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Lecture 35

BIOL 1202 Lecture Notes - Lecture 35: Axillary Bud, Vascular Plant, Bark

Biological Sciences
Course Code
BIOL 1202

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Plant Structure, Growth, and Development
The basic design of land plants has two parts (see fig 35.2):
-Root System: below ground
-Shoot System: above ground
The root is an organ that
-anchors the vascular plant
-absorbs minerals and water
-stores organic nutrients
Perennials: some lose the above ground functionality, grow for many years repeatedly
due to storage in root structure in tough times such as winter.
Annuals: can only grow for one year and then they die.
As a seed begins to grow the first root to emerge is the primary root (see fig 35.3). Stored food
in seed needs hydration. (water comes from root)
In monocots, this primary root grows out and is replaced by a fibrous root system composed of
many roots of about equal size.
In dicots, the primary roots then turn into the taproot system, which has one main root that
lateral roots branch off.
The epidermis of the root is very thin and has no waxy cuticle (holds water in plant). In addition,
the epidermis forms root hairs (see fig 35.3) to increase the surface area. These characteristics
make the root very permeable to water AND nutrients.
Root has no cuticle because it needs to take in water, but shoot system does.
Lots of surface area no barriers good at bringing things in
As the shoot of a plant grows at the apical bud it gives rise to different specialized tissues (see
fig 35.2):
Apical means top and extremes of all kinds
Growth of apex is via cell division, and differentiation occurs.
oDivides top to bottom, and cell on top remains undifferentiated. Cell on
bottom has been differentiated and some of its cells have been set aside and
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These are all tissues produced via differentiation
All of shoot structures come from small groups of cells which are left behind by the apical bud.
These groups of cells form leaf primordia (leaf producing group) and axillary buds (branch
producing group).
Leaf primordia and axillary bud and flower can all occur around the same
point in clusters of differentiated cells.
Clusters encoded in genes of plant. (tells clusters where they will be placed)
The cell groups are clustered at sites called nodes (clusters of clusters) and are usually
distributed at regular intervals along the stem. These intervals are known as internodes (the
space between two nodes on the same side of the stem)
The formation of branches from lateral buds is triggered by hormones (or the lack of certain
hormones).  signals have to occur for things to form (combination of signals)
Signals: environmental, hormonal, nutritional, etc.
Think of human development
Leaves of a plant have two main parts the blade (light gathering piece, varies in shape) and the
petiole (the leaf stem, how it attaches to main stem) (see fig 35.6)
Plants have three main tissue systems (see fig 35.8)
-Dermal Tissue System – from the protoderm - outside covering (dermal like skin)
-Ground Tissue System – from the ground meristem - the in-between stuff (gram)
-Vascular Tissue System – from the procambium - the pipes (vascular like veins)
Two types of complex tissue systems: vascular and dermal bc they go through age
related changeovers.
oGround is simple because it doesn’t go through thoe changes.
Two tissue types make up the DERMAL tissue system.
-Epidermal tissue:
The epidermal tissue forms the epidermis (skin) that covers the outside of the plant.
-Made up of thin-walled cell with a waxy cuticle.
-underground portion doesn’t have waxy cuticle
Some epidermal cells produce fine hair-like structures called root hairs (see fig 35.3) or
leaf hairs. (fruit/leaves/stems), can be used as protection
The periderm tissue can replace the epidermis in older woody stems, branches and
-replaces epidermis because when differentiation occurs, differentiated cells can’t
go through cell division again (splits so periderm can replace it)
-Made up of thick-walled cork cells (create bark of tree, plant tissue)
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