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