General Biology Study Guide: Evolution, Macromolecules, Cell Structure, and Division

1. Evolution and the Themes of Biology

Environmental Adaptations and Evolution

Evolution describes how organisms change over time through adaptation to their environments. These adaptations are driven by natural selection and other evolutionary forces.

• Adaptation: A trait that increases an organism's fitness in a particular environment.

• Levels of Biological Organization: Includes molecules, cells, tissues, organs, organisms, populations, communities, and ecosystems.

• Hypothesis Testing: Scientific hypotheses are tested through observation and experimentation. For example, the long necks of giraffes have been hypothesized to result from competition for food or sexual selection.

Example: The food competition hypothesis for giraffe necks suggests that longer necks evolved to allow giraffes to reach higher foliage.

2. Water, Carbon, and Macromolecules

Chemical Bonds and Water Properties

Chemical bonds are the forces that hold atoms together in molecules. Water's unique properties are due to its molecular structure and hydrogen bonding.

• Covalent Bonds: Atoms share electrons; can be polar (unequal sharing) or nonpolar (equal sharing).

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

• Water's Properties: High specific heat, cohesion, adhesion, surface tension, and ability to dissolve many substances.

Example: Water's high surface tension allows small insects to walk on its surface.

Macromolecules: Structure and Function

Macromolecules are large, complex molecules essential for life, including carbohydrates, proteins, nucleic acids, and lipids.

• Carbohydrates: Provide energy and structural support.

• Proteins: Made of amino acids; perform a wide range of functions including catalysis, transport, and structure.

• Nucleic Acids: DNA and RNA store and transmit genetic information.

• Lipids: Hydrophobic molecules important for membranes and energy storage.

Example: DNA's structure is a double helix with antiparallel strands held together by hydrogen bonds between complementary bases.

Table: Types of Chemical Bonds

Bond Type	Definition	Example
Covalent (Nonpolar)	Equal sharing of electrons	O2 molecule
Covalent (Polar)	Unequal sharing of electrons	H2O molecule
Hydrogen Bond	Attraction between H and electronegative atom	Between water molecules
Ionic Bond	Transfer of electrons	NaCl (table salt)

6. Inside the Cell

Cell Structure and Function

Cells are the basic units of life, with structures specialized for various functions. Eukaryotic cells have membrane-bound organelles, while prokaryotic cells do not.

• Plasma Membrane: Controls entry and exit of substances.

• Nucleus: Contains genetic material (DNA).

• Endomembrane System: Includes the ER, Golgi apparatus, lysosomes, and vesicles.

• Ribosomes: Sites of protein synthesis.

Example: The presence of a nucleus distinguishes eukaryotic cells from prokaryotic cells.

12. Mitosis

Cell Cycle and Division

Mitosis is the process by which eukaryotic cells divide to produce two genetically identical daughter cells. The cell cycle includes interphase (G1, S, G2) and mitotic phase (mitosis and cytokinesis).

• Stages of Mitosis: Prophase, Metaphase, Anaphase, Telophase.

• Cytokinesis: Division of the cytoplasm.

• Chromosome Number: DNA replication in S phase doubles the DNA content, but chromosome number remains the same until cell division.

Example: Cancer cells often have uncontrolled mitosis, leading to tumor growth.

13. Meiosis

Genetic Variation and Gamete Formation

Meiosis is a specialized cell division that produces gametes (sperm and egg) with half the chromosome number of the parent cell, increasing genetic diversity.

• Homologous Chromosomes: Pair and separate during meiosis I.

• Crossing Over: Exchange of genetic material between homologous chromosomes.

• Independent Assortment: Random distribution of chromosomes to gametes.

Example: Meiosis produces four genetically unique haploid cells from one diploid cell.

14. Mendel and Inheritance

Patterns of Genetic Inheritance

Mendelian genetics explains how traits are inherited through discrete units called genes. Dominant and recessive alleles determine trait expression.

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable traits.

• Monohybrid Cross: Inheritance of a single trait.

• Pedigree Analysis: Tracing inheritance patterns in families.

• Codominance and Incomplete Dominance: Variations in allele interactions.

Example: The ABO blood group system demonstrates codominance, where both A and B alleles are expressed.

Sample Multiple Choice and Short Answer Questions

Selected Questions and Explanations

• Phosphodiester Bond: The bond formed between the hydroxyl group of one nucleotide and the phosphate group of another, creating the sugar-phosphate backbone of DNA. $\text{Phosphodiester bond:} \quad \text{C-O-P-O-C}$

• Electronegativity and Bond Type: Atoms with similar electronegativity form nonpolar covalent bonds; differing electronegativity leads to polar covalent bonds.

• Dehydration Reaction: Polypeptides are synthesized by joining amino acids via dehydration reactions, releasing water. $\text{Amino acid}_1 + \text{Amino acid}_2 \rightarrow \text{Dipeptide} + H_2O$

• Hydrogen Bonds in DNA: Hydrogen bonds hold complementary bases together in the DNA double helix, but the backbone is formed by phosphodiester bonds.

• Properties of Water: Water's high specific heat, cohesion, adhesion, and ability to dissolve substances are due to hydrogen bonding.

• Acidification Effects: Increased CO2 in oceans lowers pH, affecting carbonate availability and harming shell-building organisms.

• Protein Structure: Primary structure is the amino acid sequence; secondary structure includes alpha helices and beta sheets stabilized by hydrogen bonds.

• Cell Cycle Phases: G1 (growth), S (DNA synthesis), G2 (preparation for mitosis), M (mitosis and cytokinesis).

• Meiosis vs. Mitosis: Meiosis produces haploid gametes; mitosis produces diploid somatic cells.

• Genetic Variation: Crossing over and independent assortment during meiosis increase genetic diversity.

Table: Comparison of Mitosis and Meiosis

Feature	Mitosis	Meiosis
Number of Divisions	1	2
Number of Daughter Cells	2	4
Genetic Identity	Identical	Unique
Chromosome Number	Diploid	Haploid
Function	Growth, repair	Sexual reproduction

Additional info:

• Some context and explanations have been expanded for clarity and completeness.

• Scientific terms and processes are described in detail to ensure self-contained study notes.