Chapter 1 — Nutrition in Plants

Autotrophic nutrition is the mode in which organisms make food themselves from simple substances — plants are autotrophs (auto = self; trophos = nourishment). Heterotrophic nutrition is when organisms take food prepared by plants or other animals — animals and most other organisms are heterotrophs.

Chlorophyll, sunlight, carbon dioxide, and water are all necessary to carry out the process of photosynthesis.

Stomata are tiny pores present on the surface of leaves through which carbon dioxide from air enters the leaf. They are surrounded by guard cells.

Photosynthesis produces carbohydrates — starch is a carbohydrate and its presence in leaves indicates photosynthesis has occurred. Oxygen is also released during the process.

Water and minerals absorbed by roots are transported to the leaves by vessels that run throughout the root, stem, branches, and leaves, forming a continuous path for nutrients to reach the leaf.

Cuscuta is a yellow wiry branched plant that has no chlorophyll and twines around the stem and branches of a host plant, taking readymade food from it. Because it deprives the host of valuable nutrients, it is called a parasite.

Saprotrophic nutrition is the mode in which organisms absorb nutrients from dead and decaying matter. Fungi such as mushrooms use this mode and are called saprotrophs.

Rhizobium is a bacterium that lives in the roots of leguminous plants like gram, peas, moong, and beans. It converts atmospheric nitrogen into a usable form for the plant. In return, the plant provides food and shelter to the bacteria — this is a symbiotic relationship.

Insectivorous plants trap and digest insects to obtain nutrients. The pitcher plant is an example — its pitcher is a modified part of the leaf with a lid; trapped insects are digested by digestive juices secreted in the pitcher and their nutrients are absorbed.

Yes. Photosynthesis also takes place in green stems and green branches. Desert plants have scale- or spine-like leaves to reduce water loss, and these plants carry out photosynthesis in their green stems.

Symbiosis is a relationship where organisms live together and share both shelter and nutrients. Two examples: (1) Rhizobium bacteria live in roots of leguminous plants, fixing nitrogen for the plant while the plant provides food and shelter; (2) In lichens, an alga and a fungus live together — the fungus provides shelter, water, and minerals, and the alga prepares food.

Solar energy is captured by chlorophyll in leaves and stored in the plant as food through photosynthesis. Almost all living organisms depend directly or indirectly on this food, making the sun the ultimate source of energy.

Red, brown, and other pigments are present in large amounts in these leaves and mask the green colour of chlorophyll, but chlorophyll is still present. Therefore, photosynthesis takes place in these leaves as well.

Plants cannot absorb nitrogen gas directly from air. Soil bacteria convert gaseous nitrogen into a usable form and release it into the soil, which plants absorb along with water. Farmers also add fertilisers rich in nitrogen, potassium, and phosphorous to the soil.

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