This chapter discusses :
  1) The Origin of Eukaryotes
  2) Evolution & Sexual Reproduction
  3) Evolution & Multicellularity
  4) Classification of Living Things

 Most of our work in this chapter will come from 19-4 over the classification of living things, but in order to understand we must review and have a base knowledge of several other topics. These topics include;

 1) Characteristics of prokaryotes & eukaryotes
 2) Binary fission & mitosis
 3) Crossing over & meiosis
 4)  Homologous Characteristics
 5) Symbiotic Relationships

 As discussed in chapter 2, a Prokaryote is a cell which does not have a nucleus and very few, if any, organelles. A Eukaryote is a cell which has a nucleus and tiny compartments which carry out specific functions called organelles.
 Binary Fission is a form of asexual reproduction that produces identical offspring. Basically this is when a cell divides and replicates( reproduces) itself. During this process Mitosis occurs, which is the splitting of the nucleus of a cell into two nuclei, each with the same number and kinds of chromosomes.
 Meiosis is cellular division of the nucleus which produces two haploid cells( cells which have half the number of chromosomes as usual), which we call sex cells or gametes. We know this type of cell in our body is called the egg or sperm. Crossing-over is a unique process that occurs during meiosis in which chromosomes pair up next to each other. The arms of the chromosomes exchange reciprocal segments of DNA. This gives one half of each chromosome to each new haploid nuclei produced.
 Homologous structures, are structures that share a common ancestry, the forelimbs of all vertebrates are constructed basically with the same array of bones( pg 256, fig. 12-12).
 Symbiosis  in review is when two organisms live together, each doing something for the existence of the other.
 
 

 As discussed in Chp. 2. What does it mean when we say that the cell is the basic unit of structure and function? It means this, that certain cells are structured by way of organelles, cell membrane, cell walls, or other characteristics which set them apart from other cells. It is these differences in cell structure which gives us different types of cell, each having the ability to do a particular function. When we link similar cells together, all doing a particular job we form a tissue, different tissues all working together to perform one task forms an organ, and many different organs working together to perform a particular job is called an organ system.
 Previous to the formation of multicellular organism there were unicellular organisms which lived in large groups, or colonies,  but there is no separation of duties and all cells carry out all life functions on their own. This was probably the earliest formation of multicellular organization. Four of the six kingdoms have multicellularity;

 1) Protista- There are only a few groups of multicellular organism in this kingdom, most are unicellular
 2) Plantae- All plants are multicellular
 3) Animalia- All animals are multicellular
 4) Fungi- Most fungi are multicellular, but there are a few unicellular fungi like yeast.

 Multicellularity requires Cell Specialization which is that certain cells do a certain specific job and they become very good at what they do. Gametes(sex cells) only pass on genetic information, red blood cells ( carry oxygen) , nerve cells (pass along impulses ).
 
 

     As long as man has been on the planet there has been a need for us to classify things around us. Classification began in the most basic of ways. We needed to understand the differences in foods         ( edible vs non-edible), materials for clothing, types of shelter, differences in animals and plants as to their usefulness.
 Aristotle (384-322 B.C.) which is over 2000 yrs ago set up the first classification system. He divided all animals into two groups, Plants and Animals. He sub-divided Animals according to where they dwelled (lived);
 1) Air Dwellers ( birds)
 2) Land Dwellers (vertebrates like tigers, man)
 3) Water Dwellers ( fish)

He divided plants according to the type of stems they had;
 1) Soft, fleshy, stems ( grass, flowers)
 2) Shrub type stems (bushes, & shrubs)
 3) Hard wood type stems (trees )

He used long scientific descriptions or common names to identify organisms within these groups.
 There were several things wrong with this classification system as you can see. Where would you put a duck, which flies in the air, rest on water, and feeds on land. How would you classify as small sapling tree, as a shrub or a tree. Long scientific descriptions are hard for the common person to understand or remember and common names usually mislead us in identifying the organisms.( jellyfish, looks nothing like a fish, but does live in the water like a fish)

This practice of naming and classifying organisms is called Taxonomy.

 It was not until the 1700ís when Carl Linnaeus came along, that we developed a more efficient process of taxonomy. He used Binomial Nomenclature, which is a two word naming process of organisms. This involves using the genus and species name for identifying organisms. This was much more simple than Aristotle's long scientific descriptions and less confusing than common names. There are three things we can get from the scientific name, 1) the range (location) 2) characteristic description ( what the organism looks like) & 3) pay honor or tribute to the identifier.
He also developed a hierarchal structure for grouping organisms. This was called the 7 Levels of Classification,  which contain organism with similar characteristics.
Kingdom- this group possesses the greatest numbers of differences in characteristics of the organisms. For example the animal kingdom contains everything from the ant to the elephant, both which are very different from each other, but both are in the animal kingdom.
Phylum- In each kingdom there are usually several phylums each phylum has many similarities, but there are also some differences which are worthy of separation
 This process continues in this fashion until we wind up with only a small group of organisms which all possess very similar characteristics, the next levels of organization is as follows
Class
Order
Family
Genus
Species- This group includes organisms which all share very similar characteristics.

Linnaeus continued as Aristotle with only classifying Plants and Animals.

Today- there have been several changes to what Linnaeus had set. Today we have 4 kingdoms besides Plant and Animal. There are two kingdoms of bacteria, Archaebacteria, and Eubacteria. Then there is the Fungi kingdom and the Protista kingdom. There are also 3 different levels of organization in a species.
1) Sub-species- Is when there is a morphological (physical characteristics) difference in organisms that are located in the same area.
2) Variety- is when there is morphological differences and geographical differences in organisms.
3) Strain- is when there are biochemical differences in organism, this can be differences in how they are chemically made up or how they function chemically.

There are charts beginning on pg. 443 of your text which give you general characteristics of the 6 kingdoms, you should be familiar with.