Plasma Membrane Chapter 7, pages 145-208 December 2-6, 2016 A View OF A CELL Plasma Membrane Chapter 7, pages 145-208 December 2-6, 2016

Plasma Membrane The Plasma Membrane controls what enters and leaves the cell maintains homeostasis (balance in the cell) Allows water, oxygen, and glucose to enter when there’s not enough Allows water, carbon dioxide, and waste to leave when there’s too much Selective permeability: the membrane allows some molecules, but not all, to pass through Made up of a molecule called a phospholipid lipid with a phosphate group

Plasma Membrane Continued Plasma membrane is a phospholipid bilayer 2 layers of phospholipids back-to-back Polar heads face the water inside and outside the cell Nonpolar tails hide from water inside the membrane

Plasma Membrane Continued In between the phospholipids in the plasma membrane, there are proteins transport proteins: move needed materials or waste across the cell membrane cholesterol carbohydrates Fluid mosaic model of the plasma membrane the membrane is fluid because the phospholipids are constantly moving over the cell the proteins in the membrane are carried around by the phospholipids, forming different mosaics (patterns)

Movement Across the Membrane 2 Types of transport across the plasma membrane Passive transport: requires no energy Simple diffusion: materials move from high to low concentration Facilitated diffusion: materials move from high to low concentration using transport proteins Osmosis: diffusion of water diffusion of water across a selectively permeable membrane is important for maintaining homeostasis water will move from where there’s more of it to where there’s less of it Active transport: requires energy Carrier proteins: Act like a swinging door to move a small substance into or out of the cell Endocytosis: Cell brings large substances into itself by swallowing them up Exocytosis: Cell exports large substances out of itself by spitting them out

Types of Transport Passive Transport No energy Active Transport Requires energy (ATP)

Membrane in Various Environments

Evolutionary Adaptation Cell Size Cells stay small because diffusion of water, oxygen, etc. is slow over large distances proteins needed for cell survival are made only so fast surface area-to-volume ratio a cell’s volume increases faster than its surface area as a cell gets bigger, you reach a point where its surface area (plasma membrane) cannot take in enough food or get rid of waste fast enough to support the large volume (cytoplasm)