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BIOLOGY II REVIEW
High School Graduation Test
Beneficial:
Harmful:
decomposers of matter, in digestive system, nitrogenfixers
can cause diseases like strep throat, pneumonia
LINNAEAN SYSTEM
In the mid-1700’s, Carolus Linnaeus developed a new
classification system that revolutionized taxonomy. He suggested that
organisms be classified with other organisms that had similar structures.
Organisms are known by their common name, such as red maple.
Organisms have been given a scientific name, the genus followed by the
species. The genus and species for the red maple tree is Acer rubrum. The
genus begins with a capital letter and the second name is always lower case.
All scientific names are written in Latin, and are italicized or underlined.
PROTISTA
Examples:
A classification key can be used as an aid to identify organism. It
uses an organisms general characteristics and special features to find its
appropriate placement.
Growth:
Reproduction:
Beneficial:
Harmful:
Characteristics:
Structures:
Most unicellular organisms - protozoa, amoeba,
zooplankton, euglena, paramecium, and algae
Animal-like organism, distinguished by method of
locomotion, eukaryotes, mainly microscopic, single
celled or multicellular; some are autotrophic (algae)
and many are heterotrophic (protozoans)
flagella, capsules, cell organelles, membrane bound,
some are photosynthetic
cell membrane, availability of food set growth limit.
asexual or sexual
some are harmless
sleeping sickness, malaria
TAXONOMY
Scientists these days study chromosome structure, reproductive
potential, biochemical similarities, and embryology to determine the
relationships among organisms. The classification levels are:
Kingdom-Phylum-Class-Order-Family-Genus-Species
(King Philip Came Over For Great Spaghetti)
KINGDOMS
MONERA includes Eubacteria and Archae
Examples:
Bacteria, blue-green bacteria, and other
microorganisms that lack nuclei
Characteristics:
prokaryote, microscopic, lives as a single cell or in
colonies in water. Most are autotrophic (producers),
a few are heterotrophic (consumers)
Structures:
flagella, capsules
Growth:
cell membrane and availability of food set growth
limit; keep moist and warm for optimal conditions
Reproduction:
binary fission (splits in two)
FUNGI
Examples:
Characteristics:
Structures:
Growth:
Reproduction:
Beneficial:
Harmful:
PLANTS
Examples:
Characteristics:
Structures:
Functions:
Systems:
Growth:
mushrooms, bread molds, slime molds, rusts and
smuts, yeast
Animal-like organism, cannot move, eukaryotes,
mainly multicellular, parasitic, heterotrophic,
root-like, caps, filaments
based on food source and availability
asexual, sexual
yeast, penicillin, decompose organic material
cereal rusts, ringworm, athlete’s foot,
All multicellular plants - Mosses, liverworts,
hornworts, ferns, gymnosperms (pine cone plants),
angiosperms (flower-bearing plants)
eukaryotes, mainly multicellular, can’t move,
autotrophic
cellulose cell walls
based on cell and tissue chemistry
all present and functioning
based on hormone action
Reproduction:
ANIMALS
Examples:
Characteristics:
Structures:
Functions:
Systems:
Growth:
Reproduction:
asexual, sexual by spores, seeds, flowers, and cones
All multicellular animals - Invertebrates (sponges,
jellyfish, coral, sea anemones, planarian, fluke,
tapeworm, hookworm, earthworm, mollusks, starfish,
insects, crustacean); vertebrates (fish – cartilaginous
and bony); amphibians – frogs, salamanders; reptiles
– snakes, lizards, turtles; birds; and mammals
eukaryotes, multicellular, heterotrophic, most are
motile at some point in their lifetime
all present and unique to the organism
based on nutrition, cell and tissue chemistry, and
individual demands
all present and functioning
based on hormone action and nutrition
asexual, sexual
PLANTS
One of the major ways that land plants differ is the way they
transport water and nutrients throughout the plant body. The majority of
land plants have an internal system of connected tubes and vessels called
vascular tissues. These plants, called vascular plants, are the plants that you
are the most familiar with –maple trees, grasses, roses, and house plants.
