Translocation and leaves Flashcards
(19 cards)
Dicotyledonous plant
A plants with leaves ( Not cactus )
Upper epidermis
Transparent layer to let sunlight in for photosynthesis in on the top of the leaf.
Waxy cuticle
Waxy layer on top of leaf, minimises water loss
Palisade mesophyll
Layer of long cylindrical cell where photosynthesis takes place. chlorophyll
Spongy mesophyll
Layer of cells with air spaces between them were gas exchange takes place
Xylem -
Transports water
Phloem
Transport dissolved sugar
Lower epidermis
Transparent layer with pores (stomata)T
Transpiration
The loss of water through stomata via diffusion
Guard cell process to open / close stomata
Swell unevenly due to thicker inner walls and thinner outer walls.
To open the guard cell becomes turgid by water entering it and its structure allows it to bend outward, revealing the opening of stoma.
Why do plants need water
Photosynthesis
Metabolite in chemical reactions
Transport minerals - phosphates and nitrates
Maintain turgidly of cells
Maintain temperature
How do plants take up nutrients like phosphates and nitrates
They are absorbed by active transport and are dissolved in the water
Nitrates examples
DNA, amino acids and chlorophyll
Phosphates example
DNA and ATP
Xylem
Transport water and minerals up the plant and provides support
Xylem walls contain
Lignin
Transpiration factors
Light ( Increases open stomata so water can diffuse out)
Temperature ( Increases kinetic energy and evaporation )
Increasing wind ( Decrease water vapor outside of leaf and increase water potential gradient
Decrease humidity
Transpiration process / Cohesion tension theory
1) Water diffuses out the leaf through the stomata (Transpiration)
2) Water lost from the air spaces is replaced by water from the cell walls of the mesophyll cells
3) This lowers the water potential of the mesophyll cells. Water is drawn from the xylem into the mesophyll cells by osmosis down a water potential gradient
4) Water moves up the xylem vessels in a continuous column to replace this lost water this upward movement is called the transpiration stream
5) The upward pulling force acting on the xylem can be so great that water is under tension exerting an inward pull on the walls of the xylem vessels known as cohesion tension theory
6) Water molecules also stick to cellulose/lignin in xylem walls (adhesion)
7) This pulls up a continuous column of water in the xylem to the mesophyll tissues leave along a water potential gradient (Transpiration pull) and generates negative pressure inside the xylem
Negative pressure
= Lower pressure inside than outside
