Form 5 Biology Chapter 1 Transport (d).docx

8/18/2019 Form 5 Biology Chapter 1 Transport (d).docx

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Form 5 Biology Chapter 1 Transport (d)

The Stem

1. The stem has an epidermal layer that helps maintain the shape of the stem.

a) In youn! plants, the epidermal cells secrete a waterproof cuticle.

b) In order plants, the epidermis may be absent, and is replaced by bar".

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The leaf

1. The leaf consists of a broad portion called the lamina (leaf blade) .

2. The blade is connected to the stem by a stal" called the petiole .

#. Inside the petiole are the vascular tissue of xylem and phloem that are

continuous with those in the stem, root and lamina.

&. The leaf blade contains leaf veins . 3ascular tissues are found in the leaf veins.

4. Xylem forms the upper part of a vascular bundle in the leaf while phloem forms

the lower part of the vascular bundle i!ure b)).

a) The xylem transports water and mineral salts to the leaves.

b) The phloem transports sucrose and other products of photosynthesis from the

leaves.

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The structure of xylem in relation to transport

. Xylem contains four types of cells:

a) Xylem vessels

b) Tracheids

c) ibres a type of sclerenchyma)

d) arenchyma

!. The parenchyma stores food substances while the fibres provide support to

the xylem .

". #ylem vessels and tracheids are water0conductin! cells.

$ow are xylem vessels and tracheids adapted to their functions%

1. Xylem vessels are elongated cells arranged end to end .

• The end walls of the xylem vessels are open so that the cells 5oin end to end to

form a lon! continuous hollow tube .

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• This arran!ement allows water to flow upwards continuously from one cell to

the next.

• 6urin! !rowth, the walls of the xylem vessels and tracheids are thic"ened with

lignin deposits, ma&ing them strong and hardy so that they do not collapse

under the tension created by the upward pull of water durin! transpiration.

• The li!nin also prevents the entry of food substances . 7ence, the cytoplasm

of these cells disinte!rates, leavin! a cavity in the centre of the cells. -s a

result, mature xylem vessels and tracheids are hollow and dead.

2. Tracheids are lon!er and have a smaller diameter compared to xylem vessels.

They are pointed at the ends. The end walls brea" down in the pits and this

allows water to pass from cell to cell .

8xplain the adaptation of xylem in performin! its function. * mar"s)

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The structure of phloem in relation to transport

1. hloem tissue is composed of four types of cells: sieve tubes, companion cells ,

parenchyma and fibres.

2. 9r!anic substances such as sucrose and amino acids are transported alon! the

sieve tubes of the phloem.

a) The sieve tube is a cylindrical column comprisin! lon! cells arran!ed end to

end.

b) The sieve tube is a living cell .

c) hen mature, it has no nucleus and its cytoplasm is pushed to the sides of the

cell.

d) The end walls of each cell are perforated by pores to form sieve plates . on!

strands of cytoplasm pass throu!h the pores in the sieve plates to allow

substances to pass from once cell to another.

e) 8ach sieve tube cell is "ept alive and its function is supported by one or more

companion cells.

#. - companion cell is a normal cell with a nucleus and a large number of

mitochondria , indicatin! that it has active metabolism.

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&. The function of the parenchyma is to store food substances while the function of

the fibres is to provide support.

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Sembilan !' "

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The Transport of rganic Substances and ater in Plants

Transport of organic substances in plants

1. $u!ars such as !lucose and fructose are produced by photosynthetic cell in the

leaves durin! the day time.2. These su!ars need to be transported as sucrose ) to the storage parts or growing

parts of the tree.

#. These su!ars may be converted into amino acids and lipids by the tar!et cells.

&. Translocation is the transport of dissolved or!anic substances by the phloem

from the leaves to the stora!e or!ans or from the stora!e or!ans to the !rowin!

re!ions.

4. 9r!anic substances are transported in the phloem by diffusion and active

transport which are assisted by the sieve tubes . Translocation occurs

downwards and upwards .

(. $tora!e or!ans such as roots, tubers, fruits or nodules store or!anic substance

in the form of starch, lipids and proteins .*. ;rowin! or!ans such as flowers, youn! shoots, root tips and leaves use these

substances for buildin! new cells and or!anic compounds.

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Transport of water in plants

1. In plants, water is lost throu!h a process called transpiration .

2. Transpiration is the loss of water vapour through evaporation from the

surface of plants .

#. 9nly 1< of this water is used by plant cell for photosynthesis and to remain

tur!id. The remainin! < evaporates from the leaves and is lost to the

atmosphere throu!h transpiration.

