Principles of Science

1. Diversity of Life
on Earth
Chapter 18: Principles of Science

2. This lecture will help you understand:
1. Classifying Life
2. The Three Domains of Life
3. Bacteria
4. Archaea
5. Protists
6. Plants
7. Moving Water Up a Tree
8. Fungi
9. Animals
10.How Birds Fly
11. Viruses and Prions
12.Science and Society: Swine Flu

3. Classifying Life
• Thousands of years ago, Aristotle organized life into a
"chain of being." Other scientists used this strategy to
arrange living things from "simple" to "complex." Humans
were at the top of the chain.

4. Classifying Life
• In the 18th century, Carolus Linnaeus developed a
system for classification that emphasized the shared
similarities of organisms.
• The Linnaean system classified organisms using a
series of hierarchical levels.

5. Classifying Life
• Biologists now classify life based on its evolutionary
history. This system
– is less arbitrary than one based on "similarities."
– allows biologists to more effectively study the
evolution of specific traits in organisms.

6. Classifying Life
• The evolutionary history and relationships of living things
can be diagrammed in an evolutionary tree.

7. Classifying Life
• Biological groups constructed based on evolutionary
history are clades. A clade is a group of species that
includes an ancestor and all of its descendants.
• Many well-known Linnaean
groups are clades.
However, others are not.
• For example, the "reptiles"
must include birds if it is to
be a clade.

8. The Three Domains of Life
• Life is classified into three domains:
– Bacteria
– Archaea
– Eukarya

9. The Three Domains of Life
• Domain Eukarya includes four kingdoms:
– Plants
– Fungi
– Animals
– Protists (everything that doesn't fit into the other three
kingdoms)

10. The Three Domains of Life

11. Bacteria
• Bacteria are diverse.
– Some bacteria are autotrophs that photosynthesize.
Some are chemoautotrophs. Some are heterotrophs.
– Most bacteria are single-celled, but others gather in
multicellular clusters.
– Bacteria reproduce asexually by dividing, but most
occasionally exchange genetic material.
– Bacteria vary in shape, and some have flagella for
locomotion.

12. Bacteria
• Importance of bacteria to humans:
– They break down organic matter, making carbon
available for photosynthesis.
– They help make nitrogen available to living things.
– Some produce vitamins in our bodies.
– Some bacteria in our bodies prevent harmful species
from infecting us.
– Some are essential for making cheese and yogurt.
– Some cause disease.
– Genetically engineered bacteria produce insulin and
other important products.

13. Archaea
• Archaea are not bacteria. They are a distinct domain of
prokaryotic organisms.
• Some archaea are "extremophiles" that thrive in harsh
environments. Some are chemoautotrophs that make
food using chemical energy from molecules such as
hydrogen sulfide.
• Certain archaea provide clues about what the earliest
living organisms may have been like.

14. Protists
• Protists are eukaryotes that are not plants, fungi, or
animals.
• They may be autotrophs or heterotrophs.
• They may be single-celled or multicellular.
• They may use asexual or sexual reproduction.

15. Protists
• Autotrophic protists:
– Diatoms
– Some dinoflagellates
– Seaweed such as kelp, red algae, and green algae

16. Protists
• Heterotrophic protists:
– Some dinoflagellates
– Amoebas
– Ciliates
– Flagellates

17. Plants
• Plants are terrestrial, multicellular, autotrophic
eukaryotes that obtain energy through photosynthesis.
• Plant adaptations to a terrestrial existence:
– Roots
– Shoots: stems and leaves
– Vascular system (found in most plants): xylem and
phloem

18. Moving Water Up a Tree
• How does a plant transport water up to its highest
branches and leaves?
• Transpiration-cohesion-tension mechanism

19. Fungi
• Fungi are heterotrophs that release digestive
enzymes over organic matter and then absorb the
nutrients.
• Many fungi are decomposers that obtain the bulk of
their nutrients from dead organic matter. They play a
crucial role in terrestrial ecosystems.
• Fungi may be single-celled
or multicellular.
• Fungi are more closely
related to animals than
to plants.

20. Fungi
• Fungi may reproduce sexually or asexually.
• Many reproduce using spores.

21. Fungi
• Importance of fungi to humans:
– Fungi play a role in decomposition.
– Mycorrhizae, the close association of plant roots with
fungi, are essential to many important plant species.
– Yeast is used in baking and brewing.
– Fungi are used to make blue cheeses.
– Fungi are a source of important medicines such as
penicillin.
– Fungal diseases include: yeast infections, ringworm,
and athlete's foot.

22. Animals
• Animals are multicellular, heterotrophic eukaryotes that
obtain nutrients by eating other organisms.
• Most reproduce sexually and are diploid during most of
their life cycle.
• The gametes—sperm and egg—are the only haploid
stage of the life cycle.
• Some go through a juvenile period as a larva.
• Most have muscles, sense organs, and nervous
systems.

