Movement Through the Membrane The Cell Membrane

In or Out? How is a window screen similar to a cell membrane? 1. What are some things that can pass through a window screen? 2. What are some things that cannot pass through a window screen? Why is it important to keep these things from moving through the screen?

In or Out Continued.. 3. Why is it important to regulate what moves into and out of a cell? Question: How does a cell membrane maintain homeostasis? Think of this as you go along…

What IS Homeostasis? Hint: Can you keep a high Temperature? Hint: Can your heart beat super fast all the time? Hint: Can you keep A LOT of water/CO2 inside you without letting it out? HOMEOSTASIS: internal environment tends to maintain a stable, relatively constant condition of properties such as temperature, heart rate, blood pressure

The Cell Membrane FUNCTION The cell membrane regulates what enters and leaves the cell and also provides protection and support.

Lipid Bi-Layer/PHOSPHOLIPID Nearly all cell membranes are composed of a lipid bi-layer. The lipid bi-layer gives the cell membrane a tough, flexible structure that forms a strong barrier between the cell and its surroundings You WILL see the word phospholipid-bilayer.

Outside of cell Inside of cell (cytoplasm Carbohydrate chains Proteins membrane Protein channel Lipid bilayer Inside of cell (cytoplasm

Protein Channels Most cell membranes also contain PROTEINS that run through the lipid bilayer. These proteins form CHANNELS that pump materials across the cell membrane.

Carbohydrate Chains Most cell membranes contain Carbohydrate molecules that run through the lipid bilayer. These Carbohydrate molecules act like chemical identification cards allowing cells to identify one another.

Cell Membrane Regulation One of the most important functions of the cell membrane is to regulate the movement of molecules from one side of the membrane to the other TO MAINTAIN HOMEOSTASIS

Types of Movement Through the Membrane 1. Diffusion is a type of movement of molecules through the cell membrane where the molecules move from an area of higher concentration to an area of low concentration. (Move from the city to the country)

Example Where are the yellow molecules MOST concentrated? Where are the yellow molecules going to move to?

The molecules move from right to left----MORE TO LESS More Examples The molecules move from right to left----MORE TO LESS

Solute…Solvent…. Concentration Solute—any substance (like salt or sugar) that can be dissolved is a solute Solvent—any substance that dissolves the solute. WATER is the greatest solvent in the world. The concentration of a solution is the mass of solute in a given volume of solution.

Diffusion So—diffusion moves solute molecules from and area of High concentration to an area of Less concentration. This happens every day in your kidneys. Diffusion causes many substances to move across a cell membrane but does not require the cell to use energy. NO ENERGY = PASSIVE TRANSPORT

Equilibrium Diffusion (and the other types of movement across a cell membrane) tries to get the solute molecules to be equal on each side of the membrane. Not equal in terms of molecules Equal amounts of molecules on BOTH sides

Equilibrium When both sides of the membrane are equal in terms of solute, the cell is in equilibrium. All cells try to attain this state. Look at the first picture. See the Red and blue dots? How many RED on each side? How many BLUE on each side? What about the second picture?

U-Tubes NOT You Tube

Permeable If a substance is able to diffuse across a membrane, the membrane is permeable to that substance.

Selectively Permeable or Semipermeable Membrane Most cell membranes are selectively permeable which means that some substances can pass across easily and others cannot.

Impermeable NOTHING can pass through the cell membrane Waste cannot get out and food cannot get in If this happens, what does the cell do?

Osmosis 2. Osmosis is the diffusion of WATER through a selectively permeable membrane. SO THIS MEANS WATER MOVES FROM MORE WATER TO LESS WATER……NOT THE MOLECULES BUT THE WATER

Osmosis With osmosis, lets look at a sugar-water solution. One side of the membrane has a concentrated sugar solution and on the other side is a dilute sugar solution. Look at the water in the picture Can sugar move across the membrane?

Movement cont.. Sugar cannot move freely across the membrane. The WATER moves from where there is more WATER to the area where there is more sugar or LESS WATER. So—in this situation, the water moves from an area of Low concentration of Solute /SUGAR to an area of High concentration of Solute/ SUGAR.

Cell membrane Higher Concentration of Water Water molecules Sugar molecules Lower Concentration of Water

Are All of These Cells?

3 types of solutions or tonicity There are 3 types of solutions for osmosis. Hypertonic Hypotonic Isotonic Which shows which in the picture?

NO NET MOVEMENT OF H2O (equal amounts entering & leaving) Isotonic Solution Hypotonic Solution Hypertonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) CYTOLYSIS PLASMOLYSIS

The Effects of Osmosis on Cells- Isotonic Osmosis has many different effects on cells. As you know a cell tries to reach equilibrium. This equal state is also known as an Isotonic solution. (Turn to page 187)

The Effects of Osmosis on Cells- Hypotonic Another effect is called a Hypotonic solution. In a Hypotonic solution, water rushes into the cell causing the cell to expand and eventually burst. This means that the concentration of the solute on the inside of the cell is greater than the outside making the water rush in.

