OCR AS Biology : Unit 1 (F212) : Cells, exchange and transport.
Module 1 Cells – part 1: Cell structure
We are learning to.......
Explain the difference between magnification and resolution
State the resolution and magnification that can be achieved
by a:



light microscope
transmission electron microscope
scanning electron microscope.
Explain why samples may require staining for light and
electron microscopy.
Describe the advantages and disadvantages of obtaining
images using a: light microscope, transmission electron
microscope, scanning electron microscope.
How to calculate the magnification /actual size of an image.
Recognise the following structures from diagrams and
electron microscope images:












nucleus
nucleolus
nuclear envelope
rough and smooth endoplasmic reticulum
golgi apparatus
ribosomes
mitochondria
lysosomes
chloroplasts
plasma (cell surface) membrane
centrioles
flagella and cilia
Describe the function of the structures listed above.
Describe the similarities and differences between the
structure of animal and plant cells
Identify animal and plant cells from diagrams and electron
micrographs
Describe how different organelles work together in cells to
produce and secrete proteins
Describe the structure of the cytoskeleton and explain its
role in:



providing mechanical strength to cells
aiding transport within cells
enabling cell movement.
Define the terms Prokaryotic and Eukaryotic.
Describe the similarities and differences between prokaryotic
and eukaryotic cells.
Identify prokaryotic and eukaryotic cells from diagrams and
electron micrographs
Covered in Class

