Biology

NIOS Biology Class 12 Root System Terminal Solutions

The chapter NIOS Class 12 Biology Chapter 6 Root System covers the structure and functions of roots in plants. Students learn about root modifications, absorption of water, and adaptations. The solved terminal exercises provide clear answers to support revision and exam preparation.

This chapter helps students connect structural details with plant physiology. It also highlights the importance of roots in maintaining plant stability and survival, making it an essential part of NIOS Biology.

NIOS Class 12 Biology Chapter 6 Root System

1. Describe any four adventitious root modifications.

(i) Tuberous root: Swollen roots developing from nodes of the prostrate stem
(ii) Fasciculated root: Swollen roots developing in clusters from the stem
(iii) Nodulose roots: Only the apices of roots become swollen like single beads.
(iv) Moniliform roots: Roots alternately swollen and constricted, presenting a beaded or moniliform appearance
(v) Annulated roots: Looks as if formed by several discs placed one above the other.
(vi) Assimilatory roots: Roots, when exposed to su, develop chlorophyll, turn green, and manufacture food.
(vii) Epiphytic roots: Aerial roots of epiphytes are greenish and covered with spongy tissue (Velamen) with which they absorb atmospheric moisture
(viii) Pneumatophores/Respiratory roots: Some roots grow vertically up (negatively geotropic) into the air. Exposed root tips possess minute pores through which roots respire, appearing like conical spikes coming out of water.
(ix) Sucking roots or haustoria: Parasitic plants give out sucking roots or haustoria, which penetrate the living host plant and suck food from the phloem.
(x) Prop roots: Roots develop from tree branches, hang downwards, and ultimately penetrate the ground, thus providing support to heavy branches.
(xi) Stilt roots: Extra roots developing from nodes near the base of the stem grow obliquely downwards and penetrate the soil, giving strong anchorage.
(xii) Climbing roots: Weak climbers twine around and clasp the support with the help of climbing roots arising from their nodes.
(xiii) Clinging roots: Special clinging roots arise, enter the crevices of support, and fix the epiphyte.
(xiv) Floating roots: Spongy, floating roots filled with air, arise from nodes of some aquatic plants, and help in floating and respiration

2. Give one point of difference between:

(i) Tap root and adventitious root (ii) Prop and stilt roots

(iii) Protoxylem and metaxylem (iv) Phelloderm and periderm

(v) Vascular cambium and cork cambium

The tap root system is the root system that develops from the radicle and continues as the primary root (tap root), which gives off lateral roots. Adventitious roots are roots that develop from any part of the plant except the radicle.
Prop roots are roots that develop from tree branches, hang downwards, and ultimately penetrate the ground, thus providing support to heavy branches. Stilt roots are extra roots developing from nodes near the base of the stem, grow obliquely downwards, and penetrate the soil, giving strong anchorage.
Protoxylem is the first-formed xylem element, and metaxylem is the xylem that is differentiated later and has wider vessels and tracheids.
Phelloderm is the secondary cortex, and periderm is the combined layer formed by phellogen, phellem, and phelloderm.
Vascular cambium originates as a strip in pericycle cells lying outside the protoxylem and in conjunctive tissue inner to each phloem bundle. Cork cambium (phellogen) also differentiates in the pericycle and gives rise to cork (phellem) towards the periphery and secondary cortex (phelloderm) towards the inside.

3. Describe the various types of edible roots that you have studied.

Tuberous root: Swollen roots developing from nodes of the prostrate stem. E.g.. Sweet potato.
Nodulose roots: Only the apices of roots become swollen like single beads. E.g.. Mango ginger.
Conical root with the base broad and tapering gradually towards the apex. E.g.. Carrot.
The fusiform root, which is swollen in the middle, tapers towards both ends. E.g.,. Radish.

4. What are pneumatophores? Where are they found and what is their function?

Pneumatophores/Respiratory roots: Some roots grow vertically up (negatively geotropic) into the air. Exposed root tips possess minute pores through which roots respire, appearing like conical spikes coming out of water. They are seen in marshy plants in mangroves.

5. Describe secondary growth in dicot roots.

The tissues involved in secondary growth of dicot roots are lateral meristems, i.e., vascular cambium and cork cambium.

