Biology Flashcards

Which type of epithelium lines the inner surface of blood vessels?

Answer: Simple squamous epithelium

Simple squamous epithelium (endothelium) lines blood vessels, allowing efficient diffusion and forming a smooth surface that reduces friction.

In the lac operon of E. coli, what role does the repressor protein play in the absence of lactose?

Answer: It blocks the operator preventing transcription

In the absence of lactose (the inducer), the repressor binds the operator sequence and prevents RNA polymerase from transcribing the structural genes.

Which phase of mitosis is characterized by chromosomes aligning at the cell's equatorial plate?

Answer: Metaphase

During metaphase, chromosomes align at the metaphase plate (cell equator) with spindle fibers attached to each sister chromatid's kinetochore.

Which hormone is produced by the posterior pituitary and triggers uterine contractions during labor?

Answer: Oxytocin

Oxytocin, released from the posterior pituitary, stimulates uterine smooth muscle contractions during labor via a positive feedback mechanism.

Which ecological relationship benefits one organism while neither harming nor helping the other?

Answer: Commensalism

Commensalism is a relationship where one organism benefits (+) while the other is unaffected (0), such as barnacles living on whale skin.

In the cross between two heterozygous individuals (Aa × Aa), what is the expected phenotypic ratio assuming complete dominance?

Answer: 3:1

With complete dominance, both AA and Aa individuals express the dominant phenotype, giving a 3 dominant : 1 recessive phenotypic ratio.

Which component of the cell membrane is responsible for its fluid mosaic structure?

Answer: Cholesterol and phospholipids

Phospholipid bilayers provide the fluid matrix while cholesterol modulates membrane fluidity, together creating the dynamic fluid mosaic structure.