Water and Organisms – –Water makes up between 60 - 95% of weight of organisms

Water and Organisms

– Water makes up between 60 - 95% of weight of organisms

Why is water important to organisms?

• Water is an important substance for maintaining life. Organisms cannot live without water.

• Water is a major cell component.

Importance of WaterImportance of Water It acts as:

solvent / reaction medium

medium for transport (e.g. blood)

metabolite (e.g. photosynthesis)

others like act as cooling agent (e.g.

sweating in hot weather)

as supporting agent (e.g. turgidity in

young plant)

for sexual reproduction

Water as a SolventWater as a Solvent dissolve most organic and

inorganic substances

needed for all biochemical reactions

remove excretory products such as urea and excess salts

in plants, root hairs absorb mineral salts present in soil in solution form

As a solvent• Inside an alveolus of the lung: O2 dissolves

in water film for diffusion

• Inside a leaf : CO2 dissolves in the water for diffusion to mesophyll cells

Water as a Water as a Medium of Medium of TransportTransport human blood plasma consists

mainly of water (90%)

carry many dissolved substances

like excretory wastes, hormones

and gases around the body

in plants, sugar and mineral salts

are transported in solution in

vascular bundles

As a medium for transport

• Human blood plasma consists mainly of water (90%)

Water as a MetaboliteWater as a Metabolite

in plants during photosynthesis,

carbohydrates are synthesized from

carbon dioxide and water

essential in hydrolytic reactions,

e.g. digestion

As a metabolite• photosynthesisphotosynthesis: water + carbon dioxide -->

carbohydrates + oxygen

To provide support and to keep shape

• water keeps plant cells turgid and provides a means of support in plants

For sexual reproduction

Sperms need water to swim to the eggs.

Ways of Gaining Water in Ways of Gaining Water in AnimalsAnimals

drinking

eating

from respiration occurs in cells

which the water formed is called

metabolic water

Ways of Losing Water in Ways of Losing Water in AnimalsAnimals

evaporation from body

surfaces

sweating

exhalation

urination

defaecation

Ways of losing water in plants:

Evaporation from body surface,

Transpiration.

Hypotonic, Hypertonic and Hypotonic, Hypertonic and Isotonic Solutions Isotonic Solutions

Hypotonic solution

- a solution has a higher water

potential than the reference

solution

Isotonic solution

- a solution has the same water

potential as the reference solution

Hypertonic solution

- solution has a lower water

potential than the reference

solution

• Osmosis in cells– water will enter the cells if the surrounding

fluid is hypotonic ( of higher water potential)– water will leave the cells if the surrounding

fluid is hypertonic ( of lower water potential)– No net water movement will occur when the

surrounding fluid is isotonic ( of equal water potential)

Water relations of organisms in the cells

OsmosisOsmosis

• The net movement of water from a region of higher water potential to a region of lower water potential through a selectively permeable membrane.

Osmosis in animal cellOsmosis in animal cell

Cell swells Cell swells and eventually burstand eventually burst Cell shrinksCell shrinks

WaterWaterConcentratedConcentratedsaline solutionsaline solution

• In animal cells– water enter, the cells swell burst – water leaves, the cells shrink.

What will happen when water enters and leaves cells?

Animal Cells Response to Animal Cells Response to Different SolutionsDifferent Solutions

tissue cells

water move in by

osmosisin hypotonic

solutio

n Cells swell and

burst

tissue cells

water move out by

osmosis

in hypertonic solution

cells shrink

Animal Cells Response to Animal Cells Response to Different SolutionsDifferent Solutions

Investigation of the Investigation of the Effects of Different Salt Effects of Different Salt Concentrations on Concentrations on

Red Blood Red Blood CellsCells

In A to E 5 test tubes, transfer a drop of the blood sample and different concentrations of sodium chloride solution to each of the test tubes.

Tube A: 0.2% sodium chloride solutionTube B: 0.6% sodium chloride solutionTube C: 0.8% sodium chloride solutionTube D: 1.6% sodium chloride solutionTube E: 3.2% sodium chloride solution

Withdraw a drop of liquid from each tube and examine it under the microscope.

Which of the five saline solutions most closely resembles the blood plasma in salt concentration ?Ans: The one in 0.8% saline solution is the most

resembles the blood plasma concentration.

red blood cell swells and is about to burst

red blood cell shrinks

red blood cell remains unchanged in appearance

In hypotonic saline solution

In hypertonic saline solution

In isotonic saline

solution

What evidence supports your answer ?Ans: Red blood cells in 0.8% saline solution

remain unchanged in appearance indicating that the solution is isotonic to blood plasma …






In isotonic saline

solution

What evidence supports your answer ?Ans: Fewer red blood cells can be observed in

0.6% saline solution and even fewer in 0.2% saline solution. This shows the two solution are hypotonic to the red blood cells …






In isotonic saline

solution

What evidence supports your answer ?Ans: The 1.6% and 3.2% saline solutions are

hypertonic to the red blood cells as a net movement of water out of the red blood cells into the saline solution is noticed.






