Biology Today — January 2018

Underground

stem

modications Tuber is an oval or spherical

underground swollen structure

that does not bear adventitious

roots, e.g., potato (Solanum

tuberosum).

Leaf

Stem

Stem tuber

Eye

Root Scar of scale leaf

Fig.:Tubers of potato

Rhizome is a perennial fleshy

underground stem which

continues its growth indefinitely in

the soil producing new leaves or

aerial shoots during the favourable

season and perennation during

the unfavourable season, e.g.,

Dryopteris.

Circinately

coiled young

leaves

Leaf base

Rhizome

Adventitious

roots

Fig.:Rootstock rhizome

ofDryopteris

Bulb is an underground pyriform-spherical modified shoot having highly reduced convex

or slightly conical disc-shaped stem and several fleshy scales enclosing a terminal bud.

Bulbs are of two types:

(a) Tunicated bulb consists of concentric layers of fleshy scales surrounding the

reduced stem having terminal bud. The outermost few scales of the bulb become dry and

membranous forming a protective covering called tunic. These bulbs are of two types-

(i) Simple tunicated bulbs, e.g., Allium cepa (onion) and (ii) Compound tunicated

bulbs, e.g., Allium sativum (garlic).

(b) Scaly: A tunic or covering sheath is absent. The fleshy scales are narrow and overlap

one another on margins only, e.g., lily.

Adventitious root

Bulb

Tunip

Fig.:Bulb of Onion

Corm is a short, thick, swollen,

usually unbranched, spherical or

subspherical underground stem

which grows vertically in the

soil and is formed annually. e.g.,

Amorphophallus, Colocasia.

Node

Internode

Scale node

Corm

Daughter

corm

Adventitious root

Fig.:Corm ofAmorphophallus

Sucker is a special non-green slender

stem branch which arises from the

underground base of an erect shoot

and grows horizontally in the soil and

ultimately comes out to form a new

aerial shoot. E.g., Chrysanthemum,

mint.

Leaves

Aerial

shoot

Scale leaf Sucker

Adventitious

Fig.:Sucker of mint roots

Functions

of stem

Storage of food,e.g.,

rhizome of ginger,

tuber of potato, etc.

Synthesis of food,e.g.,

phylloclade ofOpuntia,

cladode ofRuscus, etc.

Perennation and vegetative

propagation,e.g.,corm of

Colocasia,rhizome of ginger, etc.

Protection,e.g.,

thorns ofDuranta,

Bougainvillea, etc.

Support,e.g., tendrils

of grapevine, hooks

ofArtabotrys, etc.

Secondary

(or accessory)

functions

Bears leaves and holds them

in such a position so as to

provide maximum sunlight.

Conducts water and mineral

nutrients from the roots to the

leaves, flowers and fruits.

Conducts organic food

from the leaves to the

roots and storage organs.

Holds flowers in sucha

position so as to facilitate

pollination and fertilisation.

Primary

functions

MORPHOLOGY OF LEAF

• Leaf is a green, exogenous lateral flattened outgrowth borne on the node of a stem or branch and is specialised to perform
  photosynthesis.

MPP-9 CLASS XI ANSWER KEY

1. (b) 2. (d) 3. (d) 4. (b) 5. (d)


2. (a) 7. (b) 8. (a) 9. (c) 10. (d)


3. (a) 12. (b) 13. (c) 14. (a) 15. (d)


4. (b) 17. (b) 18. (c) 19. (c) 20. (a)


5. (b) 22. (b) 23. (a) 24. (c) 25. (a)


6. (c) 27. (d) 28. (d) 29. (a) 30. (c)


7. (c) 32. (c) 33. (c) 34. (d) 35. (d)


8. (a) 37. (b) 38. (c) 39. (d) 40. (c)


9. Cladode Pg. 22


10. Umbel Pg. 27


11. Founder eect Pg. 63


12. Dryopithecus africanus Pg. 67

ANSWERS WHO AM I ...