Plant Physiology
Photosynthesis - Transpiration - Respiration - Osmosis.
The process by which plants use the sun's light to produce food, specifically sugars. Many things must be present for photosynthesis to take place. The sun's light, water, carbon dioxide and chlorophyll are needed to complete the process vital to plant growth.
Photosynthesis is the physico-chemical process by which plants, algae and photosynthetic bacteria use light energy to drive the synthesis of organic compounds. In plants, algae and certain types of bacteria, the photosynthetic process results in the release of molecular oxygen and the removal of carbon dioxide from the atmosphere that is used to synthesize carbohydrates (oxygenic photosynthesis). Other types of bacteria use light energy to create organic compounds but do not produce oxygen (anoxygenic photosynthesis). Photosynthesis provides the energy and reduced carbon required for the survival of virtually all life on our planet, as well as the molecular oxygen necessary for the survival of oxygen consuming organisms1 . In addition, the fossil fuels currently being burned to provide energy for human activity were produced by ancient photosynthetic organisms. Although photosynthesis occurs in cells or organelles that are typically only a few microns across, the process has a profound impact on the earth's atmosphere and climate. Each year more than 10% of the total atmospheric carbon dioxide is reduced to carbohydrate by photosynthetic organisms. Most, if not all, of the reduced carbon is returned to the atmosphere as carbon dioxide by microbial, plant and animal metabolism, and by biomass combustion. In turn, the performance of photosynthetic organisms depends on the earth's atmosphere and climate. Over the next century, the large increase in the amount of atmospheric carbon dioxide created by human activity is certain to have a profound impact on the performance and competition of photosynthetic organisms. Knowledge of the physico-chemical process of photosynthesis is essential for understanding the relationship between living organisms and the atmosphere and the balance of life on earth.
The overall equation for photosynthesis is deceptively simple. In fact, a complex set of physical and chemical reactions must occur in a coordinated manner for the synthesis of carbohydrates. To produce a sugar molecule such as sucrose, plants require nearly 30 distinct proteins that work within a complicated membrane structure. Research into the mechanism of photosynthesis centers on understanding the structure of the photosynthetic components and the molecular processes that use radiant energy to drive carbohydrate synthesis. The research involves several disciplines, including physics, biophysics, chemistry, structural biology, biochemistry, molecular biology and physiology, and serves as an outstanding example of the success of multidisciplinary research. As such, photosynthesis presents a special challenge in understanding several interrelated molecular processes.
6CO2 + 6H2O + light energy = C6H12O6 + 6O2
The product of photosynthesis is a carbohydrate, such as the sugar glucose, and oxygen
which is released to the atmosphere. All of the sugar produced in the photosynthetic cells
of plants and other organisms is derived from the initial chemical combining of carbon
dioxide and water with sunlight. This chemical reaction is catalyzed by chlorophyll acting
in concert with other pigment, lipid, sugars, protein, and nucleic acid molecules. Sugars
created in photosynthesis can be later converted by the plant to starch for storage, or it
can be combined with other sugar molecules to form specialized carbohydrates such as
cellulose, or it can be combined with other nutrients such as nitrogen, phosphorus, and
sulfur, to build complex molecules such as proteins and nucleic acids.
Because all the energy fixed by the plant is converted into sugar, it is theoretically
possible to determine plant's energy uptake by measuring the amount of sugar produced.
This quantity is called gross primary productivity. Measurements of the build-up of sugar
in the plant reflect gross primary productivity less respiration, or net primary
productivity.
In general, animals cannot produce their own energy via photosynthesis. Instead, they
capture their energy by the consumption of plants or other animals.
Plants release water through pores in their
leaves. The evaporative loss of this water is called transpiration. As hot air passes over
the surface of the leaves, the moisture absorbs some of the heat and evaporates. The air
surrounding the leaf surface is thus cooled by the process. This interaction is called
evaporative cooling, and air temperatures surrounding vegetation can be lowered by as much
as 9 degrees F (5 degrees C) by its effects.
The greater the amount of leaf area in the landscape, the greater the cooling effects of
transpiration. The use of plants for shade and wind control instead of structural features
such as fences and arbors thus provides an additional benefit toward maintaining thermal
comfort during Florida's long summer. Air temperatures near shade trees and foundation
shrubs will be considerably lower than open areas, resulting in lower heat gains through
nearby walls or windows. If summer breezes are channeled through and across vegetation,
their cooling capacity will be increased.
To maximize the effects of evaporative cooling, increase the amount of plant cover around
the home. Use turf and/or ground covers to their fullest potential in the landscape, as
alternatives to paved surfaces such as asphalt or concrete. Many ground covers require
less maintenance than turf grasses, and can be used as energy saving alternatives to large
expanses of lawn.
Is the typical process where mitochondria of
cells of organisms release chemical energy from sugar and other organic molecules through
chemical oxidation. This process occurs in both plants and animals. In most organisms,
respiration releases the energy required for all metabolic processes. This chemical
reaction can be described by the following simple equation:
C6H12O6 + 6O2 = 6CO2 + 6H2O
+ released energy
The movement of solvent molecules by diffusion through a plant cell membrane. This is a process of equilibrium. It does not take any energy to perform, but is actually the result of random molecular movements. Sugars produced from photosynthesis for example, is a normal solute in the water of plant cells or protoplasm. Sugar levels can reach up to 3% causing the water to be impure. If such a cell was surrounded by 100%pure water, there would be a natural passage of water into the cell (where their concentration is less). As long as the concentration of water molecules inside the cell is less than that outside, the rate of entry of solventshould exceed the rate of exit of solvent. But since the sugar does not escape through the membrane, the concentration of water inside the cell can never reach 100%.Equilibrium is is permantly upset by the presence of solute inside the cell, hence water continues to travel by osmosis. Ideally there would be no limit to osmotic entry of the solvent water but a natural swelling of the cells equalizes the amount of water entering asd leaving the cell. This is what gives plants, especially herbacous plants, their turgor or rigidity.
Osmosis can work in either direction. If a cell was placed into a solution even more impure than itself it would give up all it's water to dillute the surrounding solution. This is what happens when too much fertilizer is applied. The salts in the fertilizer draw out the water in the plant.
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