Which of the given statements is incorrect about glycogen?

We start by recalling the structural facts about glycogen. Glycogen is the main reserve carbohydrate of animals, especially abundant in liver and muscles. It is a polysaccharide composed entirely of glucose units. In the backbone each glucose residue is joined to the next through $$\alpha(1\rightarrow4)$$ glycosidic bonds, and at the branch points every $$8\text{-}12$$ residues a glucose is attached through an $$\alpha(1\rightarrow6)$$ linkage. Thus the molecule is highly branched.

Now we examine each option and compare it with these established facts.

Option A states, “It is present in animal cells.” We have just noted that glycogen is the principal reserve carbohydrate of animals, so this statement is true.

Option B says, “It is a straight chain polymer similar to amylose.” A straight chain polymer would possess only the $$\alpha(1\rightarrow4)$$ linkages and no branches. However, glycogen is characterized by frequent $$\alpha(1\rightarrow6)$$ branch points, making it a highly branched polymer, more so than amylopectin and certainly not straight like amylose. Therefore this statement conflicts with the known structure of glycogen.

Option C claims, “It is present in some yeast and fungi.” Besides animals, certain microorganisms such as yeast and fungi also store glycogen. Hence this statement is correct.

Option D asserts, “Only α-linkages are present in the molecule.” In glycogen the linkages are $$\alpha(1\rightarrow4)$$ and $$\alpha(1\rightarrow6)$$, both of which are indeed α-type linkages, with no β-linkages involved. So the statement is true.

From this detailed comparison we see that the sole statement contradictory to the true nature of glycogen is Option B.

Hence, the correct answer is Option B.