biology chapter 1 EXAM 1

The Science of Biology

Biology unifies much of natural science.

• Living systems are the most complex chemical systems on Earth.

• Life is constrained by the properties of chemistry and physics.

• Science is becoming more interdisciplinary, combining multiple fields.

• Life defies simple definition.

Characteristics of Living Organisms

1. Cellular organization

2. Ordered complexity

3. Sensitivity to environment

4. Growth, development, and reproduction

5. Energy utilization

6. Homeostasis

7. Evolutionary adaptation

Hierarchical Organization of Living Systems

Living systems show hierarchical organization:

• Cellular level:

  • Atoms, molecules, organelles, cells

  • Cell is the basic unit of life (Cell Theory).

• Organismal level:

  • Tissues, organs, organ systems

Levels of Organization

Atoms > Molecules > Organelles > Cells > Tissues > Organs > Organ Systems > Organism.

Example:

• Atoms of element.

• Molecules: $H_2O$ (water).

• Organelles: Nucleus, Endoplasmic Reticulum, Mitochondria.

• Cells: Cytoplasm, Epithelia.

• Tissues: Muscles, Connective.

• Organs: Heart, Skin, Stomach.

• Organ systems: Cardiovascular, Nervous, Skeletal Muscle.

• Organism: Homosapien.

Additional Levels

• Populational level: Population, community.

• Ecosystem level.

• Biosphere:

  • Earth is an ecosystem we call the biosphere.

• Each level has emergent properties.

  • Result from interaction of components.

  • Cannot be deduced by looking at parts themselves.

  • “Life” is an emergent property.

The Nature of Science

Science aims to understand the natural world through observation and reasoning.

• Science begins with observations; therefore, much of science is purely descriptive.

  • Classification of all life on Earth.

  • Human genome sequencing.

Scientific Method

1. Observe

2. Ask a Question

3. Develop a Hypothesis

   • A statement based upon your knowledge.

   • Also known as an educated guess.

4. Experimental Design

   • To test the hypothesis.

5. Result

   • Prove or disprove the hypothesis.

6. Conclusion

Reasoning in Science

• Deductive reasoning:

  • Uses general principles to make specific predictions.

  • Example: Estimate of the circumference of the Earth.

• Inductive reasoning:

  • Uses specific observations to develop general conclusions.

Hypothesis-Driven Science

Scientists use a systematic approach to gain understanding of the natural world.

• A hypothesis is a possible explanation for an observation.

• A hypothesis:

  • Must be tested to determine its validity.

  • Is often tested in many different ways.

  • Allows for predictions to be made.

• Iterative:

  • Hypotheses can be changed and refined with new data.

Experiments

• Experiment:

  • Tests the hypothesis.

  • Must be carefully designed to test only one variable at a time.

  • Consists of a test experiment and a control experiment.

• Using Predictions:

  • Hypotheses should make predictions.

  • Predictions provide a way to test the validity of hypotheses.

  • Hypothesis must be rejected if the experiment produces results inconsistent with the predictions.

  • The more experimentally supported predictions a hypothesis makes, the more valid the hypothesis.

Experiment Example

• Question: What is the source of contamination that occurs in a flask of nutrient broth left exposed to the air?

• Germ Hypothesis: Preexisting microorganisms present in the air contaminate nutrient broth.

  • Prediction: Sterilized broth will remain sterile if microorganisms are prevented from entering flask.

• Spontaneous Generation Hypothesis: Living organisms will spontaneously generate from nonliving organic molecules in broth.

  • Prediction: Organisms will spontaneously generate from organic molecules in broth after sterilization.

• Test: Use swan-necked flasks to prevent entry of microorganisms. To ensure that broth can still support life, break swan- neck after sterilization.

• Result: No growth occurs in sterile swan-necked flasks. When the neck is broken, and the broth is exposed to air, growth occurs.

• Conclusion: Growth in broth is of preexisting microorganisms.

Philosophical Approaches to Science

• Reductionism:

  • To break a complex process down to its simpler parts.

• Systems biology:

  • Focus on emergent properties that can’t be understood by looking at simpler parts.

Models in Science

• Way to organize thought.

• Parts provided by reductionist approach.

• Model shows how parts fit together.

• Models can suggest experiments to test how components work together.

Scientific Theory

A body of interconnected concepts.

• Supported by much experimental evidence and scientific reasoning.

• Expresses ideas of which we are most certain.

