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

2. 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

3. 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

4. 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)

5. 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

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

7. Membrane in Various Environments

8. 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)