Plants CellPlants Cell

cell wall cytoplasm

cell membrane

vacuole

cell wall freely permeable so it lets

most of molecules to go

through

osmosis does not occur

cell membrane

beneath cell wall

selectively permeable

Water Relations of Plant Water Relations of Plant - Turgor - Turgor

plant cell put in distilled water

plant cell contains solutes

water potential lower than pure

water

net water movement into the cell by osmosis

vacuole and cytoplasm swells

cell wall is rigid and strong, cell bursting is

prevented

turgor is present because: turgor

hydrostatic pressure develops inside the cell

cytoplasm is pushed against cell wall

tendency of the cell to give out water increases

water potential increases When water potential of cell

= water potential of waterTurgor occur (cell cannot take in

any water) the cell is turgid

Water Relations of Plant Water Relations of Plant - Plasmolysis - Plasmolysis

plant cell in concentrated

solution

net water movement out of the cell by

osmosis

vacuole and cytoplasm shrink

cytoplasm is torn away from cell wall

flaccid

The whole phenomenon is called plasmolysis and

cell is plasmolysed

Turgidity of Plant CellsTurgidity of Plant Cells

turgid cell(in hypotonic sol.)

plasmolysed cell(in hypertonic sol)

cell wall

cytoplasm

vacuoleenlarged

solution here is the same as the external solution

cell membrane separated from cell wall vacuole

very small

Cells in Different Cells in Different SolutionsSolutions

Solution Concentration

animal cells(e.g. RBC)

plant cells

hypotonic hypertonic

haemolysis

turgid

shrink

plasmolysis(cell is flaccid)

To Investigate the Effects To Investigate the Effects of Sucrose Solution and of Sucrose Solution and Tap Water on Epidermal Tap Water on Epidermal Cells of Red Onion Scale Cells of Red Onion Scale Leaf or Leaf or Rhoeo Discolor Rhoeo Discolor

LeafLeaf

fleshy scale leaf of red onion

bulb forceps

filter paper

epidermis

What do you observe when the epidermal strip is placed in the concentrated sucrose solution ?Ans: The coloured cytoplasm shrinks.

Explain your observation.Ans: When the piece of epidermis is placed in

concentrated solution, cells lose water by osmosis as the cells have a higher water potential than the sugar solution.

fleshy scale leaf of red onion

bulb forceps

filter paper

epidermis

What has happened to the cells in tap water ?Ans: The coloured cytoplasm swells and cells

become turgid.

fleshy scale leaf of red onion

bulb forceps

filter paper

epidermis

Explain your answer.Ans: When the piece of epidermis is placed in

tap water, cells gain water by osmosis as the surrounding tap water has a higher water potential than the cells.

fleshy scale leaf of red onion

bulb forceps

filter paper

epidermis

Effects of Effects of Concentrated Concentrated

Sucrose Solution and Sucrose Solution and Tap Water on Raw Tap Water on Raw

Potato StripsPotato Strips

What has happened to the potato strips ?Ans: Potato strip A increases in both weight

and length while potato strip B decreases in both weight and length.

petri dish

water20% surcose solution

raw potato strips

A B

Explain your answer.Ans: For potato strip A, it gains water by

osmosis so both of its weight and length increase but for potato strip B, it loses water by osmosis so its weight and length decrease.

petri dish

water20% surcose solution

raw potato strips

A B

TranspirationTranspiration

an evaporation of water in form of

water vapour from the surface of

plant to atmosphere

it mainly takes place in leaves

where there are some openings

called stomata

more water loses from the lower

surface of the leaf than the upper

one as more stomata present on

the lower surface it also happens in lenticels and

cuticle

Transpiration in LeavesTranspiration in Leaves

a thin film of moisture is covered

with each mesophyll cell

the moisture evaporates from

mesophyll cells into intercellular

spaces and diffuses out of stomata

into atmosphere

water potential of cells losing water

decreases so they draw water from

deeper cells in the leaf by osmosis.

