Biology Semester 2 Review: Units 4-10

Comprehensive review flashcards covering gene expression, inheritance, evolution, speciation, anatomy, and ecology based on Biology Semester 2 lecture notes.

What is the primary function of cell division in eukaryotes?

It supports growth, tissue repair, and asexual reproduction.

List the steps of prokaryotic binary fission.

1. Chromosome folds inside. 2. Chromosome is duplicated. 3. Copy moves to the opposite end. 4. Cell elongates and copies separate. 5. Plasma membrane pinches inward and cell wall is added. 6. Parent cell splits into two daughter cells.

How do eukaryotic chromosomes change before division?

Chromosomes duplicate to form sister chromatids, which are identical strands of DNA attached at the centromere.

What are the three main stages of the eukaryotic cell cycle?

Interphase, Mitosis, and Cytokinesis.

What occurs during the S phase of interphase?

DNA is replicated; each chromosome goes from being single to being composed of two sister chromatids.

Define the function of the $G1$ checkpoint.

It checks overall cell size, nutrients, DNA condition, and external signals; if the signal is not received, the cell may enter a nondividing state called $G0$.

What are the four stages of mitosis in order?

Prophase, Metaphase, Anaphase, and Telophase.

How does cytokinesis differ between animal and plant cells?

Animal cells form a cleavage furrow to pinch the cell in two, while plant cells form a cell plate from vesicles that pushes outward.

What was discovered by Griffith in his study of Streptococcus pneumoniae?

The "transforming principle," where harmless Rough (R) strain bacteria acquired traits from dead Smooth (S) strain bacteria to become virulent.

How did Hershey and Chase confirm DNA is the genetic material?

They used radioactive $^{32}\text{P}$ to label DNA and $^{35}\text{S}$ to label proteins in T2 bacteriophages; only the $^{32}\text{P}$ was found inside the bacterial pellet.

State Chargaff’s rules.

The amount of Adenine (A) equals Thymine (T) and the amount of Guanine (G) equals Cytosine (C).

What is semiconservative replication?

A model where the two parental DNA strands separate, each serving as a template for a new strand, resulting in two daughter molecules with one old and one new strand.

What are the reactants of transcription in eukaryotes?

A gene (DNA template strand), free RNA nucleotides, and the enzyme RNA polymerase.

Describe the three steps of RNA processing in eukaryotes.

1. Addition of a 5’ cap (modified G nucleotides). 2. Addition of a poly-A tail. 3. RNA splicing where introns are removed and exons are joined.

What are the roles of the A and P sites in a ribosome?

The A site is where a new charged tRNA enters; the P site holds the tRNA that is attached to the growing polypeptide chain.

Define a nonsense mutation.

A base-pair substitution that changes an amino acid codon into a stop codon, resulting in a shortened, likely nonfunctional polypeptide.

What is a frameshift mutation?

An insertion or deletion of nucleotides not in multiples of three, which shifts the reading frame and alters every amino acid after the mutation.

What is the diploid ($2n$) number for a typical human somatic cell?

$46$ chromosomes, arranged as $23$ pairs of homologous chromosomes.

How does meiosis maintain a constant chromosome number across generations?

It reduces the chromosome number from diploid ($2n$) to haploid ($n$) so that fertilization restores the diploid state in the zygote.

When does crossing over occur in meiosis?

During Prophase 1.

Explain the Law of Independent Assortment.

Homologous chromosomes line up randomly during Metaphase 1, creating unique combinations of maternal and paternal chromosomes in gametes.

What phenotypic ratio is expected from a Mendelian dihybrid cross (e.g., $RrYy \times RrYy$)?

$9:3:3:1$.

What is the Rule of Multiplication in genetics?

It is used to determine the probability of two independent events occurring together (e.g., $1/2 \times 1/2 = 1/4$).

Define incomplete dominance and provide an example.

Neither allele is completely dominant, and the heterozygote shows an intermediate phenotype; e.g., red and white snapdragons producing pink flowers.

Why are X-linked recessive disorders more common in males?

Males have only one X chromosome ($XY$); if that X carries the recessive allele, it is expressed because there is no second X to mask it.

Name the three domains of life.

Bacteria, Archaea, and Eukarya.

List the five conditions required for Hardy-Weinberg equilibrium.

1. Very large population. 2. No gene flow. 3. No mutations. 4. Random mating. 5. No natural selection.

Compare the bottleneck effect and the founder effect.

The bottleneck effect is a sudden reduction in population size due to a disaster, while the founder effect occurs when a few individuals colonize a new habitat; both cause random shifts in allele frequencies.

Distinguish between stabilizing, directional, and disruptive selection.

Stabilizing favors intermediate phenotypes; Directional favors one phenotypic extreme; Disruptive favors both extremes over the intermediate.

What is the difference between prezygotic and postzygotic barriers?

Prezygotic barriers prevent mating or fertilization (e.g., temporal or habitat isolation); postzygotic barriers prevent hybrid zygotes from developing into fertile adults (e.g., reduced hybrid fertility).

Define sympatric speciation.

The emergence of a new species within the same geographic area as the parent population, often through polyploidy in plants or sexual selection in animals.

What is the hierarchy of taxonomic categories from most specific to broadest?

Species, Genus, Family, Order, Class, Phylum, Kingdom, Domain.

Compare homologous and analogous structures.

Homologous structures are structurally similar due to common ancestry; analogous structures function similarly but evolved independently due to convergent evolution.

What are the four levels of structural hierarchy in an animal?

