1. Aim: How does the Structure of the
Cell Membrane Contribute to its
Function?
HW #3.: Intro to the Cell Membrane
Video: http://www.teachersdomain.org/resource/tdc02.sci.life.cell.nucleus/
Structure of Cell Membrane: http://www.susanahalpine.com/anim/Life/memb.htm
2. UNIT 3 :PASSIVE MOVEMENT ACROSS A
CELL MEMBRANE
3.0 Introduction
Our bodies are made of cells that carry out
several metabolic and physiological
processes.
In order to carry out these life processes, a
cell needs to take in various substances
It also produces certain substances, some of
which are waste products which may be toxic
and can harm the organism, hence need to
be removed from cells.
3. Therefore substances are always moving into
and out of the cells.
The way substances move into and out of the
cells depends on certain properties of the
substances, for example, size of the molecule
and the type of substance.
There are three main physiological processes
by which substances move in and out of cells.
These are diffusion, osmosis and active
transport.
4. Cell membrane
(a)Function
It regulates (controls) what enters and exits
the cell, maintaining homeostasis
(b)Characteristics of the Cell Membrane
• It is semi-permeable/partially permeable i.e it
allows some materials to enter and denies
others
• It is a bilayer
• It has protein carriers
• It is made up of phospholipids and
cholesterol
5. c)Structure of the Cell
Membrane
• Fluid Mosaic Model – flexible
organization of a mixture of lipids & proteins
6. 3.1.Diffusion
Diffusion involves movement of particles (gas
or liquid molecules) from a region of high
concentration to a region of low concentration.
Molecules move down a concentration
gradient, as a result of their random
movement
7. For living cells, the principle of the
movement down a concentration gradient is
the same, but the cell is surrounded by
a cell membrane which can restrict the
free movement of the molecules.
The cell membrane is a partially permeable
membrane - this means it allows some
molecules to cross easily, but others with
difficulty or not at all.
The simplest sort of selection is based on
the size of the molecules
8. This means that SOME substances can
easily diffuse through it, like oxygen, or
carbon dioxide,ammonia,glucose( diffuse
while transported),etc. Other substances
which are big like sodium ions, are unable to
pass through the cell membrane unless they
are specifically transported via proteins
embedded in the membrane itself.
9.
10. Experiment to demonstrate diffusion
Dissolve some KMnO4 in beaker full of water.
KMnO4 diffuses in water. This process
continues until the particles are uniformly
distributed throughout the system or until
equilibrium is reached.
11. This means there will be an equal distribution of
molecules throughout the system.
This is why food coloring moves throughout a
beaker of water; why odors smell strong at first
and then disappear over time.
Diffusion helps living organisms to:
obtain many of their requirements
get rid of many of their waste products
carry out gas exchange for respiration
12. Site Moving from From To
Small
intestin
e
Digested products-
glucose,amino
acids,fatty acids
and glycerol
Lumen of
small
intestine
Blood/lymph
in villi
Leaf Oxygen and carbon
dioxide
Airspace
between
mesophylls
Mitochondria
in all cells
Leaf Water vapors Stomatal
pores
Air outside
stomata
Lungs Oxygen Alveolar air
space
Blood
capillaries
around
alveoli
Lungs carbon dioxide Blood Alveolar air
13. Factors that affect the rate of diffusion
The rate at which molecules of a gas or liquid
diffuses is affected by a number of factors described
below:
i) Temperature:
The rate of diffusion increases as the temperature
increases. At higher temperature particles move
faster while the lower the temperature the lower the
rate of diffusion.
ii) Concentration gradient:
This is the difference in the amount of particles
present in two regions The rate of diffusion
increases as the concentration difference increases.
14. iii) Diffusion distance:
The rate of diffusion is directly proportional to a
particle’s distance. It takes longer for a particle to
diffuse when it is placed away than it does for a
particle that is closer to the point of diffusion.
iv) Surface area to volume ratio
The larger the surface area, the higher the rate of
diffusion simply because there is more space/surface
area through which it has diffuse.
• For example, putting a whole potato in a pot of
water to cook, will take a lot longer than it would if
you chopped up the potato increasing the surface
area considerably.
