botany. plants are either woody (long living) or herbaceous (short lived and green). woody plants...

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BOTANY

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BOTANY

Plants are either woody (long living) or herbaceous (short lived and green). Woody plants have both woody and herbaceous structures.

Plant Organs and Tissues

There are two groups of plant organs:

1. Vegetative - which have leaves, roots and stems

2. Reproductive - which have flowers, fruits and seeds

Plant organs are made of several types of tissues:1. Meristematic - these tissues contain cells

that are capable of mitosis and can develop into any tissue found in that plant. They are found in growing areas of the plant, like buds, root tips and stems.

a. Apical meristem - is found at the tips and roots of stems

b. Lateral meristem - includes the vascular cambium, cork cambuim and pericycle

2. Vascular - these tissues are composed of different types of cells; the xylem, which carries water and dissolved minerals upward in the plant and the phloem which carries water and dissolved food

3. Structural - these tissues produce food, store food, cover, support and protect plant.

The LeafThe function of a plant’s leaves is to absorb

energy from the sun (photosynthesis).

The blade of the leaf is a large, flattened area connected to the stem by a petiole (if there is no petiole the leaf is sessile). Stipules may cover the leaf during development. They may be wing-like, photosynthetic, or may be thorns. Make a drawing of a leaf, including the blade, petiole, stipules and stem.

Leaves may have several shapes, or margins (the edge of the leaf). Make drawings of the following margins: entire, lobed, serrate, and repand

See http://www.fnr.purdue.edu/extension/kp/lm.html

Leaves may also have several venations:1.parallel - found in corn, grass, iris’ and

orchids2.netted - where large veins branch to form

a network of smaller veinsa. pinnate - the veins branch off of one central

vein, as in oaks, African violets, and apple trees

b.palmate - two or more main veins coming from a single point, as in maples, ivies and geraniums

See: http://www.pssc.ttu.edu/pss1411cd/STRUCTUR/leaves/venation.htm

Leaves may also be simple, where there is one blade on one petiole, or compound, with leaflets. The difference between a leaf and a leaflet is that leaves have stipules and leaflets don’t.

The Covering of a Leaf1. The upper and lower epidermis

are one cell layer thick. They protect the leaf.

2. The cuticle consists of a waxy substance secreted by the epidermis. It helps the leaf retain water in hot weather

3. The stomata are for gas exchange. They are found on the underside of the leaf and are regulated by the guard cells. Guard cells make sugars that will cause a change in the turgor pressure of the cells. When turgor pressure in the guard cells is high, the stomata are open; when the turgor pressure in the guard cells is low, the stomata are closed.

The Internal Structure of a Leaf

1. The parenchyma consists of the palisade and spongy mesophylls. They are the primary photosynthetic areas of the leaf. The palisade mesophyll has a larger number of cells in a smaller surface area. The cells contain many chloroplasts. The spongy mesophyll is involved in carbon dioxide-oxygen exchange.

2. The vein is composed of the xylem, phloem and the collenchyma. We have already discussed the xylem and phloem; the collenchyma strengthens the vein.

Draw and label a diagram of a leaf on your paper. Include the palisade mesophyll, spongy mesophyll, upper epidermis, lower epidermis, cuticle, stomata, guard cells, xylem, and phloem. See page 647 in your textbook.

Root Systems

Roots have four main functions:

1. They anchor the plant

2. They absorb water & minerals necessary for plant growth

3. They transport absorbed substances to where they are needed in the plant

4. They store food (in carrots, radishes, & beets)

A taproot system has the original root that sprouted from a seed. It continues to grow as the predominant root. Taproots are often long, thin, and produce small, branching secondary roots. A fibrous root system has no taproot but has many secondary roots. In general, roots usually spread outward more than they grow downward. Why do you think this type of growth would be beneficial for the plant?

