Life Science
Chapter 27
Diversity of Life on Earth
The Main Idea
 Earth is home to millions of living species,
including one celled bacteria, giant redwood trees
and animals like us.
 About 1.5 million known species live on earth.
 Many more- estimated to be anywhere between 10 100 million have yet to be discovered.
 How do we keep track of all of this and make it
easier to study?
27.1 Classifying Living
Origin of current classification system
1. Originated by Carolus Linnaeus – 18th
century
2. Came up with the division of the
system: domain, kingdom, phylum,
class, order, family, genus, species
Linnaeus continued
 Also came up with rules for how an
organism is named
 All species have a two-part scientific name
made up of the genus name and the species
name
Examples:
Homo sapiens – human (wise human)
Canis familiaris – dog (intimate dog)
Rules for naming
 Genus name is always capitalized;
species name is always lower case.
 Italicize or underline scientific
names.
Homo sapiens history
 Humans are primates. We belong to a
group that also includes monkeys and
apes.
 Humans are also hominids, a group of
primates that includes modern man
(Homo sapiens) as well as some of our
extinct relatives.
Hominids
Humans are the only
hominid species in existence
today.
Fossil hominids provide
clues as to how humans
evolved.
Extinct Hominids
 Earliest known hominids- belongs to the
group Australopithecus (dated 3.2 million
years old) fossil found called Lucy- 3 ft. 8 in.
tall with a brain the size of a chimpanzeebut it is clear she walked upright.
 Homo habilis fossils 2.2 million years old –
larger brains, made stone tools (name means
‘handy man’), males much larger than
females
Homo erectus
 Homo erectus fossils 400,000 – 2 million years
old- even larger brains, skilled tool maker,
first species to leave Africa and spread to
Europe and Asia. Size differences between
males and females slowly changed to make it
closer to what it is today.
Homo sapiens
 Neanderthals- Homo sapiens neandethalensis
are closely related to modern humans
 Lived 30,000 to 200,000 years ago
 Thick muscles, brains about the same size as they
are now, complex burial rituals and used plants
to treat disease
 Earliest fossils of modern human, Homo
sapiens sapiens are from Ethiopia and are
195,000 years old
 Cultural traits such as religion, art, music
appeared only 50,000 years ago
 There is a major gap that can’t be explained.
 Scientists believe it was the evolution of
language that allowed human culture to blossom
50,000 years ago.
Linnaean system-Species are grouped
based on how similar they are
Domain
Kingdom
Phylum
Class
Order
Family
Genus
Speices
27.2 Evolution and
Classification
 Linnaeus came up with his classification
system long before Charles Darwin
published his theory of evolution
 We now know that Earth’s species are the
result of billions of years of evolution,
including numerous instances of speciation.
Knowing how speciation produced different
species allos scientists to describe how
different species are related.
Speciation
 A species is a group of organisms whose
members can breed with one another but
not with members of other species and
produce viable offspring (children that
can produce offspring).
 Speciation- the formation of new speciesis the evolution of reproductive barriers
that stop two different groups of
organisms from breeding.
Types of Reproductive
Barriers
 Some reproductive barriers stop
individuals of different species form
mating.
 Different species may mate in different
places, at different times, or after different
mating courtship behaviors.
 In other cases, individuals of different species
will not mate because their sexual organs
simply do not fit together.
Other reproductive
barriers
 A second type of reproductive barrier causes matings
between different species to fail
 The mating may not produce offspring, or may
produce offspring that die or are sterile (unable to
reproduce themselves)
 Example – when a lion
and tiger mate,
a liger is produced.
The liger is sterile.
Geographic barriers
 Most common cause of speciation
 A geographic barrier arises when two populations
become physically separated. Can include mountain
ranges, glaciers, rivers, oceans, canyons, or land (in
the case of aquatic organisms.
 Geographic barriers allow different populations to
evolve independently and sometimes to evolve
reproductive barriers.
 If this happens, the different populations become
separate species.
Evolutionary trees
 Evolutionary trees are diagrams that show how
different species are related.
 The divergent lines
show when speciation
occurred.
27.3 Three Domains of Life
 Life is classified into three domains Bacteria
 Archaea
 Eukarya
 Probably 2.5 – 3.5 billion years ago, living
organisms split into two separate lineages –
one that produced Bacteria and the other that
produced Archaea and Eukarya
Domains
 Bacteria and Archaea are prokaryotic
organisms
 Eukarya are eukaryotic organisms





Further divided into four kingdoms
Protists
Fungi
Plants
Animals
 Check out main characteristics on pg 574.
27.4 Bacteria
 Live on your body by the millions, occupy habitats
no other organism can survive and devastate
human populations with diseases such a plague and
tuberculosis.
