Transcript Invitation to Biology

Exploring Biology
Chapter 1
Overview
• Introduction to Biology
• Levels of Organization in Nature
• Cells as the Basis of Life
• Unity of Life
• Diversity & Classification of Organisms
• Evolution
What is Biology?
The study of life
Observation of living systems & organisms
Cause & effect relationships in nature:
Asks questions about underlying causes/reasons for
observations
(“Why”, “how”, etc.)
Saddleback caterpillar
Four-eyed butterfly fish
Unifying Concepts of Biology
Structure & function are interrelated
Structure dictates function
e.g. blood flows in one direction through heart
because heart has valves that prevent backflow
e.g. opposable thumb of humans allows grasping
Homeostasis
State of equilibrium or balance
Unifying Concepts of Biology continued
Emergent properties
“The whole is greater than the sum of its parts”
i.e. complex systems formed from comparatively
simple parts
Hierarchy of nature’s levels of organization
From simple (atoms) to complex (biosphere)
Levels of Organization in Nature
• Atom
– Smallest unit of nature’s
substances
• Molecule
– Combos of atoms
– “Molecules of life” made only
by living cells
Levels of Organization continued
• Cell
– Smallest unit of life
– Vary in shape, size, function
– Single-celled vs. multicellular
organisms
Levels of Organization continued
• Tissue
– Groups of similar cells with
common function
– 4 types: epithelial, muscle,
connective, nervous
• Organ
– 2 or more (usually 4) tissue
types performing specific
function
– Allow complex physiological
processes
Levels of Organization continued
• Organ System
– Organs working together
towards a common task
• Multicellular Organism
– All structural levels
working in unison
– “Individual”
Levels of Organization continued
• Population
– Groups of individuals of
same species in given
area
• Community
– All populations of all
species in given area
Levels of Organization continued
• Ecosystem
– Biotic & abiotic
components
• Biosphere
– Earth’s crust, waters,
& atmosphere
Cells
Structural & functional units of life
A cell can:
• Regulate its internal environment
• Obtain & use energy
• Respond to external environment
• Develop & maintain complex organization
• Divide to form new cells
All cells share the same generalized structure:
• Plasma membrane
• Region of DNA
• Cytoplasm
Several different types of cells will be
encountered by you while working on your
Microworlds project for lab:
Prokaryotic (bacteria)
Eukaryotic (protists, fungi, plants, animals)
Prokaryotic Cells
Small & simple
No membrane-bound compartments
No nucleus
DNA floats freely in the cytoplasm
e.g. bacteria
Eukaryotic Cells
Larger than prokaryotic cells
Membrane-bound compartments (organelles)
Nucleus contains DNA
e.g. plant & animal cells
Things to look for:
Bacterial Cells
Cell
wall
Colony
Cytoplasm
Bacterial cell
Coccus
Spirillium
Bacillus
Things to look for:
Plant (& Fungi) Cells
Nucleus
Cell wall
Cytoplasm
Chloroplasts
(plant cells
only)
Things to look for:
Animal Cells
Nucleus
Cytoplasm
Cell membrane
Note: NO cell walls in animal cells!
Overview of Life’s Unity
All living things:
Require energy inputs
Exhibit order
Sense & respond to change
Regulate themselves
Grow & develop
Reproduce
(1) Energy Flow & Nutrient Cycling
Cells get energy from environment & convert it
to usable forms
Ultimate source of energy = sun
Producers
Make own food from sun
Consumers
Can’t synthesize
own food
Eat producers &
other organisms
Primary to tertiary
levels
Decomposers/Detritivores
Break down dead
organisms & waste
products
Allow recycling of
nutrients
Energy Flow
Ecosystems gain & lose energy continuously
Enters system as light energy
Passes through food web
as chemical energy (food)
Leaves as heat energy
Nutrient Cycling
Carbon, nitrogen, etc.
cycle through
ecosystems
From air / soil / water to
plants, animals, &
decomposers, then back
to air / soil / water
(2) Responsiveness
Organisms sense & respond to external &
internal changes
stimulus
receptor
control centre
effector
Receptors: usually stimuli-specific
response
Homeostasis
= “unchanging”
Dynamic state of equilibrium
Internal conditions vary within narrow range
Types of Feedback
Negative Feedback: output shuts off or decreases
in intensity to return to “normal” range
Positive Feedback: output is enhanced or increased
to push value away from normal value
Homeostatic Imbalance
= disease
3 possible causes:
1. Receptor not responding to stimuli
2. Control centre not
analyzing/responding to information
correctly
3. Effector over- or under-reacting
(3) Growth & Reproduction
Development
= from first cell of individual to adult form
Growth
= increase in size of body part or organism
Reproduction
Cellular = body growth & repair
Organismal = production of whole new
organism
Determined by information located in DNA
Organism inherits DNA from parents
(4) Other Life Processes
Maintenance of Boundaries
(keeps internal & external environments separate)
Digestion
Breaking down of ingested food-stuffs into simpler
molecules
Extraction of nutrients from food-stuffs
Metabolism
Chemical reactions occurring within cells
Excretion
Removal of wastes from body
Diversity
Variation in traits
e.g. body form, functions of
body structures,
behaviour
From 7 to 100 million
species
(1.8 million named)
Only 0.1% of all species that
have ever existed!!!
