Homeostasis

Homeostasis Keeping an organism’s internal environment stable Examples Blood pressure 60% H2O Water balance Temperature pH

homeostasis “the tendency of an organism or cell to regulate its internal environment and maintain equilibrium, usually by a system of feedback controls, so as to stabilize health and functioning”

Feedback Mechanisms Help the organism respond to stimuli and maintain homeostasis on a large scale (whole body) Negative Feedback Positive Feedback

shiver, blood vessels constrict and lower blood flow to the skin Negative Feedback When a situation causes a response that reverses the first condition Most common in the body COLD skin cells detect cold brain gets message normal body temp home thermostat (heating system). The thermostat contains the receptor (thermometer) and control center. If the heating system is set at 70 degrees Fahrenheit, the heat (effector) is turned on if the temperature drops below 70 degrees Fahrenheit. After the heater heats the house to 70 degrees Fahrenheit, it shuts off effectively maintaining the ideal temperature. response shiver, blood vessels constrict and lower blood flow to the skin

normal blood glucose level normal blood glucose level Pancreas secretes insulin Liver coverts glucose to glycogen Too High Blood glucose level falls Soon after a meal normal blood glucose level normal blood glucose level Too Low Pancreas secretes less insulin Blood glucose level rises Long after a meal The control of blood sugar (glucose) by insulin is another good example of a negative feedback mechanism. When blood sugar rises, receptors in the body sense a change . In turn, the control center (pancreas) secretes insulin into the blood effectively lowering blood sugar levels. Once blood sugar levels reach homeostasis, the pancreas stops releasing insulin. Liver converts glycogen to glucose

Positive Feedback When a situation causes a response that amplifies (increases) the initial (1st) condition Ex. Milk production, labor pains, blood clots A positive feedback mechanism is the exact opposite of a negative feedback mechanism. With negative feedback, the output reduces the original effect of the stimulus. In a positive feedback system, the output enhances the original stimulus. A good example of a positive feedback system is child birth. During labor, a hormone called oxytocin is released that intensifies and speeds up contractions. The increase in contractions causes more oxytocin to be released and the cycle goes on until the baby is born. The birth ends the release of oxytocin and ends the positive feedback mechanism. Another good example of a positive feedback mechanism is blood clotting. Once a vessel is damaged, platelets start to cling to the injured site and release chemicals that attract more platelets. The platelets continue to pile up and release chemicals until a clot is formed.

On a small scale, individual cells maintain homeostasis by controlling what gets into and out of a cell.

Cell transport Cells move molecules in and out 2 ways: PASSIVE TRANSPORT: does not use energy, moves from high to low concentration. ACTIVE TRANSPORT: uses energy, moves from low to high concentration.

How do materials move in & out of the cell? Materials like glucose, water, solutes, and oxygen can move through the cell membrane in one of two ways: Between the phospholipids Through a carrier protein

Moving between phospholipids There is a small amount of space between the round heads of the phospholipids that make up a majority of the cell membrane.

Moving through carrier proteins Carrier (enzyme) proteins allow larger molecules to pass through Sugars, amino acids, small proteins Molecules “too big” to fit between phospholipids

Solutions Solutions are mixtures of different substances: Solvent: the medium in which a substance is dissolved Solute: the substance dissolved in the solvent Solution: the uniform mixture of the solute and solvent Example – Kool-Aid (solution) = Solvent is water and powder is the solute Medium = an intervening substance (water) Solvent > Solute

Solutions Molecules move to equalize concentration

Concentrations Anything that is dissolved in water is called a SOLUTE E.g. In sugar water, the solute is sugar. In salt water the solute is salt 90% water concentration = 10% solute concentration 40% water concentration = 60% solute concentration

PASSIVE TRANSPORT Molecules move with the flow, from high to low concentrations. No Energy Required! This will continue until they are evenly spread out or reached equilibrium 3 Types: Diffusion Facilitated Diffusion Osmosis

PASSIVE TRANSPORT - Diffusion Diffusion: the movement of molecules from areas of high concentration to areas of low concentration

Diffusion

Gas spreads out by diffusion!

Diffusion

PASSIVE TRANSPORT – Facilitated diffusion Facilitated Diffusion: Movement of molecules from high to low concentration. A protein in the membrane helps make bigger spaces in the membrane.

Facilitated Diffusion 3. Movement of larger molecules (ex. glucose) from high concentration to low concentration with the help of a carrier protein inside cell outside cell

PASSIVE TRANSPORT - Osmosis Greek, osmos “to push” Osmosis: movement of water from high to low concentration across a membrane. Specific type of Diffusion – Water The movement of water across a membrane from an area of high concentration of water to an area of lower water concentration Remember what a solution is and the parts of a solution?

Osmosis

PASSIVE TRANSPORT - Osmosis Need to understand the concentrations of solvents & solutes on either side of the membrane.

90% Water 70% Water 80% Water 80% Water

Water moves from high concentration of water to lower concentration of water 15% Sugar (85% H2O) H2O H2O 30% Sugar (70% H2O) Cell H2O H2O Environment

Diffusion / osmosis and cells Solutions are classified in 3 ways based on their concentrations of water in relation to the inside of cells Hypertonic: Higher H2O concentration inside the cell Hypotonic: Higher H2O concentration outside the cell Isotonic: Equal concentrations of H2O inside and outside the cell

Isotonic solution When the cell is at equilibrium with its environment, equal amounts of water move into and out of the cell In isotonic solutions, animal cells will have no net change because the water inside is equal to the concentration outside. 60% H2O

Hypertonic solution When there is more water in a cell than outside of a cell, water will leave the cell. This can cause a cell to shrink 2% H2O 75% H2O In hypertonic solutions, animal cells will loose water because The water inside is a higher concentration outside. The rules of diffusion/osmosis say that water will move from the area of high concentration to low concentration

Hypotonic solution When there is more water outside a cell than inside of a cell Water will enter the cell This can be bad, if too much water enters then the cell may lyse (burst)  Cytolysis 80% H2O 60% H2O In hypotonic solutions, animal cells will gain water because The water inside is a lower concentration than outside. The rules of diffusion/osmosis say that water will move from the area of high concentration to low concentration

The effects of diffusion & osmosis on living cells Both diffusion and osmosis will result in changes to living cells The movement of water & other solutes back and forth across the membrane will change the volume and pressure inside of the cell Since plant cells are surrounded by a rigid outer layer, the overall shape will NOT change, but the pressure inside will

PLASMOLYSIS Plant cells respond differently to osmosis because of their cell wall When water leaves a plant cell, the cell wall’s shape does not change, but the cell membrane pulls away and creates an air pocket between the two. This causes the plant to WILT. 85% H2O 5% H2O

Turgor Pressure When water enters a plant cell, the cell membrane pushes against the cell wall and creates pressure. 85% H2O 98% H2O

Active transport Move molecules against the flow, from low to high concentration. Uses ENERGY! Its like pushing something up hill instead of letting it roll downhill

ENERGY!

Active transport For Multicellular Organisms: Uses a carrier protein, to carry them across the membrane

Active transport For Unicellular Organisms VESICLE --> organelle that transports materials through, into, or out of a cell ENDOCYTOSIS --> into the cell vesicle Pinocytosis --> fluids Phagocytosis --> foods

Active transport EXOCYTOSIS --> out of the cell

Process of Endocytosis Plasma membrane surrounds material Edges of membrane meet Membranes fuse to form vesicle

Exocytosis Reverse of endocytosis Cell discharges material

Exocytosis Vesicle moves to cell surface Membrane of vesicle fuses Materials expelled