Homeostasis

Diffusion, Osmosis and Active Transport

Homeostasis

The process by which an organism maintains a constant internal environment despite the variations in the external environment

Ex. Your body stays at 98.6 degrees Fahrenheit even though the temperature outside changes.

In or Out?

How is a window screen similar to a cell membrane? Read on to find out. 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? 3. The cell is surrounded by a cell membrane, which regulates what enters and leaves the cell. Why is it important to regulate what moves into

and out of a cell?

Section 7-3

Interest Grabber

Cell Membrane Lipid bilayer = gives the cell a flexible

structure that forms a strong barrier between the cell and its surroundings.

Proteins = form channels and pumps that help move material across the membrane.

Carbohydrate chains = chemical identifiers, help cells to indentify other cells.

Outsideof cell

Insideof cell(cytoplasm)

Cellmembrane

Proteins

Proteinchannel Lipid bilayer

Carbohydratechains

Section 7-3

The Structure of the Cell Membrane

Homeostasis, Diffusion, and Osmosis

Homeostasis is the maintenance of a stable internal state within an organism. Examples of homeostasis in our bodies are: Regulation of water content Regulation of body temperature Regulation of blood glucose levels

Concentration

The mass of solute in a given volume of solution

Which has a higher concentration? 12 grams of salt in 3 liters of water 12 grams of salt in 6 liters of water

Diffusion

The spontaneous movement of particles from an area of higher concentration to an area of lower concentration.

Transportation of molecules in plant cells: Osmosis

The diffusion of water through a selectively permeable membrane.

Section 7-3

Figure 7-15 Osmosis

Types of Solutions

Isotonic = concentrations of water and solute are the same on both sides of the membrane.

Hypertonic = more concentrated solution (water moves in)

Hypotonic = less concentrated solution (water moves out)

Evaluation:Osmosis

Think about what happens to the skin on your hands and toes after soaking in water or going swimming.

(Osmosis)Next slide:

Evaluation: answer a or b

Osmosis

1. Place your hand in salt water. What happens to the cells of the skin?

A. Wrinkled hands B. Smooth hands

OR

Evaluation: answer a, b, or c

Osmosis

2. Cells placed in pure distilled water without any minerals will:

A. Remain normal

B. C.

Evaluation: answer a or b

Osmosis

Predict what will happen to the cells of the fish.3. Place a salt water fish from the Gulf of Mexico into an

aquarium of fresh water. A. Fish cells swell and burst B. Fish cells lose water and

dehydrate

OR

4. Describe the transportation of molecules in these slides of onion cells.

Facilitated Diffusion

Molecules that cannot diffuse across the cell membrane’s lipid bilayer on their own move through protein channels instead.

HighConcentration

LowConcentration

CellMembrane

Glucosemolecules

Proteinchannel

Section 7-3

Facilitated Diffusion

Active Transport

Movement of materials from low concentrations to a higher concentration.

Requires energy Carried out by transport proteins

(pumps) found in the membrane. Diffusion and osmosis are passive

transport. Do not need energy.

Molecule tobe carried

Moleculebeing carried

Energy

Section 7-3

Active Transport

Bulk Transport

Endocytosis = process of taking material into the cell by means of infoldings, or pockets, of the cell membrane (forms a vacuole in the cell) Phagocytosis – cytoplasm surrounds

and engulfs large particles Pinocytosis – cell takes in liquid from

the surrounding environment

Bulk Transport

Exocytosis = the membrane of the vacoule fuses with the cell membrane, forcing the contents out of the cell.