Bio 220 Lecture
3: Plant structure
Campbell,
5th, Ch. 35
I.
Comparison of components of plant and animal
cells(cont.)
B. Outside
Moving
outside, there are more differences between plant and animal
cells.
1.
Extracellular
matrix7.29
Animal cells are surrounded by a
loose aggregation of proteins known as the extracellular
matrixor ECM for
short.
The ECM
is a very variable
structurein both form and
function. The composition varies between different tissues
and it can even change over time.
The ECM
also fulfills a variety of roles:
- it can provide a track for cells to migrate along;
- it can alter the development of cells it covers;
- it can trap calcium salts and become the hard part of
bone.
What
the ECM doesn'tdo is
confine cells or keep them apart. Animal cells can
often
moveabout and are
usually in close
contactwith their
neighbors. Often there are
channels between cells. We'll discuss the significance of
these later in the course.
2.
Cell Wall
Plant cells are surrounded by
a cell wall made of
cellulose(a glucose
polymer). Cellulose is
rigidand it
does confinethe
cells of a plant, but it
doesn't keep them apart. Plant cells are connected by
channels through the cell wall known as
plasmodesma.
a.
Primary5.8
All plant cells secrete a
primary cell wallmade
up of cellulose microfibrils
embedded in a matrix of polysaccharides and protein. The
primary cell wall is relatively thin and flexible, and
allows the cell some room to grow and to change shape.
b.
Secondary7.28
When most plant cells stop
growing, they reinforce the cell wall. Some secrete lignin,
a polymer that hardens, into the primary cell wall. Others
secrete a secondary cell wall.
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