Characteristics and Organization of Life

Characteristics of Life

Living organisms share a set of fundamental characteristics that distinguish them from non-living matter.

• Order: Living things exhibit complex but ordered organization.

• Regulation: Organisms maintain stable internal conditions (homeostasis).

• Growth and Development: Organisms grow and develop according to specific instructions coded in their DNA.

• Energy Processing: Living things acquire and use energy for metabolism and work.

• Response to Environment: Organisms respond to environmental stimuli.

• Reproduction: Organisms reproduce their own kind.

• Evolutionary Adaptation: Populations evolve over generations through adaptations.

Example: A plant growing toward sunlight demonstrates response to environment and growth.

Hierarchical Organization of Life

Biological systems are organized in a hierarchy from smallest to largest:

• Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biosphere

Example: A heart (organ) is made of tissues, which are made of cells, which contain organelles, etc.

Scientific Reasoning and Experimental Design

Inductive vs. Deductive Reasoning

Scientific inquiry uses two main types of logical reasoning:

• Inductive Reasoning: Deriving general principles from specific observations. Example: Observing that all swans seen are white and concluding all swans are white.

• Deductive Reasoning: Making specific predictions based on general principles. Example: If all mammals have hair, and a whale is a mammal, then whales have hair.

Hypotheses and Testing

A hypothesis is a testable explanation for an observation or question. A good hypothesis is:

• Testable and falsifiable

• Specific and based on prior knowledge

Testing a Hypothesis: Design an experiment with controls and variables to test predictions derived from the hypothesis.

Experimental Design Components

• Control: The standard for comparison in an experiment.

• Independent Variable: The factor that is changed or manipulated.

• Dependent Variable: The factor that is measured or observed.

Example: Testing plant growth with different fertilizers: fertilizer type (independent), plant height (dependent), plants with no fertilizer (control).

Theory in Science

A theory is a well-substantiated explanation of some aspect of the natural world, based on a body of evidence and repeatedly confirmed through observation and experimentation.

Example: The theory of evolution by natural selection.

Unifying Themes and Atomic Structure

Unifying Themes in Biology

Major themes connect all areas of biology:

• Evolution

• Structure and Function

• Information Flow, Exchange, and Storage

• Pathways and Transformations of Energy and Matter

• Systems Interactions

Example: DNA as the molecule of heredity (information flow).

Structure of an Atom

An atom consists of three main subatomic particles:

• Protons: Positively charged, found in the nucleus

• Neutrons: No charge, found in the nucleus

• Electrons: Negatively charged, orbit the nucleus

Example: A carbon atom has 6 protons, 6 neutrons, and 6 electrons.

Atomic Properties and the Periodic Table

Atomic Number, Atomic Mass, Isotopes, Ions, and Elements

• Atomic Number (Z): Number of protons in the nucleus; defines the element.

• Atomic Mass (A): Total number of protons and neutrons.

• Isotopes: Atoms of the same element with different numbers of neutrons.

• Ions: Atoms or molecules with a net electric charge due to loss or gain of electrons.

• Elements: Pure substances consisting of only one type of atom.

Example: Carbon-12 and Carbon-14 are isotopes of carbon.

Periodic Table and Element Information

The periodic table organizes elements by increasing atomic number and groups elements with similar properties.

• Element Symbol: One- or two-letter abbreviation (e.g., H for hydrogen).

• Atomic Number: Number of protons.

• Atomic Mass: Average mass of all isotopes.

Example: Sodium (Na) has atomic number 11.

Chemical Bonds and Water

Biologically Important Atoms

Key elements in biology include:

• Hydrogen (H)

• Carbon (C)

• Nitrogen (N)

• Oxygen (O)

• Phosphorus (P)

• Sulfur (S)

Types of Chemical Bonds

• Ionic Bonds: Transfer of electrons from one atom to another, forming charged ions.

• Covalent Bonds: Sharing of electron pairs between atoms.

• Hydrogen Bonds: Weak attractions between a hydrogen atom and an electronegative atom (e.g., oxygen or nitrogen).

Example: NaCl (table salt) is held together by ionic bonds; H2O (water) by covalent bonds.

Polar vs. Non-Polar Covalent Bonds

• Polar Covalent Bonds: Electrons are shared unequally, resulting in partial charges (e.g., H2O).

• Non-Polar Covalent Bonds: Electrons are shared equally (e.g., O2).

Example: The bond in H2O is polar; in O2 it is non-polar.

Importance of Hydrogen Bonds and Water Properties

Hydrogen bonds are crucial for the unique properties of water, which are vital for life:

• Cohesion: Water molecules stick together, aiding transport in plants.

• Adhesion: Water molecules stick to other substances.

• High Specific Heat: Water resists temperature changes.

• Solvent Properties: Water dissolves many substances, facilitating chemical reactions.

Example: Water's high heat capacity helps regulate Earth's climate.

Summary Table: Types of Chemical Bonds