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AP Biology

Unit 2, Topics 2.1–2.10

Shared by Ashton · Oct 20, 2026 · 4 plays

Organelles and cell size through membrane transport, water potential and endosymbiosis, plus a round on the osmosis and potato water-potential lab.

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73 questions across 11 sections. After every answer you’ll see why each choice is right or wrong, not just the one you picked.

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Sample questions

Open a question to see the answer choices and the correct answer.

Ribosomes are found in every known prokaryotic and eukaryotic cell. Which conclusion does this best support?
  1. A. All living cells descend from an ancestor that made proteins on ribosomes ✓
  2. B. Prokaryotes gained their ribosomes from eukaryotes by gene transfer
  3. C. Ribosomes must be membrane-bound, since all cells have membranes
  4. D. Ribosomes entered all cells through an ancient endosymbiosis event

Correct answer: A. Ribosomes (rRNA + protein, no membrane) are universal, and their shared structure and function is evidence of common ancestry. A feature present in every lineage most likely was present in the last common ancestor of all cells.

A mutation disrupts the nucleolus so it can no longer assemble ribosomal subunits. Which effect would appear first?
  1. A. DNA replication stops because the chromosomes can't be copied
  2. B. The nuclear envelope breaks down because it loses structural support
  3. C. Protein synthesis slows as the cell's ribosome supply runs down ✓
  4. D. Lipid synthesis stops because phospholipids are made in the nucleolus

Correct answer: C. The nucleolus is where rRNA is made and combined with proteins into ribosomal subunits, which then exit through nuclear pores. Without new ribosomes, existing ones wear out and translation capacity falls.

Researchers feed pancreatic cells radioactive amino acids for 3 minutes, then switch to unlabeled ones. In what order would the label appear?
  1. A. Free ribosomes, then nucleus, then Golgi, then outside the cell
  2. B. Golgi, then rough ER, then lysosomes, then outside the cell
  3. C. Smooth ER, then rough ER, then mitochondria, then outside the cell
  4. D. Rough ER, then Golgi, then secretory vesicles, then outside the cell ✓

Correct answer: D. This is the classic pulse-chase result. Secreted proteins are made by ribosomes on the rough ER, modified and sorted in the Golgi, packaged into vesicles, and released by exocytosis, so the label moves along that path over time.

A scientist attaches an ER signal sequence to the gene for a normally cytosolic enzyme. Where will the new protein most likely end up?
  1. A. In the nucleus, since signal sequences send proteins through nuclear pores
  2. B. In the cytosol, since the enzyme's original function decides its location
  3. C. Inside the ER, moving on through the Golgi and possibly out of the cell ✓
  4. D. In the mitochondrion, since all signal-tagged proteins go there for folding

Correct answer: C. A signal sequence directs the ribosome to dock on the rough ER while translating, so the protein is threaded into the ER lumen and enters the endomembrane system. Location follows the targeting signal, not the protein's original job.

Cells in the root of a carrot plant never receive light. Which organelle do these cells rely on to make most of their ATP?
  1. A. The central vacuole, which breaks down sugar stored in the cell sap
  2. B. Chloroplasts, which make ATP from stored sugar when light is absent
  3. C. Mitochondria, which carry out cellular respiration in plant cells too ✓
  4. D. Nothing, because plant cells make ATP only by photosynthesis

Correct answer: C. Plant cells have mitochondria as well as (in green tissue) chloroplasts. Root cells lack functional chloroplasts and depend on sugar shipped from the leaves, which their mitochondria break down to make ATP.