Photosynthetic organisms can be divided into two classes: those which produce oxygen and those which do not. Photosynthetic bacteria do not produce oxygen in fact some of them called anaerobes cannot tolerate oxygen and this is considered a more primitive type of photosynthesis in which the hydrogen donor is hydrogen sulfide, lactate or other compounds, but not water. Plants and one type of bacteria cyanobacteria do produce oxygen, an evolutionarily more advanced type of photosynthesis in which the hydrogen donor is water.
In a broad chemical sense, the opposite of photosynthesis is respiration. Most of life on this planet all except in the deep sea vents depends on the reciprocal photosynthesis-driven production of carbon containing compounds by a series of reducing adding electrons chemical reactions carried out by plants and then the opposite process of oxidative removing electrons chemical reactions by animals and plants, which are capable of both photosynthesis and respiration in which these carbon compounds are broken down to carbon dioxide and water.
The oxidative chemical reactions of respiration release energy, some of which is heat and some of it is captured in the form of high energy compunds such as Adenosine triphosphate ATP and Nicotinamide adenide dinucleotide phosphate NADPH. These compounds have a high energy unstable terminal phosphate bond and that terminal phosphate is easily detached with the transfer of the energy to drive chemical reactions in the synthesis of other biomolecules. The energy releasing reactions which converts them back to energy-depleted ADP and NADP is known as Dark Phase Reactions Calvin Cycle does not require light in which the synthesis of glucose and other carbohydrates occurs.
So we can summarize by saying that the photosynthetic plants trap solar energy to form ATP and NADPH Light Phase and then use these as the energy source to make carbohydrates and other biomolecules from carbon dioxide and water Dark Phase , simultaneously releasing oxygen in to the atmosphere. The chemoheterotrophic animals reverse this process by using the oxygen to degrade the energy-rich organic products of photosynthesis to CO2 and water in order to generate ATP for their own synthesis of biomolecules.
Animals store the energy obtained from the breakdown of food as ATP. Likewise, plants capture and store the energy they derive from light during photosynthesis in ATP molecules. Several modifications of chlorophyll occur among plants and other photosynthetic organisms.
All photosynthetic organisms have chlorophyll a. Accessory 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. Chlorophyll - click on image to open All chlorophylls have: a lipid-soluble hydrocarbon tail C20H39 - a flat hydrophilic head with a magnesium ion at its centre; different chlorophylls have different side-groups on the head The tail and head are linked by an ester bond.
Leaves and leaf structure 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 vessels.
What I want to do in this video is get a better appreciation of why that is. Adenosine triposphate. At first this seems like a fairly complicated term, adenosine triphosphate, and even when we look at its molecular structure it seems quite involved, but if we break it down into its constituent parts it becomes a little bit more understandable and we'll begin to appreciate why, how it is a store of energy in biological systems.
The first part is to break down this molecule between the part that is adenosine and the part that is the triphosphates, or the three phosphoryl groups.
The adenosine is this part of the molecule, let me do it in that same color. This part right over here is adenosine, and it's an adenine connected to a ribose right over there, that's the adenosine part. And then you have three phosphoryl groups, and when they break off they can turn into a phosphate. The triphosphate part you have, triphosphate, you have one phosphoryl group, two phosphoryl groups, two phosphoryl groups and three phosphoryl groups.
One way that you can conceptualize this molecule which will make it a little bit easier to understand how it's a store of energy in biological systems is to represent this whole adenosine group, let's just represent that as an A. Actually let's make that an Ad. Then let's just show it bonded to the three phosphoryl groups.
So we can summarize by saying that the photosynthetic plants trap solar energy to form ATP and NADPH Light Phase and then use these as the energy source to make carbohydrates and other biomolecules from carbon dioxide and water Dark Phase , simultaneously releasing oxygen in to the atmosphere. The absorption spectra for chlorphylls a and b are shown below.
What I want to do in this video is get a better appreciation of why that is. Unfortunately for the plant, while these gases are moving between the inside and outside of the leaf, a great deal of water is also lost.
I just have to do a little thing and I'm going to fall through, I'm going to fall down, and as I fall down I can release energy. The triphosphate part you have, triphosphate, you have one phosphoryl group, two phosphoryl groups, two phosphoryl groups and three phosphoryl groups.