15. Lipid Bilayer
• Two layers of phospholipids
• Allows the cell membrane to be
flexible/fluid
“repelled by water”
“attracted to water”
27. Cell Membrane Proteins
• Transport Protein: channel where
molecules enter and exit the cell
• Receptor Protein: specifically shaped
proteins that aid in cell communication
Messenger molecule:
hormone or
neurotransmitter
Protein
Receptor
Transport
Protein
28. Importance of Cell Receptors
•Allow for cell to cell communication
•Involve two body systems:
• Nervous System - Neurotransmitters
• Endocrine System - Hormones
An Example of Cell Communication: The Flight or Fight Response
29. Cholesterol in the Cell Membrane
• Cholesterol helps the
membrane stay fluid
• The cholesterol holds
the phospholipids
together so the
movement of
molecules into and
out of the cell is not
disrupted
33. Aim: How do Molecules Travel Across
a Cell Membrane?
Do Now:
CL HW
34. Types of Cellular Transport
– Passive Transport
• Diffusion
• Facilitated Diffusion
• Osmosis
– Active Transport
(endocytosis and
Exocytosis)
35. (d) Concentration
• Number of molecules in a given area
When you have different concentrations on either
side, we call this a concentration gradient and
molecules are able to move
36. HIGHER CONCENTRATION LOWER CONCENTRATION
No Gradient – EQUILIUBRIUM
Molecules Move Back and Forth CONTINUOUSLY
40. Real Life Examples of Diffusion
The above image represents a real life example of
diffusion. Can you think of any other examples?
41. How to Determine if Diffusion is Occurring?
Step 1. Determine the Concentration Gradient.
Count the number of molecules on each side of the cell
membrane.
• How many O2 molecules are in the:
• Inside?
• Outside?
• Will O2 DIFFUSE INTO or OUT of the cell?
42. Step 1. Determine the Concentration Gradient.
Count the number of molecules on each side of the cell
membrane.
• How many of molecule 1 are there on the:
• Inside?
• Outside?
• Will Molecule 1 DIFFUSE INTO or OUT of the cell?
44. • Molecules continuously diffuse causing
equal concentration of molecules on both
sides of the membrane
Dynamic Equilibrium
Low
High
45. 1. List 3 substances that MUST be able to
pass through the cell membrane.
2. Explain why the cell needs each of these
substances.
46. Aim: How do Cell Membranes Select
what can Enter the Cell?
Do Now:
Regents
Review
Questions
47. •Cell membrane SELECTS which molecules
enter and exit the cell based on SIZE.
Selectively Permeable
• Harmful substances
(viruses/bacteria)
may enter the cell
48. Small Molecules
• Easily
DIFFUSE
through the
cell membrane
•Water
•Carbon
Dioxide
•Oxygen
•Glucose
http://www.phschool.com/science/biology_place/labbench/lab1/cell.html
49. Large Molecules
•Large organic molecules CANNOT easily
DIFFUSE through the cell membrane
•They need to be DIGESTED into their
building blocks
•Starch
•Proteins
•Lipids
Fatty Acids + Glycerol
Digested
food can
DIFFUSE
Undigested food is TOO large to DIFFUSE
50.
51. IMPORTANCE OF DIFFUSION IN PLANTS
AND ANIMALS
• Diffusion is important since it enables useful
molecules to enter the cell and waste
products to be removed.
• Plants absorb water, mineral salts and
oxygen from the soil through the root hairs by
diffusion.
52. • Digested food such as glucose and amino-
acids move from the small intestine into the
blood of animals by diffusion. These
substances move from the blood to the cells
and tissues by diffusion as well.
• Cells and unicellular organisms such as
Amoeba get rid of waste substances and
enter oxygen by diffusion.
• Diffusion is involved in exchange of gases in
stomata, skin of frogs and in the lungs of
animals.
53. Examples:
Substance
diffused
Site of diffusion
Oxygen From the alveoli into blood
capillaries
Carbon dioxide From blood capillaries into the
alveoli.
From air, through stomata & into
the leaf for photosynthesis.
Soluble products
of digestion
From small intestine to the blood
capillaries.
Scent made of
tiny molecules
From flowers into the bee’s body.
54. 3.1.2. FACTORS THAT AFFECT THE RATE
OF DIFFUSION
The rate of diffusion of particles refers to the
time taken for the particles to move within an
available space (fixed) until they are evenly
distributed. Several factors affect the rate of
diffusion. They include:
• Diffusion distance (the shorter the better)
e.g. thin walls of alveoli and the capillaries.
• Concentration gradient (the bigger the
better). This can be maintained by removing
the substance as it passes across the
diffusion surface.
55. • Size of the molecules (the smaller the
better).
• Surface area for diffusion (the larger the
better) e.g. there is millions of alveoli in a
lung, giving a huge surface area for diffusion
of oxygen.
