General Biology Study Guide: Energy, Photosynthesis, Cellular Respiration, Cell Division, and Genetics

Energy in Biological Systems

Potential and Kinetic Energy

Energy is fundamental to all biological processes. Organisms use energy to perform work, grow, and maintain homeostasis.

• Potential Energy: Stored energy due to position or structure (e.g., chemical bonds in glucose).

• Kinetic Energy: Energy of motion (e.g., movement of molecules).

• Energy Conversion: Biological systems convert energy from one form to another, such as during cellular respiration.

• Lowest Potential Energy: The state in which a system has the least stored energy, often after energy has been released.

ATP: The Energy Currency of the Cell

Adenosine triphosphate (ATP) is the primary molecule for storing and transferring energy in cells.

• ATP Structure: Composed of adenine, ribose, and three phosphate groups.

• ATP Hydrolysis: Releases energy when the terminal phosphate bond is broken.

• Equation:

$\text{ATP} + \text{H}_2\text{O} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

• Energy Use: Powers cellular processes such as muscle contraction, active transport, and biosynthesis.

Energy Transfer in Cells

Cells transfer energy through chemical reactions, often involving electron movement and changes in chemical bonds.

• Exergonic Reaction: Releases energy (e.g., cellular respiration).

• Endergonic Reaction: Requires energy input (e.g., photosynthesis).

Photosynthesis and Cellular Respiration

Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy.

• Producers: Organisms that perform photosynthesis (e.g., plants, algae).

• Consumers: Organisms that obtain energy by eating other organisms.

• Photosynthetic Equation:

$6\text{CO}_2 + 6\text{H}_2\text{O} + \text{light energy} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2$

• Chlorophyll: Pigment that absorbs light energy; reflects green light.

• Light Reactions: Occur in thylakoid membranes; convert light energy to chemical energy (ATP and NADPH).

• Calvin Cycle: Uses ATP and NADPH to fix carbon dioxide into glucose.

• Stomata: Pores in leaves for gas exchange.

• Water Uptake: Roots absorb water, which is transported to leaves.

Cellular Respiration

Cellular respiration is the process by which cells break down glucose to produce ATP.

• Equation:

$\text{C}_6\text{H}_{12}\text{O}_6 + 6\text{O}_2 \rightarrow 6\text{CO}_2 + 6\text{H}_2\text{O} + \text{ATP}$

• Stages: Glycolysis, Krebs Cycle (Citric Acid Cycle), Electron Transport Chain.

• Glycolysis: Occurs in cytoplasm; splits glucose into pyruvate.

• Krebs Cycle: Occurs in mitochondria; processes pyruvate, releases CO2, produces NADH and FADH2.

• Electron Transport Chain: Uses NADH and FADH2 to produce ATP; oxygen is the final electron acceptor.

• Products: ATP, CO2, H2O.

Comparison Table: Photosynthesis vs. Cellular Respiration

Feature	Photosynthesis	Cellular Respiration
Location	Chloroplasts	Mitochondria
Reactants	CO2, H2O, Light	Glucose, O2
Products	Glucose, O2	CO2, H2O, ATP
Energy Conversion	Light to Chemical	Chemical to Usable (ATP)

Cell Division: Mitosis and Meiosis

Mitosis

Mitosis is the process by which somatic (body) cells divide to produce two genetically identical daughter cells.

• Purpose: Growth, repair, and maintenance of tissues.

• Phases: Prophase, Metaphase, Anaphase, Telophase, Cytokinesis.

• Products: Two diploid cells (same chromosome number as parent).

• Chromosome Duplication: Occurs before mitosis during the S phase of the cell cycle.

Meiosis

Meiosis is the process by which gametes (sperm and egg cells) are produced, reducing the chromosome number by half.

• Purpose: Sexual reproduction; increases genetic diversity.

• Phases: Meiosis I and Meiosis II, each with Prophase, Metaphase, Anaphase, Telophase.

• Products: Four haploid cells (gametes).

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

• Independent Assortment: Random distribution of chromosomes to gametes.

Comparison Table: Mitosis vs. 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	Gamete Formation

Genetics: Chromosomes, Genes, and Inheritance

Chromosomes and Genes

Genetic information is organized into chromosomes, which are made of DNA and proteins.

• Chromosome: Structure containing DNA; humans have 46 chromosomes (23 pairs).

• Gene: Segment of DNA that codes for a specific protein.

• Karyotype: Visual representation of an individual's chromosomes.

• Allele: Different forms of a gene.

Inheritance Patterns

Inheritance follows predictable patterns described by Mendel's laws.

• Homozygous: Two identical alleles for a gene.

• Heterozygous: Two different alleles for a gene.

• Dominant Allele: Expressed when present.

• Recessive Allele: Expressed only when two copies are present.

• Genotype: Genetic makeup of an organism.

• Phenotype: Observable traits.

• Carrier: Individual who has one copy of a recessive allele but does not express the trait.

• Sex-linked Genes: Genes located on sex chromosomes (X or Y); X-linked disorders are more common in males.

Mendelian Laws

• Law of Segregation: Each organism carries two alleles for each trait, which separate during gamete formation.

• Law of Independent Assortment: Genes for different traits are inherited independently.

Genetic Crosses and Probability

Punnett squares are used to predict the outcome of genetic crosses.

• Monohybrid Cross: Cross involving one trait.

• Dihybrid Cross: Cross involving two traits.

• Incomplete Dominance: Heterozygote shows intermediate phenotype.

• Codominance: Both alleles are expressed equally.

Genetic Disorders

• Nondisjunction: Failure of chromosomes to separate properly during meiosis, leading to disorders such as Down syndrome.

• X-linked Disorders: Disorders caused by mutations on the X chromosome; males are more frequently affected.

Additional info:

• Some questions referenced the chemical formula for glucose: $\text{C}_6\text{H}_{12}\text{O}_6$.

• Questions about the cell cycle, gene location, and chromosome composition were included to reinforce understanding of cell division and genetics.