Cells, Tissues, Organs, and Organ Systems.

How does the hypothalamus regulate body temperature through negative feedback?

If temperature rises, it triggers sweating and blood vessel dilation; if it drops, it triggers shivering and vessel constriction to return to the $37^\text{o}C$ set point.

What happens to air pressure in the lungs during inhalation?

The thoracic cavity volume increases, causing alveolar pressure to drop below atmospheric pressure, drawing air into the lungs.

Trace the pathway of oxygen-poor blood through the heart.

Superior/inferior vena cava → right atrium → right ventricle → pulmonary arteries → lungs.

Identify the primary functions of the excretory and endocrine systems.

The excretory system eliminates urea waste; the endocrine system secretes hormones to regulate growth and metabolism.

Explain the difference between exponential and logistic growth.

Exponential growth occurs with unlimited resources (J-shaped curve); logistic growth includes limiting factors and levels off at the carrying capacity ($K$) (S-shaped curve).

Define a keystone species.

A species whose impact on its community is disproportionately large compared to its abundance, holding the community structure together.

Why is only about $10\%$ of energy transferred between trophic levels?

Most energy is lost as heat, waste, or used for the organism's own metabolism, creating an energy pyramid with fewer consumers than producers.

What is the purpose of the $G2$ checkpoint?

It checks for DNA damage, ensures all DNA is replicated correctly, and assesses cell size before mitosis begins.

What are sister chromatids?

Identical copies of a single chromosome that are connected by a centromere, formed during DNA replication in the S phase.

What is the outcome of mitosis?

It results in two genetically identical daughter cells, each with the same number of chromosomes as the original cell.

Define epigenetics.

The study of heritable changes in gene expression that do not involve changes to the underlying DNA sequence.

What is a mutation?

A change in the DNA sequence that can lead to changes in the structure and function of proteins.

What is the role of the centromere?

It is the region of a chromosome where the two sister chromatids are joined and where the spindle fibers attach during cell division.

What are exons and introns?

Exons are the coding regions of a gene that are expressed, while introns are non-coding regions that are removed during RNA processing.

Define genetic recombination.

The process by which genetic material is physically mixed during sexual reproduction, leading to variation in offspring.

What role do histones play in DNA packaging?

Histones are proteins that help package DNA into a compact, dense shape by forming nucleosomes, allowing for efficient storage in the nucleus.

What is an allele?

A variant form of a gene that can produce different phenotypes for a particular trait.

What are plasmids?

Small circular DNA molecules found in bacteria that can replicate independently of chromosomal DNA, often used in genetic engineering.

What is a diploid organism?

An organism that contains two complete sets of chromosomes, one from each parent.

What is an organism's phenotype?

The observable physical and physiological traits of an organism, resulting from the interaction of its genotype and environment.

What is the purpose of messenger RNA (mRNA)?

It serves as a template for protein synthesis, carrying genetic information from DNA to ribosomes where proteins are made.

Define sexual reproduction.

A process that involves the combination of genetic material from two parents, resulting in genetically diverse offspring.

What are the stages of the eukaryotic cell cycle?

G1 phase, S phase, G2 phase, M phase (mitosis and cytokinesis).

Explain the significance of the $G1$ checkpoint.

It ensures that the cell is large enough and has adequate nutrients and undamaged DNA before proceeding to the S phase.

What happens during telophase in mitosis?

The chromosomes decondense back into chromatin, nuclear envelopes re-form around each set of chromosomes, and the cell prepares to divide.

Describe the difference between mitosis and meiosis.

Mitosis results in two identical daughter cells; meiosis produces four genetically diverse haploid gametes.

What is the function of DNA ligase?

It joins Okazaki fragments on the lagging strand during DNA replication, sealing any nicks in the sugar-phosphate backbone.

What are mutations and why are they important?

Mutations are changes in the DNA sequence that can introduce genetic diversity, affecting traits and possibly leading to evolution or diseases.

Define the term 'transcription'.

The process by which the DNA sequence of a gene is copied into messenger RNA (mRNA).

What is the role of RNA polymerase in transcription?

RNA polymerase is the enzyme that synthesizes RNA from the DNA template during transcription.

What are the phases of transcription?

1. Initiation: RNA polymerase binds to the promoter and unwinds the DNA. 2. Elongation: RNA strand is synthesized. 3. Termination: RNA polymerase detaches from DNA when a termination signal is encountered.

What is the function of the prometaphase stage in mitosis?

The nuclear envelope breaks down, and spindle fibers attach to kinetochores on the chromosomes, preparing them for alignment.

What is alternation of generations in plant life cycles?

A reproductive cycle in which a multicellular diploid stage (sporophyte) alternates with a multicellular haploid stage (gametophyte).

What is a chromosome?

A structure composed of DNA and proteins that carries genetic information; each human somatic cell typically contains 46 chromosomes.

Define homologous recombination.

A process occurring during meiosis where DNA is exchanged between homologous chromosomes, increasing genetic diversity in gametes.

What is the role of the spindle apparatus?

It separates duplicated chromosomes during nuclear division and ensures accurate distribution to daughter cells.

Explain what happens during the S phase of interphase.

DNA is duplicated, resulting in the formation of sister chromatids for each chromosome.

What is the importance of the centromere during cell division?

It ensures that sister chromatids are pulled apart and distributed to daughter cells during mitosis and meiosis.

Describe the process of cytokinesis.

The physical division of the cytoplasm, resulting in two separate daughter cells at the end of cell division.