L4: Meristems II, Secondary growth and vascular system

Question 1

What is meant by the root:shoot ratio?

Answer 1

Balance needs to be maintained between total SA available for food manufacturing and SA available for water & mineral absorption.

Question 2

What happens to the root:shoot ratio as plants age?

Answer 2

Decreases gradually.

Question 3

What trend do roots follow as they grow through soil?

Answer 3

Follow the path of least resistance.

Question 4

What is the rootcap?

Answer 4

Mass of living parenchyma cells that protects apical meristem and aids in penetration of the soil.

Question 5

What is produced by cells in the root cap? What does it do?

Answer 5

Mucilage; lubricates root during passage through soil.

Question 6

What are the mucilage-producing cells called?

Answer 6

Border cells

Question 7

What are some additional roles of border cells and their exudates?

Answer 7

Protect meristem from infection
Maintaining root-soil contact
Mobilization of elements taken up by roots
Short-term desiccation prevention
Specific bacteria attraction or repulsion

Question 8

Why is the rootcap called the multifunctional molecular relay station?

Answer 8

Because in addition to protection, it senses, processes, and transmits signals to meristem and elongation region of the root.

Question 9

What is the columella of the root cap?

Answer 9

Central column of cells.

Question 10

What is the lateral rootcap?

Answer 10

Lateral portion of cells on the rootcap that surrounds columella.

Question 11

What part of the rootcap senses gravity and water potential gradients?

Answer 11

Columella.

Question 12

What is the difference between open type and closed type meristems?

Answer 12

Closed type: rootcap, vascular cylinder, and cortex are their own individual layers and have their own initials.
Open type: all regions arise from one group of initials.

Question 13

What is the quiescent center of the rootcap?

Answer 13

The relatively inactive region of the meristem (i.e., does not divide as often).

Question 14

What is the region of cell division?

Answer 14

Region where cells divide actively.

Question 15

What causes the majority of root length increase?

Answer 15

Elongation of cells in the area of elongation.

Question 16

Where does root growth occur in the root?

Answer 16

Near the root tip

Question 17

What is the region of maturation?

Answer 17

Where most cells of primary tissues mature and where root hairs are produced.

Question 18

Why are root hairs developed in the region of maturation and not the region of elongation?

Answer 18

If produced in region of elongation, they would be sheared off by the roots pushing through the soil.

Question 19

Are there strict boundaries between the regions of cell division, elongation, and maturation?

Answer 19

No, there are gradual transitions between each region. Sometimes they overlap.

Question 20

What are the three tissue systems of the root in the primary stage of growth?

Answer 20

epidermis, cortex and vascular tissues.

Question 21

What shape do vascular tissues typically form in the root?

Answer 21

Cylinder

Question 22

What facilitates the uptake and water of minerals in the roots?

Answer 22

The root hairs

Question 23

Why are root hairs ideal for taking in water and minerals?

Answer 23

Greatly increase the absorptive surface area of the root.

Question 24

Where are root hairs mainly confined?

Answer 24

Region of maturation.

Question 25

What are mycorrhizae?

Answer 25

Symbiotic associations between fungi and roots

Question 26

Why are micorrhizae beneficial?

Answer 26

Enables plant to obtain water and nutrients from much larger volume of soil than made possible by root hairs.

Question 27

What tissue takes up the majority of the primary body of roots?

Answer 27

The cortex

Question 28

Why does cortical tissue have an abundance of intracellular spaceS?

Answer 28

Essential for aeration of roots.

Question 29

What are aerenchyma?

Answer 29

Parenchyma cells with large and abundant intercellular spaces.

Question 30

How are cortical cells attached to each other?

Answer 30

Plasmodesmata attach protoplasts to each other.

Question 31

What pathways can substances moving across the cortex take?

Answer 31

Symplastic - protoplast to protoplast
Apoplastic - via cell walls
Both

Question 32

How does the endodermis differ from the cortex?

Answer 32

Tightly packed, lacks air spaces.

Question 33

What do the Casparian strips in the endodermis do?

Answer 33

Prevent movement of water and ions

Question 34

What is the exodermis?

Answer 34

Compact layers of cells with Casparian strips in most angiosperm roots.

Question 35

What does the exodermis do?

Answer 35

Prevent water loss and protect against microorganism attacks.

Question 36

What makes up the vascular cylinder?

Answer 36

Primary vascular tissue and the pericycle.

Question 37

Why is the pericycle considered part of the vascular cylinder?

Answer 37

It originates from procambium like vascular tissues.

Question 38

What does secondary growth consist of?

Answer 38

1. Formation of secondary vascular tissue
2. Formation of periderm

Question 39

Does the shoot apical meristem have its own version of a rootcap?

Answer 39

No. But it is usually covered by young leaves, which offer some protection.

Question 40

Differentiate between the ways in which tunica and corpus cells divide. What do these divisions result in in terms of plant growth?

Answer 40

Tunica divide anticlinally, contributing to surface growth.
Corpus divides periclinally, adding bulk to the developing shoot.

Question 41

Outline the layers of eudicot apices.

Answer 41

L1 and L2 = tunica
L3 = initial corpus