophyll: Chlorophyll pigment is present in all the green parts of the plant in cell organelles and is called chloroplast. It traps solar energy from sunlight. Photosynthesis can not take place without chlorophyll.
• Carbon dioxide: Carbon dioxide is obtained from the atmosphere through stomata on plants' leaf surfaces. 
• Water: Water and minerals in the soil are absorbed by the roots and transported to the leaves by the vessels that run like pipes throughout the root, the stem, the branches, and the leaves. 

Role of the Leaf in Photosynthesis

Stomata 

• The tiny pores on the surface of the leaves surrounded by two kidney-shaped guard cells are called stomata. 
• Guard cells regulate the opening and closing of stomata. 
• These kidney-shaped cells cover a single stoma and also contain chloroplasts. 

Functions of stomata 

• Exchange of gasses takes place (carbon dioxide from air is taken in and oxygen is released) through stomata. 
• Transpiration takes place through stomata. 

Synthesis of food other than carbohydrates

• Soil has certain bacteria that convert gaseous nitrogen into a usable form and release it into the soil. The plants, along with water, absorb these soluble forms. 
• Farmers are adding fertilizers rich in nitrogen to the soil. In this way, the plants and other constituents fulfil their nitrogen requirements.

3.0Other Modes of Nutrition in Plants

Some plants lack chlorophyll, so they cannot synthesize their own food. Like humans and animals, these plants depend on the food produced by other plants. They follow a heterotrophic mode of nutrition. 

1. Saprotrophic Nutrition

• The mode of nutrition in which organisms take in nutrients in solution form from dead & decaying matter is called saprotrophic nutrition. Plants which use such a mode of nutrition are called saprotrophs. 
• These plants are usually whitish. They have no green leaves; often, they even have no leaves at all.

Examples of fungi are:

• Mushrooms are fluffy umbrella-like patches growing on rotting wood during the rainy season. 
• Bread molds are cotton-like threads spread on the bread.

2. Parasitic

• Certain plants lack chlorophyll pigments (without which photosynthesis cannot take place) and are thus parasites on other plants. 
• These plants obtain the food prepared by other organisms. Examples are Cuscuta (Dodder), Rafflesia, etc.

3. Symbiotic Relationship

• Mutually beneficial association in which two organisms live together and share shelter and nutrients. 
• This is called a symbiotic relationship—for example, Mycorrhiza and lichen.

4. Insectivorous or carnivorous plants

• Insectivorous plants are autotrophic but obtain nitrogen from insects. 
• They generally grow in soil that is deficient in nitrogen, such as Nepenthes or Pitcher plants. Venus flytrap, Sundew etc.