CELL SIZE AND CELL MEMBRANE SB1.a. Explain the role of cell organelles for both prokaryotic and eukaryotic cells, including the cell membrane, in maintaining homeostasis and cell reproduction.

How do we know what membranes are made of?

Why are cells so small? If cell is too big, takes too long for necessary chemicals to get around the cell. Insects and elephants have cells that are the same size, the elephant just has more of them and the ones they have are more specialized.

Why is the cell membrane said to be selectively permeable? Controls what goes in and out. What goes in and out is controlled by proteins embedded in the cell membrane.

What is the Cell Membrane Composed of? 1. Phospholipid Bilayer Phospholipid- “Phospho”- phosphate heads hydrophilic (polar); form outer boundary of cell membrane “Lipid”- two lipid tails Hydrophobic (nonpolar) form inner layer of cell membrane Bilayer- two layers of phospholipid molecules

What is the Cell Membrane Composed of? Proteins Channel proteins- allow larger molecules in/out Carrier proteins- allow larger molecules in/out but change shape to do so. Glycoproteins- allow cells to recognize each other

What is the Cell Membrane Composed of? 3. Cholesterol- stabilizes the cell membrane so not too “loose.”

Why is the cell membrane described as a fluid mosaic? Fluid Mosaic Model “Fluid”- Phospholipids & proteins can drift sideways in the membrane. “mosaic”- membrane is studded with many different kinds of proteins. Fluid Mosaic Animation

Quiz 1 Which part of the cell membrane repels water? a. proteins b. phospholipids c. enzyme 2. Hydrophilic means? a. water loving b. water hating c. contains water 3. Which part of the cell membrane has pores? a. proteins b. phospholipids c. enzyme layer 4. What part of the cell membrane acts as recognition markers? a. proteins b. phospholipids c. enzymes