Revised

Understanding
Looking at cells
Text book ref:
Key objectives:
 What are cells?
 How do we measure cells?
 What is the difference between Magnification and Resolution?
 How do you calculating magnification?
 What are the different types of microscope?
Background
The history of microscopy dates back to Hooke (1665) and van Leeuwenhoek (1676) whose
observations ultimately lead to development of the cell theory. The cell theory has four
basic ideas:
1. Cells are the smallest unit capable of independent life.
2. Cells are the basic unit of all living organisms i.e. all living things are made of cells.
3. Cells arise from other cells by a process of cell division.
4. The cell contains information that acts as the instructions for growth. This
information is passed on to new cells.
There 3 types of microscope used to study cells: light microscope, transmission electron
microscope (TEM) and Scanning electron microscope (SEM). Modern light microscopes can
achieve an effective magnification of up to 1500x and have a maximum resolving power of
200nm. Electron microscopes can achieve magnifications of up to 500000x and resolutions
of 1nm.
The “power” of a microscope depends both on its magnification and resolution, the higher
the resolution of a microscope the greater the detail you can see. The maximum resolution
achievable with a microscope is equal to half the energy source used to create the image.
Cell Theory
1) What is a cell? [2]
Units of measurement
1) Complete the diagram below to show: names of the units of measurement, unit
symbols, mathematical operations for converting between units.
2) Complete the table below to show the corresponding value nanometres, micrometres
and millimetres for the measurements given in each row. The first row has been
completed for you. Ensure that your answers use the correct unit symbols.
Nanometre
5
1
Micrometre
0.005
Millimetre
0.000005
1
1
3
7
0.5
3) When studying cells structure using a microscope the smallest unit of measurement
commonly used to describe findings is the nanometre. Explain why.
Magnification and Resolution
1) Define the following terms:
Magnification:
Resolution:
2) Visible light has a wavelength of 400-700 nm. Calculate the best resolution achievable
with a light microscope? Show your working out:
3) If the electron gun produces an electron beam with 2 nm wavelength, what is the best
resolution achievable?
Calculating total Magnification of a compound light microscope
Eyepiece
Objective
Overall
Magnification Magnification Magnification
X10
X4
X10
X10
X10
X40
X10
X100
Calculating Cell Magnification from images
The diagram below shows the general structure of an animal cell as seen under an
electron microscope.
_________
5m
1) Calculate the magnification factor of the diagram
2) Calculate the length of structure G
3) Calculate the diameter of the nucleolus (structure B)
4) Calculate the diameter of the nucleus
5) Calculate the diameter of the cell at its widest point
The diagram below shows the general structure of a plant cell when viewed under
and electron microscope.
___________
40m
1) Calculate the magnification factor of the diagram
2) Calculate the thickness of the cellulose cell wall.
3) Calculate the length of the cell.
4) Calculate the length of structure C.
5) Calculate the length of the vacuole.
Types of microscope
Feature
Source of
image
How is the
beam focused
Maximum
effective
magnification
Maximum
resolution
Can a live
specimen be
used?
Section or
external view
of the
specimen
Cost
Can the image
be viewed
directly
Is staining of
the specimen
required?
Light Microscope
Transmission electron
microscope (TEM)
Scanning electron
microscope (SEM)
1) Why is the maximum effective magnification of a light microscope said to be 1500x when
it is possible to produce higher magnifications with improved lenses?
2) Use a named example to explain the need for staining when using a light microscope.
3) State a possible disadvantage of staining a specimen for observation when using a light
microscope
4) State 2 advantages of using electron microscopes to study cells over a light microscope.
5) State 2 disadvantages of using electron microscopes to study cells.
6) Describe with reference to the role of staining how the transmission electron microscope
differs from a scanning electron microscope?
7) Explain why a vacuum necessary in an electron microscope?
Which microscope?
1) State which type of microscope has been used to create the image below, give a reason
for your answer.
2) The two images below of human chromosomes were produced using a light microscope
and SEM. State which is which; give a reason for your answer.
3) The image below was produced by staining a section of gut epithelium. The image is not
shown in false colour. Which type of microscope was used to produce the image?
Explain your answer.
4) The three images below are of human cheek cells. One image has been produced using a
light microscope, one using a SEM and one using a TEM. For each image identify the
microscope used and justify your choice
.
Cell structure
Text book ref: p10-15
Key objectives:
 What is the role of the cytoskeleton?
 Which organelles may be present in a cell and why?
 How can we recognise organelles in micrographs / diagrams?
 What are the differences between plant and animal cells?
 How do organelles in a cell work together?
 What are the differences between prokaryotic and eukaryotic cells?
Background
All living things are cells or are made of cells. From your GCSE course you should be familiar
with the basic structure of plant and animal cells. Since the development of the electron
microscope a large number of structures have been identified within cells; those structures
with a specialised function are termed organelles. Organelles within a cell work together to
enable the cell to carry out its function. The fact that each organelle performs a different
function within the cell is referred to as division of labour. The type, number and position of
organelles will vary between cells dependent upon the cells role, environment and “life
stage”.
Cytoskeleton
There is a network of fine filaments or fibres that run through the cytoplasm of the cell. This is
known as the cytoskeleton. There are three types of fibre:
1) microfilaments
2) intermediate filaments
3) microtubules
Complete the table to compare the structure and functions of the components of the cytoskeleton:
Cytoskeleton Component
Microfilament
Size:
Composition:
Intermediate filament
Size:
Composition:
Microtubule
Size:
Composition:
Function
1) Describe two ways in which the cytoskeleton can aid the movement of an entire cell.
2) Name a type of human cell (not a sperm cell) that is able to move and explain why this is
important to the cells function
3) Why might chloroplasts need to be moved around a plant cell
4) Many of the cells that line the human respiratory system are ciliated. Explain why
Which organelles may be present in a cell and what do they do?