• Compare to general meaning of theory:

  • Implies a lack of knowledge or an educated guess.

Basic Versus Applied Research

• Basic research is intended to extend the boundaries of what we know.

• Applied research:

  • Foundation provided by basic research.

  • May involve the manufacture of goods such as food additives or drugs.

Darwin and the Theory of Evolution

• Example of how a scientist develops a hypothesis and a theory gains acceptance.

• Charles Darwin served as naturalist on a mapping expedition around coastal South America.

• 30 years of observation and study before publishing On the Origin of Species by Means of Natural Selection.

Natural Selection

• Darwin was not the first to propose evolution.

  • Living things have changed over time.

• Darwin’s contribution was a mechanism.

  • Natural selection.

• Darwin Observed Differences in Related Organisms.

• On the Beagle, Darwin saw that characteristics of similar species varied from place to place.

• Galápagos Finches:

  • 14 related species differ only slightly.

  • “Descent with modification” or evolution.

• Darwin and Malthus.

• Darwin studied Thomas Malthus’s An Essay on the Principle of Population.

  • Populations of plants and animals increase geometrically.

  • Humans can only increase their food supply arithmetically.

  • Populations of species remain constant because death limits population numbers.

• Darwin saw that although every organism has the potential to produce more offspring, only a limited number survive and reproduce themselves.

Evidence for Natural Selection

Evidence supporting Darwin’s theory has only grown.

• Fossil record.

  • Transitional forms have been found at predicted positions in time.

• Earth’s age.

  • Physicists of Darwin’s time were wrong about the age of the Earth.

  • Earth is very old – 4.5 billion years old.

Additional Evidence:

• Mechanism for heredity.

  • Mendel’s laws of inheritance were unknown to Darwin.

• Comparative anatomy.

  • Vertebrate forelimbs all share the same basic array of bones.

  • Homologous – same evolutionary origin but now differ in structure and function.

  • Analogous – structures of different origin used for the same purpose (for example butterfly and bird wings).

• Molecular Evidence for Evolution.

  • Compare genomes or proteins of different organisms.

  • Phylogenetic trees – based on tracing origin of particular nucleotide changes to reconstruct an evolutionary history.

Core Concepts in Biology

• Life is subject to chemical and physical laws.

  • Biological systems follow known chemical properties, such as molecular bonding.

  • Properties of physics, such as thermodynamics, are also key determining factors of biological systems.

• Structure Determines Function.

  • Study structure to learn function.

  • Know a function – look for that structure in other organisms.

  • Examples.

    • Receptor on human cell for insulin known.

    • Find similar molecule in a worm.

    • Might conclude this molecule functions the same in the worm.

• Living Systems Transform Energy and Matter.

  • All life constantly requires energy.

  • Energy enters environments in one form, typically as solar energy, and is constantly transformed by organisms.

    • Photosynthetic organisms transform solar energy into chemical energy as matter (carbohydrates).

    • Other organisms, humans included, transform chemical energy into other forms of energy (for example kinetic) and matter (for example proteins).

• Living Systems Depend on Information Transactions.

  • Deoxyribonucleic acid (DNA).

    • Sequence of 4 nucleotides encode cell’s information.

  • Gene – discrete unit of information.

  • Genome – entire set of DNA instructions.

  • Continuity of life depends on faithful copying of DNA into daughter cells.

DNA

DNA consists of nucleotides:

• Phosphate + 5 Carbon Sugar (Deoxyribose) + Base

• Bases: Adenine, Thymine, Guanine, Cytosine

• Gene is a characteristic.

• Information in DNA used to direct synthesis of cellular components.

  • ‘ Control of gene expression leads to different cells/ tissue types.

• Cells process environmental information.

  • Glucose levels, presence of hormones.

• Cells in multicellular organisms must coordinate with each other.

Evolution

• Evolution Explains Unity and Diversity of Life.

  • All organisms today descended from a simple creature 3.5 BYA.

  • Some characteristics preserved – use of DNA.

  • Conservation reflects that they have a fundamental role.

• Biochemistry and Genetics.

  • Underlying unity of biochemistry and genetics argues for life from the same origin event.

• Diversity due to evolutionary change over time.

  • Homeodomain proteins, regulators of development in fungi, plants, and animals, are an example of a conserved feature of life that has diversified via evolution.

  • The sequence of homeodomain proteins can be more similar between groups (plants versus animals) than within, evidence of shared ancestry followed by evolutionary diversification.