I. Knowledge structure
Second, the teaching purpose
1. The concept of cell respiration (c: understanding).
2. Biological aerobic respiration and anaerobic respiration (C: understanding).
3. The meaning of cell respiration (c: understanding).
Three. Important and difficult
1. Teaching focus
Knowledge of aerobic respiration and anaerobic respiration.
(2) the meaning of breathing.
2. Teaching difficulties
Knowledge of aerobic respiration and anaerobic respiration.
Fourth, teaching suggestions
At the beginning of this teaching, teachers should first make it clear that breathing is an important physiological function of all living organisms and living cells, not a macroscopic gas exchange process, but a process of oxidative decomposition, energy release and production of high-energy compound ATP by each living cell.
In the teaching process, we should grasp the following key issues to make complex knowledge easy to understand.
First, organic substances such as sugar, fat and protein are rich in energy, which comes from fixed light energy in photosynthesis.
Second, only when these organic substances are oxidized into simpler organic substances or completely oxidized into water and carbon dioxide can the stored energy be partially or completely released.
Third, the released energy is either dissipated in the form of heat energy or used to keep the body temperature constant. More importantly, a considerable amount of energy must be captured during the conversion from ADP→ATP ATP, and stored in the high-energy phosphate bond of ATP molecules, so as to become the "energy currency" of various life activities.
Fourthly, the structural basis of energy release and transfer is cytoplasmic matrix and mitochondria, as well as related enzyme systems.
Fifth, in the history of biological evolution, the atmosphere of the ancient earth was anoxic, when organisms lived by anaerobic breathing. With the emergence and prosperity of green plants, the oxygen in the atmosphere has increased, so the organisms that make a living by aerobic respiration occupy a dominant position. At the same time, mitochondria, a specialized organelle for aerobic respiration, have been found in the cytoplasm, but they still retain the ability of anaerobic respiration.
Sixth, the process and difference between anaerobic respiration and aerobic respiration are discussed by comparison. Perhaps it is more logical to introduce microbial fermentation (alcohol fermentation and lactic acid fermentation) first, then aerobic respiration, and finally point out anaerobic respiration of higher animals and plants.
Seventh, summarize the physiological significance of cell respiration.
In addition, for senior high school students, it should be pointed out that anaerobic respiration and aerobic respiration are both redox reactions. Oxidation does not depend on whether molecular oxygen participates. Losing electrons is oxidation, and gaining electrons is reduction. Pointing out this point can make students understand it more easily and combine it with basic chemistry knowledge.
Verb (abbreviation for verb) Review the questions and refer to the answers.
1. 1.(╳); 2.(╳).
Second, 1. (d) providing information; 2. (4)
3. Tip: The same point is that pyruvate is completely oxidized and decomposed into carbon dioxide and water, and more energy is released in the whole process. The difference is that pyruvate is decomposed into alcohol and carbon dioxide, or converted into lactic acid, and the whole process releases less energy.
Apple produces alcohol through anaerobic respiration during storage, so it has a wine taste.
Reference of intransitive verbs
The process of aerobic respiration
During breathing, glucose molecules will not be oxidized into carbon dioxide and water at once like combustion, but will undergo a series of complex chemical reactions. The process of aerobic respiration can be divided into the following three steps:
(1) glycolysis-breaking down one molecule of glucose into two molecules of pyruvate, and oxidizing (dehydrogenating) to generate a small amount of ATP.
(2) Tricarboxylic acid cycle-Pyruvic acid is completely decomposed into carbon dioxide and hydrogen (this hydrogen is carried by coenzyme that transmits hydrogen), and a small amount of ATP is generated at the same time.
(3) oxidative phosphorylation-hydrogen (hydrogen ions and electrons) is transferred to oxygen to generate water, and most of the energy is released to generate ATP.
The three-step chemical reaction of aerobic respiration mentioned in the senior high school biology (compulsory) textbook refers to these three steps.
glycolysis
The origin of the name glycolysis is that when animals breathe, glycogen (animal starch) is first used as a respiratory substrate to convert it into glucose, and then glucose is decomposed under anaerobic conditions to produce lactic acid, so this process is called glycolysis.
The process of glycolysis is mainly divided into the following two steps (Figure 3-9):
① Glucose was phosphorylated twice and isomerized to 1, 6- fructose diphosphate. In other words, a six-carbon compound becomes a compound with two phosphoric acids. This process consumes two molecules of ATP.
② 1, 6- fructose diphosphate is an unstable compound. Under the action of aldolase, it is easy to decompose into two kinds of triose phosphate-dihydroxyacetone phosphate and glyceraldehyde phosphate, which can be transformed into each other and are in equilibrium. When glyceraldehyde phosphate is further converted and consumed, dihydroxyacetone phosphate will also be converted into glyceraldehyde phosphate to participate in the subsequent reaction.
When glyceraldehyde phosphate is converted into glycerophosphate, the released hydrogen is carried by oxidized coenzyme I(NAD) and becomes reduced coenzyme I (NADH2). The energy released in this oxidation process is carried by ATP, which is also produced in the conversion of phosphoenolpyruvate into pyruvate.
