Transcript Cell Membrane

Section 1
Introduction to Cells
Animal Cell
nucleus
cytoplasm
cell
membrane
nucleus
cell wall
Plant Cell
vacuole
green chloroplast
cytoplasm
cell
membrane
Nucleus
•The nucleus contains
the genetic material of
an organism.
•It controls all the cell’s
chemical reactions.
nucleus
•It also controls the
growth and
development of a cell,
and so determines the
cell’s structure and
function.
Cell membrane
•Cells take in many
chemicals from their
surroundings, and
release other
chemicals into their
surroundings.
•The cell membrane is
a very thin boundary
which controls the
entry and exit of these
materials.
Cytoplasm
•There are many
chemical reactions
happening in all of
your cells.
•These reactions
keep the cell alive
and allow it to carry
out its specific
function.
Cell wall
•The cell wall is a
rigid structure
made of a tough
mesh of cellulose
fibres.
•It helps to support
a plant cell.
Vacuole
•The vacuole is
filled with water
and pushes out
towards the cell
wall.
•This provides
support for the
plant.
Chloroplasts
•Plant cells may also
contain chloroplasts
in the cytoplasm.
•These contain a
chemical called
chlorophyll which
absorbs light energy
for photosynthesis.
•This allows plant
cells to make food.
•Only the green
parts of a plant
contain chloroplasts.
Structure
Nucleus
Cell Membrane
Cytoplasm
Cell Wall
Vacuole
Chloroplasts
Feature
Large, usually round structure
containing genetic materials
Function
Controls all cell activities
Very thin layer surrounds the
Controls the passage of substances
cytoplasm
into and out of the cell
Fluid, jelly-like material
Site of all bio-chemical reactions
Outer layer made of basket-like mesh
of cellulose fibres
Provides plant cells with support
Fluid-filled sac-like structure in the
Stores water and minerals and
cytoplasm
provides extra support for plant
Disk-like structure containing green
Trap light energy for making food
chlorophyll
by photosynthesis
Microscopes
• Cells are usually too small to be seen with the
naked eye
• Microscopes are used to magnify them
• Stains (eg. methylene blue or iodine) can be
applied to highlight certain cell structures
• Your teacher will demonstrate how to
prepare slides of onion cells and cheek cells,
and you will then prepare your own slides
and view them under the microscope.
• You should make labelled drawings of what
you see. Include the magnification used.
Examining Onion Cells
Aim:
To observe and draw onion cells using a microscope.
Equipment:
• Glass slide
• Cover slip
• Onion skin
• Iodine stain
• Microscope
• Lamp
Method:
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Collect a thin piece of onion skin.
Spread the skin on a slide. The skin must not overlap.
Stain the cells by adding 2 drops of iodine stain.
Place a cover slip over the skin. Use a pencil to lower the
cover slip gently so the air is pushed out.
Examine the cells under low then medium power. You should
be able to see lots of cells arranged like bricks in a wall.
Adjust the microscope to a higher power.
Draw exactly what you see through the “field of view” using a
pencil.
Label as many structures as you can see.
Return the slide and pack your microscope away carefully.
Onion cells in iodine
nucleus
cell wall
cytoplasm
Examining Cheek Cells
Aim:
To make a slide of cheek cells and draw them.
Equipment:
• Glass slide
• Cover slip
• Cotton bud
• Methylene blue stain
• Microscope and lamp
• Paper towel
Method:
• Rub the cotton bud over the inside of your cheek to remove
some of the cells.
• Wipe the cotton bud over the surface of a glass slide.
• Place the cotton bud in disinfectant.
• Stain the cells with 1 drop of methylene blue stain.
• Remove some of the stain using paper towel.
• Use a pencil to lower the cover slip so the air is pushed out.
• Draw the cells and label the structures.
• Once you have finished, place the slide and cover slip in
disinfectant.
• Pack away your microscope carefully.
Cheek cells in methylene blue
nucleus
cell membrane
cytoplasm
Plant Cells
• Some plant cells have chloroplasts.