This in turn, draws water in xylem

vessels into leaf to replace the loss

Experiment to Show Experiment to Show that Water is Given that Water is Given

Off During Off During TranspirationTranspiration

What do you observe in the polythene bags ?Ans: The one enclosing plant A becomes

misty while nothing can be noticed in the one enclosing plant B.

polythene bag

A BB

How can you show that it is water ?Ans: We can use anhydrous cobalt chloride

paper to test it. It will turn the paper from blue to pink or we can use anhydrous copper sulphate. Water will turn it from white to blue.

polythene bag

A BB

What conclusions can you draw from the results ?Ans: We can conclude that a leafy shoot gives

off water during transpiration.

polythene bag

A BB

To Measure the Rate To Measure the Rate of Transpiration by of Transpiration by

Using a Simple Using a Simple PotometerPotometer

What are the environmental conditions under which transpiration occurs quickly ?Ans: It is under dry, warm and windy

conditions.

air/water meniscus

graduated capillary tube

reservoir

leafy shoot

tap

Does this apparatus give you an accurate measurement of the rate of transpiration ?Ans: No. It is because it only measures the rate

of water uptake by the leafy shoot … Ans: In addition, it is too small to fit the whole

root system and this may affect the rate of water uptake.

air/water meniscus

graduated capillary tube

reservoir

leafy shoot

tap

Sometimes you may introduce an air bubble into the capillary tube. State the advantage of this method.Ans: Movement of the air bubble is easier to

observe than that of air/water meniscus.

air/water meniscus

graduated capillary tube

reservoir

leafy shoot

tap

Sometimes you may introduce an air bubble into the capillary tube. State the disadvantage of this method.Ans: Friction between the capillary wall and

the bubble may affect the movement of bubble.

air/water meniscus

graduated capillary tube

reservoir

leafy shoot

tap

Environmental Factors Environmental Factors Affecting the Rate of Affecting the Rate of

TranspirationTranspirationThere are five environmental factors

which affect the rate of transpiration.

They are:

(I) Light Intensity

(II) Temperature

(III) Humidity

(IV) Wind Speed

(V) Water Supply

Light IntensityLight Intensity

stomata open in light, so plants can

get enough carbon dioxide from

atmosphere for carrying out

photosynthesis

light will increase temperature so

increases the rate of transpiration

TemperatureTemperature

temperatur

erelative humidity of air outside

leaf

rate of evaporation of

water from mesophyll cells

rate of diffusion of water vapour from intercellular space in leaf to outside

HumidityHumidity

humidity

outside

rate of

transpiration

it makes the diffusion gradient of

water vapour from moist

intercellular space of a leaf to the

external atmosphere steeper

Wind Speed & Water SupplyWind Speed & Water Supplywind

blows

water vapour around

the leaf sweeps

awaytranspiration

rateINCREASES

lack of water

soil dries, plant wilts

and stomata

close

transpiration

rateDECREAS

ES

StomataStomata stomata are pores in the epidermis

which gaseous exchange takes

place during photosynthesis (or

respiration)

find mainly in lower epidermis of

dicotyledonous leaves and stems

Guard CellsGuard Cells each stomata is surrounded

by two guard cells

which possess

chloroplasts

its inner wall is thicker than

outer wall

it is kidney-shaped

guard cell

stoma

Distribution of Stomata Distribution of Stomata in Leaves in Leaves

normal plants

mainly on the lower surface of leaves

floating plants

mainly on the upper surface

leaves may also have air sacs to keep them afloat so they can carry out gaseous exchange

submerged aquatic plants

no stomata (not required since gaseous

exchange can be carried out by

diffusion though the leave surface)

no cuticle (the primary function of

cuticle is to prevent excess water

transpiration which is not present in

aquatic plants)

Experiment to Experiment to Investigate Stomatal Investigate Stomatal Distribution in a Leaf Distribution in a Leaf

by Using Cobalt by Using Cobalt Chloride PaperChloride Paper

cobalt chloride paper

sellotape

Obtain a potted plant. Using sellotape stick a small squareof anhydrous cobalt chloride paper onto each surface of a leaf of the plant. Record the time taken for the cobalt chloride paper on each surface of the leaf to turn pink.

Which piece of cobalt chloride paper turns pink first? Ans: The piece of cobalt chloride paper

attached to the lower epidermis of the leaf turns pink first.

cobalt chloride paper

sellotape

Explain your answer.

Ans: It is because more stomata are present in the lower epidermis.

cobalt chloride paper

sellotape

Why is it important to handle cobalt chloride paper with forceps? Ans: It is because there is moisture on human

fingers so the paper may turn pink before sticking onto the surfaces of leaves.

cobalt chloride paper

sellotape

To Observe the To Observe the Release of Air Release of Air

Bubbles from Leaves Bubbles from Leaves placed in Hot Waterplaced in Hot Water

Which surface has more air bubbles coming off?Ans: There are more air bubbles appear on

the lower surface of the leaf.

forceps

hot water

leaf

Where does the air come from?Ans: It is in the air spaces between the

mesophyll cells in leaf which expands on heating and passes out through stomata of the leaf.