Roots exhibit primary and secondary growth. Primary growth of a root is growth of a root in length. This growth results from the manufacturing of cells in the meristematic region. Lengthening, however, is due to cell growth in the elongation region. Once elongated, growth stops. The primary tissues of a root are located above the maturation region and are made during primary growth. These tissues have root hairs that are able to reach water that may be out of the root’s reach.

Secondary growth of a root is growth in diameter, and it usually occurs in woody plants. Secondary growth occurs when secondary xylem and phloem are produced. Because the vein is enlarged, the epidermis is crushed (remember the epidermis is important for water absorption). Cork cells will protect the enlarged veins but the vein must grow in length if it is to continue absorbing water. Secondary growth leads to the production of extensive root systems.

StemsStems have two major functions:

1. They manufacture, support and display leaves

2. They conduct many of the materials needed for and manufactured by photosynthesis to and from the leaves

How Plants Use Water

Plants use water in four ways:A. For photosynthesis (think about the

equation)B. For turgor-using water to stiffen parts of

the herbaceous plantC. For hydrolysis-adding water to break

large molecules apartD. For translocation-moving dissolved

materials from one place to another

Translocation is the movement of water and dissolved minerals within a plant. The movement of water may result from:

A. Root pressure - which causes the movement of water up the xylem

B. Passive absorption - which is the movement of water according to a concentration gradient

What causes the movement of water in plants?

C. capillarity - which is the tendency of water to move up a thin tube (like the xylem)

D. transpiration - which is the release of water vapor, by the plant, into the atmosphere

E. cohesion - which is the “sticking together” of a group of water molecules

F. transpiration-cohesion theory - which states that as water molecules are removed from the top of the plant (due to transpiration) additional water molecules that are “stuck together” rush into the bottom

Plant HormonesPlant hormones are chemical growth

regulators produced by the meristematic regions of a plant. There are two main groups of plant hormones:

A. Auxins - which are found in stems, seeds, leaves, fruits and roots, Auxins cause elongation of cells, cause unfertilized flowers to develop into seedless fruits, and stimulate the formation of roots in wood stem cuttings.

B. Gibberellins - stimulate cell division and elongation, growth of seeds, flower formation, pollen formation and fruit formation.

TropismsA tropism is a growth response in plant that

is caused by hormonal action. There are four kinds of tropisms:

A. phototropism - a growth response to lightB. thigmotropism - a growth response to

touchC. chemotropism - a growth response to

chemicals; for example, hydrotropism is a growth response to water

D. geotropism - a growth response to gravity

In general, a positive tropism is a growth response toward a particular factor and a negative tropism is a growth response away from a particular factor.

Plants and Light

Light is important for plants. A plant that does not receive enough light may be pale green, yellow or white. The stem elongates abnormally and the plant bends toward any available light. Such a plant is said to be etiolated.

• Photoperiodism is the response of a plant to changes in light intensity and length of days.

• Short day plants flower when the period of light is less than 12 hours.

• Long day plants flower when the period of light is more than 12 hours.

• Neutral day plants flower independently of the photoperiod; they usually flower continuously if proper conditions are met.

Reproduction of Flowering Plants

Accessory Flower Parts

A. Sepals – leaflike, green structures that encircle the flower stem beneath the petals

B. Petals – leaflike, colorful structures arranges in a circle called a corolla around the top of a flower stem

Reproductive Flower Parts

A. Stamen (male)

• filament – the long structure that supports the anther

• anther – the structure at the tip of the filament that produces pollen containing sperm

B. Pistil (female)

• stigma – at the top of the pistil; a sticky or feathery surface on which the pollen grains land and grow

• style – the slender stalk of the pistil that connects the stigma to the ovary

• ovary – eventually becomes the fruit; contains the ovules

• ovules – will become seeds if they are fertilized

Use the diagram on page 656 to draw a typical flower and label the accessory and reproductive parts.

Kinds of Flowers

• Complete – a flower that has all 4 organs (sepals, petals, stamens and pistils)

• Incomplete – a flower that lacks one or more organs

• Male – have stamens but no pistils

• Female – have pistils but no stamens