1. Section 3: Plant Growth and Development
Preview
Bellringer
Key Ideas
The Plant Embryo
Meristems
Primary Growth
Secondary Growth
Summary

2. Bellringer
Observe a cross-section of a tree trunk. How might the rings form? Why they are called “annual rings?”

3. Key Ideas What are the characteristics of a seed plant embryo?
How do meristems relate to plant growth?
What is the result of primary growth on a plant?
What is secondary growth, and what type of meristem is involved?

4. The Plant Embryo
As in animals, genes guide the development of plants, but the patterns of development in plants and animals are very different.
Plants continuously make new cells, which differentiate and replace or add to existing tissues.
A seed develops from an ovule and contains a plant embryo.

5. The Plant Embryo, continued
The plant embryo possesses an embryonic root and an embryonic shoot.
Leaflike structures called cotyledons, or seed leaves, are attached to the embryonic shoot.
In angiosperms (flowering plants), embryos have one or two cotyledons. Monocots have a single cotyledon, and dicots have two cotyledons.

6. The Plant Embryo

7. The Plant Embryo, continued
The process by which a plant embryo resumes its growth after a period of suspended animation, or dormancy, is called germination.
Seeds sprout in response to certain changes in the environment.
Changes such as rising temperature and increasing soil moisture usually signal the start of favorable growing conditions.
Some seeds must be exposed to cold, fire, or damage before they can sprout.

8. Seed Germination

9. Visual Concept: Germination of a Dicot

10. Visual Concept: Germination of a Monocot

11. Meristems
Plants grow by producing new cells in regions of active cell division called meristems.
Meristems are made up of undifferentiated cells that divide and can develop into specialized tissues.

12. Meristems, continued
Growth that increases the length or height of a plant is called primary growth.
The tissues that result from primary growth are primary tissues.
Growth that increases the width of stems and roots is called secondary growth.
The tissues that result from secondary growth are secondary tissues.

13. Visual Concept: Meristem

14. Primary Growth
Apical meristems, which are located at the tips of stems and roots, produce primary growth through cell division.
The new cells produced by apical meristems differentiate into the primary tissues of roots, stems, and leaves.
Primary growth makes a plant’s stems and roots get longer without becoming wider.
Each branch of a stem and each branch of a root has its own apical meristem that produces new primary tissues as the branch grows.

15. Visual Concept: Primary Growth in Plants

16. Secondary Growth
Some of the undifferentiated cells that are left behind as stems and roots lengthen and produce lateral meristems.
Lateral meristems are responsible for increases in the width of stems and roots. This increase is called secondary growth.
The two lateral meristems responsible for secondary growth are called the cork cambium and the vascular cambium.

17. Secondary Growth in Plants

18. Visual Concept: Secondary Growth in Plants

19. Summary
The plant embryo possesses an embryonic root and an embryonic shoot. Leaflike structures called cotyledons, or seed leaves, are attached to the embryonic shoot.
Plants grow by producing new cells in regions of active cell division called meristems.
Apical meristems are responsible for primary growth, which makes a plant’s stems and roots get longer without becoming wider.

20. Summary, continued
Lateral meristems are responsible for increases in the width of stems and roots. This increase is called secondary growth.