Ch. 3
Solar radiation (light) is essential for the existence of life on earth. Plants algae and some bacteria absorb sunlight and assimilate it energy by photosynthesis. Light is the primary source of energy for the biosphere.
Plants capture the energy of sunlight through photosynthesis. Photosynthetic organisms convert the light that they capture (the energy) into chemical energy stored in the high-energy bonds of organic compounds.
The balance of this single equation of reactants and products often represents photosynthesis:
6CO2 + 6H2O + Photons -> C6H12O6 + 6O2
Much of the influence of temperature on physiological processes results from the way in which heat affects organic molecules. Heat impacts high imparts a high kinetic energy to living systems, causing biological molecules to move and change their shapes rapidly.
Moisture gradient: aquatic, and terrestrial
Latitudinal gradient: tropical, temperate, and polar
Light absorption: leaves contain several kinds of pigments; particularly chlorophyll and carotenoids that absorb this light and harness its energy. Chlorophyll, which is primarily responsible for capturing light energy in the light reactions of photosynthesis, absorbs red and violet light while reflecting green and blue light. This is why photosynthetic plants look green.
The visible portion of the spectrum, which corresponds to the wavelengths of light that are suitable for photosynthesis, ranges between about 400 nm (violet) and 700 nm (red). This range is the photosynthetically active region (PAR) of the spectrum.
Although it appears colorless in small quantities, water absorbs or scatters enough light to limit the depth of the sunlit zone of the sea (referred to as the photic zone). In pure seawater, the intensity of light in the visible part of the spectrum diminishes to 50% of the surface value at a depth of 10 m, and it drops to less than 7% within 100 m. Moreover, water absorbs longer (red) wavelengths more strongly than shorter ones; most infrared radiation disappears within the topmost meter of water. The shortest visible wavelengths (violet and blue) tend to scatter when they strike water molecules, so they too fail to penetrate deeply. Because of the absorption and scattering of these wavelengths by water, green light predominates with increasing depth.
Photorespiration: When Rubisco binds O2 instead of CO2, it initiates a series of reactions that reverse the light reactions:
2 G3P → CO2 + RuBP
The overall process resembles respiration in that it uses O2 and produces CO2. Because it also requires ATP and NADPH from the light reactions, it is referred to as photorespiration.
To address the problem of photorespiration many herbaceous plants, particularly grasses growing in hot climates, have modified the usual C3 photosynthetic process by adding a step to the initial assimilation of CO2; this is known as C4 photosynthesis, because CO2 is first joined with a three carbon molecule PEP (phosphenol pyruvate) to produce a four carbon oxaloacetic acid (OAA).
CO2 + PEP → OAA
Many of our most important crop plants, such as corn (maize), sorghum, and sugarcane, are C4 plants that are highly productive during hot growing seasons. C4 plants are spatially and temporally variated. C4 grasses prefer high CO2
CAM plants: Open their stomata at night to take in CO2, live in dry areas, and conserve a lot of water. CAM photosynthesis results in extremely high water use efficiencies and enables some types of plants to exist in habitats too hot and dry for other, more conventional species.
In addition to these biochemical modifications of photosynthesis, heat- and drought-adapted plants have anatomic and physiological modifications that reduce transpiration across their surfaces, reduce heat loads, and enable the plants to tolerate high temperatures. When plants absorb sunlight, they heat up, and as their temperatures increase, they lose water more rapidly. Plants can minimize over- heating by protecting their surfaces from direct sunlight with dense hairs and spines. Spines and hairs also produce a still boundary layer of air that traps moisture and reduces evaporation.
Each organism generally has a narrow range of environmental conditions to which it is best suited, which define its optimum. The optimum is determined by the properties of its enzymes and lipids, the structures of its cells and tissues, the form of its body, and other characteristics that influence the ability of the organism to function well under the particular conditions of its environment.
I.e. Optimal temperatures:
Too Cold
Low metabolic rate
Lipids more viscous and stiff
Too hot
Need more food
Enzymes denature
DNA unstable
Conduction is the transfer of the kinetic energy of heat between substances in contact with one another.
Convection is the transfer of heat by the movement of liquids and gases: molecules of air or water next to a warm surface gain energy and move away from the surface.
Evaporation removes heat from a surface.
All of the gains and losses of heat by an organism constitute its heat budget, which relates the rate of change in its heat content to gains and losses through radiation, conduction, convection, and evaporation, plus the internal heat it generates by metabolizing foods.
Plant Morphology: many plants in hot deserts reduce their heat loads by producing finely subdivided leaves with a large ratio of edge to surface area.
Thermoconformer: (poikilotherm): the body temperatures of poikilothermic organisms, such as frogs and grasshoppers, conform to the external temperature (the Greek root poikilo means “varying”).
Thermoregulator: (homeotherm): temperature regulation, which is referred to as homeothermy (the Greek root homos means “same”), creates constant temperature (homeothermic) conditions within the cells, under which biochemical processes can proceed efficiently
Ectotherm: Because the heat they use to elevate their body temperatures comes from outside the body, biologists refer to these animals as ectotherms (the Greek root ecto means “outside”). Ectotherms tend to be small (insects) or have low metabolic rates (reptiles and amphibians) that are not sufficient to offset heat loss in most environments.
Endotherm: animals that can generate sufficient heat metabolically to raise their body temperatures are referred to as endotherms (the Greek root endo means “inside”).
