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Plant Growth

Plant Growth. AP Biology Unit 5. Plant Growth. Plant growth occurs at specific tissues called meristems Apical Meristem Lateral Meristems. Plant Growth. Plants can go through two different types of growth Primary Growth- growth in length Secondary Growth- growth in width.

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Plant Growth

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  1. Plant Growth AP Biology Unit 5

  2. Plant Growth • Plant growth occurs at specific tissues called meristems • Apical Meristem • Lateral Meristems

  3. Plant Growth • Plants can go through two different types of growth • Primary Growth- growth in length • Secondary Growth- growth in width

  4. Primary Growth- in Roots • In roots, primary growth occurs in 3 different zones • Zone of Cell Division (contains root apical meristem) • Zone of Elongation • Zone of Maturation

  5. Zone of Cell Division • Lots of mitosis occurring in the cells here • Contains the newest cells (newly divided)

  6. Zone of Elongation • Cells get longer to push the root tip into the soil • Cells start developing their specialized functions

  7. Zone of Maturation • Cells become fully specialized • Considered mature cells

  8. Root Cap • Root cap protects the root apical meristem as root pushes through the soil • Like a helmet for the root cells

  9. Primary Growth- Stems • Growth occurs at the shoot apical meristems • Shoot apical meristems are located at the tips of buds • Plants grow from the top, not the bottom of the stem

  10. Secondary Growth • Growth in width of stems and roots • Degree of secondary growth varies– some plants barely have any, others have extensive secondary growth. • Results in the formation of wood and bark • Results from activity in the lateral meristems • Vascular Cambium • Cork Cambium

  11. Vascular Cambium • Divides into • Secondary Xylem • On the side closer to the center of the stem/root • Secondary Phloem • On the side closer to the outside of the stem/root • As the vascular cambium divides, it continues to push older cells farther away.

  12. Cork Cambium • As the secondary phloem grows, it breaks the outer layer of the stems and root (epidermis) • Secondary phloem on the very outside becomes cork cambium • Cork cambium grows into cork • Cork cells contain suberin to protect from water loss, physical damage and harmful substances.

  13. Question… • Where is the oldest part of a tree? • The very center – oldest xylem that has been pushed all the way in • Outer layers keep flaking off

  14. Types of wood • Heartwood • Older secondary xylem • Cells get clogged  stop conducting water • Darker in color • Sapwood • Newer secondary xylem • Still actively conducting water (and minerals) • Lighter in color

  15. Annual Rings in Wood • The age of a tree can be determined by looking at the number of rings that it has. • Wood = secondary xylem • What forms the rings? • Spring: water most available, water transport cells are large and have thin walls • Summer: less water available, water transport cells have thicker walls and are darker

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