• These disc-like structures contain a green
pigment called chlorophyll that traps light
so that the plant can make its own food by
a process called photosynthesis
cell wall
chloroplasts
Comparison of Cell Types
Structure
cell wall
cell membrane
nucleus
cytoplasm
chloroplasts
vacuole
Plant Cell
Animal Cell
Comparison of Cell Types
Structure
Plant Cell
Animal Cell
cell wall
Yes
No
cell membrane
Yes
Yes
nucleus
Yes
Yes
cytoplasm
Yes
Yes
chloroplasts
Yes
No
vacuole
Yes
No
Textbook questions
Answer q. 1-4 on page 4 in sentences
Multicellular Organisms
• Organisms are usually made up of
millions of cells that work together
e.g. oak tree or human
• These are called multicellular
organisms
Unicellular Organisms
• But there are also organisms that are
made up of just one single cell
• These are called unicellular
organisms and are very small
e.g. Amoeba
Different types of cells
Microbes: a word used to describe a
microscopic unicellular organism such
as bacteria and fungi.
Microbes
• Some microbes are harmful and can
cause disease.
• Others can be useful e.g. helping to
make useful products in biotechnology
industries.
• An example of a useful fungus is
penicillium, which produces the
chemical penicillin, an antibiotic.
Cells & Biotechnology
• Yeast cells are important to biotechnology
because under the right conditions they
can convert sugars into alcohol and carbon
dioxide – this process is called fermentation
yeast
sugar
carbon dioxide and alcohol
Yeast
• Is a unicellular fungus.
• It cannot photosynthesise, it
has no chloroplasts.
• It needs a food source e.g.
sugar.
• It can respire anaerobically
( in the absence of oxygen).
• It is widely used in the brewing
and baking industries.
• It reproduces by ‘budding’.
• Yeast cells can reproduce
rapidly if they have a source of
food and a suitable
temperature.
30 mins
1 hour 30 mins
2 hours
2 hours 30 mins
1 hour
Yeast dividing calculation
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One yeast cell is placed in a sugar
solution. It divides to form 2 cells
in 30 minutes. How many yeast
cells will there be after 12 hours?
How to work it out
12 hours = 24 divisions
Number doubles each division
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2.
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2
4
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16
32
64
128
256
512
1024
2048
4096
8192
16384
32768
65536
131072
262144
524288
1048576
2097152
4194304
8388608
16777216
Answer = 16,777,216 yeast cells
Looking at microbes
• Yeast is a very useful
microbe, it is a fungi.
• Looking at yeast…
Collect the following:
• Microscope, slide, 1 drop of
yeast, cover slip.
• Prepare a yeast cell slide.
 View the yeast cells at low
and high power. Look for
cells that are budding.
Looking at yeast cells
Applications of Fermentation
by Yeast
Brewing
Industries
Alternative
Fuel Industries
e.g. Gasohol
(alcohol mixed
with petrol)
Bread-making
Industries
Yeast and alcohol
• Yeast can make alcohol when it has
a source of sugar.
• This is called alcoholic fermentation
and is used in the brewing industries
to make wine and beer.
Yeast and alternative fuels
• Yeast can be added to sugar to make
alcohol.
• Alcohol is flammable and can be used as
fuel. However, it must first be mixed
with petrol.
• This forms an alternative fuel called
gasohol.
alcohol (made by yeast) + petrol = gasohol
Yeast and breadmaking
• Yeast is added to flour,
water and a little sugar
(to feed the yeast!).
• The dough is then left
for about and hour in a
warm place. During this
time the yeast produce
carbon dioxide and a
little alcohol.
• The carbon dioxide gas
causes the dough to
rise.
• It is then put in an oven
to bake. This kills the
yeast and evaporates
off the alcohol.
Yeast and breadmaking
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Label two beakers A and B.
Add 3 spoons of flour and half a spoon of
sugar to each beaker.
Add yeast suspension to beaker A and mix
with a stirring rod to make a dough.
