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Biology: The Study of Life – Chapter 1 Study Notes

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Biology: The Study of Life

1.1 What Does It Mean to Say That Something is Alive?

Biologists define life by a set of five fundamental characteristics shared by all living organisms. Understanding these characteristics helps distinguish living things from non-living matter.

  • Cells: All organisms are composed of one or more membrane-bound cells, which are the basic units of life.

  • Replication: All organisms are capable of reproduction, ensuring the continuation of their species.

  • Information: Organisms process hereditary information encoded in genes (DNA) and respond to information from their environment.

  • Energy: All organisms acquire and use energy to maintain internal order and sustain life processes.

  • Evolution: Populations of organisms are continually evolving, leading to diversity and adaptation over time.

Example: A bacterium reproduces by cell division, uses nutrients for energy, responds to environmental changes, and evolves over generations.

Theory in Biology

A theory in science is a well-substantiated explanation for a broad set of observations, supported by a large body of evidence. This differs from the everyday use of "theory" as a mere guess.

  • Cell Theory: What are organisms made of? Where do they come from?

  • Theory of Evolution by Natural Selection: How are organisms related to one another?

  • Chromosome Theory of Inheritance: How is hereditary information transmitted from one generation to the next?

1.2 Life is Cellular and Replicates through Cell Division

Discovery of Cells

  • Robert Hooke (1665): Used a microscope (30x) to observe small compartments in cork, which he called "cells."

  • Anton van Leeuwenhoek: Improved the microscope (300x) and observed single-celled organisms, termed "animalcules."

These discoveries led to the cell theory:

  • All organisms are made up of cells.

  • All cells come from preexisting cells.

Cell Theory vs. Spontaneous Generation

  • Cell Theory: Cells arise only from preexisting cells by growth and division.

  • Spontaneous Generation: The (now disproven) belief that organisms could arise spontaneously under certain conditions.

Louis Pasteur's Experiment: Demonstrated that cells do not arise by spontaneous generation. Using swan-necked flasks, he showed that nutrient broth remained sterile unless exposed to preexisting cells from the air.

Cell Division and Lineage

  • Cells must replicate for life to exist.

  • All cells in a multicellular organism descend from a common ancestor cell.

  • Evidence suggests life arose from non-life via chemical evolution early in Earth's history.

1.3 Life Processes Information and Requires Energy

Chromosomal Theory of Inheritance

  • Proposed by Sutton and Boveri: Hereditary information is encoded in genes located on chromosomes.

  • Chromosomes are made of deoxyribonucleic acid (DNA).

  • Genes are segments of DNA that code for cell products.

Structure and Function of DNA

  • DNA is a double helix composed of four building blocks: Adenine (A), Thymine (T), Cytosine (C), and Guanine (G).

  • Base pairing: A pairs with T, C pairs with G.

  • This complementary pairing allows DNA to be copied accurately, preserving genetic information.

The Central Dogma of Molecular Biology

  • Describes the flow of information in cells:

  • RNA: Molecules that carry out specialized functions; messenger RNA (mRNA) is read to make proteins.

  • Proteins: Perform essential cellular tasks and form structural components.

Genetic Variation and Mutation

  • DNA is copied to pass genetic information to offspring.

  • Mutations (changes in DNA sequence) can alter proteins, leading to heritable variation and diversity of life.

Energy and Nutritional Needs

  • Chemical reactions in cells require energy.

  • Organisms need:

    • Chemical energy in the form of adenosine triphosphate (ATP).

    • Molecules for building DNA, RNA, proteins, etc.

  • How organisms acquire energy is central to the diversification of life.

Example: Plants and bacteria can produce sugar using sunlight (photosynthesis), use sugar to make ATP, or absorb molecules from the environment as food.

1.4 Life Evolves

Evolution and Population

  • Evolution: Change in the characteristics of a population over time; species are related and can change through time.

  • Population: Group of individuals of the same species living in the same area at the same time.

Natural Selection

  • Explains how evolution occurs.

  • Two conditions for natural selection:

    1. Individuals vary in heritable characteristics.

    2. Certain heritable traits help individuals reproduce more successfully in a given environment.

  • Natural selection acts on individuals, but evolutionary change occurs in populations.

  • Speciation occurs when populations diverge to form new species.

Fitness and Adaptation

  • Fitness: The ability of an individual to produce surviving offspring.

  • Adaptation: A trait that increases fitness in a particular environment.

Example: Finches with small, pointed beaks had higher fitness during periods when small, soft seeds were abundant, leading to an increase in this trait in the population.

1.5 The Tree of Life and Phylogeny

Tree of Life

  • The tree of life depicts evolutionary relationships among species, with a single ancestral species at its base.

  • Phylogeny: The actual genealogical relationships among all organisms.

Analyzing Genetic Variation

  • Biologists compare DNA and RNA sequences to determine evolutionary relationships.

  • Fewer sequence differences indicate a closer relationship.

Base Position #

1

2

3

4

5

6

7

8

Land plant DNA

A

T

A

T

C

G

A

G

Green algae DNA

A

T

A

T

G

G

A

G

Brown algae DNA

A

A

A

T

G

G

A

C

Example: Green algae is more closely related to land plants than to brown algae, based on DNA sequence similarity.

Major Groups of Life

  • Three major domains: Bacteria, Archaea, and Eukarya.

  • Eukaryotes have a nucleus; prokaryotes (Bacteria and Archaea) do not.

Taxonomy and Scientific Naming

  • Taxonomy: The effort to name and classify organisms.

  • Domain: The highest taxonomic level, including Bacteria, Archaea, and Eukarya.

  • Phylum: Major lineage within a domain.

  • Binomial Nomenclature: Each species is given a unique two-part scientific name (Genus species), e.g., Homo sapiens.

  • Genus names are capitalized; species names are not. Both are italicized.

1.6 Doing Biology: The Scientific Method

The Nature of Science

  • Science involves asking testable questions and collecting data to answer them.

  • Key steps:

    1. Formulate a hypothesis and make predictions.

    2. Design experiments or observational studies to test predictions.

    3. Use a null hypothesis to specify what should be observed if the hypothesis is incorrect.

Experimental Design

  • Include a control group to compare with the treatment group.

  • Keep experimental conditions constant except for the independent variable.

  • Use large sample sizes and repeat tests for reliability.

Example: Testing whether supplemental nitrogen is needed for corn plants:

  • Independent variable: Presence or absence of nitrogen in water.

  • Dependent variables: Leaf length, leaf number, and leaf yellowing.

  • Control group: Plants watered with distilled water only.

  • Treatment group: Plants watered with nitrogen-supplemented water.

Importance of Controls and Constants

  • Controls allow scientists to determine if the independent variable causes the observed effect.

  • Constants (e.g., light source, soil type) ensure that only the independent variable differs between groups.

Take-home lesson: Experimental controls are essential for interpreting results and drawing valid conclusions.

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