Vascular plants have roots, stems, and leaves.
The other group of plants is called bryophytes. They lack vascular
tissue. They transport water and nutrients by osmosis and diffusion.
NONVASCULAR PLANTS
Bryophytes need a lot of water to survive. Remember that they
transport materials by osmosis and diffusion. This requires a lot of water.
Almost all bryophytes are small plants and they grow close to the ground.
Gravity can restrict the processes of osmosis and diffusion.
Bryophytes do not have true stems, leaves, and roots. What you
think are their “roots” are actually rhizoids. They anchor the plant to the
ground, but they do not absorb water like real roots do. The part of the
bryophyte that is above the ground gets its water from the air through its
leaves. Bryophyte leaves are usually only two cells thick.
The main type if Bryophytes are: mosses, liverworts, and
hornworts
VASCULAR PLANTS
Plants with vascular tissue are called tracheophytes. They have
true roots, stems, and leaves. They have an internal network of tubes that
carry water, nutrients and glucose made from photosynthesis throughout the
plant.
The roots absorb water and nutrients from the soil and they anchor
the plant. The roots also store food that was made in the leaves. The stem
contains vascular tissue that transports substances between the roots and the
leaves. The stem also supports plant growth above the ground. It is the
backbone of the plant. There are two types of vascular tissue: xylem and
phloem. Xylem transports water and minerals absorbed by the roots up to
those parts of the plant that are above the ground. The phloem carries sugar
and other soluble organic materials produced by photosynthesis from the
leaves to the rest of the plant.
The leaves use sunlight, water, and carbon dioxide to carry out
photosynthesis. They also transport the food they produce to the rest of the
plant in a process called translocation. In addition leaves exchange gases
and water vapor with the atmosphere. The outside of the leave is covered
with a waxy layer that slows the evaporation of water from the leaf. The
waxy layer covers the epidermis, a single transparent layer of cells. The
epidermis has openings called stomata. Each stomata has a guard cell on
each side. The guard cells change shape to control the exit and entry of
water and gases. Most guard cells are located on the underside of the leaf
where the surface is shaded. Ninety percent of the water that enters the
roots is lost through the leaves in a process called transpiration.
The middle portion of the cell is called mesophyll. The cells of the
mesophyll contain the chlorophyll and other pigments. Vascular bundles
extend into the tissue of the mesophyll. They are seen in the leaves as
veins.
The vascular plants can be divided into those that have seeds and
those that have spores. Ferns, horsetails, whisk ferns, and club mosses all
have spores. All other plants have seed – either in a cone or in a fruit.
FERNS
Ferns are seedless plants that contain vascular tissue. Other
seedless plant groups include whisk ferns, horsetails, and club mosses.
Ferns have underground rhizomes (underground stem) that produce roots.
Each fern frond has a stem (called a stipe) many leaf blades that make up
the frond. Fern fronds spread out over a large area and so ferns are able to
survive in dim sunlight.
GYMNOSPERMS
Gymnosperms are one of two groups of vascular plants.
Gymnosperms produce their seeds in cones and generally keep their leaves
throughout the year (evergreen). The main gymnosperms alive today – are
Conifers.
Conifers means “cone-bearer”. Pines, spruce, fir, and other
conifers are characterized by their stiff cones and needle-like leaves.
Conifers can thrive in harsh conditions because they have special
adaptations. Their needles are covered in a hard waxy cuticle and have little
exposed surface area. This means that they do not lose much moisture.
They shed their needles throughout the year instead of once a year. They
send their roots out into a wide area of soil instead of deep into the soil.
This allows them to survive in areas where the soil is not very deep.
ANGIOSPERMS
Angiosperms are flowering plants. They produce seeds enclosed
in fruits. (Gymnosperm seeds are uncovered in their cones.) Angiosperms
are deciduous plants. That means that they lose their leaves every fall.
Angiosperms produce seeds with a cotyledon (seed leaf) inside. A
cotyledon provides food for the plant embryo in the seed when it begins to
grow.