Add water to beaker B and stir to form a
dough.
Transfer the doughs to two measuring
cylinders and transfer the labels A and B onto
them.
Leave in a warm place for 30 minutes.
Look at the height of the dough in each
cylinder.
Yeast and breadmaking
Results
Complete the results table.
Conclusion:
What effect does yeast have in
breadmaking?
Antibiotic Production using
other fungi
Alexander Fleming
Video clip
Antibiotic Production
• Antibiotics are antibacterial chemicals
produced by microbes such as fungi.
• They prevent the growth and may cause the
death of other microbes.
• Antibiotics do not work against viruses so
cannot be used to treat the cold or the flu.
• Many bacteria are now resistant to antibiotics.
Video clip
bacterial
colony
bacteria cannot grow
near the Penicillium
Penicillium colony
Antibiotic multidisc
• A disc with several antibiotics on the ‘arms’
can be used to find out which is the most
effective antibiotic to treat an illness.
• This is used in labs where swabs from patients
are sent for checking.
Clear zone around
arm shows that the
bacteria is killed
by the antibiotic.
This would be a good
antibiotic to give the
patient.
Resistant bacteria
In the above example, the
bacteria S.Albus is not killed
by the antibiotic V.
We say that the bacteria is
resistant to the antibiotic.
In the above example,
the bacteria M.Luteus
is killed by antibiotic V.
We say that the
bacteria is sensitive to
the antibiotic.
Resistant bacteria
• If a bacteria is not killed by an antibiotic
we say that the bacteria is resistant to
the antibiotic.
• If a bacteria is killed by an antibiotic we
say that the bacteria is sensitive to the
antibiotic.
• An antibiotic multidisc can show which
antibiotic is best to treat each bacteria.
The use of bacteria
• Bacteria can be used to produce
-Yoghurt
-Biogas (another alternative fuel)
Yoghurt Making
• During the souring of milk, bacteria growing in the milk
will feed on the milk sugar (lactose) and break it down
to lactic acid. This process is called lactic acid
fermentation
Lactose
bacteria
Lactic Acid
Lactic acid makes milk curdle. The manufacture of
yoghurt depends on the curdling of milk
Investigating Microbes…
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True or False…
Microbes are all harmful and can cause disease
Fungi can be used in yoghurt making
Bacteria can be killed by antibiotics
Yeast make their own food through the process of
photosynthesis
Some bacteria are resistant to antibiotics
Fungi carry out fermentation
Fermentation releases oxygen
Yeast use glucose as an energy source for respiration
Gasohol is petrol mixed with alcohol
Antibiotics are produced by fungi
Diffusion
• Diffusion is the movement of
molecules in a liquid or gas from high
to low concentration until they are
evenly spread out
Diffusion clip – BBC learning zone
Cells and diffusion
• The entry and exit of substances in
and out of cells is called diffusion.
• This happens across the cell
membrane.
• Animal cells take in glucose and
oxygen by diffusion.
• Carbon dioxide and waste materials
leave animal cells by diffusion.
Cells & Osmosis
• Water also enters and leaves cells
by a similar process called osmosis.
• Osmosis is the special diffusion of
water from high water
concentration to low water
concentration through a selectively
permeable membrane.
Selectively Permeable Membranes
• Pores in the membrane are
small, only small molecules
such as glucose, oxygen and
carbon dioxide can get
through.
cytoplasm
nucleus
• Large molecules such as
starch cannot pass through.
• Selectively permeable
membranes allow certain
molecules to pass through
but not others.
selectively
permeable
membrane
Selectively Permeable Membranes
• Cell membranes are described as selectively
permeable.
• This means that they allow small molecules like
oxygen and water to pass through them freely.
• This is because the membrane has tiny holes in it
called pores that make it permeable.
• Large molecules like starch are unable to pass
through.
Visking tubing
• Visking tubing is a selectively permeable
material that can be used to show the
effect of osmosis on cells.
• The visking tubing behaves like a cell
membrane, and we can use it to make
model cells.
