Diffusion and Osmosis
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Transcript of Diffusion and Osmosis
Functions of Cell Membrane
1. Protect cell2.Control incoming and outgoing
substances3.Selectively permeable - allows some
molecules in, others are kept out
Phospholipid Bilayer
polarhead
nonpolartails
P –
hydrophobic molecules
hydrophilic molecules
cytosol
Phospholipid bilayer
Plasma membrane components
Membrane Permeability
Selective permeability The ability of a cell membrane to control
which substances and how much of them enter or leave the cell
Allows the cell to maintain a difference between its internal environment and extracellular fluid
Supplies the cell with nutrients, removes wastes, and maintains volume and pH
The Selectively Permeable Nature of Cell Membranes
Types of Membrane Proteins
Methods of Transport Across Membranes1. Diffusion -passive transport – no
energy expended2. Osmosis - Passive transport of
water across membrane3. Facilitated Diffusion - Use of
proteins to carry polar molecules or ions across
4. Active Transport- requires energy to transport molecules against a concentration gradient – energy is in the form of ATP
Concentration and Gradients
Concentration The number of molecules (or ions) of
substance per unit volume of fluid
Concentration gradient The difference in concentration between two
adjacent regions Molecules always move from a region of
higher concentration to one of lower concentration
Diffusion
Solute molecules moving from an area of high concentration to an area of low concentration
Random motion drives diffusion
Equilibrium is reached when there is an even distribution of solute molecules
(water)
Diffusion
Osmosis
Diffusion of water through a semi-permeable membrane Semi-permeable: permeable
to solvents (WATER), but not to large molecules
High [water] to low [water]
Dissolved molecules (i.e. glucose, starch) are called solutes
REMEMBER:
Water = solvent
Glucose, Starch = solutes
Osmosis
Effect of Water on Cells
Hypertonic Environment High [solute], low [water]
Hypotonic Environment High [water], low [solute]
Isotonic Environment [water] = [solute]
Isotonic
HypotonicHypertonic
Part 3 pg. 85
Osmosis in Living Cells
Cellulose in cell wall
Osmosis in Red Blood Cells
Isotonic
Hypotonic
Hypertonic
• Observe sheep RBCs via a wet mount of the sample
• Aliquot one drop the following solutions with a ½ drop of RBC to a slide
0.9% saline
10% NaCl
Distilled water
• Record observation in the table on page 85
Predictions?
Crenation
Effect of Water on RBC
Osmosis in Plant Cells
• Observe Elodea leaves via a wet mount of the sample
• Aliquot two drops the following solutions with a new Elodea leaf to a slide. Incubate for 10 minutes @ room temp.
10% NaCl
Distilled water
• Record observation in the table on page 85
Hypertonic
Hypotonic
Predictions?
Plasmolysis
Hydrostatic Pressure in Plants
a. Normal tomato on left – salt water gives effect (r) in 30min
b. Iris petal cells
c. Iris petal cells in wilted stage
Types of Transport
Transportation of Molecules
• Passive Transport
-Movement of molecules across a semi-permeable membrane
- no energy required
• Active Transport
-Movement of molecules across a semi-permeable membrane against a concentration gradient
- ENERGY – ATP
• Facilitated Diffusion
-Movement of molecules across a semi-permeable membrane with a protein
- no energy required
Active transport in two solutes across a membrane
Na+/K+ pump
Protein shape change
Figure 5.18
Transportprotein
1
FLUIDOUTSIDECELL
Firstsolute
First solute, inside cell, binds to protein
Phosphorylated transport protein
2 ATP transfers phosphate to protein
3 Protein releases solute outside cell
4 Second solute binds to protein
Second solute
5 Phosphate detaches from protein
6 Protein releases second solute into cell
exocytosis = vesicle fuses with the membrane and expels its contents
Exocytosis and endocytosis transport large molecules
Figure 5.19A
FLUID OUTSIDE CELL
CYTOPLASM
or the membrane may fold inward, trapping material from the outside (endocytosis)
Figure 5.19B
Receptor-mediated endocytosis
Cholesterol can accumulate in the blood if membranes lack cholesterol receptors
Figure 5.20
LDL PARTICLEPhospholipid outer layer
Protein
Cholesterol
Plasma membraneCYTOPLASM
Receptor protein
Vesicle
Membrane-Crossing Mechanisms