Homeostasis Notes (if needed)

I. External and Internal Environments

A. The environment can be thought of as an organism’s surroundings
1. external environment – the outside world (ex. air temperature)
2. internal environment – the inside of the organism (ex. cells, organs, etc.)
B. The external environment is always affecting organisms
1. When the external environment disturbs an organism and its internal environment, we call that a stress or stressor
2. Organisms need to respond to stress in order to survive

II. Homeostasis

A. Organisms must respond to changes in the external environment to survive. Why?
1. Organisms must maintain a constant internal environment to survive
2. Organisms must maintain balance in their bodies/cells
a. If it is out of ‘balance’ for too long, then an organism will die
b. The process of maintaining a balanced internal environment is called homeostasis

III. Moving materials (Part 1)

A. Living organisms need different materials to be moved in order to survive
1.Food and water need to be moved into the internal environment
2.Wastes need to be moved out to the external environment
B. When there is a lot of a material in a certain area, we say that there is a high concentration of that material
1. When there is very little of a material in a certain area, we say that there is a low concentration of that material
C. Materials naturally move from areas of HIGH concentration to areas of LOW concentration
1. We call this diffusion
2. Basically, “stuff” likes to spread out
D. A thin layer called a membrane separates internal and external environments
1.The membrane keeps the inside in and the outside out and also decides what is allowed to enter the internal environment from the external and vice versa
E. Membranes are usually semi-permeable, which means that they let some materials through easily and some materials cannot pass through
1. Semi = half or somewhat
2.Permeable = will allow passage through

IV. Osmosis (Moving Materials – Part 2)

A. Water can diffuse (move) across a membrane - this is called osmosis
B. So why would water diffuse into or out of an egg?
1. Water was not the only substance inside of a cell – there were many other materials such as fats, sugars, and proteins
2. These materials in the water are called solutes and when dissolved (spread out) in a liquid it creates a solution (mixture of solids and liquids)
3. More solutes (stuff besides water) inside the cell means there is less room for water . . .
a. So the concentration of water is lower when the concentration of solutes is high
b. When two different concentrations of water are separated by a membrane, water can be pulled across the membrane by osmosis