Angiosperms can be divided into one of two groups. This group is
based on characteristics of their seeds: monocot and dicot. Monocots are
plants with only one cotyledon. Monocots also have vascular tissue that is
scattered in separate bundles throughout the stem. The leaves have parallel
veins and the root system is fibrous with string-like branches.
Dicots have two cotyledons. Dicots have vascular tissue arranged
in a circle around the outside of the stem. The leaves have net-like veins.
The root is a large central taproot.
REPRODUCTION
Vascular plant life is different from non-vascular plant life.
Nonvascular plants spend the majority of their life in the gametophyte
phase. In vascular plants, the sporophyte generation is the dominant
generation. The sporophyte is physically larger and shows more complex
development.
The reproductive cycle of a conifer involves separate male and
female cones that are grown on the same tree. The male pollen cones
produce the pollen grains. The female seed cones contain egg cells. Both
pollen and eggs are gametophytes. When the egg cells mature, the female
cells produce a sticky sap that traps the pollen grain. The pollen grain
produces sperm, which fertilize the eggs. A conifer embryo develops,
enclosed in the seed.
Reproduction in angiosperms is different. All angiosperms
produce flowers. Some flowers have both male and female parts and some
have just one sex. The flower attracts insects for pollination and thus
fertilization to make a seed. After fertilization, the flower petals die and the
remaining flower structures form a fruit. The fruit protects the seed and
helps to disperse them in various ways. Then, an animal eats the fruit and
leaves the seed in its feces elsewhere.
SEXUAL REPRODUCTION
In plants that produce them, the flower functions in sexual
reproduction. Flowers consist of modified leaves. The essential flower
parts are the ones that produce gametes and carry out sexual reproduction.
These include male parts called stamens and female parts call pistils.
Most flowers have three, four, or five stamens. The thin stem-like
portion of a stamen is called the filament. Pollen is produced at the tip of
the filament, generally in an oblong structure called the anther. Most
flowers have a single pistil. The pistil contains three parts. The swollen
base of the pistil is called the ovary. Within the ovary, one or more ovules
produce the egg cells. The slender middle part of the pistil is called the
style. At the tip of the style is the stigma. The stigma produces a sticky
substance to which pollen grains become attached.
During pollination, pollen grains stick to the top of the stigma.
From there, the pollen grain grows a pollen tube down through the style to
the ovary where it fertilizes the egg.
In cross-pollination, the pollen from one flower sticks to insects,
which in turn deposit, it on other flowers. In self-pollination, the pollen is
transferred to the stigma of the same flower. In the anther and the ovary,
cell division takes place, which reduces the number of chromosomes in half.
Animals, wind, and water all transport pollen from flower to
flower. The nonessential flower parts are modified to aid the specific type
of pollination a plant undergoes. In flowers that are pollinated by animals,
the stem and receptacle hold the flower out where its colors and scent are
most obvious. Some flowers produce nectar, a sweet liquid.
Fruits are formed when the egg is fertilized and the ovary begins to
swell and ripen. It changes color and becomes fleshy or dry. Animals eat
the fruit and pass the seed out to new places through their waste.
ASEXUAL REPRODUCTION
Many plants can produce new plants without the aid of
fertilization.. Asexual reproduction is common in strawberries, potatoes,
irises, spider plants, and grasses. Remember that any plant produced
asexually has the same genes as its parent plant.
Asexual reproduction can be accomplished naturally through
vegetative propagation. This means that the plant sends out runners or long
modified stems (rhizomes) and grows new plants from these parts.
Artificial propagation involves things like cuttings and graftings.
With cuttings, pieces of stem are cut from the parent plant and kept in soil
or water until roots grow. Then the plant is placed in soil to grow. Grafting
is a method used to propagate fruit trees, roses, and grapes. Sections of one
plant’s stem are cut and attached to another plant’s stem that is already
rooted in the soil.
SEEDS
Seeds gave the animal world a new high-energy food source. They
provide food for mammals that need lots of food to help maintain their body
temperature. People have depended upon angiosperms for food, lumber,
fibers, clothing, and medicines.
