A level-readyAll subjects · Biology · WBI12 (Unit 2)
Core practical 7: plant tissues under the microscope
Core practical 7 asks you to draw plan diagrams of transverse sections of roots, stems and leaves, and to identify sclerenchyma, phloem, sieve tubes and xylem.
Preparing and observing
Use prepared slides or cut thin transverse sections with a sharp blade. A stain helps: for example toluidine blue stains lignified walls (xylem, sclerenchyma) blue-green and non-lignified walls pinkish-purple. Look at low power for the plan, then high power for individual cells.
Plan diagrams
A plan diagram shows the outlines of tissues only, with no individual cells, in the correct proportions.
- Stem (dicot): epidermis, cortex, a ring of vascular bundles near the edge, pith in the centre. In each bundle: sclerenchyma cap on the outside, then phloem, then xylem towards the centre.
- Root: epidermis (with root hairs), wide cortex, and a central vascular cylinder with xylem in an X or star shape in the middle and phloem between its arms.
- Leaf: upper epidermis, palisade mesophyll, spongy mesophyll, lower epidermis with stomata; in the midrib, xylem on the upper side of the bundle and phloem below.
Drawing cells
At high power, draw a few cells of each tissue, showing wall thickness. Xylem vessels: wide, empty, thick lignified walls. Sclerenchyma: small, thick-walled, almost no lumen. Phloem sieve tubes: thin walls, sometimes with visible sieve plates, and small companion cells beside them.
Use the same drawing rules as in core practical 5: pencil, clear lines, no shading, ruled labels.
Worked example
Why is the vascular tissue in the centre of a root but near the edge of a stem?
- A root must resist pulling forces as the plant moves; central vascular tissue suits this.
- A stem must resist bending; a ring of strong tissue near the edge suits this.
Answer: Central in roots to resist pulling; peripheral in stems to resist bending.
Check yourself
- What does a plan diagram show?
- Every cell in detail
- Outlines of tissues with no individual cells
- Organelles within one cell
- Shading to show colour
Show answer
Outlines of tissues with no individual cells. Plan diagrams show where tissues are.
- How is the xylem arranged in a dicotyledonous root?
- In a ring of bundles near the edge
- Only in the epidermis
- Scattered throughout the cortex
- In a central X or star shape
Show answer
In a central X or star shape. Root xylem is central, with phloem between its arms.
- In a dicotyledonous stem, the vascular bundles are
- in a single central cylinder
- arranged in a ring near the outside
- only in the leaves
- in the pith
Show answer
arranged in a ring near the outside. A ring of bundles resists bending.
- In a stem vascular bundle, going from the outside in, the order is
- xylem, phloem, sclerenchyma
- phloem, sclerenchyma, xylem
- sclerenchyma, phloem, xylem
- xylem, sclerenchyma, phloem
Show answer
sclerenchyma, phloem, xylem. Sclerenchyma caps the phloem; xylem is towards the centre.
- With toluidine blue, which tissues stain blue-green?
- Lignified tissues such as xylem and sclerenchyma
- Phloem only
- All cytoplasm
- Starch grains
Show answer
Lignified tissues such as xylem and sclerenchyma. Lignin stains blue-green with toluidine blue.
- A cell in a section is wide, empty and has thick walls. Which tissue is it most likely to be?
- Companion cell
- Palisade cell
- Xylem vessel
- Phloem sieve tube
Show answer
Xylem vessel. Xylem vessels are wide, hollow and lignified.
Sources
Last updated 7 November 2026. Spotted a mistake? Tell us.