# 2.1.3 Cell Structure and Functions.

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2.1.3 Cell Structure and Functions.

2.1.4 comparing the relative sizes of molecules………………..
You have 3 minutes to answer the following: Give two reasons why we use light microscopes and give the main reason why we use the electron microscope.

What units of measurement do we use in biology?
International System. Why? So that the same units are used in every country in the world. Copy the following information.

SI units (international system)
1 metre (m) = 1m 1 millimeter (mm) = 1mm = 1x10-3m 1 micrometre (μm) = 1μm = 1x10-6m 1 nanometre (nm) = 1nm = 1x10-9m 1 centimetre cubed = 1cm3 1 decimetre cubed = 1dm3 (deci = 1/10 of a metre = 10 cm) 1 second = 1s 1 minute = 1min 1 hour = 1h Concentration is measured in mol dm-3 This just means mols per decimetre cubed.

Activity In pairs: Consider the following structures:
Put them in order of size starting with the smallest. a hydrogen molecule. a human cheek cell. a cell organelle(mitochondrion). a virus. a bacterium. plasma membrane

Answers a hydrogen molecule. plasma membrane a virus. a bacterium.
a cell organelle(mitochondrion). a human cheek cell. See page 10 of your text book.

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