The development of plants that have seeds really helped plants to
survive in a variety of places. Seeds can lie dormant (asleep) if the
conditions aren’t right for growing. Some seeds, because they have burrs or
stickers, can travel a long way on animals or in the wind before developing
into a plant. This spreading of seeds, called dispersal, is good for plants. It
helps to spread the plant’s genes over a wider area.
INVERTEBRATES
The major difference between animals and plants is that animals
can move. Animals cannot produce their own food so they must move to
find it. The arrangement of body parts is related to how a particular animal
species meets the challenges of living, which includes gathering food,
protecting itself, and reproducing. Differences in body structure are useful
in classifying animals. Invertebrates make up 97% of the animal kingdom.
Invertebrate are animal that do not have a backbone such as: worms,
octopus and all insects.
VERTEBRATES
Vertebrates have a strong flexible backbone. Three classes live
entirely in water - jawless fish, cartilaginous fish, and bony fish.
Amphibians are adapted to life on land as well as the water. Reptiles and
mammals are primarily land animals. All but a few birds can fly.
Vertebrates have a number of characteristics in common. They
have bilateral symmetry. The major sense organs are located in the head.
All vertebrates have a closed circulatory system and a coelom (large central
body cavity that contains the important organs). They all have an
endoskeleton which supports and protects them. A distinctive feature of the
skeleton is the backbone - vertebral column. The endoskeleton can be made
of cartilage or bone. They have pairs of muscles that work in opposite
directions to push and pull the bones.
Their bodies are covered with scales, skin, feathers, or hair. There
is contractile tissue attached to the bone or cartilage. They have a digestive
tube that goes from mouth to anus. They have gills or lungs for breathing
and have a closed circulatory system with two-, three-, or four-chambered
hearts. They have arteries to take the blood from the heart and veins to take
it back to the heart.
Their excretory (waste) system consist of kidneys, and associated
tubes. Heir nervous system includes a spinal cord, brain, nerves, and sense
organs. There are male and female sexes.
Fish
Most of the world’s fishes have skeletons made of bone, and have
jaws and scaly skin. They get their oxygen from the water through gills.
They have a swim bladder to help with buoyancy and a two-chambered
heart. They are ectothermic. They have separate sexes and the eggs are
fertilized outside the body.
Class Amphibia
Amphibians live on land and in the water. They have internal
lungs that are not very efficient and they also get oxygen through their
moist skin. They keep their skin moist with a mucus and they can never
venture too far from water. They return to the water to lay their eggs and
their young pass through a larval stage in the water before beginning their
life on land.
Adult amphibians are carnivores. They have a three chambered
heart and are ectothermic. They have a brain which is the central part of
their nervous system. They have separate sexes and have external
fertilization. Amphibians include frogs, toads, and salamanders.
In frogs, the young are called tadpoles and live in the water. The
tadpoles go through metamorphosis, or change, as it develops into an adult.
A tadpole begins life with a short tail and breathes through gills. Gradually
it develops arms and legs and its tail begins to disappear. The lungs replace
the gills and the frog leaves the water.
Class Reptilia
Reptiles were the first animals that were truly independent of the
water. They do not need to keep their body moist for their skin is thick and
covered with scales. They do not need to return to water to have babies for
their young are laid in eggs. These eggs hold food for the embryo to live
off of while it is growing.
Some are herbivores and some are carnivores. They have strong,
bony skeletons and their feet have toes with claws. They have welldeveloped lungs and a three chambered heart (except for crocodiles). They
are ectothermic. The reptile’s nervous system is similar to that of
amphibians and they have a small brains.
Reptiles include the extinct dinosaurs, turtles, tortoises, alligators,
crocodiles, lizards, and snakes.
Class Aves
This is the class of all birds. Birds arose from reptiles and they
grew feathers instead of scales to insulate themselves. The feathers
distinguish birds from other classes of vertebrates. Birds are endothermic warm-blooded - their body temperature remains constant. They have a
four-chambered heart.
