Plants and Plant Structure

Photosynthesis

6CO2 + 6H2O >>> radiant energy, chlorophyll >>>>> C6H12O6 + 6O2

Photosynthesis occurs

in chloroplasts inside the leaves. Gases enter and exit the plants through the stomata (openings) in the leaves, and water and minerals enter the plant through the roots.

Meristem

Plant growth originates in meristem tissue. Meristem consists of undifferentiated (unspecialized) cells that divide continually.

Apical meristem

is found only at the tips of shoots and roots - so it is only at those places that increase in height or root length occurs.

Vascular cambium or lateral meristem tissue

enables plants to grow in girth (width).

Intercalary meristem

gives rise to new leaves

Ground tissue

cortex cells, unspecialized, for food storage and to supply replacement cells.

Dermal tissue

forms epidermis, root hairs and has guard cells that border stomata

Vascular tissue

forms tubes through which water, nutrients and gases can move around the plant, eg. xylem and phloem.

The Root Function

to anchor the plant, store food and to absorb water and minerals from the soil.

Root cap

protects the apical meristem as it moves through the soil.

Root apical meristem (zone of cell division)

these cells constantly divide to produce new specialized root cells and meristem cells. These new cells are very small.

Zone of elongation

here the new cells increase in length and that results in the root elongating.

Zone of maturation/cell differentiation

here the new cells become specialized into phloem, cortex etc.

Epidermis

Covers the exterior of the root for protection.

Root hairs

extensions of epidermal cells that absorb water and minerals (increase surface area).

Cortex

large cells, just inside the epidermis. Food (starch) storage.

Endodermis

the innermost layer of cortex cells. A single layer of cells that contain a waxy water-repellent material in their cell walls (the casparian strip). These cells guide water into xylem and form a size-selective barrier.

Pericycle

Produces lateral roots.

Xylem

These cells form continuous tubes that stretch the length of the plant and transport water and minerals from the roots upwards. These cells have very thick cells walls to provide rigid support and the cells are dead at maturity.

Phloem

These cells are continuous throughout the length of the plant and they transport dissolved sugars and other food. Mature phloem cells are alive, although lacking a nucleus. Companion cells associate with the phloem cells and direct their function. Excess sugar can be stored in the root cortex.

Roots are

fibrous (monocots) or tap root (dicot).

The Stem Function

To act as a conduction area between the roots and the leaves, and to hold the leaves in a favorable position for photosynthesis.

The outer layer (The Stem)

is still the epidermis, but here the epidermal cells are covered with a waxy layer called the cuticle.

The cuticle

protects the stem and prevents dehydration.

The vascular bundles

are arranged in a ring in dicot stems, while the vascular bundles are randomly scattered in monocots.

Vascular cambium in dicots

lateral meristematic tissue that produces new xylem and phloem.

Secondary growth

Secondary growth is growth beyond the first year and occurs mainly in dicots. The stem's organization changes. Each year concentric bands (rings) of new xylem and phloem are formed by the vascular cambium

The cambium (The Stem)

is lateral meristem tissue that divides to increase the girth of the plant stem by making new xylem and phloem each year.

Lumber (wood)

is old layers of xylem and consists of the cell walls of the dead xylem cells.

Knots in the wood are

where lateral branches once arose.

The dead xylem layers

provide support to the tree and enable it to remain upright.

Spring wood

is the first xylem of the new growing season laid down and the cells are usually bigger and thinner walled than the summer wood xylem which is laid down the rest of the season.

An annual tree ring

is a cylinder of spring and summer wood from one growing season.

The Leaf Purpose

photosynthesis. Leaves want to optimize light, CO2 and O2 collection and minimize water loss.

The epidermal cells

form the external layer of the leaf and they have a waxy outer coating called the cuticle. Epidermal cells allow light to penetrate them.

The lower epidermis

contain openings called stomata through which CO2 enters the leaf and O2 and water exits.

Each stoma

is encircled by two guard cells which open and close the stoma.

Ground tissue called palisade mesophyll and spongy mesophyll cells

contain chloroplasts and are responsible for photosynthesis.

The air spaces between the cells

allow for gas exchange with the air.

Vascular bundles (The Leaf)

branch into the leaf, forming the venation pattern: branched vein pattern in dicots, parallel veins in monocots.

Monocots eg. corn, rice, wheat (cereals)

# seed leaves (cotyledons) is one

Vascular bundles in stem is scattered

Leaf Veins is parallel

Flower parts is multiple of 3

Root type is fibrous

Dicots eg. peanuts, trees, rose

# seed leaves (cotyledons) is two

Vascular bundles in stem is in a ring

Leaf veins is branched

Flower parts is multiples of 4 or 5

Root type is tap root