• Your teacher will show you how to use it.
Osmosis experiment
A
B
Visking tubing bag
10% sugar solution
water
Boiling tube
Results
A
Mass of bag
and contents
at start (g)
Mass of bag
and contents
after 20
minutes (g)
Difference in
mass (g)
B
Conclusion
• Bag A increased/decreased in mass.
This was because water moved in/out
by osmosis.
• Bag B increased/decreased in mass.
This was because water moved in/out
by osmosis.
• Water always moves from ________
water concentration to ______ water
concentration.
Answer the following questions
in sentences
1. Why was the visking tubing bag dried in
a paper towel before being weighed?
2. Why was visking tubing used in this
experiment? What property does it
have that makes it a good model cell?
3. What would happen to an onion cell
placed in pure water?
4. What would happen to a cheek cell
placed in 10% sucrose solution?
Concentration Gradient
ball
ball rolls down gradient
high
ground
ball stops
gradient
(slope)
low
ground
Concentration Gradient
• Like the ball on the slope, water always
moves down a gradient from high to low
• Solutions are made up of a solute dissolved
in a solvent e.g. sugar dissolved in water
• Concentrations of the mass of solute are
written in percentages e.g. 1 % sugar
solution contain 1% sugar and 99% water.
Concentration Gradient
sugar
molecule
water
molecule
The difference in concentration of two
solutions is called a concentration gradient
Concentration Gradient
• Water moves down a concentration
gradient by osmosis from high to
lower water concentration. The
water will stop moving when the two
concentrations are equal.
Osmotic Effect On Cells
Water concentrations
• If we think about solutions in terms of
their water concentrations, it is easier to
recognise which direction water
molecules will flow in.
• A dilute sugar solution will have a high
concentration of water, whereas a
concentrated sugar solution will have a
lower water concentration
Concentrated
Sugar Solution
Dilute Sugar
Solution
Low water concentration
High water concentration
High sugar concentration
Low sugar concentration
Water Concentrations
Solutions in the body fall into one of three
categories:
• Hypotonic – Where the solution has a higher
water concentration than the cell.
• Isotonic – Where the solution and the cell
have an equal water concentration.
• Hypertonic – Where the solution has a lower
water concentration than the cell.
• In a hypotonic solution, the water will
move from the solution into the cell.
• In an isotonic solution the water
concentration will stay the same.
• In a hypertonic solution the water will
move from the cell into solution.
Water Concentrations
Hypotonic Solution
Direction of water
movement
H2O
concentration >
cell
A hypotonic solution has a higher water
concentration than the water concentration
within the cell, so water enters by osmosis.
Water Concentrations
Hypertonic Solution
H2O
concentration <
cell
A hypertonic solution has a lower water
concentration than the water concentration within
the cell, so water leaves the cell by osmosis.
Water Concentrations
Isotonic Solution
H2O concentration =
cell
An isotonic solution has a water
concentration that is equal to the water
concentration within the cell, so there is
no gain or loss of water by osmosis.
Osmosis in potato tissue
Plant Cells and Osmosis
Hypotonic solution: more
water outside of the cell than
inside, therefore water will
move into the cell by osmosis.
This causes the cell to swell
and become turgid
Hypertonic solution: more
water inside the cell than
outside, therefore water will
move out of the cell by
osmosis. This causes the cell
to become softer or flaccid
Animal Cells & Osmosis
• The effects of osmosis on animals
cells are totally different to plant
cells because animals cell structures
are different
• Animals cells do not have:
Cell walls
Vacuoles
Animal Cells & Osmosis
• Red blood cells (RBCs) float in a solution
called plasma which is isotonic
• RBCs in isotonic plasma do not change
size because the water has no
concentration gradient to follow
• RBCs in hypotonic and hypertonic plasma
will change because there is a
concentration gradient for water to
follow
Cell loses
water and
shrinks
RBC in isotonic solution
Normal RBC
No net
osmosis,
cell stays
the same
Cell takes in
water,
swells and
eventually
bursts