Module 2 - Autotrophs

Function of roots

-anchors the plant into the ground
- absorbs water and dissolved minerals from the soil for growth and photosynthesis

root hairs

larger surface area for which absorption can occur

Internal structures of roots

Epidermis- protective outer layer
• Cortex- act as a storage area for excess materials but also air spaces between cells for the circulation of gases
• Vascular tissue- forms a cylinder in the centre consisting of xylem and phloem

Stems

structural axes of the plant

stem function

• Support for and the elevation of leaves, flowers and fruits.
• Transport of fluids between the roots and the shoots in the xylem and phloem
Storage of nutrients
Production of new living tissue.

node

holds one or more leaves which can grow into branches

Leaves

external structure visible to naked eye

why are most leaves broad, thin and flat

to achieve a larger surface area for sunlight and gas exchange

Leaf diagram labelled

Internal structures of a leaf

• Cuticle- maintains shape and provides protection
• Epidermis- single, transparent layer for sun to penetrate
• Stomates- Pores that open and close for gas exchange
• Mesophyll- contain chlorophyll for gas exchange
• Veins- tubes of vascular tissues

Internal lead structures diagram

Gas exchange- Stomata

Opening to an air space located in the lower epidermis of a leaf. Each stoma consists of two highly specialised epidermal cells called guard cells.

Vascular system

Vascular tissue is used by vascular plants to transport water and mineral ions absorbed from the soil and sugars produced in the leaves to cells throughout the plant
It is visible as parallel veins in grasses, branching veins in many other leaves

Xylem

Transports water and inorganic nutrients (mineral ions) absorbed by the roots from the soil to the aerial (above ground) parts of the plant

what is xylem composed of

It is composed of xylem vessels and elongated cells called tracheids

Xylem vessels

long, water-filled tube consisting of elongated cells joined end to end. As the cells mature, the cell wall is strengthened with lignin, making them stronger and more rigid

phloem

Phloem
Transports organic nutrients (dissolved sugars) produced in the leaves by photosynthesis throughout the plant. Other organic substances, such as amino acids, are also transported in the phloem
The main material transported through the phloem is known as phloem sap.
Plants can store sugar in their cells as starch. Starch can be used for structural support, or as an energy source when the plant cannot photosynthesise

Transpiration - water pathways

Extracellular pathway- most water and some mineral ions pass in or between cell walls
• Cytoplasmic pathway- most mineral ions and some water pass through the cytoplasm of living root cells. Involves substances entering a root hair cell by crossing the cell's membrane, and then passing from cell to cell through plasmodesmata,

Xylem transport types

Xylem- Transport Types
Active transport- most dissolved mineral ions are selectively taken into roots by active transport.
Osmosis- the high concentration of ions in the vascular tissues of terrestrial plants creates a very large osmotic concentration gradient.
Diffusion- some mineral ions, such as potassium and phosphate, enter the roots by diffusion. The uptake of these nutrients therefore depends on the rate of water uptake

What is transpiration

The passive movement of water through the xylem of vascular plants, from the roots to the leaves

What does transpiration enable the plant to do

• Absorb the water necessary for photosynthesis
• Transport mineral salts to leaf cells and fruits
• Cool down and not become overheated.

What is the theory that explains the primary mechanisms of water movement in plants?

Transpiration-Cohesion-tension theory

features of Transpiration-cohesion-tension theory

• Cohesion between water molecules- evaporation from the surface of the leaf pulls adjacent water molecules and is replaced from the roots
• Adhesion between water molecules and plant cell walls
• Tension (differential pressure) created when water evaporates from the leaves

Transpiration stream

continuous one-way flow of water from roots to leaves

Factors that affect transpiration rates

• Humidity- rate decreases when there is a lot of water vapour in the air
• Temperature- rates increase as temperature increases because heat energy increases the rate of evaporation of water
• Wind- air currents increase the rate of transpiration by moving water vapour away from the leaf and increasing the rate of evaporation of water

translocation

the transport of dissolved material within a plant

Sources of translocation

Sources: sites where sugars are produced during photosynthesis- leaves in plants.

Sinks of translocation

sites where sugars are translocated to. Includes roots, bulbs, stems, flowers and fruits