• Temperature (molecules have more
kinetic energy at higher temperatures).
56. 3.2. OSMOSIS
3.2.1. UNDERSTANDING OSMOSIS
(a)Osmosis: The movement of water from an
area of low concentration to an area of high
concentration across a partially permeable
membrane.
(b) Water potential: a measure of how freely
water molecules can move .
Pure water has the highest water potential
(which zero).
57. Water potential doesn’t have a positive
value. For example salty water will have a
negative water potential.
Water potential ᴪ is measured in Pascal.
Water potential allows to define also osmosis
as passive movement of water from an area
of less negative water potential to an area of
more negative water potential across a
partially permeable membrane
60. • Hypotonic Solution - One solution has a
lower concentration of solute than another.
• Hypertonic Solution - one solution has a
higher concentration of solute than another.
• Isotonic Solution - both solutions have same
concentrations of solute.
• Plasmolysis: detachment of the protoplasm
from a plant or bacterial cell wall due to
water loss by osmosis.
• Turgidity is the state of being turgid or
swollen, especially due to high fluid content.
61. • Turgor pressure is the force
(pressure) exerted by water inside
the cell against the cell wall.
• Flaccidity means weak; soft; lax; lacking
vigor. Flaccidity of a plant cell occurs in an
isotonic solution such that the plasma
membrane is not pressed tightly against the
cell wall, and therefore, is neither swollen
(turgid) nor plasmolyzed.
62. In (1),dissolved salts and sugars gives a cell a
low water potential. Water enters by osmosis.
The cell content increases and pushes
outwards the cell membrane, making the cell
turgid.
TURGOR is the expansion of a cell resulting
from the absorption of water by the vacuole.
In plants, turgid cells help young leaves and
plants to stand upright and firm.
In animals cells ,turgid cells burst because
there is no cell wall to withstand turgor
pressure.
63. In (2) the solution outside the cell is more
concentrated than the content inside. Water
passes out of the vacuole by osmosis.
The vacuole shrinks, pulling the cytoplasm
away from the cell and leaving the cell
PLASMOLYSED.
65. In B, water molecules moved by osmosis
from the region of high concentration (inside
the Petri dish) to the region of low water
concentration(in the potato depression
across the semi-permeable membrane of
the cells of the potato tuber.
Water does not enter in the hollowed portion
of A because the cell potato A have equal
concentrations. Potato A serves as a control
experiment.
66. Water does note enter potato C because
boiling it kills the cells and makes the
membrane to lose its properties. So, potato
C is used to confirm that osmosis only
takes place in living cells only.
71. 3.2.3 IMPORTANCE OF OSMOSIS IN
PLANTS AND ANIMAL CELLS
• Uptake of water by roots
Usually, the water in the soil is more dilute
than that in root hair cells. So water enters
root hair cells by osmosis (a passive
process – requiring no energy). Plants
absorb water from the soil inner cells in
the root.
72. • Regulation of
transpiration
When photosynthesis does
not occur, stomata close.
– Potassium ions leave guard
cells.
– Thus, water leaves.
– Guard cells become less
turgid and stomata close.
73. • Movement of water from cell in
tissues
• Feeding in insectivorous plants
Insectivorous plants such as pitcher plant
prey on insects.They trap insects when
there is a sudden change in their turgor
pressure when disturbed by the insect.
74. 3.3. DIFFUSION AND OSMOSIS
3.3.1. DIFFERENCES AND SIMILARITIES
BETWEEN OSMOSIS AND DIFFUSION
(a)Differences
Osmosis Diffusion
It occurs only in liquid medium It occurs both in gas and liquid
There is a semi-permeable
membrane
There is no semi-permeable
membrane
It involves the movement of high
water concentration to low water
concentration
It involves solute particles from
high concentrated regions to low
concentrated regions
75. (a) Similarities
Both processes involve the movement of
molecules
In both processes there is the need for a
concentration gradient.
76. 3.3.2. APPLICATIONS OF DIFFUSION AND
OSMOSIS IN OUR DAILY LIFE ACTIVITIES
• The process of osmosis is used for drying fishes.
This is when water is removed from the fish.
• The process of diffusion is used for slating fishes
• Concentrated form of fruit juices do not spoil due to
osmosis
• The use of diffusion process is used for killing
pests.