forceps

hot water

leaf

What does the result show?Ans: The result shows that more stomata are

present on the lower epidermis of the leaf.

forceps

hot water

leaf

Structure of RootStructure of RootRoot Cap

a protective layer at the very tip of root

to protect the delicate cells of root from being damaged as the root grows down through the soil

Epidermis

cover the rest of root

absence of cuticle so water can enter

Growing Point

behind root cap

cells are capable of active division

Region of Elongation

more elongated than cells in growing

point and have large vacuoles

Region of Root Hair

little way behind root tip

root hair are thin-walled extension

of epidermal cells of root

increase surface area for uptake of

water and mineral salts

Vascular Tissue

further from the tip of root

contain xylem and phloem

xylem transport absorbed water to

every part of plant

Absorption of Soil Water Absorption of Soil Water by Root Hairs by Root Hairs

soil water is a dilute solution of salts

which is more dilute than cell sap and

cytoplasm in root hair

water will pass by osmosis into root hair

through cell wall and cell membrane

transpiration occurs in leaves so water is continuously removed

from the plant

flow of water through plant: transpiration stream tension produced to draw up water:

transpiration pull

reduction of effective pressure at the top of xylem vessel

water flows upwards from roots continuously

Transverse Transport Transverse Transport of Water to of Water to

Xylem Xylem epidermal cells gain water by

osmosis

NOTE: some water may travel inwards along or between cell walls without entering cytoplasm or vacuole of each cortical cell

cytoplasm and cell sap have higher water

potential than neighbouring cortical cells

water travels by osmosis

inwards from cell to cell

~ ~ End End ~~

Functions of Transport Functions of Transport System System

in Angiospermsin Angiosperms carries water and mineral salts

from the roots to the

mesophyll cells of the leaves for

photosynthesis by xylem

xylem and phloem are together

called vascular bundles

carries foods made in the leaves

by photosynthesis to other cells

of the plant by phloem

Arrangement of Conducting Arrangement of Conducting Tissues in AngiospermsTissues in Angiosperms

in root

- close to central position in which

xylem is found in the centre in a

star-like arrangement and

phloem lies between the radial arms

of the xylem

in stem

- close to the epidermis where the

conducting tissues are arranged

in a ring near the outside edge, with

phloem lying outside and

xylem inside

- to resist the strong pulling force

from the wind blowing the shoot

- to resist the strong bending force

produced by wind

in leaves

- vascular bundles are often called

veins in which xylem lies

above the phloem

XylemXylem consists of long tubular vessels

each vessel is made up of many dead cells

which are hollow and joined end to end

xylem vessels run from the root,

through the stem and finally branch

out into every leaf of the plant

the end walls of the cells have disappeared

and so a long and open tube is formed

xylem vessels contain no cytoplasm

or nuclei

to prevent xylem from collapsing, they

have thick cell walls made of cellulose

and strengthened by rings of a

woody substance called lignin

PhloemPhloem made up of tube cells called sieve tubes

which are living cells joined end to end by

perforated horizontal walls called sieve plate

the perforations allow dissolved substances to

flow through them so food made in the leaves

can be carried to other parts of the plant

sieve tubes contain cytoplasm but

no nuclei and they do not

have lignin in their cell walls

each sieve tube has a companion cell

next to it. The companion cell does

have a nucleus and contain many

other organelles

Comparison between Comparison between Sieve Tubes and Sieve Tubes and

VesselsVesselsSieve Tubes

Vessels

living cells dead cells

smaller diameter

larger diameter

walls relatively thin, flexible, composed of

cellulose

walls relatively thick, hard,

strengthened by rings of lignin

Comparison between Comparison between Sieve Tubes and Sieve Tubes and

VesselsVesselsSieve Tubes

Vessels

the lumens of mature cells are

filled with cytoplasm

the lumens of mature cells are empty

end walls of adjacent sieve

tubes from sieve plates

end walls of adjacent vessels

cells break down

Upward Transportation of Water Upward Transportation of Water and Mineral Saltsand Mineral Salts

• root pressure

• capillarity

• by transpiration pull

Transpiration PullTranspiration Pull most of the water rising up in the xylem of the stem is pulled up by this

during transpiration, water is continually removed from the top of xylem

vessels to supply cells in the leaves so pressure at the top of xylem

reduces and water flows up

Transport of Organic Transport of Organic NutrientsNutrients

translocation is the process of

transporting the manufactured

carbohydrates in photosynthesis via

phloem from the leaves to other parts

of the plant

~ ~ EndEnd ~~