Warm-Up 12/5

Apical meristems	Lateral meristems
Occur in the tips of stems and roots	Occur between xylem and phloem in stems
Produces soft tissues	Produces hard xylem tissue: wood
Lengthens roots and stems	Widens stems to support the weight of tall plants
Allows plants to develop special structures like leaves and flowers	Allows trees to grow tall, helping them to compete effectively for light.
Found in all phyla of plants	Absent in mosses and horsetails.

2. Plants use hormones to control the growth of roots and stems. When a plant releases a growth hormone in response to an external stimulus we call the resulting directional growth a tropism.

One type of tropism is phototropism: growth in response to light. Phototropism may be either positive (towards the light) or negative (away from the light).

Phototropism requires the absorption of light by proteins known as phototropins. Phototropins change to a new conformation (a new shape) when they absorb certain wavelengths of light. The new shape causes phototropins to act as ‘on switches’ for a gene that regulates the activity of auxins.

Auxins cause cells to become longer. Therefore, by releasing auxins on one side of a stem but not on the other side, a stem will bend because one side becomes longer than the other.

When a stem detects directional light it moves auxins from its sunny side to its shady side, which causes the shady side to bend toward the light. Bending toward light allows plants to absorb more sunlight and be able to photosynthesize at a faster rate.

Auxins cause cells to become larger in the following way: 1) they cause cells to actively transport hydrogen ions out of the cell, making the outside acidic; 2) the acid outside the cell makes the cell wall softer; 3) softer cell walls make the cells more stretchable; and 4) stretchy cells are bigger because the internal pressure inside the cell causes the cell wall to bulge out.

3. The xylem is a system of long hollow tubes responsible for replacing water lost during transpiration and photosynthesis. The xylem is made of two kinds of cells: tracheids and vessels. Xylem cells die before they are functional: after they die they become long, narrow tubes with pores at each end that allow water to pass through them.

The xylem sap moves from roots, through the stem, to the leaves without any energy being spent by the plant.

Three processes cause water to rise up the xylem tube:

Root pressure: Water moves into roots by osmosis because the roots have high concentrations of solute. This causes a positive pressure that forces sap up the xylem towards the leaves. Root pressure is highest in the morning before the stomata open and allow transpiration to begin.

Capillary action: The xylem is a long tube that is microscopically thin. When water molecules contact the surface of the xylem there is adhesion. Adhesion tends to pull water molecules upward by a process called capillary action.

Transpiration pull: When water molecules evaporate from leaves the water potential drops at the stomata. The low pressure then pulls new water molecules towards the stomata from the xylem vessels. As these water molecules move they pull on water molecules behind them due to cohesion (caused by hydrogen bonding). The pull is transmitted from one water molecule to the next, all the way to the roots.

Warm-Up

Embryo	The dicotyledons embryo has two cotyledons.	Monocotyledons have one cotyledon.
Leaf venation	Leaf veins are reticulated (branched).	Leaf veins are parallel.
Flowers	Petals in multiples of four or five. May bear fruit ( if tree)	multiples of three
Secondary growth	Often present	Absent
Stem and vascular system	Bundles of vascular tissue arranged in a ring. The vascular system is divided into a cortex and stele.	Bundles of vascular tissue scattered throughout the stem with no particular arrangement, and has no cortex.
Pollen	Pollen with three furrows or pores	Pollen with a single furrow or pore
Examples	Legumes (pea, beans, lentils, peanuts) daisies, mint, lettuce, tomato, oak, tree, etc.	Grains, (wheat, corn, rice, millet) lilies, daffodils, sugarcane, banana, palm, ginger, onions, bamboo, sugar, cone, palm tree, banana tree,grass
Root Pattern	Taproot system	Fibrous roots
Presence or absence of wood	both herbaceous and woody	herbaceous
# of seed leaves	2 seed leaves	1 seed leaf

2. Stem tubers are produced by the stems of some plants. They are used by plants to over-winter and re-grow the next year and as a means of asexual reproduction. Example: ceropegia. A root tuber is an enlarged root that functions as a storage organ. Root tubers store nutrients over periods when the plant can not actively grow, thus permitting survival from one year to the next. Example: sweet potatoes. A bulb is an underground shoot that has modified leaves that are used as food storage organs by a dormant plant. A bulb contains food reserves to enable the plant to survive adverse conditions. Roots emerge from the underside of the base, and new stems and leaves from the upper side. Example: Onions. A tendril is a specialized stem or leaf with a threadlike shape that is used by climbing plants for support and attachment, generally by twining around whatever it touches. Example: garden peas.

Warm Up

1.        Denaturation is when a protein or nucleic acid loses some to all of its function. 

2.      

3.       A competitive inhibitor has a molecular shape similar to the enzyme itself, and binds to the substrate on the active site, thus blocking the enzyme from binding. A noncompetitive inhibitor does not anywhere near the active site, instead it bind to the substrate at another location on its surface.

4.       INDUCED FIT MEANS THAT THE ENZYME RECOGNISES THE SUBSTRATES THEN SLIGHTLY CHANGES IT'S SHAPE, BRING THE TWO SUBSTRATES TOGETHER. LOCK AND KEY----THE SUBSTRATE FITS EXACTLY INTO THE ACTIVE SITE OF THE PROTEIN