• The use of body perfume also uses the diffusion
process
77. <UNIT 4>
ACTIVE TRANSPORT
Molecules and ions can also move from an
area of low concentration to that of higher
concentration. They are said to move
against a concentration gradient. Such a
process requires the use of energy and is
called active transport.
4.1. ACTIVE TRANSPORT AND ITS
IMPORTANCE
4.1.1. DEFINITION
78. Active transport is the movement of
particles through the cell membrane from
a region of low concentration to a region
of high concentration using energy.
79.
80. 4.1.2. IMPORTANCE OF ACTIVE
TRANSPORT IN LIVING ORGANISMS
• Through active transport, root hair cells in
plants absorb mineral salts and ions from
the surrounding soil.
• The cells lining the human small
intestines continue to absorb food
molecules by active transport even when
the concentration of these molecules is high
in the cells than in the intestinal lumen.
• Sodium and Potassium ion pump in nerves.
81. • Reabsorption of molecules by nephrons
Note: Since active transport uses energy(ATP)
provided by a mitochondrion, it can only take
place in a living cell.
4.1.3. DIFFERENCES BETWEEN DIFFUSION AND
ACTIVE TRANSPORT
• Two big differences between diffusion and active
transport are:
• Direction of movement (down or up a gradient)
• Use of energy for movement.
82. Passive transport Active transport
Transport occurs from a high
concentration of molecules and ions
to low concentration, in order to
maintain equilibrium in the cells.
Transport occurs from a low
concentration of solute to
high concentration of solute.
Does not require cellular energy. Requires cellular energy.
Involves osmosis and diffusion
processes.
Involves endocytosis and
exocytosis processes.
Transports anything soluble in water,
oxygen and carbon dioxide.
Transports proteins, ions,
large cells and complex
sugars.
83. 4.2. FACTORS THAT AFFECT THE ACTIVE
TRANSPORT
Any factor that affects energy production also
affects active transport. The main factors
affecting the active transport are explained
here below.
• Concentration of oxygen
• At higher oxygen concentration, the cells
produced by a cell produce more energy.
This leads to rapid active transport by the
protein carriers.
84.
85. • pH
Abnormal changes in pH in the
environment of the cell can alter the
structure of the protein carries. This will
reduce their ability to transport molecules
across the cell membrane.
4.3. THE ROLE OF PROTEINS IN ACTIVE
TRANSPORT
Carrier protein molecules have binding sites
for the molecules. The molecules to be
transported bind to the carrier protein
using energy.
87. 4.4. ENDOCYTOSIS AND EXOCYTOSIS
The movement of macromolecules such as
proteins or polysaccharides into or out of
the cell is called Cytosis or bulk transport.
There are two types of bulk transport,
exocytosis and endocytosis, and both
require the expenditure of energy.
88. Endocytosis
• Movement of large material
– Particles
– Organisms
– Large molecules
• Movement is into cells
• Types of endocytosis
– bulk-phase (nonspecific)
– receptor-mediated (specific)
89. PROCESS OF ENDOCYTOSIS
• Plasma membrane surrounds material
• Edges of membrane meet
• Membranes fuse to form vesicle
90. • Phagocytosis
Phagocytosis means “cell eating”. This is the
process where a cell incorporates a particle
by extending pseudopodia and drawing the
particle into a vacuole of its cytoplasm.
• Pinocytosis
Pinocytosis means “cell drinking”. This is the
process in which materials enter a cell
through its membrane and is incorporated
in vesicles for digestion.
93. Examples of Exocytosis:
• Secretion of digestive enzymes by
pancreas
• Secretion of milk from mammary glands.
• Secretion of Mucus by Salivary Glands.
94. COMPARISON BETWEEN EXOCYTOSIS AND ENDOCYTOSIS
Exocytosis Endocytosis
It results is expelling molecules
outside the cell.
It helps to ingest molecules towards the cell
interior.
This process leads to the
destruction of vesicles.
This process leads to creation of vesicles.
There is a discharge of enzymes,
hormones, proteins, and glucose.
All these constituents are used for
the functioning of other body
parts.
By this process, nutrients, food particles, and
proteins are received by the body cells. Apart
from this, some bacteria and pathogens can
also gain entry into the body through this
process.
This process helps in expelling
wastes from the body.
This process serves as a signal receptor.
Examples:
1) Neurotransmitters released
from the neuron cells.
2) In case of an infection, the cells
communicate among
themselves, and strengthen the
immune system of the body by
the process of exocytosis.
Examples:
1) The body cells engulf pathogens and
destroy them.
2) Endocytosis is used in case of cell
migration and adhesion related functions.
