Both involve electron transport chains 2
Both provide power for cellular activity
During photosynthesis, a plant is able to convert solar energy into a chemical form. It does this by capturing light coming from the sun and, through a series of reactions, using its energy to help build a sugar molecule called glucose. Glucose is made of six carbon atoms, six oxygen atoms, and twelve hydrogen atoms. When the plant makes the glucose molecule, it gets the carbon and oxygen atoms it needs from carbon dioxide, which it takes from the air. Carbon dioxide doesn't have any hydrogen in it, though, so the plant must use another source for hydrogen. The source that it uses is water. There is a lot of water on the earth, and every water molecule is composed of two hydrogen atoms and one oxygen atom. In order to take the hydrogen it needs to build glucose molecules, the plant uses the energy from the sun to break the water molecule apart, taking electrons and hydrogen from it and releasing the oxygen into the air. The electrons it takes are put into an electron transport system, where they are used to produce energy molecules called ATP that are used to build the glucose molecule-- all made possible by the sun's energy. Thus, during photosynthesis a plant consumes water, carbon dioxide, and light energy, and produces glucose and oxygen.
The sugar glucose is important because it is necessary for cellular respiration. During cellular respiration, the chemical energy in the glucose molecule is converted into a form that the plant can use for growth and reproduction. In the first step of respiration, called glycolysis, the glucose molecule is broken down into two smaller molecules called pyruvate, and a little energy is released in the form of ATP. This step in respiration does not require any oxygen and is therefore called anaerobic respiration. In the second step of respiration, the pyruvate molecules are rearranged and combined and rearranged again in a cycle. While the molecules are being rearranged in this cycle, carbon dioxide is produced, and electrons are pulled off and passed into an electron transport system which, just as in photosynthesis, generates a lot of ATP for the plant to use for growth and reproduction. This last step requires oxygen, and therefore is called aerobic respiration. Thus, the final result of cellular respiration is that the plant consumes glucose and oxygen and produces carbon dioxide, water, and ATP energy molecules.
At first, this doesn't seem to make any sense! If the plant can use the energy from the sun to make ATP, why does it go through all the trouble of then using up the ATP to make glucose, just so it can get ATP again? There are two reasons why the plant does this. First, in addition to ATP, the plant needs materials to grow. Glucose is an important building block that is necessary to produce all of the proteins, DNA, cells, tissues, etc. that are important to life, growth, and reproduction. Second, one problem with the sun is that it goes away every night, and during winter it isn't very bright. The plant needs energy all of the time. So, by producing glucose, the plant can store this molecule and then use it to produce energy during the night and over winter when there isn't enough sun to provide good photosynthesis.
It is very interesting how photosynthesis and cellular respiration help each other. During photosynthesis, the plant needs carbon dioxide and water-- both of which are released into the air during respiration. And during respiration, the plant needs oxygen and glucose, which are both produced through photosynthesis! So in a way, the products of photosynthesis support respiration, and the products of respiration support photosynthesis, forming a cycle.
While plants can complete this cycle by themselves, animals cannot, since animals aren't capable of photosynthesis! This means that animals have to survive solely through respiration. Also, since we animals can't produce glucose by ourselves, we have to get it from somewhere else-- from eating plants. We produce carbon dioxide that the plants need, and they produce the oxygen that we need, and then we eat them to get the glucose that we need. It seems that we need the plants a lot more than they need us!
similarities and differences between photosynthesis …
photosynthesis , process in which green plants, algae, and cyanobacteria utilize the energy of sunlight to manufacture carbohydrates from carbon dioxide and water in the presence of chlorophyll. Some of the plants that lack chlorophyll, e.g., the , secure their nutrients from organic material, as do animals, and a few bacteria manufacture their own carbohydrates with hydrogen and energy obtained from inorganic compounds (e.g., hydrogen sulfide) in a process called . However, the vast majority of plants contain chlorophyll—concentrated, in the higher land plants, in the leaves.
In these plants water is absorbed by the roots and carried to the leaves by the xylem, and carbon dioxide is obtained from air that enters the leaves through the stomata and diffuses to the cells containing chlorophyll. The green pigment is uniquely capable of converting the active energy of light into a latent form that can be stored (in food) and used when needed.
The Photosynthetic Process
The initial process in photosynthesis is the decomposition of water (HO) into oxygen, which is released, and hydrogen; direct light is required for this process. The hydrogen and the carbon and oxygen of carbon dioxide (CO) are then converted into a series of increasingly complex compounds that result finally in a stable organic compound, glucose (CHO), and water. This phase of photosynthesis utilizes stored energy and therefore can proceed in the dark. The simplified equation used to represent this overall process is 6CO+12HO+energy=CHO+6O+6HO. In general, the results of this process are the reverse of those in respiration, in which carbohydrates are oxidized to release energy, with the production of carbon dioxide and water.
The intermediary reactions before glucose is formed involve several enzymes, which react with the coenzyme ATP (see ) to produce various molecules. Studies using radioactive carbon have indicated that among the intermediate products are three-carbon molecules from which acids and amino acids, as well as glucose, are derived. This suggests that fats and proteins are also products of photosynthesis. The main product, glucose, is the fundamental building block of carbohydrates (e.g., sugars, starches, and cellulose). The water-soluble sugars (e.g., sucrose and maltose) are used for immediate energy. The insoluble starches are stored as tiny granules in various parts of the plant—chiefly the leaves, roots (including tubers), and fruits—and can be broken down again when energy is needed. Cellulose is used to build the rigid cell walls that are the principal supporting structure of plants.
Importance of Photosynthesis
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 vapor, in transpiration) as a photosynthetic byproduct, 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.
See I. Asimov, (1969); R. M. Devlin and A. V. Barker, (1972); O. Morton, (2009).