Bi Sci 001
Friday February 12, 1999
Announcements:
Lecture notes:
Plant Chart
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Phylum or Division |
Is Fertilization H2O dependent? |
Sporophyte or gametophyte |
Most usual habitat |
True Root system? |
True vascular system? |
Examples |
|
Moss |
Yes |
Gametophyte |
Moist Environment |
No |
No |
|
|
Fern |
Yes |
*2 plants |
Moist Environment |
No |
Yes |
|
|
Gymnosperm |
No |
Sporophyte |
Land |
Yes |
Yes |
Ginko, Spruce, Pine |
|
Angiosperm |
No |
Sporophyte |
Land* with exceptions |
Yes |
Yes |
Grass, apple tree |
Two Types of Growth
Primary: The ends of the roots and shoots grow. "Annual" plants show this growth pattern.
Secondary: Growth at sites other than the root and shoot tips. It increases the girth of older tissues. (Trees show both
types)
Three Types of Plant Tissues
Ground Tissues: make up the bulk of a plant body.
Parenchyma: The most abundant type
Thin cell walls
Big central vacuole
Lots of sugar
Example: "packing" in stems, roots, leaves, the flesh of fruits
Collenchyma: "pliable" strengthening tissues.
Cell walls contain cellulose and pectin (jelly gel)
Example: walnut shells, fibers of flax, "grit" in pears
Vascular Tissues
Xylem: Conducts water and minerals from the soil to other parts of the plant. At maturity these cells are dead.
These tissues are made of long cells on top of one another with holes between the cells.
Cell walls have lots of cellulose and lignin.
Phloem: Conducts sugar and other solutes to other parts of the plant. At maturity cells are alive, but often have
no nuclei. (no nuclei means no DNA, no RNA and no protien)
Adjacent "companion cells" often direct cellular activities of phloem cells.
Dermal Tissues
Epdermis: Covers the plant
Above ground, waxes and cutin cover leaves and stem to restrict water loss and retard microbial
attack.
This non-cellular cover is called the cuticle.
On roots, root "hairs" increase the surface area for absorption.
Guard Cells (two make a stoma) regulate water and CO2 transport in leaves.
Periderm: covers the outside of plants that undergo secondary growth.
The outer cork tissue (bark) is dead tissue
The cork cambium underneath has transport tissues
Cell walls secrete suberin, a waxy substance that waterproofs.
How do things get transported in the plant?
There are two processes involved:
1. How does water get from the roots of a tree all the way up to the leaves? (oak trees can grow up to 300 feet)
2. How does the sugar made by photosynthetsis get to the rest of the plant?
Moving water and dissolved minerals to the leaves from the roots of plants involves processes called TRANSPIRATION and WATER CONDUCTION.
Negative water pressures extend from the leaf to the root system of the plant. (suction)
The power of the hydrogen bond and the phenomenon of osmosis are responsible for the negative pressure.
Step 1 is Transpiration (water evaporating from the leaves)
Step 2 - Water conduction
As water leaves a leaf, more comes from the stem to take its place. As water in the stem moves up, etc.,
until a pressure gradient "pulls" water into the plant through the roots.
This is made possible by the strength of the hydrogen bonding in water.
** Also at work at the bottom of the plant high concentrations of mineral ions in the roots of the plant help
"encourage" water to enter by osmosis. This pressure is strong enough to raise a column of water only
about 6 feet. The rest is supplied by the negative pressure (suction) brought about by transpiration.
How does sugar made in the leaf move from the leaf to the rest of the plant?
This process is called translocation
Dissolved sugar can move up to 1 meter/hour
The pressure can be as great as 5 times the pressure in a tire.
This Pressure Flow Theory is called the "Source to Sink" Pattern.
The source includes the sites of photosynthesis that produce the sugar for the plant.
The sink includes the parts of the plants that need or store products of the leaves.
Molecules move from an area or higher concentration to that of a lower concentration.
Why doesn't the pressure gradient eventually even up?
The sugar (and other materials) made in the leaves is continuously being used up to make: a. ATP
b. fats (for seeds)
c. proteins
d. starches
Once changed into these other molecules they are no longer "sugar" molecules and can't be used to set up and equilibrium.
Plants can adjust to environmental conditions
They can add more roots where they find a lot of nutrients.
Roots travel deeper into the soil to find water.
Plants can close stomata (plural of stoma) to conserve water.
Tropisms
Plants can alter their growth pattern in response to environmental conditions.
Phototropism: plants lean toward a light source.
Gravitropism: a plant stem on its side will turn and grow upward, roots grow downward.
Thigmotropism: tendrils and vine stems wrap around a support.
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