The Structure Of A Leaf Flashcards
Epidermal tissue
Tissue that covers and protects the plant, acts as a physical defence in plants, transparent to allow light through
Waxy cuticle
A layer on the surface of the leaf which protects the plant and reduces water loss, thicker on the upper surface, transparent
Palisade mesophyll
Photosynthetic tissue below the epidermis in a leaf, palisade cells are compacted together and contain high concentrations of chlorophyll and high quantities of chloroplasts for photosynthesis
Spongy mesophyll
Layer of tissue found beneath the palisade mesophyll that is packed loosely for efficient gas exchange of carbon dioxide and oxygen, spongy mesophyll cells have increased surface areas for gas exchange
Intercellular space
The space between cells, specifically the large amount of space between spongy mesophyll cells, provides room for an increased rate of diffusion
Stomata
Small openings on the underside of a leaf through which oxygen, carbon dioxide and water can move
Role of the stomata
The stomata opens to allow gas exchange where carbon dioxide can enter the plant for photosynthesis and excess oxygen from respiration leaves the plant, water is also lost from the plant here
Guard cells
Pairs of cells that surround the stomata and control their opening and closing to optimise gas exchange and reduce water loss
Activity of guard cells
Guard cells open the stomata in light conditions suitable for photosynthesis, guard cells close the stomata at night when photosynthesis cannot occur to reduce water loss
Gas exchange in plants
Carbon dioxide diffuses into the plant in exchange for oxygen that diffuses out of the plant, this process is regulated by guard cells in the leaves that can open and close the stomata efficiently
Xylem
Non-living vascular tissue that carries water and dissolved minerals from the roots of a plant to its leaves, the xylem is hollow and nearby cells are lignified or dead so water can move continuously
Lignin
A chemical that provides support to xylem cells and prevents the unwanted movement of water into nearby cells
Phloem
Living and elongated vascular tissue that carries sugar and organic substances throughout a plant, the phloem has sieve plates that act as pores to allow molecules to diffuse between cells
Transpiration
The process of the movement of water through a plant and the loss of water from a plant through its leaves
Rate of transpiration
The rate of water loss from a plant
In hot and dry environments
Plants have waxy cuticles to reduce water loss and fewer stomata, they may also have thin needle-like leaves or spines to reduce water loss and to defend the plant, large surface area of roots that branch to reach water, large stems and reservoirs to store water
In humid environments such as rainforests
Plants have broad leaves to optimise exposure to light in shaded environments for photosynthesis, waxy surface that rain can run off to prevent damage, many stomata to allow sufficient transpiration and gas exchange
Marram grass
A type of grass that is adapted to windy, exposed conditions, it can fold up its leaf structure to reduce water loss in dry conditions
Aquatic plants such as water lilies
Have stomata on the upper surface of the leaf to allow gas exchange with the air, increased water loss as water does not need to be conserved
