Chapter 24

Question 1

Primary function of roots

Answer 1

Anchorage and Absorption, others are storage and conduction, synthesize wife variety of secondary metabolites (nicotine)

Question 2

Cytokinins and gibberellins

Answer 2

Hormones synthesized in meristematic regions of the roots are transported upward in the xylem to the aerial parts to stimulate growth and development

Question 3

Clonal regeneration

Answer 3

Redistribution of water in soil

Secretion of a vast array of substances into the primary root, termed the taproot that grows directly downward giving rise to Lateral roots

Question 4

Roots environmental parameters

Answer 4

Gravity

Light

Gradients of moisture

Temperature

Nutrients in soil

Question 5

Rhizosphere

Answer 5

The volume of soil around living plant roots that is influenced by root activity

Question 6

Rootcap

Answer 6

Thimblelike mass of living parenchyma cells that protects the apical meristem behind it and aids the root in its penetration of the soil

Question 7

Mucilage

Answer 7

As roots grow longer and rootcap is pushed forward, cells on the periphery of rootcap secrete this in large amounts to lubricate the root during its passage through the soil

Question 8

Border cells

Answer 8

Programmed to separate from the rootcap and each other to reach rootcap periphery, they undergo changes in gene expression that enable them to produce and exude specific proteins that are completely different from those of the rootcap, new cells are them added

Question 9

Border cell functions

Answer 9

Protect apical meristem from infection, maintainence if intimate root soil contact, mobilization of essential elements for uptake by the roots, short term protection from drying out and specific attraction or repulsion of bacteria, decrease the frictional resistance for the growing root

Question 10

Rootcap components

Answer 10

Central column of cells, the columella, a Lateral portion, the Lateral rootcap surrounds the columella.

The columella perceived gravity and water potential gradients

Question 11

Promeristem

Answer 11

Most distal and least differentiated part of apical meristem, composed of the initials and their immediate derivatives

Question 12

Type of root apical organization

Answer 12

Closed type: rootcap, vascular cylinder, and cortex (independent layers) each has own initials

Open type: cortex and rootcap arise from one group of initials

Question 13

Quiescent center

Answer 13

The inactive reaction of apical meristem, which corresponds to the promeristem. Does not include initials of the rootcap.

Able to repopulate the bordering meristematic regions when they are injured

Question 14

Region of elongation

Answer 14

Few millimeters, causes increase in length of roots. Above this region no growth occurs

Question 15

Region of cell division

Answer 15

Region of actively dividing cells in apical meristem

Question 16

Region of maturation

Answer 16

Differentiation in which most of the cells of the primary tissues mature. Includes Root hairs zone

Question 17

3 tissue systems of root in primary stage

Answer 17

Epidermis, cortex, and vascular tissues

Question 18

Cortex

Answer 18

Occupies greatest area of the primary body of most roots

The plastids of cortical cells store starch but are devoid of chlorophyll

Gymonosperms and angiosperm
Roots shed cortex early, remaining parenchymatous

Monocots and herbaceous eudicots the cortex is retained for life

Question 19

Substances moving across cortex pathways

Answer 19

Symplastic pathway: moving from one protoplast to another by way of plasmodesmata

Apoplastic pathway: via cell walls or both

Question 20

Endodermis Casparian strips

Answer 20

Innermost layer of cortex compactly arranged and lacks air spaces in anticlinical walls. Impregnated with suberin and lignin making cell wall hydrophobic

Plasma membranes of mesodermal cells attach to these strips

Development is followed by deposition of suberin lamella and of a cellulosic layer too (reduce water loss and defend against microorganisms)

Question 21

Air roots or pneumatophores

Answer 21

Grow upward out of the mud and so provide adequate aeration via numerous lenticles and a broad cortex composed of aerenchyma