2.3 TRANSPORT SYSTEM IN PLANTS

TRANSPIRATIONTRANSPIRATION

How wilting occurs ?

Wilting occurs in non-woody plants when water loss through the stomata exceeds water absorption by the roots in the soil.

1.Cells in the plants lose their turgidity.

2.The plants droops or wilts

Advantages of wilting 1.The leaf surfaces are

removed from the direct rays of the sun.

2. The stomata close

So that , water loss from the plants will be reduced

What is transpiration?• The process of losing excess water

from a plant to atmosphere in the form of water vapour.

• These water vapour passes out of the leaf through tiny pores called stomata.

• More stomata are found on the lower epidermis of the leaf compared to the upper epidermis.

• Stoma – a tiny pore between a pair of cells known as guard cells ( kidney shaped & contain chloroplast).

• Guard cells – control the opening & closing of the stoma.

• Water vapour is expelled out from the stoma during transpiration.

•Gases like O2 & CO2 diffuse in & out of the leaf through the stoma.

stoma

1. A closed stoma

2. The stomata of a plant may be closed on a hot day to reduce the loss of water by transpiration.

1. An open stoma

2. Normally open during the day to allow the exchange of CO2 & O2 for photosynthesis.

3. Results in the loss of water by transpiration

FACTORS THAT AFFECT THE RATE OF TRANSPIRATION

1. Air movement (wind) – Transpiration is faster on windy days. Wind blows away water vapour from around the leaf, allowing better diffusion through stomata.

2. Humidity – Transpiration is faster when the air is dry, because diffusion of water vapour is quicker.

3. Temperature – Hot weather increases transpiration.

4. Light intensity – when the light intensity increases, the rate of transpiration also increases Generally transpiration is much reduced at night time because the stoma close in the dark.

Factors affect the rate of

transpiration

AIR MOVEMENT

HUMIDITY

TEMPERATURE

LIGHT INTENSITY

• On windy days, the wind blows away the water vapour surrounding the stomata

• Thus, more water is lost

• The rate of transpiration increases

Wind

• The lower the humidity, the higher the rate of transpiration

• When the air is humid, It contains a lot of water vapour. So less water vapour evaporates from the leaves.

Humidity

Temperature

• The higher the temperature, the more water vapour evaporates.

• Thus the rate of transpiration increases.

Light Intensity

• When the light intensity increases, the rate of transpiration also increases.

• The presence of light causes the stomata to be wide open and more water vapour is lost to the environment.

The Role of Transpiration in Transport

1. To get rid of excess water.

2. To cool the plant through evaporation at

the surface of the leaf and avoid heat

damage.3. To transport water and dissolved mineral

salts from the roots to the other parts of the

plant.

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3

The Role of water in Plant

Water is a raw material need for photosynthesis.

Water helps to maintain turgor pressure of cells. Without turgor pressure herbaceous plants wilt and eventually die.

During transpiration plants are at risk of dehydration because the air is drying medium. Although transpiration is essential it must be controlled. To do this leaves have the following features:

Cuticle – A waxy, waterproof covering that reduces water loss.

Guard cells – These can close the stomata, pores and so reduce transpirational water loss.

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Glossary1. Wilt = Layu

2. Pore = liang

3. Vapour = wap water vapour = wap air

4. Leaf (s) / leave (p) = daun

5. Turgid = segah

6. Evaporation = pengewapan / penyejatan

7. Light intensity = keamatan cahaya

8. Humidity = kelembapan

9. Environment = persekitaran

Q1. What is the process by which plants lose water via the leaves?

A Translocation

B Osmosis

C Filtration

D Transpiration

Q2. The transpiration rate of a well-watered plant will be greatest during a

A hot, dry and windy area

D cool, rainy day

C cool, dry and windless day

B hot, rainy and windy area

A I , II and III only

Q1. Transpiration plays the following role

I Cool the plant

II helps the plant make new cells

III protects the plant against disease

B I and III D I only

C II dan III only

Incorrect ,

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Yes ,

you are right

Incorrect ,

TRY again

Yes ,

you are right

The transpiration stream brings mineral salts into the plant from the soil.

Evaporation from the leaf surfaces helps to cool them and avoid heat damage.