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Photosynthesis and Respiration
• Two processes that are necessary for all life to exist on this planet
• Ultimately all energy comes from the sun and in must be converted into a usable form for living organisms
Photosynthesis and Respiration
• Plants depend on photosynthesis to derive their energy sources.
• Through evolution, plant cells have acquired chlorophylls to help carry out the photosynthetic reaction.
• Photosynthesis is carried out in two steps the photo stage (light dependant reaction) and the synthesis stage (light independent stage)
Photosynthesis
• Occurs in specialized organelles called chloroplasts
• These contain pigments which are specialized molecules that absorb specific colors of light.
• Main pigments are chlorophyll (green), xanthophylls (red) and carotene (yellow/orange)
Chloroplasts
• It is within the chloroplast that photosynthesis occurs
• The pigments absorb the light energy but it requires many enzymes to carry out the process of photosynthesis
Photo Stage
• The main purpose of this stage is to convert the sun’s energy into a form that can be used in the synthesis stage of photosynthesis
• Chlorophyll molecules arranged within the thylakoid membranes in clusters called photosystems
• Each photosystem is composed of a few hundred pigment molecules that act together
• Their combined function is to concentrate the sun’s energy so it can be converted to a form that the plant can use
(cont’d)
• When the energy reaches the reaction centre it us used to break water into 2 hydrogen and an oxygen molecule
• Enzymes in the thylakoid break the hydrogen atoms into protons and electrons
• This released energy is used to covert ADP and P into ATP
• ATP is required for the next stage of photosynthesis
Synthesis stage
• The main purpose of this stage is to make simple sugars by using energy from the photo stage and carbon dioxide
• The synthesis stage of photosynthesis takes place in the stroma (the fluid portion of the chloroplast)
• Energy from the photo stage is necessary to drive the synthesis of simple sugars
(cont’d)
• There are many separate reactions that make up the synthesis stage of photosynthesis and they are collectively called the Calvin cycle
Photosynthesis
• Through this process, the plant is able to convert sunlight, water, and CO2 into glucose and ATP.
• As a byproduct of this process, O2 is released. • The plant's ability to convert water and CO2 into
glucose and O2 also provides great benefit for animal species that depend on glucose for energy.
• The photosynthetic reaction can be summarized as follows: 6CO2 + 12H2O + sunlight -> C6H12O6 + 6H2O + 6O2
Respiration
• Cells, like all things, need energy to operate.
• MP3 players use batteries for energy, cells use adenosine triphosphate (ATP) for energy.
• Unlike MP3 players, cells can produce their own energy.
• People don't eat ATP, though. Their food consists mostly of proteins, lipids, and polysaccharides (sugars) which need to be broken down into ATP.
Respiration
• Respiration can be either aerobic (in the presence of oxygen) or anaerobic (in the absence of oxygen). Anaerobic respiration may also be called fermentation.
• In both cases the process begins with the initial breakdown of glucose through the process of glycolysis.
Cellular Respiration
• The four basic phases of respiration are :– Glycolysis– Transition Reaction– Krebs Cycle– Electron Transport chain
• Each phase is a series of complex reactions that results in the production of ATP (chemical energy for the cell)
Aerobic Respiration
The end products of glycolysis undergoes further breakdown through a process called aerobic respiration in most organisms.
• This process requires oxygen and yields much more energy than glycolysis.
Aerobic Respiration
• The end result of ATP would be the production of 36 ATP
• The energy conversion is as follows:
• C6H12O6 + 6O2 -> 6CO2 + 6H2O + energy (ATP)
Anaerobic Respiration
• Occurs in aerobic organisms when there is a lack of oxygen
• This type of respiration is very inefficient – only 2 ATP are produced
• The product of this type of respiration is lactic acid and 2 ATP
• When we exercise strenuously our muscles perform this type of respiration
• It is the lactic acid that build up in the muscle that causes pain after this type of exercise
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