Respiration is a reaction that occurs in the mitochondria. It is when glucose is broken down, in the presence of oxygen to release ATP (energy), water and carbon dioxide. Glucose comes from our food and, when broken down, releases ATP which can be used to power many processes such as growth, cell division and reproduction.
Where does it occur?
It depends on the type of respiration
Aerobic respiration
Aerobic respiration is a process that occurs in 3 steps. The fist step (glycolysis) occurs in the cytoplasm of the cell. The second two steps occur in the mitochondria. This allows glucose to be fully broken down and a large amount of ATP to be released, making this type of respiration more efficient.
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Anaerobic respiration
Anaerobic respiration occurs only in the cytoplasm. It is when glucose is partially broken down (glycolysis) to release a small amount of ATP (only 2 of them!) and then the remaining products are further broken down into lactic acid and carbon dioxide, as the necessary machinery needed to fully break down glucose are not present in the cytoplasm.
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How come aerobic respiration releases more ATP?
It involves the mitochondria which makes
the breakdown of glucose very efficient
the breakdown of glucose very efficient
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Mitochondria
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Rod shape
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Double membrane
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Folded cristae
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Liquid matrix
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Mitochondria are rod-shaped organelles and have a huge amount of membranes to maximize the space for the reactions involved in respiration to occur. Mitochondria have a double membrane which allows for compartmentalization. The outer membrane is selectively permeable to the outside environment (the environment within the cell) and allows many molecules to pass through with ease. The inner membrane is a lot more complex, consisting of structures called cristae. Cristae are wrinkles/folds which are organised into layers. Having a huge amount of membrane folded inside the cell means there is more space for which the reactants for aerobic respiration (oxygen and H+) can cross into the middle of the organelle. Enclosed in the inner membrane is the matrix - the fluid-filled space containing many enzymes. The enzymes need to be distributed around the cristae as this is where they function. The job of these enzymes is to break down glucose products into carbon dioxide and water.
Increases the surface area for reactions to occur. The cristae is lined with electron acceptor molecules.
- The greater the number of folds, the more electron acceptor molecules can fit along the inner membrane and the more energy is produced from the movement of electrons down the membrane, producing the energy ATP synthase (an enzyme) needs to re-attach a phosphate to ADP to make ATP (more on this below).
and mitochondria are found within
nearly every type of cell
but in different amounts depending on the cell's
but in different amounts depending on the cell's
energy demands
Cardiac cells
Hundreds of mitochondria High energy demands Muscle contracting and relaxing 24/7 |
Skin cells
Few mitochondria Low energy demands For mitosis and not much else |
Red blood cells
No mitochondria No energy demands Heart pumps cells around body |
Plant cells
Differing numbers of mitochondria, meristems have high number as they are continuously doing mitosis |
Is ATP energy? How does it work?
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ATP the molecule
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ATP to ADP
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ADP to ATP
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Energy is stored in the chemical bonds of the ATP molecule. We've always really thought of ATP as being energy however it just houses the energy until it gets used. As ATP, energy is most accessible to the body. The name adenosine triphosphate means there's an adenine, a sugar (ribose) and three(tri-) phosphate groups. Bonds between molecules hold energy.
When energy is required by the cell, one phosphate is removed from ATP to produce ADP (adenosine diphosphate - two phosphates, not three). Breaking the bond between the two phosphate groups is actually where energy comes from. Energy is released when the bond is broken.
When glucose is broken down, hydrogen molecules are left over. They lose electrons (becoming ions) and these electrons provide energy for an enzyme, ATP synthase, to rejoin a phosphate to ADP, forming ATP.
You can think of it like putting petrol in your car so that your car can go again - ADP is like a car with an empty tank - and when you put petrol in the car it becomes ATP - it holds the energy the car can use to get from A to B.
You can think of it like putting petrol in your car so that your car can go again - ADP is like a car with an empty tank - and when you put petrol in the car it becomes ATP - it holds the energy the car can use to get from A to B.
Aerobic respiration occurs in three parts
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Step 1. Glycolysis
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Step 2. Krebs cycle
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Step 3. Electron transport chain
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Factors that affect respiratiom
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In the cytoplasm glucose (C6H12O6) is broken down into 2 pyruvate molecules (C3H4O3) and some hydrogen molecules. This part does not require oxygen (so it also the main step of anaerobic respiration). Energy from the bonds broken in glucose are used to add a phosphate to two molecules of ADP (to make ATP). So this step releases 2 ATP molecules.
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In anaerobic respiration, the pyruvate molecules are further broken down into lactic acid and carbon dioxide. Lactic acid causes our muscles to fatigue and feel sore. Oxygen helps to break down this lactic acid down further into harmless waste products.
In aerobic respiration, the pyruvate molecules diffuse into the mitochondria and into the matrix. Hydrogen also travels there, however is carried by a carrier molecule called NAD, who picks up hydrogen (becoming NADH) and takes them there.
In aerobic respiration, the pyruvate molecules diffuse into the mitochondria and into the matrix. Hydrogen also travels there, however is carried by a carrier molecule called NAD, who picks up hydrogen (becoming NADH) and takes them there.
The carbon dioxide diffuses out of the mitochondria and the cell, as it is a waste product.
The hydrogen molecules are taken to the cristae by NAD for the final step, the electron transport chain.
The hydrogen molecules are taken to the cristae by NAD for the final step, the electron transport chain.
All the hydrogen molecules are brought to the cristae where they become ions, meaning they lose an electron. The electrons are passed down the cristae (lined with electron receptor molecules) which produces energy. This energy gives ATP synthase the ability to join a phosphate molecule on ADP to form ATP. Oxygen diffuses in here, as it is required to bond with hydrogen (after an electron has joined back on) to form water, a harmless waste product which is now able to leave the mitochondria and cell via osmosis. From 1 glucose molecule, through aerobic respiration, enough energy is produced from the electrons to give ATP synthase enough every to put 34 phosphates on 34 ADP molecules - forming 34 ATP molecules.
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In total you get 2 ATP from glycolysis + 2 ATP from krebs cycle + 34 from the ETC = 38ATP per 1 glucose molecule.
Enzymes control the reactions in respiration. As temperature increases, the rate of respiration increases. However, if the temperature increased past the optimum temperature then the enzymes would denature. This would mean the substrate will be unable to fit into the active site of the enzyme and will not be turned into the required product. In humans, the optimum temperature for our enzymes to work is 37 degrees Celsius.
When we have a temperature, we are at risk at having many enzymes denature! |
The rate of respiration will increase as the energy demand from tissues increases. This will be up to a maximum where as demand increases, the cell cannot produce energy any faster. This is because the amount of oxygen needed increases and the body's ability to deliver this oxygen cannot keep up. Breathing rate increases to compensate. Carbon dioxide buildup also acts as a feedback mechanism which slows the rate of respiration down.
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the overall reaction is written as
Glucose + Oxygen → Carbon dioxide + Water + ATP
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