Honors Biology: Semester 1 Cumulative Study Guide

Homeostasis

Definition and Importance

• Homeostasis is the maintenance of a stable internal environment within an organism, despite changes in external conditions.

• It is essential for the survival of living organisms, allowing them to function optimally.

• Examples include regulation of body temperature, blood glucose levels, and water balance.

Feedback Mechanisms

• Negative feedback loops counteract changes, bringing the system back to a set point (e.g., body temperature regulation).

• Positive feedback loops amplify changes (e.g., blood clotting).

• Feedback mechanisms involve sensors, control centers, and effectors.

Multicellularity and Specialization

• Multicellular organisms consist of specialized cells organized into tissues, organs, and systems.

• Division of labor allows for complex functions and efficient regulation of homeostasis.

The Cell Cycle & Cancer

Phases of the Cell Cycle

• The cell cycle consists of Interphase (G1, S, G2) and Mitosis (M phase).

• During Interphase, the cell grows, replicates DNA, and prepares for division.

• Mitosis is the process of nuclear division, followed by Cytokinesis (division of the cytoplasm).

DNA Replication

• DNA replication is semiconservative, meaning each new DNA molecule consists of one old and one new strand.

• Key enzymes: DNA polymerase, helicase, ligase.

• Replication involves leading and lagging strands, Okazaki fragments, and the formation of replication forks.

• Example DNA sequence: GACCTCGTAGC

Cancer and Cell Regulation

• Cancer results from uncontrolled cell division due to mutations in genes regulating the cell cycle (e.g., proto-oncogenes, tumor suppressor genes).

• Apoptosis (programmed cell death) and contact inhibition are mechanisms that prevent abnormal cell growth.

Reproduction & Development

Types of Reproduction

• Asexual reproduction produces genetically identical offspring (e.g., binary fission, budding).

• Sexual reproduction involves the fusion of gametes, resulting in genetic variation.

Developmental Processes

• Fertilization forms a zygote, which undergoes cleavage, gastrulation, and organogenesis.

• Model organisms (e.g., planaria) are used to study differentiation and development.

Protein Synthesis & Mendelian Genetics

Central Dogma of Molecular Biology

• Genetic information flows from DNA → RNA → Protein.

• Transcription: DNA is used as a template to synthesize mRNA.

• Translation: mRNA is decoded by ribosomes to assemble amino acids into proteins.

Types of RNA

• mRNA (messenger RNA): carries genetic code from DNA to ribosomes.

• tRNA (transfer RNA): brings amino acids to ribosomes during translation.

• rRNA (ribosomal RNA): structural component of ribosomes.

Genetic Code and Mutations

• The genetic code is read in triplets (codons), each coding for a specific amino acid.

• Mutations can be point mutations, insertions, deletions, or frameshifts, affecting protein function.

Mendelian Genetics

• Genotype: genetic makeup; Phenotype: observable traits.

• Dominant and recessive alleles determine trait expression.

• Homozygous: two identical alleles; Heterozygous: two different alleles.

• Punnett squares are used to predict genetic crosses.

Evolution

Mechanisms of Evolution

• Natural selection: differential survival and reproduction of individuals with advantageous traits.

• Genetic drift: random changes in allele frequencies, especially in small populations.

• Gene flow: movement of alleles between populations.

• Mutation: source of genetic variation.

• Non-random mating: affects genotype frequencies.

Evidence for Evolution

• Fossil record, comparative anatomy (homologous structures), molecular evidence, and observed evolutionary changes support the theory of evolution.

Population Genetics

• Hardy-Weinberg equilibrium describes a non-evolving population: $p^2 + 2pq + q^2 = 1$ and $p + q = 1$

• Allele frequencies can be calculated to study evolution in populations.

Adaptation and Fitness

• Adaptation: inherited trait that increases an organism's chance of survival and reproduction.

• Fitness: measure of reproductive success.

Sample Table: Types of Selection

Type of Selection	Description	Example
Stabilizing	Favors intermediate phenotypes	Human birth weight
Directional	Favors one extreme phenotype	Antibiotic resistance in bacteria
Disruptive	Favors both extreme phenotypes	Beak size in finches