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Biology Flashcards

7 cards from real MCAT practice questions. Tap to flip, then mark Knew It or Still Learning — missed cards come back until you master them.

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  1. Which of the following best explains why facilitated diffusion does not require ATP?

    Answer: Molecules move down their concentration gradient

    Facilitated diffusion is passive; channel and carrier proteins simply provide a pathway for molecules to move spontaneously down their electrochemical gradient.

  2. During the light-dependent reactions of photosynthesis, which molecule directly donates electrons to Photosystem II?

    Answer: Water

    Water is oxidized by the oxygen-evolving complex associated with PSII, providing electrons to replace those excited by light energy and releasing O2 as a byproduct.

  3. A frameshift mutation caused by a single nucleotide insertion would have the most severe effect if it occurred at which location?

    Answer: Near the 5' end of the coding sequence

    A frameshift near the 5' end alters the reading frame for nearly the entire protein, causing the most extensive change in amino acid sequence.

  4. Which of the following hormones acts via a G-protein coupled receptor to increase intracellular cAMP?

    Answer: Epinephrine

    Epinephrine binds β-adrenergic receptors (GPCRs) that activate adenylyl cyclase through Gs proteins, increasing intracellular cAMP levels.

  5. In an experiment, researchers block the sodium-potassium ATPase in a neuron. Which immediate effect would be observed?

    Answer: Gradual depolarization of the resting membrane potential

    Without Na+/K+-ATPase, Na+ accumulates inside the cell while K+ decreases, gradually reducing the resting membrane potential toward zero (depolarization).

  6. Which type of immunity involves the transfer of pre-formed antibodies from one individual to another?

    Answer: Passive immunity

    Passive immunity involves receiving pre-formed antibodies (e.g., maternal IgG across placenta or immune serum injection) without the recipient mounting an immune response.

  7. Which statement correctly describes the function of telomerase?

    Answer: It adds repetitive DNA sequences to chromosome ends

    Telomerase is a reverse transcriptase that uses its internal RNA template to add TTAGGG repeat sequences to the 3' ends of chromosomes, counteracting shortening.