General Biology Study Guide: Key Concepts and Review Topics

Introduction to the Science of Biology

What is Biology?

Biology is the scientific study of life and living organisms. It encompasses a wide range of topics, from the molecular mechanisms within cells to the interactions of organisms with their environment.

• Properties of Life: Organization, metabolism, homeostasis, growth, reproduction, response to stimuli, and evolution.

• Basic Components of Cells: All living things are composed of cells, which are the basic units of life.

Prokaryotic vs. Eukaryotic Cells

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles; examples include bacteria and archaea.

• Eukaryotic Cells: Have a nucleus and membrane-bound organelles; examples include plants, animals, fungi, and protists.

• Key Differences: Eukaryotic cells are generally larger and more complex than prokaryotic cells.

Reproduction

Asexual and Sexual Reproduction

Reproduction is the biological process by which new individual organisms are produced. It can occur via asexual or sexual means.

• Asexual Reproduction: Involves a single parent and produces offspring genetically identical to the parent. Examples include binary fission, budding, and vegetative propagation.

• Sexual Reproduction: Involves two parents and the fusion of gametes, resulting in genetically diverse offspring.

• Advantages of Asexual Reproduction: Rapid population increase, no need for a mate.

• Disadvantages of Asexual Reproduction: Lack of genetic diversity, which can make populations more susceptible to disease.

• Advantages of Sexual Reproduction: Genetic variation, which can enhance survival in changing environments.

• Disadvantages of Sexual Reproduction: Requires more energy and time, and finding a mate can be challenging.

Cell Division

Chromosomes and Cell Cycle

• Homologous Chromosomes: Pairs of chromosomes with the same genes but possibly different alleles, one inherited from each parent.

• Phases of Mitosis: Prophase, metaphase, anaphase, telophase, and cytokinesis.

• Phases of Meiosis: Meiosis I (separates homologous chromosomes) and Meiosis II (separates sister chromatids).

• Key Differences: Mitosis produces two identical diploid cells; meiosis produces four genetically unique haploid cells.

Genetic Variation in Meiosis

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

• Random Assortment: Homologous chromosomes are randomly distributed to daughter cells, increasing genetic diversity.

Genetics and Inheritance

Principle of Segregation

The principle of segregation states that during the formation of gametes, the two alleles for a gene separate so that each gamete receives only one allele.

Genotype and Phenotype

• Genotype: The genetic makeup of an organism (e.g., AA, Aa, aa).

• Phenotype: The observable traits of an organism (e.g., flower color).

• Homozygous: Having two identical alleles for a gene (e.g., AA or aa).

• Heterozygous: Having two different alleles for a gene (e.g., Aa).

• Dominant Allele: Expressed in the phenotype even if only one copy is present.

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

Punnett Squares

• Punnett squares are used to predict the genotypic and phenotypic ratios of offspring from genetic crosses.

• Monohybrid Cross: A cross involving one gene.

• Dihybrid Cross: A cross involving two genes.

Test Cross

• A test cross is used to determine if an individual with a dominant phenotype is homozygous or heterozygous by crossing it with a homozygous recessive individual.

Incomplete Dominance

• Definition: A form of inheritance in which the phenotype of a heterozygote is intermediate between the phenotypes of the two homozygotes.

• Example: In snapdragons, crossing a red-flowered plant (RR) with a white-flowered plant (WW) produces pink-flowered offspring (RW).

Darwin and Evolution

Evolution and Natural Selection

• Evolution: The change in the genetic composition of a population over time.

• Factors Influencing Darwin: Observations of variation in nature, fossil records, and the work of other scientists such as Lyell and Malthus.

• Natural Selection: The process by which individuals with advantageous traits survive and reproduce more successfully, leading to adaptation.

• Are Evolution and Natural Selection Synonymous? No; natural selection is a mechanism of evolution, but evolution can also occur through other processes such as genetic drift and gene flow.

• Requirements for Natural Selection: Variation, heritability, and differential reproductive success.

Darwin's Ideas and Evidence for Evolution

• Darwin proposed that natural selection leads to adaptation, where organisms become better suited to their environment over generations.

• Example: The evolution of beak shapes in Galápagos finches in response to available food sources.

• Lines of Evidence: Fossil records, comparative anatomy, embryology, molecular biology, and biogeography all support the theory of evolution.