Studying Cells with a Microscope Lesson 3 Task

Studying Cells with a Microscope – Lesson 3 Task 1 – Practical skills: making a slide of onion cells and viewing it with a microscope A piece of onion A pair of forceps A microscope A coverslip Iodine solution A microscope slide A mounted needle Safety goggles Watch the video below to show you how to make a microscope slide to view onion cells. (from 2: 43 to (9: 00). https: //www. youtube. com/watch? v=SX 6 mow 1 AEx. I Use the video to write a method on how to prepare a slide to view onion cells observe under a microscope.

Task 1 – Practical skills: making a slide of onion cells and viewing it with a microscope Check your method and self assess! • Cut a section of onion and then peel a thin layer of onion. • Place thin layer of onion onto a glass slide (be careful to only hold the slide by the edges to avoid fingerprints). • Make the piece of onion skin as flat as you can on the slide to avoid cells overlapping. • Add a few drops of iodine to stain your onion cells. This will make them easier to see. • Carefully lower the coverslip over the onion at an angle. You can use a mounted needle to help with this. This reduces the chance of air bubbles forming.

Task 2 – Numeracy - Magnification 1. Use the information given to work out the magnification. No calculators! Magnification = eye piece lens x objective lens Eye piece lens Objective lens (x) Magnification (x) 10 10 100 40 20 100 30 800 25 7 55 12 3000 175 660

Task 2 – Numeracy - Magnification Actual size = image size magnification or Actual size = image size ÷ magnification Image size = actual size x magnification Magnification = image size or Magnification = image size ÷ actual size Actual size = how big the cell is in real life (without being magnified) Image size = The size of the cell in a drawing or what you can now see down the microscope Magnification = How much bigger you’ve made the cell look on your microscope

Task 2 – Numeracy - Magnification If an onion cell was observed through a x 100 magnification and it measured 17 mm, what would be the actual size of the cell? Actual size = 17 mm = 0. 17 mm 100 2. Apply what you know to work out the actual size of the following. a. An animal cell measures 10 mm under magnification x 250. Actual size = image size ÷ magnification = 0. 04 mm the size of the cell in real life (actual size) 10 250 a. A piece of muscle tissue measures 25 mm under magnification x 100. Actual size = image size ÷ magnification 25 100 = 0. 25 mm A red blood cell measures 5 mm under magnification x 40. Actual size = image size ÷ magnification 5 40 = 0. 125 mm

Light microscope 1. 2. objective lens Eye piece lens How to calculate total magnification? Eye piece magnification x objective lens magnification What is the main limitation of a light microscope? Maximum magnification is quite low (x 1000) compared to an electron microscope (x 500 000 or more). What is the main limitation of an electron microscope? Can only be used to view dead tissues.

Preparing a slide to view cells Why do we use substances like iodine solution and methylene blue? They act as a stain to make the cells more visible. Why is a mounted needle used when preparing a glass slide? Prevents the formation of air bubbles.