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Structure - Roots

What are three important functions of roots?

  • mechanical (support/anchorage)
  • uptake of water and nutrients
  • food storage

What kinds of plants produce taproots and which do not?

Many dicots have taproots, monocots do not.

Typically, where in the soil are most of the roots of a plant?

in the top two feet

What are two functions of the root cap?

protection of apical meristem and lubrication

Contrast the position of the apical meristem in a root with that in a shoot.

apical meristem in the root is underneath the root cap.

the apical meristem in a shoot is at the tip of the shoot.

What is the quiescent center - do all roots have one?

the zone in the apical meristem where cell division is slow.

no, not all roots have one.

Would you expect to find root hairs near the meristem?

No, the root hairs would be torn off by elongation of the root.

How does the primary vascular tissue of the root differ from that in the stem?

It is a simple central cylinderin the root but more complex in the shoot.

What is special about the innermost cells of the cortex?

They have thickened walls (casparian strip) and form the endodermis.

Where does cell division begin to generate a lateral root meristem?

in the parenchyma cells in the pericycle

What kinds of plants develop aerial roots and what functions do they serve?

epiphytes, for anchorage and water absorption

What kinds of plants have nitrogen fixing nodules and mycorrhizae?

  • legumes and a few other plants have nodules
  • most plants can form mychorrhizae, although they may not when we grow them

What kinds of organisms are associated with the plant to make these structures?

Rhizobium bacteria in nodules

various fungi in mycorrhizae

New roots arise from an existing root:

  1. at the tip
  2. from the cortex
  3. from the pericycle

  1. Root tips, unlike shoot tips, never branch, they keep going in a straight line.

     

  2. Lateral roots break through the cortex on their way out but they arise from deeper within the root.

     

  3. The pericycle is just inside the endodermis and remains meristematic. so that new root apical meristems can arise within it.

Root hairs are formed on:

  1. the root apical meristem
  2. the zone of elongation
  3. the zone of maturation

  1. The root apical meristem is covered by the root cap, so how could hairs grow out at this point?

     

  2. What would happen to root hairs on a region of a root that is elongating?

     

  3. Right, if they formed ahead of this zone they would be torn off as the tip advances through the soil.

Water, nutrients and other solutes entering a root must move symplastically once they reach the:

  1. cortex
  2. endodermis
  3. pericycle

  1. In the cortex water and dissolved substances can move apoplastically (between cells) as well as symplastically (through cells)

     

  2. Yes only at the endodermis are water and nutrients forced to enter the cytoplasm; so this is the main opportunity for roots to select what moves on in the xylem stream

     

  3. Once they are in the pericycle, water and solutes can take any path to the xylem.

The most common cell type in a young root is:

  1. parenchyma
  2. sclerenchyma
  3. collenchyma

  1. Yes most of the root mass is cortex which is made up of parenchyma cells and provides a site of storage of starch and organic nitrogen compounds.

     

  2. Sclerenchyma are usually fiber cells that occur in stems

     

  3. Collenchyma cells have thickened primary walls and tend to occur in petioles

Adventitious roots arise on a stem from the:

  1. apical meristem
  2. internodes
  3. nodes

  1. The shoot apical meristem makes leaf and bud primordia but not root primordia.

     

  2. Internodes have less meristematic potential than other parts of the stem.

     

  3. Nodes retain meristematic potential longer than internodes and this is where new roots as well as new shoots tend to grow out.

Which of the following vegetables is a root:

  1. potato
  2. carrot
  3. radish

  1. Potatoes grow underground, but they have axillary buds (eyes) and are modified stems.

     

  2. A carrot is indeed, although not everything that grows in the ground turns out to be a root.

     

  3. If you look closely at a radish you can often see the remains of the cotyledons at the top; it is mostly hypocotyl.

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