Plant Structure and Growth

1. Plant Structure and Growth Ch. 35

2. Plant Tissues • Plants have three types of tissue: • Dermal Tissue • Vascular Tissue • Ground Tissue • Each tissue has a different function

4. Dermal Tissue • Covers the plant, acts as protection • Made of endodermis, epidermis, guard cells, root hairs, and cuticle. • Vascular Tissue • Transports water and nutrients throughout the plant • Made of xylem and phloem • Xylem: Carries water and minerals and is made of two type of cells:

5. Tracheids: long, skinny cells that overlap and are tapered at the ends. • Water goes from one cell to the next through areas with no secondary wall called pits • The secondary walls of the tracheids are hardened with lignin, making tracheids useful for support as well as transport • Vessel Elements: Usually wider, shorter, thinner walls and less tapered than tracheids • Linked together end to end, while water flows from cell to cell through perforated end walls • Water can also move laterally to neighbor cells through pits

7. Phloem: Carries sugars from the leaves to the rest of the plant using active transport. Consists of: • Sieve tube members: end walls contain sieve plates that allow the flow of fluid from one cell to the next. • Unlike xylem, phloem cells are alive at maturity even though they don’t have nuclei, ribosomes, or vacuoles. • Every sieve tube member has at least one companion cell which has a full set of cell organelles, so it can nurture the sieve tube member

9. Ground Tissue • Most common type of tissue in a plant. • Main function is support • Ground tissue consists of three types of cells: • Parenchyma • Look like traditional plant cells • Primary cell wall is thin and flexible • No secondary wall • One large vacuole • Carries out most metabolic functions • When turgid with water give support and shape to plant • Ability to divide and differentiate into other cell types when a plant has been injured

10. Collenchyma • Unevenly thickened primary cell walls • No secondary cell walls • Mature collenchymal cells are alive • Function is to support the growing stem • Sclerenchyma • Very thick primary & secondary cell walls that are fortified with lignin • Function is to support the plant • Two forms: • Fibers: long, thing, fibrous, occur in bundles • Sclerids: short, irregular shape

12. Plant Organs • Plants have three basic organs: • Roots • Stems • Leaves • Roots • Absorbs nutrients from soil • Anchors the plant • Stores Food

13. Root surfaces are covered by epidermis which is modified for absorption • Root hairs: Skinny extensions from the epidermal cells that extend out and increase surface area • Cortex: parenchymal cells that contain plastids for storage of starch and other materials • Stele: Vascular cylinder of the root made of xylem and phloem covered by a layer of pericycle which gives rise to lateral roots • Endoderm: Tightly packed layer of cells surrounding the stele. Selects what minerals enter the stele and the body of the plant

15. Types of roots: • Taproot: single, large root that gives rise to lateral roots called branch roots • Taproot is the primary root in many dicots and some go deep in soil for water • Fibrous Root System: Common in monocots and hold plant firmly in place • Adventitious Roots: Rise above ground and help support the plant

16. Stems • Vascular tissue called vascular bundles run through stems • Vascular bundles have xylem facing outward and phloem facing inward, with meristem tissue between the two. • Monocots have vascular bundles scattered throughout the stem • Dicots have vascular bundles formed in a ring on the edge of the stem • Ground tissue of the stem is made of parenchymal tissues modified for storage called cortex and pith

18. Leaves • Designed to maximize sugar production and limit water loss • Epidermis is covered with waxy material called cutin to minimize water loss • Guard cells: control opening of stomates • Inner section of leaves are made of palisade and spongy mesophyll cells used for photosynthesis • Vascular bundles (also called veins) located in the mesophyll carry water and nutrients from the soil to the leaves • Vascular bundles can also carry sugar from leaves to other parts of the plant

20. Plant Growth • Meristems: embryonic tissue that continually divides, creating new cells • Plant growth is based on meristems • Primary Growth: Elongation of the plant down into soil and up into the air • Apical Meristems are responsible for primary growth and are located at tips of roots and in buds of shoots • Secondary Growth: Increase in girth • Lateral Meristems are responsible for secondary growth

22. Growth in length is concentrated at the root’s tip • There are three zones: • Zone of Cell Division • Meristem cells that are actively dividing • Produce new cells that extend down into soil • Zone of Elongation • Cells elongate • Push root cap down into soil • Zone of Maturation • Cells undergo specialization • Root Cap: Protects root tip by secreting substance that helps digest earth so the root tip can grow into soil