How does the cell membrane maintain homeostasis?

-Regulates what enters and leaves the cell (“gatekeeper”)

-Recognition and response to chemical signals (RECEPTORS)

***The cell membrane is a LIVING barrier that separates the inside environment of a cell from the outside environment

The Cell membrane is also known as the PLASMA MEMBRANE

What is the cell membrane made of? -It is a double layered sheet called a Phospho-lipid Bilayer

1. Lipids (fats)-resist water 2. Proteins-perform important functions 3. Carbohydrate chains

The Cell Membrane is often called a “Fluid Mosaic Model”

(work of art made from many pieces)

What is selective permeability? -The cell membrane ONLY permits certain substances to pass through

EX: Oxygen, water, and nutrients pass INTO a cell

Carbon-dioxide and wastes pass OUT of a cell

The Cell membrane is semi-permeable: -Allows small molecules in/out

Ex: glucose, O2, CO2

The function revolves around the membrane proteins

What is diffusion?

-The process by which molecules of a substance move from areas of HIGH concentration (crowded) to areas of LOW concentration (less crowded) of that same substance until DYNAMIC EQUILIBRIUM is reached

H

L

How do molecules enter and leave a cell? -Diffusion -Osmosis -Active Transport

Molecules want to SPREAD OUT!

Dynamic Equilibrium=Active Balancing=

-Molecules ALWAYS moving

Area of High Concentration (crowded)

Area of Low Concentration (less crowded)

Where is the HIGH concentration of Carbon dioxide molecules? Inside the cell

LOW Concentration? Outside of the cell

In which direction will the carbon dioxide molecules diffuse? Out of the cell

In what direction will the oxygen molecules diffuse?

Into the cell

How can molecules pass through a cell membrane? -They are small enough

-They are soluble (can dissolve)

What might prevent a molecule from passing through a cell membrane?

-they are too LARGE -they are not soluble

The starch

Is TOO

BIG to pass

through!!

Where in the human body does diffusion take place? 1. Small intestine- nutrients INTO bloodstream 2. Alveoli- O2 INTO bloodstream;CO2 FROM bloodstream 3. Capillaries- O2 , nutrients, and waste exchanged between cells and bloodstream 4. Large Intestine- water INTO bloodstream

What is osmosis? -The diffusion of water ONLY across the cell membrane (HIGH LOW)

Salt is a SOLUTE (something that dissolves in water) -When it is concentrated inside the cell, water Will move INTO the cell -When it is concentrated outside the cell, water Will move OUT of the cell -Salt draws water in it’s direction

This is why you get thirsty after eating salty foods!!

Hypo= LESS solute (more H2O)

Iso= the SAME

Hyper= MORE solute (less H2O)

Water moves INTO a cell

Water moves in BOTH directions at the same rate

Water moves OUT of a cell

Hypotonic Solution

Isotonic Solution

Hypertonic Solution

H (H2O)

L

Water moves out of cell

Cell shrinks

Equilibrium

Normal Cell

Plasmolysis-water leaves a plant cell causing it to Shrink (cell membrane pulls away from cell wall) Cell membrane

L (H2O)

H

Water moves into cell

Cell grows (can burst)

Cell grows

Inside Outside

What happens to a red onion cell when you add saline solution to it (salt water)?

Normal Red Onion Cell

Cell Wall

Cell membrane

Cytoplasm

Red Onion in Salt Water

Cell Membrane Cytoplasm

(Cell membrane pulls away from the cell wall)

Think about why plants wilt…

What is passive transport?

-Passive transport is transport that requires NO ENERGY (ATP)

EX: Diffusion Osmosis

**Diffusion and Osmosis occur NATURALLY

What makes the cell membrane go back to normal? -Add Distilled Water (Pure Water)

Distilled water makes a cell GROW the most

What is active transport?

-Process in which molecules move from areas of LOW concentration (less crowded) to areas of HIGH concentration (crowded) of that same substance.

Requires ENERGY (ATP)

TYPES OF TRANSPORT:

Passive Transport: Requires NO ENERGY (High to Low)

Ex: Diffusion and osmosis

Active Transport: Requires ENERGY (Low to High)

Facilitated- Using transport proteins in cell membrane

Facilitated

Passive

Active