3.1 Cell Theory

Water• Most important compound in living

organisms

Polar • molecule with an unequal distribution of

charge

Hydrogen Bond • attraction of opposite charges • forms a weak bond • forms between water molecules

3.4 Diffusion and Osmosis

3.1 Cell Theory

Adhesion – attraction between unlike substances

Cohesion – attraction between like substances

Capillarity – Due to adhesion & cohesion water is pulled up through tiny tubes

Surface Tension – caused from cohesion

3.4 Diffusion and Osmosis

3.1 Cell Theory

Requires more heat to increase its T than do most other common liquids

Loses a lot of heat when it cools

Due to the hydrogen bonds

Insulator that helps maintain a steady environment when conditions fluctuate (homeostasis)

3.4 Diffusion and Osmosis

3.1 Cell TheoryHow Polarity Makes Water act Strange

http://www.youtube.com/watch?v=ASLUY2U1M-8&list=PLJicmE8fK0Ehrg3meytY7DT8LJiwuU3Th&index=65

3.1 Cell Theory

The cell membrane is a barrier that separates a cell from the external environment.

3.3 Cell Membrane

3.1 Cell Theory

Cell membranes are composed of two phospholipid layers.

3.3 Cell Membrane

3.1 Cell Theory

Cell membranes are composed of two phospholipid layers.• The cell membrane has two major functions.

– forms a boundary between inside and outside of the cell– controls passage of materials

cell membrane outside cell

inside cell

3.3 Cell Membrane

3.1 Cell Theory

Cell membranes are composed of two phospholipid layers.• The cell membrane is selectively permeable

Some molecules can cross the membrane while others cannot.

3.3 Cell Membrane

3.1 Cell Theory

Cell membranes are composed of two phospholipid layers.• The cell membrane is selectively permeable.

Some molecules can cross the membrane while others cannot.

3.3

3.1 Cell Theory

Materials move across membranes because of concentration differences.

3.4 Diffusion and Osmosis

3.1 Cell Theory

• Molecules move down a concentration gradient. • From High to Low concentration

3.4 Diffusion and Osmosis

3.1 Cell Theory

Molecules move in RANDOM STRAIGHT line until they run into another particle and are deflected

Movement continues until they reach equilibrium

equal concentration throughout the space

Movement never STOPS – maintains equilibrium

Concentration, Temperature, & Pressure affect rates of diffusion

3.4 Diffusion and Osmosis

3.1 Cell Theory

Passive transport does not require energy input from a cell

1. Facilitated Diffusion2. Diffusion Through Ion Channels3. Osmosis

Molecules move down the concentration gradient•Diffusion

•3 types of diffusion

3.4 Diffusion and Osmosis

3.1 Cell Theory

Some molecules can only diffuse through transport proteins.

• Facilitated diffusion is diffusion through channel proteins. • High to low concentration

3.4 Diffusion and Osmosis

Channel Protein

3.1 Cell Theory

Diffusion through Ion Channels

Na+ sodium K+ potassium

Ca2+ calcium Cl- chloride

(not soluble in lipids)

Ion channels allow ions to diffuse into and out of cell

Ion channels are either open all the time or gates which open in response to stimuli

1. stretching of cell membrane

2. electrical signals

3. chemical signals

3.4 Diffusion and Osmosis

3.1 Cell Theory

Solution = A mixture in which a solute is dissolved evenly in a solvent

Solute – What gets dissolved

Solvent – What does the dissolving

Water is the universal solvent

Because its polar• Dissolves both positive and negative solutes

3.4 Diffusion and Osmosis

3.1 Cell Theory

Osmosis is the diffusion of water molecules across a semipermeable membrane

3.4 Diffusion and Osmosis

3.1 Cell Theory

Hypotonic

Concentration of dissolved substances (solute) is lower in the solution outside the cell than inside the cell

What Happens:• Water moves through the membrane into the cell• Cell swells

Cytolysis – cell bursts (animal cells)

Turgor Pressure – plant cells

3.4 Diffusion and Osmosis

3.1 Cell Theory

Hypertonic

Concentration of dissolved substances outside the cell is higher than inside the cell

What Happens:• Water flows out of cell• Plant cells – loss of turgor pressure – Plasmolysis – wilting

3.4 Diffusion and Osmosis

3.1 Cell Theory

IsotonicConcentration of solute in solution is the same outside as inside the cell – equilibriumWhat happens: • Water diffuses at the same rate in and out of the cell• Maintaining equilibrium - homeostasis

3.4 Diffusion and Osmosis

3.1 Cell Theory

Active transport requires energy input from a cell and enables a cell to move a substance against (up) the concentration gradient.

• Powered by chemical energy (ATP).

• Cells use active transport to maintain homeostasis.

• Active transport occurs through transport protein - pumps (carrier proteins)• EX: Na-K pump

3.5 Active Transport

3.1 Cell Theory

A cell can import and export large materials or large amounts of material in vesicles• Cells use energy to transport material in vesicles. • Endocytosis - process of taking material into the cell.

• Phagocytosis – endocytosis of solid particles.• Pinocytosis – endocytosis of liquids

3.5 Active Transport

3.1 Cell Theory

A cell can import and export large materials or large amounts of material in vesicles• Cells use energy to transport material in vesicles.

• Exocytosis is the process of moving material out of the cell.

3.5 Active Transport