importance of atp a level biology essay mark scheme

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The uses and importance of ATP in organisms One of the major processes for plants is photosynthesis. Photosynthesis is the process which transfers light energy into chemical energy in biological molecules. In ecosystems where light and water are available, photosynthesis enables plants to synthesize organic compounds from CO 2. ATP is important for the light-dependent reaction because it is an electron-carrier molecule. Photoionisation is the process of light energy being absorbed by chlorophyll, this excites electrons causing them to be released from the chlorophyll. When the electrons are excited, they are taken up by electron carriers and passed down an electron transport chain. Electrons lose energy which produces ATP. Electrons lost during photoionisation are replaced by electrons released during the photolysis of water. In the Calvin cycle in the light-independent reaction, ATP also plays a major role. CO 2 binds with RuBP using the enzyme Rubisco, which produces 2 GP. ATP and NADPH are used to activate TP. 2 ATP lose its Pi to form 2 ADP and 2 NADPH lose a H+ to form 2 NADP. Some of the TP produced is converted into useful organic substances such as amino acids, lipids, and hexose sugars. The remaining TP reforms RuBP by using ATP. This ATP loses its Pi to form ADP which releases energy. Another biological process which uses ATP in organisms is active transport. Active transport is the movement of molecules and ions through a cell membrane from a region of low concentration to high concentration. This requires the hydrolysis of ATP because molecules are being moved against a concentration gradient. Similarly to the Calvin cycle, ATP loses a Pi to form ADP. This Pi binds to the protein on the membrane, which causes it to change its tertiary structure and allows the molecule to travel through the channel. The Pi is then released and binds to ADP to reform the initial ATP molecule. Exocytosis is also an active process because ATP is required for the movement of vesicles through the cytoplasm. Exocytosis is the bulk transport of materials out of cells. ATP allows vesicles to move towards the cell membrane and fuse with it, as the membrane fuses the contents are released out of the cell. An example of where this occurs is in Cholinergic Synapses. The vesicles containing the neurotransmitter Acetylcholine bind to the pre-synaptic cleft and are released by exocytosis, it then diffuses across the synaptic cleft, binds to the post-synaptic membrane receptors, and leads to a wave of depolarisation sending an impulse. ATP is important for respiration as it’s an energy-carrying molecule, therefore, it can synthesise the movement of protons back into the matrix of the mitochondria. The first stage of aerobic respiration is glycolysis. 2 ATP phosphorylate glucose to form fructose biphosphate. This 6C molecule then splits into 2 molecules of TP. The TP is then oxidised, and hydrogen is removed from each molecule and transferred to coenzyme NAD to form 2 reduced NAD. Dephosphorylation is the next step, 4 Pi from the intermediate substrate molecules bind to 4 ADP and form 4 ATP through a process called substrate-linked phosphorylation. 2 TP then finally form 2 pyruvate molecules. The next step of aerobic respiration is the link reaction. As mentioned previously, active transport is a process which involves ATP. The pyruvate produced by glycolysis is actively transported to the mitochondria. The pyruvate is then oxidised to form acetate and CO 2 by the reduction of NAD to NADH. Acetate then combines with coenzyme A to form acetyl CoA. The next stage is the Krebs cycle. This consists of a series of enzyme-controlled reactions. Acetyl CoA binds to a 4C oxaloacetate molecule to form a 6C citrate. Citrate is then converted back into oxaloacetate through a series of redox reactions. Citrate is decarboxylated

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Subject : Biology

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