&. -bout /< of transpiration ta"es place throu!h the stomata of the leaves.

Transpiration also ta"es place throu!h the lenticels of woody stems.

4. Transpiration

a) 7elps in the absorption and transport of water and mineral ions from the

roots to the different parts of the plants.

b) roduces a cooling effect in plants

c) 7elp to supply water to all plant cells for metabolic processes

d) 7elps to prevent plants from wilting by maintainin! cell tur!idity.

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The movement of water from soil to leaves

*ovement of water through the roots

1. The cytoplasm of root hair cells is usually hypertonic to the surroundin! soil

water.2. This means that root cells have a higher concentration of solutes than the water

in the surroundin! soil

#. 7ence, water enters the root hair cells via osmosis .

&. The root hair cell is now hypotonic to the ad5acent cells

4. ater then diffuses into the ad5acent cells by osmosis.

(. In this way, water moves inwards from cell to cell in the cortex until eventually it

reaches the xylem vessels in the root.

*. The !radient of water concentration which exists across the cortex creates a

pushin! force that results in the inflow of water into the xylem.

. -t the same time, ions from the soil are actively secreted into the xylem and

this causes osmotic pressure to increase .. -s a result, water flows continuously into the xylem. This !enerates a pressure

"nown as root pressure .

1/. 'oot pressure results in an upward push of water and mineral ions into

the xylem of the stem.

11. 'oot pressure can be demonstrated when a stem is cut at soil level. -fter

some time, water can be seen flowin! out from the cut surface.

12. 'oot pressure causes an upward movement of water in plants but it is

insufficient to overcome the force of gravity to push water upward to the

maximum hei!hts of many trees. The water also moves too slowly to account for

the rapid transport of minerals from the roots to the leaves.

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". 7ence, the upward movement of water throu!h the xylem vessels in the

stems is helped by the adhesive and cohesive properties of the water

molecules.

• ater flows throu!h the cytoplasm, vacuoles and cell walls of the parenchyma

cells in the cortex until it reaches the endodermis.

• 9nce it reaches the endodermal cells, the water moves throu!h the cytoplasm and

vacuoles instead of the cell walls.

• This is because the endodermal cells have special features called the =asparian

strips which line the sides of the endodermal cells.

• $ince the =asparian strip is impermeable to water, this means that the water

movement throu!h the cell walls is bloc"ed.• Instead, the water moves from the cytoplasm and the vacuole in the endodermal

cells to the xylem vessels.

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+uttation

1. -t ni!ht, the roots of some small plants continue to actively transport ions and

water into the xylem.

2. This causes root pressure to increase.

#. >ecause the transpiration rate is low during the night , root pressure can push

water all the way up the stem and out of special pores called hydathodes at the

ed!es of the leaves.

&. This natural process is called !uttation.

4. ;uttation also occurs on cool humid mornin!s when the air is too saturated for

water droplets to evaporate from the leaves.

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*ovement of water from the leaves to the atmosphere

. The water on the external surfaces of the mesophyll cells evaporates, saturating

the air spaces in the mesophyll with water vapour.

2. The air in the atmosphere is less saturated .

#. This means that the concentration of water vapour in the atmosphere is lower

than the concentration of water vapour in the air spaces of the leaf.

&. 7ence, the water vapour in the air spaces evaporates and diffuses through the

stomata .

4. The movement of air carries water vapour away from the stomata.

(. The loss of water from a mesophyll cell ma"es the cell hypertonic to an ad5acent

cell.

*. ater from the ad5acent cell diffuses into mesophyll cell by osmosis. ater

continues to diffuse from the nei!hbourin! cells into the ad5acent cells.

. 8ventually, water is drawn from the xylem vessels in the veins.

. - tension or pulling force is thus created to pull water up the xylem vessels as a

result of the evaporation of water vapour from the mesophyll cells.

1/. This transpiration in the leaves forces the movement of water from the soil

up the stem.

11. The pullin! or suction force is "nown as transpirational pull.

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S-P !' "

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The external conditions that affect the rate of transpiration

1. The external conditions that affect the rate of transpiration are li!ht intensity,

relative humidity, temperature and air moment.

a) ight intensity

• -n increase in li!ht intensity increases the rate of transpiration.

• i!ht stimulates the openin! of the stomata.

• -s a result, the stomata open wider, 7ence, more water vapour evaporates

throu!h the stomata.

b) Temperature

• -n increase in temperature increases the rate of transpiration.

