How to Use This Section
Anatomy is examined almost entirely as "name the layer" and "tell the two sections apart". There is one long descriptive answer - the dorsiventral leaf - and one reasoning answer - why plant anatomy is worth studying. Everything else is a labelled ring or a two-column difference.
The 40 questions are organised in three tiers:
- Concept Checks - the definitions and the layer names.
- Application and Scenarios - a section described, and you identify it.
- Analytical and Multi-Concept - the comparisons and the reasons behind the structures.
Every item is set as a Question with a worked Answer, written the way you would write it in the exam.
Coverage of the chapter-end exercises
| Exercise | Where it is answered |
|---|---|
| 1(a) - Anatomical difference between a monocot root and a dicot root | Question 29 |
| 1(b) - Anatomical difference between a monocot stem and a dicot stem | Question 30 |
| 2 - How to ascertain whether a young stem is monocot or dicot | Question 37 |
| 3 - Identify the material from its scattered sheathed bundles | Question 23 |
| 4 - The stomatal apparatus and the structure of stomata | Question 38 |
| 5 - The three basic tissue systems and their tissues | Question 31 |
| 6 - How the study of plant anatomy is useful to us | Question 39 |
| 7 - The internal structure of a dorsiventral leaf | Question 40 |
Every chapter-end exercise is worked here, so this section is the one place to check that you have covered the textbook in full.
The Facts These Questions Draw On
Tissues. Meristematic - apical (tips, primary growth, length), intercalary (base of leaves, above nodes, grasses), lateral (mature regions, secondary growth, girth). Simple permanent - parenchyma (isodiametric, thin cellulose walls), collenchyma (below epidermis in dicot stem and petiole, thickened at the corners, no intercellular spaces), sclerenchyma (long, narrow, thick lignified walls with pits, usually dead; fibres and sclereids). Complex - xylem (tracheids, vessels, xylem fibres, xylem parenchyma) and phloem (sieve tube elements, companion cells, phloem parenchyma, phloem fibres).
Three tissue systems. Epidermal, ground or fundamental, vascular or conducting.
Epidermis. Usually single-layered, parenchymatous, cuticle prevents water loss and is absent in roots. Stomata - two bean-shaped guard cells, dumb-bell shaped in grasses; outer wall thin, inner wall highly thickened; chloroplasts present; subsidiary cells; stomatal apparatus = aperture + guard cells + subsidiary cells. Root hairs unicellular and absorb; trichomes multicellular and prevent water loss.
Ground tissue. All tissues except epidermis and vascular bundles. In leaves it is the mesophyll.
Vascular bundles. Open (cambium present, dicot stems) against closed (no cambium, monocots); radial (roots) against conjoint (stems and leaves, phloem outside xylem). Endarch in stems, exarch in roots.
Dicot root. Epiblema, cortex, endodermis with casparian strips of suberin, pericycle (lateral roots and vascular cambium), two to four xylem patches, conjunctive tissue, small pith, stele.
Monocot root. Same rings; more than six xylem bundles - polyarch; large pith; no secondary growth.
Dicot stem. Epidermis with cuticle, trichomes and a few stomata; collenchymatous hypodermis; parenchymatous cortex; endodermis as the starch sheath; pericycle as semi-lunar patches of sclerenchyma above the phloem; medullary rays; bundles in a ring, each conjoint, open, endarch; pith.
Monocot stem. Sclerenchymatous hypodermis; scattered bundles with sclerenchymatous bundle sheaths; large parenchymatous ground tissue; bundles conjoint and closed; peripheral bundles smaller; no phloem parenchyma; water-containing cavities.
Dorsiventral leaf. Adaxial and abaxial epidermis, more stomata below; mesophyll of palisade (adaxial, elongated, vertical) and spongy (loose, air cavities); bundles in veins and midrib with a thick-walled bundle sheath.
Isobilateral leaf. Stomata on both surfaces; mesophyll not differentiated; bulliform cells in grasses; bundles of near similar size.
Tier 1 - Concept Checks
Question 1
Q. What is anatomy?
Answer. The study of the internal structure of plants.
Question 2
Q. Name the three tissue systems.
Answer. The epidermal, the ground or fundamental, and the vascular or conducting tissue systems. This is one of the chapter-end exercises.
Question 3
Q. On what basis are the tissue systems classified?
Answer. On the basis of their structure and location in the plant body.
Question 4
Q. Define the ground tissue system.
Answer. All tissues except the epidermis and the vascular bundles.
Question 5
Q. What is the stomatal apparatus?
Answer. The stomatal aperture, the guard cells and the surrounding subsidiary cells taken together. This is one of the chapter-end exercises.
