Cells, Tissues, Organs, and Organ Systems of

Animals

Chapter 2

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

Tissues

• tissue: similar cells specialized for the performance of a common function

Organs and Organ Systems

• organ: functional units of an animal’s body that are made up of more than one type of tissue

• organ system: association of organs that perform related functions

• homeostasis: maintaining a constant internal environment