Green plants: The awesome cooks!

Nimashi Amaleeta
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 like this:

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 specialized structures.

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 (green-yellow-orange) wavelengths.

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 the chloroplasts.

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 tree grows.
* 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 hundred grams.
* 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.











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