Introduction to cells 1.1

Cell theory states that all organisms are made of cells. This is true in most cases but there are some notable exceptions, like skeletal muscle. This topic covers the cell theory, the exceptions to cell theory and how cells differentiate during cell growth. Using microscopes is part of the topic, as is measuring the size of cells.

Key concepts

Learn the biological vocabulary for 1.1 Introduction to cells and test yourself using these flash cards.


Essentials - quick revision through the whole topic

These slides summarise the essential understanding and skills in this topic. 
They contain short explanations in text and images - good revision for all students.

Read the slides and look up any words or details you find difficult to understand.


Summary list for 1.1 Introduction to cells

Cell theory

  • According to cell theory, living organisms are composed of cells.
  • Organisms consisting of only one cell carry out all functions of life in that cell, e.g. Paramecium, Chlorella.
  • Identifying the characteristics of living things (Mr H. Gren - metabolism, response, homeostasis, growth, reproduction, excretion & nutrition).
  • Surface area to volume ratio is important in the limitation of cell size.
  • Multicellular organisms have properties that emerge from the interaction of their cellular components, (Emergent properties).
  • Specialised tissues can develop by cell differentiation in multicellular organisms.
  • Differentiation involves the expression of some genes and not others in a cell.
  • Stem cells can divide and differentiate along different pathways in embryonic development which makes stem cells useful for therapeutic uses (e.g. Stargardt's disease).
  • There are ethical concerns about the use of embryo stem cells.

Calculating magnification and size

  • Calculate the magnification of an electron microscope image from a scale bar.
  • Calculate specimen size using a scale bar.
  • Calculate specimen size using magnification.


These diagrams summarise the main sections of topic 1.1.
Test if you can draw something like these concept maps from memory.
Can you ask several questions about the points using command terms, e.g  List,  Describe, Outline, Explain,

Exam style questions

Skills video tutorial

How to calculate the size of a cell using the scale bar.

Calculating cell size using a scale bar from David Faure on Vimeo.

Extra exam question

This short video explains how to answer this type of question.
Try to write an answer first then compare your answer with the model answer shown in the video.

[Many thanks to Catarina Gouveia, St. Dominic's International School, Portugal, for this question and mark scheme]

Test yourself

This quiz contains a set of multiple choice questions covering the topic. Explanations of each answer are displayed after you click to check the answer(s).


Just for fun

If you want to review key terminology and have some fun with your revision try this word shoot game.
It will help you remember the terms through repetition.