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CELL TRANSPORT
Fluid Mosaic Model
Fluid Mosaic Model
Hydrophilic Heads
Hydrophobic tails
Polarity
• Hydrophilic (water
loving/ attracted to)
- phosphate heads
• Hydrophobic (water
fearing/ Repelling)
– lipid tails
Effects of polarity on
permeability
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Polarity
Types of Transport
Passive Transport
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No energy (ATP) needed
High to low concentration
simple diffusion
facilitated diffusion
osmosis
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Simple diffusion
• Process by which molecules of a
substance move from areas of higher
concentration to areas of lower
concentration.
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Diffusion
• first a concentration gradient is necessary,
• diffusion occurs moving from higher to
lower concentration
• results in dynamic equilibrium, then
• equal particles keep moving in each
direction, no further change in
concentration
Osmosis
• The diffusion of water through a selectively
permeable membrane
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Solutions
• Hypotonic: below strength
– solutions having lower concentrations of solutes outside the cell
• Example: 15% salt outside of the cell and 20% inside. Which way will the
water diffuse?
– water leaves solution and goes into cell
• Hypertonic: above strength
– solutions having higher concentrations of solutes outside the cell
• Example: 70% H2O inside the cell and 40% salt outside of the cell.
– water leaves cells and goes into solution
• Isotonic: equal strength
– Solutions having equal concentrations of solutes inside and
outside the cell
– the same amount of water leaves the cell as the water that
enters the cell
Animal Cells (red blood cells)
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Osmotic Pressure
• pressure exerted on hypertonic side of a
semipermeable membrane
• necessary to achieve equilibrium
Plant Cells
Turgor Pressure
• main pressure of cell contents against the
cell wall
• determined by water content of the
vacuole, resulting from osmotic pressure
More on Plant Cell Osmosis
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Turgid:
– when in dilute solutions,
– plant cell is swollen and hard
– pressure is so high, no more water can enter
– pressure works against osmosis
– makes plants stand up
Flaccid
– when in concentrated solutions
– plant wilts
Plasmolyzed:
– plasma membrane pulls away from cell wall due to loss of water
– cell wall eventually collapses if not placed in a hypotonic solution
Facilitated Diffusion
• Carrier molecules (protein channels) assist in
moving large particles from a high concentration
to a low concentration
• These particles fit through the membrane but
are assisted
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Facilitated Diffusion
Active Transport
• energy needed
• moving from low to
high concentration
• moving against the
concentration
gradient
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Active Transport
Endocytosis
• process of taking material into the cell by
means of infoldings of the cell membrane
• these “pockets” break loose from the outer
portion of the cell membrane and forms a
vacuole (inside cytoplasm)
• phagocytosis and pinocytosis
Endocytosis
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Phagoyctosis
• cell eating
• extensions of cytoplasm surround a
particle and package it within a food
vacuole
• the cell engulfs it
• considered active transport
• requires energy
Phagocytosis
Pinocytosis
• cell drinking
• cells take up liquid from the surrounding
environment
• small pockets form along cell membrane
• pockets fill with liquid
• pockets pinch off to form vacuoles inside
the cell
Pinocytosis
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Exocytosis
• cells release large amounts of material
from the cell
• membrane of the vacuole surrounding
material to be released fuses with cell
membrane
• forces material out of the cell
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