Numeracy Activity 3 – Mean and multiplication

Mean and Multiplication - Cell Counting [Stage 4]

 * Main focus: LW2a. identify that living things are made of cells
 * Additional outcomes and content statements:
 * LW2 Cells are the basic units of living things and have specialised structures and functions
 * WS7.1 Students process data and information by:
 * e. applying simple numerical procedures, eg calculating means when processing data and information, as appropriate

Activity Outline
In this lesson, students will use a simplified version of methods microbiologists use to count cells under the microscope. This will follow a lesson on cells as the smallest unit of life and serve as an introduction to the rest of syllabus section LW2. This lesson will not only exercise student numeracy skills, but also their competencies in using ICT and technology to solve problems.

Students will be given a link of an image (see link ), more specifically a human blood smear. They will be required to estimate the amount of cells in the sample by using a grid. Students (in pairs) will be instructed to use the following steps: Once all students estimate the number of cells in the image, the teacher will give the actual cell count. Students will compare this to their number and assess how accurate their counting method was. Finally, students will discuss in an open forum the benefits and limitations of this counting method as well as the accuracy and validity of their final result.
 * Save the image to the computer they are using.
 * Using a simple photo editor (such as PhotoShop or GIMP), students are to draw an even grid of squares. The amount of squares they use is up to them).
 * Count the amount of red blood cells in a single square and record the number. Repeat this with 2-3 more squares.
 * Using the total number of cells counted, students are to find the average amount of cells per square
 * Students will multiply the average cell count by the number of squares in the grid in order to create an estimate count

Differentiation and Considerations

 * If students are not confident with their image-editing abilities OR if computers with image-editing are not available, students can instead draw a grid onto a printed image using a ruler.
 * For students who excel at the activity, ask them to do another count. However for this second count, they are to use a different number of squares and see how this affects the average
 * For students who need an additional challenge, ask them to reflect on how differing approaches to the method may change the result and accuracy. Ask them the benefits/limitations of counting the squares all in one section as opposed to counting random squares around the whole image. Ask them to predict how the result may be affected if only the squares in the furthest corners of the image were used.