life science chapter 27 diversity of life on earth diversity of life on earth
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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