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 words

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

Clean sweep - 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.

Know the tricky details - for grade 7

These slides cover difficult parts of this topic - important if you are aiming for a high grade.
If grade 5 is your target, then save time, move on, study this information later, once you have revised the other topics.

Skills and applications

How to calculate cell size using the magnification of an image.

Calculating cell size using the magnification from David Faure on Vimeo.


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

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


How to calculate magnification of microscope images

Calculating magnification of cells using a scale bar from David Faure on Vimeo.


Explaining SA to Vol ratios

Surface area to volume ratio explained. from David Faure on Vimeo.

Revision 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. Stargart'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?

Revision mind map

This diagram summaries the main sections of topic 1.1.
Test if you can draw something like these concept maps from memory.

Can you ask a several questions about the points?

Try to include different command terms, e.g  List,  Describe, Outline, Explain,

Review questions

A quiz containing self marking questions covering the topic outlined above:

1

The 'Cell theory' explains the nature of living things.
Which statement best describes Cell theory?

According to cell theory, living organisms are composed of cells.
Cells come from pre-existing cells and cells are the smallest using of life.

2

Cell theory covers most, but not all cases.
Which one of these statements is an exception?

Exceptions to cell theory are : multinucleated striated muscle the giant single celled Acetabularia algae?
Also, organisms consisting of only one cell carry out all functions of life in that cell. e.g. Paramecium, Chlorella.

3

There are seven processes which are said to be possessed by all living things.
This sweet pea plant has grown a tendril around some string, to help support its upward growth.

Which of the characteristics of living things is illustrated in this photo?

The characteristics of living things (Mr H. Gren - metabolism, response, , homeostasis, growth, reproduction, excretion & nutrition)

The fly is responding to the closing trap, and the trap has responded to the presence of the fly.

4

What is the importance of surface area to volume ratio to cells?

Surface area to volume ratio is important in the limitation of cell size.

5

When nerve cells form brain tissue they can; store memories, create thoughts and coordinate movement.

If you only ever studied individual nerve cells you would never see these abilities which the brain has.

What is this type of property called?

Multicellular organisms have properties that emerge from the interaction of their cellular components. (Emergent properties)

6

The image shows a range of different cell types in the leaf of a Yucca plant.
How do stem cells form this range of cells?
What is the process called?

Specialised tissues can develop by cell differentiation in multicellular organisms.

Differentiation involves the expression of some genes and not others in a cell.

7

Stargardts disease is vision loss caused by the death of both cone cells and rod cells in the part of the retina around the fovea. One potential treatment for Stargardts disease is the use of human embryonic stem cells.
What are the properties of these stem cells, which other cells don't have, that makes them so useful for this treatment?

Stem cells can divide and this help researchers to grow them in the lab.

They can differentiate along different pathways in embryonic development which makes stem cells useful for therapeutic uses (e.g. Stargart's disease) because they can be grown into many different tissues.

8

The electron microscope image below shows a scale bar marked with 100µm.

The large 'goblet cell' in the centre is producing mucous which will protect the surface of the epithelium.

What is the diameter of the goblet cell?

Calculate specimen size using a scale bar?

You can often estimate the size using the scale bar and your thumb?

More accurately, measure the scale bar length in mm, measure the diameter of the cell, in mm
divide cell diameter by scalebar and multiply by 100µm

9

The image below shows erythrocytes and leucocytes.l.

Using the scale bar and the ruler placed on the image, estimate the magnification of the image.
Which answer is the best estimate

Calculate the magnification of an electron microscope image from a scale bar?

Convert the ruler measurement to the same units written on the scale bar, in this case 25mm is 25000µm

then divide the ruler measurement 25000 by the number on the scalebar, 25.

10

The blood cells below were imaged using an electron microscope.

The magnification is x3000 and the ruler measures the central cell as being 2 cm in diameter.

Estimate the actual size of this white blood cell.

Calculate specimen size using magnification?

First change the size measurement into µm units = 20000µm

Then divide by the magnification. 20000 / 3000 = 20 / 3 = 6.6 µm

11

If you know someone with a disease that might be cured by stem cell therapy then you might be a supporter of this research. You probably also know that some other people have deep concerns.

Which of the following is not a potential benefits of the use of stem cells?

There are ethical concerns about the use of embryo stem cells.

The research is expensive, and potential treatments are also likely to be expensive, and probably not available to all.

Many people who are against stem cells say that it is because cells are taken from human embryos, which have the potential for human live, and should be protected. There are other sources of stem cells, they argue.

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Longer written answer questions

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Revision fun

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