Cell Boundaries
Jan 21, 2016
Cell Boundaries
How is a window screen like a cell membrane?
What are some things that can pass through a window screen?
What are some things that cannot?
Why is it important for a cell membrane to regulate what moves into and out of a cell?
PSRsPrefixes, Suffixes, Roots
Cyto – cell Endo – within/insideHyper – above Hypo – beneithIso – equal Trans – acrossPhag – eat Exo – outsideSemi – half Per – through/beyond
Write these PSRs in your journal
Cell Borders Cell Membrane (semi-permeable) Controls what enters and leaves cell.
made of Phospholipid bilayer 2 layers of phospholipids with a “mosaic” of
proteins and carbs. (In ALL cells!)
Cell Wall – (in plants) Provides support and protection.
made of cellulose – a tough carb.
2 Ways to Cross the Membrane
Passive Transport – NO energy is required to move a substance across the membrane (moves along gradient)
Active Transport – Energy IS REQUIRED to move a substance across the membrane (moves against gradient)
Passive Transport - Diffusion Diffusion - movement of particles from
areas of high concentration of solute to areas of low concentration of solute. What is concentration? What is a solute?
When the concentration is the same throughout, equilibrium is reached.
Temperature and size of molecule affect the rate of diffusion.
Diffusion Animation
Passive Transport - Osmosis
Osmosis – the diffusion of water particles across a membrane.
Water moves from low solute to high solute.
Why is osmosis important for cells?
Animated demonstration
How Osmosis Works in the Cell Isotonic – Concentration of solutes
outside and inside cell are equal.Equilibrium – water moves in and out at
the same rate Hypertonic - Concentration of solutes
outside is higher than inside the cell. Water out
Hypotonic - Concentration of solutes outside is lower than it is inside the cell. Water in
1. Animated Review of Hypertonic, Hypotonic and Isotonic Solutions
What type of solution are these cells in?
A CB
Hypertonic Isotonic Hypotonic
Passive Transport:Facilitated Diffusion
Facilitated Diffusion – Large molecules (like glucose) move across the membrane with the help of protein channels.
Moves from high concentration of molecules to low – no energy required.
Diffusion / Passive TransportActive Transport = ATP
Active Transport
Larger molecules (sugar) and ions (Na+, K+, Ca+2) pass across the membrane using proteins using ENERGY.
Substances move from low to high concentrations.
Active Transport: Exocytosis and Endocytosis
Exocytosis - Wastes and products are packaged in vesicle by the Golgi and sent OUT of cell
Endocytosis – cell membrane forms vesicle and brings things INTO the cell.
7. TRANSPORT of 7. TRANSPORT of LARGE LARGE PARTICLESPARTICLES Endocytosis (Endo = In): cell surrounds and takes in
material from environment. Material does not pass through the membrane; instead, it is engulfed and closed by a portion of
membrane and cytoplasm. Pinocytosis: water
Phagocytosis: food/ minerals/ large particles
Exocytosis (Exo = Out): transport of materials out of cell across cell membrane.
WATCH VIDEO OF ENDOCYTOSIS, FORMATION OF FOOD VACUOLES OF PARAMECIUM
WATCH VIDEO OF EXOCYTOSIS, SECRETION OF FOOD VACUOLES FROM PARAMECIUM
Exocytosis
(extracellular fluid)
(cytoplasm)
vesicle
plasma membrane
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plasma membranesecretedmaterial
0.2 micrometer
Types of Endocytosis
Phagocytosis – engulfs by surrounding membrane around solids.
“Phago-” means “to eat”
Pinocytosis – pinches membrane and brings in liquids.
“Pino-” think “to pinch”
(extracellular fluid)
(cytoplasm)
food particle
particle enclosed in vesicle
phagocytosis
vesicle containing extracellular fluid
cell
pseudopod
pinocytosis
(a)
(b)
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Animated Review of Phagocytosis, Pinocytosis and Receptor Mediated Endocytosis.
Click on Active Transport, watch the brief overview of Active Transport and then click on Endocytosis in the bar below the animation