Plant Tissues and Systems

Epidermal tissue

Covers the entire plant and has a waxy cuticle which helps reduce water loss from the leaf surface.

Palisade mesophyll tissue

Contains lots of chloroplasts which allows rapid rate of photosynthesis.

Epidermal tissue

Covers the entire plant and has a waxy cuticle which helps reduce water loss from the leaf surface.

Palisade mesophyll tissue

Contains lots of chloroplasts which allows rapid rate of photosynthesis.

Spongy mesophyll tissue

Has lots of air spaces which allow gases (including oxygen and carbon dioxide) to diffuse in and out.

Xylem function and adaptations

Function: A continuous hollow tube to allows the movement of water and mineral ions from the roots to the leaves.

- Strengthened by lignin: makes the vessel strong and waterproof.

- Has bordered pits: allow minerals to be transported to specific places.

Phloem function and adaptation

Function: Transportation of sugars around a plant.

- Made up of elongated living cells that have sieve plates - Sieve tube cells have few organelles to allow the efficient transport of substances.

Meristem tissue

Made up of undifferentiated stem cells which allows plant to grow.

Leaf organ tissues

Contains epidermis, palisade mesophyll, spongy mesophyll, xylem, phloem, and guard cells.

Guard cells

Control the opening and closing of the stomata according to the water content of the plant.

Stomata function and adaptations

Function: Allow the control of gaseous exchange and water loss from the leaf.

• More stomata on the base of the leaf - minimises water loss as this side is cooler and shaded.

• Have guard cells which control their opening and closing.

Root hair cells function and adaptations

Function: Allow the uptake of water and mineral ions from the soil.

• Large surface area - maximises rate of absorption.

• Contain lots of mitochondria - release energy for active transport of mineral ions.

Translocation

The movement of dissolved sugars from the leaves to other parts of the plant.

Transpiration

The evaporation of water vapour from the surface of a plant.

Transpiration stream

1. Water enters roots through root hair cells

2. Water vapour diffuses through air spaces in spongy mesophyll and out of leaf through stomata

3. Water passes from xylem into leaf to replace water that has been lost

4. Water is drawn into root hair cells and up the xylem vessels to the leaf

Temperature effect on transpiration

Increasing the temperature increases the rate of transpiration.

→ Higher rate of evaporation and diffusion of water - therefore rate of transpiration is increased.

Humidity effect on transpiration

Increasing relative humidity decreases the rate of transpiration.

→ High relative humidity will reduce the water vapour concentration gradient. The rate of evaporation will decrease, and so will the rate of transpiration.

Wind speed effect on transpiration

Increasing wind speed/air movement increases the rate of transpiration.

→ Increased air movement lowers water vapour concentration outside of the leaf and allows more water to evaporate, thereby increasing the rate of evaporation and transpiration.

Light intensity effect on transpiration

Increasing the light intensity increases the rate of transpiration.

→ The rate of photosynthesis increases, so more stomata open. This allows the rate of evaporation to increase, increasing the rate of transpiration.