Chapter 28, Problem 1TYK

What important role does lignin play in vascular plants?

a. It is the major component of the cuticle, which prevents plants from drying out.

b. It forms the outer layer of pollen grains.

c. It forms the tough, rigid cell walls of water-conducting cells.

d. It nourishes the embryo in seed plants.

Summary Introduction

Introduction:

The lignin is the polymer made of the monomers of monolignol. The polymers of the lignin are filled in the voids in the cell walls. The xylem is the tissue, which performs the function of the conduction of the water and dissolved minerals in the plant.

Answer to Problem 1TYK

Correct answer:

It makes rigid and tough cell walls of water-conducting cells.

Explanation of Solution

Explanation/justification for the correct answer:

Option (c) is given as forming of rigid and tough cells walls for water-conducting cells. The lignin is present in the xylem tissues. The hemicellulose is linked with the lignin by the covalent bonding to provide the strength to the vascular cell wall, which further provides strength to the vascular plants. Therefore, the lignin forms the rigid and tough cell walls of the vascular cells. Hence, the Option (c) is correct.

Explanation for incorrect answer:

Option (a) is given as a major component of the cuticle, which plays a role in preventing drying out of a plant. The plant organs, such as leaves and young shoots are covered with the thin layer of a waxy substance called the cuticle. The cuticle is composed of the cutin, which is hydrophobic in nature. The cutin is present instead of lignin in the cuticle. So, it is a wrong answer.

Option (b) is given as forming the outer layer of pollen grains. The outer layer of the pollen grain is called exine. The exine is made up of the substance sporopollenin. The sporopollenin is the chemically inert substance found in the pollen grain. The lignin is not present in the outer layer of the pollen grains. So, it is a wrong answer.

Option (d) is given as nourishment of embryo in the seed plants. The embryo is the developing tissue inside the seed of the plant. The embryo requires the nutrients for the further development. The necessary nutrients are provided by the endosperm. The main constituent of the endosperm is the starch. The endosperm surrounds the developing embryo. Therefore, the lignin does not provide the nourishment to the embryo cells.

Hence, the options (a), (b), and (d) are incorrect.

Conclusion

Lignin is responsible for providing strength to the plant by forming the tough and rigid cell wall. The cuticle is present on the surface of leaves and shoots that prevent drying out of a plant. Exine forms the outer layer of pollen grains and endosperm provide nourishment to the developing embryo.