4-2: Introduction to Cells

Cell Diversity (cont.)

• Shape– The shape of the cell reflects the function of the

cell (“form follows function”)• Examples:– Nerve cells have extensions on them to help

transmit + receive impulses– Skin cells are flat to help cover the body surface– Blood cells can change shape to move through

openings in blood vessels

Cell Diversity– Remember: Not all cells are alike!

• Size– Most cells are only visible with a microscope• 10 to 50 µm in diameter

– Cells are limited to their size by the ratio between their outer surface area-to-volume• If cell is too big, rate at which molecules travel through

slows down A LOT!– Nutrients or wastes

– Volume increases faster than surface area

Basic Parts of a Cell• No matter how different cells are, they

share 3 things in common:–Outer boundary– Inner substance–Control region

Outer Boundary• Plasma Membrane– Aka Cell Membrane• Covers a cells surface• Acts as a barrier between the inside + outside of cell –

allows things to enter or leave

Inner Substance• Cytoplasm– Located between the plasma membrane + nucleus– Includes fluid, cytoskeleton, and various

organelles– Cytosol – part of cytoplasm that includes

molecules + small particles, such as ribosomes• Proteins make up 20% of cytosol

Control Center• Nucleus– Membrane bound organelle that contains a cell’s

DNA• Has its own protein skeleton – nuclear matrix

2 Basic Types of Cells• Prokaryotes– Organisms that lack a membrane-bound nucleus +

membrane-bound organelles– DNA located in nucleoid– Divided into two Domains• Bacteria• Archaea

2 Basic Types of Cells• Eukaryotes– Organisms that have a membrane-bound nucleus

and membrane-bound organelles– Also contain organelles• Intracellular bodies that perform specific functions for

the cell• Most organelles are surrounded by a membrane

Comparison of Prokaryote vs. Eukaryote

Cellular Organization• Over time, individual cells formed groups that

functioned together• Colonies– Colonial organism• Collection of genetically identical cells that live together

in a connected group– Not truly multicellular due to lack of coordinated

activities– Example: Volvox

Cellular Organization• True Multicellularity – unable to survive independently• Tissues (group of cells)• Organs (group of tissues)• Organ Systems (group of organs)• Organism (group of systems)