Green plants: The awesome cooks!
Have you ever stopped to think how you get your food? Ever realized the
crucial role played by green plants? Ever wondered who gives you the
oxygen you breathe? Yes, it’s the community of green plants and that
includes trees, vines, shrubs, and so on. In fact we owe them a lot.
Let’s learn to appreciate their service.
Green plants, as you already know, produce food and oxygen for all other
living things via a process known as photosynthesis. Photosynthesis is
the conversion of light energy into chemical energy. The raw materials
are carbon dioxide and water, the energy source is sunlight, and the
end-products include glucose and oxygen. It’s in fact the most important
biochemical pathway, since nearly all life depends on it. It is a
complex process occurring in higher plants, (i.e., what we normally
refer to as green plants) phytoplankton, algae, as well as bacteria such
as cyanobacteria. Photosynthetic organisms are also referred to as ‘photoautotrophs.’
(Break it down like this, when pronouncing: photo-auto-trophs )
The chemical conversion involved in photosynthesis can be written down
6H2O + 6CO2 ----------> C6H12O6+ 6O2
Six molecules of water plus six molecules of carbon dioxide produce one
molecule of sugar plus six molecules of oxygen, so to speak.
Plants are the only photosynthetic organisms to have leaves (and not all
plants have leaves). A leaf may be viewed as a solar collector crammed
full of photosynthetic cells.
The raw materials of photosynthesis, water and carbon dioxide, enter the
cells of the leaf, and the products of photosynthesis, sugar and oxygen,
leave the leaf.
Water enters the root and is transported up to the leaves through
specialized plant cells known as xylem (pronounces zigh-lem). Land
plants must guard against drying out (desiccation) and, thus they have
evolved specialized structures known as stomata to allow gas to enter
and leave the leaf. Carbon dioxide cannot pass through the protective
waxy layer covering the leaf (cuticle), but it can enter the leaf
through an opening (the stoma; plural = stomata; Greek for hole) flanked
by two guard cells. Likewise, oxygen produced during photosynthesis can
only pass out of the leaf through the opened stomata. Unfortunately
though, while these gases are moving between the inside and outside of
the leaf, a great deal water is also lost. Cottonwood trees, for
example, will lose 100 gallons of water per hour during hot desert days.
Carbon dioxide enters single-celled and aquatic autotrophs through no
Chlorophyll is a green pigment found in plants. A pigment is any
substance that absorbs light. Chlorophyll is common to all
photosynthetic cells, absorbs all wavelengths of visible light except
green, which it reflects to be detected by our eyes. The colour of the
pigment comes from the wavelengths of light reflected. Black pigments
absorb all of the wavelengths that strike them. White pigments/lighter
colours reflect all or almost all of the energy striking them.
Chlorophyll is a complex molecule. Several modifications of chlorophyll
occur among plants and other photosynthetic organisms. All
photosynthetic organisms have ‘chlorophyll a’. Accessory (additional)
pigments absorb energy that ‘chlorophyll a’ does not absorb. Accessory
pigments include ‘chlorophyll b’ (also c, d, and e in algae and
protistans), xanthophylls, and carotenoids (such as beta-carotene).
‘Chlorophyll a’ absorbs its energy from the Violet-Blue and Reddish
orange-Red wavelengths, and little from the intermediate
Stages of photosynthesis
Photosynthesis is a two-stage process. The first process is the
Light Dependent Process (Light Reactions), requires the direct energy of
light to make energy carrier molecules that are used in the second
process. The Light Independent Process (or Dark Reactions) occurs when
the products of the Light Reaction are used to form C-C covalent bonds
(read as ‘carbon carbon covalent bonds’) of carbohydrates. As the name
implies, these bonds occur between two carbon atoms, and therefore are
important to keep the entire carbohydrate molecule in place.
The Dark Reactions can usually occur in the dark. The Light Reactions
occur in the grana and the Dark Reactions take place in the stroma of
Importance of the process
Animals and plants both synthesize fats and proteins from
carbohydrates; thus glucose is a basic energy source for all living
organisms. The oxygen released (with water vapour, in transpiration) as
a photosynthetic by-product, principally of phytoplankton, provides most
of the atmospheric oxygen vital to respiration in plants and animals,
and animals in turn produce carbon dioxide necessary to plants.
Photosynthesis can therefore be considered the ultimate source of life
for nearly all plants and animals by providing the source of energy that
drives all their metabolic processes.
The carbon cycle
I hope you are familiar with the term ‘carbon sink’. Plants may be
viewed as carbon sinks, for, they remove carbon dioxide from the
atmosphere and oceans by fixing it into organic chemicals. Plants also
produce some carbon dioxide by their respiration, but this is quickly
used by photosynthesis. Plants also convert energy from light into
chemical energy of C-C covalent bonds. Animals are carbon dioxide
producers that derive their energy from carbohydrates and other
chemicals produced by plants by the process of photosynthesis.
The balance between the plant carbon dioxide removal and animal carbon
dioxide generation is equalized also by the formation of carbonates in
the oceans. This removes excess carbon dioxide from the air and water
(both of which are in equilibrium with regard to carbon dioxide).
Fossil fuels, such as petroleum and coal, as well as more recent fuels
such as peat and wood generate carbon dioxide when burned. Fossil fuels
are formed ultimately by organic processes, and represent also a
tremendous carbon sink. Human activity has greatly increased the
concentration of carbon dioxide in air. This increase has led to global
warming, an increase in temperatures around the world, the Greenhouse
Effect. The Global Warming problem can lead to melting of the ice caps
in Greenland and Antarctica, raising sea-level as much as 120 metres.
Changes in sea-level and temperature would affect climate changes,
altering belts of grain production and rainfall patterns.
Here’s an activity
Prepare a poster for your science class, elaborating on the process of
photosynthesis. For instance, you can say what photosynthesis is, where
it happens, its importance…etc. You can use bristol-board, diagrams or
even create your own drawings. Use less of text and more of drawings.
Make it colourful and attractive.
This I am sure, would be an interesting activity.
Plants fun facts:
* 84% of a raw apple is water.
* A cucumber is 96% water.
* A notch in a tree will remain the same distance from the ground as the
* A pineapple is a berry.
* Almonds are the oldest, most widely cultivated and extensively used
nuts in the world.
* An average ear of corn has 800 kernels, arranged in 16 rows.
* Avocados have the highest calories of any fruit at 167 calories per
* Banana oil never saw a banana; it’s made from petroleum.
* Eggplant is a member of the thistle family.
* No species of wild plant produces a flower or blossom that is
absolutely black, and so far, none has been developed artificially.
* Nutmeg is extremely poisonous if injected intravenously.
* Oak trees do not have acorns until they are fifty years old or older.
* Oranges, lemons, watermelons, and tomatoes are berries.
* Orchids have the smallest seeds. It takes more than 1.25 million seeds
to weigh 1 gram.
* Peanuts are beans.
* The California redwood - coast redwood and giant sequoia - are the
tallest and largest living organism in the world.
* The pineapple was symbol of welcome in the 1700-1800’s. That is why in
New England you will see so many pineapples on door knockers. An arch in
Providence RI, leading into the Federal Hill neighborhood, has a
pineapple on it for that very reason. Pineapples were brought home by
seafarers as gifts.
* The plant life in the oceans make up about 85 percent of all the
greenery on the Earth.