Lecture Eight

Question 1

purpose of roots

Answer 1

Anchor the plant in the soil (and stabilize the soil).

Support for the upright growth of the plant

Site of symbiotic relationship with particular beneficial fungi and bacteria

Absorb water and dissolved minerals from the soil.

Store nutrients like starch for subsequent use by the plant

Question 2

angiosperm

Answer 2

flowering plants (have two types of roots)

Question 3

radicle

Answer 3

embryonic root

Question 4

lateral root (or secondary root)

Answer 4

arise from primary root and tertiary roots arise from secondary

Question 5

adventitious or fibrous root

Answer 5

in plants of this type, the primary root, which originates from the radicle, weakens prior to maturity and new, vigorous, adventitious roots arise from stem tissue

grow from nodes and internodes

originate from parenchyma cells in the cortex

Question 6

internal root structure comprised of…

Answer 6

root cap, root apical meristem, region/zone elongation, region of differentiation, root-hairs

Question 7

root cap

Answer 7

Shaped like a thimble, this structure covers the tip of the root and provides protection as the root drives into the soil.

These cells are produced by the root’s apical meristem which is just behind the root cap.

The outer cells of the root cap are continuously being worn away and new cells are added to the inner portion.

The cells may be covered with a lubricating slime.

Question 8

root apical meristem

Answer 8

The cells here divide rapidly to form new cells.

New cells are laid down toward the root cap to replace those worn away during root growth, and also laid down away from the root cap.

These new cells laid away from the root cap elongate and then mature into more specialized root tissues.

Question 9

region/zone elongation

Answer 9

in this region the cells previously produced by the root apical meristem undergo rapid elongation

contains protoderm, procambium, and ground meristem

Question 10

protoderm

Answer 10

these are new cells laid down toward the exterior of the root which will mature to become the root dermal tissue (primarily epidermis cells).

Question 11

procambium

Answer 11

these new cells in the central part of the root will mature to become the the vascular tissue (xylem, phloem and vascular cambium) which is labeled in the cartoon as vascular cylinder.

Question 12

ground meristem

Answer 12

these are the new cells lying between the protoderm and procambium that will mature to become the cortex tissue (primarily parenchyma)

Question 13

region of differentiation (region of maturation)

Answer 13

here the root becomes thicker and secondary or lateral roots are initiated. In this region the protoderm, procambium and ground meristem cells undergo differentiation into the specialized cells associated with the dermal, vascular and cortex tissues

Question 14

root hairs

Answer 14

Root hairs are fine outgrowths of epidermis cell walls and membranes. They increase the area of absorption of the root.

Question 15

What two processes result in root growth?

Answer 15

production of new cells and elongation/increase in volume of cells

Question 16

Protoderm will mature into what type of tissue?

Answer 16

dermal tissue, epidermis

Question 17

Procambium will mature into what type of tissue?

Answer 17

vascular tissue

Question 18

Ground Meristem will mature into what type of tissue?

Answer 18

cortex

Question 19

epidermis

Answer 19

one-cell thick layer of cells surrounding root

no waxy covering because it’s underground

Question 20

cotex

Answer 20

cells inside the epidermis

consist of parenchyma cells with numerous intercullular spaces

Question 21

endodermis

Answer 21

innermost cells of the cortex

rectangular in shape with thicker walls, stacked close together, band-like deposit of waterproof suberin

Question 22

casparian strip

Answer 22

thick band of suberin

closes up the intercellular space between cells

forms barrier to the water that has been moving freely through intercellular spaces and forces water to instead move internally into the xlylem

Question 23

xylem shape

Answer 23

typically an X (sometimes more round than a distinct X)

Question 24

cortex functions

Answer 24

allows for the diffusion of water, minerals and oxygen from the root hairs inwards.

stores food reserves, especially starch.

the endodermis, with the aid of the Casparian strips, facilitates the regulated movement of water from cortex to xylem.

Question 25

Vascular Cylinder or Stele

Answer 25

begins just inside the endodermis

Question 26

pericycle

Answer 26

The first set of cells you encounter as you move into the vascular cylinder is a single layer of tightly packed cells

divide and produce new cells

Question 27

How could you tell the difference between a monocot and dicot root based on the vascular cylinder?

Answer 27

cross section has xylem as an X, it’s a dicot

if it has bundles of xylem in circular arrangement it’s a monocot

Question 28

herbaceous plants

Answer 28

above ground plant parts die back to the soil surface

grow in length and diameter the same way roots do

typically do not thicken very much and rely instead on branching to grow laterally

Question 29

Dicotyledonous Stems

Answer 29

comprised of epidermis, cortex, vascular bundle and pith

Question 30

Monocotyledonous Stems

Answer 30

same tissues as dicotyledonous

Question 31

Herbaceous perennials die back to the ground in the spring. Where do they get the energy to grow the next spring, and from what tissue do new shoots emerge?

Answer 31

energy from carbs and water stored in their roots

new tissue is formed from stems that have small buds with meristems in them to provide new shoots

Question 32

Dicots typically have a pith while monocots do not. Why?

Answer 32

because of the way the stem is formed… there is no inside or outside of cell system in monocots… dicots have inner and outer structure

Question 33

Could you distinguish between a monocot and dicot stem based on the arrangement of the vascular bundles?

Answer 33

circle = dicot
scatter = monocot

Question 34

Monocot vascular bundle

Answer 34

The phloem is always oriented toward the outside of the plant and the xylem toward the inside. There is no cambium and no secondary growth. Around the outside of the vascular bundle is a layer of parenchyma cells called the bundle sheath. I’ll refer to this layer of cells later when we review photosynthesis. For now we will consider it a protective covering and supportive sheath around the vascular bundle.

Question 35

palm tree is an exception because… (don’t need to memorize)

Answer 35

it is a monocot but the primary stems do increase in girth without a secondary cambium