7.1.17 · Transport in Plants
Plant Transverse Sections — Cambridge AS & A Level Biology 9700 Revision Notes & Topical Questions
5 min read 10 parts Lesson 3 of 15 1 quiz
Lesson summary
7.1.1 Plant Transverse Sections — CAMBRIDGE AS & A LEVEL BIOLOGY 9700 — REVISION NOTES notes: Interpret and draw plan diagrams of transverse sections of a herbaceous dicotyledonous root, stem and leaf, identifying tissues from their position and structure.
- Dicotyledon focus
- Transverse section (TS)
- Longitudinal section (LS)
- Transport systems
- Size and proportion
- High-power drawing
Part 1 of 8Why transverse sections are used
Why transverse sections are used
Dicotyledon focus
- Dicotyledon focus the syllabus uses a herbaceous dicotyledon, a plant with a soft, non-woody stem.
Transverse section (TS)
- Transverse section (TS) a thin slice cut at right angles to the long axis of an organ, showing how xylem, phloem and supporting tissues are arranged.
Longitudinal section (LS)
- Longitudinal section (LS) a slice cut along the long axis.
Staining
- Staining toluidine blue or safranin colour lignified xylem blue-green or red under a light microscope, which makes it easy to find.
Transport systems
- Transport systems the vascular system is a network of vessels through leaves, stem and roots.
- Xylem carries water and mineral ions from the roots to the rest of the plant.
- Phloem carries substances from source to sink.
Part 2 of 8Drawing plan diagrams
Plan diagram
- Plan diagram it shows the distribution of tissues without individual cells.
Lines
- Lines use a sharp pencil with clear, continuous lines, no shading and no colouring.
Content
- Content draw the outline of each tissue region only, and add simple detail such as xylem at the centre of a root.
Size and proportion
- Size and proportion make the drawing large, taking up at least half the page, with tissues in correct proportion.
- (an eyepiece graticule can help)
Labels
- Labels use ruled straight lines that stop exactly at the structure with no arrows and no crossing, label all requested tissues,
- and add a title and magnification or scale bar.
High-power drawing
- High-power drawing draw only a few cells, with each cell wall as a line and contents such as nuclei or chloroplasts.
Part 3 of 8The herbaceous dicot root
1Epidermis
- Epidermis the outer layer, with root hair cells.
2Cortex
- Cortex wide, of parenchyma cells that store starch and have air spaces.
3Endodermis
- Endodermis the innermost cortex layer, whose cells have a waterproof Casparian strip.
4Pericycle
- Pericycle the layer inside the endodermis.
5Vascular cylinder
- Vascular cylinder central, with xylem as an X or star and phloem between the arms, and no pith.
6Central position
- Central position it resists the pulling forces exerted on the root as the shoot moves in wind.
Part 4 of 8The herbaceous dicot stem
Epidermis and cuticle
- Epidermis and cuticle on the outside, covered by a waxy cuticle.
Cortex
- Cortex beneath it, which may include collenchyma for support.
Vascular bundles
- Vascular bundles arranged in a ring near the edge, which gives rigidity and resistance to bending.
- Xylem is on the inner side, phloem on the outer side, and a thin layer of dividing cambium lies between.
Pith
- Pith parenchyma cells at the centre that store food.
Part 5 of 8The dicot leaf
| Tissue | Position | Function |
|---|---|---|
| Upper epidermis | Top, covered by cuticle | Protection and reduced water loss |
| Palisade mesophyll | Below the upper epidermis; tall cells packed with chloroplasts | Main site of photosynthesis |
| Spongy mesophyll | Below the palisade; rounded cells with large air spaces | Gas diffusion and some photosynthesis |
| Vascular bundle (midrib and veins) | Middle; xylem above phloem | Transport of water and assimilates |
| Lower epidermis with stomata | Bottom | Gas exchange; guard cells control the stomata |
- Shape
- the leaf is flat and thin to give a large surface for light and a short diffusion path for carbon dioxide.
Part 6 of 8Identifying the organ
Root
- Root a central star of xylem.
Stem
- Stem a ring of bundles with pith in the centre.
Leaf
- Leaf a flat blade with a palisade layer and stomata.
Tissue clues
- Tissue clues xylem is the lignified, thick-walled tissue, and phloem has small companion cells and larger sieve tube elements.
Part 7 of 8Making and examining a section
1
Use a very sharp blade or razor to cut the thinnest possible slice, so light can pass through.
2
Float the sections in water to prevent drying and select the thinnest.
3
Stain with a drop of toluidine blue or safranin for about a minute, then rinse.
4
Mount in water under a coverslip, lowering it at an angle to exclude air bubbles.
5
Observe on low power to locate the tissue layers, then use high power for cell detail.
1Magnification from a drawing
- Magnification from a drawing divide the measured length on the drawing by the actual length of the same structure, using the same units.
2Scale bar
- Scale bar measure the bar in millimetres, convert to micrometres and divide by the length it represents.
Part 8 of 8More from the specification
More from the specification
Micrograph Identification of Xylem
- Under a light microscope image or transverse section micrograph, mature xylem vessels appear as non-living hollow tubes with lignified cell walls that provide tensile support and conduct water and dissolved mineral ions.
Phloem Sieve Tube Elements and Sieve Plates
- Sieve tube elements are living conducting cells in vascular plants that possess reduced cytoplasm, no nucleus,
- and perforated end walls called sieve plates that facilitate the mass flow of dissolved organic compounds like sucrose converted from glucose.
Vascular Tissue Distribution in Plant Organs
- In dicotyledonous roots, xylem forms a distinct central star-shaped arrangement enclosed by phloem patches,
- whereas in dicot stems, vascular bundles containing xylem, cambium,
- and phloem are arranged in a peripheral ring.
Companion Cell Ultrastructure
- Companion cells remain metabolically active with dense cytoplasm, numerous mitochondria,
- and large nuclei, actively loading manufactured assimilates into adjacent sieve tubes via plasmodesmata.
Micrograph
- A photograph taken through a microscope.
Compound
- A substance of two or more kinds of atoms chemically combined
Glucose
- A simple sugar; the unit that starch, glycogen and cellulose are built from.
Organic compound
- Compound containing carbon and hydrogen.
Sieve plate
- Perforated end wall between phloem cells.
Key terms
| Term | Meaning |
|---|---|
| Transverse section | A thin slice cut at right angles to the long axis of an organ. |
| Plan diagram | A drawing showing the distribution of tissues without individual cells. |
| Vascular bundle | A strand of xylem and phloem running through a plant organ. |
| Cortex | Tissue between the epidermis and the vascular tissue, made mainly of parenchyma. |
| Pith | Parenchyma tissue at the centre of a dicot stem. |
| Endodermis | The innermost layer of the root cortex surrounding the vascular tissue. |
| Palisade mesophyll | Leaf tissue of tall, chloroplast-rich cells where most photosynthesis occurs. |
Avoid these mistakes
1
Drawing individual cells in a plan diagram — it shows only tissue outlines.
2
Putting the xylem on the outside of the phloem in a stem bundle — xylem is on the inner side towards the pith.
3
Saying the root has pith — a dicot root has a solid central vascular cylinder.
4
Using shading or colouring in biological drawings.
5
Giving a magnification without units or a scale bar, or measuring drawing and specimen in different units.
Topic quiz · 5 questionsQuiz for this lesson
Last updated: