Anatomy of Flowering Plants

What to remember

• Meristems add new cells: apical meristems give primary growth in length, intercalary meristems add length at nodes or internode bases in grasses, and lateral meristems (vascular cambium and cork cambium) give secondary growth in girth.
• Xylem conducts water and minerals; phloem conducts food. Xylem has tracheids, vessels, fibres and parenchyma; phloem has sieve tube elements, companion cells, phloem parenchyma and phloem fibres.
• Dicot stems have open, conjoint, collateral bundles in a ring; monocot stems have closed, scattered bundles. Roots have radial bundles with exarch xylem.
• Secondary growth forms secondary xylem and phloem from vascular cambium, and periderm from cork cambium. Heartwood is dead and dark; sapwood conducts.

Tissues: meristematic and permanent

A tissue is a group of similar cells that perform a common function. In plants, growth is confined to regions of dividing cells called meristems.

Cells produced by meristems differentiate and lose the ability to divide. They form permanent tissues. Permanent tissues are simple (one type of cell) or complex (more than one type of cell working as a unit).

Simple tissues

Fibres are long, thick-walled and pointed at both ends. Sclereids are spherical, oval or cylindrical, with very narrow cavities.

Complex tissues

Xylem conducts water and minerals from roots to the stem and leaves, and gives mechanical strength. It has four elements.

• Tracheids: elongated cells with tapering ends; dead and lignified. They are the main water-conducting elements in gymnosperms.
• Vessels: long, tube-like structures made of many cells with large central cavities and lignified walls. They are dead and joined end to end through perforations. Vessels are a characteristic feature of angiosperms.
• Xylem fibres: highly thickened walls with very narrow cavities.
• Xylem parenchyma: living, thin-walled cells that store food. Ray parenchyma helps radial conduction of water.

The first-formed primary xylem is protoxylem and the later-formed is metaxylem. In stems, protoxylem lies towards the centre (pith) and metaxylem towards the periphery. This condition is endarch. In roots, protoxylem lies towards the periphery and metaxylem towards the centre. This condition is exarch.

Phloem transports food (sugars) from leaves to other parts. It has four elements.

• Sieve tube elements: long tubular cells joined end to end, with perforated end walls called sieve plates. A mature sieve tube element has no nucleus but has peripheral cytoplasm and a large vacuole.
• Companion cells: specialised parenchyma cells closely associated with sieve tube elements. They are connected to them through pit fields. Their nucleus controls the sieve tube function.
• Phloem parenchyma: living, elongated and tapering cells with dense cytoplasm and nucleus. It is absent in most monocots.
• Phloem fibres (bast fibres): sclerenchymatous, generally absent in primary phloem but present in secondary phloem.

Gymnosperms have sieve cells and albuminous cells in place of sieve tubes and companion cells.

The tissue systems

The tissues are grouped into three systems.

Epidermal system: the epidermis is the outermost layer, usually of one layer of parenchyma cells. Aerial parts have a waxy cuticle of cutin that reduces water loss. The cuticle is absent in roots.

• Stomata regulate transpiration and gas exchange. Each stoma has two guard cells, which are bean-shaped in dicots and dumb-bell shaped in grasses. The outer walls of guard cells are thin and the inner walls are thick. Neighbouring epidermal cells that become specialised are subsidiary cells. The stomatal aperture, guard cells and subsidiary cells together form the stomatal apparatus.
• Root hairs are unicellular elongations of root epidermal cells and absorb water and minerals.
• Trichomes are usually multicellular hairs on the shoot epidermis. They may be branched or unbranched, soft or stiff, and may be secretory. They help reduce water loss by transpiration.

Vascular bundles are of three kinds.

Anatomy of the dicot and monocot root and stem

Dicot root (young): epidermis with root hairs; a cortex of several layers of thin-walled parenchyma; a single-layered endodermis of barrel-shaped cells with Casparian strips of suberin; a pericycle of thick-walled parenchyma from which lateral roots and the vascular cambium arise; two to four xylem bundles (diarch to tetrarch) with phloem bundles in between; parenchymatous conjunctive tissue between xylem and phloem; and a small pith.

Monocot root: similar, but with more than six xylem bundles (polyarch) and a large, well-developed pith. It shows no secondary growth.

Dicot stem: the epidermis is covered with cuticle, with a few stomata and trichomes. The cortex has three zones: the hypodermis of collenchyma, the middle cortical layers of parenchyma, and the innermost endodermis, rich in starch grains and therefore called the starch sheath. The pericycle lies as patches of sclerenchyma above the bundles. Medullary rays lie between bundles. Vascular bundles are in a ring, conjoint, open and endarch. The pith is large.

Monocot stem: the hypodermis is sclerenchymatous. Vascular bundles are many and scattered in the ground tissue. Each bundle is surrounded by a sclerenchymatous bundle sheath. There is no cortex, medullary ray or pith differentiation. Bundles are conjoint and closed. Peripheral bundles are smaller than those in the centre. Phloem parenchyma is absent, and water-containing cavities are present within the bundles.

Anatomy of the leaf

The leaf has epidermis, mesophyll and vascular system.

Bulliform cells are large, empty, colourless cells. When they are turgid, the leaf surface is exposed. When they are flaccid in water stress, the leaves curl inward to minimise water loss. Vascular bundles in leaves are surrounded by thick-walled bundle sheath cells.

Secondary growth

Secondary growth is the increase in girth due to the activity of lateral meristems. It occurs in dicot stems and roots and in gymnosperms, not in monocots.

Vascular cambium. In a dicot stem, the cambium between xylem and phloem in a bundle is the intrafascicular cambium. Cells of the medullary rays next to it become meristematic and form the interfascicular cambium. The two join to form a continuous cambial ring. The ring cuts off cells on the inner side that become secondary xylem and on the outer side that become secondary phloem. The cambium is more active on the inner side, so more secondary xylem is formed. Primary xylem remains near the centre. The primary and older secondary phloem are crushed by the pressure of the growing xylem. Narrow bands of parenchyma, secondary medullary rays, pass through secondary xylem and phloem.

Annual rings. Spring wood (early wood) forms when the cambium is very active. It has wide vessels and is lighter in colour with lower density. Autumn wood (late wood) forms when the cambium is less active. It has narrow vessels and is darker with higher density. The two together form one annual ring. Counting annual rings gives the age of the tree.

Heartwood and sapwood. Heartwood is the dark central part of secondary xylem. Its cells are dead and are filled with tannins, resins, oils, gums and aromatic substances. It does not conduct water but gives mechanical support. Sapwood is the lighter, peripheral secondary xylem that conducts water and minerals.

Cork cambium. As the stem grows in girth, the outer cortical and epidermal layers break. A cork cambium (phellogen) forms in the cortex. It is a meristem of thin-walled narrow cells. It cuts off the outer cork (phellem), whose cells have suberin deposits and are impervious to water, and the inner secondary cortex (phelloderm), which is parenchymatous. Phellogen, phellem and phelloderm together form the periderm.

Bark is a non-technical term for all tissues outside the vascular cambium, namely the periderm and the secondary phloem. Early (soft) bark forms in the beginning of the season and late (hard) bark at its end.

Lenticels are lens-shaped openings in the bark. They form where the phellogen cuts off loosely arranged parenchyma (complementary cells) instead of cork. They allow exchange of gases between the outer air and the inner tissues.

Secondary growth in roots. In dicot roots the vascular cambium arises from the conjunctive tissue below the phloem bundles and from the pericycle opposite the protoxylem. It first forms a wavy ring that later becomes circular. Further events are similar to those of the dicot stem.

NEET traps

• Collenchyma is living with pectin-rich corner thickening. Sclerenchyma is dead with lignified walls.
• Protoxylem is towards the pith in stems (endarch) but towards the periphery in roots (exarch).
• Vessels are typical of angiosperms. Tracheids are the main conducting cells in gymnosperms.
• Mature sieve tube elements lack a nucleus. Companion cells have one and control them.
• Guard cells are bean-shaped in dicots and dumb-bell shaped in grasses.
• Dicot roots are di- to tetrarch. Monocot roots are polyarch with a large pith.
• Dicot stem bundles are open and in a ring. Monocot stem bundles are closed and scattered.
• Dicot stem hypodermis is collenchymatous. Monocot stem hypodermis is sclerenchymatous.
• Spring wood has wide vessels and is light. Autumn wood has narrow vessels and is dark.
• Heartwood does not conduct water. Sapwood does. Bark includes secondary phloem, not only cork.

One-liners

• Intercalary meristem is present in grasses.
• Sclereids occur in guava pulp and tea leaves.
• Collenchyma gives support to growing parts.
• Sieve plates are perforated end walls of sieve tube elements.
• Phloem parenchyma is absent in most monocots.
• Casparian strips are in the endodermis and contain suberin.
• Pericycle gives rise to lateral roots.
• The endodermis of the dicot stem is the starch sheath.
• Bulliform cells are present in the upper epidermis of grass leaves.
• Dorsiventral leaves have more stomata on the lower surface.
• Interfascicular cambium arises from medullary ray cells.
• Annual rings help to find the age of a tree.
• Phellogen is also called cork cambium.
• Periderm is phellogen with phellem and phelloderm.
• Lenticels allow gas exchange in woody stems.

Practice questions

1. The meristem responsible for the increase in girth of a stem is the

   1. shoot apical meristem
   2. lateral meristem
   3. intercalary meristem
   4. root apical meristem
   Answer

   B. lateral meristem

   Lateral meristems (vascular cambium and cork cambium) give secondary growth in thickness.

2. The thickening at the corners of collenchyma cells is made of

   1. lignin only
   2. cellulose, hemicellulose and pectin
   3. suberin and cutin
   4. chitin and wax
   Answer

   B. cellulose, hemicellulose and pectin

   Collenchyma walls are thickened with cellulose, hemicellulose and pectin; they lack lignin.

3. Sclereids are found in

   1. the epidermis of leaves
   2. the hypodermis of a sunflower stem
   3. sieve tubes of phloem
   4. the pulp of guava
   Answer

   D. the pulp of guava

   Sclereids occur in guava pulp, pear, nut shells, tea leaves and legume seed coats.

4. Vessels are a characteristic feature of

   1. algae
   2. all non-flowering plants
   3. angiosperms
   4. gymnosperms
   Answer

   C. angiosperms

   Vessels are typical of angiosperms; gymnosperm xylem has tracheids.

5. Which phloem element lacks a nucleus at maturity?

   1. Sieve tube element
   2. Phloem parenchyma
   3. Companion cell
   4. Albuminous cell
   Answer

   A. Sieve tube element

   Mature sieve tube elements have no nucleus; their function is controlled by companion cells.

6. In a root, the protoxylem lies towards the

   1. periphery, a condition called endarch
   2. centre, a condition called exarch
   3. periphery, a condition called exarch
   4. centre, a condition called endarch
   Answer

   C. periphery, a condition called exarch

   Roots are exarch: protoxylem towards the periphery. Stems are endarch.

7. Dumb-bell shaped guard cells are present in

   1. sunflower leaves
   2. dicot stems
   3. bean leaves
   4. grasses
   Answer

   D. grasses

   Guard cells are bean-shaped in dicots and dumb-bell shaped in grasses.

8. Casparian strips are found in the

   1. endodermis
   2. epidermis
   3. hypodermis
   4. pericycle
   Answer

   A. endodermis

   Endodermis cells have suberised Casparian strips on their radial and tangential walls.

9. The starch sheath of a dicot stem is another name for its

   1. bundle sheath
   2. endodermis
   3. hypodermis
   4. pericycle
   Answer

   B. endodermis

   The endodermis of the dicot stem is rich in starch grains.

10. Vascular bundles are scattered in the ground tissue of a

    1. monocot stem
    2. dicot stem
    3. young dicot stem after secondary growth
    4. dicot root
    Answer

    A. monocot stem

    A monocot stem has many scattered, closed, conjoint bundles; a dicot stem has a ring.