They have wings and can fly. The body is divided into a head,
neck, trunk, and tail. They do not have teeth - they have a horny beak.
Their front limbs are modified into wings. They lay eggs and incubate them
in the nest.
There are four common bird types: flightless birds (penguins,
ostriches), water birds (ducks, geese, swans), perching birds (sparrows,
robins), and birds of prey (hawks, eagles, owls).
Class Mammalia
Mammals have several characteristics not found in other
vertebrates. They nurse their young using milk from mammary glands.
Mammals have live births - the young are born live after spending time in
their parents developing.
They have body hair that acts as insulation and also protects the
body from injury. Mammals have a large well-developed brain and they are
the only animals that have an external outer ear for hearing. Their body is
divided into two parts - the chest and the abdomen. The diaphragm
separates the two parts.
They are endothermic. They have a four-chambered heart and an
efficient, closed circulatory system. Mammals have a well-developed
cerebral cortex and have a complex nervous system.
Mammals include monotremes (duck-billed platypus, spiny
anteater). They have mammary glands, which make them mammals, but
they lay eggs. Mammals also include marsupials (kangaroos, koalas,
opossums). They bear live young, but the young are not as developed as
other mammals. These babies complete their development inside a pouch
attached to the mother.
Placental mammals include 95% of all mammals. The embryo of a
placental mammal is implanted in the mother’s uterus - the mother’s
reproductive organ. The placenta forms, connecting the young mammal
directly to the mother.
ECOLOGY
ECOSYSTEMS
Life on earth extends from the ocean depths to a few kilometers
above the earth’s surface. The area where life exists is called the biosphere.
The biosphere can be more easily understood by breaking it into smaller
components called ecosystems.
An ecosystem is a physically distinct, self-supporting unit of
interacting organisms and their surrounding environment. It is made up of
biotic and abiotic interactions. The biotic factors of an ecosystem are the
living organisms in the area. The abiotic factors are the non-living, or
physical, components of the area like light, soil, water, temperature, wind,
and nutrients. The essential factors that make an ecosystem successful are a
source of energy, a storage of water, and the ability to recycle water,
oxygen, carbon, and nitrogen.
Ecosystems must maintain an ecological balance. This can be
helpful or harmful to the members that make up the community depending
upon whether they are predators or prey. A predator is an animal that feeds
on other living things. The animal it feeds upon is the prey. Lions
(predator) hunt down and kill antelope (prey).
Each of the biotic organisms in an ecosystem interrelate with the
others. A symbiotic relationship between two members of a community is
one in which one or both parties benefit. Commensalism is a relationship in
which one member is the host, but causes no harm to the other organism
(barnacles on whales). Mutualism is a relationship in which two living
organisms live together in dependency on each other (the protozoa in the
human intestine). Parasitism is a relationship that involves a host organism
which is harmed by the presence of the other organism (fleas on dogs and
cats).
COMMUNITIES
An ecosystem’s biotic factors interact with each other and
compose a community of living things that coexist. Each community is
composed of populations. A population is a group of small individuals of a
single species that occupy a common area and share common resources.
The number of populations within a community varies. A tropical rain
forest community may have thousands of populations while a desert
community may have very few.
Just like communities are made up of populations, each
populations is composed of interacting individuals. Each individual
organism lives in a specific environment and pursues a particular way of
life. The surroundings in which a particular species can be found is called
its habitat. An organism can inhabit an entire ecosystem like a woodpecker
might occupy the whole oak forest. But the spider may only inhabit the
trunk of one of the oak trees.
The way of life that a species pursues within its habitat is called its
ecological niche. An organism’s niche is composed of biotic and abiotic
factors. Some niches can be very broad (rats) while others can be very
limited (panda).
THE FLOW OF MATERIALS
Each ecosystem has its producers, consumers, and decomposers.
They make up a cycle called a food chain. Food passes from one organism
to another in the food chain. Energy is used up by each consumer in the
food chain. Plants make food, animals eat plants, some animals eat other
animals, and some animals eat plants and other animals. Herbivores are
animals that eat only plants. Carnivores are animals that each only other
animals. Omnivores are animals that eat both plants and animals. A
Saprophyte is an organisms that feeds on dead organisms.
