Making Biological Drawings & Using Keys

Learning Objectives:• How to draw a biological organism and

calculate the magnification.• How to use a dichotomous key to identify

organisms.

Making Biological Drawings.

Biologists need to be able to look closely at specimens and note significant features of them.

It is important to be able to make simple drawings to record these features.

Making Biological Drawings.

Do:– Make good use of the

space on your paper.– Make your drawing large.– Leave space around it for

labels.– Always use a sharp HB

pencil and a rubber.– Keep all lines single and

clear.

Don’t:– Use shading unless

it’s absolutely necessary.

– Use colours.

Labelling Biological Drawings

• Use a ruler to draw each label line.• Make sure the end of the label line actually

touches the structure being labelled.• Write the labels horizontally.• Keep the labels away from the edges of your

drawing.• Print your labels.

Can you spot the mistakes?

• Scientific drawing

• From 1m50

Your turn.● You will receive a specimen to draw:● Use page 13 in your coursebook to help.

Calculating magnification.

Formula:

Magnification = size of the drawingsize of the real object

Important things to remember!

• You must use the same units for all the measurements.– Usually, millimetres are the best units to use.

• You should not include any units for the final answer. Magnification doesn’t have a unit but you must include a times sign.

Have a go:

• Page 14 – Activity 1.2– Questions: A1 & A2

Keys and Identification

• Keys are used to identify different species. A key will usually ask questions based on easily identifiable features of an organism.

• Dichotomous keys use questions to which there are only two answers. They can be presented as a table of questions, or as a branching tree of questions.

Dichotomous Keys

• The following key could help you identify a new vertebrate.

• For example, – if it had no fur or feathers and

dry skin, you would follow the right-hand pathway at the first and second junctions, but the left-hand pathway at the third junction. This would lead you to identify the animal as a reptile.

Dichotomous Keys

Cambridge Biology Workbook:• Page 5 & 6• Using Keys• Complete all questions.

Exercise 1.2 Using keysNote that students cannot write in italic, so shouldunderline the binomials instead.a • A (given) 1b, 2a, 3a, Crocodylus niloticus• B 1a, Geochelone elephantopus• C 1b, 2b, Ophiophagus hannah• D 1b, 2a, 3b, Chamaeleo gracilisb • i binomial• ii The first part is the genus the organism belongs

to, and the second part is its species.c • They all have scales.

Writing a key

Exercise - Writing a key

• Page 16 in Coursebook.– Figure 1.23– Write a key for the 4 flowers.

• Pairs of characters that can be distinguished clearly, while looking only at one leaf (so, for example, pairing ‘large’ and ‘small’ is not suitable)

• Pairs of characters that are related to one another (e.g. so, for example, pairing ‘serrated margin’ and ‘network of veins’ is not suitable)

• A key that works in as few pairs of points as possible.