CELL TRANSPORT

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Fluid Mosaic Model

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Fluid Mosaic ModelHydrophilic Heads

Hydrophobic tails

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Polarity

• Hydrophilic (water loving/ attracted to)- phosphate heads

• Hydrophobic (water fearing/ Repelling) – lipid tails

Effects of polarity on permeability

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Polarity

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Types of Transport

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Passive Transport

• 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

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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

• 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

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Active Transport

• energy needed• moving from low to

high concentration• moving against the

concentration gradient

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Active Transport

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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

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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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