OCR A Level Biology: Foundations in Biology — Practice Questions

These are original questions written for Marlbridge, in the style and at the standard of the examination. They are not reproduced past-paper questions — examination boards hold copyright in their own papers. Use these alongside the official past papers available free from your board.

Related: Foundations in Biology study guide | Foundations in Biology revision notes

Note: these written questions assess Module 2 content only. Practical competence itself is assessed separately, through the non-exam Practical Endorsement across the twelve Practical Activity Groups (PAGs), which does not contribute marks to the three written papers.

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1. Define magnification and resolution, and explain why an electron microscope reveals detail invisible under a light microscope. [3]

2. State two ways in which a prokaryotic cell differs from a eukaryotic cell. [2]

3. A mitochondrion appears 4.5 cm wide in a photomicrograph taken at a magnification of 15,000×.

(a) Calculate the real width of the mitochondrion, giving your answer in micrometres. [3] (b) State one structural feature of a mitochondrion visible only with electron, not light, microscopy. [1]

4. For each organelle, state its function: (a) rough endoplasmic reticulum (b) Golgi apparatus (c) lysosome. [3]

5. Explain, in terms of hydrogen bonding, why water is an effective solvent for polar and ionic substances. [3]

6. Distinguish between a condensation reaction and a hydrolysis reaction, using the formation and breakdown of a polymer as your example. [4]

7. Describe the sequence of organelles involved in producing and secreting a protein. [3]

8. State the monomer of DNA and RNA, and explain one structural difference between the two nucleic acids. [2]

Answers

1. Magnification is how much bigger an image appears compared with the real object [1]; resolution is the ability to distinguish two close points as separate rather than as one blurred point [1]. An electron microscope reveals detail invisible under a light microscope because it achieves far higher resolution, not simply because it magnifies more [1].

2. Any two: a prokaryotic cell lacks a membrane-bound nucleus, whereas a eukaryotic cell has one [1]; a prokaryotic cell lacks membrane-bound organelles such as mitochondria, whereas a eukaryotic cell has them [1]; a prokaryotic cell is typically much smaller than a eukaryotic cell [1].

3. (a) Convert image size to consistent units: 4.5 cm = 45,000 μm [1]; rearranging magnification = image size ÷ object size gives object size = image size ÷ magnification [1]; object size = 45,000 ÷ 15,000 = 3 μm [1]. (b) Any one: the internal folded membrane (cristae), or the double membrane structure [1].

4. (a) Rough endoplasmic reticulum — processes and folds proteins synthesised by the ribosomes attached to its surface [1]. (b) Golgi apparatus — modifies, packages and sorts proteins (and lipids) for transport, often into secretory vesicles [1]. (c) Lysosome — contains digestive enzymes that break down waste material, old organelles or invading pathogens [1].

5. Water is a polar molecule, with a slightly negative oxygen end and slightly positive hydrogen ends [1], which allows it to form hydrogen bonds with other polar or charged particles [1]. This lets water molecules surround and separate the ions or polar molecules of a solute, drawing them into solution [1].

6. A condensation reaction joins two monomers together to form a polymer, releasing a molecule of water in the process [2]. A hydrolysis reaction breaks a polymer back down into its constituent monomers, using a molecule of water to do so [2] — the two reactions are the reverse of each other, with water released in one and consumed in the other.

7. Proteins are synthesised by ribosomes attached to the rough endoplasmic reticulum, which processes and folds them [1]; the proteins are then transported, often in vesicles, to the Golgi apparatus, which modifies and packages them [1]; the Golgi apparatus then buds off secretory vesicles that move to and fuse with the plasma membrane, releasing the protein outside the cell [1].

8. The monomer of both DNA and RNA is a nucleotide [1]. One structural difference: DNA is typically double-stranded, while RNA is typically single-stranded [1] (also accept: DNA contains deoxyribose sugar and the base thymine, while RNA contains ribose sugar and the base uracil in place of thymine).

A note on the magnification formula

Question 3 tests the version of the magnification formula that students most often find unfamiliar: rearranging to find object size, rather than calculating magnification itself. The formula magnification = image size ÷ object size can be rearranged for any one of its three variables, and exam questions deliberately vary which one is missing to test genuine algebraic fluency rather than memorised substitution. The step most commonly skipped, and the one most likely to cost marks, is converting the image size and object size to the same unit before dividing — a mismatch of even one order of magnitude (millimetres against micrometres, for instance) produces an answer that is a power of ten out, which is easy to miss if the final figure is not sanity-checked against a realistic cell or organelle size.

Where marks are usually lost

• Describing electron microscopes as revealing more detail because they “magnify more,” rather than because they achieve higher resolution.
• Failing to convert image size and object size to the same unit before applying the magnification formula.
• Naming an organelle without stating its function, when questions consistently ask for both together.
• Confusing the roles of the rough endoplasmic reticulum and the Golgi apparatus in the secretory pathway.
• Listing water’s properties as unconnected facts rather than explicitly linking them back to hydrogen bonding and polarity.

Approaching foundations in biology questions

Before attempting any magnification calculation, identify which of the three quantities — image size, object size, or magnification — is missing, and rearrange the formula for that variable before substituting numbers, converting both given measurements to the same unit as the very first step. For questions on organelles, always pair a named structure with its function in the same sentence, since OCR mark schemes typically award separate marks for each and a correct name alone earns only partial credit. When a question asks about biological molecules, look for an opportunity to trace the answer back to a more fundamental principle — hydrogen bonding for water’s properties, or the condensation/hydrolysis pair for how monomers and polymers interconvert — since this kind of explanatory depth is what distinguishes full-mark answers from ones that only state a fact without justifying it.