Plants and animal cells
Monacia Williams, Contributor

Hello again! Welcome to another lesson. I hope that you have been finding them useful so far. Today we are going to look at another aspect of the plant and animal cell. The syllabus requires that you draw and label simple diagrams of these cells to show their structures. I find that this is a good opportunity to introduce you to the concept of biological drawings.

Yes, I know that you have been drawing from the time you started to study science in first form, but you might not have been told that the production of good biological diagrams requires that you observe certain rules. Be guided by these rules and I assure you that you will always get a good mark for your drawings. Remember that drawing is one of the skills tested in the school-based assessment! If you already know these rules, don't stop reading. Use this as a revision lesson!

First, you need to know that there are two words that are often confused; drawing and diagram. Let us make a distinction between the two.

Drawing

This is a representation of an actual specimen (model or apparatus).

Diagrams

These include all other forms of illustration, for example:

• graphs - line or bar
• area diagrams - pie charts, maps, flow charts.

Use drawings and diagrams

• when it will make the answer clearer
• when the question asks you to:
  - illustrate
  - give annotated diagrams
  - make a sketch
  - draw
  - describe with the aid of diagrams

How are you going to practise the skill? Here is what I need you to do. Find a drawing of the animal cell in your textbook - every text has this diagram; this is going to become the model of your specimen. Reproduce this drawing in your notebook.

Guidelines for drawings

• Use an HB or #2 pencil and a good, clean eraser.
• Make a faint outline of what you wish to draw.
• Fill in the details with clear, continuous lines of even thickness.
• Make your drawings as large as possible - occupying at least 70 per cent of the available space.
• Position your drawing to the left of the page so that enough space is left on the right for the labels.
• Always use a ruler to draw straight labelling lines.
• Do not shade.
  Your drawing is not complete until it is labelled.

Guidelines for labels and labelling lines

Labels

• Must be written neatly, in script, against the labelling lines and not on top of it.
• Must be accurate, specific and spelt correctly.

Labelling lines

• Must be horizontal where possible.
• Must touch what they are indicating.
• Must not cross each other.
• Must not carry arrowheads or dots.
• Your drawing must have a title, which must include:
• The name of the organism.
• The name of the structure being drawn.
• The magnification of the drawing.

I have just included a new word. Did you notice? That word is magnification! This enables the viewer to compare the size of your drawing with the size of the actual specimen. This is a calculated value and is found using the following formula:

Magnification = Size of drawing/Size of specimen

How do you do this? First, measure any dimension of your specimen, either the length or the width, then measure the same dimension on your drawing. Finally, put the values in the formula and divide. The answer is your magnification! Bear in mind that this can be any value, even a fraction that should be converted to a decimal.

Go ahead; try your hand at this! Good luck! Join me again next week to see what is in store for you.

Students of McGrath High School perform during the launch of the Centre of Excellence, at the school in St Catherine, recently. - Ian Allen/Staff Photographer

Monacia Williams teaches at Glenmuir High School.