11. Bulliform cells help in

    1. photosynthesis
    2. storage of starch
    3. curling of the leaf during water stress
    4. gas exchange
    Answer

    C. curling of the leaf during water stress

    Flaccid bulliform cells make the grass leaf curl inward and reduce water loss.

12. Spring wood is characterised by

    1. narrow vessels and a darker colour
    2. wide vessels and a darker colour
    3. narrow vessels and a lighter colour
    4. wide vessels and a lighter colour
    Answer

    D. wide vessels and a lighter colour

    Spring wood forms when the cambium is very active and has wide vessels and lower density.

13. The dark colour of heartwood is due to deposition of

    1. tannins, resins, gums and oils
    2. chlorophyll and carotene
    3. suberin only
    4. cellulose only
    Answer

    A. tannins, resins, gums and oils

    Organic compounds such as tannins, resins and gums fill the dead cells of heartwood.

14. The substance that makes cork cells impervious to water is

    1. lignin
    2. cellulose
    3. suberin
    4. pectin
    Answer

    C. suberin

    Phellem cells have suberin deposits in their walls.

15. Lenticels function in

    1. storage of food
    2. gaseous exchange in woody stems
    3. secretion of resin
    4. absorption of water
    Answer

    B. gaseous exchange in woody stems

    Lenticels are lens-shaped openings in the bark that allow gas exchange.

16. The periderm consists of

    1. phellogen, phellem and secondary phloem
    2. vascular cambium, phellem and phelloderm
    3. phellem, phelloderm and secondary xylem
    4. phellogen, phellem and phelloderm
    Answer

    D. phellogen, phellem and phelloderm

    Periderm is the cork cambium with the tissues it cuts off: cork outside, secondary cortex inside.

17. Given below are two statements: Statement I: Collenchyma has walls thickened with lignin. Statement II: Sclerenchyma cells have thin walls and a large lumen. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Collenchyma is thickened with pectin and cellulose; sclerenchyma has thick lignified walls with a narrow lumen.

18. Given below are two statements: Statement I: Phloem parenchyma is absent in most monocots. Statement II: Phloem fibres are generally absent in primary phloem. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Both are correct.

19. Given below are two statements: Statement I: Protoxylem lies towards the pith in roots. Statement II: Metaxylem is the later-formed primary xylem. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    D. Statement I is incorrect but Statement II is correct

    In roots the protoxylem is towards the periphery, so I is incorrect; metaxylem forms later, so II is correct.

20. Given below are two statements: Statement I: Tracheids and vessels are dead at maturity. Statement II: Xylem parenchyma cells are dead. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Tracheids and vessels are dead; xylem parenchyma is living.

21. Which of the following statements are correct? 1. In radial bundles xylem and phloem lie on different radii. 2. In conjoint bundles xylem and phloem lie on the same radius. 3. The vascular bundles of a dicot stem are closed.

    1. 1 and 2 only
    2. 2 and 3 only
    3. 1 and 3 only
    4. 1, 2 and 3
    Answer

    A. 1 and 2 only

    Dicot stem bundles are open, so statement 3 is wrong.

22. Given below are two statements: Statement I: The vascular bundles of a dicot stem are arranged in a ring. Statement II: The hypodermis of a monocot stem is parenchymatous. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    A monocot stem has a sclerenchymatous hypodermis.

23. Given below are two statements: Statement I: Dicot roots have more than six xylem bundles. Statement II: Monocot roots have a small pith. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    B. Both Statement I and Statement II are incorrect

    Dicot roots are di- to tetrarch and monocot roots are polyarch with a large pith.

24. Given below are two statements: Statement I: Intrafascicular cambium lies within the vascular bundles of a dicot stem. Statement II: Interfascicular cambium arises from the cells of medullary rays. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    A. Both Statement I and Statement II are correct

    Both are correct and together form the cambial ring.

25. Which of the following statements are correct? 1. Annual rings form because the cambium is active seasonally. 2. Sapwood conducts water and minerals. 3. Heartwood conducts water and minerals.

    1. 1 and 2 only
    2. 1 and 3 only
    3. 2 and 3 only
    4. 1, 2 and 3
    Answer

    A. 1 and 2 only

    Heartwood is dead and gives support only.

