|
The
basic
unit
of life
Joanna
George-Johnson, Contributor
The
smallest unit or entity that can be
considered as living is a cell. For
an entity to be considered living,
it must exhibit all the characteristics
of living things.
 |
|
An
Ascot High School student stitches
material while her classmate
hems a piece of cloth during
a clothing and textile class
at Ascot High School, recently.
-Anthony Minott Freelance reporter
|
Photosynthesis
is the process that green plants use
to make their own food. Using carbon
dioxide and water with energy from
sunlight, plants are able to synthesise
carbohydrates, namely glucose, which
can later be convert to starch and
other organic substances.
The
general formula for the process of
photosynthesis is: (See table below)
Photosynthesis
is an extremely complicated process,
but for ease of understanding, we
normally break it down into two parts.
Light
reaction: here is where the energy,
harnessed by chlorophyll from the
sun, is used to split water molecules
in a reaction called photolysis. Water
is split into hydrogen and oxygen.
This part of photosynthesis must occur
in the presence of light. (Although
sunlight is the light energy of choice,
this can happen under a light bulb
with the right amount of energy.)
Dark
reaction: the hydrogen and energy
from the light reaction, along with
the carbon dioxide, is used to synthesise
glucose. This is done through a series
of reactions. N.B. although called
the dark reaction, it can occur in
the light, it just does not need light
to happen. (See table above right)
The
fate of the glucose
that is made
Glucose
made from the process of photosynthesis
may be used for several different
things. These include:
- May
be used directly by the plant to
provide energy
- Some
will be converted to sucrose for
transportation to various parts
of the plant that do not photosynthesise.
- Some
of the glucose will be converted
to starch to be stored for future
use. Some of which form the fruits
of some plants.
- Some
of the glucose can also be combined
with other substances to form other
nutrients needed by the plant, such
as proteins and lipids. (See image
above)
Questions
1.
Why is glucose converted to sucrose
to be transported?
2.
Why is starch used as the storage
molecule?
Answers:
1.
A good transport molecule must be
relatively unreactive, small and soluble.
Although glucose is smaller than sucrose
and more soluble, it is too reactive
and therefore, is not a suitable transport
molecule. The glucose will get involved
with reactions that it should not
if it were the transport molecule.
2.
A good storage molecule should have
the following characteristics: must
be insoluble, take up little space
and be relatively unreactive. Glucose,
therefore, could not fit these criteria
for a number of reasons: 1) It is
too reactive and will get involved
in reactions it shouldn't and could
cause problems; 2) It is soluble in
water and will therefore change the
concentration of the cell contents,
and this could damage the cell because
it could lead to excessive osmosis;
3) It will not be compact enough and
thus will take up too much space.
For
these reasons, starch is the preferred
storage molecule.
|
Requirements
for Photosynthesis and their
source
|
| Requirement |
Route
of entry into plant |
Use
of photosynthesis |
|
Carbon
dioxide
Water
|
This
gas diffuses into the leaf through
the stomata which are the undersize
of the leaf. comes through its
roots from the soil via a process
known as Osmosis (Hence the
reason for watering your plants.)
The water then travels up
the stem towards the leaf through
specialized cells known as xylem.
|
Combines with the hydrogen
to make glucose.
Provides the source of the
hydrogen for the production
of glucose.
|
| Sunlight |
It
penetrates through the transparent
epidermis into the chloroplast
of the mesophyll cells(light
sources other than sunlight can
be used to power the process as
long as the light source has the
correct wave length). |
Provides the energy for th
eprocess.
|
Joanna
George-Johnson teaches at Ardenne
High School.
Email: Masterbio@gmail.com.
|
