What are cells?• prokaryotes: no nucleus or organelles
• Domains: Archaea and Eubacteria
• eukaryotes: nucleus and organelles
• organelle: structure in cells that perform specific functions
• plasma membrane: outer boundary of cell
• cytoplasm: portion of the cell outside the nucleus
• nucleus: cell control center; contains DNA
Why are cells small?• if a cell’s volume becomes too large, the surface-area-to-volume ratio
is too small for an appropriate exchange of nutrients and waste
Cell Membranes
• phospholipid bilayer: phospholipids have one polar end and one nonpolar end.
• “tails” attract each other (hydrophobic)
• “heads” attract water (hydrophilic)
Function of Cell Membranes• regulate material moving into and
out of the cell and from one part of the cell to another
• selective permeability: ability of plasma membrane to let some substances in and keep others out
• separate inside from outside
• separate organelles
• provide a large surface area for chemical reactions to occur
Diffusion
• diffusion: movement of molecules from areas of high concentration to areas of low concentration
• facilitated diffusion: large molecules and some of those not soluble require assistance passing across the plasma membrane
Osmosis• osmosis: diffusion of water across a selectively permeable membrane
from an area of higher concentration to an area of lower concentration
Tonicity
isotonic: concentration
inside and outside the cell
are equal
hypertonic: concentration is higher outside
than inside
hypotonic: concentration is lower outside the cell than
inside
Active Transport• active transport: moves molecules across a selectively permeable
membrane against a concentration gradient
Bulk Transport• endocytosis:
plasma membrane envelops large particles and molecules and moves them in bulk across the membrane
• exocytosis: vesicles release their contents into the extracellular environment
Organelles
• ribosomes: create proteins from RNA
• endoplasmic reticulum: produces, transports, and stores enzymes/proteins
Organelles
• golgi apparatus: sorts, packages, and secretes proteins and lipids
• lysosomes: digest organic molecules
Organelles
• mitochondria: convert energy to ATP; have their own DNA that is passed from mother to offspring
• cilia/flagella: help the cell move
• vacuole: membrane sac
Nucleus
• nucleus: contains DNA; control and information center for the cell
• nuclear envelope: membrane that separates nucleus from cytoplasm
• chromatin: DNA and protein
• chromosomes: DNA, made of tightly coiled chromatin
Levels of Organization
• cellular organization: cells, but no tissues/organs
• tissue organization: tissues, but no organs
• organ organization: organs, but no organ systems
• system organization: organs organized into organ systems