Sub 1.8 - Transport of Organic Compound

7/28/2019 Sub 1.8 - Transport of Organic Compound

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PREPARED BY :

EN. MUHD FAZLI B. DOLLAH

BIOLOGY FORM 5 CHAPTER 1 : TRANSPORT


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LEARNING OUTCOMES

To state what translocation is.

To explain the importance of translocation in plants.

To describe the process of transpiration.

To explain the importance of transpiration.

To describe the pathway of water from the soil to the leaves.

To state external conditions affecting transpiration


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TRANSLOCATION The transport of dissolved organic food substances by the phloem.

IMPORTANCE OF TRANSLOCATION Ensures a plants survival

Organic food molecules can be transported :

To the growing regions in the plant for growth & development

To the plant cells for metabolism

Downwards from the leaves to the storage organs such as the roots


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TRANSPIRATION The loss of water as water vapour from a living plant to the

atmosphere due to evaporation.

Most of the water is lost through the stomataof leaves.

A small amount is lost through the cuticle or through thelenticels in woody stem


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Three main sitesof transpiration are :

STOMATA 90% of transpiration takes place through minute pores onleaves called stomata

CUTICLE 10% of transpiration takes place through the cuticle. Theamount of water loss varies with the thickness of the waxy cuticle

LENTICELS small pores in the stem which allow gaseous exchange. Onlysmall amounts of water are lost through the lenticels.


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Transpiration occurs mainly during the day when the stomata

are opened.

Heat from the sun causes the water to evaporate from the walls

of the spongy mesophyll cells.

The water vapour accumulates in the substomatal air chambers

before diffusing from the plant through the open stomata


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Water move into the mesophyll cells by osmosis

from the adjacent cell

Water flows from the xylem vessels along a chain of

cells to the outermost mesophyll cell.

Water is pulled through the xylem vessels from theroot to the leaves.


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The Importance of Transpiration Creates a transpirational pull that pulls water & dissolved

mineral ions from the root to the leaves.

Water supplied to the plant is used for photosynthesis & cell

metabolism. Mineral ions is used for cell activities & growth &

development of the plant.


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Water keeps the cell turgid give support to leaves & young

stems (herbaceous plants).

To keep the plant cool, an important effect particularly in hot

condition.

Water evaporates from the plants to the atmosphere faster than

it can be absorbed from the soil, it is withdrawn from the plant

cells flaccid leading to wilting


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PATHWAY OF WATER FROM THE SOIL TOTHE LEAVES

Water & mineral ions are absorbed by young roots with thin epidermis.(osmotic forces + active transport)

The pressure of root hairs increases the surface area for absorption.

The cell sap in the root hair cell contains sugars, amino acids, &

minerals more concentrated than the surrounding dilute soilsolution.


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Water diffuses into the root cells by osmosis.

The entry of water into the root cells dilutes its cell sap.

The cell sap of the adjacent cortex cell is now more

concentrated water molecules diffuse into the adjacent

root cell.


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The process continues & water is transported from one

root cell to another by osmosis.

In the cells of the endodermis, mineral ions are actively

pumped from these cells into the solution in the xylem

vessels in the root.

Solution in xylem more concentrated water enters

xylem by osmosis.


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This process creates an upward force called

ROOT PRESSURE.

Helps to push water in the xylem up to a

certain height in the plant.

Root pressure alone is insufficient to force the

water to the top part of a tall tree.

Need CAPILLARITY ACTION &

TRANSPIRATIONAL PULL.


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GUTTATION In small plants, root pressure can push

water all the way up the stem & out of

special pores called hydathodes at the

edges of leavesGuttation

Occurs on cool humid morning when the

air is too saturated for the water drops toevaporate from the leaves.


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THE EXTERNAL CONDITIONS AFFECTING THERATE OF TRANSPIRATION

The external factors that affect the rate of

evaporation.

Air movement

Temperature

Light intensity

Relative humidity


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AIR MOVEMENT Movement of air carries away water

molecules that have diffused from theleaves.

The faster the air movement (wind speed)

the greater the rate of transpiration. When there is little air movement/ in still

air, water vapour diffusing out of the leaf

accumulates around the stomata. Decreases the concentration gradient of

water, the transpiration rate reduces.


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TEMPERATURE A rise in temperature increases the kinetic energyof water

molecules & increase the rate of evaporation (transpiration).

Lowers the relative humidity of the air increase the rate of

transpiration.

Temperature low, kinetic energy of water molecules is decreased.

Relative humidity of the air is higher decrease the rate oftranspiration


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LIGHT INTENSITY

The light intensity increased, the rateof evaporation increases.

Light not effects evaporation butcauses the stomata to openincreasing water loss from the plant.

At night @ dark, stomata close

rate of transpiration decreases


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RELATIVE HUMIDITY The rate of evaporation depends on the difference in concentration of

water molecules in the sub-stomatal spaces & in the surrounding

atmosphere.

The lower the relative humidity of the surrounding atmosphere, the faster

will the water vapour escape from the stomata.

High relative humidity reduces water loss.


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ROOT PRESSURE If a stem is cut just above ground level, a considerable

amount of sap will exude from the cut stump, showing

that there is a force pushing water up the stem from the

roots.

Its ROOT PRESSURE The result of an active processin which energy from ATP is used.


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ROOT PRESSURE Root pressure alone is not strong enough to drive water to the

tops of tall trees at the speeds achieved during a normal growing

season.


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COHESION &ADHESION OF WATER COHESION = the force of attraction between the same

molecules

The cohesive forces between water molecules hold the continuous

columns of water together & when water transpires from the

leaf, the whole of the water column moves up the xylem vessels.


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ADHESION= the force of attraction between different molecules

Water molecules tend to adhere to the walls of the xylem vessels.

The adhesive forces can support a considerable mass of water.

Cohesion + adhesion = capillarity(the rise of water in a capillarytube).


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OPENING & CLOSING OFSTOMATA

Dicotyledonous leaves = on the lower surface

Monocotyledonous leaves = both the upper & lower surfaces.

Each stoma consists of a pair of kidney-shaped guard cells surrounding a

stomatal pore.


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A guard cell has a thinner elastic outer cell wall & a

thicker, less elastic inner cell wall. It has a nucleus,

cytoplasm & chloroplasts.

The opening & closing of the stomata in the leaf controls

the diffusion of CO2 & O2 into & out of a leaf as well as

the rate of transpiration.


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STOMATAL OPENING DAY : photosynthesis occurs & CO2 level is low in the leaf.

Potassium ions (K+) diffuse from surrounding epidermal subsidiary cells

into the guard cells.

In many plant species, starch stored in the guard cell is converted into

malate.

The accumulation of K+ & malate ions increase the osmotic pressure inthe guard cell.


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Water enters by osmosis from surrounding epidermal cells into

the guard cells

Two guard cells become turgid & curve outward & the stoma

opens.


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STOMATAL CLOSING NIGHT : no photosynthesis & CO2 level is high. Potassium

ions move out of the guard cells into the epidermal cells.

Malate ions are converted to starch. The osmotic pressure in

the guard cells decreases.

Water diffuses out to the surrounding epidermal cells by

osmosis.


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Guard cells become flaccid & stoma closes.

The stomata also close, when there is insufficient water supply &the transpiration rate is high.


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Rasulullah bersabda:

Yang menjadikan orang mukmin itu pemurah adalah

agamanya,yang menjadikan orang mukmin itu

mempunyai kehormatan adalah akalnya dan yang

menjadikan orang mukmin itu mulia adalah budi

pekertinya


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Sub 1.8 - Transport of Organic Compound

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