2. 13.1 How Cells Arose
There are three possibilities for the appearance of the first living organisms on Earth
1. Extraterrestrial origin
Life was transferred to Earth from a distant planet
2. Special creation
Life was created by supernatural or divine forces
3. Evolution
Life may have evolved from inanimate matter, with selection as the driving force
Only the third possibility is scientifically testable

3. Earth is formed 4.5 billion years ago
Fig A clock of biological time

4. Forming Life’s Building Blocks
Life originated ~ 2.5 billion years ago
The Earth’s atmosphere then had no oxygen
It was rich with hydrogen-rich gases (NH3, CH4)
These simple molecules combined to form more complex molecules
Lightning provided the energy

5. Forming Life’s Building Blocks
Stanley Miller and Harold Urey reconstructed the oxygen-free atmosphere of early Earth in their lab
Cellular building blocks form spontaneously, when the system is subjected to lightning or UV light
They concluded that life may have evolved in a “primordial soup” of biological molecules

6. Forming Life’s Building Blocks
Concerns have been raised about the “primordial soup” hypothesis
No oxygen => no protective ozone layer
Therefore, the UV light would have destroyed the essential ammonia and methane gases
Louis Lerman, in 1986, proposed the bubble model
Key chemical life-building processes took place within bubbles on the ocean’s surface
Inside the bubbles the essential gases would be protected from UV light

7. Fig. 13.2

8. The First Cells
The first step may have been the formation of tiny bubbles termed microspheres
These have cell-like properties
Those microspheres better able to incorporate molecules and energy persisted longer than others
The first macromolecule produced was RNA
It provided a possible early mechanism of inheritance
Later, RNA was replaced as hereditary material by the much more stable double-stranded DNA

9. 13.2 The Simplest Organisms
The fossil record indicates that prokaryotes appeared 2.5 billion years ago
Eukaryotes, on the other hand, appeared only 1.5 billion years ago
Today prokaryotes are the simplest and most abundant form of life on earth
Prokaryotes occupy a very important place in the web of life on earth

10. The Structure of a Prokaryote
Prokaryotes are small, simply organized, single cells that lack a nucleus
Fig. 4.9
Rod
Spherical
Spiral
Prokaryotes include the bacteria and archaea
They come in three main shapes
Rod-shaped (bacilli)
Spherical (cocci)
Spirally coiled (spirilla)

11. The Structure of a Prokaryote
The cell membrane of prokaryotes is encased in a cell wall
Bacterial cell walls are composed of peptidoglycan
Network of polysaccharides linked together by peptide cross-links
Archaeal cell walls lack peptidoglycan
They are made of proteins, sugars or both

12. Bacteria can be divided into two groups based on their cell wall architecture
Gram-positive
Have a thick peptidoglycan layer
Lack outer membrane
Gram-negative
Have a thin peptidoglycan layer
Have an outer membrane containing lipopolysaccharide
The name refers to a differential stain developed by Hans Christian Gram
Gram-positive cells retain the primary crystal violet stain
Gram-negative cells don’t and are stained by a safranin (red) counterstain

13. Fig. 13.3 The structures of bacterial cell walls

14. Many bacteria have capsules
A gelatinous layer found external to the cell wall
Many bacteria possess threadlike flagella
Long external appendages used for locomotion
Some bacteria also possess pili
Short external appendages used for attachment
In harsh conditions, a few bacteria can form endospores
Highly-resistant structures that may germinate into active bacteria when conditions improve

15. Prokaryotes reproduce by binary fission
Fig. 7.1

16. Some bacteria undergo a process called conjugation
The undirectional transfer of plasmid DNA following cell-to-cell contact
Fig. 13.4
Both cells contain a complete copy of the plasmid
Pilus connecting the two cells together

17. 13.3 Comparing Prokaryotes to Eukaryotes
Prokaryotes differ from eukaryotes in many respects
They have very little internal organization
They are unicellular and much smaller
They possess a single chromosome
They are far more metabolically diverse

18. TABLE 13.1

19. TABLE 13.1

20. Prokaryotic Metabolism
Prokaryotes have evolved many more ways than eukaryotes to acquire carbon and energy
Acquisition of Carbon
Autotrophs = Use CO2 as their only carbon source
Heterotrophs = Use preformed organic compounds as carbon sources
Acquisition of Energy
Phototrophs = Use light as energy source
Chemotrophs = Use chemicals as energy source

