1. BOTANY Chapter 6 OBJECTIVES
Understand the 3 main parts of a vascular plant
Understand the external organization of stems
Understand the internal organization of stems
Identify modifications to stems, roots and leaves
Distinguish between Dicots and Monocots

2. BACKGROUND Land plants evolved from algae washed onto shore
Mutations for upright growth gave selective advantage
Upright growth requires specialized tissues!
Stems—support, storage, vegetative reproduction, transport
Leaves—photosynthesis, sexual reproduction
Roots—water/nutrient absorption, anchoring

3. Non-vascular Plants (mosses) Vascular Plants
All Plants
Non-vascular Plants (mosses)
Vascular Plants
Non-seed producers (ferns)
Seed Producers
Non-protected seeds (gymnosperms)
Protected seeds (angiosperms)
Monocots
Dicots

4. Divisions of Plants

5. ANGIOSPERMS (Flowering Plants)
Largest group of plants
Very Successful—most plants we know
Evolved ~100 m.y.a. (relatively recently) (toward the end of the dinosaurs)

6. 2 groups of Angiosperms Monocots Dicots One seed leaf
Parallel leaf veins (Grass-like leaves)
Vascular bundles scattered throughout stem
Flower parts in groups of 3
Dicots
Two seed leaves
Network of leaf veins (Broad leaves)
Vascular bundles arranged in a circle around the stem
Flower parts in groups of 5 (or 4)

8. Plant Bodies Primary Plant Body Secondary Plant Body
Derived from apical meristem
Composed of primary tissues
Constitutes the herbaceous (fleshy) parts of plants
Herbaceous plants are only a primary body
Secondary Plant Body
Derived from other meristem
Composed of secondary tissue: wood and bark
Constitutes the woody part of a plant
Woody plants have primary body at root and shoot tips

11. External Organization
Nodes—area where leaves are attached
Leaf axils just above node
Leaf axils have axillary buds—a dormant apical meristem w/ young leaves.
Leaf buds are covered by bud scales that protect the buds
Axillary buds may grow to form branches.
The end of the stem has a terminal bud that is responsible for (new) growth.
Leaves can be arranged alternate, opposite, (or whorled).
A leaf always begins where there is a bud. (Sometimes it doesn’t look like it)

12. External Organization (cont’d)
Internodes—area of the stem between nodes
Internodes may be long (vines) or short (onions)
Length and number of internodes can indicate conditions during growing season.
Monocots vs. Dicots:
Dicots often have petiole (the leaf stem)
Gets the leaf away from stem
Prevents self-shading
Monocots often have sheathing leaf base
Provides support for stem
Provides protection to stem

13. Cell Types 3 main types of cells in plants
Parenchyma
Collenchyma
Schlerenchyma
Cell type use depends on what it is used for: “form follows function”
Remember! Energy is the currency of the natural world. Plants are limited in what they can do by the amount of energy they can obtain.

14. Cell Types (cont’d) Parenchyma Thin primary walls.
Cells are typically alive at maturity and active metabolically.
The most common type of cell (and tissue) in soft plant parts.
Functions include:
photosynthesis (sunlight can get in)
nectar and fragrance secretions (odors can get out)
resin and oil production
nutrient transport (phloem)
Any tissue where thin walls are advantageous will be made from parenchyma due to the small amount of energy spent in making these cells.

15. Cell Types (cont’d) Collenchyma
Primary walls are thin in some areas, thick in others. (usually at the corners)
Primary walls exhibit “plasticity”, i.e., the walls can stretch with pressure and retain the new shape.
Works in conjunction with turgid parenchyma for support in elongating shoot tips. (like a tire and air pressure)
Located under the epidermis or next to vascular bundles
Found in shoot tips where both strength and flexibility are needed.
The amount of energy needed to produce these cells is more than that for parenchyma cells.

16. Cell Types (cont’d) Sclerenchyma
Primary wall and a thick secondary wall
Secondary walls are “elastic”, i.e., they can bend but return to their original shape.
NOT good for tissue that is growing, but good for mature tissue that needs strength and some flexibility, e.g., limbs or twigs.
Also good for conducting water (xylem)
These cells require the most energy to produce!

17. Modifications to leaves & stems
Tendrils—modified leaves or lateral braches that can wrap around an object to provide support. (Vines)
Stolons—elongated internodes (runners) that can propagate vegetatively (asexually).
Bulbs—short shoot with thick fleshy leaves (onion, garlic)
Rhizomes—fleshy, horizontal, underground stem used for vegetative propagation
Tubers—horizontal rhizomes used for storing nutrients (potato)

18. Internal Organization
Primary Tissues—make up all primary plant body
Epidermis—outermost surface
Prevents water loss—cuticle
Protects against disease
Allows for the exchange of gas/water—stoma
Stoma controlled by guard cells
Cortex
Consists of cells between vascular bundles
May secrete resins, latex, etc.
Vascular Tissue
Xylem—water and nutrients from root to leaves
Phloem—sugars and food from leaves to roots
Xylem and Phloem together are Vascular Bundles

19. Internal Organization (cont’d)
Monocots vs. Dicots
Monocots
Vascular bundles scattered through stem
No pith
Dicots
Vascular bundles in ring just under epidermis
Has pith

20. (x.s.)