Organelle
Nucleus
Nucleolus
Diagram
Structure
Function
Animal Plant Visible under
cell?
cell? a light
microscope
The nucleus is the
largest organelle (1020m diameter)
Roughly spherical.
Surrounded by a
double membrane
called the nuclear
envelope
The nuclear envelope
contains openings
called nuclear pores.
Outer membrane joins
up to the endoplasmic
reticulum
The nucleoplasm
contains chromatin
(DNA + histones)
which can be seen as
dark blobs or fibre.)
Contains nearly all
of a cells genetic
material;
instructions for
making proteins
Controls protein
synthesis (makes
mRNA)
Yes
Nucleolus is not
surrounded by A
membrane
Dense spherical
structure inside the
nucleus
Ribosome
Nucleolus makes
RNA and
Ribsosmes.
These pass into
the cytoplasm
through the
nuclear pores
Yes
Yes
Rough
endoplasmic
reticulum
Smooth
endoplasmic
reticulum
Golgi
apparatus
Mitochondrion
(mitochondria)
Chloroplast
Lysosome
Centrioles
Plasma
membrane
Cellulose cell
wall
Vacuole
Vesicle
1) Describe three structures / organelles present in generalised plant cells but absent from
animal cells.
A)
B)
C)
2) Name the structures in the diagram below
3) Sperm cells contain large numbers of mitochondria. Explain why?
4) What evidence can be seen in the diagram that suggests that the cell is:
o metabolically active and involved in secretion of enzymes [3]
o involved in production or modification of lipids? [1]
The diagram is a line drawing of a cell as seen with an electron microscope.
A
B
C
20 μm
D
H
E
F
G
Complete the table by matching the label to the function and then naming the appropriate
part. The first one has been completed for you.
Function of Structure
Label
Name of Part of
the Cell
Controls the activity of the cell.
A
Nucleus
Protein/polypeptides are made here.
Aerobic respiration takes place here.
Produces secretary vesicles.
Controls the entry of substances into the cell.
Contains hydrolytic enzymes.
Makes lipids, including steroids.
By reference to the diagram: Is the cell that of an animal or a plant? Give a reason for your
answer.
Identifying organelles from micrographs
4) Name the large round organelle in the micrograph below
5) Is it found in animal or plant cells
6) Name the structures A,B and C
7) Name the large organelle shown in the micrograph below
8) Is it found in animal or plant cells?
9) Suggest what structure D could be
10) Name the organelle shown in the micrograph below
11) State the role of the organelle
12) Name the structures visible in the transmission electron micrographs below
13) Name the structure shown in the micrograph
14) Name the structure shown in the micrograph below
15) Name the structure shown in the micrograph below
Test yourself on a full cell micrograph
Is this an animal or plant cell? Can you name the structure 1-4
Use the word bank at the bottom of the page to label this plant cell
Nuclear envelope, Nucleolus, Chloroplast, Mitochondria, cytoplasm
Endoplasmic reticulum, starch grain, Cell wall, plasma membrane, vacuole
Parts of the cell working together
Complete the paragraph below to describe how organelles in a cell work together to
produce and secrete proteins such as hormones
The nucleus carries all the necessary instructions for the cell to function. The code for
protein synthesis is carried in the ____________ which are made of ____________ or
histones. The instructions are ____________ or copied into mRNA (messenger ribonucleic
acid). The mRNA then leaves the nucleus via the _________________ and travels to the
______________ where the message is read and translated into protein. The newly
manufactured proteins are transported to forming face of Golgi body/apparatus in transport
__________. Within the Golgi apparatus the proteins are processed. Vesicles are budded off
from the maturing face of Golgi and are transferred to the ___________________ for
secretion. Glandular cells (e.g. pancreas) contain large amounts of __________________
(this is encrusted with ribosomes and is where protein synthesis takes place) and Golgi
body. These cells also contain many mitochondria since protein synthesis requires a lot of
__________.
(ii) State the function of structures B. [1]
(iii) Describe the role of structure C in secretion. [3]
Prokaryotes and Eukaryotes
1) The diagram below shows Staphylococcus, which is a prokaryotic cell. Label parts A to D
2) The following table compares some features of a prokaryotic and eukaryotic animal cell.
Complete the table by using ‘present’, ‘absent’ or a short descriptive phrase. The first
has been completed for you.
Cellular Feature
Prokaryotic Cell
Eukaryotic Animal Cell
Cell wall
Present
Absent
Cell surface membrane
Nucleus
Membrane bound organelles
DNA
Plasmids in the cytoplasm
Read p14-15 OCR Biology text book
1) Fill in the gaps
It was once common practice to classify all living organisms as either animals or plants. With
improved knowledge of living things it has become apparent that there are ______
fundamentally different types of cell. The most obvious difference between the two types is
that one possesses a nucleus and the other does not.
The cells of animals, ___________ and fungi contain many organelles some of which are
bound by a membrane. These are referred to as ______________ cells. The cells of bacteria
are very different, they lack membrane bound organelles such as a _____________. This
type of cell is referred to as a _______________ cell (meaning before nucleus). Prokaryotic
cells are about 1000 to 10000 times smaller than eukaryotic cells and are much simpler in
structure. Biologists believe eukaryotes evolved from ________________.
2) Eukaryotic cells contain membrane bound organelles, give 5 examples:
3) Prokaryotic cells have one membrane, where is it?
4) Use table 1 to compare plant (eukaryote), animal (eukaryote) and prokaryotic cells. For
each cell type indicate whether the feature is present or absent using a tick or cross.
Feature
Chloroplasts
Large permanent vacuole
Cellulose cell wall
Peptidoglycan (murein) cell wall
Linear chromosome
Circular chromosome
Plasmids
Endoplastic Reticulum
Golgi body
DNA free in the cytoplasm
ATP is produced in the
mitochondria
ATP is produced at infolded
regions of the cell membrane
called mesosomes
Undulipodia contain 9 + 2 circular
arrangement of microtubules
Flagella made form spiral protein
called Flagellin
Ribosomes
Cell membrane
Plant cells
Animal cells
Prokaryote cells
5) Give 2 ways in which prokaryotes are useful to humans
6) Mitochondria and chloroplasts contain small loops of DNA similar to the plasmids found
in prokaryotic cells. These organelles also contain ribosomes that are the same size as
prokaryotic ribosomes. Can you suggest an explanation for these features?
7) Give one way in which a eukaryotic plant cell is similar to a prokaryote.
8) Give two ways in which a eukaryotic plant cell is different from a prokaryote.
9) Label the highlighted features on the diagram of the bacterium E.coli shown in the
diagram below.