23. Animals
• Relationships among the major groups of animals

24. Animals
• Sponges
– Sponges are sedentary marine animals.
– Special cells in the sponge beat flagella that
move water through the sponge, allowing cells to
capture bacteria, digest them, and then distribute
nutrients to other cells.

25. Animals
• Cnidarians
– include jellyfish, sea anemones, and corals.
– have two distinct tissue layers separated by a jellylike
middle layer.
– use tentacles armed with
barbed stinging cells to
catch prey.
– alternate between a sedentary
polyp stage and a mobile
bell-shaped medusa stage.
– may exist primarily in one form
(corals are polyps, jellyfish
are medusae).

26. Animals
• Flatworms
– Flatworms have distinct head and tail ends and back
and belly sides.
– A single opening serves as mouth and anus.
– The flat shape allows the
animal to obtain oxygen
across the skin via diffusion.
– Example: tapeworms

27. Animals
• Roundworms
– have small, slender bodies with tapered ends and
a round cross-section.
– have both a mouth and an anus.
– shed a tough outer cuticle periodically during
growth.
– have a longitudinal muscles
that cause them to move like
flailing whips.
– are responsible for hookworm,
pinworm, elephantiasis, and
trichinosis.

28. Animals
• Arthropods
– Include crustaceans, chelicerates, and uniramians
– Features:
• Exoskeleton
• Segmented bodies and jointed legs
• A brain and well-developed sense organs

29. Animals
• Mollusks
– Mollusks include bivalves, cephalopods, and
gastropods.
– Most have a protective shell.
– They use a muscular "foot" for locomotion.
– A visceral mass holds the digestive and
reproductive organs.
– A mantle secretes the shell.

30. Animals
• Annelids
– Annelids are segmented worms such as
earthworms and leeches.
– The muscles of earthworms are oriented both
circularly and longitudinally, providing flexibility in
motion.

31. Animals
• Echinoderms
– Include starfish, sea urchins, and sea cucumbers
• Features:
– Endoskeleton
– Tube feet

32. Animals
• Chordates
– Chordates include tunicates, lancelets, and
vertebrates.
– All chordates have, at some point in their life history:
– A brain and spinal cord
– A notochord that supports the back
– Gill slits
– A tail that extends beyond the anus
– Some of the chordate features are not apparent in
adults. For example, humans have no tails, but
human embryos do go through a tailed stage.

33. Animals
• Tunicates
– Sedentary filter feeders
• Lancelets
– Small, blade-shaped swimmers
– Filter feeders

34. Animals
• Vertebrates
– Animals with backbones
– Include:
• Jawless fishes
• Cartilaginous fishes
• Ray-finned fishes
• Lungfishes and coelacanths
• Amphibians
• Reptiles
• Mammals

35. Animals
• Lamprey, a jawless fish
• Lungfish

36. Animals
• Amphibians
– Amphibians include salamanders, frogs, and caecilians.
– Amphibians may have aquatic larvae and terrestrial adults.
– They must live in moist environments to prevent their skin
and eggs from drying out.
– Many species have gone extinct in the last few decades.

37. Animals
• Amniotes
– Include reptiles and mammals
– Features:
• Skin made of dead cells, protecting from water loss
• Shelled eggs
– Well adapted to diverse terrestrial habitats

38. Animals
• Reptiles
– Include turtles, lizards and snakes, crocodilians, and
birds

39. Animals
• Mammals
– Include monotremes, marsupials, and placentals
– Features:
• Have hair
• Feed their young milk
– Some are terrestrial,
some are aquatic, and
some are able to fly.

40. Animals
• Ectotherms use behavior to regulate their body
temperature.
– All reptiles except birds are ectotherms.
• Endotherms maintain a constant body temperature by
breaking down relatively large amounts of food.
– Birds and mammals are endotherms.

41. Viruses and Prions
• Viruses
– are small pieces of genetic material wrapped in a protein
coat.
– have some, but not all, of the characteristics of life:
• Not made of cells
• Reproduce only within a host cell
• Have genes
• Evolve
– may have genes made of
DNA or RNA.
– have genes that mutate quickly.
– are responsible for many human
diseases, as well as those
of other species.

42. Viruses and Prions
• Prions
– are incorrectly folded proteins.
– "reproduce" by converting normal proteins into
misfolded prions.
– cause mad cow disease and Creutzfeldt-Jacob
disease in humans.

43. Science and Society: Swine Flu
• A swine flu epidemic started in March 2009.
• It caused an unusual number of severe illnesses and
deaths, including in young, healthy people.
• The H1N1 virus responsible for swine flu combines
genes from swine, human, and bird flu viruses.
• A vaccine was developed relatively quickly, but
manufacturing enough vaccine quickly proved difficult.
• This virus can now be spread from person to person.