Plant Cell Organisation and Transport

• The epidermal tissue covers the whole plant
• The palisade mesophyll tissue is where photosynthesis takes place
• The spongey mesophyll tissue contains big air spaces to allow gases to diffuse in ant out of cells
• The xylem transports water and mineral ions
• The phloem transports food substances
• The meristem tissue is found in the tips of shoots and roots and is able it differentiate into different types of plant cell
• The epidermal tissues are covered in a waxy cuticle which helps reduce water loss
• The upper epidermis is transparent to allow light to pass through to the palisade mesophyll layer
• The palisade layer has a lot of chloroplasts near the top of the leaf to get the most light
• Phloem tissue transports dissolved sugars from the leaves to the rest of the plant for immediate use or storage
• The movement of food molecules through phloem tissue is called translocation
• Phloem is composed of tubes of elongated cells where cell sap can move from one phloem cell to the next through pores in the end walls
• Xylem tissue transports water and mineral ions from the roots to the stems and leaves
• The xylem is composed of hollow tubes strengthened by lignin adapted for the transport of water in the transpiration stream
• Root hair cells are adapted for the efficient uptake of water by osmosis, and mineral ions by active transport
• The role of stomata and guard cells are to control gas exchange and water loss
• Transpiration is the movement of water in leaves
• When the light intensity is high the rate of transpiration increases
• Stomata begin to close when it gets darker since photosynthesis cannot occur so little water can escape
• When the temperature increases the rate of transpiration increases as particles have more energy to diffuse out of the stomata
• A good airflow around a leaf increases the rate of transpiration as the difference in concentration of water is larger so water can diffuse more easily
• Low humidity increases the rate of transpiration as the concentration gradient is more steep so water can diffuse out of the leaf more quickly
• The guard cells are adapted to open and close the stomata
• When a plant has lots of water the guard cells go plump and turgid which opens the stomata for gases to be exchanged
• Guard cells are sensitive to light and close at night to save water
• Guard cells and stomata are on the undersides of leaves in a shaded area to prevent water loss