26. Given below are two statements: Statement I: Phellogen cuts off phellem on its outer side and phelloderm on its inner side. Statement II: Bark consists only of cork. Choose the correct option.

    1. Both Statement I and Statement II are correct
    2. Both Statement I and Statement II are incorrect
    3. Statement I is correct but Statement II is incorrect
    4. Statement I is incorrect but Statement II is correct
    Answer

    C. Statement I is correct but Statement II is incorrect

    Bark includes all tissues outside the vascular cambium: periderm and secondary phloem.

27. Assertion (A): Grasses regrow quickly after being grazed. Reason (R): Intercalary meristem lies between mature tissues and regenerates the removed parts.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    Intercalary meristem at nodes or internode bases adds new tissue.

28. Assertion (A): A dicot stem has its vascular bundles in a ring. Reason (R): A monocot stem has scattered vascular bundles.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    B. Both A and R are true but R is not the correct explanation of A

    Both true, but the second fact does not explain the first.

29. Assertion (A): Root hairs are unicellular outgrowths of the root epidermis. Reason (R): The root epidermis has a thick cuticle and many stomata.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    C. A is true but R is false

    Root epidermis lacks both cuticle and stomata, so R is false.

30. Assertion (A): Spring wood is darker than autumn wood. Reason (R): Spring wood has wider xylem vessels.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    D. A is false but R is true

    Spring wood is lighter and has wide vessels; A is false, R is true.

31. Assertion (A): Lenticels allow gas exchange in woody stems. Reason (R): Lenticels are lens-shaped openings made of loosely arranged cells that rupture the epidermis.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    A. Both A and R are true and R is the correct explanation of A

    The loose complementary cells leave air spaces for gas exchange.

32. Assertion (A): Phellem cells are dead at maturity. Reason (R): Phellem cells have thin cellulosic walls without suberin.

    1. Both A and R are true and R is the correct explanation of A
    2. Both A and R are true but R is not the correct explanation of A
    3. A is true but R is false
    4. A is false but R is true
    Answer

    C. A is true but R is false

    Phellem walls are suberised, which is why the cells are dead and impermeable; R is false.

33. Match List I with List II. List I: a. Parenchyma b. Collenchyma c. Sclerenchyma d. Xylem List II: i. Lignified dead cells ii. Photosynthesis and storage iii. Pectin thickening at corners iv. Water conduction

    1. a-iii, b-ii, c-i, d-iv
    2. a-ii, b-iii, c-iv, d-i
    3. a-i, b-iii, c-ii, d-iv
    4. a-ii, b-iii, c-i, d-iv
    Answer

    D. a-ii, b-iii, c-i, d-iv

    Parenchyma stores and photosynthesises; collenchyma has pectin corners; sclerenchyma is lignified; xylem conducts water.

34. Match List I with List II. List I: a. Guard cell b. Companion cell c. Bulliform cell d. Root hair List II: i. Leaf curling ii. Water absorption iii. Stomatal opening iv. Support to sieve tube

    1. a-iii, b-iv, c-ii, d-i
    2. a-iv, b-iii, c-i, d-ii
    3. a-i, b-iv, c-iii, d-ii
    4. a-iii, b-iv, c-i, d-ii
    Answer

    D. a-iii, b-iv, c-i, d-ii

    Guard cells open stomata; companion cells support sieve tubes; bulliform cells curl leaves; root hairs absorb water.

35. Match List I with List II. List I: a. Endodermis b. Pericycle c. Hypodermis of dicot stem d. Pith of dicot stem List II: i. Large parenchymatous central region ii. Collenchymatous iii. Suberin bands iv. Origin of lateral roots

    1. a-iii, b-iv, c-i, d-ii
    2. a-iii, b-iv, c-ii, d-i
    3. a-iv, b-iii, c-ii, d-i
    4. a-ii, b-iv, c-iii, d-i
    Answer

    B. a-iii, b-iv, c-ii, d-i

    Endodermis has Casparian strips of suberin; pericycle forms lateral roots; hypodermis is collenchyma; pith is large and parenchymatous.

