Root physiology 1

Question 1

What is the process of the root growing?

Answer 1

Branching and elongation occur at the same time.
First roots grow down deep and once a certain depth has been reached the roots will begin to branch at the top layers of the soil.

Question 2

What are tap roots?

Answer 2

Lateral roots branching from a main primary (tap) root.​
For most of them this is the radicle, the baby root in the seedling when the seed has germinated that grows into the primary root.

Question 3

What are fibrous roots?

Answer 3

Adventitious roots branching from the radicle and stem. No main root.​ (roots branch from stem not a main root).
Some roots will grow from the radicle but this radicle itself dies quite early on the other roots will grow directly from the stem. No main root.

Question 4

What are the 6 subgroups in the kingdom of plants and what are examples?

Answer 4

charophytes=moss and algae
Bryophytes=moss
Lycophytes= clubmosses
Pteridophytes=ferns
Gymnosperms=seed producing
Angiosperms=flowering plants (biggest group in terms of number of species)

Question 5

Within the angiosperms there are monocots and dicots.
name examples of them?

Answer 5

Monocots=cereals, bamboo, palm trees, lilies and orchids normally have fibrous roots.
dicots= everything in the angiosperms that isn’t a monocot e.g legumes.

Question 6

What are eudicots

Answer 6

A clade of flowering plants mainly characterized by having two seed leaves upon germination. These normally have tap roots.
Include fabacea

Question 7

What are rhizomes?

Answer 7

Rhizomes are modified stems growing horizontally in the soil. They are probably the ancestors of roots.​

In some rhizomatous plants, shoots and roots grow from the rhizome, which can be used as a propagation system.​

Question 8

What are the cell walls structure?

Answer 8

Going from outside the cell towards the cell membrane: ​
*middle lamella (formed during cell division, mostly pectin)​ found in between two plant cells to help them stick together )(made first)
*primary cell wall​ (tough and flexible so allows the cell to grow and extend)
*secondary cell wall (formed after cell growth in specialised cell types) not every cell has this and its the last part that is made in mature cells

Question 9

What are cell walls made of?

Answer 9

The primary cell wall exists in all cells and is made of cellulose, hemicellulose and pectin.​
The secondary cell wall is formed after cell growth in specialised tissues. It contains cellulose, hemicellulose, pectin and lignin. The lignin which replaces some of the pectin gives it a higher strength and rigidity than the primary wall and provides hydrophobicity (waterproof).​

Question 10

What are the roles of the cell wall?

Answer 10

Shape​
Strength​
Anchorage

Question 11

What are the three main plant tissues?

Answer 11

*Ground tissue​ (basic tissue)
-Sclerenchyma​=provides mechanical stiffness and strength.
-Collenchyma​=a supporting tissue composed of elongated living cells with unevenly thickened, nonlignified primary walls. It is in regions of primary growth in stems and leaves.
-Parenchyma= Provides a route of exchange for materials within and between the xylem and the phloem.
(no secondary walls) Parenchyma forms the bulk of plant ground tissue, may be specialised in photosynthesis, storage, or transport.

*Vascular tissue​
-Xylem​
-Phloem​​
These two have secondary cell wall

*Dermal tissue​
-Epiderm is ​non woody
-Periderm​ (just under epidermis) woody

Question 12

Describe parenchyma tissues

Answer 12

Parenchyma cells have thin primary walls.​
Parenchyma tissue contains intercellular air spaces.​
Most plant organs contain parenchyma tissue (“bulk”).​
​

Question 13

Describe the internal structure of a root (radial) and what are the roles

Answer 13

The epidermis which is the outer layer (like skin) Then the cortex which is the bulk and finally the stele in the middle.
Cortex = parenchyma cells + endodermis​ (last layer of cell before stele)
Stele = pericycle (one layer) + phloem + xylem​

roles;
Epidermis: absorption​
Cortex: bulk of the root​ (horizontal transport)
Stele: transport​ (vertical)

Question 14

What is the casparian strip (innermost layer of the cortex)?

Answer 14

This is the same as the endodermis and it is a diffusion barrier.
This is like an inside skin that protects the root as the cell walls contain lignin or suberin. These are both very hydrophobic which means water and other substances have to go through transporters (selective) preventing toxic molecules or pathogens entering the root.
Hydrophobic plug between cells: forces passage through cytoplasm (selective)​

Question 15

Describe the tip of the root

Answer 15

This is called the apex and it is where the roots grow. Here is also where you find apical meristem is the supply and source of cells.
There are different zones first the epidermis​ (EP), RAM = root apical meristem​ and then at the tip RC = root cap

Question 16

What does the root cap do?

Answer 16

It acts as a shield (protect the meristem), sensor and steering wheel​. It secretes mucous that helps lubricate the tip of the roots to go through the soil. root cap cells only live for a week but they detect water, gravity by (amyloplasts in the root cap​), pressure and they control root direction.

Question 17

What are Columella Cells?

Answer 17

These contribute to Root Gravity Sensing in the root caps. These cells have plastids called amyloplasts that contain granules of starch and the granules are heavier than everything ese in the cell so they tend to go down giving direction

Question 18

Zone of elongation (root hair cells)

Answer 18

This is where root hair start growing. Root hairs are not cells they are just extensions of cells so are still part of epidermis cells. They can be dense and are very important for absorption of nutrients and water as they increase the surface area and reach other areas of the soil. Hair cells increase the volume of soil that is explored by the root. They only live for 1-3 weeks so root hairs are only found on newer cells

Question 19

Zone of differentiation (lateral roots)

Answer 19

Lateral roots are actual roots branching from the main root. The pericycle layer is where these roots start growing (first layer of stele) The reason for this is so that new vascular tissue will link to the vascular tissue of the main root supplying nutrients. These grow a little bit horizontally and then grow downwards.