Primary growth makes a plant longer, and secondary growth makes it wider. To compare them well, use the same criteria on both sides.
This lesson follows relating plant tissues to function in the plant organisation and growth chapter.
How do the two kinds of growth differ?
Put the comparison in a table and fill both columns for every row.
| Criterion | Primary growth | Secondary growth |
|---|---|---|
| What increases | Length of shoot and root | Width (girth) of stem and root |
| Meristem involved | Apical meristem | Lateral meristems: vascular cambium and cork cambium |
| Where it happens | Tips of shoots and roots | Along the sides of stems and roots |
| Plants that show it | All plants during growth | Woody dicotyledons, such as trees |
| Result | Plant reaches higher and deeper | Trunk thickens with more xylem (wood) and phloem |
Worked example: a comparison question
Question: compare primary growth and secondary growth in a tree. [4 marks]
A full answer pairs each point with its partner:
- Primary growth increases the length of the plant, but secondary growth increases its girth.
- Primary growth is caused by the apical meristem, but secondary growth is caused by the vascular cambium and cork cambium.
- Primary growth happens at the tips of the shoot and root, but secondary growth happens along the stem and root.
- Primary growth occurs in all plants, but secondary growth occurs mainly in woody dicotyledons.
Each point has a partner on both sides, joined by “but”. This shows that the two processes are being compared, not just described.
The mistake that costs marks
The common slip is to describe only one side, for example “secondary growth makes the trunk wider because the cambium divides”. That answer is true, but it gives no statement about primary growth, so the comparison mark is lost.
| One-sided | Comparison | |
|---|---|---|
| Wording | Secondary growth increases width | Primary growth increases length, but secondary growth increases width |
| Result | Only half the comparison | Full comparison |
Another slip is to say that secondary growth happens “only when the tree is old”. The better reason is the active meristem: secondary growth depends on the cambium being active, not on the age in years.
Check yourself
A gardener ties a coloured tape around a tree trunk 1 m above the ground. Ten years later, the tape is still 1 m above the ground, but the trunk is thicker. Explain both observations.
Answer
The tape has not moved upward because primary growth only adds length at the shoot tip. The trunk below the tip does not lengthen, so the tape stays at 1 m.
The trunk is thicker because of secondary growth. The vascular cambium divides and adds new xylem and phloem, which increases the girth of the trunk.
What to study next
The next lesson, interpreting meristem activity, shows where new cells are made. After that, test the chapter with the practice set.
Record any comparison you wrote one-sidedly in the mistake log and paper-error review. If you want a teacher to mark your comparison answers, see online one-to-one Biology tuition.