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BIOL 2010 Quiz: Tropisms

Course Code
BIOL 2010
Roger Lew
Study Guide

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The life of a Plant
Radicle Emergence and Root Growth
Anatomy [structure and function]
Quiescent zone
-Positive gravitropism
-Negative gravitropism
Trees were the first natural flowering plant.
Breaking of dormancy in the context of germination of a seed.
Get inhibition thing going on in the seed and bud then you get the emergence
of a radicle which is the first thing that happens under normal
circumstances- absolutely crucial in terms of survivability of the seed in
the long run in terms of water uptake to the plant. Tend to have an initial
radicle that goes straight down with gravity- have root hairs that are
single celled- increase surface area for absorption of water. Not long after
that you’ll begin to see emergence of secondary leaves and all of this is
occurring in the root prior to the development of anything significant
above the soil.
Most of the biomass is in the root and is important for the plant in terms of
collecting its nutrition.
You see different stages of development in the root and thus gives you an
idea of the various active zones that exists in the root.
Larger cells on the outside and the smaller cells on the inside- outer cells-
xylem and the inner cels embedded in is the phloem for carbohydrate
synthase. Down below within the root cap, you begin to see various
zones that are visible. U shaped line that goes up and there are zone
below and above that each which have a different structure or shape and
function associated with it. Cells hanging out of the side of the root cap
are known as cell sloughing. [ Example sloughing off extra layers of your
skin] In terms of a plant- cell sloughing is important for the viability of the
The root has to push down through the soil and is bound to get damaged. It
minimizes the effect of damage by creating a root cap, cells get sloughed
off and new cells appear within the root cap.
Mucilage- mucilage secretion out of these root caps is like an oil that makes it
easier and acts as a lubricant for the cells to penetrate through the soil.
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Cells within the root get bigger as you go up the root. The cells below are
shorter. The larger cells are newer and this is the region of the plant that
is growing and expanding due to turgor pressure and as the root cap
pushes through the soil, these cells expand and this is where elongation
As the root grows there are regions where elongation occurs- have an
increase in the volume of cells due to elongation that pushes the root cap
down into the soil. When you’re going down through the system, you
know you’ll need cells in order to push down through the soil and so you
need cellular division. Cellular division occurs in the small cells near the
tip below the elongation zone.
That zone of cellular division is in between the root cap and the elongation
region of the root. This is of functional interest in terms of the
developmental biology point of view. This positional determination is very
common in plant development and not common in animals. Looking at
positional roles- where a cell in each location within the root cap have
different roles associated with them. When new cells form they take over
the function of the previous cell because they are in the right position to
do so.
What kind of experimental technique would you use to determine cell division?
Can either look at it and wait for cell division to occur. Another method,
think about it in terms of DNA which has to double and can add a
radioactive tracer which is a specific precursor for a purine or pyrimidine
and will be present in newly synthesized cells. Can then visualize the
radioactivity caused by thymidine. If you look at the cells that have
undergone cell division on the basis of the DNA tracer added to it, all the
white spaces are where cell division is occurring. Black space in
between the dividing cells where cells haven’t divided is known as
the quiescent zone where cells do not divide. These are stem cells.
[Refer to the picture below]
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