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Carbohydrates are stored in plants mainly in the form of:
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Answer: Option D — Starch
Detailed Solution
Plants make their food through photosynthesis, in which carbon dioxide and water are combined using light energy captured by chlorophyll to form glucose, a simple sugar, and oxygen. Glucose is used by the plant for energy and to build other substances. The excess glucose is converted into starch for storage.
Starch is a complex carbohydrate (a polysaccharide) made up of long chains of glucose units joined together. It is the main storage form of carbohydrates in plants. Starch is suitable for storage because:
It is insoluble in water, so it does not affect the water balance of cells.
It is compact, so a large amount of energy can be stored in a small space.
It can be easily broken down into glucose when the plant needs energy, for example at night, during germination or for growth.
Starch is made of two kinds of molecules: amylose, which has straight chains, and amylopectin, which has branched chains. It is stored in organelles called amyloplasts and in chloroplasts.
Plants store starch in various organs, such as:
- Seeds and grains: rice, wheat, maize and pulses.
- Tubers: potatoes (stem tubers) and sweet potatoes (root tubers).
- Roots and rhizomes: cassava (tapioca) and ginger.
- Fruits: bananas.
The presence of starch can be tested using iodine solution, which turns blue-black when it reacts with starch. This test is used in school experiments to show that photosynthesis has taken place in a leaf.
In humans, starch is an important source of energy in the diet. Digestion of starch begins in the mouth with salivary amylase and is completed in the small intestine, where it is broken down into glucose.
Animals and fungi store carbohydrates in a different form, called glycogen, which is mainly found in the liver and muscles. Glycogen is more highly branched than starch and is sometimes called "animal starch".
Why not the other options?
- ✗Glycogen is the storage carbohydrate of animals and fungi.
- ✗Cellulose is a structural carbohydrate that forms plant cell walls.
- ✗Glucose is the product of photosynthesis, but it is not the storage form.
Quick tip
Remember: Plants store carbohydrates as starch (test: iodine turns blue-black); animals store glycogen (liver and muscles); cellulose = plant cell walls; all three are polymers of glucose.
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Plant Physiology & Nutrition in Plants — Preparation
This question tests your understanding of Plant Physiology & Nutrition in Plants, a key topic in the General Knowledge section. The detailed solution above uses a step-by-step approach to show the reasoning, and where available, a shortcut that helps you solve similar questions in under 90 seconds during the actual exam.
This topic covers how plants live and grow: photosynthesis, transpiration, respiration in plants, the transport of water and food through xylem and phloem, plant hormones, modes of nutrition in plants, and plant tissues. Questions usually ask what is needed for photosynthesis and what it produces, where it takes place (in the chloroplasts), which tissue carries water (xylem) and which carries food (phloem), and what each plant hormone does, such as auxins for growth and ethylene for fruit ripening. Insectivorous plants such as the pitcher plant are also commonly tested. Practise the plant physiology questions below, written in the style of the general awareness sections of exams such as SSC, banking, railways, CUET GAT, MAH CET and CLAT. Each question comes with a detailed explanation that adds related facts, so every question helps you revise more than one point.