2. Water and Organisms
Water makes up between % of weight of organisms

3. 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.

4. 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

5. 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

6. 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

7. 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

8. As a medium for transport
Human blood plasma consists mainly of water (90%)

9. Water as a Metabolite
in plants during photosynthesis, carbohydrates are synthesized from carbon dioxide and water
essential in hydrolytic reactions, e.g. digestion

10. As a metabolite
photosynthesis: water + carbon dioxide --> carbohydrates + oxygen

11. To provide support and to keep shape
water keeps plant cells turgid and provides a means of support in plants

12. For sexual reproduction
Sperms need water to swim to the eggs.

13. Ways of Gaining Water in Animals
drinking
eating
from respiration occurs in cells which the water formed is called metabolic water

14. Ways of Losing Water in Animals
evaporation from body surfaces
sweating
exhalation
urination
defaecation

15. Ways of losing water in plants:
Evaporation from body surface,
Transpiration.

16. Hypotonic, Hypertonic and Isotonic Solutions
Hypotonic solution
- a solution has a higher water potential than the reference solution

17. 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

18. 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)

19. 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.

20. Osmosis in animal cell Concentrated saline solution Water Cell swells
and eventually burst
Cell shrinks

21. What will happen when water enters and leaves cells?
In animal cells
water enter, the cells swell burst
water leaves, the cells shrink.

22. Animal Cells Response to Different Solutions
water move in by osmosis
Cells swell and burst
in hypotonic solution
tissue cells

23. Animal Cells Response to Different Solutions
tissue cells
in hypertonic solution
water move out by osmosis
cells shrink

24. Investigation 11.1
Investigation of the Effects of Different Salt Concentrations on Red Blood Cells

25. Tube A: 0.2% sodium chloride solution
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

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

27. 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
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.

28. What evidence supports your answer ?
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 …

29. What evidence supports your answer ?
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: 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 …

30. What evidence supports your answer ?
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: 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.

31. 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

32. 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

33. The kidney’s role in osmoregulation

34. Human Urinary System
kidney
ureter
urinary bladder
urethra

35. Human Urinary System Inferior vena cava aorta left kidney renal vein
renal artery
right kidney
ureters
sphincter muscle
urinary bladder
urethra
Human Urinary System

36. 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

37. 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

38. 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

39. Urination
normally, the sphincter muscle is tightly contracted, so no urination occurs
Adults can control the sphincter muscle but children cannot, it relaxes automatically when the bladder is full
when urinary bladder is full
sphincter muscle relaxes wall of urinary bladder contracts
urination occurs

40. Structure of Mammalian Kidney
cortex
medulla
nephron
renal artery
pelvis
renal vein
ureter

41. 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

42. 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)

43. 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

44. Nephron Bowman’s capsule glomerulus efferent arteriole
afferent arteriole
distal convoluted tubule (second convolution)
renal artery
proximal convoluted tubule (first convolution)
capillaries
around nephron
renal vein
collecting
duct
Loop of
Henle

45. …... How Nephron is Connected with Blood Vessel
afferent arteriole (branches from renal artery)
renal artery
enters Bowman’s capsule
Glomerulus (a tightly bunched group of capillaries)
efferent arteriole (capillaries join up)
…...

46. How Nephron is Connected with Blood Vessel
leaves Bowman’s capsule
capillaries (spread out and wrap around tubule)
venule (capillaries join up)
renal vein

47. Structure of Nephron first & second convolution Bowman’s capsule
(with glomerulus)
afferent arteriole
efferent arteriole
venule
loop of Henle
collecting duct

48. How Nephron Works ?
By two ways, one is ultrafiltration and the other is reabsorption

50. Capillaries Diffusion It is the smallest blood vessels
It is the site of exchange (by diffusion)
Thin wall (one cell)
Nutrients O2
Diffusion
CO2
Waste

51. 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

52. 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

53. 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

54. 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

55. reabsorption of glucose, amino acids and some salts begins in the first convolution and finished when the fluid reaches loop of Henle

56. 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

57. Functions of Kidney kidney mainly has three functions: osmoregulation
removal of excess salt
excretion

58. 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

59. 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

60. Functions of Kidney - Removal of Excess Salt
after eating a salty meal
concentration of urine is higher
salt enters blood, concentration of salt in blood increase
volume of urine increase
man feels thirsty
drink water

