Download 3 Movement of substances across cell membrane 3.1 Cell membrane

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3 Movement of substances
across cell membrane
3.1
A
Cell membrane
(Book 1A, p. 3-3)
Structure of the cell membrane
(Book 1A, p. 3-3)
Singer and Nicolson proposed the (1) ______________ _______________ _______________
(流動鑲嵌模型)
-
in 1972, which suggests that:
the cell membrane is mainly made up of (2) _______________ (磷脂) and
(3) _______________
-
phospholipid molecules are arranged in a (4) _______________ and protein molecules
are (5) _______________ (散佈) among them.
protein molecules
carbohydrate molecule
outside of cell
glycoprotein
(糖蛋白)
phospholipid
bilayer
inside of cell
(cytoplasm)
protein molecules
▲ The fluid mosaic model of the cell membrane
Meaning
Fluid
Phospholipid molecules can move (6) ______________ (橫向地).
Mosaic
Protein molecules are interspersed among the (7) _______________ molecules in
a mosaic pattern.
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1
Phospholipids
Phospholipids are a type of lipid. Their structure is similar to that of triglycerides except one
of the fatty acid molecules is replaced by a (8) _____________ _____________ (磷酸鹽基團).
Triglyceride molecule
Phospholipid molecule
phosphate
group
one glycerol molecule
three fatty acid molecules
glycerol
two fatty acid molecules
Features of a phospholipid molecule:
Phosphate group
Fatty acid
(9) ______________ (Polar / Non-polar)
(12) ______________ (Polar / Non-polar)
Forms the (10) _______________ ‘head’
Forms the (13) _______________ ‘tails’
(11) _____________ (Attracted / Repelled)
(14) _____________ (Attracted / Repelled)
by water molecules
by water molecules
Arrangement of phospholipid molecules in the cell membrane:
outside of cell
The (15) _____________
heads face the aqueous
environment inside and
outside of cell.
The (16) ___________
tails point inwards.
inside of cell
▲ Phospholipid molecules arranged in a bilayer
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2
Proteins
Some proteins are attached to the surface of the phospholipid bilayer, some are
(17) _______________ half-way in the bilayer and others (18) _______________ the entire
bilayer.
Carbohydrates are attached to some proteins to form (19) _______________, which may act
as antigens or receptors.
Membrane protein
Function
I
Channel protein
a
Involved in active transport to carry substances across the membrane
II
Carrier protein
b
Receives chemical messengers (e.g. hormones) outside the cell
III
Antigen
c
Provides channels across the membrane for transporting certain ions
and small, polar molecules
IV Receptor
V
Enzyme
d
Speeds up reactions in the cell
e
For cell recognition (識別)
I: (20) _______________
II: (21) _______________
III: (22) _______________
IV: (23) _______________ V: (24) _______________
B
How is the membrane structure related to its properties and
functions? (Book 1A, p. 3-6)
small, non-polar
molecule
small, polar
molecules and
certain ions
large molecule
outside of cell
inside of cell
channel
protein
carrier protein
▲ Different substances move across the cell membrane along different paths
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Structure of cell membrane
Property and function
The cell membrane is mainly
This makes the cell membrane (28) ____________
made up of (25) ______________
permeable.
and (26) _______________.
Only small, (29) _____________ molecules can
The phospholipid molecules are
move across the phospholipid bilayer.
arranged in a (27) ____________.
Small, (30) _____________ molecules and certain
Some protein molecules act as
ions can move across the membrane through
channels or carriers.
channel proteins or carrier proteins.
The phospholipid molecules can
This makes the cell membrane (32) ___________,
move laterally, i.e. the cell
so that it can change its (33) _____________ and
membrane is (31)______________
fuse during phagocytosis and cell division.
in nature.
(34) _______________ molecules
This makes the cell membrane strong enough to
are interspersed among the
(35)_____________ the cell contents.
phospholipid bilayer.
3.2 Movement of substances across membranes
A
Diffusion
(Book 1A, p. 3-9)
(Book 1A, p. 3-9)
Particles of liquids and gases can move about freely. They tend to distribute evenly.
Diffusion (擴散) is the net movement of particles down a (1) ____________ _____________,
i.e. from a region of (2)_____________ (higher / lower) concentration to a region of
(3)_____________ (higher / lower) concentration, until the particles become evenly
distributed.
When the particles are evenly distributed, there is no (4)_____________ movement of
particles between the two regions but the particles are still moving (5)_____________ in all
directions.
Diffusion is a (6)_____________ process and does not require (7)_____________.
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concentration gradient exists
particles are evenly distributed
higher
lower
concentration
concentration
net movement of particles
particles move randomly in all directions
▲ Diffusion
Factors affecting the rate of diffusion:
Factor
Concentration gradient
Effect on the rate of diffusion
The steeper the concentration gradient is, the (8) _____________ the
rate of diffusion.
Temperature
At higher temperatures, particles have (9)_____________ kinetic
energy and collide (10)_____________ frequently, resulting in a
(11)_____________ rate of diffusion.
Size of particles
Small particles diffuse (12) _____________ than large particles.
Distance
The (13) _____________ the distance is between two regions of
different concentrations, the higher the rate of diffusion.
Surface area
For the diffusion through a membrane, the (14) _____________ the
surface area of the membrane is, the higher the rate of diffusion.
Diffusion is important for:
(15) _____________ of materials between the cell and the environment, e.g. obtaining
(16) _____________ and nutrients, and removing (17) _____________ like carbon dioxide
allowing substances in cells to be (18) _____________ throughout the cytoplasm.
