OCR GCSE Biology: Scaling Up — 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: Scaling Up study guide | Scaling Up revision notes

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Section A

1. State whether each transport mechanism requires energy: diffusion, osmosis, active transport. [3]

2. State two places, other than embryonic animals, where stem cells are found. [2]

Section B

3. Explain why a large multicellular organism cannot rely on diffusion alone to supply its cells with oxygen, in terms of surface area to volume ratio. [4]

4. Calculate the surface area to volume ratio of a cube of side 5 cm, showing your working, and state whether this ratio would be larger or smaller for a cube of side 10 cm. [4]

5. A student states that blood flows slowly through capillaries because capillaries are narrow. Explain why this statement is incorrect, and give the correct biological explanation. [3]

6. Explain how a red blood cell’s structure is adapted to its function of transporting oxygen. [4]

7. Explain the difference between xylem and phloem in terms of the substances transported, direction of movement and cell type. [6]

8. Root hair cells absorb mineral ions from soil even when the concentration of minerals in the soil is lower than inside the cell. Explain, using the term active transport, how this is possible. [4]

9. A potometer is used to measure the rate of water uptake by a plant shoot. An air bubble moves 4 cm along the scale in 2 minutes. Calculate the rate of water uptake in cm per minute, and suggest one factor that could be changed to investigate its effect on this rate. [4]

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Answers

1. Diffusion — no energy needed [1]. Osmosis — no energy needed [1]. Active transport — requires energy [1].

2. Adult animals (e.g. bone marrow) [1]; meristems in plants [1].

3. As an organism gets larger, its volume increases faster than its surface area, so the surface area to volume ratio falls [1] [1]. A large organism’s surface area is too small, relative to its volume, for diffusion alone to supply oxygen to every cell quickly enough [1], which is why multicellular organisms need specialised exchange surfaces and transport systems instead [1].

4. Surface area = 6 × (5 × 5) = 150 cm² [1]. Volume = 5 × 5 × 5 = 125 cm³ [1]. Ratio = 150:125 = 1.2:1 [1]. For a 10 cm cube, the ratio would be smaller, since surface area to volume ratio decreases as size increases [1].

5. The statement is incorrect because individual capillary width is not the reason for slow flow [1]. The correct explanation is that the total cross-sectional area of all the capillaries in a tissue is far greater than that of the aorta, so the total blood flow slows down even though each individual capillary is narrow [1]; this slow flow is what allows time for diffusion of oxygen, nutrients and waste between the blood and the tissue [1].

6. A red blood cell has a biconcave shape, which gives it a large surface area relative to its volume, increasing the rate of oxygen diffusion in and out [1] [1]. It also has no nucleus, leaving more space inside the cell for haemoglobin, which binds and carries oxygen [1] [1].

7. Xylem transports water and dissolved mineral ions, one-way, upward from the roots, and is made of dead cells [1] [1] [1]. Phloem transports dissolved food (sugars), in both directions around the plant (translocation), and is made of living cells [1] [1] [1].

8. Because the soil mineral concentration is lower than inside the root hair cell, minerals cannot enter by diffusion, since diffusion only moves substances down a concentration gradient [1] [1]. Instead, the cell uses active transport, which moves substances against the concentration gradient and requires energy to do so [1] [1].

9. Rate = distance moved ÷ time = 4 ÷ 2 = 2 cm per minute [1] [1]. A suitable factor to investigate: any one of light intensity, air movement (wind speed), or temperature [1] [1].

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Where marks are usually lost

• Describing diffusion, osmosis and active transport interchangeably rather than identifying which one applies to a given scenario.
• Explaining slow capillary blood flow by capillary width alone, instead of total cross-sectional area.
• Confusing xylem and phloem on direction of movement, substance transported, or cell type.
• Treating “stem cell” as meaning only “embryonic stem cell,” rather than including adult and meristem stem cells.
• Miscalculating surface area to volume ratio, or stating that the ratio increases (rather than decreases) as an organism gets larger.

Approaching scaling up questions

Open any question about why a large organism needs exchange surfaces or transport systems with the surface-area-to-volume-ratio argument before describing the specific adaptation, since this single idea is what the specification is actually testing across lungs, gut, capillaries, xylem, phloem and root hairs alike. For any transport-mechanism question, work through diffusion, osmosis and active transport as a three-row comparison (what moves, along or against which gradient, whether energy is needed) rather than defining one in isolation, since most exam questions test the ability to distinguish between them in an unfamiliar scenario. For structure-function questions on a specialised cell such as a red blood cell or root hair cell, use the same reusable structure-function-link pattern every time: name the structural feature, state the function it enables, then explain explicitly how the structure increases the rate or efficiency of that function.