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1.1.1
thebiotutor
AS Biology OCR
Unit F211: Cells, Exchange & Transport
Module 1.1 Cell Structure
Notes & Questions
Andy Todd
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Explain the difference between magnification and resolution.

Magnification
o
The number of times an image is greater in size than the object.
o Increases the ability to see details

Resolution
o The ability to distinguish two objects as separate from each other.
o Allows details to be seen with more clarity
o Determined by the wavelength of light or electron beam
State the resolution and magnification that can be achieved by a light
microscope, a transmission electron microscope and a scanning electron
microscope.

Light Microscope
o Uses light
o Light passes through thin specimen
sample
o Sample

Living or non-living
o Low magnification = x1,500
o Low resolution = 200µm (half the λ
of visible light)
o Stains - Dyes

Iodine

methyl blue

acetic orcein
o Easy and cheap to create samples
o Easy and cheap to setup
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
Transmission Electron Microscope (TEM)
o Uses a beam of electrons which
pass through the sample
o High magnification = x500,000
o High resolution = 0.1nm (The λ of
electron beam).
o Sample

Non-living
o Creates a 2D image
o Contrast is created by structures of
different densities.

Dense structures absorb
more electrons and sop
appear darker
o Stains

salts of heavy metals
o Difficult and expensive to create samples.
o Difficult and expensive to setup and use.
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
Scanning Electron Microscope (SEM)
o Uses a beam of electrons which
bounce off the surface of the
specimen.
o High magnification = x100,000
o High resolution = 0.1nm (The λ of
electron beam).
o Sample

Non-living
o Creates a 3D image of the surface
o Stains

salts of heavy metals
o Difficult and expensive to create samples.
o Difficult and expensive to setup and use.
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1.1.1
Explain the need for staining samples for use in light and electron microscopy.


It is necessary to give contrast between structures.
Stains are taken up differentially by objects with different densities.
o Light microscopy:
o Electron microscopy:
e.g. iodine, methyl blue, acetic orcein
e.g. salts of heavy metals
Calculate the linear magnification of an image.
o Units of microscopy is always micrometers (µm)
o You MUST always write you answer in µm.
o Be careful that you convert the units of the image size into µm.
 1 mm = 1,000 µm
 1 cm = 10,000 µm
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A = actual size
I = image size
M = magnification

Using a graticule to measure specimens (practical exercise)
o Place micrometer on the microscope stage. This is a tiny ruler, 1mm long
and divided into 100 divisions
o Replace eyepiece with graticule eyepiece. This is marked in arbitrary units
and needs to be calibrated.
o Calibrate the eyepiece by lining it up against the stage micrometer
o You can now exchange the stage micrometer with the slide of the specimen
to be measured and use the calibrated eyepiece graticule to measure it.
o REMEMBER. You need to recalibrate the eyepiece for each different
objective lens magnification.
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1 To convert millimetres to micrometres:
A multiply by 1000
B divide by 100
C divide by 1000
D multiply by 100
2 The resolving power of a microscope is its ability to:
A produce an enlarged image
B separate two nearby points
C show a large field of view
D reduce the depth of view
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3 Actual size, apparent size and magnification are related by the formula:
A actual size = image size x magnification
B image size = actual size divided by magnification
C magnification = image size x
D image size = actual size x magnification
4 In comparison with optical microscopes, transmission electron microscopes have:
A higher resolution but lower magnification
B lower resolution but higher magnification
C lower resolution and lower magnification
D higher resolution and higher magnification
5 In the scanning electron microscope, the image is created from:
A electrons that pass through the specimen
B electrons that are reflected from the specimen
C both A and B
D neither A nor B
Describe and interpret drawings and photographs of eukaryotic cells as seen
under an electron microscope and be able to recognise the following
Answers: 1.A 2.B 3.D
4.D
5.B
structures:

Animal Cell
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E
D
A
B
C

Plant Cell
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
Nucleus & Nucleolus
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

Rough and smooth endoplasmic reticulum
Golgi apparatus
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
Mitochondria

Lysosomes
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
Chloroplasts

Centrioles
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
Undulipodia (Flagella) and cilia
Outline the functions of the structures listed above.

