AP Biology

The Cell Membrane - Diffusion & Osmosis

NOTEBOOK

Table of Contents:31. Transport in Cells

Assignment Page:Wednesday November 16, 2016

Transport in CellsReminders:1. Moodle Homework Due Sun 11:55pm2. Organelle Campaign Speeches & Voting on November

18th3. Test 7 and Midterm Notebook Check 11/22

OBJECTIVES1. Define osmosis as the movement of water

molecules through a selectively permeable membrane from a less concentrated solution (more water) to a more concentrated solution (less water).

2. Understand that both the random movement of water molecules and concentration gradient help maintain water balance across cell membranes.

3. Correctly use the terms hypotonic, isotonic, hypertonic, plasmolysed, turgid, lysis, and crenated when discussing relative solution concentrations and cell appearance.

AP Biology 2007-2008

Movement across the Cell Membrane

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Diffusion▪ 2nd Law of Thermodynamics

governs biological systems◆ universe tends towards disorder (entropy)

▪ Diffusion◆ movement from high → low concentration

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Diffusion▪ Move from HIGH to LOW concentration

◆ “passive transport”◆ no energy needed

diffusion osmosis

movement of water

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Diffusion▪ Want more info?? Check out these links:◆ https://www.youtube.com/watch?v=w3_8FSrqc-I

&spfreload=5

◆ https://www.khanacademy.org/science/biology/membranes-and-transport/diffusion-and-osmosis/v/diffusion-and-osmosis

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Diffusion across cell membrane▪ Cell membrane is the boundary between

inside & outside…◆ separates cell from its environment

INfoodcarbohydratessugars, proteinsamino acidslipidssalts, O2, H2O

OUTwasteammoniasaltsCO2H2O products

cell needs materials in & products or waste out

IN

OUT

Can it be an impenetrable boundary? NO!

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Facilitated Diffusion▪ Diffusion through protein channels

◆ channels move specific molecules across cell membrane

◆ no energy needed

“The Bouncer”

open channel = fast transport

facilitated = with help

high

low

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Active Transport

“The Doorman”

conformational change

▪ Cells may need to move molecules against concentration gradient◆ shape change transports solute from

one side of membrane to other ◆ protein “pump”◆ “costs” energy = ATP

ATP

low

high

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Getting through cell membrane▪ Passive Transport

◆ Simple diffusion▪ diffusion of nonpolar, hydrophobic molecules

• lipids• high → low concentration gradient

◆ Facilitated transport▪ diffusion of polar, hydrophilic molecules▪ through a protein channel

• high → low concentration gradient

▪ Active transport◆ diffusion against concentration gradient

▪ low → high◆ uses a protein pump◆ requires ATP

ATP

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Transport summarysimplediffusion

facilitateddiffusion

activetransport

ATP

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How about large molecules?▪ Moving large molecules into & out of cell

◆ through vesicles & vacuoles◆ endocytosis

▪ phagocytosis = “cellular eating”▪ pinocytosis = “cellular drinking”

◆ exocytosis

exocytosis

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Endocytosis

phagocytosis

pinocytosis

fuse with lysosome for digestion

non-specificprocess