General Biology: Core Concepts and Applications Study Guide

Characteristics of Living Things

Defining Life and Viruses

Biologists use several criteria to define living organisms, including reproduction, metabolism, and locomotion. Viruses challenge these definitions because they share some, but not all, characteristics of life.

• Reproduction: Both viruses and living organisms can reproduce, but viruses require a host cell.

• Metabolism: Living organisms carry out metabolism; viruses do not.

• Locomotion: Some living organisms move; viruses do not exhibit true locomotion.

• Key Point: Not all characteristics are shared among all living things (e.g., photosynthesis is unique to certain organisms).

• Example: Plants perform photosynthesis, but animals do not.

Levels of Biological Organization

Molecular Level in Biology

Biological hierarchy ranges from atoms to molecules, cells, tissues, organs, and organisms. The molecular level focuses on the interactions and ratios of biomolecules, such as DNA bases.

• Chargaff's Rule: In DNA, the amount of adenine equals thymine, and guanine equals cytosine.

• Key Point: This rule is best studied at the molecular level.

• Example: $[A] = [T]$ and $[G] = [C]$ in double-stranded DNA.

Evolution and Natural Selection

Survival and Adaptation

Natural selection is the process by which organisms better adapted to their environment tend to survive and reproduce more successfully.

• Adaptation: Traits that increase an organism's fitness in its environment.

• Key Point: Organisms more adapted to their environment are more likely to survive and reproduce.

• Example: Peppered moths in polluted environments.

Common Ancestry and Evolutionary Relationships

Phylogenetic Relationships

All living organisms share common ancestors, but some pairs are more distantly related than others.

• Common Ancestor: The most recent organism from which all organisms in a group are directly descended.

• Key Point: Whales and sharks do not share a recent common ancestor; whales are mammals, sharks are fish.

• Example: Humans and apes share a common ancestor.

Scientific Method and Experimental Design

Controlled Experiments

Controlled experiments are designed to test the effect of one variable while keeping all other variables constant.

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

• Dependent Variable: The factor that is measured.

• Control Variable: Factors kept constant.

• Example: Testing plant growth with different fertilizers, keeping light and water constant.

Atoms, Elements, and Chemical Bonds

Noble Gases and Halogens

Noble gases have full valence electron shells, making them stable and unreactive. Halogens are highly reactive due to their need for one more electron to complete their shell.

• Noble Gases: Stable, low reactivity.

• Halogens: Highly reactive, seek electrons.

• Key Point: Halogens are more reactive than noble gases.

Radioactive Isotopes in Biology

Radioactive isotopes are used in biological science for diagnosis, treatment, and research.

• Imaging: Diagnosing diseases (e.g., PET scans).

• Treatment: Treating thyroid disorders with radioactive iodine.

• Labeling: Studying genetic processes by labeling DNA.

Chemical Bonding

Atoms form chemical bonds based on their electronegativity differences.

• Ionic Bonds: Formed between atoms with large electronegativity differences.

• Covalent Bonds: Formed when atoms share electrons.

• Key Point: The type of bond depends on electronegativity difference.

• Equation: $\Delta EN = |EN_1 - EN_2|$

Electronegativity and Bond Polarity

Non-polar covalent bonds form between atoms with similar electronegativities.

Elements	Electronegativity
Sodium	0.9
Cesium	0.8
Hydrogen	2
Fluorine	4
Oxygen	3.5
Chlorine	3

• Example: Chlorine and Chlorine form a non-polar covalent bond ($\Delta EN = 0$).

Covalent and Non-Covalent Interactions

Covalent bonds involve sharing electrons; hydrogen bonds are non-covalent and involve attraction between polar molecules.

• Peptide, Disulfide, Glycosidic Bonds: Covalent.

• Hydrogen Bond: Non-covalent.

Ionic Bond Formation

Ionic bonds form when one atom donates an electron to another, typically between metals and nonmetals.

• Example: Sodium (Na) donates an electron to Chlorine (Cl) to form NaCl.

Hydrogen Bond Formation

Hydrogen bonds form between a hydrogen atom and an atom with high electronegativity (e.g., oxygen, nitrogen).

• Key Point: High electronegativity is required for hydrogen bond formation.

Extremophiles and Water Properties

Halophiles

Halophiles are extremophilic microorganisms that thrive in environments with high salt concentrations.

• Example: Halobacterium species in salt lakes.

Water Properties

Water exhibits unique properties due to hydrogen bonding, including surface tension, adhesion, and density differences.

• Surface Tension: Causes water droplets to form on leaves.

• Density: Ice floats on water because it is less dense.

• Equation: $\text{Density} = \frac{\text{Mass}}{\text{Volume}}$

Hydration Shells

When ionic compounds dissolve in water, ions are surrounded by hydration shells formed by water molecules.

• Example: Na+ and Cl- ions in NaCl solution.

Acids, Bases, and pH Regulation

Strong Acids and Bases

Strong acids and bases dissociate completely in water, affecting pH and chemical reactions.

• Equation: $\text{HA} \rightarrow \text{H}^+ + \text{A}^-$ (complete dissociation)

pH Regulation in the Human Body

The human body maintains specific pH levels in different organs to prevent infection and support physiological functions.

• Example: Slightly acidic vaginal pH prevents growth of harmful yeast and bacteria.

Organic Molecules and Functional Groups

Definition of Organic Molecules

Organic molecules contain carbon and hydrogen atoms covalently bonded to other atoms.

• Key Point: Organic molecules are the basis of life.

Functional Groups

Attachment of functional groups to carbon backbones determines the properties of organic molecules.

• Hydroxyl Group: Attachment forms alcohols.

• Example: Ethanol ($\text{CH}_3\text{CH}_2\text{OH}$) is an alcohol.

Biomolecules: Carbohydrates and Proteins

Carbohydrases

Carbohydrases are enzymes that break down carbohydrates.

• Key Point: Carbohydrases belong to the carbohydrate class of biomolecules.

Starch vs. Chitin

Starch and chitin are polysaccharides with different structures and functions.

• Starch: Storage polysaccharide of alpha glucose; contains $\alpha(1 \rightarrow 4)$ glycosidic bonds.

• Chitin: Structural polysaccharide; polymer of N-acetylglucosamine; contains $\beta(1 \rightarrow 4)$ linkages.

Protein Structure Hierarchy

Levels of Protein Structure

Proteins have four levels of structure: primary, secondary, tertiary, and quaternary.

Level	Description
Primary	Amino acid sequence
Secondary	Alpha helices and beta-pleated sheets
Tertiary	3-Dimensional shape
Quaternary	Multiple amino acid chains

• Example: Hemoglobin has quaternary structure with multiple polypeptide chains.