Cell membrane powerpoint diffusion and osmosis revised
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Transcript of Cell membrane powerpoint diffusion and osmosis revised
Cell Boundaries
Chapter 6
What are boundaries? We have borders
surrounding countries
We have boundaries on a playing field
Why are borders important?
What are the borders of a cell?
Cell membrane Thin, flexible barrier
Cell wall Plant, algae, fungi, prokaryotes Strong supporting layer
Cell Membrane What does it do for cell?
Controls what goes in and out Regulates molecules moving from one liquid side of the
cell to the other liquid side of the cell
Protects Supports
Cell Membrane Lipid bilayer
What are lipids? What does bi- mean? What’s a layer?
A cell membrane is made of two
layers of lipid molecules
Cell membrane Phospholipids bilayer
Made of a negatively charged phosphate “head” PO4
3-
Attracts water because the phosphate is charged (-)
Water is a polar , slightly positive ends and slightly
negative ends
Attached to the phosphate group are 2 fatty acid chains Hydrophobic= don’t like water So the inside of the cell
membrane doesn’t let water in but the outside allows cells to be dissolved in aqueous environments
Other things in the membrane…
Proteins embedded in lipid bilayer
Carbohydrates attached to proteins
So many different molecules in membrane, we call it a “mosaic” of different molecules
Proteins
Proteins help things get across membrane
Kinda like a pump
Carbohydrates…
Chemical identification cards
“ID” card of cell Helps individual cells
id each other
Cell Walls
Outside cell membrane (does NOT replace membrane!!!)
Plants, algae, fungi, prokaryotes
Have pores to allow things in
Function: SUPPORT and PROTECT
Cell walls made of…
Protein and carbs Plant cell walls made
up of CELLULOSE This is a tough
carbohydrate Wood and paper
A biological membrane Cells exist in liquid environments Things need to get in and out of cell Different ways to do this….
The Cell Membrane
Concentration (conc.) Solution
Mix of 2 or more substances Solutes
Substance dissolved in solution Concentration
Molarity (M) is # of Moles of a substance per liter of solution 6.02 x 1023 “small things” (molecules, atoms, ions, electrons, ions, etc)
Moles is a unit for measuring EXTREMELY small things is mass of SOLUTE in a given volume of solution (g/L) What is the concentration of 12 grams of salt dissolved in 3
liters of water? 12g/3L= 4g/L
Diffusion Particles constantly move Collide randomly Spread out randomly Diffusion is moving from area of HIGH conc. to
area of LOW conc. This is what we call the CONCENTRATION
GRADIENT
Equilibrium
When the conc. Of a system is the same throughout
(same conc. on both sides)
What’s this have to do with cells?
Cell have liquid inside and are found in liquid environment
We have substances (solutes) inside and outside cell
Unequal concentrations means we get DIFFUSION!!!
B/c diffusion depends on random particle movements, substances diffuse across membranes without requiring the cell to use energy
What happens when we reach equilibrium?
Particles continue moving across membrane but in both directions!***No more changes in concentration
Problems for diffusion…
Things too large Charged molecules
Positive/negative Opposites attract but likes do not… These all present serious problems for
things getting across membranes…
If things can cross a membrane we call the membrane PERMEABLE
If things canNOT cross a membrane we call the membrane IMPERMEABLE
Biological membranes are…
SEMI-PERMEABLE Aka… Selectively permeable Cell membranes are picky
Osmosis Water (H2O) can pass
easily through most biological membranes
Def: Diffusion of Water
through a semi-permeable membrane
How Osmosis works… We have water molecules and some
other molecules, let’s say sugar If we have more water on one side of the
membrane (HIGH conc. of H2O), then the water will diffuse across…
Membrane will let water thru but not sugar
Water can move back and forth (not sugar)
Water moves from areas of HIGH conc. To areas of LOW conc.
Water moves across till equilibrium is reached Isotonic:
when conc. Of both solutions is equal Hypertonic: “above strength”
When we begin with more sugar in water More concentrated sugar solution on side A
Hypotonic: “below strength” When we end with less sugar Dilute sugar solution on side A
Osmotic Pressure
Central vacuole fills with water and exerts and out ward pressure on cell membrane and cell wall
Cell wall does NOT allow cell to expand past a certain size
How do big molecules diffuse across a membrane so quickly if the membrane is selectively permeable?
Facilitated Diffusion What does facilitate mean? Proteins are the extra help “escorts” across the membrane We call these protein channels…
Allow specific things thru
Facilitated Diffusion (continued)
FAST SPECIFIC Still diffusion
so we only see it from high concentration to low
Does NOT require energy
What about when we want to go against the concentration?
(From low concentration to high?)
What do we need???
ENERGY!!!!
ACTIVE transport Process that moves molecules against the concentration
gradient Requires ENERGY A protein pumps small molecules and ions across a cell
membrane against the conc. Gradient Electrochemical gradient
membrane potential To pump large molecules and clumps…
2 other processes: Exocytosis Endocytosis The can change shape of membrane
Types of Active transport
Molecular Transport When small ions and molecules are carried
across membrane Endocytosis
Endo- means…. -Cyto- means… -sis mean….
Exocytosis Exo- means…. -Cyto- means… -sis mean….
Molecular Transport
Proteins are used to pump small molecules and ions across membrane even against the conc. Gradient
The cell devotes a lot of ENERGY to pumping things across membrane
Potassium, calcium, and sodium are some things that need to pumped across
Endocytosis When cells need to take in large material Process of taking material into the cell by
process of infolding, or pockets, of the cell membrane
Pocket breaks loose from cell membrane and forms a vacuole or vesicle inside the cell
Two Types… Phagocytosis Pinocytosis
Two types of endocytosis:1. Phagocytosis
“cell eating” Extensions of cytoplasm surround the particle
and package it within a food vacuole Cell then engulfs the package Amoebas
2. Pinocytosis “cell drinking” When cell needs to take up liquid Tiny pockets in cell membrane form Fill with liquid Then pinch off to form vacuoles inside of cell
Exocytosis Exo- means… Cyto means… Sis means… When cell releases large amounts of material Excretes stuff Membrane of vacuole surrounding particle
inside cell fuses with the cell membrane The contents in vacuole are then forced out of
the cell We see this in removal of water by contractile
vacuoles
MEMBRANE MAMBO!!!