[Music] hi and welcome back to Freez lessons. co.uk by the end of this video you should be able to describe the size of cells you should then be able to use the prefixes CTI Millie micro and Nano now I should point out that this material may seem quite tricky you might need to watch this video a couple of times to get the ideas in the last video we started looking at cells we looked at the similarities and differences between eukariotic cells such as animal and plant cells and procaryotic cells such as bacteria one of the key differences is that procaryotic cells are much smaller than eukariotic cells in this video we're going to look at the sizes of cells so let's get started all sizes in science are based on the meter but the problem is that objects in biology are often much smaller than that let's look at some examples I'm sure sh you here a German shepherd and the average length of a dog like this is around 1 M now if we divide 1 M into 100 equal parts then we've got 1 cm the word CTI means 100th so 1 cenm is 100 of a meter now scientists often use standard form and you could be expected to use that in your exams 1 cm is 1 * 10 ^ of - 2 m just to give you an idea of the size of that the width of your little finger is around 1 cm now again in biology 1 cm is large if we divide 1 cm into 10 equal parts then we've got 1 mm so 1 cm is 10 mm again just to give you an idea of that the tip of a ballpoint pen is around 1 mm now the word Millie means 1,000th so 1 mm means 1,000th of a meter and again using Standard Form 1 mm is 1 * 10^ of - 3 m going back to the dog we can see that this is 1,000 mm long in other words 1 M now again in biology 1 millim is pretty big so scientists work with even smaller sizes if we take a meter and divide this into 1 million equal parts then we've got a micrometer the word micro means 1 millionth so one micrometer is 1 millionth of a meter a micrometer has this symbol and I'd recommend that you learn that in standard form 1 micrometer is 1 * 10 the^ of - 6 M now a typical human cell such as this one is around 10 to 20 micrometers in size that means that biologists find a micrometer a very useful unit especially when looking at cells now cells contain small Parts such as ribosomes and we're going to look at those in a later video this means that we need an even smaller unit to talk about the sizes of objects inside cells so the final unit we're going to look at is called the nanometer the word Nano means one billionth so 1 nanometer is 1 billionth of a meter in standard form a nanometer is 1 * 10 ^ of - 9 M now I should point out that a nanometer is a very small size Pro proteins and cells are measured using nanometers this shows the protein hemoglobin which is found in red blood cells a molecule of hemoglobin is around 5 nanometers in diameter remember you'll find plenty of questions on the size of cells in my vision workbook which you can get by clicking on the link above okay so hopefully now you should be able to describe the size of cells you should then be able to use the prefixes CTI Millie micro and Nano [Music]