Photosynthesis
- Plants obtain energy directly from the sun - Organisms that do this are autotrophs (make their own food from inorganic forms) - Photosynthesis is a series of chemical reactions where the product of one reaction is consumed in the next reaction A + B = C C + D = E E + F = A
Inputs/Outputs - The inputs of photosynthesis are light, water, and CO2 - The outputs of photosynthesis are Oxygen and glucose (sugar) - Photosynthesis works in a cycle where the products of photosynthesis are used in cellular respiration (performed by animals), and cellular respiration produces the inputs of photosynthesis (with the exception of light)
Light Reactions - Occur in the thylakoid membrane of chloroplasts - Thylakoids are flattened sacks that are layered upon one another - Surrounding the thylakoids is a solution called the stroma - Chloroplasts absorb blue and red light, and reflect green. This is what makes plants green!
- There are two types of chlorophyll: A and B - Chlorophyll A is directly involved in the light reaction, whereas chlorophyll B is an accessory pigment - Other accessory pigments include carotenoids (yellows, oranges, and browns)
Electron Transport - The chlorophyll and carotenoids are found in clusters in the thylakoid membrane - Each cluster of pigments is known as a photosystem - There are two photosystems: Photosystem I and Photosystem II - Light enters in the photosystems and is passed along from molecule to molecule until reaching a specific pair of chlorophyll molecules
Water Splitting For every two molecules of water that are split, four electrons become available to replace those lost by chlorophyll molecules. The protons that are produced are left inside the thylakoid, while the oxygen diffuses out of the chloroplast and can then leave the plant. Thus, oxygen can be regarded as a byproduct of the light reactions - it is not needed for photosynthesis to occur but is needed for the process of cellular respiration.
The protons left over from the water splitting reaction end up in a high concentration within the lumen. This high concentration represents potential energy. Through the ATP Synthase, the protons move down the concentration gradient, and their passive transport binds a phosphate molecule to ADP+, creating ATP (adenosine triphosphate; an energy molecule).
Calvin Cycle - Is a light independent reaction - Occurs in the stroma - Produces organic compounds using the energy stored in ATP and NADPH during the light reactions
There are 3 components of the Calvin Cycle: 1. Carbon fixation - the Carbon atoms from the CO2 combine with a 5 carbon molecule known as RuBP. These are then fixed into 3-C molecule known as PGA 2. Reduction - PGA is converted into another 3-C molecule known as PGAL, releasing ADP, NADP, and phosphate to be used again in the light reactions 3. Regeneration - PGAL is converted back into RrBP through a series of reactions, and requires ATP. Some PGAL is not converted back, and becomes organic compounds
Cellular Respiration
- Occurs in the mitochondrial membrane of animal cells - Inputs are glucose + oxygen - Outputs are CO2 and H2O - Cellular respiration can be broken down into 2 main parts
1. Glycolysis: creates a small amount of ATP through oxidizing glucose into two 3-Carbon molecules. The process can take an anaerobic or aerobic route. Like in photosynthesis, it is a series of biochemical pathways that convert glucose into pyruvic acid. 2. Kreb s cycle: The pyruvate enters into aerobic respiration after being transformed into acetyl CoA. Because two molecules are formed by glucose, the Kreb s cycle can occur twice. The products of the Kreb s cycle are six NADH, two FADH2, two ATP, and 4 CO2 molecules 3. The Electron Transport Chain: The electrons flowing through the system must be accepted to allow the oxygen in the system to be cycled continually. Accepting the electrons is what allows H2O to forn as a product of respiration.