Life ScienceChapter 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 namedAll species have a two-part scientific

name made up of the genus name and the species nameExamples:

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 chimpanzee- but 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 humansLived 30,000 to 200,000 years agoThick 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 oldCultural traits such as religion, art, music

appeared only 50,000 years agoThere 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 species- is 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-BacteriaArchaeaEukarya

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 organismsFurther divided into four kingdomsProtistsFungiPlantsAnimals

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 characteristicsSome 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 Archaea- pronounced 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 ProtistsEukaryotes 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

Diatoms

Single-celled protists that float in the ocean.

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 photosynthet

icprotists

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 behind- called cytoplasmic streaming

They eat by engulfing their prey

Other heterotrophi

c protists

Ciliates – move by beating numerous hairlike projections called cilia

• Flagellates- move by whipping a long flagellum

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 bodies- fungus 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 photosynthesize- use 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 Plants- mosses, ferns, seed

plantsMosses

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 plantsConifers- redwoods, pines, cedars &

firsgymnosperms

Waxy, needle-like leaves

Reproductive structures called conesMale cones produce pollen that is carried

by the wind to female conesFertilization occurs in the female cones

and seeds are eventually dropped form the female cones

Male and female cones from a gymnosperm

Flowering Plants- angiosperms

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 plant- helps 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

SpongesSedentary (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

Cnidarians

Animals such as jellyfish, sea anemones and corals

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

Flatworms

Long, ribbon-like worms

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

Roundworms

Live either in the water or on land

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 All have an outer

skeleton- exoskeleton- 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)

Huge group of animals that includes lobsters,

barnacles, spiders, scorpions, ticks,

centipedes, insects, and many other species

Found in every known habitat on earth

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)

Annelids

Worms such as earthworms and leeches

Bodies divided into segments

Earthworms-important decomposers

Leeches- parasites that eat blood of host

Echinoderms

Starfish, sea urchins, sea cucumbers

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

Chordates-groups of

fishCartilaginous fish-

sharks, rays, skates Don’t have bones-

skeletons 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

Chordates- amphibians

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

Chordates-reptiles

Includes turtles, lizards and snakes, crocodiles

All are ectoderms- what we used to call ‘cold-blooded’ 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)

Chordates-birds

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