Question 6
Q. What are subsidiary cells?
Answer. Epidermal cells in the vicinity of the guard cells that have become specialised in their shape and size.
Question 7
Q. Where is the cuticle absent, and why does that make sense?
Answer. In roots. The cuticle prevents the loss of water, and a root has to absorb water, so a waterproof layer there would be self-defeating.
Question 8
Q. How does a root hair differ from a trichome in cell number and in job?
Answer. A root hair is unicellular and absorbs water and minerals. A trichome is usually multicellular and prevents water loss due to transpiration.
Question 9
Q. What are casparian strips and what are they made of?
Answer. Deposits of the water-impermeable waxy material suberin on the tangential and radial walls of the endodermal cells of a root.
Question 10
Q. Define the stele.
Answer. All the tissues on the inner side of the endodermis - the pericycle, vascular bundles and pith.
Question 11
Q. What is conjunctive tissue?
Answer. The parenchymatous cells lying between the xylem and the phloem in a root.
Question 12
Q. Why is the endodermis of a dicot stem called the starch sheath?
Answer. Because its cells are rich in starch grains.
Question 13
Q. What are medullary rays?
Answer. A few layers of radially placed parenchymatous cells lying between the vascular bundles of a dicot stem.
Question 14
Q. What is the mesophyll?
Answer. The ground tissue of a leaf - the tissue between the upper and lower epidermis, made of parenchyma containing chloroplasts, which carries out photosynthesis.
Question 15
Q. Name the two kinds of mesophyll cell in a dorsiventral leaf.
Answer. Palisade parenchyma and spongy parenchyma.
Question 16
Q. What are bulliform cells?
Answer. In grasses, adaxial epidermal cells along the veins that have become large, empty and colourless.
Tier 2 - Application and Scenarios
Question 17
Q. A tissue below the epidermis of a petiole has living cells thickened only at the corners and no intercellular spaces. Name it and say what it does.
Answer. Collenchyma. It provides mechanical support to the growing parts of the plant.
Question 18
Q. A tissue is made of long narrow dead cells with thick lignified walls carrying pits. Name it and its two cell types.
Answer. Sclerenchyma, made of fibres and sclereids. It gives mechanical support.
Question 19
Q. A vascular bundle has xylem and phloem lying on alternate radii. Name the bundle type and the organ.
Answer. Radial, so it is from a root.
Question 20
Q. A vascular bundle is conjoint with a cambium between the xylem and the phloem. What organ is it from, and what class of plant?
Answer. Conjoint means a stem or leaf, and the cambium makes it open, which means a dicot. So it is a dicot stem.
Question 21
Q. A root section shows eight xylem patches and a large pith. Identify it.
Answer. A monocot root. More than six xylem bundles is polyarch, and the large well developed pith confirms it.
Question 22
Q. A stem section has a collenchymatous hypodermis and vascular bundles arranged in a ring. Identify it.
Answer. A dicot stem. Both features are characteristic of it - the ring arrangement of bundles especially.
Question 23
Q. The transverse section of a plant material shows vascular bundles that are conjoint, scattered and surrounded by sclerenchymatous bundle sheaths, and the phloem parenchyma is absent. What will you identify it as?
Answer. A monocotyledonous stem. Each of the three features points to it, and together they are conclusive - scattered bundles, a sclerenchymatous bundle sheath round each one, and no phloem parenchyma. This is one of the chapter-end exercises.
Question 24
Q. A leaf section shows stomata on both surfaces and a mesophyll that is uniform throughout. Identify the leaf and the class of plant.
Answer. An isobilateral leaf, so a monocotyledon. Those two features are exactly the two characteristic differences from a dorsiventral leaf.
Question 25
Q. A leaf epidermis shows dumb-bell shaped guard cells. What does that tell you?
Answer. The plant is a grass. Guard cells are bean-shaped in most plants and dumb-bell shaped in grasses.
Question 26
Q. A grass leaf has curled inward on a hot dry afternoon. Explain what happened.
Answer. The bulliform cells have gone flaccid because of water stress, and flaccid bulliform cells make the leaves curl inwards. The curling minimises water loss. When they take up water and become turgid again, the leaf surface is exposed and the leaf opens out.
Question 27
Q. A root section is examined and lateral roots are seen emerging from deep inside rather than from the surface. Which layer are they starting in?
Answer. The pericycle. Initiation of lateral roots takes place in the pericycle, which lies inside the endodermis, so a lateral root has to push out through the cortex and epidermis.
Question 28
Q. A stem section is examined and there is no separate cortex or pith - just one large parenchymatous mass with bundles through it. Identify the stem.