Today’s Classification of Organisms
3 domains:
• Bacteria
• Archaea
• Eukarya
Domain Bacteria
Prokaryotic
– No membrane-bound organelles
or nucleus
Single-celled but can form
colonies
Most are heterotrophic
– Some are parasites and
pathogens (but only small %)
– Others are decomposers
Found everywhere
Domain Archaea
Prokaryotic
Similar to Bacteria but more closely-related to Eukarya
Tend to live in more extreme environments
e.g. around hydrothermal vents
Domain Eukarya
Eukaryotic
(membrane-bound organelles & nucleus)
Single-celled or multicellular
Kingdom Protista
Simplest eukaryotes
Very diverse
– Everything not in another
kingdom
– Currently being reclassified
Found everywhere
Includes algae, protozoa,
slime molds
Kingdom Fungi
Mostly multicellular
– Except yeast
Heterotrophic (= consumers)
Most are decomposers
Many involved in symbiotic
relationships
Includes mushrooms, mold,
Penicillium
Kingdom Plantae
Mostly multicellular
Photosynthetic
Autotrophic (= producers)
Diverse in morphology, life
cycle, habitat
Includes mosses, ferns,
conifers, flowering plants
Kingdom Animalia
All are multicellular
consumers
(= heterotrophic)
Most reproduce sexually
Most are capable of
movement
Most are invertebrates
35 known phyla
Taxonomic Classification of Organisms
Organization of information about diversity
A way to show relationships among species
Carolus Linnaeus (1707-1778)
Born Carl von Linnè
Swedish botanist
Derived the hierarchical
classification system still used
today
Linnaeus’ Taxonomic Classification
Kingdom (most inclusive)
Phylum
Class
Order
Family
Genus
Species (most exclusive)
Linnaeus’ Genus-Species Concept
Two-part Latin species names:
1st part: Genus
– 1 or more species with certain unique traits
2nd part: Species
– Within a genus, has 1 or more trait that none of
the other species do
e.g. Canis lupus (wolf), C. familiaris (dog)
Linnaeus’ Hierarchy:
Based on theory that Earth & all of its
organisms were created simultaneously in
present form
Catalogued diversity of life on earth
Grouped organisms based on certain
morphological characteristics
e.g. humans & wolves in class Mammalia
because both have backbone, hair,
homeothermy, etc.
An Evolutionary View of Diversity
Individuals of the same species share common
traits
Individuals within species differ in variety of ways
Variations happen via:
1. Random mutations (changes in DNA)
(happen spontaneously & regularly; can be
good, bad, or neutral)
2. Evolutionary pathways
Evolution
Allele:
– DNA sequence that codes for a gene
– Determines genotype for individual
Allele frequency:
– Proportion of a given allele in a population
Evolution:
– Changes in allele frequency over time via
random & non-random processes
Genetic Drift
Random change in allele frequency from one
generation to the next
Important evolutionary force when population
size drastically drops (disease, low food
supply, disaster, etc.)
= genetic bottleneck
Unpredictable combinations of alleles in
generations occurring after bottleneck
If population is small enough, can lead to
loss of all but one possible allele on any
gene locus
= “Fixed” allele
Beneficial alleles can be eliminated via
genetic drift
Example of genetic drift
• 2 individuals (2 alleles each) in a small population
– Each is Aa so proportion of A:a is 50:50
• Next generation, 2 more offspring
– One is AA, one is Aa so A:a is 75:25
• Next generation, 2 more offspring:
– One is AA, one is Aa so A:a is 75:25
• And so on, until:
– Both are AA so A:a is 100:0
• Allele fixation: good vs. bad allele?
