Homeostasis and Transport

The Cell Membrane Balanced internal condition of cell is called homeostasis/equilibrium Maintained by plasma membrane controlling what enters & leaves the cell

Semipermeable Membrane The Plasma Membrane 11/13/2018 Semipermeable Membrane Selectively permeable Small molecules move through easily. O2, CO2, H2O G. Podgorski, Biol. 1010

Jobs of The Cell Membrane Protective barrier Regulate transport Communication Anchoring sites for filaments of cytoskeleton

Passive Transport

Passive Transport The movement of substances across the membrane without any input of energy is known as passive transport Types of passive transport are: Diffusion Osmosis Facilitated Diffusion

What is Diffusion? Small molecules can pass through the cell membrane = diffusion. Diffusion happens because molecules move from higher concentration to an area of lower concentration. Diffusion is passive transport because it does not require energy.

Why do molecules move? Kinetic energy keeps molecules in constant motion . The rate of diffusion depends on temperature, size of the molecule, and type of molecule diffusing. Diffusion is faster at higher temperatures Smaller molecules move faster

Why does diffusion happen? The difference in the concentration of molecules across a membrane is called a concentration gradient. Diffusion occurs down a concentration gradient.

Diffusion When equilibrium is reached - molecules will continue to move equally back and forth across a membrane.

Osmosis Osmosis occurs from an area of high water concentration (less solute) to an area of lower water concentration (more solute). Water moves down its concentration gradient and does not require energy. Water moves across a membrane in one direction until equilibrium is reached.

Osmosis Water is the universal solvent for all living organisms. Osmosis is the movement of water across a membrane.

Facilitated Diffusion Facilitated diffusion is a type of passive transport that allows substances to cross membranes with the assistance of special transport proteins. Some molecules such as glucose need help across a cell membrane.

Facilitated Diffusion The channel proteins are regulated by the cell and are either open or closed to control the passage of substances into and out of the cell. Carrier proteins bind to specific molecules, change shape and then deposit the molecules across the membrane.

Facilitated Diffusion The Plasma Membrane 11/13/2018 Facilitated Diffusion Some Carrier proteins do not extend through the membrane. They are called peripheral proteins. They bond and drag molecules through the lipid bilayer and release them on the opposite side. G. Podgorski, Biol. 1010

Types of Solutions

Hypertonic Solutions Solute concentration outside the cell is higher (solution=less pure water/ cell=more pure water) Water diffuses out of the cell until equilibrium is reached Cells will shrink and die if too much water is lost…called plasmolysis. Plant cells become flaccid (wilt).

Hypotonic Solutions Solute concentration is greater inside the cell (solution= more pure water/ cell= less pure water) Water moves into the cell until equilibrium is reached Animal cells swell and burst if they take in too much water this is called cytolysis Plant cells become turgid. Turgor pressure in plant cells helps them keep their shape Plant cells do best in hypotonic solutions

Paramecium Paramecium live in fresh water. Maintain homeostasis through their contractile vacuole. The contractile vacuole pumps water out so he does not burst.

Isotonic Solution Concentration of solutes are the same inside and outside of cell Water moves into and out of cell at an equal rate so there is no net movement of water. Animal cells do best in isotonic solutions.

The Three types of Solutions The Plasma Membrane 11/13/2018 The Three types of Solutions Hypertonic Solution Isotonic Solution Hypotonic Solution NO NET MOVEMENT OF H2O (equal amounts entering & leaving) PLASMOLYSIS CYTOLYSIS G. Podgorski, Biol. 1010

Plants prefer Hypotonic Solutions: Turgor Pressure

Animals prefer isotonic solutions The Plasma Membrane 11/13/2018 Animals prefer isotonic solutions Isotonic Hypertonic Hypotonic G. Podgorski, Biol. 1010

Active Transport

Active Transport Active transport is the movement of molecules up/against their concentration gradient from an area of lower to higher concentration using energy (ATP). May involve transport proteins. Used to move ions such as Na+ and K+ across the cell membrane.

Sodium Potassium Pump The sodium-potassium pump ships Na+ outside the cell and K+ inside the cell, against their concentration gradients. 3 Na+ are pumped out of the cell while 2 K+ are pumped into the cell. ATP drives the energy.

Sodium Potassium Pump The Plasma Membrane 11/13/2018 G. Podgorski, Biol. 1010

Moving the “Big Stuff”

Two types of Endocytosis Endocytosis “ENTER” is the movement of large particles into a cell. The two types of endocytosis are: Phagocytosis Pinocytosis

Phagocytosis “Cell Eating” Pseudopod surrounds the particle. Membrane pouch encloses the material and pinches off inside the cell making a vesicle. Vesicle can fuse with lysosomes or release their contents in the cytoplasm. Used by amoeba to feed and white blood cells to kill bacteria.

Phagocytosis

Phagocytosis The Plasma Membrane 11/13/2018 Capture of a Yeast Cell (yellow) by Membrane Extensions of an Immune System Cell (blue) G. Podgorski, Biol. 1010

Phagocytosis about to occur The Plasma Membrane 11/13/2018 Phagocytosis about to occur G. Podgorski, Biol. 1010

Pinocytosis “Cell Drinking” Cell membrane surrounds fluid droplets Fluids taken into membrane-bound vesicle.

Exocytosis Large molecules that are manufactured in the cell are released through the cell membrane.

Exocytosis This is how many hormones are secreted and how nerve cells communicate with one another.

The End