There are many food chains in an ecosystem. The least amount of
energy consumed is the item highest in the food chain. In the preceding
example that would be the human. All the food chains in an ecosystem
make up the food web of the area. Most food chains overlap because many
organism can eat more than one type of food.
All organisms need certain chemicals in order to live. The most
important ones are water, oxygen, carbon, and nitrogen. The continuous
movement of chemicals throughout an ecosystem is called recycling.
ECOLOGICAL SUCCESSION
An ecosystem goes through a series of changes known as
ecological succession. Succession occurs when one community slowly
replaces another as the environment changes. As succession in a
community continues, it finally reaches a climax community. A few
organisms establish themselves and become the dominant species in the
area. The complete process of succession may take anywhere from a
hundred to thousands of years, depending upon the communities.
POPULATIONS IN ECOSYSTEMS
The population of an area is affected by the new offspring
produced in the area. New plants and animals moving in from other places
increase the size of the
population. The death of organisms
Evoluti
and animals moving out of the on
area decrease the size of the
population. There is a direct
relationship between the number of
plants and animals in an area which is in ecological balance. If the number
of one of them is increased or decreased, it will affect the numbers of the
other. During deer season, the number of deer is reduced by man. The
plants that the deer eats will increase during this season.
A change in populations may be helpful or harmful to the
community. If insects are killed by insecticide, the animals that depend on
they for food must move elsewhere. Even the human population changes as
he seasons change. In the summertime, the coastal area is more widely
populated by vacationing people. In the wintertime, the snowy,
mountainous areas are more populated by snow skiers.
BIOMES
Communities are members of a larger ecological unit called a
biome. A biome is an extensive area of similar climate and vegetation. A
biome’s abiotic (non-living) factors determine what plants and animals live
there. The major influences are temperature, light intensity, and patterns of
rainfall, which determine the availability of water. There are six basic
biomes on earth: tundra, taiga, grassland, deciduous forest, desert, tropical
rain forest.
Biomes that are closest to the poles experience the coldest weather
conditions for they are furthest away from the sun due to the tilting of the
earth.
ECOLOGICAL PROBLEMS
Natural resources are necessary for human survival and the making
of necessary products. The natural resources are water, air, soil, wildlife,
and forests. Problems that are now being faced are related to erosion, soil
depletion, species extinction, deforestation, desertification, and water
shortages. Efforts to reverse these problems and their environmental
damages are found in the planned programs of reforestation, captive
breeding, and planned farming through efficient plowing and planting
procedures.
Disruptive changes can easily upset the stability of an ecosystem.
Destructive acts of nature can occur. A forest fire can destroy all plant and
---animal life in a forest, along a river, and around the shore of
a pond. It can also pollute a pond with ash.
Humans are unique in our ability to modify our ecosystem.
Pollution from human acts can also affect an ecosystem. A chemical spill
or pesticides sprayed overhead can kill all plant and animal life with which
it comes in contact with. A housing development along the bank of a river
or on the shore of a pond can bring both garbage and noise pollution, in
addition to direct physical destruction of these habitats.
Pollution is damaging to both the ecosystems and living organisms.
Air, soil, and food resources are being affected by pollution. Pollutants
include automobile exhaust, fertilizers, pesticides, industrial wastes,
radioactive wastes, and household wastes. Pesticides like DDT become
absorbed by the animal and concentrated in their bodies. Acid rain forms
from the exhausts of automobiles which emit sulfur and nitrogen oxides.
These combine with water in the air to form sulfuric and nitric acids.
The growing population and modern conveniences greatly
contribute to the problems of pollution. Government regulations,
community efforts, and changes in habits of industries and individuals are
necessary to solve pollution problems.
EVOLUTION
Evolution means change over time.
The theory of evolution begins with the origin of life on the early
Earth. The conditions of early Earth were very different - there was no
oxygen, the continents were connected, and constant lightning and
volcanoes provided a great deal of energy.
