A speech please on Photosynthesis for std VIII of about 2 mins.?

Answer 1

Photosynthesis (photo=light, synthesis=putting together), generally, is the synthesis of sugar from light, carbon dioxide and water, with oxygen as a waste product. It is arguably the most important biochemical pathway known; nearly all life depends on it. It is an extremely complex process, comprised of many coordinated biochemical reactions. It occurs in higher plants, algae, some bacteria, and some protists, organisms collectively referred to as photoautotrophs.

Photosynthesis uses the energy of light to make the sugar, glucose. A simple general equation for photosynthesis follows.

6 CO2 + 12 H2O + photons → C6H12O6 + 6 O2 + 6 H2O
carbon dioxide + water + light energy → glucose + oxygen + water
Photosynthesis occurs in two stages. In the first phase light-dependent reactions or photosynthetic reactions (also called the Light reactions) capture the energy of light and use it to make high-energy molecules. During the second phase, the light-independent reactions (also called the Calvin-Benson Cycle, and formerly known as the Dark Reactions) use the high-energy molecules to capture carbon dioxide (CO2) and make the precursors of glucose.

In the light-dependent reactions one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron excites pheophytin allowing the start of a flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP into NADPH. In addition, it serves to create a proton gradient across the chloroplast membrane; its dissipation is used by ATP Synthase for the concomitant synthesis of ATP. The chlorophyll molecule regains the lost electron by taking one from a water molecule through a process called photolysis, that releases oxygen gas as a waste product.

In the Light-independent or dark reactions the enzyme RuBisCO captures CO2 from the atmosphere and in a process that requires the newly formed NADPH, called the Calvin-Benson cycle releases three-carbon sugars which are later combined to form glucose.

Photosynthesis may simply be defined as the conversion of light energy into chemical energy by living organisms. It is affected by its surroundings and the rate of photosynthesis is affected by the concentration of carbon dioxide, light intensity and the temperature.

In plants
Most plants are photoautotrophs, which means that they are able to synthesize food directly from inorganic compounds using light energy - for example from the sun, instead of eating other organisms or relying on nutrients derived from them. This is distinct from chemoautotrophs that do not depend on light energy, but use energy from inorganic compounds.

The energy for photosynthesis ultimately comes from absorbed photons and involves a reducing agent, which is water in the case of plants, releasing oxygen as a waste product. The light energy is converted to chemical energy (known as light-dependent reactions), in the form of ATP and NADPH, which is used for synthetic reactions in photoautotrophs. Most notably plants use the chemical energy to fix carbon dioxide into carbohydrates and other organic compounds through light-independent reactions. The overall equation for carbon fixation (sometimes referred to as carbon reduction) in green plants is

n CO2 + 2n H2O + ATP + NADPH → (CH2O)n + n H2O + n O2,
Where n is defined according to the structure of the resulting carbohydrate.
More specifically, carbon fixation produces an intermediate product, which is then converted to the final hexose carbohydrate products. These carbohydrate products are then variously used to form other organic compounds, such as the building material cellulose, as precursors for lipid and amino acid biosynthesis or as a fuel in cellular respiration. The latter not only occurs in plants, but also in animals when the energy from plants get passed through a food chain. Organisms dependent on photosynthetic and chemosynthetic organisms are called heterotrophs. In general outline, cellular respiration is the opposite of photosynthesis: glucose and other compounds are oxidised to produce carbon dioxide, water, and chemical energy. However, both processes actually take place through a different sequence of reactions and in different cellular compartments.

Plants absorb light primarily using the pigment chlorophyll, which is the reason that most plants have a green color. The function of chlorophyll is often supported by other accessory pigments such as carotenes and xanthophylls. Both chlorophyll and accessory pigments are contained in organelles (compartments within the cell) called chloroplasts. Although all cells in the green parts of a plant have chloroplasts, most of the energy is captured in the leaves. The cells in the interior tissues of a leaf, called the mesophyll, contain about half a million chloroplasts for every square millimeter of leaf. The surface of the leaf is uniformly coated with a water-resistant, waxy cuticle, that protects the leaf from excessive evaporation of water and decreases the absorption of ultraviolet or blue light to reduce heating. The transparent epidermis layer allows light to pass through to the palisade mesophyll cells where most of the photosynthesis takes place.


In algae and bacteria
Algae is a range from multicellular forms like kelp to microscopic, single-celled organisms. Although they are not as complex as land plants, photosynthesis takes place biochemically the same way. Very much like plants, algae have chloroplasts and chlorophyll, but various accessory pigments are present in some algae such as phycoerythrin in red algae (rhodophytes), resulting in a wide variety of colours. All algae produce oxygen, and many are autotrophic. However, some are heterotrophic, relying on materials produced by other organisms. For example, in coral reefs, there is a symbiotic relationship between zooxanthellae and the coral polyps.

