Introduction to Biology and the Tree of Life

1
Chapter 1

• Introduction to Biology and the Tree of Life

2
Intro

• Development of 2 unifying theories in biology
• Cell Theory cell is fundamental structural unit
  in all organisms and all cells arise from
  pre-existing cells
• Theory of Evolution by Natural Selection all
  organisms related by common ancestry and have
  changed over time in response to natural
  selection
• Phylogenetic trees graphical depiction of
  evolutionary relationships
• Scientific method

3
Intro

• Theory explanation for phenomena/observation
• based on research
• difference btwn theory and hypothesis
• 2 components
• pattern observations of pattern
• process mechanism or process that creates
  pattern

4
The Cell Theory

• Pattern component of Cell Theory
• Hooke (1665), van Leeuwenhoek - cells first
  described and identified in cork and pond water
• Malphigi (1670's) - plant tissues composed of
  cells
• Oken (1805) all organisms composed of cells
• Schleiden and Schwann (1830s) confirm all
  organisms composed of cells

5
The Cell Theory

• Process component of the Cell Theory
• Virchow hypothesis (1858) - all cells arise from
  pre-existing cells
• alternative hypothesis - spontaneous generation
• cells arise from non-living materials
• Pasteurs tested hypotheses

6
Figure 1.2
Both hypotheses supported
Cells
1. Place nutrient broth in straight-necked flask.
3. Preexisting cells enter flask from air.
2. Boil broth to sterilize it.
4. Broth fills with cells.
PASTEUR EXPERIMENT WITH SWAN-NECKED FLASK
Spontaneous generation hypothesis rejected
Spontaneous generation hypothesis Cells will
appear in broth
All-cells-from-cells hypothesis Cells will not
appear in broth
Cells
Condensation settles in neck
1. Place nutrient broth in swan-necked flask.
3. Preexisting cells from air are trapped in
swan neck.
2. Boil broth to sterilize it.
4. Broth remains sterile.
7
The Cell Theory

• Implications of Cell Theory
• all individuals in population of single-celled
  organisms related by ancestry
• all cells in multicellular organism descended
  from same ancestral cell (zygote)
• cell highly organized compartment bound by
  thin, flexible membrane and contains concentrated
  chemicals in aqueous soln, capable of division,
  chemical rxns

8
The Theory of Evolution by Natural Selection

• Pattern component of Theory of Evolution
• all species past and present related common
  ancestry
• species change through time
• characteristics of can be modified from
  generation to generation
• current species arose via descent with
  modification
• species are not independent and unchanging but
  are related and change over time
• Darwin and Wallace (1858)

9
The Theory of Evolution by Natural Selection

• Process component of Theory of Evolution by
  Natural Selection
• mechanism for evolution natural selection
• proposed by Darwin/Wallace, 1859 Origin of
  Species published
• natural selection occurs when
• individuals w/i population vary in their
  characteristics and these variable traits are
  heritable
• population group of indiv. of same sp. living
  in same area at same time
• heritable can be passed on to offspring
• certain heritable traits help individuals survive
  better or reproduce more offspring in particular
  environments

10
The Theory of Evolution by Natural Selection

• terms
• fitness ability of indiv. to survive and
  reproduce, measured by offspring
• adaptation trait that increases fitness of
  indiv. in particular environment

11
The Theory of Evolution by Natural Selection

• artificial selection of domesticated crops
  demonstrates change in population over time

1. Breed individuals w/ largest side buds
Wild member of Brassica oleracea small side buds
2. Of offspring, select individuals w/ largest
buds and breed
3. Of offspring, select individuals w/ largest
buds and breed
Individuals
4. After several generations, bud size increases
0
1
2
3
Size of buds (cm)
12
Brussels sprouts extremely large side buds
13
Unifying Theories

• Development of 2 unifying theories in biology
  central to biological sciences
• medicine, agriculture, forestry, etc.
• Cell Theory cell is fundamental structural unit
  in all organisms and all cells arise from
  pre-existing cells
• Theory of Evolution by Natural Selection all
  organisms related by common ancestry and have
  changed over time in response to natural
  selection

14
The Tree of Life

• Prior Theory of Evolution scientists document
  divergence of species (speciation)
• Linnaeus(1735) developed taxonomic
  classification system
• taxonomy naming and classification
• Binomial System of Nomenclature
• genus and species
• hierarchical system of taxa
• organisms placed into two kingdoms
  (plants and animals)

15
The Tree of Life

• After Theory of Evolution classification systems
  modified to reflect evolutionary history
  (phylogeny)
• fundamental differences in prokaryotes vs.
  eukaryotes

Nucleus
eukaryotic cells have membrane bound nucleus
1.45 µm
prokaryotic cells lack membrane bound nucleus
0.29 µm
16
The Tree of Life

• After Theory of Evolution classification systems
  modified to reflect phylogeny (based on physical
  characteristics)
• 5 kingdom system Whittaker, 1969

17
The Tree of Life

• After Theory of Evolution classification systems
  modified to reflect phylogeny (based on molecular
  evidence)
• Woese (1970s) SSU RNA
• contained in all organisms, highly conserved
• nucleotide sequences of same genes from different
  organisms should be very similar if closely
  related and more different if distantly related
• 4 types of ribonucleotides (A, U, G, C)

18
The Tree of Life

• Tree of Life constantly revised to reflect new
  data
• still debated
• humans at one tip, appearing 100,000 yrs ago
• 3 major groups (domains)
• humans arise 1 hr before midnight
• fungi more closely related to animals than plants