Plant tissues, fibres and mineral nutrition — Edexcel International A Level Biology
Sclerenchyma, xylem and phloem, plan diagrams and tissue drawings, sustainable plant products, why plants need water and ions, and tensile strength.
Revision notes
5 short notes, in the order of the specification. Each one in short:
Sclerenchyma fibres give support, xylem vessels support the plant and transport water and mineral ions upwards, and phloem translocates organic solutes such as sucrose. Fibres and vessels are dead, lignified cells, whereas sieve tube elements are living cells with companion cells. In a dicot stem all three tissues lie in vascular bundles.
A plan diagram shows the arrangement of tissues in a section using clear lines, without drawing individual cells. A high-power drawing shows the cells of one tissue. Thin sections are cut, stained, mounted and viewed with a light microscope, and the magnification of a drawing is calculated from image size divided by actual size.
Sustainability means meeting present needs without harming the ability of future generations to meet theirs. Plant fibres and starch are renewable and can be grown again, and products made from them are often biodegradable. They can replace oil-based plastics, which come from a finite resource and may persist in the environment.
Plants need water for turgor and support, as a transport medium and solvent, as a reactant in photosynthesis and for cooling through transpiration. Nitrate provides nitrogen for amino acids, proteins and nucleic acids, calcium ions form calcium pectate in the middle lamella, and magnesium ions are part of chlorophyll.
Tensile strength is the maximum force per unit cross-sectional area a fibre can withstand before it breaks. It is measured by hanging increasing masses from a fibre of known length and diameter until it snaps, then dividing the breaking force by the cross-sectional area. Fibre length, diameter and moisture must be controlled.
Exam questions
8 exam-style questions (31 marks), each with its mark scheme.
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16 cards: flip them, mark what you knew, and practise the rest.
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The whole of plant structure and function, biodiversity and conservation on one page, so you can see where this subtopic fits.
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Quick check questions
Name the tissue that carries sucrose around the plant.
Show answer
Phloem (sieve tubes).
Why can xylem vessels carry water in one continuous column?
Show answer
They are dead, have no cell contents and no end walls, so form a hollow tube.
State the formula for magnification.
Show answer
Magnification = size of image ÷ size of real object.
Why do plants need magnesium ions?
Show answer
Magnesium is the central atom in chlorophyll, so it is needed to make chlorophyll for photosynthesis.
Give the unit of tensile strength.
Show answer
N mm⁻² (equivalent to MPa) or Pa.
Frequently asked questions
What is the difference between xylem and phloem?
Xylem vessels are dead, lignified tubes that transport water and mineral ions upwards and help support the plant. Phloem sieve tubes are living cells with companion cells that translocate organic solutes such as sucrose in both directions, from sources to sinks. Xylem is on the inner side of a stem vascular bundle, phloem outside it.
How do you draw a plan diagram in biology?
Use a sharp pencil and clear single lines to draw the outline of the section and the boundaries between tissues. Do not draw individual cells or shade. Make it large, add ruled label lines that do not cross, give a title and state the magnification.
Why do plants need nitrate, calcium and magnesium?
Nitrate supplies nitrogen for amino acids, proteins and nucleic acids. Calcium ions form calcium pectate in the middle lamella and help build cell walls. Magnesium ions are the central atom of chlorophyll. Deficiency causes stunted growth, poor roots or yellowing leaves (chlorosis).
How can plant products help sustainability?
Plant fibres and starch-based plastics are renewable and often biodegradable, so they can replace oil-based plastics made from a finite resource. Carbon dioxide absorbed during growth offsets some emissions. However, growing them needs land, water and fertiliser, so they can compete with food crops.
How do you measure the tensile strength of a plant fibre?
Clamp a fibre of known length and diameter, hang a mass holder from it and add masses until it breaks. Convert the breaking mass to force (mass × 9.81), calculate the cross-sectional area (πr²) and divide force by area. Repeat and take a mean.
Written and checked against the Edexcel International A Level Biology (YBI11) specification · Updated October 2026