PLASMA MEMBRANE The Plasma Membrane is the outer membrane that covers the cell The cell activity will depend on the materials that enter and exit the cell.

SEMI-PERMEABLE The membrane is said to be semi-permeable which means it only allows certain materials to enter and exit the cell.

SEMI-PERMEABLE Only 4 items can pass through the membrane at any time!  CO 2 O 2 N, H 2 O

HOMEOSTASIS CELLS ARE STRIVING TO REACH A STATE OF BALANCE—HOMEOSTASIS- BOTH INSIDE AND OUTSIDE OF THE CELL

STRUCTURE OF PM

It is made of two fatty acids joined tail to tail Membrane Proteins are found embedded throughout the PM. They are gateways for various molecules to enter/exit the cell Cholesterol is also found throughout….they will provide structure and support for the membrane.

The PM is very flexible and therefore has the ability to move easily. Proteins and cholesterol have the ability to move left to right (sideways) throughout the membrane. Because of this ability it is called the FLUID MOSAIC MODEL!!

RANDOM MOTION OF MOLECULES Robert Brown in 1927 observed what he called the Brownian Motion. He made the observations that molecules are always in motion.

IMPORTANT TERMS Solvent-a substance that has another substance dissolved in it. Ex: water Solute- substance being dissolved in another substance Ex: Sugar, salt, etc...

DIFFUSION Some molecules can move directly through the membrane. The net movement of molecules from an area of high concentrations to an area of low concentration.

DYNAMIC EQUILIBRIUM NO DYNAMIC EQUILIBRIUM - The condition in which there is continuous movement but NO overall change. This is a key characteristic of homeostasis.

OSMOSIS The diffusion of water across a semi-permeable membrane. This works from a area of high concentration to an area of low concentration. Often said to go with the concentration gradient.

CONCENTRATION GRADIENT The difference between concentrations across space. MUST There MUST be a difference in the CG for diffusion to occur. Substance will go from High to low or with the gradient.

WATER MOVEMENT Water can move easily through a cell at any point.. Some substance cannot (sugar salt). Therefore the water must move in or out of the cell until homeostasis is reached. Three major types of solutions we will discuss Hypertonic Hypertonic Hypotonic Hypotonic Isotonic Isotonic

HYPERTONIC The concentration of solutes outside the cell is higher than the concentration of solutes inside the cell. As a result water will leave the cell and the cell will shrink Ex: Lettuce in saltwater.

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HYPOTONIC The concentration of solutes is higher inside the cell than the concentration of solutes outside the cell. As a result, water will go into the cell and the cell will swell Keep lettuce in distilled water…it will stay crisp.

ISOTONIC The concentration of solutes is the SAME both inside and outside the cell. Water still moves in and out but no OVERALL CHANGE Cell is said to be in a state of equilibrium. Most solutions that are injected in our bodies are isotonic.

A simple rule to remember is: Salt is a solute, when it is concentrated inside or outside the cell, it will draw the water in its direction. This is also why you get thirsty after eating something salty.

In PLANT CELLS… Turgor Pressure- Internal pressure in a cell. When the turgor pressure inside the cell increase the PM will push outward and cause the cell wall to become very rigid—this gives plants their shape.

In PLANT CELLS… If the plant cell does NOT have enough water the opposite will happen. No Water Turgor Pressure decreases No shape Wilting plant.

In PLANT CELLS… Loss of water from a cell resulting in a drop of Turgor Pressure is called Plasmolysis.

In ANIMAL CELLS… There is not a cell wall in animal cells so sometimes the cell will continue to grow and could possible burst. Some cells can survive in a hypotonic solution because they have the ability to adapt by forming Contractile Vacuoles- Here the excess water is squeezed out of the cell through the membrane.

PASSIVE TRANSPORT H 2 0, lipids, and lipid soluble substance pass through the plasma membrane by diffusion. NO The cell uses NO energy to move the particles that is why it is called Passive. Usually from High to Low

FACILITATED DIFFUSION is the passive transport of materials across the membrane by transport protein.

ACTIVE TRANSPORT The transport of materials against a concentration gradient that requires energy. Sometimes cell requires nutrients and materials that are available in the environment but would be going from an area of low concentration to an area of high concentration.

ENDOCYTOSIS The process in which a cell surrounds and takes in material from its enviroment….. Taking in materials by means of infolding, or pockets of the cell membrane. Some cells take in large molecules, groups of molecules, or even whole cells. Materials do not pass through the membrane…it engulfs the materials

ENDOCYTOSIS There are two types of endocytosis –Phagocytosis –Pinocytosis

Phagocytosis Phagocytosis means “cell eating”. Extensions of the cytoplasm surround a particle and package it within a food vacuole Amoebas use this method of taking in food. Requires lots of energy

Pinocytosis Pinocytosis – this process is similar to phagocytosis. Cells take up liquid from the surrounding environment. Tiny packets form along the cell membrane, filled with liquid, and pinch off to form vacuoles within the cell. Pinocytosis means “cell drinking”

Cell Eating!

Phagocytosis

Cell drinking

EXOCYTOSIS The reverse process of endoycytosis. This process is used to expel waste from the interior to the exterior of the cell This method can be used to secrete substances produced by the cell. (EX: hormones)

ACTIVE TRANSPORT ACTIVE TRANSPORT BOTH Endocytosis and Exocytosis are examples of ACTIVE TRANSPORT