OCR AS Biology : Unit 1 (F212) : Cells, exchange and transport.
Module 1 Cells – part 1: Cell structure Induction Material
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.
Covered in
induction task 
Revised

Understanding
Looking at cells
Text book ref: p4 - 9
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.
(7marks)
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
(6 marks)
3) When studying cells structure using a microscope the smallest unit of measurement
commonly used to describe findings is the nanometre. Explain why. (2 marks)
Magnification and Resolution
4) Define the following terms:
Magnification:
Resolution:
(2 marks)
5) Compare and contrast the TEM and the SEM microscope. (4 marks)
6) Why are stains used in microscopy? (2 marks)
7) Calculating total Magnification of a compound light microscope
(4 marks)
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
8) Calculate the magnification factor of the diagram. (2 marks)
9) Calculate the length of structure G. (2 marks)
10) Calculate the diameter of the nucleolus (structure B). (1 mark)
11) Calculate the diameter of the nucleus. (1 mark)
12) Calculate the diameter of the cell at its widest point (1 mark)
13) Types
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
of microscope
Light Microscope
Transmission electron
microscope (TEM)
Scanning electron
microscope (SEM)
Cost
Can the image
be viewed
directly
Is staining of
the specimen
required?
14) 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. (2 marks)
15) State which type of microscope has been used to create the image below, give a reason
for your answer. (2 marks)
16) Which organelles may be present in a cell and what do they
do? (11 marks)
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
Rough
endoplasmic
reticulum
Nucleolus makes
RNA and
Ribsosmes.
These pass into
the cytoplasm
through the
nuclear pores
Yes
Yes
Smooth
endoplasmic
reticulum
Golgi
apparatus
Mitochondrion
(mitochondria)
Chloroplast
Lysosome
Centrioles
Plasma (cell
surface)
membrane
Cellulose cell
wall
Flagella and
cilia