Answer. A monocot stem. It has a large, conspicuous parenchymatous ground tissue that is not divided into cortex and pith, because the scattered bundles run through the whole of it.
Tier 3 - Analytical and Multi-Concept
Question 29
Q. Give the anatomical differences between a monocot root and a dicot root.
Answer.
| Feature | Dicot root | Monocot root |
|---|---|---|
| Xylem bundles | Two to four | More than six, polyarch |
| Pith | Small or inconspicuous | Large and well developed |
| Secondary growth | Occurs | Does not occur |
| Cambium | A cambium ring develops between xylem and phloem | Never forms |
Both have the same rings - epidermis, cortex, endodermis with casparian strips, pericycle, vascular bundles and pith - and in both the bundles are radial. This is one of the chapter-end exercises.
Question 30
Q. Give the anatomical differences between a monocot stem and a dicot stem.
Answer.
| Feature | Dicot stem | Monocot stem |
|---|---|---|
| Hypodermis | Collenchymatous | Sclerenchymatous |
| Vascular bundles | In a ring | Scattered |
| Bundle type | Conjoint, open, endarch | Conjoint and closed |
| Bundle sheath | Absent | Sclerenchymatous, round each bundle |
| Ground tissue | Split into cortex, endodermis, pericycle, medullary rays, pith | One large parenchymatous mass |
| Phloem parenchyma | Present | Absent |
| Water-containing cavities | Absent | Present in the bundles |
| Secondary growth | Occurs | Does not occur |
This is one of the chapter-end exercises.
Question 31
Q. Name the three tissue systems and give the tissues under each.
Answer.
| Tissue system | Tissues under it |
|---|---|
| Epidermal | Epidermal cells, stomata with their guard cells and subsidiary cells, and the epidermal appendages - root hairs and trichomes |
| Ground or fundamental | The simple tissues - parenchyma, collenchyma and sclerenchyma - forming the cortex, pericycle, pith and medullary rays, and the mesophyll in leaves |
| Vascular or conducting | The complex tissues - xylem (tracheids, vessels, xylem fibres, xylem parenchyma) and phloem (sieve tube elements, companion cells, phloem parenchyma, phloem fibres) |
This is one of the chapter-end exercises.
Question 32
Q. Why does a leaf have palisade cells above and spongy cells below rather than one uniform mesophyll?
Answer. The two layers do two different jobs. Palisade parenchyma is adaxial - on the side facing the light - and its elongated cells arranged vertically and parallel to each other pack a lot of chloroplasts into the brightest part of the leaf. Spongy parenchyma sits below, and its loosely arranged cells with numerous large spaces and air cavities leave open channels for gases to move to and from the stomata, which are concentrated on the abaxial surface. Light above, gas exchange below.
Question 33
Q. Three tissues in this chapter give mechanical support. Name them and say where each is used.
Answer. Collenchyma supports the growing parts - the young dicot stem and the petiole - because it is living and can stretch. Sclerenchyma supports where rigidity is wanted and growth has stopped, which is why it forms the hypodermis of a monocot stem, the bundle sheaths round its vascular bundles and the semi-lunar pericycle patches of a dicot stem. Xylem gives mechanical strength as well as conducting, through its tracheids and fibres.
Question 34
Q. Which structures in this chapter exist to control water loss, and how does each work?
Answer.
- Cuticle - a waxy thick layer over the epidermis that prevents the loss of water; absent in roots.
- Stomata - the guard cells regulate the opening and closing of the pore, so the plant can shut down transpiration when it needs to.
- Trichomes - epidermal hairs on the shoot that prevent water loss due to transpiration.
- Bulliform cells - in grasses, they go flaccid under water stress and curl the leaf inwards to minimise water loss.
Question 35
Q. Both the pericycle of a root and the pericycle of a dicot stem carry the same name. How do they differ?
Answer. In a root the pericycle is a few layers of thick-walled parenchymatous cells, and it is where lateral roots and the vascular cambium are initiated. In a dicot stem the pericycle sits above the phloem as semi-lunar patches of sclerenchyma, and its job is support. Same position in the sequence of layers, different tissue and different function.
Question 36
Q. Build the shortest set of checks that would let you place any section you are handed.
Answer.
- Are the vascular bundles radial or conjoint? Radial means a root; conjoint means a stem or leaf.
- If a root - count the xylem patches. Two to four with a small pith means dicot; more than six with a large pith means monocot.
- If a stem - look at the bundle arrangement. A ring means dicot; scattered means monocot. Confirm with the hypodermis: collenchymatous for dicot, sclerenchymatous for monocot.
- If a leaf - look at the mesophyll. Split into palisade and spongy means dorsiventral, a dicot; uniform, with stomata on both surfaces, means isobilateral, a monocot.
