TEM (transmission EM)	SEM (scanning EM)
transmits through specimen studies the internal cell uses electromagnets to enhance the image	scans the surface of the specimen develops a 3-D image of the cell uses a surface coated with gold, e- beam excites the surface of the sample and the e- are collected and focused on a screen

Cytology is the study of the cell's structure.

Cell Fractionation attempts to take cell's apart, separating major organelles so that their individual properties can be studied.

1. utilizes high-speed centrifuges to fractionate cells
2. applies up 500000 Gs on the particles being fractionated

Homogenization is an attempt to break cells open without severely damaging their organelles.  Spinning the homogenate after homogenization produces the pellet (larger structures packed on the bottom that have to be fractionated) and the supernatent
(smaller parts suspended in liquid above the pellet)

Prokaryote	Eukaryote
DNA concentrated in nucleoid region No nuclear envelope or any compartmentalization for that matter	DNA in nuclear envelope Cytosol (fluid) fills cytoplasm (space) Plasma membrane:  for each sq. micrometer of membrane, only so much of a certain substance can cross per second

Compartmental Organization

Animals and Plants

What is referred to as the "nucleus" is the nuclear envelope plus the chromatin (DNA and proteins that condense to form chromosomes) plus the nucleolus (involved in ribosome production).  The endoplasmic reticulum (ER) has two forms:  the rough ER (RER) is studded with ribosomes and the smooth ER (SER) lacks ribosomes on its surface.  RER assembles other membranes in the cell.  The golgi apparatus perfoms an active role in synthesis, refinement, storage, sorting, and distribution of chemical products.  Lysosomes are membranes containing a mixture of digestive enzymes that hydrolyze (digest) macromolecules.  Peroxisomes are membranes containing specialized enzymes that perform various specific metabolic processes.  Vacuoles have varying storage and metabolic functions.  Mitochondria generate ATP through cellular respiration.  Microtubules form the cytoskeleton (for infrastructure), centrioles (for cell division), and flagella and cilia (for motility--movement)

Plants Only

Plastids are often considered the most important difference between animal and plant cells.  For example, plant cells have chloroplast for photosynthesis.  The central vacuole stores chemicals, hydrolyzes macromolecules, and enlarges during plant growth.  The tonoplast is the membrane surrounding the central vacuole.  Plasmodesmata are channels connecting cytosol of plant cells through the cell wall.