36. Match List I with List II. List I: a. Phellogen b. Phellem c. Phelloderm d. Lenticel List II: i. Secondary cortex ii. Cork cambium iii. Gas exchange iv. Cork

    1. a-iv, b-ii, c-i, d-iii
    2. a-ii, b-iv, c-i, d-iii
    3. a-ii, b-iv, c-iii, d-i
    4. a-i, b-iv, c-ii, d-iii
    Answer

    B. a-ii, b-iv, c-i, d-iii

    Phellogen is the cork cambium; phellem is cork; phelloderm is secondary cortex; lenticels allow gas exchange.

37. Match List I with List II. List I: a. Heartwood b. Sapwood c. Spring wood d. Autumn wood List II: i. Narrow vessels ii. Conducts water iii. Dark, does not conduct iv. Wide vessels

    1. a-iii, b-ii, c-i, d-iv
    2. a-iii, b-i, c-iv, d-ii
    3. a-ii, b-iii, c-iv, d-i
    4. a-iii, b-ii, c-iv, d-i
    Answer

    D. a-iii, b-ii, c-iv, d-i

    Heartwood is dark and non-conducting; sapwood conducts; spring wood has wide vessels; autumn wood has narrow vessels.

38. Match List I with List II. List I: a. Dicot root b. Monocot root c. Dicot leaf d. Monocot leaf List II: i. Isobilateral ii. Polyarch iii. Diarch to tetrarch iv. Palisade and spongy mesophyll

    1. a-ii, b-iii, c-iv, d-i
    2. a-iii, b-ii, c-iv, d-i
    3. a-iii, b-ii, c-i, d-iv
    4. a-iv, b-ii, c-iii, d-i
    Answer

    B. a-iii, b-ii, c-iv, d-i

    Dicot root is di- to tetrarch; monocot root is polyarch; dicot leaf has palisade and spongy tissue; monocot leaf is isobilateral.

39. A trunk is cut and 40 annual rings are counted. This indicates

    1. 40 lenticels
    2. 40 lateral branches
    3. about 40 years of seasonal cambial activity
    4. 40 cork layers
    Answer

    C. about 40 years of seasonal cambial activity

    One annual ring (spring plus autumn wood) forms each year.

40. A stem section shows scattered conjoint closed bundles with a sclerenchymatous hypodermis and no cortex or pith differentiation. The stem is

    1. a woody dicot
    2. dicot
    3. gymnosperm
    4. monocot
    Answer

    D. monocot

    These are the features of a monocot stem.

41. A ring of bark, including the tissue just outside the cambium, is removed all round a tree trunk. Which tissue is lost?

    1. Pith
    2. Secondary xylem
    3. Primary xylem
    4. Secondary phloem
    Answer

    D. Secondary phloem

    Bark includes the periderm and the secondary phloem, which carries food.

42. A leaf section shows elongated palisade cells under the upper epidermis, loosely arranged spongy cells below and more stomata on the lower surface. The leaf is

    1. isobilateral, as in a monocot
    2. dorsiventral, as in a dicot
    3. dorsiventral, as in a monocot
    4. isobilateral, as in a dicot
    Answer

    B. dorsiventral, as in a dicot

    Differentiated mesophyll with more stomata beneath is dorsiventral, typical of dicots.

43. A root section shows eight xylem bundles, a large pith and no cambium. The root is

    1. monocot
    2. dicot
    3. a gymnosperm root with secondary growth
    4. dicot with tetrarch xylem
    Answer

    A. monocot

    More than six bundles (polyarch) with a large pith is a monocot root.

44. A wood sample is dark, its cells are dead and filled with tannins. It gives strength but cannot conduct water. It is

    1. spring wood
    2. sapwood
    3. heartwood
    4. secondary phloem
    Answer

    C. heartwood

    Heartwood is dark, dead and non-conducting but gives mechanical support.

45. In an old dicot stem, which tissue is crushed by pressure from the growing secondary xylem?

    1. Primary phloem
    2. Heartwood
    3. Primary xylem
    4. Secondary xylem
    Answer

    A. Primary phloem

    Primary and older secondary phloem are crushed; primary xylem remains near the centre.