Download Plant tissue systems - Science with Stacey

Plant tissue systems
Compare the structures, position in the stem and function of
sclerenchyma fibres and xylem vessels.
Review of cell walls
 Plant cells are strong because they are wrapped in a
protective layer of cellulose which forms the cell wall
 Cellulose is a polysaccharide made from β glucose
monomers. Alternate glucose molecules “flip over” in
the chain, forming hydrogen bonds between adjacent
cellulose chains.
 Because cellulose has no side branches the chains can be
packed closely which increases the strength of the
hydrogen bonds further.
Cellulose
 Individual cellulose chains are
packaged together into microfibrils.
The microfibrils wind around each
other forming cellulose fibres.
 The cell wall is build from layers of
these fibres. The two structure you
need to be aware of are the:
 Primary cell wall: first to form,
cellulose fibres laid down in the same
direction
 Secondary cell wall: forms later,
cellulose fibres laid down at right
angles to those in the primary wall.
Provides much greater strength.
Introduction to plant
tissues
 Like other organisms, plant cells are grouped
together into various tissue.
 There are three types of tissue systems in
plants:
 Dermal tissue
 Vascular tissue
 Ground tissue
? What are the primary functions of a stem?
Dermal tissue
 Dermal tissue consists of the epidermis and the periderm.
 The epidermis is generally a single layer of closely packed
cells. It both covers and protects the plant. It can be though of
as the plant’s skin.
 Depending on the part of the plant that it covers, the dermal
tissue can be specialized to a certain extent.
? Refer to p 206 and give two ways in which the epidermis may
specialized.
 The periderm, also called bark, replaces the epidermis in
plants that undergo secondary growth. The periderm is
multilayered as opposed to the single layered epidermis.
Ground tissue
 The ground tissue system synthesizes organic compounds,
supports the plant and provides storage for the plant. It is
made up of three types of cells:
 Packing tissue called parenchyma - which holds everything in
place.
 Strengthening tissues that help support the plant:
 Collenchyma - this tissue can stretch as the plant grows
 Sclerenchyma - provides more strength in mature plants.
 Ground tissue is mostly made up of parenchyma cells but can
also include some collenchyma and sclerenchyma cells as
well. Parenchyma cells are unspecialized cells that can
synthesize and store organic products in a plant.
? Refer to p 207 and give two ways in which parenchyma cells
may specialized.
Ground tissue
 Collenchyma cells have a support function in plants,
particularly in young plants. These cells help to support
plants while not restraining growth due to their lack of
secondary walls and the absence of a hardening agent in
their primary walls.
? Where can collenchyma
cells be found?
? Give an example of
collenchyma tissue.
Ground tissue
 Sclerenchyma cells are also formed from parenchyma cells
and also have a support function in plants as a plant gets
larger.
 Unlike collenchyma cells,
they have a hardening agent
called lignin and are much
more rigid.
? Where is sclerenchyma tissue found?
? What makes sclerenchyma so strong and flexible?
? What name is given to sclerenchyma cells that are completely
filled with lignin? Where are these found?
? Answer the two questions on p 207
Homework:
Vascular tissue
 Xylem and phloem throughout the plant make up the
vascular tissue system. They allow water and other
nutrients to be transported throughout the plant.
? Refer to p 208. What are the primary functions of xylem
and phloem?
? What is cambium?
? Summarise how the structure of xylem is formed using a
diagram. (Refer to fig. 4.1.12)
? Answer the questions on p 209.