General Biology 1 Midterm Study Guide – Core Concepts and Practice

• Introduction to Biology

Characteristics of Life

Biology is the study of living organisms and their interactions with the environment. All living things share certain characteristics that distinguish them from non-living matter.

• Reproduction: The ability to produce new individuals, either sexually or asexually.

• Metabolism: The sum of all chemical reactions that occur within an organism to maintain life.

• Homeostasis: The regulation of internal conditions to maintain a stable state.

• Locomotion: Movement, though not all living things are motile.

• Common Ancestor: Most organisms share a common evolutionary origin, except for distantly related groups (e.g., whales and sharks do not share a recent common ancestor).

Example: Viruses can reproduce (with a host) but lack metabolism, so their status as living is debated.

Life's Organizational Hierarchy

Levels of Biological Organization

Biological systems are organized into a hierarchy from atoms to the biosphere.

• Atomic Level: Atoms are the basic units of matter.

• Molecular Level: Molecules are formed by atoms bonded together (e.g., DNA).

• Cellular Level: Cells are the basic units of life.

• Tissue Level: Groups of similar cells performing a function.

Example: Chargaff's rules about DNA base pairing are studied at the molecular level.

Evolution and Natural Selection

Natural Selection

Natural selection is a mechanism of evolution where organisms better adapted to their environment tend to survive and reproduce more successfully.

• Adaptation: Traits that enhance survival and reproduction become more common in a population.

• Specialization: Organisms that are highly specialized may be less adaptable to environmental changes.

Example: Organisms with traits suited to their environment are more likely to survive and reproduce.

Experimental Design

Variables in Experiments

Controlled experiments are designed to test the effect of a single variable while keeping all other factors constant.

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

• Dependent Variable: The factor that is measured.

• Control Variable: Factors kept constant to ensure a fair test.

Chemistry of Life

Atoms and Elements

Atoms are the smallest units of matter that retain the properties of an element. Elements differ in their number of protons, neutrons, and electrons.

• Noble Gases: Have full electron shells and are chemically inert.

• Halogens: Highly reactive, readily gain electrons to fill their outer shell.

Isotopes

Isotopes are atoms of the same element with different numbers of neutrons. Radioactive isotopes have important uses in biology.

• Diagnosing diseases (imaging techniques)

• Treating thyroid disorders

• Labeling DNA for genetic studies

Chemical Bonding

Atoms form chemical bonds to achieve stable electron configurations.

• Ionic Bonds: Formed when electrons are transferred from one atom to another.

• Covalent Bonds: Formed when atoms share electrons.

• Electronegativity: The ability of an atom to attract electrons in a bond. The type of bond depends on the difference in electronegativity.

Table: Electronegativity Values

Element	Electronegativity
Sodium	0.9
Cesium	0.8
Hydrogen	2.1
Fluorine	4.0
Oxygen	3.5
Chlorine	3.0

Example: Non-polar covalent bonds form between atoms with similar electronegativities (e.g., Cl-Cl).

Noncovalent and Covalent Interactions

• Covalent Bonds: Peptide, disulfide, and glycosidic bonds are covalent.

• Hydrogen Bonds: Noncovalent interactions important in water and biological molecules.

Ionic Bonding

• In ionic bonding, a metal atom donates an electron to a nonmetal atom, resulting in oppositely charged ions that attract each other.

Hydrogen Bonding

• Hydrogen bonds form when hydrogen is covalently bonded to a highly electronegative atom (e.g., O, N, F).

Water and Its Properties

Water as a Solvent

Water is a universal solvent due to its polarity and ability to form hydrogen bonds.

• Hydration Shells: Water molecules surround ions in solution, stabilizing them.

Properties of Water

• Cohesion: Water molecules stick to each other (surface tension).

• Adhesion: Water molecules stick to other substances.

• Density: Ice is less dense than liquid water, so it floats.

Acids, Bases, and pH

• Strong acids and bases: Dissociate completely in water.

• pH Regulation: The human body maintains pH to prevent harmful microbial growth and protect tissues.

Biomolecules

Organic Molecules

• Organic molecules contain carbon and hydrogen, often bonded to other elements.

Functional Groups

• Hydroxyl Group (-OH): When attached to a carbon backbone, forms an alcohol.

Carbohydrates

• Carbohydrates are biomolecules consisting of carbon, hydrogen, and oxygen.

• Starch is a storage polysaccharide; chitin is a structural polysaccharide.

• Starch: Polymer of alpha-glucose; Chitin: Polymer of N-acetylglucosamine.

Proteins

• Proteins are polymers of amino acids and have four levels of structure:

Level	Description
Primary	Amino acid sequence
Secondary	Alpha helices and beta sheets
Tertiary	3-dimensional folding
Quaternary	Multiple polypeptide chains

Example: Hemoglobin has quaternary structure as it consists of multiple polypeptide subunits.

Additional info: Where questions referenced diagrams or tables, the main academic context and logical structure were inferred and expanded for clarity.