Cell Biology

Honors CS2

Ms. Levensailor

The Cell Theory

All living things are made of cells!– Lowest level of structure.

Cells are the basic unit of structure and function in living things!– Capable of performing all the activities of life.

All cells come from pre-existing cells.

Two Major Classes of Cells

Prokaryotic Cells: lacks a nucleus and other organelles.– Bacteria– Archaea

Eukaryotic Cells: has a nucleus and organelles surrounded by membranes.– Protists, fungi, plants and animals

Eukaryotic

Greek meaning “true kernel”– Kernel refers to the nucleus

10 to 100 micrometers

Prokaryotic

Much simpler in structure Smaller in size (1 to 10 micrometers in

diameter)

Cell Size

Size directly relates to function! Logistics of carrying out metabolism sets

limits to cell size. Lower limits: Mycoplasmas (bacteria)

– Smallest packages with enough DNA to program metabolism

– Also enough enzymes to sustain itself and reproduce.

Cell Size Continued

Upper limits: as a object increases in size, its volume grows proportionately more than its surface area. – Area is proportional to a linear dimension squared

cm2

– Volume is proportional to the linear dimension cubed.

cm3

Surface-to-Volume Ratio

The smaller the object, the greater its ratio of surface area to volume.

Area / Volume

Cell shape and rates of diffusion

With your face partner do pre-lab 6 www.biology.com A high surface-to-volume ratio facilitates the

exchange of materials between a cell and its environment.

Cell shape and rates of diffusion

Plasma membranes function as a selective barrier that allows sufficient passage of:– Oxygen, nutrients, and wastes

For each square micrometer of membrane, only so much of a particular substance can cross per second.

Cell shape and rates of diffusion

If a cell were very large, rates of chemical exchange would be inadequate to maintain the cell.

This explains the microscopic size of most cells.

Larger organisms don’t have larger cells, just more cells.