Transpiration Flashcards
What is the definition of transpiration?
The loss of water from the leaves by evaporation from the mesophyll cells followed by diffusion of water vapour through air spaces and stomata.
What is the transpiration stream?
Water taken in through roots, transported around the plant through a system of tubes, and lost through leaves in transpiration.
Transpiration is necessary as it ensures water moves continually around the plant.
Why are there more stomata on the lower surface of the leaves of most plants than the upper?
The lower surface is shielded from heat and sun.
How do stomata work?
When there is little water in the plant the plant the guard cells become flaccid and remain closed.
When there is an abundance of water in the plant the guard cells become turgid, opening the stomatal pore.
What are the factors influencing the rate of transpiration?
Temperature- water evaporates faster at warmer temperatures
Wind speed- moves water vapour away from the leaf to keep a steep concentration gradient
Humidity- transpiration is reduced in humid conditions as there is a shallow concentration gradient
Surface area of leaf- more space for stomata therefore more transpiration
What plant vessels carry water?
Xylem
What are the adaptations for Xylem vessels?
Specialised cells for carrying water.
No top or base so cells form continuous hollow tube
Run from roots to stem and subdivide into veins in the leaves.
What is active transport?
Uptake of minerals from the soil by root hair cells against the concentration gradient- requires energy
What is passive transport.
Diffusion, such as osmosis
What is the definition of diffusion?
Random movement of molecules from an area of high concentration to an area of low concentration, down a concentration gradient.
What is the definition of Osmosis?
Net movement of water molecules down a concentration gradient from an area of greater water concentration to an area of lower water concentration though a partially permeable membrane.
What are the factors that affect the movement of substances across plasma membranes?
Size of particles
Concentration gradient
What happens to animal cells when placed in pure water?
Osmosis will occur as water goes down the concentration gradient into the cell, until it swells and bursts (cell lysis)
What happens to animal cells in concentrated solutions?
Water diffuses out of the cell and it shrivels up.
What do plant cells do when placed in pure water.
They swell up, but don’t burst. The cell wall resists the cytoplasm pushing against it. It becomes turgid.