Plasma Membrane
o Description

Creates the outer surface of animal cells and lies just on the inside of
the cell wall in plants and prokaryotes

It is made of lipids and proteins.
o Function


Regulates the movement of substances into and out of cells

Also used in cell signaling
Cell Wall (Plant = cellulose and Fungi = chitin)
o Description

Rigid structure that surrounds plant cells and prokaryotes

Plant cell walls are made from a cellulose (carbohydrate) network

Prokaryotes cell walls are made from peptidoglycan
o Function

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Supports cells
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
Nucleus
o Description

Large organelle surrounded by a nuclear envelope (double
membrane), which contains many pores.

Contains chromatin and often a structure called the nucleolus
o Function


Chromatin is made from proteins and DNA

Pores allow RNA to move between the nucleus and the cytoplasm

Nucleolus makes ribosomes
Lysosome
o Description

A round organelle surrounded by a membrane, with no clear internal
structure
o Function


Contains digestive enzymes.

These are kept separate from the cytoplasm by the surrounding
membrane, and can be used to digest invading cells or to break down
worn out components of the cell.
Ribosome
o Description

A very small organelle that either floats free in the cytoplasm or is
attached to the rough endoplasmic reticulum
o Function


Site where proteins are made.
Rough Endoplasmic Reticulum
o Description

A system of membranes enclosing a fluid-filled space.

The surface is covered in ribosomes giving the rough appearance.
o Function

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Folds and processes proteins by adding sugar chains that have been
synthesized at the ribosomes.
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
Smooth Endoplasmic Reticulum
o Description

Similar to rough endoplasmic reticulum, except with no ribosomes.
o Function


Synthesises and processes lipids
Vesicle
o Description

A small fluid-filled sac in the cytoplasm, surrounded by a membrane.
o Function


Transports substances in and out of the cell (via the plasma
membrane) and between organelles.

Some are formed by the golgi apparatus or the endoplasmic
reticulum, while others are formed at the cell surface.
Golgi Apparatus
o Description

A group of fluid-filled flattened sacs.

Vesicles are often seen at the edges of sacs.
o Function


It processes (adding or trimming sugar chains) and packages new
lipids and proteins.

It also makes liposomes. Very useful at transporting hydrophillic
substances
Mitochondrion
o Description

They are usually oval-shaped.

They have a double membrane – the inner one is folded to form
structures called cristae.

Inside is the matrix, which contains enzymes involved in respiration.
o Function
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
The site of aerobic respiration, where ATP is produced.

They’re found in large numbers in cells that are very active and
require a lot of energy.
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1.1.1

Chloroplast (Plant Only)
o Description

A small, flattened structure found in plant cells.

Surrounded by a double membrane and also has membranes inside
called thylakoids

Thylakoids are stacked up to form grana

Grana are linked together by lamellae – thin, flat pieces of thylakoid
membrane.
o Function


The site where photosynthesis takes place
Centriole (not in plants)
o Description

Small hollow cylinders containing a ring of microtubules
o Function


Involved in the separation of chromosomes during cell division.
Cilia
o Description

Small, hair-like structures found in large numbers on the surface
membrane of some animal cells.

In cross section, they have an outer membrane and a ring of 9 pairs
of protein microtubules inside, with a single pair of microtubules in
the middle.
o Function


Microtubules allow the cilia to move.

This movement (wafting) is used to move substances along the cell
surface.
Undulipodia (Flagellum in prokaryotes)
o Description

Like cilia but longer and found in fewer numbers.

They protrude from the cell surface and are surrounded by the
plasma membrane
o Function
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
The microtubules contract to move the undulipodia

They propel the cell forward (E.g. sperm).
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1.1.1
Outline the interrelationship between the organelles involved in the production
and secretion of proteins.
1. Messenger RNA leaves the nucleus after transcription of the DNA code
2. Protein synthesis occurs at ribosomes either on the RER or free in the cytoplasm.
The ribosomes translate the code into polypeptides
3. Ribosomes on the RER make proteins that are excreted from the cell or attached to
the cell membrane.
They are folded and processed (E.g sugar chains are added) in the RER.
4. Free ribosomes make proteins that stay in the cell cytoplasm.
5. Proteins are transported in vesicles which ‘bud off’ from the RER and travel to the
Golgi apparatus
6. The Golgi apparatus processes the proteins further by trimming the sugar chains or
adding additional chains.
7. The proteins enter more vesicles to be transported around the cell
8. Proteins leave the cell by exocytosis. The vesicle membrane fuses with the plasma
membrane. Requires ATP
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1
7
2
6
4
3
5
Explain the importance of the cytoskeleton in providing mechanical strength to
cells, aiding transport within cells and enabling cell movement.

