transportinplantstransportinplantstransportinplantstranspo ... · pdf filexylem and phloem....

transportinplantstransportinplantstransportinplantstransportinplantstransportinplantstransportinplantstransportinplantstransportinplantstransportinplantstransportin


[transport] in plants



learningOBJECTIVES

• Identify the main parts of the transport system in plants –

xylem and phloem.

• Explain the structural adaptation of the xylem (ie lumen,

lignin and dead cells)

• Explain the function of the phloem and the structure. (not

in detail)

• Identify the arrangement of vascular tissues in the leaf

and stem.



learningOBJECTIVES

• Describe the process of absorption of water and mineral

salts in the plant through the roots.

• Briefly explain transpiration in regards to movement of

water up the plant.



transportinPLANTS

transport

watermanufactured

food

osmosiscapillary

action

transpirational

pulltranslocation

root

hair

cells

xylem xylem phloem

transport

watermanufactured

food

osmosiscapillary

action

transpirational

pulltranslocation

root

hair

cells

xylem xylem phloem



transportVESSELS

In flowering plants, the transport tissue consists of the

xylem and the phloem.



xylemVESSELS

• The xylem is a long hollow tube-like structure that

conducts water and mineral salts up the stem.

• It is also able to provide mechanical support for the

plant.



xylemFORMATION

Cells grow

together

end to end

Cross-walls

disintegrate

Lignin

deposits to

strengthen

the xylem vessel



xylemFUNCTIONS

Function Adaptation

Conducting water and

dissolved mineral salts from

the roots to the stems and

leaves

• Continuous long, hollow

tube

• Empty lumen without

protoplasm or cross-walls

Providing mechanical

support for the plant

• Walls are thickened with

lignin, which is a hard and

rigid substance



phloemVESSELS

Made up of sieve tubes and companion cells

Transports food manufactured in the leaves to other

parts of the plant by translocation.



vascularBUNDLES

• The xylem and the phloem group together to

form a vascular bundle (literally a bundle of

vessels)

• The distribution of the vascular bundles differ in

different parts of the plant



relativeDISTRIBUTION

Root

Stem

Leaf



waterTRANSPORT

Root

• Sap in root hair cell (A) has lower water potential than

soil solution

• Water molecules enters root hair cell from soil solution

by osmosis



waterTRANSPORT

Root

• The water potential in the sap of the root hair cell is

now higher than that in the adjacent cell (B)

• Water molecules thus move from root hair cell (A) to

adjacent cell (B) by osmosis

•This process continues from cell B to cell E until water

reaches the xylem



waterTRANSPORT

Root

• When the concentration of the ions in the root hair cell

sap is lower than that in the soil solution, the ions move

into the cell by diffusion.



waterTRANSPORT



Root Hair Cell

These are enlarged images of a root hair cell. Analyse

and discuss why root hair cells absorb water efficiently.



Root Hair Cell Adaptations

Structural Adaptation Function

Root hair cell is long

and narrow

Increases surface area

to volume ratio for

faster absorption

Cell membrane

prevents leaking of cell

sap

Maintains low water

potential in cell for

osmosis

Living cell Provides energy from

respiration for active

transport of ions



Transpiration • Only a small portion of

water absorbed by plants

is used

• A large portion of water

that is absorbed is lost by

evaporation through the

stomata of the leaves

• This process of water

vapour being lost mainly

through the stomata is

called transpiration



Transpiration •Transpiration is important

because it

•cools the leaf

•transports water from

the roots to the leaves

for photosynthesis

•transports mineral

salts from the roots to

the leaves



Transpiration • In the stem, water

moves up the xylem

primarily via

transpirational pull

•The evaporation of

water from the leaves

removes water from the

xylem vessels

•This creates a suction

force which pulls water

up the xylem vessels

•This suction force due to

transpiration is known as

transpirational pull

Stem

Root

Xylem

Leaf

Water escapes from

leaf by evaporation

Water is pulled from the

xylem vessel into the

leaves

This creates a suction

force in the xylem vessel

The column of water in the

xylem is pulled upwards to

replace the water lost

Water from the xylem

vessels in roots is pulled

out to replace the water

column in the stem xylem

vessels



Transpiration •The rate of transpiration

is higher when

•the temperature is

high

•the humidity (amount

of water vapour in the

air) is low

•there is wind to blow

away the humidity

shell



In summary,

•Water enters a plant

by osmosis in the roots

•Water moves up the

stem by transpirational

pull in the xylem

•Water vapour leaves

a plant by

transpiration

(evaporation) in the

leaves

Transpirational

Pull



Show the movement of water molecules in the

figure below when transpiration occurs:

transportinplantstransportinplantstransportinplantstranspo ... · pdf filexylem and phloem....

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