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B
Osmosis
(Book 1A, p. 3-11)
Osmosis (滲透) is the net movement of (19) _____________ molecules through a
(20)_____________ _____________ membrane from a less concentrated solution to a more
concentrated solution.
It is a (21) _____________ process and does not require (22) _____________.
(23) _____________ _____________ (水勢) describes the tendency of water molecules to
move from one place to another. Pure water has the (24) _____________ (highest / lowest)
water potential which is defined as (25) _____________.
The presence of solute particles (26) _____________ (raises / lowers) the water potential of a
solution. All solutions have a water potential lower than that of pure water, i.e. a
(27)_____________ value.
Osmosis can be redefined as the net movement of water molecules from a region of
(28)_____________ (higher / lower) water potential to a region of (29) _____________
(higher / lower) water potential.
differentially permeable membrane
water molecule
sucrose molecule
higher water potential
(dilute sucrose solution)
lower water potential
(concentrated sucrose
solution)
net movement of water molecules
▲ Osmosis
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Go to
Practical 3.1
Demonstration of osmosis using dialysis tubing
(Book 1A, p. 3-12; Practical Workbook for SBA 1A, p. 3-1)
Practical 3.2
Demonstration of osmosis using living animal tissue
(Book 1A, p. 3-13; Practical Workbook for SBA 1A, p. 3-5)
Cells and osmosis:
Net movement of
water
In hypotonic
(低滲的)
solution
(高滲的)
solution
In isotonic
(等滲的)
Plant cell
(30) _____________ (31)_______________ and
Becomes
(Enters / Leaves) the finally (32) ___________
(33) ____________ (膨脹)
cell
In hypertonic
Animal cell
(爆裂)
(34) _____________ (35) _______________
Becomes flaccid (軟縮)
(Enters / Leaves) the (萎縮) and becomes
and (36) ______________
cell
wrinkled (皺褶)
(質壁分離)
No net movement
Remains the same
Remains the same
solution
Osmosis is important for the movement of (37) _____________ in and out of cells, e.g. during
absorption of water in small intestines and plant roots.
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Go to
Practical 3.3
Study of osmosis in red blood cells
(Book 1A, p. 3-16; Practical Workbook for SBA 1A, p. 3-8)
Practical 3.4
Study of osmosis in living plant cells
(Book 1A, p. 3-17; Practical Workbook for SBA 1A, p. 3-10)
Practical 3.5
Study of osmosis in living plant tissue
(Book 1A, p. 3-18; Practical Workbook for SBA 1A, p. 3-13)
C
Active transport
(Book 1A, p. 3-21)
Active transport (主動轉運) is the transport of substances across the cell membrane
(38) ______________ a concentration gradient.
It involves (39) ______________ proteins. Only substances that fit the (40) _____________
of the carrier proteins can be transported by active transport.
It is an (41) ______________ process and requires energy. Therefore it only occurs in
(42) ______________ cells which can release energy by (43) ______________.
lower
concentration
carrier protein
higher
concentration
The substance to be
transported binds to a
carrier protein.
The carrier protein changes
its shape using energy.
The substance is released
on the other side of the cell
membrane.
▲ Active transport
Active transport is important for obtaining useful substances, e.g.
the absorption of (44) _____________ in human small intestines
the absorption of (45) _____________ from the soil into the roots of plants.
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D
Phagocytosis
(Book 1A, p. 3-22)
Phagocytosis (吞噬) is the uptake of large particles into the cell by the formation of a
(46) _______________ or (47) _______________ (偽足) at the cell membrane.
It is an (48) _____________ process and requires energy.
cell membrane
1 At the cell membrane, a
pit or pseudopodium is
formed to engulf the target
particle
outside of cell
inside of cell
digested
products
2 The particle is
enclosed in a small
vacuole.
4 The digested products
diffuse to the cytoplasm.
3 The cell releases enzymes
to digest the particle in the
vacuole.
enzyme
▲ A particle is taken into a cell by phagocytosis and is then digested
Phagocytosis is important for:
(49) _______________ of some unicellular organisms, e.g. Amoeba engulfs food particles
body defence against diseases, e.g. in humans and other mammals, certain
(50) _____________ _____________ cells engulf harmful microorganisms.
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Answers
Ch 3
Movement of substances across cell membrane
3.1
1
fluid mosaic model 2
phospholipids
3
proteins
4
bilayer
5
interspersed
6
laterally
7
phospholipid
8
phosphate group
9
Polar
10
hydrophilic
11
Attracted
12
Non-polar
13
hydrophobic
14
Repelled
15
hydrophilic
16
hydrophobic
17
embedded
18
span
19
glycoproteins
20
c
21
a
22
e
23
b
24
d
25
phospholipids
26
proteins
27
bilayer
28
differentially
29
non-polar
30
polar
31
fluid
32
flexible
33
shape
34
Protein
35
support
2
higher
3
lower
4
net
3.2
1
concentration gradient
5
randomly
6
all
7
energy
8
higher
9
more
10
more
11
higher
12
faster
13
shorter
14
larger
15
exchange
16
oxygen
17
waste
18
distributed
19
water
20
differentially permeable
21
passive
22
energy
23
Water potential
24
highest
25
zero
26
lowers
27
negative
28
higher
29
lower
30
Enters
31
Swells
32
bursts
33
turgid
34
Leaves
35
Shrinks
36
plasmolysed
37
water
38
against
39
carrier
40
shape
41
active
42
living
43
respiration
44
glucose
45
minerals
46
pit
47
pseudopodium
48
active
49
nutrition
50
white blood
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