Chapter 6 Cellular Respiration Obtaining Energy From Food Guided Reading

Photosynthesis- uses light energy from the sun to power a chemical process that builds organic molecules. Plants use photosynthesis to convert the energy of sunlight to the chemical energy of sugars and other organic molecules. ** See diagram below**

Photosynthesis diagram

Autotrophs ("self-feeders")- These are organisms that make all their own organic matter. They make up carbohydrates, lipids, proteins, and nucleic acids from carbon dioxide, air, water, and minerals from the soil. These are mostly plants and they are the Producers of the ecosystem.

Heterotrophs ("other-feeders")- These are humans and other animals and they are organisms that cannot make organic molecules from inorganic ones. They need to eat organic material to get nutrients. The organisms that make up this group are the Consumers of the ecosystem.

Chemical Cycling between Photosynthesis and Cellular Respiration

The chemical ingredients needed for photosynthesis are carbon dioxide, gas that comes from the air into the plant through tiny pores, and water. Chloroplasts inside the leaf cells use light energy to produce sugars, like glucose, and other organic molecules. The by-product of all this is oxygen which is vital to living organisms. Cellular respiration harvests energy and converts it to ATP (which cells need for everything) that is stored in the sugars and organic molecules from photosynthesis. In other words, plants store chemical energy through photosynthesis and then harvest it through cellular respiration.

Cellular Respiration- This is the main way that chemical energy is harvested from food and converted to ATP energy. This is an aerobic process. The chemical reaction takes glucose and oxygen and turns it into carbon dioxide, water, and ATP energy. This is not a single chemical reaction, but a series of reactions. There are three main stages: Glycolysis, the citric acid cycle(Krebs cycle), and electron transport.

Role of Oxygen in Cellular Respiration

Oxygen makes it possible to follow the transfer of electrons in cellular respiration. It also makes it so water can form during the reaction when hydrogen and its electrons change from sugar.

Redox Reactions (oxidation reactions)- These are chemical reactions that transfer electrons from one substance to another substance. The loss of electrons during the reaction is called Oxidation and gaining electrons during the reaction is called Reduction.

NADH and Electron Transport Chains

The transfer of electrons from food to NAD+ reduces it to NADH. All of this takes place on an electron transport chain. A series of redox reactions goes across the transport chain.

Glycolysis- This is stage 1 of cellular respiration. In step 1, a molecule of glucose is split into two molecules of a compound called pyruvic acid. Then in step 2, the two molecules donate high-energy electrons to NAD+ which forms NADH. Step 3, along with NADH, four ATP molecules are also made. Glycolysis produces two molecules of ATP per molecule of glucose. All that remains at the end of stage 1 are the two molecules of pyruvic acid.

Krebs cycle (citric acid cycle)- This is stage 2 of cellular respiration. Step 1, each pyruvic acid loses a carbon and changes to acetic acid with only two carbons remaining. Step 2, oxidation of the fuel generates NADH. Step 3, each acetic acid is attached to a molecule called coenzyme A (CoA), to form acetyl CoA. Then the CoA is stripped and recycled. Step 1, acetic acid joins a four-carbon acceptor molecule to form a six-carbon product called citric acid. Step 2, two carbon dioxide molecules exit as waste product and along the way citric acid cycle harvests energy from fuel. Step 3-5, some energy is used to produce ATP directly but the cycle gets much more energy in the form of NADH and FADH_2.Step 6, all of the carbon atoms are accounted for as CO₂ exhaust, and the acetic acid molecule is left.

Electron Transport- This is the final stage of cellular respiration and is built into the inner walls of the mitochondria. ATP Synthase are structures in the mitochondria that act like turbines. Step 1-2, NADH and FADH _{2 transfer electrons to the electron transport chains. Step 3, the transport chain uses this energy to pump H+ across the inner mitochondrial membrane. Step 4, oxygen pulls electrons down the transport chain. Step 5, the H+ rushes back downhill through an ATP synthase which causes the component to spin. Step 6, the rotation activates parts of the synthase molecule that attach phosphate groups to ADP molecules to generate ATP.}

Results of Cellular Respiration

The overall function of cellular respiration is to make about 32 molecules of ATP for every molecule of glucose. Glycolysis and the Krebs cycle will each make 2 ATP directly and the rest will be made by the ATP synthase. Energy flows from glucose to carrier molecules and then into ATP.

Fermentation- is the harvest of food energy without oxygen. This is an anaerobic (without oxygen) process. Fermentation relies on glycolysis which is the also the first stage of cellular respiration.

Fermentation in Human Muscle Cells

To work, your muscles need a constant supply of ATP which is generated by cellular respiration. Under strenuous conditions, your muscles can use ATP faster than your bloodstream can deliver oxygen and your muscles will start to work anaerobically. After functioning anaerobically for about 15 seconds, your muscle cells will begin to make ATP through fermentation. Fermentation relies on glycolysis which does not need oxygen and directly produces to ATP for each glucose broken down. NAD+ and NADH is recycled but in a slightly different way than in cell respiration. NADH disposes of the electrons by adding them to pyruvic acid produced by glycolysis and the NAD+ is restored. This also produces the waste product of lactic acid. This is then transported to the liver where it is changed back to pyruvic acid.

Muscle Burn

Muscles produce lactic acid in anaerobic conditions and after an experiment, scientist A.V. Hill, concluded that the buildup of lactic acid in muscles is what causes your muscles to burn. Also, the accumulation of lactic acid is the primary cause of failure in muscle tissue.

Fermentation in microorganisms

The two ATP molecules produced per glucose molecule during fermentation is enough to sustain many microorganisms. The food industry uses fermentation to produce certain foods from others. Yeast is a microscopic fungus that is capable of both cellular respiration and fermentation. When yeast ferments it produces ethyl alcohol as a waste product instead of lactic acid.

Video links

ATP and Respiration

Chapter 6 Cellular Respiration Obtaining Energy From Food Guided Reading

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