21. Prokaryotic Metabolism
Based on carbon and energy sources, prokaryotes can be divided into four categories
1. Photoautotrophs
Use the energy of sunlight to build organic molecules from CO2
Cyanobacteria
2. Chemoautotrophs
Obtain energy by oxidizing inorganic substances
Nitrifiers oxidize ammonia or nitrite

22. Prokaryotic Metabolism
Based on carbon and energy sources, prokaryotes can be divided into four categories
3. Photoheterotrophs
Use light as energy and pre-formed organic molecules as carbon sources
Purple nonsulfur bacteria
4. Chemoheterotrophs
Use organic molecules as carbon and energy sources Decomposers and most pathogens

23. 13.4 Viruses Infect Organisms
Viruses are not living organisms
Rather, they are “parasitic” chemicals that can only reproduce within living cells
Viruses are very small
Range from 17 – 1,000 nm
Viruses occur in all organisms
In every case, the basic structure is the same
Segments of DNA or RNA wrapped in a protein coat called the capsid
There is considerable difference, however, in the details

24. Not found in all viruses
Fig The structure of bacterial, plant, and animal viruses
Membrane-like layer
Not found in all viruses
Capsid

25. The Origin of Viral Diseases
Influenza
Perhaps the most lethal virus in human history
Natural reservoirs ducks and pigs in central Asia
AIDS (HIV)
First entered humans from chimpanzees in Africa
The chimpanzee virus is called simian immunodeficiency virus (SIV)
Ebola virus
Filamentous virus that attacks connective tissue
Natural host of the virus is unknown

26. The Origin of Viral Diseases
Hantavirus
Discovered in 1993
Natural host is deer mice
SARS
Severe acute respiratory syndrome
Caused by a coronavirus
Natural host is most likely the civet
West Nile Virus
Mosquito-borne virus
Natural host is birds

27. 13.5 The Origin of Eukaryotic Cells
The microfossil records suggests that eukaryotic cells appeared 1.7 billion years ago
The word eukaryote is derived from the Greek words for “true” and “nucleus”
The endoplasmic reticulum and nucleus of eukaryotes may have evolved from infoldings of prokaryotic cell membranes

28. Endosymbiosis
The endosymbiotic theory proposes that engulfed bacteria gave rise to mitochondria and chloroplasts
Evidence
Organelles are surrounded by two membranes
Organelles have circular DNA
Organelles have ribosomes that resemble those of prokaryotes
Organelles divide by binary fission

29. Fig. 13.7 The theory of endosymbiosis

30. 13.6 General Biology of Protists
Protists are highly variable eukaryotes that share one characteristic:
They are not fungi, plants or animals
Protists have varied types of cell surfaces
Some have cell walls
Movement is also accomplished by diverse mechanisms
Flagella
Cilia
Pseudopodia

31. Many protists form cysts Dormant cells with resistant outer covering
Protists employ all forms of nutrition except chemoautotrophy
Phototrophs
Heterotrophs
Phagotrophs (or holozoic feeders)
Ingest visible particles of food
Osmotrophs (or saprozoic feeders)
Ingest food in soluble form

32. Protists typically reproduce asexually Binary fission  Equal halves
Budding  Progeny cell smaller than parent cell
Schizogony  Multiple fission
Sexual reproduction occurs in times of stress
Zygotic meiosis
In the Sporozoans
Gametic meiosis
In ciliates and some flagellates
Sporic meiosis
In algae

33. Multicellularity Complex multicellular organisms
Individuals are composed of many highly specialized cells that coordinate their activities
Three kingdoms exhibit multicellularity
Plants
Animals
Fungi

34. Multicellularity
Two key characteristics distinguish between complex multicellular and simple multicellular organisms
Cell specialization
Different cells use different genes
They therefore develop in different ways
Intercell coordination
Cells adjust their activity in response to what other cells are doing

35. Colony moves by beating of flagella of individual cells
Multicellularity
Colony moves by beating of flagella of individual cells
Colonies
Permanent association of cells, but little or no integration of cell activities
Volvox
Unicellular green alga
Colony is hollow ball of cells
Fig. 13.9