In isotonic saline

solution

Importance of Importance of OsmoregulationOsmoregulation

osmoregulation is the maintenance of

correct levels of water in the body

any excessive gain or loss of water will

upset the proper functioning of cells in

an organism

metabolic reactions are affected and

organisms may die

The importance of The importance of osmoregulation for animal cellsosmoregulation for animal cells• Osmoregulation: The process of regulating

body fluid to keep it at a constant concentration.

• In mammals, osmoregulation is achieved by controlling the amount of water and the amount of dissolved substances in the blood.

• The major organ responsible are the kidneys

The kidney’s role in osmoregulation

Human Urinary SystemHuman Urinary System

kidney

ureter

urinary bladder

urethra

Human Urinary Human Urinary SystemSystem

aorta

renal arteryureter

surinary

bladder

left kidne

y

renal vein

right kidne

ysphincter muscle

urethra

Inferior vena cava

Human Urinary Human Urinary System System - Location of - Location of KidneysKidneysmammals have two kidneys which

are reddish and bean-shaped

they are situated at one on each side

of the vertebral column, below the

ribs and are not protected by any

part of the skeletal system

renal artery brings blood to kidney

while renal vein takes blood away

from it

Human Urinary Human Urinary System System - Ureter - Ureter

carries urine from kidney down to urinary bladder where stores urine temporarily

valves are present in ureter to prevent urine from flowing upwards

back flow of urine may happen when urinary bladder empties if valves do not close properly.This may lead to infection and damage of kidney

Human Urinary Human Urinary System System - Urinary Bladder - Urinary Bladder

a muscular bag situated towards the

bottom of the abdominal cavity

urethra is led out from it

on the top of urethra is surrounded

by ring of sphincter muscle

Urination Urination normally, the sphincter muscle is

tightly contracted, so no urination

occurs when urinary bladder is full

sphincter muscle relaxes +

wall of urinary bladder contracts

urination occurs

Adults can control the sphincter muscle but children cannot, it relaxes automatically when the bladder is full

Structure of Structure of Mammalian Mammalian

Kidney Kidney cortex

medulla

renal arteryrenal vein

ureterpelvis

nephron

Structure of Structure of Mammalian Kidney Mammalian Kidney

made up of three parts:

- a light outer

region - cortex

- a dark inner region - medulla

- a whitish central region leads to

ureter - pelvis

contain numerous tiny tubules called

nephrons

Structure of Nephron Structure of Nephron consists of a swollen end called

Bowman’s capsule which is connected

to a narrow

tubulethe tubule begins in

cortex

after leaving the capsule, it coils up

(proximal convoluted tubule)

It is then descends into the medulla and

becomes U-shaped (loop of Henle)

It goes back into the cortex and coils up

again (distal convoluted tubule)

Finally, it drains into a collecting duct

which goes through the medulla and

down to pelvis

NephronNephron

renal artery

renal veinproximal

convoluted tubule (first convolution)

capillaries around nephron

Loop of Henle

afferent arteriole

glomerulusefferent arteriole

collecting duct

distal convoluted

tubule (second convolution)

BowmaBowman’s n’s capsulecapsule

How Nephron is How Nephron is Connected with Blood Connected with Blood

VesselVesselrenal

arteryenters

Bowman’s

capsule

Glomerulus (a tightly

bunched group of

capillaries)

afferent arteriole

(branches from renal

artery)

efferent arteriole

(capillaries join up)…...

How Nephron is How Nephron is Connected with Blood Connected with Blood VesselVessel

leaves Bowman’s

capsule

capillaries (spread out

and wrap around

tubule)venule

(capillaries join

up)renal vein

Bowman’s capsule(with glomerulus)

afferent arteriole

efferent arteriole

loop of Henle

Structure Structure of of

NephronNephron

collecting duct

first & second convolution

venule

How Nephron Works ?How Nephron Works ?

By two ways, one is

ultrafiltration and the other

is reabsorption

CapillariesCapillariesIt is the smallest blood vesselsIt is the site of exchange (by diffusion)

Diffusion

Thin wall (one cell)

CO2 Waste

Nutrients

O2

UltrafiltrationUltrafiltration

diameter of tiny artery leading to

the glomerulus is larger than the

leaving one so increase in pressure

is resulted as blood tries to force its

way out of the smaller tube

the high hydrostatic pressure forces

small molecules through the walls of

capillaries and Bowman’s capsule

into the capsular space

fluid which filtered into the nephron is

glomerular filtrate

glomerular filtrate has the same

composition as that of blood except

that it hasn’t got red blood cells, blood

proteins & blood platelets

Reabsorption reabsorption is the process of

absorbing useful substances into

capillaries which wrapped around

tubule

as in glomerular filtrate, some

substances like glucose and amino

acid are useful to human so they are

absorbed back while fluid travels

along the tubule

those urea which remains in the fluid

pass the whole nephron and finally

drains into collecting duct which

leads to pelvis and form urine

urine contains mostly water, with

urea and excess mineral salts

reabsorption of glucose, amino acids

and some salts begins in the first

convolution and finished when the fluid

reaches loop of Henle

useful substances are reabsorbed by

diffusion down the concentration

gradient and active transport against

concentration gradient in collecting duct, water is mainly

reabsorbed by osmosis but the first

convolution actually reabsorbs the

largest amount of water

Functions of KidneyFunctions of Kidney

kidney mainly has three functions:

osmoregulation

removal of excess salt

excretion

Functions of Kidney Functions of Kidney - -

OsmoregulationOsmoregulationdrink a lot of

water

blood becomes

diluted

More dilute urine

produce

small proportion of

water is reabsorbed

Amount of water in blood:

CONSTANT

after sweating

blood becomes

concentratedlarge proportion of

water is reabsorbed

Less concentrate urine produce

Amount of water in blood:

CONSTANT

Functions of Kidney Functions of Kidney - -

OsmoregulationOsmoregulation

Functions of Kidney Functions of Kidney - Removal of - Removal of

Excess SaltExcess Saltafter eating a salty meal

salt enters blood, concentration of salt

in blood increase

volume of urine increase

concentration of urine is higher

man feels thirsty drink water

Functions of Kidney Functions of Kidney - Excretion - Excretion

protein cannot be stored in human

body, excess protein are broken

down in liver

removing of amino groups from

amino acids is called deamination

amino groups are incorporated into

urea molecules and then excreted in

urine

Kidney Failure and Kidney Failure and Artificial Kidney Artificial Kidney

some kidney diseases can lead to

kidney failure which kidney can no

longer function properly

toxic substances will accumulate in

blood and patient will die

artificial kidney is a bulky machine

attached to patient which is used to

filter and clean patient’s blood

artificial kidney make use of the

principle of dialysis. It has a filter

made of cellophane which acts as a

selectively permeable membrane

along one side of the membrane is

the patient’s blood while the other

side is dialysis fluid which has the

same contain as plasma except urea

only urea diffuses from patient’s

blood into dialysis fluid through

cellophane filter

blood without urea will return to

patient through his vein

dialysis fluid flows in direction

opposite to that of blood flow to

increase the efficiency of diffusion of

urea into dialysis fluid other than using artificial kidney,

kidney transplant is another possible

method but only few people are

willing to donate their kidneys after

death

Excretion in HumanExcretion in Human metabolism are reactions take place

inside cells of an organism

most of the by-products of

metabolism are toxic and should be

removed once they are produced by

excretion

there are four major excretory

organs in human body: Lungs,

Kidneys, Liver and Skin

Excretory Organs - Excretory Organs - LungsLungs excrete carbon dioxide which is

produced by cells during respiration

and is carried by blood to lungs

carbon dioxide diffuses out of the

blood capillaries surrounding the

lungs and passes into the air sac

it is excreted when people breathe

out. Water is lost during respiration,

too

Excretory Organs - Excretory Organs - KidneysKidneys

deamination (break down of excess

amino acids) in liver forms urea and

uric acid

urea and uric acid are called

nitrogenous wastes

the wastes are carried by blood to

kidneys which excrete them from the

body in form of urine

Excretory Organs - Excretory Organs - LiverLiver old red blood cells are destroyed in

liver and haemoglobin are

released

haemoglobin will turned into bile

and excreted with bile into small

intestine

finally, haemoglobin will expel with

faeces and leave the body

Excretory Organs - SkinExcretory Organs - Skin skin is the largest excretory organ

in human body

it carries out its function through

sweating

sweat contains water, salts and

urea, and sweating can excrete

these substances from the body

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

Plasmolysed cellsPlasmolysed cells

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

• In plant cells– water enter, the cells become turgid.– water leaves, the cells become less turgid

flaccid plasmolyzed

What will happen when water enters and leaves cells?

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.

Plasmolysis of red onion epidermal cells (400X)Plasmolysis of red onion epidermal cells (400X)

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.


bulb forceps

filter paper

epidermis

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

become turgid.


bulb forceps

filter paper

epidermis

Fully turgid red onion epidermal cells (400X)Fully turgid red onion epidermal cells (400X)

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.


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

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

TranspirationTranspiration an evaporation of water in form of

water vapour from the surface of

plant to atmosphere

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

it mainly takes place in leaves

where there

are some openings called stomata

How does transpiration take place?

How water lost from leaves causes transpiration and how the transpiration pull is formed.

How transpiration occurs

1. Water evaporates into sub-stomatal air space

2. Water diffuses out through stoma

How transpiration pull is formed

1. Water is lost from the cell surface, this is replaced by water in the cell. Each cell then pulls water from its neighbouring cells

( through cell wall through cytoplasm

and vacuoles)

2. Eventually, water is pulled from the xylem, pulling water up the plant.

Substomatal air space with higher concentration of water

Lower concentration of water vapour

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

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


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


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


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 stoma 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 through 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.


sellotape

Explain your answer.

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


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.


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 Structure of RootRoot

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

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

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

~ ~ End End ~~

Documents

Water and Organisms – –Water makes up between 60 - 95% of weight of organisms