Organelles in cells are surrounded by the cytoskeleton.

The cytoskeleton is a network of protein threads running through the cytoplasm.

In eukaryotic cells the protein threads are arranged as microfilaments (small solid
strands) and microtubules (tiny protein cylinders)

The Cytoskeleton has 4 main functions
o Support the cells organelles, keeping them in position.
o Strengthen the cell and maintain its shape
o Transport materials within the cell
o Cause the cell to move, either moving cilia or the whole cell as with
undulipodia.
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Compare and contrast, with the aid of diagrams and electron micrographs, the
structure of prokaryotic cells and eukaryotic cells
Prokaryote
Diameter of Cell
Nucleus
Membrane bound
organelles
Cell wall
Eukaryote
Prokaryote
Eukaryote
0.2 - 2.0µm
10 - 100µm
No nuclear membrane
True nucleus
Absent
Present
Cellulose (plants)
or chitin (fungi)
Carbohydrates and sterols
present
Peptidoglycan
Plasma membrane Lacks carbohydrates and sterols
Ribosomes
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Chromosome
70s Smaller
Single circular chromosome
lacks histones
80s larger
Multiple chromosomes
with histones
Cell Division
Binary fission
Involves mitosis
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1.1.1
Compare and contrast, with the aid of diagrams and electron micrographs, the
structure and ultrastructure of plant cells and animal cells.
Eukaryote
Animal Cell
Plant Cell
Plasma Membrane
Cell Wall
Nucleus
Lysosome
Ribosome
Rough ER
Smooth ER
Vesicle
Golgi apparatus
Mitochondrion
Chloroplast
Centriole
Cilia
Undulipodia
1.
Prokaryote
Bacterial Cell














Cellulose












Peptidoglycan







Mesomes



Flagella
State the maximum magnification that can be achieved by a light microscope and a
transmission electron microscope.
Select your answers from the list below.
10x
40x
100x
400x
1500x
25 000x
50 000x
light microscope
................................... x
transmission electron microscope
................................... x
500 000x
[Total 2 marks]
2.
Describe what is meant by the term resolution.
..................................................................................................................................
..................................................................................................................................
..................................................................................................................................
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..................................................................................................................................
[Total 2 marks]
3.
In the lungs, goblet cells secrete mucus. The mucus is then moved by cilia.
Name one cellular structure from the list below that is associated with each of the
following functions. You must select a structure once only.
mitochondria
ribosome
Golgi vesicle
centriole
nucleus
cytoskeleton
(i)
release of energy .......................................................................................
(ii)
movement of cilia .......................................................................................
(iii)
secrete mucus ............................................................................................
[Total 3 marks]
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4.
The figure below is a diagram of an animal cell as seen using a transmission electron
microscope.
A
B
C
D
E
F
20 µ m
(i)
Name the structures of the cell labelled A, B, C and D.
A ....................................................................
B ....................................................................
C ....................................................................
D ....................................................................
[4]
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(ii)
Structures C and E are examples of the same organelle.
Suggest why E looks so different to C.
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
.........................................................................................................................
[2]
(iii)
Calculate the actual length of structure C.
Show your working and give your answer in micrometres (µm).
Answer = .................................................. µm
[2]
[Total 8 marks]
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5.
The table below compares features of typical eukaryotic and prokaryotic cells.
(i)
Complete the table by placing one of the following, as appropriate, in each empty
box of the table.
•
a tick ( )
•
a cross (
•
the words ‘sometimes present’
)
Some of the boxes have been completed for you.
eukaryotic cell
cell wall
prokaryotic cell
sometimes present
nuclear envelope
Golgi apparatus
ribosomes
flagellum
(ii)
sometimes present
Outline the roles of the Golgi apparatus and the ribosomes.
Golgi apparatus ..............................................................................................
.........................................................................................................................
.........................................................................................................................
[4]
Ribosomes ......................................................................................................
.........................................................................................................................
[2]
[Total 6 marks]
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