Photosynthetic bacteria do not have chloroplasts (or any membrane-bound organelles), instead, photosynthesis takes place directly within the cell. Cyanobacteria contain thylakoid membranes very similar to those in chloroplasts and are the only prokaryotes that perform oxygen-generating photosynthesis, in fact chloroplasts are now considered to have evolved from an endosymbiotic bacterium, which was also an ancestor of and later gave rise to cyanobacterium. The other photosynthetic bacteria have a variety of different pigments, called bacteriochlorophylls, and do not produce oxygen. Some bacteria such as Chromatium, oxidize hydrogen sulfide instead of water for photosynthesis, producing sulfur as waste.


The evolution of photosynthesis
The ability to convert light energy to chemical energy confers a significant evolutionary advantage to living organisms. Early photosynthetic systems, such as those from green and purple sulphur and green and purple non-sulphur bacteria, are thought to have been anoxygenic, using various molecules as electron donors. Green and purple sulphur bacteria are thought to have used hydrogen and sulphur as an electron donor. Green nonsulphur bacteria used various amino and other organic acids. Purple nonsulphur bacteria used a variety of non-specific organic molecules. The use of these molecules is consistent with the geological evidence that the atmosphere was highly reduced at that time. [citation needed]

Fossils have been found of what are thought to be filamentous photosynthetic organisms dating from 3400 million years ago (New Scientist, 19 Aug., 2006).

The oxygen in the atmosphere today exists due to the evolution of oxygenic photosynthesis, sometimes referred to as the oxygen catastrophe. Geological evidence suggests that oxygenic photosynthesis, such as that in cyanobacteria, became important during the Paleoproterozoic era around 2 billion years ago. Modern photosynthesis in plants and most photosynthetic prokaryotes is oxygenic. Oxygenic photosynthesis uses water as an electron donor which is oxidized into molecular oxygen by the absorption of a photon by the photosynthetic reaction centre.

Discovery
Although some of the steps in photosynthesis are still not completely understood, the overall photosynthetic equation has been known since the 1800s.

Jan van Helmont began the research of the process in the mid-1600s when he carefully measured the mass of the soil used by a plant and the mass of the plant as it grew. After noticing that the soil mass changed very little, he hypothesized that the mass of the growing plant must come from the water, the only substance he added to the potted plant. His hypothesis was partially accurate - much of the gained mass also comes from carbon dioxide as well as water. However, this was a signaling point to the idea that the bulk of a plant's biomass comes from the inputs of photosynthesis, not the soil itself.

Joseph Priestley, a chemist and minister, discovered that when he isolated a volume of air under an inverted jar, and burned a candle in it, the candle would burn out very quickly, much before it ran out of wax. He further discovered that a mouse could similarly "injure" air. He then showed that the air that had been "injured" by the candle and the mouse could be restored by a plant.

In 1778, Jan Ingenhousz, court physician to the Austrian Empress, repeated Priestley's experiments. He discovered that it was the influence of sun and light on the plant that could cause it to rescue a mouse in a matter of hours.

In 1796, Jean Senebier, a Swiss pastor, botanist, and naturalist who demonstrated that green plants consume carbon dioxide and release oxygen under the influence of light. Soon afterwards, Nicolas-Théodore de Saussure showed that the increase in mass of the plant as it grows could not be due only to uptake of CO2, but also to the incorporation of water. Thus the basic reaction by which photosynthesis is used to produce food (such as glucose) was outlined.

Modern scientists built on the foundation of knowledge from those scientists centuries ago and were able to discover many things.

Cornelis Van Niel made key discoveries explaining the chemistry of photosynthesis. By studying purple sulfur bacteria and green bacteria he was the first scientist to demonstrate that photosynthesis is a light-dependent redox reaction, in which hydrogen reduces carbon dioxide.

Further experiments to prove that the oxygen developed during the photosynthesis of green plants came from water, were performed by Robert Hill in 1937 and 1939. He showed that isolated chloroplasts give off oxygen in the presence of unnatural reducing agents like iron oxalate, ferricyanide or benzoquinone after exposure to light. The Hill reaction is as follows:

2 H2O + 2 A + (light, chloroplasts) → 2 AH2 + O2
where A is the electron acceptor. Therefore, in light the electron acceptor is reduced and oxygen is evolved.

Samuel Ruben and Martin Kamen used radioactive isotopes to determine that the oxygen liberated in photosynthesis came from the water.

Melvin Calvin and Andrew Benson, along with James Bassham, elucidated the path of carbon assimilation (the photosynthetic carbon reduction cycle) in plants. The carbon reduction cycle is known as the Calvin cycle, which inappropriately ignores the contribution of Bassham and Benson. Many scientists refer to the cycle as the Calvin-Benson Cycle, Benson-Calvin, and some even call it the Calvin-Benson-Bassham (or CBB) Cycle.

