Lesson 6 making biological drawings & using keys

1. Making Biological Drawings &
Using Keys

2. Learning Objectives:
• How to draw a biological organism and
calculate the magnification.
• How to use a dichotomous key to identify
organisms.

3. 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.

4. 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.

5. 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.

7. Can you spot the mistakes?
• Scientific drawing
• From 1m50

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

9. Calculating magnification.
Formula:
Magnification = size of the drawing
size of the real object

10. 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.

11. Have a go:
• Page 14 – Activity 1.2
– Questions: A1 & A2

12. 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.

13. 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.

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

15. Exercise 1.2 Using keys
Note that students cannot write in italic, so should
underline 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 gracilis
b
• 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.

16. Writing a key

17. 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.