Entry of water into plants

Entry of water into plants

Vascular tissues

Phloem

Xylem

Stem Root

Xylem and phloem in ‘vascular bundle’ , arranged in a ring around the pith.

Xylem and phloem alternate with each other and found at the centre of a root

Absorption of water by roots

Root hair cell has Large surface area : volume ratio for efficient absorption

Epidermal layer and root hair cell Piliferous layer

Root hair

High conc. of sugar and salts

Dilute solution of mineral salt.

Root hair cell Soil

Lower water potential

Higher water potential

Water would enter root hair cell by osmosis.

Absorption of water by roots

Higher water potential

Lower water potential

Water would pass from root hair cell to the inner cell by osmosis

Water would pass from one cell to the next cell in the cortex until the water enters the xylem tube

Cortex – cells in between epidermis and xylem

http://www.kscience.co.uk/animations/transpiration.swf

transpiration.swf

Absorption of mineral salts by roots

Higher conc. of ions

Lower conc. of ions (K, Na)

•Ions enter mainly by active transport •Energy from cellular respiration

Absorption of mineral salts by roots

Lower conc. of ions

Higher conc. of mineral ions

•Ions also by diffusion (not common)

This plant has been given excessive potassium fertilizer.

Explain why the plant will die although fertilizer is suppose to support plant growth.

Recap

• What is the main process by which water moves from cell to cell and finally into the xylem vessel called?

Recap !

http://www.kscience.co.uk/animations/anim_1.htm

Recap!

• Mineral salts enter the root hair cell mainly by ______________.

Moving water up the xylem vessels

Moving water up the xylem vessels

• Via 3 processes: – Root pressure– Capillary action– Transpiration pull

the main process

Process 1: Root pressure

What will happen to the water level?

Pump water in

Water level

Movement of water from the root hair cells to the xylem vessels would create an upward force to push the water up the xylem vessels. This is known as root pressure.

How is root pressure generated?

1) Ions pumped from cortex into xylem

2) Water enters by osmosis

Cell in coretx xylem

Angular in shape

Movement of water from the root hair cells to the xylem vessels would create an upward force to push the water up the xylem vessels. This is known as root pressure.

A demonstration to show root pressure

Connector Cut stem with roots

Glass tubing

What would happen to the water level after 5 hrs?

• A experiment to demonstrate capillary action.• What did you observe?

Capillary action

• Movement of water up a narrow tube

The narrower the tube, the higher level the water level

Capillary action

Force of attraction between water molecules and wall of vessel ‘pulls’ water molecules into a vessel. (adhesion force)

Force of attraction between water molecules ‘pull’ the next molecule along. (cohesion force)

Drinking ribena Transpiration pull Sucking of water up the straw

Transpiration of water from the leaves

Movement of water up straw

Movement of water up a xylem tube

Transpiration pull is a suction force caused by transpiration, that pulls the water up the xylem tube.

It is the strongest force that moves water up a xylem tube.

Do not be confuse between…..

• Transpiration evaporation of water

• Transpiration pull suction force

• Transpiration stream the stream of water up the xylem vessels

Adhesion and cohesion forces move the stream of water molecules up a xylem vessel.

2)water evaporates from the thin film of moisture and moves into the intercellular air spaces as water vapour.

1) Water continuously moves out of mesophyll cells to form a thin layer of moisture.

Moving water up the xylem vessels

• Via 3 processes: – Root pressure– Capillary action– Transpiration pull the main process the causes

water to move up a xylem tube.

Transpiration

What is transpiration? – The evaporation loss

of water vapour through the stomata of the leaves is known as transpiration.

How is the suction force being created at the leaves by transpiration?

Transpiration occurs here

Lower conc. of water vapour

Water vapour would move down the concentration gradient into the atmosphere.

Water evaporates from the thin film of moisture to give water vapour.

Water moves out of mesophyll cells to replace the thin film of moisture surrounding the mesophyll cell.

Mesophyll cell A

Transpiration set up an

suction force to pull water up the xylem

tube

True or false

• When transpiration stops for a long time, photosynthesis ceases.

• The sun provides energy for water to moves through the xylem.

• Usually, only 99% of the water absorbed is lost through transpiration.

• Where is the remaining 1% of water?

Think about it!

Importance of transpiration

• To pull water and mineral salts from roots to leaves.

• Evaporation of water cools the leaves.

• Water used for photosynthesis; to keep cell frim and turgid.

Factors affecting the rate of transpiration

• Humidity• Wind or air movement• Temperature • Light

Humidity

• What is humidity?- >Refers to the amount of water vapour that the air can hold.

Higher conc. of water vapour (100% saturated)

Lower conc. of water vapour

The drier the air, the steeper the concentration gradient, the faster the rate of transpiration.

Wilting

What happens to the leaves when they wilt?

How does wilting benefit the plant?

Rate of transpiration > rate of absorption of water