Download The Living World

Lecture 1
Introduction to Biology
The Diversity of Life
 Biology is the study of living things
 Living things can be divided into six kingdoms
Archaea
Fungi
Protista
Bacteria
Plantae
Animalia
What is Life?

Biology is the study of life - but what does it mean to be
alive?
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Ludwig von Bertalanffy – life is a system where the whole is greater
than the sum of the parts
Modern physiology – life is an electron in search of a resting place
Living organisms and many non-living things share three
properties
1. Complexity
2. Movement
3. Response to stimulation
Properties of Life

All living organisms share five basic properties
1. Cellular Organization

All living organisms are composed of at least one cell
2. Metabolism

All living organisms use energy
3. Homeostasis

All living organisms maintain stable internal conditions
4. Growth and reproduction

All living organisms grow and reproduce
5. Heredity

All living organisms possess a genetic system that is based on
DNA (Deoxyribonucleic acid)
The Organization of Life
 Living organisms function and
interact with each other at
many levels
1.
 These levels are organized in
a hierarchy of increasing
complexity:
1. Cellular Level
2. Organismal Level
3. Population Level
2.
3.
Life is an Emergent Property
 Each higher level of organization contains novel properties
not present at the simpler level of organization
 Birth rate & death rate – populations NOT individuals
 Evolution – populations evolve biologically NOT individuals
 These properties are termed emergent properties
 They are a consequence of the structural organization that is the
hallmark of life
 They characterize many aspects of the living world
Five Themes That Unify Biology
1. Evolution

The gene frequencies change in a species over time
 Causes include:
 Genetic drift
 Natural & artificial selection
 Founder effects
2. The Flow of Energy
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All living organisms require energy
The sun is the source of energy for most ecosystems
Plants capture energy via photosynthesis
 They then act as an energy source for other organisms
3. Interaction

Interaction between organisms is critical for evolution
 Social behavior occurs when organisms of the same species live in direct contact
 Community dynamics occur when organisms of different species live in direct
contact (Competition, Predation, Symbiosis)
4. Structure Determines Function

Biological structures are well suited to their function
 This is true at every level of organization
5. Homeostasis

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All living organisms act to maintain a relatively stable internal environment
Maintaining homeostasis requires energy and a lot of signaling back-and-forth between
cells
How Scientists Think
 Inductive Reasoning
 Is used by scientists to develop
hypotheses about how the
world works
 Deductive Reasoning
 Uses accepted general principles
as a “guide” to explain specific
observations
Inference vs. Observation
 An observation is limited to a description of actions or
events without interpretation
 An inference is a conclusion we draw based on what we
observe
 Inference or observation?
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Example 1 (The cat is happy)
Example 2 (The cat is chewing on the plant leaves)
Example 3 (The cat is sleeping)
Example 4 (The cat is a female)
Theory and Certainty in Science
 A theory is a set of hypotheses that have been tested many
times and not rejected
 It indicates a high degree of certainty
 However, there is no absolute truth in science
 So the acceptance of a theory is always provisional
 Note:
 To the general public, the word theory is often used to mean what a
scientist would call a hypothesis, a lack of knowledge or a guess
 To scientists, a theory represents that of which they are most certain,
explanations supported by a wealth of evidence and experimental data
The Limitations of Science
 Science is limited to organisms and processes that can be
observed and measured
 Spiritual and religious phenomena are beyond the scope of science
 Most religious explanations do not allow formation of a realistic null
hypothesis
 There are also practical limits
 Science can provide options and understanding
 Science cannot be relied upon to solve all problems
 For example, what constitutes “acceptable risk” cannot be answered
by science!
Four Theories Unify Biology & This Class
1. The Gene Theory
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The information that determines what an organism is like is encoded in its
genes
Genes are located along DNA molecules
The entire set of DNA instructions that specifies a cell is termed its genome
2. The Cell Theory
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All living organisms are composed of cells
Cells are the basic units of life
All cells come from other cells
3. The Theory of Heredity
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Genes represent traits of an organism and are inherited as discrete units
Chromosomal theory of inheritance: Genes are physically located on
chromosomes
4. The Theory of Evolution
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All living organisms are related to one another in a common tree of life
Diversity of the living world is the result of natural selection