 Earth’s oldest fossils – 3.5 billion years old are of
bacteria
 Prokaryotes that are so diverse it is hard to make
generalizations about them
Bacteria characteristics
 Some make their own food through photosynthesis; Some
obtain food from other organisms
 Most are single-celled but others gather together in
multicellular clusters
 Come in different shapes- including spheres, rods and spirals
 Many can move with flagella
 Reproduce asexually by dividing (as often as every 20 minutes)
 In poor conditions many can form spores (tough, thick-walled
structures) that can survive for long periods of time until
conditions improve.
More on bacteria
 Important role as decomposers- break down organic
material; life on earth would be impossible without them
 Important for humans- help with digestion, make vitamins
that we can use; good bacteria keep bad bacteria away
 Used to make foods such as yogurt and cheese
 Help make human insulin and other medicines
 Can also cause disease (tuberculosis, syphilis, Lyme) but
antibiotics (substances that kill bacteria) have helped with
this.
27.5 Archaea
 Once considered a funny looking bacteria
 Now considered to be a distinct group of prokaryotes
that are more closely related to eukaryotes than
prokaryotes.
 Many live in extreme environments
 This group is called ‘extremophiles’ because they can
survive in extremely salty environments, very hot
springs and hydrothermal vents.
More on Archaeapronounced our-kee-uh
 Not all are extremists. Many live in the ocean.
 Some are chemoautotrophs that make food using
chemical energy rather than energy from sunlight.
 Those that live in hydrothermal
vents get energy from
hydrogen sulfide- entirely
independent of the sun.
27.6 Protists
 Eukaryotes that are not plants, fungus or animals are lumped
together in a group called protists.
 Include species that can photosynthesize as well as those that
get their food form other organisms.
 Some are single-celled, others are multicellular.
 Many reproduce asexually, while others reproduce sexually.
 Because there are so many different species that are just
lumped together, scientists are in the process of splitting this
group up.
Photosynthetic
protists
Single-celled protists
that float in the
ocean.
Diatoms
Have elaborate
shells made out of
silica
Used in man-made
products like
toothpaste
Dinoflagellates
• Singled-celled protists
that live in the ocean.
• When sunlight and
nutrients are plentiful,
they ‘bloom’ (reproduce
rapidly) causing ‘red
tides’ – ocean actually
turns red because of the
large amount of them
• Some red tides are toxic
• When shellfish eat the
dinoflagellates, they
become contaminated
and poisonous to
humans.
Multi-cellular
photosynthetic
protists
 All seaweeds are protists.
 Kelp is a protist that forms
huge ocean forests.
Heterotrophic
Protists –
getting their
food from
other
organisms
 Most are active, single-celled
hunters
 Amoebas move by extending
part of their body forward and
then pulling the rest behindcalled cytoplasmic streaming
 They eat by engulfing their
prey
Other
heterotrophic
protists
• Flagellates- move
by whipping a
long flagellum
 Ciliates – move by beating
numerous hairlike
projections called cilia
Diseases from protists
 Malaria- protist divides its time between
mosquitoes and humans
 African sleeping sickness- protist divides
time between tsetse fly and humans
 Amoebic dysentery- Montezuma's revenge
27.8 Fungi
 Because they don’t move, scientists used to put
fungus with plants. But they are more closely
related to animals than they are plants.
 Like animals, they obtain their food from other
organisms.
 They obtain food by releasing digestive enzymes
over organic matter and then absorbing the
nutrients..
 Animals digest their food inside their bodiesfungus digest their food outside their bodies.
More on fungi
 Reproduce asexually or sexually
 Reproduce by making spores- tiny reproductive bodies that can
exist in a dormant state for long periods until conditions are
good for growth.
 Fungal spores spread through the air or water.
 Examples of fungus: mushrooms, mold, mildew, yeast
 Some Fungal diseases: yeast infections, ringworm, athlete's foot
 Uses: yeast- baking, brewing; mushrooms- food; cheese
making; antibiotics (penicillin) found in a fungus
27.7 Plants
 Multi-cellular organisms that can photosynthesizeuse the energy from sunlight to make their own
food and organic molecules.
