Pearson Edexcel International A Level Biology: Plant Cells, Starch, Cellulose and Fibres (YBI11) – Practice Questions

These are original questions written for Marlbridge, for revision and practice on this content. They are not reproduced past-paper questions, and they do not replicate the exam’s exact structure, question count or mark tariffs – examination boards hold copyright in their own papers. Use these alongside the official past papers from your board or school.

These questions follow the Pearson Edexcel International Advanced Subsidiary/Advanced Level Biology specification (YBI11), Issue 2, Topic 4, statements 4.1 to 4.7 including Core Practical 7. This is International AS (IAS) content, with no tiers. Read the study guide and revision notes first. Hub: Edexcel A Level Biology. Checklist: Edexcel biology checklist. Not sure where to start? Take the free diagnostics.

Questions

1. State the function of each of the following in a plant.

(a) The middle lamella. [1] (b) The tonoplast. [1] (c) Plasmodesmata. [1]

2. Compare the ultrastructure of a palisade mesophyll cell with that of a human liver cell. Give two differences and two similarities. [4]

3. An electron micrograph shows part of a plant cell wall. A scale bar on the image is 20 mm long and represents 0.5 µm. The wall measures 46 mm across on the image.

(a) Calculate the magnification of the image. [2] (b) Calculate the actual thickness of the wall, in µm. [2]

4. Starch is stored in potato tubers.

(a) Describe the structural differences between amylose and amylopectin. [2] (b) Explain two ways in which the properties of starch suit it as an energy store. [2]

5. Explain how the structure of cellulose, including the role of hydrogen bonds, makes cell walls strong. [4]

6. Explain how secondary thickening and the arrangement of cellulose microfibrils adapt xylem vessels for their functions. [5]

7. A transverse section of a herbaceous stem shows vascular bundles in a ring.

(a) State where sclerenchyma fibres, xylem vessels and phloem are found in the stem. [3] (b) Explain two structural differences between a xylem vessel and a phloem sieve tube, and link each to function. [3]

8. In Core Practical 7 a student prepares a plan diagram from a stem cross-section. The stem section has an actual diameter of 4.0 mm and the drawing is 120 mm across.

(a) State two rules for drawing a plan diagram. [2] (b) Calculate the magnification of the drawing. [1] (c) The xylem in one vascular bundle measures 15 mm radially on the drawing. Calculate its actual width, in µm. [2] (d) Explain why individual cells are not drawn on a plan diagram. [1]

9. Structure P is surrounded by two membranes and contains stacks of flattened discs in a granular background, with a few small pale oval grains. Structure R is also surrounded by two membranes, but contains several large pale grains and no stacked discs. Structure T is bounded by a single membrane and has a clear, featureless interior that occupies most of the cell.

(a) Identify P, R and T. [3] (b) State one function of R. [1]

10. A company compares the carbon dioxide released in making 1 kg of three packaging materials. The data are supplied: oil-based plastic 3.1 kg, starch-based plastic 1.9 kg, hemp-fibre composite 2.4 kg.

(a) Calculate the percentage reduction in carbon dioxide released for each plant-based material compared with the oil-based plastic. [3] (b) Evaluate the use of plant-based materials to replace oil-based plastics. [4]

11. The table gives data supplied for three fibre samples.

Sample	Breaking force (N)	Cross-sectional area (mm²)	Microfibril angle (degrees)
X	540	0.9	10
Y	810	1.5	25
Z	380	0.4	5

(a) Calculate the breaking stress (force ÷ area) for each sample, in N per mm². [3] (b) Describe and explain the relationship between microfibril angle and breaking stress. [3] (c) Suggest why sclerenchyma fibres are suited to being made into rope. [2]

12. Describe and explain how water and dissolved substances could move from one parenchyma cell to the next through the wall, and how the structure of the wall allows this. [5]

Answers

1. (a) It cements adjacent cells together (pectin-rich layer). [1] (b) It is the membrane surrounding the vacuole and controls movement of substances into and out of it. [1] (c) They are channels through cell walls carrying cytoplasm, allowing transport and communication between cells. [1] Examiner insight: Each part needs a function, not just a description of where the structure is; “found in the wall” alone is a description.

2. Differences, any two: plant cell has a cellulose cell wall, liver cell does not; plant cell has chloroplasts, liver cell does not; plant cell has a large permanent vacuole bounded by a tonoplast, liver cell has none or small vesicles (any two for [1][1]). Similarities, any two: both have a nucleus, mitochondria, rough ER, Golgi apparatus, ribosomes or a plasma membrane [1][1]. Credit any two differences and any two similarities; maximum 4. Examiner insight: A comparison answer should name the feature in both cells; saying only “plants have a wall” may not show the comparison clearly.

3. (a) 20 mm = 20 000 µm, so magnification = 20 000 ÷ 0.5 [1] = ×40 000 [1] (b) Actual = 46 000 ÷ 40 000 [1] = 1.15 µm [1] Examiner insight: Show the unit conversion; an answer in mm that is not converted is the usual way to lose the final mark.

4. (a) Amylose is unbranched with α-1,4 bonds and coiled into a helix [1]; amylopectin has α-1,4 chains with α-1,6 branches [1]. (b) It is insoluble, so does not affect water potential or leave the cell [1]; it is compact (coiled, or in grains) so it stores a lot of glucose in a small space, or it is easily hydrolysed to glucose for respiration [1]. Examiner insight: “Explain” requires the property and the reason it matters for storage; naming the property alone gains little.