A Nobel Prize winning scientist, Rudolph A. Marcus, was able to discover the function and significance of the electron transport chain.


Factors affecting photosynthesis
There are three main factors affecting photosynthesis and several corollary factors. The three main are:

1. Light irradiance and wavelength
2. Carbon dioxide concentration
3. Temperature

Answer 2

Photosynthesis is the process of converting light energy to chemical energy and storing it in the bonds of sugar. This process occurs in plants and some algae (Kingdom Protista). Plants need only light energy, CO2, and H2O to make sugar. The process of photosynthesis takes place in the chloroplasts, specifically using chlorophyll, the green pigment involved in photosynthesis.

Photosynthesis takes place primarily in plant leaves, and little to none occurs in stems, etc. The parts of a typical leaf include the upper and lower epidermis, the mesophyll, the vascular bundle(s) (veins), and the stomates. The upper and lower epidermal cells do not have chloroplasts, thus photosynthesis does not occur there. They serve primarily as protection for the rest of the leaf. The stomates are holes which occur primarily in the lower epidermis and are for air exchange: they let CO2 in and O2 out. The vascular bundles or veins in a leaf are part of the plant's transportation system, moving water and nutrients around the plant as needed. The mesophyll cells have chloroplasts and this is where photosynthesis occurs.

Answer 3

Photosynthesis uses the energy of light to make the sugar, glucose. A simple general equation for photosynthesis follows.

6 CO2 + 12 H2O + photons → C6H12O6 + 6 O2 + 6 H2O
carbon dioxide + water + light energy → glucose + oxygen + water
Photosynthesis occurs in two stages. In the first phase light-dependent reactions or photosynthetic reactions (also called the Light reactions) capture the energy of light and use it to make high-energy molecules. During the second phase, the light-independent reactions (also called the Calvin-Benson Cycle, and formerly known as the Dark Reactions) use the high-energy molecules to capture carbon dioxide (CO2) and make the precursors of glucose.

In the light-dependent reactions one molecule of the pigment chlorophyll absorbs one photon and loses one electron. This electron excites pheophytin allowing the start of a flow of electrons down an electron transport chain that leads to the ultimate reduction of NADP into NADPH. In addition, it serves to create a proton gradient across the chloroplast membrane; its dissipation is used by ATP Synthase for the concomitant synthesis of ATP. The chlorophyll molecule regains the lost electron by taking one from a water molecule through a process called photolysis, that releases oxygen gas as a waste product.

In the Light-independent or dark reactions the enzyme RuBisCO captures CO2 from the atmosphere and in a process that requires the newly formed NADPH, called the Calvin-Benson cycle releases three-carbon sugars which are later combined to form glucose.

Photosynthesis may simply be defined as the conversion of light energy into chemical energy by living organisms. It is affected by its surroundings and the rate of photosynthesis is affected by the concentration of carbon dioxide, light intensity and the temperature.

Answer 4

Energy, the Mysterious Everything, pours onto the earth in the form of electromagnetic radiation that most of us call sunshine. The sun's energy heats the earth, makes weather, keeps us warm - thanks a lot.
But if that was all, this would still be a pretty dead planet, and there would be no me and no you.

Plants and animals need energy to live, to grow, and to make more of themselves.
All that solar energy pouring onto the earth everyday wouldn't do us any good if we didn't have some way to turn it into a form of energy that we can use.
Well, some under appreciated autotrophic life forms have "stepped-up" to save the day. They've developed a way to take sunshine, and a few common molecules from air and water, and turn them into something that the rest of us "non-autotrophs" can use.
Everyday, without fanfare or thanks, or anyone hardly noticing, these humble life forms make thousands of tons of glucose (and other carbohydrates) and put thousands of tons of oxygen into the atmosphere. Without all that oxygen and carbohydrates we animals would be in big trouble.
Photosynthesis is the beginning of the amazing journey of energy and the basic materials of life from plant to animal to animal to decomposer
For the molecules and atoms that living things are made of, the journey is a cycle that repeats itself over and over. You might be made of a few carbon or oxygen atoms that were once part of a dinosaur or a wooly mammoth.

For energy, the trip is sort of a one time thing - in and out. All the energy that moves through life eventually ends up as heat and radiates back into space - from whence it came. If it wasn't for that nice big dose of new energy coming in from the sun every day, we would all soon be very cold and in a permanent frozen state of "not-living".

Answer 5

Oh great and wondrous time lord, the tardis is due a 20 millennium service. Book it in for the full service and don't forget the tyre pressures

Answer 6

stop being a lazy cheater and do the homework yourself! did you honestly think that some stranger would actually write a speech for you with nothing in return?