 They share many adaptations
 Roots- anchor the plant to the ground and absorb
water and nutrients from the soil
 Shoots- stems and leaves of the plant- where
photosynthesis occurs
 Many have a vascular system- a plant ‘circulatory
system’ that distributes water and other resources –
called sap
Major Groups of Plantsmosses, ferns, seed plants
Mosses
 Small plants with no vascular system
 Absorb water directly through the environment through
diffusion
 To reproduce, sperm
have to swim through a film
of water to the eggs
 Have to live in moist
habitats like bogs and
shady forests
Ferns
 Have a vascular system
 Sperm must swim to eggs
 Must live is moist environment
 Have distinctive feathery leaves
Seed Plants- largest group
 Key to their success – pollen and seeds
 Pollen- male reproductive cells wrapped in a
protective coating
 Can be transported to female reproductive structures
by wind or by animals – don’t need to swim
 Seed- a small plant embryo that is placed inside a
tough outer covering with a supply of food
 Can survive in a dormant state where no growth or
development occurs until environmental conditions
are good
Two main groups of seed
plants- conifers and flowering
plants
 Conifers- redwoods, pines, cedars & firs
 gymnosperms
 Waxy, needle-like leaves
 Reproductive structures called cones
 Male cones produce pollen that is carried by the
wind to female cones
 Fertilization occurs in the female cones and
seeds are eventually dropped form the female
cones
Male and female cones from a gymnosperm
Flowering Plantsangiosperms
 Biggest and most successful group because they
have flowers and fruit
 Flowers function in reproduction- they contain male
structures that make pollen and female structures
that produce eggs
 In many flowering plants, pollen is transported by
insects or animals
 Flower petals, scent and nectar have evolved to
attract these polinators
fruit
 Flowering plants surround their seeds with a structure
called a fruit
 Fruits help flowering plants spread their seeds around
 Animals can eat the fruit and the seeds get dispersed
through their digestive tracks
 Or, the fruit can attach itself to the animal’s fur (burrs)
 Allows the seeds to be moved far from the parent planthelps ensure survival
Important:
Fruit is the
name for
the seed
covering of
a flowering
plant- it
refers not
to just our
’fruits’ but
also many
of our
vegetables
27.9 Animals
 Multi-cellular organisms that obtain
nutrients by eating other organisms. They
usually take food into their bodies for
digestion
 Most animals also have muscles for moving,
sense organs for making sense of their
environments, and nervous systems for
controlling their actions.
Major Animal groups
 Sponges
 Cnidarians
 Flatworms
 Roundworms
 Arthropods
 Mollusks
 Annelids
 Echinodrems
 Chordates
Sponges
 Sedentary (nonmoving)
animals that live in the
ocean
 Most have a tube-like
shape with a large central
cavity
 Water enters the cavity
through many pores
carrying food with it and
exits through the top
 Animals such as jellyfish,
sea anemones and corals
Cnidarians
 Catch prey using stinging
tentacles
 Many start their lives as
polyps (sedentary) and
grow into medusa that
swim. Some (corals, sea
anemones) spend their
lives as polyps
 Long, ribbon-like worms
Flatworms
 Many are parasites that
live in or on organisms
doing them harm
 Best known flatworm- the
tapeworm that lives as a
parasite in humans and
other animals
 Live either in the water or
on land
Roundworms
 Different from
earthworms, they are very
small (can be thousands in
a handful of soil)
 Slender bodies with
muscles that run from
head to tail
Arthropods
Huge group of animals that
includes lobsters, barnacles,
spiders, scorpions, ticks,
centipedes, insects, and many
other species
Found in every known
habitat on earth
 All have an outer skeletonexoskeleton- that protects
and supports the organism
 Exoskeleton doesn’t grow- it
is shed repeatedly as the
organism grows
 Insects are the largest group
of living organisms on the
planet- more than a million
known insect species
 Important as plant
pollinators; many can carry
disease (West Nile virus,
malaria, etc)
Mollusks
 Soft-bodied animals such
as clams, oysters, squids,
octopuses, snails, slugs
 Most have a protective
shell although the shell is
tiny in some species
(squid) and absent in
some (octopus, slugs)
 Worms such as
earthworms and leeches
Annelids
 Bodies divided into
segments
 Earthworms-important
decomposers
 Leeches- parasites that eat
blood of host
 Starfish, sea urchins, sea
cucumbers
Echinoderms
 Have small sucker-like
tube feet that they use to
move
 Can use them to pry open
shellfish
 Move very, very slowly
Chordates
 Include vertebrates, the
group to which humans
belong
 Vertebrates are animals
with backbones- fish,
amphibians, reptiles,
mammals
Chordatesgroups of fish
 Cartilaginous fish- sharks,
rays, skates
 Don’t have bonesskeletons made of
cartilage
 Ray-finned fish (bony fish)
 what we think of as fish
 Tuna, bass, salmon, etc.
 Swim bladders allow
them to maintain the same
density as the water- they
don’t sink or float- gives
them great mobility
Chordatesamphibians
 Live both on land and in
the water
 Include animals like
salamanders and frogs
 Can live only in moist
environments or their skin
dries out
 Amphibian eggs have no
shell and require moisture
to develop
Chordatesreptiles
 Includes turtles, lizards
and snakes, crocodiles
 All are ectoderms- what
we used to call ‘coldblooded’ they use
behaviors to regulate their
body temperature
 All reptiles- skin made of
dead cells (doesn’t dry
out)
 Eggs have shells (keeps
them form drying out)
Chordatesbirds
 Birds have adaptations for
flight – wings, feathers,
hollow bones (lightweight)
 Endoderms- keep a
constant, high body
temperature by breaking
down large amounts of
food- this process generates
heat
Chordates- mammals
 Have hair and feed their
young milk
 All are endoderms
 Most live on land, but bats
fly and two groups, seals
and whales are partly or
fully aquatic
 3 major groups
 Monotremes- (platypus) lay
eggs
 Marsupials – (possums,
koalas, kangaroos)- give
birth to immarture young
that develop in a pouch
 Placentals- give birth to
more mature live young