In what form excess of glucose is stored in human body?

Correct — B, Glycogen. When blood glucose rises after a meal, insulin drives the liver and skeletal muscle to link the surplus glucose molecules into glycogen, a highly branched polymer of glucose. The liver holds roughly 100 grams of it and releases glucose back into the blood between meals; muscle holds around 400 grams but keeps it for its own contraction. Because glycogen is branched, enzymes can attack many ends at once and mobilise glucose quickly, which is what a working muscle needs. Longer-term surplus beyond the glycogen stores is converted to fat.

• (a)Fructose — Fructose is a single sugar, not a storage form. The liver does convert dietary fructose, but into glucose, glycogen or fat; nothing is stored as fructose.
• (c)Glucose — Glucose itself circulates in the blood at a tightly held concentration and is not stockpiled as free glucose. Storing it in that form would raise the osmotic pressure of the cell sharply, which is precisely why a polymer is used instead.
• (d)Starch — Starch is the plant storage polysaccharide, made in plastids and stored in seeds and tubers. Animals have no enzyme system for making it, though they digest it readily.

Both starch and glycogen are polymers of glucose, and both solve the same problem: storing a large number of glucose units without raising the cell's osmotic pressure. They differ in branching. Starch is a mixture of largely unbranched amylose and moderately branched amylopectin, and is found in plants. Glycogen is much more heavily branched, with a branch point roughly every ten residues, and is found in animals and in fungi. The extra branching gives more free ends and therefore faster mobilisation.

The trap is the option 'glucose', which reads as if the body simply keeps a pool of the sugar. It does not, and the reason is worth carrying: a polymer of a thousand glucose units exerts one thousandth of the osmotic effect of a thousand free molecules, so polymerising is how a cell stores energy without drawing in water. The paired fact examiners test alongside this is that starch is the plant version and glycogen the animal one, sometimes phrased as animal starch.

• Surplus glucose is stored in animals as glycogen, chiefly in liver and skeletal muscle.
• Liver glycogen is released back into the blood; muscle glycogen is used only by that muscle.
• Glycogen is a branched polymer of glucose, with branch points roughly every tenth residue.
• Starch is the equivalent storage polysaccharide in plants and is far less branched.
• Storing glucose as a polymer avoids the osmotic load that free glucose would impose.

• Answering 'glucose' and missing that storage requires a polymer.
• Swapping starch and glycogen between plants and animals.
• Treating fructose as a storage sugar because it is found in fruit.

A single-word recall item with the trap sitting in plain sight — the substance being stored is offered as one of the options.

• practice — not a real PYQ

  Glycogen in the human body is stored mainly in

  • (a)liver and skeletal muscle
  • (b)brain and kidney
  • (c)blood plasma
  • (d)bone marrow

  Answer(a) liver and skeletal muscle — the liver's store supplies the blood, the muscle's supplies itself.

• practice — not a real PYQ

  The chief storage carbohydrate of plants is

  • (a)glycogen
  • (b)cellulose
  • (c)starch
  • (d)chitin

  Answer(c) starch — cellulose and chitin are structural, not storage, polysaccharides.