Four checks, and every section in the chapter is placed.
Question 37
Q. You cut a transverse section of a young stem from your school garden and observe it under the microscope. How would you ascertain whether it is a monocot stem or a dicot stem? Give reasons.
Answer. Check three things in order.
- Arrangement of the vascular bundles. In a ring means dicot; scattered through the section means monocot. This one check is usually decisive, because the ring arrangement is described as a characteristic of the dicot stem.
- The hypodermis. Collenchymatous means dicot; sclerenchymatous means monocot.
- The bundle itself. A cambium between the xylem and the phloem, making the bundle open, means dicot. No cambium, so closed, plus a sclerenchymatous bundle sheath and no phloem parenchyma, means monocot.
A dicot stem also shows a distinct cortex, endodermis, pericycle and pith, where a monocot stem has a single undivided parenchymatous ground tissue. This is one of the chapter-end exercises.
Question 38
Q. What is the stomatal apparatus? Explain the structure of stomata with a labelled diagram.
Answer. The stomatal apparatus is the stomatal aperture, the guard cells and the surrounding subsidiary cells taken together.
Structure of a stoma.
- Stomata are structures present in the epidermis of leaves, and they regulate transpiration and gaseous exchange.
- Each stoma is composed of two bean-shaped cells called guard cells, which enclose the stomatal pore. In grasses the guard cells are dumb-bell shaped.
- The outer walls of the guard cells, away from the pore, are thin, and the inner walls, towards the pore, are highly thickened. That unequal thickening is what lets the cells bend and open the pore.
- The guard cells possess chloroplasts and regulate the opening and closing of the stoma.
- A few epidermal cells near the guard cells become specialised in their shape and size and are the subsidiary cells.
Label on the diagram: epidermal cells, subsidiary cells, guard cells, chloroplast, stomatal pore. This is one of the chapter-end exercises.
Question 39
Q. How is the study of plant anatomy useful to us?
Answer. In several ways, and a full answer should give more than one.
- It lets us identify plants and plant material. Two plants that look alike from outside may be quite different inside, and a transverse section will separate them. This is how a monocot is told from a dicot even when only a fragment is available.
- It identifies timber and other commercial plant products. Wood is named from the arrangement and structure of its vessels, fibres and rays, which is how timber is graded and how one species is told from another after the tree has been cut.
- It detects adulteration in plant drugs and foods. Powdered plant material keeps its cell and tissue structure, so anatomy is what shows whether a sample is what it claims to be.
- It supports classification. Internal features such as the type and arrangement of the vascular bundles are used alongside external morphology to decide relationships, which is what the chapter means when it says monocots and dicots are anatomically different.
- It explains how a plant works. You cannot understand the conduction of water and minerals without the xylem, or the movement of food without the phloem, or transpiration and gaseous exchange without the stomatal apparatus. Anatomy supplies the structures that plant physiology then explains.
- It shows how plants are adapted to their environment. Internal structures show adaptations to diverse environments - the thick cuticle of a dry-habitat leaf, or the bulliform cells that curl a grass leaf inwards under water stress.
- It underpins practical work in agriculture, horticulture and plant breeding, where grafting, tissue culture and disease diagnosis all depend on knowing which tissue is which.
This is one of the chapter-end exercises.
Question 40
Q. Describe the internal structure of a dorsiventral leaf with the help of labelled diagrams.
Answer. A vertical section through the lamina shows three main parts: epidermis, mesophyll and vascular system.
1. Epidermis. It covers both surfaces - the adaxial epidermis above and the abaxial epidermis below - and carries a conspicuous cuticle. The abaxial epidermis generally bears more stomata than the adaxial, and the adaxial may even lack stomata altogether.
2. Mesophyll. The tissue between the upper and the lower epidermis. It is made of parenchyma, possesses chloroplasts and carries out photosynthesis. It has two kinds of cell:
- Palisade parenchyma - adaxially placed, of elongated cells arranged vertically and parallel to each other.
- Spongy parenchyma - oval or round and loosely arranged, lying below the palisade cells and extending to the lower epidermis, with numerous large spaces and air cavities between the cells.
3. Vascular system. Vascular bundles are present in the veins and the midrib. The size of a bundle depends on the size of its vein, and the veins vary in thickness in the reticulate venation of dicot leaves. Each bundle is surrounded by a layer of thick-walled bundle sheath cells.
Label on the diagram: adaxial epidermis, cuticle, palisade parenchyma, spongy parenchyma, air cavity, vascular bundle with xylem and phloem, bundle sheath, abaxial epidermis, stoma and guard cells. This is one of the chapter-end exercises.