The Cell and its Environment Finzer 2013

The Plasma Membrane The Plasma Membrane - Gateway to the Cell

Structure of the Cell Membrane

Homeostasis- “steady state” or balance -cells constantly seek homeostasis

The Cell Membrane is responsible for maintaining the steady state within cells. - Most cells live in some kind of fluid -Single celled organisms- ponds, oceans, inside other bodies…

-Multicellular organisms- cells are surrounded by body fluid - Cells have limits to changes they can survive - Temperature - Salt concentrations in the H2O - Interstitial fluid- body fluid between cells

Diffusion of Liquids

Diffusion- molecules move from an area of high concentration to an area of low concentration - takes place in both solutions and air - Gradual spreading out of molecules - They spread out until they reach equilibrium def. equilibrium- molecules evenly spread out

Simple Diffusion NORequires NO energy HIGH to LOWMolecules move from area of HIGH to LOW concentration

DIFFUSION THROUGH MEMBRANES Permeable- when membranes allow all substances to pass through Selectively Permeable- when membranes allow some substances to pass through, & others not

DIFFUSION PASSIVE Diffusion is a PASSIVE process which means no energy is used to make the molecules move, they have a natural KINETIC ENERGY

CELL MEMBRANES ARE SELECTIVELY PERMEABLE!

Osmosis- diffusion of water through a selectively permeable membrane (from high concentration to low concentration)

Q? What decides what moves into the cell??? A. Compare the solution outside the cell to the solution inside the cell.

Diffusion of H 2 O Across A Membrane High H 2 O potential Low solute concentration Low H 2 O potential High solute concentration

Hypotonic- a solution having a lower concentration of solutes than the cell – water goes into the cell

Cell in Hypotonic Solution CELL 10% NaCL 90% H 2 O 20% NaCL 80% H 2 O What is the direction of water movement?

Hypertonic- a solution having a higher concentration of solutes than the cell – water exits the cell

Cell in Hypertonic Solution CELL 15% NaCL 85% H 2 O 5% NaCL 95% H 2 O What is the direction of water movement? ENVIRONMENT

Isotonic- a solution having the same concentration of solutes as the cell – equal movement of water into and out of the cell

Cell in Isotonic Solution CELL 10% NaCL 90% H 2 O 10% NaCL 90% H 2 O What is the direction of water movement? The cell is at _______________. equilibrium ENVIRONMENT NO NET MOVEMENT

Isotonic Solution NO NET MOVEMENT OF H 2 O (equal amounts entering & leaving) Hypotonic Solution CYTOLYSIS Hypertonic Solution PLASMOLYSIS

Osmosis in Red Blood Cells Isotonic Hypotonic Hypertonic

Rules for deciding what will happen to cells… 1. look at the solute concentrations to set up the picture puzzle 2. water moves first and fastest….so 3. look at the water concentrations to decide what will happen to the cell …try some problems

Turgor Pressure- term used to describe water pressure within a cell, (usually plant cells) -will continue to build up until equilibrium is reached

Plasmolysis- water diffuses out of a cell and turgor pressure is lost - Plants “wilt” - Cells shrink

Cytolysis- when cells burst because water pressure inside the cell is too great

Cytolysis & Plasmolysis Cytolysis Plasmolysis

hypotonichypertonicisotonic hypertonicisotonichypotonic

What happens to fresh water organisms? Contractile vacuoles- organelles that pump water out through the cell membrane

2 WAYS SUBSTANCES ARE TRANSPORTED THROUGH MEMBRANES

Three Forms of Transport Across the Membrane

PASSIVE TRANSPORT- the movement of substances through the cell membrane when NO ENERGY taken from the cell Ex- diffusion……osmosis -these both happen “naturally”

PT uses kinetic energy- the natural movement of molecules Substances using PT: -Water -Carbon dioxide -Oxygen -Steroids -Alcohol -Glucose

Q ? Do these substances move into or out of the cell???

Proteins Are Critical to Membrane Function

Facilitated Diffusion Molecules will randomly move through the pores in Channel Proteins.

Facilitated Diffusion Some Carrier proteins do not extend through the membrane.Some Carrier proteins do not extend through the membrane. They bond and drag molecules through the lipid bilayer and release them on the opposite side.They bond and drag molecules through the lipid bilayer and release them on the opposite side.

ACTIVE TRANSPORT- transporting substances across cell membranes USING ENERGY from the cell Ex. Sodium (Na) & potassium (K) (the cell have high needs of these ions)

AC moves against natural diffusion Plants have the ability to absorb Na & K when concentrations are higher inside the cell than outside the cell

Sodium-Potassium Pump 3 Na+ pumped in for every 2 K+ pumped out; creates a membrane potential

Endocytosis- taking into a cell – “cell eating”

Exocytosis- putting out of a cell

*Phagocytosis- taking in large solids *Pinocytosis- taking in or putting out fluid drops - excrete or secrete – “cell drinking” * Cell reaches around the particle to be taken in and forms a pouch-à vacuole

Pinocytosis Cell forms an invaginationCell forms an invagination Materials dissolve in water to be brought into cellMaterials dissolve in water to be brought into cell Called “Cell Drinking”Called “Cell Drinking”