Questions: Plant Tissues and Primary and Secondary Growth

Question 1

A farmer hammers a nail into a young tree trunk 1 meter above the ground. Ten years later the tree is twice as tall. Where is the nail?

• A. About 2 meters above the ground
• B. About 1 meter above the ground
• C. Buried in the roots
• D. At the top of the tree

Answer: (B)

Growth in height happens only at the apical meristems at the tips of shoots. The trunk at 1 meter does not lengthen after it has formed. It only gets thicker by secondary growth, so the nail stays near 1 meter, although new wood may grow around it.

Question 2

The cells of xylem that conduct water, such as vessel elements, are alive when they are carrying water.

• T. True
• F. False

Answer: False

Tracheids and vessel elements die when they mature. Their cytoplasm is gone, leaving hollow tubes with strong lignified walls. In contrast, the sieve-tube elements of phloem are alive, although they lack a nucleus and depend on companion cells.

Question 3

Which tissue produces the wood that makes a tree trunk thicker each year?

• A. The apical meristem
• B. The epidermis
• C. The vascular cambium
• D. The root cap

Answer: (C)

The vascular cambium is a lateral meristem, a cylinder of dividing cells. It adds secondary xylem (wood) to its inside and secondary phloem to its outside. The apical meristem adds length, not width.

Question 4

Why do many temperate trees show visible annual rings?

Model answer: The vascular cambium makes wide, thin-walled xylem cells in spring when water is plentiful and narrower, thicker-walled cells later in the season. The contrast between late wood of one year and early wood of the next forms a visible ring for each growing season.

Rings record seasonal changes in cambium activity. Where growth is seasonal, counting rings estimates the age of the stem, and ring width reflects growing conditions in each year.