The Root System

Functions:

• Anchor the plant in the ground

• Absorb water and minerals

• Transport absorbed materials to shoot

• Storage of food

Types of Root:

• Tap Root
  One main long root that comes from the radicle (young root) of the seed, lateral/secondary roots emerge from this and usualy have root hairs.
  Present in dicots
  e.g. dandelion, carrot

• Fibrous Root
  Formed when the radicle dies and leaves equal sized roots coming out of the stem
  Present in monocots
  e.g. daffodil, grass

• Adventitious Root
  These do not grow from the radicle, are found in odd places.
  Fibrous roots and gripping roots are in this category.
  e.g. ivy, strawberry plant

Root Zones:

• Zone of Protection
  Root cap protects the meristem as it pushes through soil.

• Meristematic Zone
  Contains cells that divide by mitosis. Apical meristems found at root and shoot tips.
  Lateral meristems at side of plants (side branching)..

• Zone of Elongation
  Newly formed cells absorb water and plant growth regulators (Auxin) stimulate cells to grow longer.

• Zone of Differentiation
  Elongated cells are undifferentiated. They develop into:
  - Dermal Tissue
  - Vascular Tissue
  - Ground Tissue (between dermal and vascular)

The Shoot System

Functions:

• Support aerial parts of the plants

• Transport water and minerals from the roots to the leaves and flowers

• Transport food made in the leaves to the roots

• They carry out photosynthesis when they are green

• They may store food

The Leaves

Also known as lamina

Functions:

• Photosynthesis

• Gas Exchange

• Transpiration (water loss)

• Food storage (grasses, lettuce, cabbage)

Some leaves are attached to stem via a petiole.
Others are joined directly (sessile).

• Parallel Venetion
  Veins run parallel to eachother
  Monocot

• Net Venetion (reticulate)
  Veins are branched
  Dicot

Plant Tissue

Meristematic Tissue

• Small simple cells with no vacuoles

• Function: Mitosis (new cells for growth)

• Apical meristems are located at tip (apex) of root and shoot

• Also found at buds (areas of growth)

Dermal Tissue

• Similar to skin on humans

• Primary Function: Protective cover on stem, leaves and root. Stops entry of pathogenic organisms.

• Secondary Function: Epidermal cells at root tips designed to absorb water and minerals.

• Epidermis in stem and leaves have a waxy cuticle to prevently water loss.

Ground Tissue

• Forms the bulk of plants. Fills the interior of the plant body.

• Function: Photosynthesis, food storage and provides strength to the plant.

Vascular Tissue

• Function: Transport substances within the plant

• Has two types, xylem and phloem

Xylem

• Function: Transports water and mineral salts from the roots to the leaves, mechanical support

• Located in roots, stem, leaves and flowers

• Consists of two kinds of conducting cells, xylem tracheids and xylem vessels.

• Both tracheids and vessels die before maturity. Thus, xylem tissue is said to be dead.

- Xylem Tracheids

• Long cells tapered at both ends

• Contains pits (allow water and minerals to move sideways from cell to cell)

• Only found in conifers

- Xylem Vessels

• Form when numerous cells join end-to-end.

• Wider than xylem tracheids and stacked together.

• Have no end walls forming a continuous conducting tube

• Contains pits

• Both vessels and tracheid contains lignin (structural polysaccharide)

Phloem

• Function: Transportation of food made in leaves, companion cells controls sieve tube element

• Located in vascular bundles in roots, stems, leaves, and flowers.

• Consists of phloem sieve tube elements and companion cells

• Are elongated cylindrical cells stacked end-to-end

• End walls have holes called sieve plates (this allows cytoplasm to pass from celll to cell)

• When mature, the nucleus degenerates - the cytoplasm remains

• Each sieve element has a companion cell (connected by cytoplasmic connections)

Monocotyledon

• One cotyledon

• Vascular bundles are scattered

• Parallel veins

• Flowers have petals in multiples of 3

Dicotyledon

• Two cotyledons

• Vascular bundles in ring shape

• Dendritic veins (net veins)

• Flowers have petals in multiples of 4/5

Tropisms

Growth response of a plant to stimulus

• Plants respond to stimuli by changing their growth

Phototropism

• Growth of a plant in response to light, so that it can receive the maximum amount of light for photosynthesis.

Geotropism

• Growth in response to gravity, it allows the root to get the water and nutrients it needs from the soil, and raises the leaves up into the light for photosynthesis.

Thigmotropism

• Growth of a plant in response to contact, gives support to the plant.

Hydrotropism

• Growth of a plant in response to water, they will grow towards a water source.

Chemotropism

• Growth of a plant in response to chemicals.

Plant Growth Regulators

• Plant growth regulators (hormones) are chemicals that interact with one another to control a particular development or response.

• Plants only grow at their tips in small regions of active cell division called meristems - the tips of shoots, roots, and side buds.

• Plant growth regulators are produced in the meristems and transported through the vascular system (xylem and phloem) of the plant.

• Active in very small amounts.

• Their effects depend on concentration.

• A small amount of growth regulator can have a great effect on growth.

Promote growth:
Auxins, Gibberellins, Cytokinins

Inhibit Growth:
Abscisic acid, Ethene

Auxin

• Promote cell enlargement and growth.

• Are involved in phototropism and apical dominance.

• In shoots, light causes auxin to move down the shaded parts of the stem, causing the shoot to grow towards the sunlight.

• Can be used to kill weeds and stimulate root formation.

Gibberellin

• Causes stem lengething.

• Mobilise the stored food in germinating seeds.

• Break dormancy in buds and seeds in spring.

Cytokinins

• Stimulate cell division and trigger leaf growth in spring.

Abscisic Acid

• Triggers bud and seed dormancy in autumn and inhibits cell growth.

Ethene

• Promotes ripening of fruit and the fall of leaves, flowers and fruits.

Structure of the Flower