*****SPECIAL THANKS TO K.A. :)
Solar radiation (light) is essential for the existence of life on earth. Plants algae and some bacteria absorb sunlight and assimilate it energy by photosynthesis. Light is the primary source of energy for the biosphere.
Plants capture the energy of sunlight through photosynthesis. Photosynthetic organisms convert the light that they capture (the energy) into chemical energy stored in the high-energy bonds of organic compounds.
The balance of this single equation of reactants and products often represents photosynthesis:
6CO2 + 6H2O + Photons -> C6H12O6 + 6O2
Much of the influence of temperature on physiological processes results from the way in which heat affects organic molecules. Heat impacts high imparts a high kinetic energy to living systems, causing biological molecules to move and change their shapes rapidly.
Moisture gradient: aquatic, and terrestrial
Latitudinal gradient: tropical, temperate, and polar
Light absorption: leaves contain several kinds of pigments; particularly chlorophyll and carotenoids that absorb this light and harness its energy. Chlorophyll, which is primarily responsible for capturing light energy in the light reactions of photosynthesis, absorbs red and violet light while reflecting green and blue light. This is why photosynthetic plants look green.
The visible portion of the spectrum, which corresponds to the wavelengths of light that are suitable for photosynthesis, ranges between about 400 nm (violet) and 700 nm (red). This range is the photosynthetically active region (PAR) of the spectrum.
Although it appears colorless in small quantities, water absorbs or scatters enough light to limit the depth of the sunlit zone of the sea (referred to as the photic zone). In pure seawater, the intensity of light in the visible part of the spectrum diminishes to 50% of the surface value at a depth of 10 m, and it drops to less than 7% within 100 m. Moreover, water absorbs longer (red) wavelengths more strongly than shorter ones; most infrared radiation disappears within the topmost meter of water. The shortest visible wavelengths (violet and blue) tend to scatter when they strike water molecules, so they too fail to penetrate deeply. Because of the absorption and scattering of these wavelengths by water, green light predominates with increasing depth.
Photorespiration: When Rubisco binds O2 instead of CO2, it initiates a series of reactions that reverse the light reactions:
2 G3P → CO2 + RuBP
The overall process resembles respiration in that it uses O2 and produces CO2. Because it also requires ATP and NADPH from the light reactions, it is referred to as photorespiration.
To address the problem of photorespiration many herbaceous plants, particularly grasses growing in hot climates, have modified the usual C3 photosynthetic process by adding a step to the initial assimilation of CO2; this is known as C4 photosynthesis, because CO2 is first joined with a three carbon molecule PEP (phosphenol pyruvate) to produce a four carbon oxaloacetic acid (OAA).
CO2 + PEP → OAA
Many of our most important crop plants, such as corn (maize), sorghum, and sugarcane, are C4 plants that are highly productive during hot growing seasons. C4 plants are spatially and temporally variated. C4 grasses prefer high CO2
CAM plants: Open their stomata at night to take in CO2, live in dry areas, and conserve a lot of water. CAM photosynthesis results in extremely high water use efficiencies and enables some types of plants to exist in habitats too hot and dry for other, more conventional species.
In addition to these biochemical modifications of photosynthesis, heat- and drought-adapted plants have anatomic and physiological modifications that reduce transpiration across their surfaces, reduce heat loads, and enable the plants to tolerate high temperatures. When plants absorb sunlight, they heat up, and as their temperatures increase, they lose water more rapidly. Plants can minimize over- heating by protecting their surfaces from direct sunlight with dense hairs and spines. Spines and hairs also produce a still boundary layer of air that traps moisture and reduces evaporation.
Each organism generally has a narrow range of environmental conditions to which it is best suited, which define its optimum. The optimum is determined by the properties of its enzymes and lipids, the structures of its cells and tissues, the form of its body, and other characteristics that influence the ability of the organism to function well under the particular conditions of its environment.
I.e. Optimal temperatures:
Too Cold
Low metabolic rate
Lipids more viscous and stiff
Too hot
Need more food
Enzymes denature
DNA unstable
Conduction is the transfer of the kinetic energy of heat between substances in contact with one another.
Convection is the transfer of heat by the movement of liquids and gases: molecules of air or water next to a warm surface gain energy and move away from the surface.
Evaporation removes heat from a surface.
All of the gains and losses of heat by an organism constitute its heat budget, which relates the rate of change in its heat content to gains and losses through radiation, conduction, convection, and evaporation, plus the internal heat it generates by metabolizing foods.
Plant Morphology: many plants in hot deserts reduce their heat loads by producing finely subdivided leaves with a large ratio of edge to surface area.
Thermoconformer: (poikilotherm): the body temperatures of poikilothermic organisms, such as frogs and grasshoppers, conform to the external temperature (the Greek root poikilo means “varying”).
Thermoregulator: (homeotherm): temperature regulation, which is referred to as homeothermy (the Greek root homos means “same”), creates constant temperature (homeothermic) conditions within the cells, under which biochemical processes can proceed efficiently
Ectotherm: Because the heat they use to elevate their body temperatures comes from outside the body, biologists refer to these animals as ectotherms (the Greek root ecto means “outside”). Ectotherms tend to be small (insects) or have low metabolic rates (reptiles and amphibians) that are not sufficient to offset heat loss in most environments.
Endotherm: animals that can generate sufficient heat metabolically to raise their body temperatures are referred to as endotherms (the Greek root endo means “inside”).
*****SPECIAL THANKS TO K.A. :)