97. 1. What does the term selectively permeable mean?
2. What molecules are able to easily pass through
the membrane?
3. What molecules are able to easily pass through
the membrane?
4. Explain how the selectively permeable cell
membrane aids in the maintenance of
homeostasis.
Selectively Permeable - Ability to select and
choose which materials enter & exit the cell.
Small Molecules: Water, Simple Sugars
(Glucose), Oxygen, Carbon Dioxide
They must be broken down. Ex: Starch (Sugar)
Regulates what comes in and out of
the cell; helping to keep toxic substances out
98. QUIZ
Q1.(a)What does the term selectively
permeable mean?
(b) What molecules are able to easily
pass through the membrane?
Q2. Which of the following causes juice
to ooze out when you would sprinkle
salt on a cut tree?
A Osmosis C Active transport B
Diffusion D Saturation
99. Q3.(a)Define diffusion.
(b) Explain why diffusion is important in
all living organisms
Q4. By use of a table of two points, compare
diffusion and osmosis.
100. Aim: Why does Water Diffuse
Across a Cell Membrane?
Do Now:
HW
http://www.akscience.org/assets/advinstitute/Unit%20on%20Cell%20Function.pdf Foldables
101. Osmosis
• Water molecules DIFFUSE from HIGH to LOW
water concentration
–H2Osmosis
• NO ENERGY (ATP)
http://www.tvdsb.on.ca/westmin/science/sbi3a1/Cells/Osmosis.htm
105. DISTILLED WATER - Hypotonic
• In which direction will the water DIFFUSE?
106. Cells in DISTILLED Water
• Water moves INTO the cell
from HIGH to LOW water
concentration
–ANIMAL cells: SWELL and
burst
–PLANT cells: do NOT burst
due to a rigid cell wall
Distilled Water
107. Real Life Example of a Cell Living in a
DISTILLED (hypotonic) Environment
• Paramecium are single-celled freshwater organisms
– Fresh water is HYPOtonic when compared to the cell
• Water DIFFUSES into the cell due to osmosis
• Cell contains a contractile vacuole to pump out
excess water
109. SALT WATER - Hypertonic
• In which direction will the water DIFFUSE?
110. Cells in SALT Solution
• Water moves OUT of the
cell from HIGH to LOW
water concentration
–ANIMAL cells shrink
–PLANT cells undergo
plasmolysis
• Cytoplasm pulls away from
the cell wall
Salt water
111. Real Life Example of a Cell Living in a SALT
(hypertonic) Environment
• During the winter, salt on the road NEGATIVELY
affects plants. This is because water diffuses out of
their cells (highlow concentration).
112. Cells in BALANCED Solutions
• Isotonic Solution
– The water concentration on
both sides of the membrane is
equal - equilibrium
• Real-life example: Blood
–water flows across
membrane equally,
in both directions
balanced
113. Using your knowledge of osmosis,
answer the following questions.
In picture A, what type of solution was
Sponge Bob placed in.
Explain your reasoning
In picture B, what type of solution was
Sponge Bob placed in.
Explain your reasoning.
114. Using your knowledge of osmosis, explain what
would happen to the slugs if they were covered
with salt.
115. Red onion cells undergo the
change represented in the diagram.
Explain why the cytoplasm pulled
away from the cell wall.
Hospital patients are often given intravenous fluids (IVs) to
maintain proper levels of water and salts in the body. If a
manufacturer accidentally prepared a batch of IV fluid that
contained distilled water, harm to the patient could result.
Explain why an IV filled with distilled water could harm the
patient. (Hint: what do you know about distilled water?)
116. Aim: How do Molecules Travel
AGAINST the Gradient?
Do Now:
Regents Review
Questions
117. Active Transport
•Movement of molecules
from LOW to HIGH
concentration
•Against the
concentration gradient
•Requires Energy (ATP)
Low
High
119. • COUNT: Determine the concentration for molecule
3 both inside and outside of the cell.
• If molecule 3 moves OUT of the cell, is that active
or passive transport? Explain your reasoning.
(DRAW an to indicate that the molecule is
moving out)
121. 1. Molecules 1 and 2 enter the cell and glucose leaves the cell through
the process of
2. Which molecule would require the use of energy in order to be
brought into the cell? Explain your reasoning.
122. 3. Using information from the diagram, state one reason why
the movement of molecules in method C represents active
transport.
4. Methods A and B are classified as methods of passive
transport because they do not require . Explain
your reasoning.
