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

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

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.

Mindmaps

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 on calculating size

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

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

Exam question on multicelluar organisms

This short video explains how to answer this type of question.

Explain the origins of multicellular organisms and its biological significance.  [8]

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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]

Extra exam question on cell function   - - - click the + symbol to open it -- >

This question requires knowledge of the functioning of single celled and multicellular organisms.

Write your answer and then compare it with the model answer

Distinguish between single celled condition and the multicellular condition. (4 marks).

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Write your answer and then click on the "+" icon for a model answer.

Extra exam question on specialised cells   - - - click the + symbol to open it -- >

Exam style question on cell differentiation.

This question requires knowledge of the mechanism of cell differentiation.

Write your answer to the question and then compare your answer with the model answer.

Explain how stem cells replicate to produce mature, specialised cells (4 marks)

Command term hints: Explain means that you must include details of reasons and causes.

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Write your answer then click on the "+" icon to see a model answer

Extra exam question on calculating magnification   - - - click the + to open it -- >

You previously looked at a video on cell size.  Now see if you can do a true size calculation.

This question requires knowledge of converting to true size using magnification.

The size of a mitochondrion on an electron micrograph is 43 mm.


If the magnification of the micrograph is x20000 calculate the true size of the mitochondrion. (2 marks).

Show your calculation, you may gain marks for the method of the calculation even if your answer is incorrect.

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Click on the "+" icon to see a model answer of the calculation.

Test yourself

Multiple Choice questions

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).


START QUIZ!

Click the '+' symbol to open the next quiz.

Multiple choice quiz 2


START QUIZ!

Drag and drop activities

Test your construction of biological explanations using the drag and drop questions below.

The multicellular nature of many organisms.

Drag and drop the correct term into the gap to describe differentiation.

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functions proteins tissues differentiation gene expression types stem

In a multicellular organism, there are specialised that develop from cells by . Differentiation involves altering gene , genes that code for needed for cell development are expressed in the cells, hence the cells have varied due to the of protein synthesised.

Correct terminology is needed to discuss cell development.


Click the '+' symbol to open the next explanation.

Drag and drop explanation of the limited size of cells

Stem cells

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inefficient volume exchanging oxygen surface area plasma materials

Cells are limited in size by their efficiency in exchanging through the membrane As the cell's increases, so does its need for materials such as or nutrients. However, the larger the cell, the lower the to volume ratio and the cell becomes in materials with the outside of the cell.

A cube of side 1x1x1mm has a surface area of 6mm2. It has a volume of 1mm3.

A cube of side 3x3x3mm has a surface area of 54mm2. It has a volume of 27mm3, 9 times the surface area but 27 times the volume of the smaller "cell".


Drag and drop explanation of stem cell therapy and ethics

  Ethics

The ethical use of stem cells.

Drag and drop the correct term into the gap to describe sources, uses and etics of stem cell therapy.

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ethical embryos Stargardt's foetus umbilical cord tissue divide therapeutic differentiate

Stem cells are able to by mitosis and into mature cells. This makes them have many uses, such as the treatment of disease. Stem cells can be obtained from and from an adult patients own cells. They can also be obtained from 3 to 5 days sfter fertilisation (usually unused embryos from fertility treatment) but this raises issues as it involves the destruction of a .

You need to know uses, sources and ethical issues of stem cell therapy


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.