CELL THEORY & CELL DIVERSITY

An intro to the CELL!

What is a cell?

• (Def) the smallest unit of life that can carry out all the functions of a living organism

The Cell Theory:

1. Cells are the basic units of all life.

2. All organisms are made of one or more cells.

3. All cells arise from pre-existing cells.

#1 Cells are the basic unit of life.• All organisms are composed of one or more

cells.– Reminder:

• One cell = unicellular

• Many cells = multicellular

– each cell is capable of carrying out all of the functions of living organisms

– EXCEPTION to this theory - viruses*

#2 All organisms are made of one or more cells.

• UNICELLULAR organisms are single-celled, independently living cells

• I.e… bacteria, algae, yeasts & protozoa• http://videos.howstuffworks.com/hsw/12340-the-basic-units-of-life-unicellular-organisms-video.htm

MULTICELLULAR organisms are composed of many cells, each type differentiated to perform a specific function essential to the organism

I.e…plants and animals

#3 All cells arise from existing cells.

• BIOGENESIS – “life comes from existing life”

• By means of either asexual or sexual reproduction

How did we discover the cell?

• Hint: remember cells are MICROSCOPIC…

• the discovery & study of cells progressed with the invention & improvement of the MICROSCOPE!

• Let’s learn the basics of the microscope .

CELL DIVERSITY

• Although all organisms are composed of cells, there is great variety amongst the different types of cells in terms of…• SIZE

• SHAPE

• INTERNAL ORGANIZATION

•Although most cells are microscopic, they vary greatly in SIZE!

• A human egg cell (oocyte), seen here with red blood cells, is the smallest cell in the human body.

• An ostrich egg is the largest animal cell.

The size, or volume, of all cells is determined by the cell membrane.

The SHAPE of any particular cell is determined by that cell’s specific function.

Muscle cells are elongated so that they can contract.

Nerve cells have any long projections which allow them to carry impulses to and from the brain.

Red blood cells are circular discs, allowing them flow easily through narrow blood vessels.

Cells differ in what organelles they have inside of them (aka: INTERNAL

ORGANIZATION.)

• Organelles – structures that perform specific functions within a cell

• PROKARYOTIC cells vs EUKARYOTIC cells

• Plant cells vs Animal Cells• Cells vs. Viruses

PROKARYOTIC CELLS …

• are believed to be the first cells– primitive

• are smaller than eukaryotic cells

• are simpler (less complex) than eukaryotic cells

– lack most membrane-bound organelles

• Contain genetic material (DNA) but lack a true nucleus

• Examples: bacteria

EUKAYROTIC CELLS…

• Evolved from prokaryotic cells

• Are generally larger than prokaryotic cells

• Are more complex than prokaryotic cells

– they have differentiated organelles

• Have genetic material contained in a true nucleus

• Examples: amoeba, skin cell

Plant and animal cells have different organelles because they have different methods of gaining energy….

AUTOTROPHS – organisms that produce their own energy I.e…plants, some bacteria and algae

HETEROTROPHS – organisms that consume other organisms / chemicals as sources of energy

I.e…animals, fungi and some bacteria

So what is a virus then?• Virus - a core of nucleic

acid (either DNA or RNA) surrounded by a protein coat– Living?

• They can only reproduce within a host cell.

– Using all of the cell’s energy and resources!

• Outside of a host, virus are inactive and cannot grow or reproduce.