36. Multicellularity Aggregates Multicellular organisms
Transient collection of cells
Cellular slime molds
Cells come together during starvation
Multicellular organisms
Individuals are composed of many interacting cells that regulate the activities of one another
True but simple multicellularity has been achieved by three groups of protists
Brown, green, and red algae

37. 13.7 Kinds of Protists
Protists are the most diverse eukaryotic kingdoms
The kingdom Protista is an artificial group
Not representative of evolutionary relationships
There is little consensus, even among experts, as to how protists should be classified
Single, very diverse kingdom
vs.
Several different kingdoms

38. There are 15 distinct phyla of protists
These are grouped into five general groups based on shared characteristics
1. Presence/absence of flagella/cilia
2. Presence and kinds of pigments
3. The type of mitosis
4. The types of cristae in mitochondria
5. Molecular genetics of the ribosomal “S” subunit
6. Types of inclusions
7. Overall body form
8. Body shell or armor
9. Modes of nutrition and movement

39. Fig. 13.10 The major protist groups
Functional groupings
Accepted taxa

40. TABLE 13.2

41. TABLE 13.2

42. 13.8 A Fungus Is Not a Plant The study of fungi is called mycology
Fungi have traditionally been included in the plant kingdom
However, there are significant differences between fungi and plants
Fungi are heterotrophs
Fungi have filamentous bodies
Fungi have nonmotile sperm
Fungi have cell walls made up of chitin
Fungi have nuclear mitosis

43. The Body of a Fungus
Fungi exist mainly as slender filaments called hyphae (singular, hypha)
Hyphae are strings of cells separated by septa (singular, septum)
Pores in the septa allow for cytoplasmic streaming between cells
Because of cytoplasmic streaming, many nuclei may be connected by shared cytoplasm

44. Reproductive structures
The main body of a fungus is not the familiar mushroom
But rather an extensive network of hyphae termed a mycelium (plural, mycelia)
Reproductive structures
Fig
All parts of the fungal body are metabolically active
Morel
Amanita

45. How Fungi Reproduce Fungi reproduce both sexually and asexually
Sexual reproduction is initiated when two hyphae of different mating types come in contact and fuse
The two nuclei do not fuse immediately
Heterokaryon
Hyphae containing nuclei derived from two genetically different individuals
Homokaryon
Hyphae containing nuclei derived from two genetically similar individuals

46. How Fungi Reproduce Fungi have three types of reproductive structures
Gametangia
Form haploid gametes that fuse to form zygote
Sporangia
Produce haploid spores that are dispersed
Conidiophores
Produce asexual spores
Fig
Puffball spores
Spores are a common means of fungal reproduction

47. How Fungi Obtain Nutrients
Fungi obtain nutrients by external digestion
They secrete digestive enzymes into their surroundings and absorb the resulting organic molecules
Fig The oyster mushroom
Some fungi are active predators
Immobilizes nematodes then eats them!
Others are even more active predators
Snare or trap prey

48. 13.9 Kinds of Fungi ~ 74,000 species of fungi have been named so far
They are divided into four phyla
Zygomycota
Ascomycota
Basidiomycota
Chitrydiomycota
Distinguished primarily by their mode of sexual reproduction
A fifth group, the imperfect fungi, is artificial
It’s a “catch-all” grouping of fungi in which sexual reproduction has not been observed yet!

49. TABLE 13.3

50. Ecological Roles of Fungi as Decomposers
Fungi, together with bacteria, are the principal decomposers in the biosphere
Fungi are virtually the only organisms that can break down lignin
Fungi cause animal diseases
Fungi are the most harmful pests of living plants

51. Commercial Uses
Many commercial products are dependent on the biochemical activities of fungi
Bread
Beer
Cheese
Soy sauce
Penicillin
Some fungi are used to convert one complex organic molecule into another

52. Fungal Associations
Two kinds of mutualistic associations between fungi and autotrophic organisms are ecologically important
1. Mycorrhizae
Symbiotic association between a fungus and the roots of plants
Fig Lichens growing on rock
2. Lichens
Symbiotic association between a fungus and a green algae or cyanobacterium