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 surface area-to-volume – 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)