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Diversity of Life on Earth

Chapter 18: Principles of Science

This lecture will help you understand:

1. Classifying Life2. The Three Domains of Life3. Bacteria4. Archaea5. Protists6. Plants7. Moving Water Up a Tree8. Fungi9. Animals10.How Birds Fly11. Viruses and Prions12.Science and Society: Swine Flu

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.

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.

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.

Classifying Life

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

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 Linnaeangroups are clades. However, others are not.

• For example, the "reptiles"must include birds if it is tobe a clade.

The Three Domains of Life

• Life is classified into three domains:

– Bacteria– Archaea

– Eukarya

The Three Domains of Life

• Domain Eukarya includes four kingdoms:– Plants– Fungi

– Animals

– Protists (everything that doesn't fit into the other three kingdoms)

The Three Domains of Life

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.

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.

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.

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.

Protists

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

Protists

• Heterotrophic protists:– Some dinoflagellates– Amoebas– Ciliates

– Flagellates

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

Moving Water Up a Tree

• How does a plant transport water up to its highest branches and leaves?

• Transpiration-cohesion-tension mechanism

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-celledor multicellular.

• Fungi are more closelyrelated to animals thanto plants.

Fungi

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

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.

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.

Animals

• Relationships among the major groups of animals

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.

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 tocatch prey.

– alternate between a sedentarypolyp stage and a mobilebell-shaped medusa stage.

– may exist primarily in one form(corals are polyps, jellyfishare medusae).

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 oxygenacross the skin via diffusion.

– Example: tapeworms

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 likeflailing whips.

– are responsible for hookworm,pinworm, elephantiasis, andtrichinosis.

Animals

• Arthropods – Include crustaceans, chelicerates, and uniramians– Features:

• Exoskeleton

• Segmented bodies and jointed legs

• A brain and well-developed sense organs

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.

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.

Animals

• Echinoderms– Include starfish, sea urchins, and sea cucumbers

• Features:– Endoskeleton

– Tube feet

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.

Animals

• Tunicates– Sedentary filter feeders

• Lancelets

– Small, blade-shaped swimmers

– Filter feeders

Animals

• Vertebrates – Animals with backbones– Include:

• Jawless fishes

• Cartilaginous fishes

• Ray-finned fishes

• Lungfishes and coelacanths• Amphibians• Reptiles

• Mammals

Animals

• Lamprey, a jawless fish

• Lungfish

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.

Animals

• Amniotes

– Include reptiles and mammals– Features:

• Skin made of dead cells, protecting from water loss• Shelled eggs

– Well adapted to diverse terrestrial habitats

Animals

• Reptiles – Include turtles, lizards and snakes, crocodilians, and

birds

Animals

• Mammals– Include monotremes, marsupials, and placentals– Features:

• Have hair

• Feed their young milk

– Some are terrestrial,some are aquatic, andsome are able to fly.

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.

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 ofDNA or RNA.

– have genes that mutate quickly.– are responsible for many human

diseases, as well as thoseof other species.

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.

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.