This question asks you to name every type of glycosidic bond present in cellulose and then in starch, so both parts of the polysaccharide's structure need checking separately.
- $\beta$-1,4 and $\alpha$-1,4 glycosidic bonds only: This gets the main chain bonds right for both polymers but leaves out the branch points of starch, so it is not the complete list.
- $\beta$-1,4 and $\alpha$-1,4, $\alpha$-1,6 glycosidic bonds: This is closer, but grouping the bonds this way blurs how many distinct bond types apply to starch's branch points compared to option (4), which lists all three separately.
- $\beta$-1,6 and $\alpha$-1,4, $\alpha$-1,6 glycosidic bonds: Cellulose's glucose units are joined end to end by $\beta$-1,4 bonds, not $\beta$-1,6, so labelling cellulose with a 1,6 linkage is wrong from the start.
- $\beta$-1,4, $\alpha$-1,4 and $\alpha$-1,6 glycosidic bonds: Cellulose is a straight chain of glucose units linked only by $\beta$-1,4 bonds. Starch is a mixture of amylose, linked by $\alpha$-1,4 bonds, and amylopectin, which uses $\alpha$-1,4 bonds along its chains plus $\alpha$-1,6 bonds at every branch point. Listing all three bond types together covers both polysaccharides completely.
Since cellulose needs only $\beta$-1,4 bonds and starch needs both $\alpha$-1,4 and $\alpha$-1,6 bonds to account for its branching, all three bond types together give the full and correct answer.
Let's summarize:
- Cellulose: unbranched chain, $\beta$-1,4 bonds only.
- Amylose (in starch): unbranched chain, $\alpha$-1,4 bonds.
- Amylopectin (in starch): branched, $\alpha$-1,4 bonds plus $\alpha$-1,6 bonds at branch points.
So the complete set of bonds is $\beta$-1,4, $\alpha$-1,4 and $\alpha$-1,6 glycosidic bonds.