The Effects of Osmosis on Cells- Hypertonic Another effect is called a Hypertonic solution. In a Hypertonic solution, water rushes out of the cell causing the cell to shrivel and shrink. This means that the concentration of the solute on the outside of the cell is greater than the inside making the water rush out.

Osmosis in Red Blood Cells Isotonic Hypertonic Hypotonic

Even More Movement! Now we know that water can easily pass/diffuse through the cell membrane but what about bigger molecules like sugar? Remember the protein channels? This is how larger molecules diffuse through the membrane.

High Concentration Cell Membrane Low Concentration Glucose molecules Protein channel

Facilitated Diffusion/Transport Facilitated Diffusion is a process in which the cell membrane uses the protein channels to allow/help bigger molecules such as ions, sugars, and salts to cross in either direction. This is still diffusion! No energy is used to move these molecules. The protein channels just “help” the molecules across.

Even MORE movement! Sometimes, molecules move against the concentration gradient. This means that they are going from a lower area of solute to a higher area of solute. They are crazy! For this, they need energy to move against the gradient/difference.

Active Transport Active Transport uses the protein channels to move these molecules against the gradient with the input of energy. This is the only movement that requires energy! This type of transport is often referred to as a pump.

Molecule to be carried Low Concentration Cell Membrane High Concentration Molecule being carried Low Concentration Cell Membrane High Concentration Energy Energy

Active Transport = Na+ K+ Pump The sodium potassium pump is a type of ACTIVE transport used in nerve cells (neurons) What is the energy molecule? Sodium Potassium Pump

WITH YES Type of Movement through the Membrane PASSIVE OR ACTIVE Uses energy? WITH OR AGAINST CONCENTRA-TION GRADIENT USES A PROTEIN CHANNEL? MOVEMENT OF MOLECULES DIFFUSION NO WITH Molecules move from more concentration to less concentration OSMOSIS WATER: MOVES FROM MORE WATER TO LESS WATER CONCENTRATION: FACILITATED DIFFUSION/ TRANSPORT YES MOLECULES MOVE FROM __________ TO ____________ CONCENTRATION

3 Types of Active Transport ENDOCYTOSIS There are 3 types of Active Transport 1. Endocytosis is the process of taking material into the cell by means of in-foldings, or pockets, of the cell membrane. This pocket, breaks loose from the cell membrane and forms a type of vacuole within the cytoplasm. Large molecules, like food and other cells can be taken up by endocytosis.

The Plasma Membrane Moving the “Big Stuff” 4/7/2019 Large molecules move materials into the cell by one of three forms of endocytosis. G. Podgorski, Biol. 1010

PHAGOCYTOSIS 2. Phagocytosis is the process of large particles being taken into the cell by means of extensions of cytoplasm that go out and engulf the large particles.

Type of Phagocytosis This is a leukocyte (white blood cell) in your blood that is shooting out extensions to get the large particles that you see. The next picture is another type of phagocytosis.

Phagocytosis About to Occur The Plasma Membrane Phagocytosis About to Occur 4/7/2019 G. Podgorski, Biol. 1010

The Plasma Membrane 4/7/2019 Phagocytosis - Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) G. Podgorski, Biol. 1010

EXOCYTOSIS 3. Exocytosis is the cell’s ability to remove large amounts of materials out of the cell. During exocytosis, the membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.

The Plasma Membrane Exocytosis 4/7/2019 Exocytic vesicle immediately after fusion with plasma membrane. G. Podgorski, Biol. 1010

Exocytosis- moving things out. Moving the “Big Stuff” Exocytosis- moving things out. Molecules are moved out of the cell by vesicles that fuse with the plasma membrane. This is how many hormones are secreted and how nerve cells communicate with one another.

Homeostasis This is the ability of an organism to maintain a balanced and constant internal environment. The organism maintains homeostasis by responding to any internal or external environmental changes.

Unicellular Homeostasis These organisms have a more difficult time maintaining homeostasis than multicellular organisms, because they lack the specialized cells that help maintain a stable internal environment. However, the main organelle that unicellular organisms (ameobas, paramecium) have is a contractile vacuole.

Maintaining Homeostasis in Unicellular Organisms (Paramecia) The contractile vacuole expels excess water that enters from outside the cell. This is important form maintaining proper water balance in many freshwater protozoans since their internal concentration is higher than the outside freshwater. Top-Full Contractile Vacuole Bottom-Empty CV

Plant Homeostasis Plants have guard cells called stomata that regulate water loss from their leaves. When water is abundant, the guard cells open wider to increase the evaporation from the leaves (transpiration) When water is scarce, the guard cells close in order to conserve water for the plant-this prevents water loss.

Multicellullar Homeostasis Excretory System-sweat, urine Growing thick fur/hair in the winter Some birds molting or losing their feathers in the spring