Biology 10, Las Positas College
Plants
Chapters 25 & 26, Starr, 6th ed

I-Introduction
II-Organization & Tissues of Vascular Plants

A. 4 Tissue Types
B. Organs-Roots & Shoots
C. Movement of water & dissolved substances in vascular plants

I-Introduction-Plants are multicellular, eukaryotic, photosynthetic autotrophs

Have chlorophyll.
Some have gone back to living in water after evolving on land.
Most are vascular, ie have specialized tissues to transport fluids. 20% nonvascular.

Differ from Protista which are unicellular, multicellular, or colonial, water-living, have no true roots, stems, leaves, vascular system.

II-Organization & Tissues of Vascular Plants
Vascular plants are those having a system of tissues that transports water and nutrients.
Made up of underground roots and above ground shoots.

A. 4 tissue types. Tissue = a group of cells that work together to perform a specialized function.

1. Meristem-undifferentiated tissue -> Growth

Produces new plant cells during growth. One cell divides, one remains as meristem, capable of repeated cell division. Other differentiates into one of three kinds of plant tissue, becoming part of the plant body.
If meristem at tip of plant -> longer roots or taller plant, -> primary growth.
If in cylinder along length of stems and branches = lateral meristem, -> thicker stem and branch -& secondary growth.

2. Dermal tissue-differentiated tissue -> Protection

Outer protective covering of virtually all plants.
Acts as plant's skin and protects it from water loss and injury.
Often covered by waxy layer.

3. Vascular tissue-differentiated tissue -> Fluid Movement

Conducts water, inorganic nutrients and carbohydrates throughout the plant.
Xylem conducts water and dissolved inorganic nutrients-up Phloem conducts carbohydrates and other needed substances throughout plant-down.

Xylem-cells conduct water and dissolved inorganic nutrients only after they die and lose their cytoplasm-become hollow and thick walled. Stacked end to end, form pipelines. Have cell wall or perforations through which water moves. Joined laterally through pores.

Phloem-conducting cells (sieve-tube members) are alive, have pits that allow easy passage of sugar-filled water. Companion cells secrete substances into and remove substances from the sieve-tube members.

4. Ground tissue-differentiated tissue -> Storage

Stores the carbohydrates (usually starch) the plant produces or helps support & strengthen the ground tissue.
Forms the substance of the plant and is the tissue in which vascular tissue is embedded.
Contains large vacuoles and may also have chloroplasts.
Form the mass of leaves, stems and roots.

B. Organs-Roots and Shoots

(Organ = grouped tissues that form a structural & functional unit.)

1. Roots-anchor plants in soil and absorb H2O and inorganic nutrients.

Roots have areas of xylem and phloem
Root hairs -> larger absorption area
Roots have storage cells, meristem at root tip.
Root cap covers and protects the root's apical meristem as it grows through the soil.

2. Shoots-above ground, also have apical meristem

a. stems-support leaves, conduct water and inorganic nutrients from roots to all plant parts, bring products of photosynthesis to where they are needed or stored.
Xylem and phloem next to each other (vascular bundles).

Monocots - vascular bundles scattered throughout the stem.
Usually have parallel veins in leaves. Flower parts in 3's.

Eudicots - vascular bundles arranged around the outside of the stem.
Netlike veins in leaves (ivy). Flowering parts in 4's or 5's.

Monocot vs eudicot determined by placement of stored food in seed.

Eudicot stems and gymnosperms (pine trees) with woody stems have lateral meristems called cambia.

Between rings of phloem and xylem.
As cambial cells divide, one of resulting daughter cell remains as a cambial cell and other differentiates into either a xylem or phloem cell.
Cambium cells divide, -> xylem towards center, phloem towards outside. Xylem dies, remains as annual rings. Phloem gets crushed by dividing cambium. New phloem grows just under epidermis.
Other lateral meristem tissue -> bark.

b. leaves-outgrowth of shoot apex, light-capturing photosynthetic organs of most plants.
Veins consisting of both xylem and phloem run through the leaves.

Structure

Palisade layer-fairly dense, lots of chlorophyll

Spongy layer-less densely packed so gases can get to & from photosynthetic cells

Lower epidermis has stomata. Stoma open and close because of change in water pressure of their guard cells.

Guard cells plump, full of water, cells bow ->open. When photosynthesis is taking place, water enters the guard cells, opening the stomata because the guard cells actively transport K+ (potassium ion), water follows (osmosis). O2 produced by photosynthesis diffuses out, CO2 needed for photosynthesis diffuses in.

Control of guard cells.
Open when less CO2 or internal clock.
Excess H2O loss -> closing. (Decreased yield during drought.)

Water vapor out=transpiration. Guard cells open.

C. Movement of water and dissolved substances in vascular plants

1. Air pressure supports water column in veins of plants about 31 ft.
2. Plants concentrate inorganic nutrients which attracts water (osmosis).
3. Transpiration lets water vapor out of plant through stomatal openings in leaves, makes xylem more concentrated at leaves, pulls water up, water passes through membranes of cells.
4. Cohesion and adhesion maintain an unbroken column of water. (Adhesion = H2O attracted to cell walls. Cohesion = H2O sticks together. Help H2O flow.) Mass flow.
5. Phloem contains sucrose produced by photosynthesis, actively transported into sieve tube members by companion cells, water follows by osmosis.
In roots or other sink, companion cells actively transport sucrose out of phloem, water follows by osmosis.
Water recycled by moving back through the xylem.

Forces:

1. transpiration (-> osmosis)
2. adhesion & cohesion
3. concentration of nutrients in roots (-> osmosis)
4. mass-flow system (-> osmosis)
5. air pressure