• -n increase in temperature increases the rate of evaporation of water from

the surfaces of the mesophyll cells. The rate of diffusion of water throu!h

the stomata also increases.

c) $umidity

• 7i!h humidity surroundin! the leaves reduces the evaporation of water

from the stomata.

• This causes transpiration to slow down.

• =onversely, a rise in temperature lowers the relative humidity of

surroundin! air, and this increases the rate of transpiration.

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d) /ir movement

• -s the water vapour that diffuses throu!h the stomata accumulates near the

leaf surface, a faster air movement helps to remove the water vapour.• -ir movement increases the concentration !radient between the water

vapour in the leaf and that outside the leaf. This increases the transpiration

rate.

• hen the air is still, the transpiration rate decreases or stops alto!ether.

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0xperiment 1 Studying the effect of air movement on the rate of

transpiration by using a potometer

Problem Statement

7ow does the movement of air movement of air affect the rate of transpirationA

2ariables

• Banipulated variable: -ir movement

• 'espondin! variable: The distance travelled by air bubble in 4 minutes

• =onstant variable: $urroundin! temperature, li!ht intensity, relative humidity,

the type and si%e of plant used and time

$ypothesis

The faster the movement of air, the !reater the rate of transpiration.

*aterials

- leafy shoot, 3aseline, a dry cloth and diluted eosin solution

/pparatus

- potometer, a bea"er, secateurs, a basin of water and a stopwatch

Techni3ue

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Beasure and record the distance travelled by an air bubble in a potometer in 4

minutes by usin! a !raduated capillary tube.

Procedure

1. - leafy shoot is chosen from a plant. The shoot is cut off with secateurs and thecut end is immersed immediately into a basin of water.

2. - ra%or blade is used to cut 1 cm of the bottom of the stem obliCuely under water.

#. The potometer is immersed in the water and moved around to remove all the air

bubbles. The tap of the reservoir is turned on to fill the !raduated capillary tube

with eosin solution.

&. The cut end of the stem is inserted carefully into the rubber cor" of the potometer

under water.

4. The reservoir tap is turned off before the apparatus is removed from the water so

that the !raduated capillary tube is full.

(. The apparatus is then set up as shown below.

*. The leaves and apparatus are wiped dry with a cloth.

. The part of the stem which passes throu!h the cor" of the potometer is smeared

with 3aseline to ensure there is no water lea"a!e and the apparatus is airti!ht.

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. The end of the capillary tube is lifted out of the bea"er for a short while and then

returned to the bea"er of water to introduce an air bubble into the tube.

1/. The air bubble is allowed to move to the hori%ontal !raduated section of the

capillary tube.

11. The potometer is then placed in an enclosed room with no air movement.

12. The shoot is allowed a few minutes to reach a steady state before any

readin!s are ta"en.

1#. The stopwatch is activated and the distance travelled by the air bubble for 4

minutes is recorded. The air bubble is not allowed to reach the end of the shoot.

1&. The air bubble is sent bac" to the ri!ht hand side of the capillary tube byturnin! on the reservoir tap. The experiment is repeated to obtain two more

readin!s.

14. $tep to 1& are repeated by placin! the potometer under a movin! fan.

1(. The distances travelled by the air bubble under both the conditions are

recorded in the followin! table.

4esult

=ondition 6istance travelled by the air bubble in 4 minutescm)

'ate oftranspiration cmminute 01)1st readin! 2 nd

readin!

#rd readin! -vera!e

indy ./ .( ./ .2

+on0windy &./ #. #. #.

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Dedah 2/1#

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The regulation of transpiration by stomata

The mechanism of the opening of a stoma

. 6urin! the day, li!ht stimulates photosynthesis in the guard cells .

!. They start synthesi%in! !lucose and !enerate the ener!y reCuired for activetransport.

". The !uard cells accumulate potassium ions from ad5acent cells throu!h active

transport.

. The !uard cells become hypertonic and water from the ad5acent cells enters the

!uard cells by osmosis .

5. -s a result, the !uard cells swell up and become tur!id.

6. $ince the i nner cell walls of the guard cells are thic&er than the outer walls ,

the !uard cells bend outward and the stoma opens. This is because the thinner

outer wall stretches more than the thic"er inner wall.

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The mechanism of the closing of a stoma

1. -t ni!ht, when photosynthesis does not ta"e place, potassium ions exit the !uard

cells and water also leaves the !uard cells by osmosis.

2. The !uard cells become flaccid and the stoma closes.

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Form 5 Biology Chapter 1 Transport (d).docx

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