Transcript Water & 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 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 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 Medium
of Transport
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 Metabolite
in plants during photosynthesis,
carbohydrates are synthesized from carbon
dioxide and water
essential in hydrolytic reactions,
e.g. digestion
As a metabolite
• photosynthesis: 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 Animals
 drinking
 eating
 from respiration occurs in cells which the
water formed is called metabolic water
Ways of Losing Water in Animals
 evaporation from body surfaces
 sweating
 exhalation
 urination
 defaecation
Ways of losing water in plants:
Evaporation from body surface,
Transpiration.
Hypotonic, Hypertonic and
Isotonic Solutions
 Hypotonic solution
- a solution has a higher water potential
than the reference solution
 Hypertonic solution
- solution has a lower water potential than
the reference solution
Isotonic solution
- a solution has the same water potential as the
reference solution
Water relations of organisms in
the cells
• 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)
Osmosis
• 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 cell
Water
Cell swells
and eventually burst
Concentrated
saline solution
Cell shrinks
What will happen when water enters
and leaves cells?
• In animal cells
– water enter, the cells swell burst
– water leaves, the cells shrink.
Animal Cells Response to Different
Solutions
water move in
by osmosis
tissue
cells
Cells swell
and burst
Animal Cells Response to Different
Solutions
tissue
cells
water move out
by osmosis
cells
shrink
Investigation of the Effects
of Different Salt
Concentrations on
Red Blood Cells
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 solution
Tube B: 0.6% sodium chloride solution
Tube C: 0.8% sodium chloride solution
Tube D: 1.6% sodium chloride solution
Tube E: 3.2% sodium chloride solution
Withdraw a drop of liquid from each tube and examine it
under the microscope.
red blood cell swells
and is about to burst
In hypotonic
saline solution
red blood cell
shrinks
In hypertonic
saline solution
red blood cell remains
unchanged in appearance
In isotonic
saline solution
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
In hypotonic
saline solution
red blood cell
shrinks
In hypertonic
saline solution
red blood cell remains
unchanged in appearance
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 …
red blood cell swells
and is about to burst
In hypotonic
saline solution
red blood cell
shrinks
In hypertonic
saline solution
red blood cell remains
unchanged in appearance
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 …
red blood cell swells
and is about to burst
In hypotonic
saline solution
red blood cell
shrinks
In hypertonic
saline solution
red blood cell remains
unchanged in appearance
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.
Importance of
Osmoregulation
 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
osmoregulation 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 System
kidney
ureter
urinary
bladder
urethra
Inferior
vena cava
renal
vein
right
kidney
sphincter
muscle
aorta
left
kidney
renal
artery
ureters
urinary
bladder
urethra
Human Urinary System
Human Urinary System
- Location of Kidneys
 mammals 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 System
- 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 System
- 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
 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
Mammalian Kidney
cortex
medulla
nephron
renal artery
renal vein
ureter
pelvis
Structure of
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
 consists of a swollen end called Bowman’s
capsule which is connected
to a narrow tubule
the 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
Bowman’s
capsule
Nephron
glomerulus
afferent
arteriole
renal artery
renal vein
proximal
convoluted tubule
(first convolution)
capillaries
around nephron
efferent
arteriole
distal convoluted
tubule (second
convolution)
collecting
duct
Loop of
Henle
How Nephron is Connected
with Blood Vessel
afferent arteriole
renal artery
(branches from renal artery)
enters Bowman’s
Glomerulus (a tightly bunched
capsule
group of capillaries)
efferent arteriole
(capillaries join up)
…...
How Nephron is Connected
with Blood Vessel
leaves Bowman’s
capsule
capillaries (spread out
and wrap around tubule)
venule
(capillaries join up)
renal vein
Structure of
Nephron
Bowman’s capsule
(with glomerulus)
afferent arteriole
efferent arteriole
loop of Henle
collecting duct
venule
first & second
convolution
How Nephron Works ?
By two ways, one is ultrafiltration
and the other is reabsorption
Capillaries
It is the smallest blood vessels
It is the site of exchange (by diffusion)
Thin wall (one cell)
Nutrients
Diffusion
O2
CO2
Waste
Ultrafiltration
 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 Kidney
kidney mainly has three functions:
 osmoregulation
 removal of excess salt
 excretion
Functions of Kidney
- Osmoregulation
drink a lot of water
blood becomes diluted
small proportion of water
is reabsorbed
More dilute urine
produce
Amount of water in blood: CONSTANT
Functions of Kidney
- Osmoregulation
after sweating
blood becomes concentrated
large proportion of water
is reabsorbed
Less concentrate urine
produce
Amount of water in blood: CONSTANT
Functions of Kidney
- Removal of Excess Salt
after eating a salty meal
salt enters blood,
concentration of salt in
blood increase
man feels thirsty
concentration of
urine is higher
volume of
urine increase
drink water
Functions of Kidney
- 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
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 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 - Lungs
 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 - Kidneys
 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 - Liver
 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 - 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 Cell
cell wall
cytoplasm
vacuole
cell
membrane
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
- Turgor
plant cell put in distilled water
net water movement into the cell by osmosis
plant cell
contains solutes
water potential lower
than pure water
vacuole and cytoplasm swells

cytoplasm is pushed against cell wall
turgor
turgor is present because:
cell wall is rigid and strong,
cell bursting is prevented
hydrostatic pressure
develops inside the cell
tendency of the cell to give
out water increases
water potential increases
When water potential of cell
= water potential of water
Turgor occur (cell cannot take in
any water) the cell is turgid
Water Relations of Plant
- Plasmolysis
plant cell in
concentrated solution
net water movement out
of the cell by osmosis
vacuole and
cytoplasm shrink
The whole phenomenon
is called plasmolysis and
cell is plasmolysed
flaccid
cytoplasm is torn away
from cell wall
Plasmolysed cells
Turgidity of Plant Cells
vacuole
enlarged
cell membrane separated
cell wall from cell wall
vacuole
cytoplasm
very small
plasmolysed cell
turgid cell
(in hypertonic sol)
(in hypotonic sol.)
