WHAT IS LIFE

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WHAT IS LIFE?
It is difficult to come up with a single
definition of life.

• Chapter 01

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• All living things exhibit five characteristics in
  combination.

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A. Characteristics of Life
1. Organization 2. Energy Use
Metabolism 3. Maintenance of Homeostasis 4. Reprod
uction, Growth Development 5. Irritability
Adaptation
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• A. Characteristics of Life
• 1. Organization
• chemical (atom -gt molecule -gt macromolecule)
• organelle
• cell
• tissue
• organ
• organ system
• multicellular organism

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All living things exhibit organization

• Chemical level - atoms combine to make
  molecules molecules
• combine to make macromolecules.
• Organelle (a membrane bound structure within a
  complex
• cell) level.
• Cellular level - smallest level of organization
  that exhibits all
• characteristics of life. This is the highest
  level of organization
• exhibited by some organisms (Ameba,
  Paramecium, Euglena,
• bacteria, algae).
• Tissue level - a collection of cells that
  perform a common function.
• Organ level - a collection of tissues that
  perform a common function.
• Organ system level - a collection of organs that
  perform a common
• function.
• Multicellular organism - a living individual
  composed of many
• organ systems.

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• Each level of biological organization exhibits
  emergent properties.

Emergent property - property not present at lower
levels.
Ex. Capillaries transport blood (property not
exhibited by individual endothelial cells).
Endothelial cells must aggregate in a specific
way for them to transport blood.
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• 2. Energy Use Metabolism
• Metabolism - biochemical reactions that acquire
  use energy.
• Why do organisms need energy?
• to combat entropy
• to build new structures
• to repair/break down old structures
• to reproduce
• How do organisms obtain energy?

Organisms take in energy and transform it (by
metabolism) to do many kinds of work Entropy
the natural tendency of matter to be
disorganized.
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Organisms obtain energy from
the nonliving environment (sunlight or chemicals)
these organisms are called producers or
autotrophs. by eating other organisms
- these organisms are called consumers or
heterotrophs. by eating dead organisms or
their products feces these organisms are
called decomposers.
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• 3. Maintenance of Homeostasis
• Homeostasis - the ability of an organism to
  maintain its internal environment despite
  conditions in the external environment.
• Ex. Human body temperature is 98.6ºF
• if body temperature rises, you sweat.
• if body temperature lowers, you shiver.

Inability to maintain homeostasis leads to
illness or death of the organism. Ex. High body
temperatures inactivate enzymes, so chemical
reactions vital for life cannot occur.
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• 4. Reproduction, Growth Development
• Asexual reproduction - involves a single parent
  progeny are genetically identical to the parent.
• Sexual reproduction - involves 2 parents progeny
  are genetically diverse.
• Is it essential for an individual to reproduce?

No, but it is essential if a population is to
survive for more than one generation.
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• 5. Irritability Adaptation
• Irritability - immediate response to a stimulus.

Irritability can be essential for survival (Venus
flytrap captures a meal).
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• Adaptation - an inherited behavior or
  characteristic that enables an organism to
  survive reproduce.

Adaptations develop over time.
Examples
Camouflage is an adaptation to acquire food or
escape predation. Picture of Adder snake. Leaf
curling is an adaptation to minimize wind damage.
Over time, adaptations are modified by natural
selection.
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• Natural Selection - the enhanced survival
  reproductive success of individuals whose
  inherited traits better adapt them to a
  particular environment.

Male bird of paradise - males that are most
attractive to females will contribute more
offspring to succeeding generations. Thus, they
come to make up more of the population over
time. As the population changes, evolution
occurs. Cactus - well adapted to its desert
environment. Stem is modified to store water,
while spines (modified leaves) protect it
against being eaten. Fewer than 1 of the
species that have ever existed on earth are alive
today.
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• B. Biodiversity The different types of organisms
  on earth.
• Life on earth is diverse, yet similar.
• Similarity of life - all are composed of cells
  have DNA as their genetic material. This
  suggests that all life evolved from a common
  ancestor.
• Taxonomists place organisms into groups based
  upon evolutionary relationships.
• Broadest, most inclusive group (taxon) is the
  domain.
• Domain ? Kingdom ? Phylum or Division ? Class ?
  Order ? Family ? Genus ? Species
• Genus species refer to the organisms binomial
  (name).

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• The Three Domains
• Bacteria - unicellular prokaryotes
• Archaea - unicellular prokaryotes
• Eukarya - eukaryotes
• Kingdom Protista
• Kingdom Plantae
• Kingdom Fungi
• Kingdom Animalia

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• Bacteria Archaea
• Prokaryotes lack nuclei membrane-bound
  organelles. Some bacteria archaea are
  autotrophic, while others are heterotrophic have
  distinctive cell walls. Bacteria Archaea
  differ from each other at the molecular level.
• Eukarya
• Eukaryotes possess nuclei membrane-bound
  organelles.
• Most are multicellular.
• Kingdom Protista - most are unicellular some
  have cell
• walls some are autotrophic, while others
  are heterotrophic.
• Kingdom Plantae - multicellular have cell walls
  of cellulose
• usually autotrophic have complex organ
  systems.
• Kingdom Fungi - most multicellular have cell
  walls of chitin
• are heterotrophic (by absorption) have
  tissues.
• Kingdom Animalia - multicellular no cell walls
  are heterotrophic
• (by ingestion) have complex organ systems.

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• Human classification scheme
• Domain Eukarya
• Kingdom Animalia
• Phylum Chordata
• Class Mammalia
• Order Primates
• Family Hominidae
• Genus species Homo sapiens

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• C. The Study of Life
• Scientists study life by using the scientific
  method.

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Scientific method A systematic approach to
interpreting observations involves observing,
questioning, reasoning, predicting, testing,
interpreting, concluding posing further
questions. Hypothesis A prediction based on
previous observations or knowledge. Experiment is
done to test hypothesis. It can disprove a
hypothesis but can never prove it. Well
designed experiments compare an experimental
group to a control group. Both groups are
treated identically with exception of a single
factor, or variable. Note a large sample size
helps ensure meaningful results. Interpretation
of data has pitfalls. Experimental evidence may
lead to multiple interpretations or
misinterpretations.
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• What is the difference between hypothesis, theory
  law?
• Hypothesis - an educated guess a tentative
  explanation of phenomena.
• Theory - a widely accepted explanation of natural
  phenomena has stood up to thorough continual
  testing.
• Law - a statement of what always occurs under
  certain conditions.

Theory - Einsteins theory of relativity
Darwins theory of evolution. Laws - Mendles
laws of independent assortment segretation.