5. Cellulose is made of β-glucose in straight unbranched chains [1] because alternate residues are inverted in the β-1,4 links [1]. Hydrogen bonds form between –OH groups of parallel chains [1]. Each bond is weak but there are very many, forming microfibrils with high tensile strength that resist the cell bursting [1]. Examiner insight: State that the hydrogen bonds are between chains and that there are many; confusing them with glycosidic bonds is a common slip.

6. Secondary thickening adds extra wall inside the primary wall [1] containing lignin, which is rigid and waterproof [1]. This stops the vessel collapsing inwards under the tension of transpiration [1]. Microfibrils in layers at different angles give strength in different directions [1]. Lignin laid in rings, spirals or networks leaves unthickened gaps, and pits, which allow lateral water movement, and the dead empty lumen with no end walls forms a continuous tube [1]. Examiner insight: The points are credited when linked to function; a list of features without “so that” reasoning may not reach the top of the range.

7. (a) Sclerenchyma: outer part of vascular bundles or in the cortex [1]; xylem: inner side of each vascular bundle [1]; phloem: outer side of each vascular bundle, outside the xylem [1]. (b) Xylem vessel has no end walls and an empty lumen, giving continuous flow of water [1]; sieve tube has sieve plates and living cytoplasm so solutes can be loaded and moved [1]; xylem walls are lignified for strength and support under tension, sieve tube walls are thin and unlignified [1]. Examiner insight: Give a difference and the link to function for each point; a bare difference does not usually earn the explanation mark.

8. (a) Any two: draw outlines of tissues only, no shading, sharp single lines, correct proportions, title and magnification, ruled label lines [1][1] (b) 120 ÷ 4.0 = ×30 [1] (c) 15 ÷ 30 [1] = 0.5 mm = 500 µm [1] (d) A plan diagram shows only the arrangement and proportions of the tissues, and cell detail would obscure this. [1] Examiner insight: Give the final answer in the requested unit; 0.5 mm alone may be treated as incomplete because the question asks for µm.

9. (a) P is a chloroplast [1]; R is an amyloplast [1]; T is a vacuole [1]. (b) It stores starch. [1] Examiner insight: Support each identification with a visible feature if asked to “justify”; here the stacked discs distinguish P from R.

10. (a) Starch-based: (3.1 − 1.9) ÷ 3.1 × 100 [1] = 38.7% [1]. Hemp composite: (3.1 − 2.4) ÷ 3.1 × 100 = 22.6% [1] (b) Advantages: renewable crops, carbon dioxide taken up by the plants as they grow, and less carbon dioxide released in manufacture on these figures [1]; many products biodegrade, reducing persistent plastic waste [1]. Limitations: land, water and fertiliser needed, with possible competition with food crops [1]; processing uses energy and some bioplastics need industrial composting; the data cover only carbon dioxide from manufacture, not the whole life [1]. Examiner insight: An evaluation needs both sides and a judgement based on the data; quoting a percentage is a start, but a conclusion is needed.

11. (a) X: 540 ÷ 0.9 = 600 [1]; Y: 810 ÷ 1.5 = 540 [1]; Z: 380 ÷ 0.4 = 950 N per mm² [1] (b) The smaller the microfibril angle, the greater the breaking stress [1] (5° gives 950, 10° gives 600, 25° gives 540). [1] Microfibrils nearly parallel to the fibre axis share the pulling force along their length, with hydrogen-bonded chains resisting being pulled apart. [1] (c) They have thick lignified walls and high tensile strength [1], and they are long and flexible and can be twisted together. [1] Examiner insight: “Describe and explain” needs data quoted from the table and a reason; a trend without figures is only part of an answer.

12. Water and solutes can move through the cell wall itself, because the cellulose and matrix are fully permeable [1]. At a pit, the wall is thinner because no secondary wall has been laid down [1], so less material is crossed [1]. Plasmodesmata are channels through the wall, lined with the plasma membrane and containing cytoplasm [1], so substances can pass directly from cytoplasm to cytoplasm without crossing a membrane [1]. Examiner insight: Distinguish a pit (thin wall, no channel) from a plasmodesma (channel with cytoplasm); using the terms interchangeably loses marks.

Where marks are usually lost

• Describing where a structure is when asked for its function.
• Saying the cell wall “controls” what enters, when it is fully permeable and the plasma membrane controls entry.
• Not converting units before working out magnification.
• Writing that hydrogen bonds join glucose units in a chain.
• Calling cellulose branched or helical.
• Stating that xylem is living, or omitting lignin when explaining strength.
• Drawing cells or shading in a plan diagram.
• Quoting percentages in an evaluation without a balanced judgement.
• Describing a trend without figures from the table.

Next steps

• Review the revision notes and study guide.
• Course hub: Edexcel A Level Biology.
• Tick off statements on the checklist.
• Try all the free 10-minute diagnostics.
• Book a free trial class.

Official syllabus

Pearson Edexcel International Advanced Subsidiary/Advanced Level in Biology (YBI11), Specification, Issue 2, February 2021, Pearson Education Limited: Topic 4, statements 4.1 to 4.7.