Biology Test Practice Test: Video 1 Answers (25 Questions) Flashcards

Which cytoskeletal element is primarily responsible for maintaining cell shape in animal cells?

Answer: Microfilaments (actin)

Actin microfilaments form a network beneath the plasma membrane that supports cell shape and enables cell movement.

During meiosis, homologous chromosomes exchange genetic material through which process?

Answer: Crossing over (recombination)

Crossing over occurs during prophase I when non-sister chromatids of homologous chromosomes exchange segments at points called chiasmata.

What is a nucleosome?

Answer: DNA wrapped around a histone octamer

A nucleosome consists of approximately 147 base pairs of DNA wrapped around a core of eight histone proteins, forming the basic unit of chromatin.

What is the primary role of cyclin-CDK complexes in the cell cycle?

Answer: Regulating progression through cell cycle checkpoints

Cyclin-dependent kinase (CDK) complexes phosphorylate target proteins to drive the cell through key transitions such as G1/S and G2/M checkpoints.

Which process allows cells to engulf large particles or other cells by forming membrane vesicles?

Answer: Phagocytosis

Phagocytosis is a form of endocytosis in which the cell membrane engulfs large particles like bacteria, forming a phagosome.

Which term describes the process by which a species' population becomes so small that it loses genetic diversity and faces increased extinction risk?

Answer: Genetic bottleneck

A genetic bottleneck occurs when a population is drastically reduced, causing loss of allelic diversity and increasing vulnerability to extinction.

Which IUCN criterion classifies a species as Critically Endangered based on population size?

Answer: Fewer than 250 mature individuals

Under IUCN criteria, a population of fewer than 250 mature individuals qualifies a species for Critically Endangered status.

Which human activity is considered the single largest driver of tropical deforestation globally?

Answer: Agricultural conversion for livestock and crops

Agricultural conversion—especially for cattle ranching, palm oil, and soy—accounts for the majority of tropical forest loss worldwide.

Which treaty provides the primary international framework for regulating trade in endangered wild plants and animals?

Answer: CITES

CITES (Convention on International Trade in Endangered Species) regulates and in some cases bans international trade in threatened species.

Which principle explains why a larger reserve will typically support more species than a smaller one?

Answer: Island biogeography theory

Island biogeography theory predicts that species richness increases with area because larger areas support larger populations and more diverse habitats.

What term describes plants that complete their life cycle in two growing seasons?

Answer: Biennial

Biennials such as carrots and foxglove grow vegetatively in their first year and flower, set seed, and die in their second year.

Which plant hormone is primarily responsible for fruit ripening?

Answer: Ethylene

Ethylene is a gaseous hormone that triggers fruit ripening, leaf abscission, and other senescence processes.

Which of the following best describes apical dominance in plants?

Answer: The apical bud suppresses the growth of lateral buds

Apical dominance occurs when the apical meristem produces auxin that inhibits the growth of lateral (axillary) buds below it.

Which plant tissue type provides structural support and is composed of dead cells at maturity?

Answer: Sclerenchyma

Sclerenchyma cells have thick, lignified secondary cell walls and are dead at functional maturity, providing rigid mechanical support.

What is the role of the Casparian strip in plant roots?

Answer: Forces water through the symplast into the vascular tissue

The Casparian strip is a waxy band in endodermal cell walls that blocks the apoplastic pathway, forcing water and solutes through the symplast into the stele.

A scientist observes that a population of beetles has become resistant to an insecticide over 20 generations. This is best explained by:

Answer: Natural selection acting on pre-existing genetic variation

Pre-existing genetic variation for resistance allows individuals carrying resistance alleles to survive and reproduce, shifting allele frequencies via natural selection.

Which of the following is NOT a condition required for Hardy-Weinberg equilibrium?

Answer: High mutation rate

Hardy-Weinberg equilibrium requires no mutation, no selection, random mating, no gene flow, and a large population; a high mutation rate violates the no-mutation assumption.

Which process allows bacteria to rapidly acquire new genes, including antibiotic resistance genes, from other bacteria?

Answer: Horizontal gene transfer

Horizontal gene transfer, including conjugation, transformation, and transduction, allows bacteria to acquire genes from other organisms outside of vertical inheritance.

What is the central dogma of molecular biology?

Answer: DNA → RNA → Protein

The central dogma describes the flow of genetic information: DNA is transcribed into RNA, which is then translated into protein.

What is a frameshift mutation?

Answer: An insertion or deletion that alters the reading frame

Frameshift mutations result from insertions or deletions of nucleotides that are not multiples of three, disrupting the reading frame.