Question | Answer |
Radicle | First structure to emerge upon germination |
4 functions of roots | Anchorage, absorption, conduction, storge |
What 2 hormones are produced by roots? | Cytokinins, gibberellins |
Secondary metabolites | Chemicals produced by plant but not needed for plant's survival; can provide protection |
Examples of secondary metabolites | Nicotine, tannins |
2 types of root systems | Taproot and fibrous |
What plants have taproot | Magnoliids and eudicots |
Taproot | Radicle keeps growing deeper and smaller roots come off it |
What plants have fibrous roots | Monocots |
Fibrous roots | Radicle grows into short-lived taproot that is replaced by adventitious roots growing from hypocotyl |
Rootcap | Produced by apical meristem and forms protective armor around it |
Mucigel | Slime secreted to lubricate root |
Rhizosphere | Zone of mucigel around tip of root |
Function of rhizosphere | Prevent desiccation and feed bacteria that convert unusable nitrogen to NO3 |
What do plants use NO3 for? | To build amino acids, proteins, and compounds like chlorophyll A and B |
How does the lateral root get outside? | Produces an enzyme to break through cortex and epidermis |
Columella | Directs root growth through gravitropism |
Gravitropism | Growing in response to gravity |
How are amyloplasts involved in gravitropism? | Detect direction of gravity so roots can grow down |
2 apical meristem organizations | Open and closed |
Open | One layer of initials, not visible |
Closed | 3 layers of initials |
Top initial layer | Vascular |
Middle initial layer | Ground |
Bottom initial layer | Dermal and root cap |
Quiescent center | Area of initials, mitotically active in early root development, no divisions in older roots |
When does a quiescent center reactivate? | When root tip is injured |
3 regions of a root | Cell division, elongation, maturation |
Root epidermis | Most 1 cell layer thick, no or poorly developed cuticle, involved in absorption |
4 special epidermal features | Multi-layers, velamen, root hairs, trichoblast |
Velamen | Multiple-layered epidermis found in epaphytes like orchids |
Root hairs | Increase surface area for absorption |
Trichoblast | Epidermal cell that gives rise to a root hair |
Hypodermis | Most with secondary cell walls, normally several layers, lack suberin |
Exodermis | Primary or secondary cell wall, single layer, Casparian strip |
Endodermis | Innermost layer of cortex surrounding vascular tissue, single layer, initially primary cell wall, Casparian strip |
Casparian strip | Layer of suberin , osmotic barrier |
Endodermal cells with secondary cell walls | Above root hair region, suberin lined, passage cells |
Passage cells | Still living with no secondary cell wall, still allows lateral transport for sugar and water |
Vascular cylinder | Inside endodermis |
Pericylce | 1 or more layers of parenchyma cells just inside endodermis that completely surrounds the xylem and phloem |
Xylem arches in dicots | Tetraarch and pantaarch |
Xylem arches in monocots | Polyarch, pith |
Origin of lateral roots | Pericycle |
Pneumataphores | Grow against gravity to go above water for gas exchange, lots of intercellular spaces (aerenchyma) |
Adventitious roots | Roots with origin other than pericycle |
2 types of adventitious roots | Aerial and prop roots |
Aerial roots | Above ground, involved in absorption, can have suction cups on ends |
Prop roots | Type of aerial root at base of stem, provides support |
Where do vascular and cork cambium come from | Vascular tissue system |
Woody perennial roots | Horizontal growth, top 6 inches of soil |
Vertical anchoring roots | Several feet deep |
Feeder roots | Grow up and out, small <1/16 inch diameter, replaced regularly, grow in upper layer of soil where there are more nutrients |