13: What is wood?

Question 1

What is secondary xylem and its origin?

Answer 1

Secondary xylem is woody tissue formed from the vascular cambium.

It develops to the inside of the cambium in dicots and conifers, increasing stem diameter.

Question 2

Name two structural differences between dicot and conifer wood.

Answer 2

Dicot wood has both vessel elements and tracheids (more efficient water transport);

conifer wood mainly has tracheids and resin canals.

Question 3

What is bark, its origin, and function?

Answer 3

Bark originates from the cork cambium (phellogen) and protects against physical damage, pathogens, and water loss.

Question 4

What makes up a plant cell wall?

Answer 4

Cellulose microfibrils form the structure; middle lamella (rich in pectin) glues cells together. Some develop a secondary wall between the primary wall and plasma membrane.

Question 5

List and describe three main types of wood.

Answer 5

Dicot wood: Secondary xylem from vascular cambium.

Monocot wood: Lacks true wood (no vascular cambium).

Conifer wood: Mostly tracheids, often with resin canals.

Question 6

Describe the layers of the secondary cell wall (S1, S2, S3).

Answer 6

S1 & S3: Thin with transversely oriented microfibrils.

S2: Thickest layer, longitudinal microfibrils.

Question 7

What are resin canals and their function?

Answer 7

Hollow tubes in conifers lined with epithelial cells that secrete resin for defense and wound healing.

Question 8

Sapwood vs Heartwood – differences?

Answer 8

Sapwood: Outer, active in transport.

Heartwood: Inner, non-functional, for structural support (contains lignin, tannins).

Question 9

What are lenticels and what do they do?

Answer 9

Small, spongy pores in bark for gas exchange; found on woody stems and roots.