Calculate the linear magnification of drawings and the

• . Calculate the linear magnification of drawings and the actual size of specimens in images of known magnification http: //openlibrary. org/books/OL 9940982 M/Biology_Science_Skills_Worksheets_with_Answer_Key_(Holt_Science) Topic 1 Surface Area to Volume Ratio A B Assuming each box is 1 cm x 1 cm what is the surface area and volume of each human? 95: 23 78: 23

Today’s Lesson • Explain the importance of the surface area to volume ratio as a factor limiting cell size. • Conduct practice design for IA

SA: V • Cells are very small and cannot grow to be very large. • The volume of a cell determines the rate of exchange of materials with the outside environment. • As the volume of a cell increases, so does its surface area, but not in the same proportion.

Side of cube (cm) Surface area (cm 2) Volume (cm 3) SA: V 1 6: 1 2 3 Complete the table in your hand out and get ready to make some notes

Side of cube (cm) Surface area (cm 2) Volume (cm 3) SA: V 1 6: 1 2 24 8 3: 1 3 54 27 2: 1 Complete the table in your hand out and get ready to make some notes

• The plasma membrane is responsible for the import/export in the cell. Metabolic reactions occur on membranes. • A larger SA: V ratio means the cell can act more efficiently; for every unit of volume that requires nutrients or produces waste, there is more membrane to serve it.

Extension: Complete the worksheet in your handout

Extension: Complete the worksheet in your handout

There is a limit to the size of a single cell. Beyond this, a cell must divide and an organism must become multicellular More on this next lesson

Model Cells and Diffusion • A cube cannot be too large or there is not enough surface area to supply the volume, and the volume cannot be too small or there is not enough space for the organelles. Actual cells have developed strategies to cope with increasing size. • You are provided with a block of agar jelly that has been stained with 0. 1% DCPIP indicator, a solution of vitamin C (200 mg in 100 cm 3) and some other apparatus. Vitamin C will oxidise the DCPIP and turn it colourless. This colour change can easily be observed as the vitamin C diffuses into the jelly. The jelly can be cut to make model cells. Cut on the tile. • Carry out some preliminary investigations and then design a full investigation to show the effect of changing cell shape on diffusion. Use the handout to help you make a draft • Warning – you are NOT measuring the rate of diffusion.

Homework Complete the write up for the exploration today. The more effort you make the better your feedback for the real thing!!!