Lesson 7 calculating magnification & dichotomous keys
- 2. Learning Objectives • Calculate the magnification of a drawing. • Use a dichotomous key. • Create a dichotomous key.
- 3. Calculating magnification. Formula: Magnification = size of the drawing size of the real object
- 4. Calculate magnification video • Magnification tips
- 5. 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.
- 6. Have a go: • Page 14 – Activity 1.2 – Questions: A1 & A2
- 7. Worksheet 2.3 – Magnification Calculations • Remember: – Use the correct units of measurement • Is it metres, millimetres or micrometres.
- 8. 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 μm magnification = image size ÷ actual size = 45 000 ÷ 100 = × 450 • 5 15 mm = 15 × 1000 μm = 15 000 μm actual size = image size ÷ magnification = 15 000 ÷ 1500 = 10 μm • 6 72 mm = 72 × 1000 μm = 72 000 μm magnification = image size ÷ actual size = 72 000 ÷ 0.9 = × 80 000
- 9. 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.
- 10. Get out your Homework: Dichotomous Keys Cambridge Biology Workbook: • Page 5 & 6 • Using Keys • Complete all questions.
- 11. 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.
- 12. Writing a key
- 13. 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?
- 14. • SAPS GROUPING AND CLASSIFICATION
- 15. 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.