Sugar Cubes by Uwe Hermann on Flickr (CC) Which dissolves faster: sugar cubes or sugar crystals? Why?

What will go cold faster: French fries or a baked potato? Why? French Fries by Ian Britton on Flickr (CC)

Which makes green tea faster: tea leaves or powder? Matcha Latte by Cupcake Murder Aftermatch on Flickr (CC)

What type of crisps delivers more flavour: regular-cut or crinkle-cut? Why? Smiths Plain Chips by Penguin Cakes on Flickr (CC)

Lesson Objectives Recall the differences between single and multicellular organisms Show experimentally why surface area to volume ratio is important in the limitation of cell size.

IN:  Oxygen  Nutrients  Water OUT:  Carbon dioxide  Waste  Products (e.g. proteins) The plasma membrane of a cell is the surface of exchange for materials between the inside and the outside of the cell.

As the cell gets larger, it requires more resources to be imported and produces more products (and waste) to be exported. Therefore, a larger volume requires more exchange across the membrane.

As the cell gets larger…

As the cell gets larger… …the surface area to volume ratio actually gets smaller…

As the cell gets larger… …the surface area to volume ratio actually gets smaller… …so the exchange processes become less efficient with increasing size.

Diffusion Pathways

Quick practical You are going to experimentally show that a cell with a larger surface area will be able to transport materials through it much faster by diffusion then a larger cell. You need 3 different size blocks of agar. Method 1.Cut a piece of agar in to a 4cm x 2cm x 2cm block 2.Cut the block in half (so you have two 2cm x 2cm x 2cm pieces) 3. Cut one of these blocks in half again (so you have two 2cm x 2cm x 1cm blocks) 4.Cut one of these in half again 5.Take the beaker we NaOH (sodium hydroxide) and place all 3 blocks in at the same time. 6.Record how long it takes to get a complete colour change *The blocks of agar are impregnated with phenolphthalein which turns pink in alkaline solutions Make a table to record your data below… Calculate the surface area to volume ratios of your blocks. Write a conclusion for your data 2cm

DIVIDEDIVIDE Surface are to volume ratio is a factor that limits the size of cells. By dividing to make more, smaller cells, the efficiency of the exchange processes across the membranes (into and out of the cells) can be kept high. Shorter diffusion paths. More surfaces for reactions. Removal of heat and waste 4-cell stage of a sea biscuit by Bruno Vellutini on Flickr (CC) CELLSCELLS

Mammalian liver mitochondria: Natural selection favours adaptations that give an advantage. Folded structures are everywhere in nature, maximising the surface area to volume ratio for exchange of materials. Structure/Function

Big Cell Exceptions Caulerpa species of algae are one giant cell with many nuclei distributed throughout.

Epulpoiscium, by AJ Cann on Flickr (CC) Big Cell Exceptions Epulopiscium is a giant species of bacteria. Read more about it here: NotExactlyRocketScienceNotExactlyRocketScience. 100μm E. coli

Free images from: Presentations ETC, University of Florida. Is maximising surface area to volume ratio always an advantage?

Free images from: Presentations ETC, University of Florida. Three Minute Essay Explain the importance of surface area to volume ratio as a factor limiting cell size. ReasonConnectivesJustification Because Therefore Thus So Such as For instance Where as Unlike Instead of Explain question planner

Design an investigation into the effect of SA:Vol ratio on exchange of…

Exploration: which cools faster? 30ml Add 30ml hot water to a small cup and to a petri dish. Predict: Will one cool faster? Why? Record: Take the temperature of each one every minute. Describe or plot the results.