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The
structure of unspecialised animal
and plant cells
Monacia
Williams, Contributor
Welcome
to another lesson! I hope that you
enjoyed going through the lessons
over the last weeks and that you are
now looking at your environment in
a different way, showing appreciation
for the animals and plants around
you. As I promised last week, we are
now going to begin a new section of
the syllabus - life processes.
Have
you ever thought about how you are
made up? I know that you will tell
me that you have a head, two hands,
a torso, etc, but what makes up these?
A house may have different rooms of
varying sizes but, if we were present
at its initial stage, we would have
seen that placing blocks on top of
blocks created the final structure.
Similarly the human body has many
different sizes and shapes, but the
construction unit is always the cell.
What
is the cell?
The
cell is the basic building block of
living organisms, and today we are
going to look at the structure of
the cell, both in plants and animals.
Most diagrams show the animal cell
as a flat, two-dimensional structure
but, in reality, it is not so. The
cell is an object of three dimensions,
with its internal structures held
in place by a jelly-like substance
known as the cytoplasm.
Can
you use your mind's eye to visualise
a plastic bag filled with a solution
of starch? Well, the starch solution
would be the cytoplasm and the plastic
bag keeping the starch solution in
place would be the membrane of the
cell. If we were to place a small
lime or table tennis ball in the bag,
this would now represent a structure
known as the nucleus. Add some grains
of red kidney beans and these would
be equivalent to the mitochondria
and some sand grains added would form
the glycogen granules. Seal this now
so that it does not leak and, guess
what? If you have followed all these
steps with your mind's eye, you would
have created a mental model of the
cell! Here is another challenge. Change
the visual to the actual and go make
a model of the cell. It will change
your perception of the diagrams in
your text.
You
are probably wondering by now if I
have forgotten about the plant cell.
I have not. If you were to make another
model cell with a few changes, you
could create a plant cell. First,
you would need to remove some of the
starch solution then fill a smaller
plastic bag with water and place this
bag in the starch solution; this is
now the cell's vacuole. Add some green
peas to the cytoplasm to represent
the chloroplasts. The sand grains
will remain, but they are now called
starch grains. Finally, place your
sealed bag in a box of similar size
and, there you go, that's your plant
cell!
Let
us look at the functions of some of
the structures of the cells that we
have just created.
| Cell
Structure |
Function |
| Cell
wall-found only in plant cell |
Helps
to define the shape of the cell
and to maintain plant shape and
structure. |
|
Cell
membrane
|
Forms
the outer boundary of the cell
and it allows substances to pass
into and out of the cell. It lets
some things pass through but stops
others. |
|
Nucleus
|
Controls
what the cell does and how it
develops. It contains the chromosomes. |
| Chromosomes |
Carry
genetic information in the form
of DNA. |
Cytoplasm
|
Contaisn
the other cell structures. Most
of the chemical reactions of the
cell take place here. |
| Mitochondria |
Release
energy from food during respiration. |
Vacuoles
|
Fluid
filled sac, which stores various
substances. Plant cells usually
have one large vacuole while animal
cells may have several small ones. |
Chloroplast
- found only int he plant cell
|
Photosynthesis
- the process by hwich plants
make their own food form water
and carbon dioxide takes place
here, using the energy absorbed
from sunlight byt he chloroplasts. |
Table
showing the functions of some of the
cell's structures
Our
discussion has shown that there are
some differences between the animal
cell and the plant cell. Let us now
summarize these in a table.
| Plant
cells |
Animal
cells |
| Have
a cellulose cell wall outside
of the cell membrane |
Have
no cell wall
|
| Often
have chloroplasts |
Have
no chloroplasts |
| Often
have veyr large vacuoles, containing
cell sap |
Have
only small vacuoles
|
Often
have starch granules
|
Starch
granules are never present, glycogen
granules may be present |
| Shape
tends to be regular |
Shape
mostly irregular |
See
you next week as we continue to look
at the cell.
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|
Lieutenant
Aldene Thomas (right) gives
some information about the Jamaica
Defence Force at the Choices
Career and Education Expo at
Hilton Kingston hotel on Tuesday,
June 3.
The
event aimed to give students
access to invaluable information
regarding future career and
educational development. Several
universities and organisations
such as the Ministry of Education
participated in the event.
- Peta-Gaye Clachar/Staff
Photographer
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Monacia
Williams teaches at Glenmuir
High School.
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