Secondary growth is as follows-

Pericycle cells outside the protoxylem divide to form a strip of cambium.
Another strip of vascular cambium appears in the conjunctive tissue on the inner side of the phloem bundle.
These two vascular cambium strips join laterally to form a ring, which may initially be wavy but later becomes circular due to overproduction of secondary xylem tissue inner to primary phloem.
Cambium cells consist of brick-shaped cells that divide and add cells on either side, i.e., towards the periphery and centre. Those added towards the periphery differentiate into secondary phloem, and the ones formed towards the centre differentiate into secondary xylem.
Secondary tissue formed outer to the protoxylem bundle differentiates into a prominent primary medullary ray; thus, protoxylem does not get crushed.
Later, cork cambium (Phellogen) also differentiates in the pericycle.
The cork cambium divides and gives rise to cork (Phellem) towards the outside and secondary cortex (Phelloderm) towards the inside.
All three layers, i.e,. Phellogen, Phellem, and Phelloderm, together form the Periderm of the root and have a protective function.
Finally, all the primary tissues outside the developing cork (i.e., endodermis, cortex, and epiblema) are sloughed off.

6. Why is it difficult to break the lateral roots from the main root?

The lateral roots are endogenous, originate from the deeper layers such as the pericycle, and are difficult to break from the main root. The originating root cells form a hump in the endodermis and will later penetrate the cortex to emerge as a lateral branch.

7. What is periderm? How is it formed?

The cork cambium or phellogen, phellem or cork, and the secondary cortex or phelloderm, together form the periderm. The periderm in the root is protective in function.

8. Give four characteristics by which you can identify a root.

The main features of roots by which you can recognise them are:

Non-green due to the absence of chlorophyll;
Not divided into nodes and internodes;
Absence of leaves and buds;
Positively geotropic (grow towards gravity);
Positively hydrotropic (grows towards water);
Negatively phototropic (grow away from light).

9. What is the function of the region of maturation?

The region of maturation is next to the region of elongation, wherein the cells mature and differentiate into various tissues, constituting.

(i) Root hair or piliferous region having unicellular hairs which absorb water and mineral salts from the soil.
(ii) Permanent region which lies behind the root hair zone and is without hairs. It produces lateral roots, anchors the plant in the soil, and conducts water and minerals upwards.

10. Give one example each of plants having pneumatophores, climbing roots, floating roots, and haustoria.

Pneumatophores: Rhizophora
Climbing roots: Money plant
Floating roots: Jussiaea
Haustoria: Cuscuta

11. A cross-section of a plant organ when seen under the microscope shows radial vascular bundles, exarch xylem, single-layered pericycle, and unicellular hair. What organ is it?

Root.

12. Name the meristematic tissues that help the dicot roots to grow in length and girth.

Lateral meristems- vascular cambium and cork cambium.

13. Name the modification of the root that supports tree branches.

Prop roots.

14. If a transverse section of the root shows a polyarch condition of vascular bundles, a large pith, and no cambium, which type of root will it be?

Monocot root.

15. Differentiate between the stele of a dicot and a monocot root.

Dicot root

Pericycle: Inner to endodermis lies a single layer of pericycle. It is the seat of origin of lateral roots and vascular cambium, and cork cambium during secondary growth.
Vascular bundle: It consists of xylem and phloem patches lying on alternate radii, i.e., it is radial. Xylem is exarch, where protoxylem (first formed, having narrow vessels and tracheids) lies towards the periphery and metaxylem (differentiates later, has wider vessels and tracheids) lies towards the center.
Depending upon the number of xylem patches, a root may be diarch (di-2 patches) to hexarch (hexa-6 patches).
Pith: Sometimes the metaxylem of all xylem patches meet in the centre, and in that case, pith is absent or is small and parenchymatous.
Conjunctive parenchyma: Parenchyma that separates xylem and phloem lying on different radii.

Monocot root

Pericycle: Single-layered, having polygonal thin thin-walled cells. The lateral roots originate from this layer.
Vascular bundle: It consists of many patches of xylem and phloem arranged radially. The xylem is exarch and polyarch (poly-many).
Pith: Is situated in the center, large, well-developed, parenchymatous or sclerenchymatous, and stores food.
Conjunctive Parenchyma: Is located between the strands of xylem and phloem.