61. 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

62. 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

63. 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

64. 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

65. 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

66. 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

67. 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

68. 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

69. 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

70. 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

71. Plants Cell
cell wall
cytoplasm
vacuole
cell membrane

72. freely permeable so it lets most of molecules to go through
osmosis does not occur
cell membrane
beneath cell wall
selectively permeable
cell wall

73.  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

74. 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

75. When water potential of cell = water potential of water
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

76. Water Relations of Plant - Plasmolysis
plant cell in concentrated solution
The whole phenomenon is called plasmolysis and cell is plasmolysed
net water movement out of the cell by osmosis
flaccid
vacuole and cytoplasm shrink
cytoplasm is torn away from cell wall

77. Plasmolysed cells

78. Turgidity of Plant Cells
cell membrane separated
from cell wall
cell wall
cytoplasm
vacuole
enlarged
vacuole
very small
solution here is the same
as the external solution
plasmolysed cell
(in hypertonic sol)
turgid cell
(in hypotonic sol.)

79. 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

80. Cells in Different Solutions
Solution Concentration
hypotonic
hypertonic
animal cells
(e.g. RBC)
haemolysis
shrink
plasmolysis
(cell is flaccid)
plant cells
turgid

81. Investigation 11.2
To Investigate the Effects of Sucrose Solution and Tap Water on Epidermal Cells of Red Onion Scale Leaf or Rhoeo Discolor Leaf

82. 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.

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

84. fleshy scale leaf of red onion bulb
forceps
filter paper
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.

85. 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.

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

87. 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.

88. Investigation 11.3
Effects of Concentrated Sucrose Solution and Tap Water on Raw Potato Strips

89. What has happened to the potato strips ?
petri dish
water
20% surcose solution
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.

90. petri dish
water
20% 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.

91. Experiment to Show that Water is Given Off During Transpiration
Investigation 11.4
Experiment to Show that Water is Given Off During Transpiration

92. 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.

93. How can you show that it is water ?
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.

94. What conclusions can you draw from the results ?
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.

95. Transpiration
an evaporation of water in form of water vapour from the surface of plant to atmosphere

96. 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

97. 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
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. Water diffuses out through stoma
Lower concentration of water vapour
Substomatal air space with higher concentration of water
How water lost from leaves causes transpiration and how the transpiration pull is formed.

98. 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

99. 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

100. To Measure the Rate of Transpiration by Using a Simple Potometer
Investigation 11.5
To Measure the Rate of Transpiration by Using a Simple Potometer

101. graduated capillary tube
air/water meniscus
graduated capillary tube
reservoir
leafy shoot
tap
What are the environmental conditions under which transpiration occurs quickly ?
Ans: It is under dry, warm and windy conditions.

102. graduated capillary tube
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.

103. graduated capillary tube
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.

104. graduated capillary tube
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.

105. Environmental Factors Affecting the Rate of Transpiration
There 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

106. 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

107. 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

108.  Humidity 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 

109. Wind Speed & Water Supply
wind blows
lack of water
water vapour around the leaf sweeps away
soil dries, plant wilts and stomata close
transpiration rate
transpiration rate
INCREASES
DECREASES

110. 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

111. 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
stoma
guard cell

112. 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

113. 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)

114. Investigation 11.6
Experiment to Investigate Stomatal Distribution in a Leaf by Using Cobalt Chloride Paper

115. Obtain a potted plant. Using sellotape stick a small square
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.

116. Which piece of cobalt chloride paper turns pink first?
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.

117. Ans: It is because more stomata are present in the lower epidermis.
cobalt chloride paper
sellotape
Explain your answer.
Ans: It is because more stomata are present in the lower epidermis.

118. Why is it important to handle cobalt chloride paper with forceps?
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.

119. To Observe the Release of Air Bubbles from Leaves placed in Hot Water
Investigation 11.7
To Observe the Release of Air Bubbles from Leaves placed in Hot Water

120. Which surface has more air bubbles coming off?
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.

121. Where does the air come from?
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.

122. What does the result show?
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.

123. Structure of Root

124. 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

125. 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

126. 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

127. Vascular Tissue
further from the tip of root
contain xylem and phloem
xylem transport absorbed water to every part of plant

128. 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

129. Transverse Transport of Water to Xylem
cytoplasm and cell sap have higher water potential than neighbouring cortical cells
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
water travels by osmosis inwards from cell to cell

131. reduction of effective pressure at the top of xylem vessel
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

132. ~ End ~