Question

Algae have cell walls made up of
($1$) Cellulose, hemicellulose and pectins
($2$) Cellulose, galactans and mannans
($3$) Hemicellulose, pectins and proteins
($4$) Pectin, cellulose and proteins

Answer 1

Algae is a large and diverse group of eukaryotic, photosynthetic life forms. They are polyphyletic organisms i.e.; they do not have a common ancestor. Many of the algae are single celled with no cell wall. While some of them have a prominent cell wall. The cell wall is mainly cellulosic and also made up of glycoproteins in some algae. However, the cell wall lacks long and fibrillary carbohydrates. The cell wall protects the cell and gives them a rigid structure.

Complete answer:
Option ($1$) Cellulose, hemicellulose and pectins: The cell wall of algae is mostly cellulosic. It is also made up of hemicellulose, pectin, mucilage, alginic acid, fucin, fucoidan, calcium carbonate, silica etc. They are all present as different combinations in different groups of algae. This option is correct.
Option ($1$) is correct.
Option ($2$) Cellulose, galactans and mannans: The algal cell wall mostly contains cellulose. Only some algae contain galactans and mannans in their cell walls. Hence, this option is irrelevant.
Option ($2$) is incorrect
Option ($3$) Hemicellulose, pectins and proteins: It is already known that the algae cell wall contains hemicellulose and pectins; however proteins are mostly absent.
Option ($3$) is incorrect.
Option ($4$) Pectin, cellulose and proteins: It is already known that the algae cell wall contains pectins and cellulose however proteins are mostly absent.
Option ($4$) is incorrect.

So, Option ($1$) Cellulose, hemicellulose and pectins is the correct answer.

Note:
Some algae also contain polysaccharides like galactans and mannans in their cell wall. Red algae contain galactans while marine green algae contain mannans in the cell wall. This option however was not chosen as the correct answer because the majority of the algae have cell walls made up with cellulose, hemicellulose and pectin only. If option ($1$) is absent we can go with option ($2$).