A scientist named Oparin hypothesized that is was these conditions
that made it possible for life to begin. The idea of life coming from
nonliving material is called spontaneous generation, or abiogenesis. Miller
and Urey tested Oparin's "primordial soup" hypothesis and were able to
generate amino acids (the building blocks of protein) from simple gases
such as carbon dioxide and methane.
With the conditions of the Earth today, scientists do not believe life
can come from non-living matter. The idea that life can only come from life
is called biogenesis. This idea was supported by the experiments of Redi
(who showed the flies laying eggs are responsible for maggots, not rotting
meat) and Pasteur (who showed that microorganisms present in the air are
responsible for new microorganisms, not the air itself.)
The evolution of the cell would have led to the first organism
(living thing) on Earth. The first cells to evolve would have most likely
been prokaryotic cells (a cell with no nucleus and no complex organelles).
The evolution of the cell is described in the "heterotroph hypothesis" which
states that the first cell would have also been heterotrophic and anaerobic.
The eventual evolution of a photosynthetic cell released oxygen into the
atmosphere and led to the formation of the ozone layer.
As prokaryotic cells evolved, some may have begun to live
symbiotically within each other. The "endosymbiotic theory" describes the
evolution of the eukaryotic cell (a cell with a nucleus and complex
organelles) as the result of a aerobic prokaryotic cell (which became the
mitochondia) and a photosynthetic cell (which became the chloroplast)
living together inside a larger cell (which developed a nucleus for
protection).
Evidence for evolution includes:
J. Fossil record
2. Comparative biochemistry (comparing DNA; proteins, or cell processes)
3. Comparative anatomy (examining body structures for similarities)
4. Comparative embryology (examining developing embryos for
similarities).
In general, the more characteristics two species share, the more
related those two species are in terms of evolution. The evolutionary history
of a species, which is usually theorized based on these types of evidence, is
called that specie's phylogeny.
For example, the arm of a human and the flipper of a whale have a
similar bone arrangement. We call these structures homologous structures
because of that similarity. Both animals are mammals, and share similar
embryological development. Both animals have similar proteins the cells
use. Thus, the phylogeny of humans and whales may be more similar than
the phylogeny of humans and insects.
These types of evidence have led scientists to make several
conclusions about the way evolution works:
I. Evolution tends to move from simple organisms/structures to complex
organisms/structures. For example, the first organisms were the simplest
cells (prokaryotes) and the last organisms were complex, multicellular
organisms (mammals).
2. Evolution may happen gradually over a long period of time (gradualism)
or it may happen quickly, followed by a long period of no change
(punctuated equilibrium). Often, sudden changes such as climate shifts (ice
age) or a natural disaster (Earth hit by a meteorite) seem to be followed by
punctuated equilibrium.
3. The development of new species (speciation) may be caused by natural
selection. Natural selection occurs when the following happens:
A. Variation within a population's gene pool. Variation means
differences, and may be due to mutations or natural genetic
differences. All of the genes in a population are called the gene
pool.
B. Overproduction of offspring. Evolution can only act on a
population, not on an individual, because the genes of a
population may change but the genes of an individual will not.
C. Competition for resources
D. Survival or greater reproduction of the best adapted. An
adaptation is any heritable trait (it may be physical, physiological
or behavioral) that allows an organism to better survive or
reproduce.
.
For example, different tooth lengths in a rat population arc caused
by differences in the genes of the rats. If many rats are born within a
population, competition for food may occur. If the rats with longer teeth are
better able to eat the food source, these rats will be healthier and have more
offspring. The offspring will inherit the long tooth gene, and he better
eaters. Eventually the rat population will have more long-tooth rats than it
did before.
Darwin is credited with the theory of natural selection. He
developed this theory after noticing similarities among different species of
finches and tortoises in the Galapagos Islands. Darwin theorized that all of
the finch species evolved from a common ancestor. As the birds spread to
nearby islands, different environmental conditions caused different traits to
be more successful. Over a long period of time, the birds changed enough to
become different species. This process of evolution from a common
ancestor is called adaptive radiation.