• Can’t get a back unless immigration into population or
random mutation occurs
Founder Effect
Random change in allele frequency
Occurs when small population splinters off
from main population (e.g. colonizing a
new island)
Can also lead to fixed alleles and loss of
beneficial alleles
Natural Selection
Non-random change in allele frequency
Favours traits that increase survival and
reproduction
= “Survival of the fittest”
Charles Darwin (1809-1882)
English naturalist
1838: Theory of Natural Selection
1859: On the Origin of the
Species
“Evolution by common descent”
explains diversity in nature
Darwin’s Early Ideas
Studying to be a clergyman
Didn’t really question the young
age of the earth
Had been introduced to the idea of
evolution but didn’t embrace it
The Voyage of HMS Beagle (1831-1836)
Darwin on the trip:
Noted that the plants and animals of South America
were very distinct from those of Europe
Organisms from temperate regions of South
America were more similar to those from the
tropics of South America than to those from
temperate regions of Europe
Further, South American fossils more closely
resembled modern species from that continent
than those from Europe
The origin of the fauna of the Galapagos, 900 km
west of the South American coast, especially
puzzled Darwin
On further study after his voyage, Darwin noted
that while most of the animal species on the
Galapagos lived nowhere else, they resembled
species living on the South American mainland.
It seemed that the islands had been colonized by
plants & animals from the mainland that had
then diversified on the different islands
Large ground finch, beak
suited to large seeds
Warbler finch, beak
suited to insects
Small ground finch, beak
suited to small seeds
Vegetarian tree finch,
beak suited to leaves
Darwin’s Ideas After His Trip
Questioned the young age of
the earth
Couldn’t explain distribution of
species with creationism
Thought species that were
similar were related
Darwin’s “Origin of Species”
Took him from 1836-1844 to get main
ideas: didn’t present until 1858
Proposed a mechanism for evolution
Was pushed to publish by Alfred
Wallace’s development of the same
theory
Central to Darwin’s view of the evolution of life is
descent with modification
In descent with modification, all present day
organisms are related through descent from
unknown ancestors in the past
Descendents of these ancestors accumulated
diverse modifications or adaptations that fit them
to specific ways of life & habitats
Natural Selection: How Does It Work?
Each generation is slightly different from
preceding one
Over time, small differences add up to major
transformation
Based on 4 observations
Observation #1
All species have such great potential fertility
that their population size would increase
exponentially if all individuals that are born
reproduced successfully
Observation #2
Populations tend to remain stable in size,
except for seasonal fluctuations
Conclusion #1
Production of more individuals than the
environment can support leads to a struggle
for existence among the individuals of a
population, with only a fraction of the offspring
surviving each generation
Observation #3
Individuals of a population vary extensively in
their characteristics; no two individuals are
exactly alike
Conclusion #2
These differences determine which individuals
survive & reproduce most successfully
= natural selection
Observation #4
Much of this variation is heritable
Conclusion #3
Because fittest individuals have more offspring,
their traits are passed to a larger proportion of
individuals in the population
This unequal ability of individuals to survive &
reproduce will lead to a gradual change in a
population, with favorable characteristics
accumulating over the generations.
= evolution by natural selection
Darwin’s main ideas can be summarized in three
points:
Natural selection is differential success in reproduction
(unequal ability of individuals to survive & reproduce)
Natural selection occurs through an interaction between
the environment & the variability inherent among the
individual organisms making up a population
The product of natural selection is the adaptation of
populations of organisms to their environment
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Darwin’s views on the role of environmental
factors in the screening of heritable
variation was heavily influenced by
artificial selection
Humans have modified a variety of
domesticated plants & animals over many
generations by selecting individuals with the
desired traits as breeding stock
If artificial selection can achieve such major
changes in a relatively short time, natural
selection should be capable of major
modifications of species over hundreds or
thousands of generations
Darwin envisioned the diversity of life as
evolving by a gradual accumulation of minute
changes through the actions of natural
selection operating over vast spans of time
Modern Examples of Natural Selection
Pesticide resistance in insects
Changes in beak size/shape in
finches in the Galapagos
Industrial melanism in peppered
moths
Fig. 22.12
Copyright © 2002 Pearson Education, Inc., publishing as Benjamin Cummings
Darwin’s Theory of Common Ancestry
Evolution of organisms from common ancestors
Grouped organisms based on most recent common
ancestor
e.g. humans and wolves in class Mammalia because
both come from same common ancestor
Evolution explains the diversity of organisms
Organisms in different environments often
look different because they have different
adaptations for survival
When classifying organisms, must be able to
distinguish between similarities that result
from a common ancestor (i.e. divergent
evolution) and those that arise from
convergent evolution.
Convergent Evolution
Unrelated organisms in common environment
 develop similar adaptations for survival
Produces analogous structures
(same function, different internal anatomy)
e.g. insect wings and bird wings
Divergent Evolution (Common Ancestry)
Related organisms evolve in different habitats
 have different adaptations
Produces homologous structures
(same internal anatomy but different functions)
e.g. bird wing, whale flipper, human hand