Which biomolecule acts as the primary energy storage in animals?

Correct — A. Glycogen is a multibranched polysaccharide of glucose that serves as the energy store of animals, as well as of fungi and bacteria.

In humans it is made and stored mainly in the liver and skeletal muscle. Liver glycogen is broken back down to glucose to keep blood sugar steady between meals. That is option (a).

Why the others are wrong

• (b)
  Starch — Starch is the storage carbohydrate of plants. Glycogen is its animal counterpart, similar to the amylopectin part of starch but more heavily branched.
• (c)
  Cellulose — Cellulose is a structural polysaccharide of plant cell walls, not an energy store. Humans cannot digest it, which is why it passes through the gut as dietary fibre.
• (d)
  Sucrose — Sucrose is a disaccharide, one glucose joined to one fructose. It is the table sugar that plants such as sugarcane make, not a storage polymer in animals.

Cells store glucose by linking thousands of units into a polysaccharide. One large molecule packs the fuel away without drawing water into the cell the way thousands of free glucose molecules would.

Plants make starch for storage and cellulose for structure. Animals make glycogen, a more branched chain whose many ends can be broken down quickly when glucose is needed.

Key facts

• Glycogen is stored mainly in the liver and skeletal muscle.
• Starch is the plant storage polysaccharide and glycogen is its animal analogue.
• Cellulose is a structural polysaccharide of plant cell walls.
• Sucrose is a disaccharide of glucose and fructose.

Common traps

• Picking starch because it is the storage carbohydrate you learn first, when starch is the plant store.
• Confusing glycogen with glucagon, the pancreatic hormone that triggers glycogen breakdown.

No directly related past PYQ was found.