2.1 Osmosis and Plant Transport 💧

Osmosis

diffusion of water molecules from a dilute solution to a more concentrated solution across a selectively permeable membrane

Is energy required for osmosis

No as water moves down concentration gradient

Role of cell wall

Supports cell and limits entry of water

Animal cells in high concentration of water

Gets bigger and eventually bursts (lysis)

Animal cells in low concentration of water

Shrink and become shrivelled

Plant cells in high concentration of water

Turgid as vacuole gets bigger and pushes membrane against cell wall

Plant cells in low concentration of water

Wilts and becomes flaccid or vacuole shrinks and membrane pulls away form cell wall (Plasmolysis)

Describing osmosis

Water moves in/out of the cell by osmosis, down concentration gradient, and cell becomes ____

Transpiration

Evaporation of water from the spongy mesophyll, followed by diffusion through air spaces and out of the stomata

Uses of water for plants

• photosynthesis

• transpiration

• transport

• support

Surface area effect on transpiration (biotic)

smaller leaves contain less stomata causing decrease e.g remove leaves

Wind speed effect on transpiration (abiotic)

higher wind speed increases rate of evaporation e.g use a fan

Temperature effect on transpiration (abiotic)

higher temperature increases rate of evaporation e.g use a heater

Humidity effect on transpiration (abiotic)

higher humidity reduces rate of evaporation e.g plastic bag over shoot

Light intensity effect on transpiration (abiotic)

darkness causes stomata to close causing decrease e.g use a lamp

When water availability is limited

Plants reduce transpiration by closing stomata

Transpiration stream

water loss at the leaves and water absorption at the roots are directly proportional

Potometer

measures rate of water uptake in plants

Bubble potometer

measures by finding distance air bubbles move over time

Weight potometer

measures by weighing the plant before and after and subtracting

Why can a potometer not measure transpiration rate

some water is used by plant, only measures rate of water uptake

Label section through a leaf

• waxy cuticle

• upper epidermis

• palisade mesophyll

• spongy mesophyll

• air space

• lower epidermis

• stomata

• guard cells