HOMEOSTASIS AND CELL TRANSPORT

Chapter 5 Biology II

Vocabulary- Chapter 5 (23 words)

Passive transport facilitated diffusion

Diffusion carrier protein

Concentration gradient ion channels

Equilibrium phagocyte

Osmosis exocytosis

Hypotonic pinocytosis

Hypertonic phagocytosis

Isotonic endocytosis

Contractile vacuole vesicle

Turgor pressure active transport

Plasmolysis sodium-potassium pump

cytolysis

A. Passive Transport

*Cell membranes help organisms maintain homeostasis by controlling what substances enter or leave the cell

*passive transport: substances that pass across the cell membrane without any input of energy by the cell

1. Diffusion: the movement of molecules from an area of higher concentration to an area of lower concentration

a. Concentration gradient: the difference in the concentration of molecules across a distance

b. Driven entirely by the molecule’s kinetic energy- molecules in constant motion

c. Equilibrium: the concentration of molecules will be the same throughout the space the molecules occupy

d. Even at equilibrium, there is still balanced movement

e. Some membranes allow molecules to pass through, but not others- if allowed, it will diffuse

f. Examples: carbon dioxide and oxygen diffuse across membranes

2. Osmosis- the process by which water molecules diffuse across a cell membrane from an area of higher concentration to an area of lower concentration

a. Passive transport of water

b. Direction of Osmosis

1. depends on the concentration of solutes on both sides of the membrane

2. hypotonic: solutes lower outside, water moves in

3. hypertonic: solutes higher outside, water moves out

4. isotonic: solutes equal on both sides, water moves equally in and out

c. How cells deal with osmosis

1. Contractile vacoules: organelles that remove water

a. Occurs in organisms that live in hypotonic solutions (example: paramecia)

b. Requires the use of energy

2. Some cells pump solutes out, changing the flow of water

3. Like animal cells, most plant cells live in hypotonic solutions

4. Tugor pressure: the pressure water exerts against the cell wall- occurs in a hypotonic solution

5. Plasmolysis: the cell shrinks away from the cell wall in a hypertonic solution (example: plants wilting)

6. Some cells can’t compensate for changes in the solute concentration of their environment (example: red blood cells)

7. Cytolysis: the bursting of cells

3. Facilitated diffusion- the transport of substances through a cell membrane along a concentration gradient with the aid of carrier proteins

a. A type of passive transport

b. Example: glucose- molecule too big to cross freely

4. Diffusion through ion channels

a. Ion channels: a complex of protein molecules in a cell membrane that form a pore through which ions can pass

b. Examples: sodium (Na+), potassium (K+), calcium (Ca2+), and chloride (Cl-)

B. Active Transport- the movement of chemical substances, usually across the cell membrane, against a concentration gradient; requires cells to use energy

1. Cell membrane pumps

a. Sodium-potassium pump: a carrier protein that uses ATP to actively transport sodium ions out of a cell and potassium ions into the cell

2. Movement in Vesicles (used when molecules are too large or needed in large quantities)

a. Endocytosis: the process by which cells ingest external fluid, macromolecules, and large particles, including other cells

1. vesicle: a small cavity or sac that contains materials in a eukaryotic cell

2. pinocytosis: a type of endocytosis that involves the transport of solutes or fluids

3. phagocytosis: a type of endocytosis that involves the movement of large particles or whole cells

a. Many unicellular organisms feed this way

b. Phagocytes: a cell that ingests and destroys foreign matter or microorganisms

b. Exocytosis: the process by which a substance is released from the cell through a vesicle that transports the substance to the cell surface and then fuses with membrane to let the substance out of the cell

1. Cells use to release large molecules, wastes, or toxins