CELL BIOLOGYThe Early Discoveries

• Robert Hooke: English scientist, early microbiologist

• In 1665, he discovered that plants were composed of many individual units

• He called the units “cells” because they resembled the cells of a honeycomb

Robert Brown (1830’s)- Showed that cells contain a central nucleus, and are filled with fluid

Matthias Schleiden (1838)

-Showed that ALL plants are made of cells, and that cells are the basis for various functions of the plant

Theodor Schwann (1839) -Showed that all animals are made of cells, and that cells are the basis for various functions

Rudolf Virchow (1858) -Showed that cells come from other living cells

CELL THEORY1) All organisms are composed of cells, which are the basic units of structure and function

2) All cells are produced from other cells

Cell CharacteristicsCells can vary greatly in size, from bacteria to ostrich eggs

Cell shapes are also extremely varied, from spheres to rods to cubes

Cell FunctionsIndividual cells take in and “burn” food for energy, rid themselves of waste, exchange gases, and make new living material.

Examples of Cell Function•Storage (Orange cells)•Structure (Bone cells)•Transport (Blood cells)•Movement (Muscle cells)•Energy Capture (Leaf cells)•Communication (Nerve cells)

The Cell and its Environment• The Cell Membrane:• serves as a boundary between the

cell and its environment• holds the contents of the cell

together• acts as a “gatekeeper” for the cell

(keeps some things out, lets others in)

Properties of Cell Membranes

The cell membrane is:

1) Semi-permeable

2) Flexible and Strong

Structure of the Cell Membrane

•Composed mostly of Phospholipid molecules

•Also is imbedded with large proteins

•Some proteins go all the way through the membrane

Electron micrograph of the cell Membrane in cross section

The phospholipid bi-layer of a cell membrane

Phospholipid layers Proteins

Crossing the Membrane

The cell membrane allows materialsto pass into and out of the cell in a variety of ways.

1) Diffusion:-movement of particles from an area of high concentration to an area of low concentration-will work until both concentrationsare equal. This is called Dynamic Equilibrium

Concentration GradientHigh Low

Diffusion is responsible for most gases crossing the membrane barrier.

What gases would need to cross into or out of a cell?

2) Osmosis-movement of water into and outof a cell across the membrane.-Osmotic Balance is similar to Dynamic Equilibrium, but relatesto water , not particles

Passive Transport/Facilitated Diffusion

-For larger molecules and particles-Molecules/particles do not enter between the phospholipids, but through a special channel in a protein

Specific sites on the membrane allowfacilitated diffusion

Cross-membrane proteins make channels for things to move in or out.

Active Transport-Cell uses energy to move particlesagainst a concentration gradient.

-Things move from LOW concentration to HIGH

-Similar to Facilitated Diffusion, but cell uses

energy to go against a concentration gradient.

Compare and Contrast Active Transport and Facilitated Diffusion