Calculating Magnification & Dichotomous Keys

Learning Objectives

• Calculate the magnification of a drawing.• Use a dichotomous key.• Create a dichotomous key.

Calculating magnification.

Formula:

Magnification = size of the drawingsize of the real object

Calculate magnification video

• Magnification tips

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

Worksheet 2.3 – Magnification Calculations

• Remember:– Use the correct units of measurement• Is it metres, millimetres or micrometres.

Worksheet 2.3 - Answers

• 1 magnification = image size ÷ actual size= 36 ÷ 9 = × 4

• 2 actual size = image size ÷ magnification= 80 ÷ 4 = 20 mm

• 3 image size = magnification × actual size= 5 × 62 = 310 mm

• 4 45 mm = 45 × 1000 μm = 45 000 μmmagnification = image size ÷ actual size= 45 000 ÷ 100 = × 450

• 5 15 mm = 15 × 1000 μm = 15 000 μmactual size = image size ÷ magnification= 15 000 ÷ 1500 = 10 μm

• 6 72 mm = 72 × 1000 μm = 72 000 μmmagnification = image size ÷ actual size= 72 000 ÷ 0.9 = × 80 000

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.

Get out your Homework: 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

Worksheet 1.3 – Writing a key

• First of all:– Look at the leaves on the worksheet.– What features can you see?• Leaf shape – lobes or not?• Leaf edge – jagged or smooth?• One main vein in the middle or more than one main

vein?• Do the side veins come off in pairs or one at a time?• Is the stalk longer than 1 cm?• Anything else?

• SAPS GROUPING AND CLASSIFICATION

Homework

• Revise Unit 1

• On Monday we will review Unit 1.

• Write down any questions you have about the work covered so far and we will discuss them on Monday.