solution here is the same
as the external solution
What will happen when water enters and
leaves cells?
• In plant cells
– water enter, the cells become turgid.
– water leaves, the cells become less turgid
flaccid plasmolyzed
Cells in Different Solutions
Solution Concentration
hypotonic
hypertonic
animal cells
haemolysis
(e.g. RBC)
plant cells
turgid
shrink
plasmolysis
(cell is flaccid)
To Investigate the Effects of
Sucrose Solution and Tap Water
on Epidermal Cells of Red Onion
Scale Leaf or Rhoeo Discolor
Leaf
fleshy scale leaf of
red onion bulb
filter paper
forceps
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)
fleshy scale leaf of
red onion bulb
filter paper
forceps
epidermis
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
filter paper
forceps
epidermis
What has happened to the cells in tap water ?
Ans: The coloured cytoplasm swells and cells become
turgid.
Fully turgid red onion epidermal cells (400X)
fleshy scale leaf of
red onion bulb
filter paper
forceps
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.
Effects of Concentrated
Sucrose Solution and Tap
Water on Raw Potato Strips
petri dish
20% surcose solution
water
raw potato
strips
A
B
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
20% surcose solution
water
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.
Experiment to Show that
Water is Given Off During
Transpiration
polythene
bag
A
B
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
B
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
B
What conclusions can you draw from the results ?
Ans: We can conclude that a leafy shoot gives off water
during transpiration.
Transpiration
 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
How does transpiration take
place?
How transpiration pull is
formed
How transpiration occurs
2. Eventually, water is pulled
from the xylem, pulling water
up the plant.
1. Water evaporates into
sub-stomatal air space
2. Water diffuses out
through stoma
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
(
Lower concentration of
water vapour
through cell wall
through cytoplasm
Substomatal air space with and vacuoles)
higher concentration of water
How water lost from leaves causes transpiration and how the
transpiration pull is formed.
Transpiration 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 of
Transpiration by Using a
Simple Potometer
graduated
capillary tube
leafy shoot
reservoir
tap
air/water
meniscus
What are the environmental conditions under which
transpiration occurs quickly ?
Ans: It is under dry, warm and windy conditions.
graduated
capillary tube
leafy shoot
reservoir
tap
air/water
meniscus
Does this apparatus give you an accurate measurement of
the rate of transpiration ?
Ans: In
No.addition,
It is because
it is too
it only
small
measures
to fit thethe
whole
rateroot
of water
system
uptake
and
thisby
may
theaffect
leafy shoot
the rate
… of water uptake.
graduated
capillary tube
leafy shoot
reservoir
tap
air/water
meniscus
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.
graduated
capillary tube
leafy shoot
reservoir
tap
air/water
meniscus
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.
Environmental Factors Affecting
the Rate of Transpiration
There are five environmental factors which affect
the rate of transpiration. They are:
(I) Light Intensity
(IV) Wind Speed
(II) Temperature
(V) Water Supply
(III) Humidity
Light 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
Temperature
temperature
rate of evaporation
of water from
mesophyll cells
relative humidity of
air outside leaf
rate of diffusion of water
vapour from intercellular
space in leaf to outside
Humidity
humidity
rate of
outside
transpiration
it makes the diffusion gradient of water
vapour from moist intercellular space of a
leaf to the external atmosphere steeper

Wind Speed & Water Supply
wind blows
lack of water
water vapour around
soil dries, plant wilts
the leaf sweeps away
and stomata close
transpiration rate
INCREASES
transpiration rate
DECREASES
Stomata
 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 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
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 Investigate
Stomatal Distribution in a
Leaf by Using Cobalt
Chloride Paper
cobalt chloride paper
sellotape
Obtain a potted plant. Using sellotape stick a small square
of 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.
cobalt chloride paper
sellotape
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.
To Observe the Release of
Air Bubbles from Leaves
placed in Hot Water
forceps
hot water
leaf
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.
Structure of Root
Structure of Root
Root 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
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
of Water to 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
reduction of effective pressure at the top
of xylem vessel
water flows upwards from roots continuously
flow of water through plant: transpiration stream
tension produced to draw up water:
transpiration pull
~ End ~