During the whole process from glucose to pyruvate, the energy level gradually decreases, but only the above two reactions have a large energy level decrease, which is enough to generate ATP. Other reactions are only slightly reduced, which is not enough to produce ATP. So one molecule of fructose diphosphate can actually form two molecules of pyruvate and four molecules of ATP, but two molecules of ATP are used in the initial stage of glycolysis, so,
The process of glycolysis can be summarized as follows:
Pyruvate is an important transport point in respiration. Under aerobic conditions, it enters the tricarboxylic acid cycle. Under anaerobic conditions, it is reduced to lactic acid by NADH2, or converted to acetaldehyde (releasing CO2) after decarboxylation, and acetaldehyde is reduced to ethanol. This is the process of anaerobic breathing.
(b) Tricarboxylic acid cycle
The initial intermediate product of tricarboxylic acid cycle is citric acid. Because citric acid is a tricarboxylic acid, this process is called tricarboxylic acid cycle, also called citric acid cycle.
The simplified process of tricarboxylic acid cycle is as follows: pyruvate is oxidized (dehydrogenated) and decarboxylated (CO2 is released) to produce acetyl coenzyme A (acetyl coenzyme A). Acetyl-CoA condenses with oxaloacetic acid to form citric acid (C6), which is dehydrated to form aconitic acid, and aconitic acid is added with water to form isocitrate. Then isocitrate is oxidized and decarboxylated to produce α-ketoglutaric acid (C5), and α-ketoglutaric acid is oxidized and decarboxylated to produce succinic acid. Succinic acid is dehydrogenated and oxidized, and finally becomes oxaloacetic acid. Oxyacetic acid can combine with acetyl coenzyme A and enter the tricarboxylic acid cycle again. If this continues, the cycle will continue. Each molecule of glucose glycolysis generates two molecules of pyruvic acid, and then these two pyruvic acids are oxidized and decarboxylated, and each enters the tricarboxylic acid cycle to generate six molecules of CO2.
The process of tricarboxylic acid cycle can be summarized as follows:
In the tricarboxylic acid cycle, one * * * is dehydrogenated five times, of which the hydrogen released four times is carried by NAD, and the hydrogen released the other time (from succinic acid) is carried by yellow enzyme (FAD), and then it is oxidized into water in the process of oxidative phosphorylation. -When oxidative decarboxylation of ketoglutaric acid produces succinic acid, a molecule of ATP is also produced.
In the whole process of tricarboxylic acid cycle, only pyruvate is completely decomposed, and other acids are not completely decomposed, so as long as a small amount exists, the cycle can continue. Other acids, like conveyor belts in factories, transport pyruvate molecules forward and gradually decompose.
(iii) Oxidative phosphorylation
As mentioned above, dehydrogenation will occur in glycolysis and tricarboxylic acid cycle. One molecule of glucose will produce 2NADH2 in glycolysis and 8NADH2+2FADH2 in tricarboxylic acid cycle. After that, [H] in these compounds will combine with oxygen through a series of redox reactions, and finally generate water. First, H2 of NADH2 is transferred to FAD, so NADH2 is oxidized to NAD.
NADH2+FAD→NAD+FADH2
Later, H2 in FADH2 was separated into free hydrogen ions (H+) and electrons (e-):
FADH2→FAD+2H+ +2e-
Then, electrons are transferred in turn in various cytochrome. Cytochrome is an iron-containing porphyrin derivative, which exists in cells in combination with protein. Iron in cytochrome molecules can undergo redox reaction;
2 cytochrome Fe3+ +2e-→2 cytochrome Fe2+
There are several kinds of cytochrome A, a3, B, C and so on. It plays a role in oxidative phosphorylation of respiration. Electrons are first accepted by cytochrome B, then transferred to oxygen through C, A and a3, and 2H+ released by FAD is added to generate H2O (Figure 3- 1 1):
In this process, hydrogen ions (H+) and electrons (e-) are transferred between carriers, which is very similar to electron transfer in photosynthesis. Each carrier is a link in the whole transfer process and constitutes a "chain", so this chain is called respiratory electron transfer chain, or respiratory chain for short.
In the above redox process, the energy levels of electron transporters gradually decrease, and part of the energy released by them is retained to form ATP. This process of forming ATP by oxidizing the energy released by NADH2 or FADH2 is called oxidative phosphorylation. In this process, oxidation and phosphorylation are coupled. It is known that in the process of oxidation of NADH2 to water, A * * * is phosphorylated for three times to generate three molecules of ATP, while FADH2 is oxidized to water to generate only two molecules of ATP. The oxidative phosphorylation process of 1 molecule glucose can be summarized as follows:
Now we can sum up the whole breathing process:
(1) sugar fermentation
(2) Tricarboxylic acid cycle:
(3) oxidative phosphorylation:
In the above description, substances such as glucose are based on "molecules", while the unit used in textbooks is "moles". As we know, 1mol contains 6.02× 1023 molecules. Then, this total reaction can also be expressed as: for every 1mol of glucose oxidized, 6mol of carbon dioxide and 6mol of water are generated. At the same time, it takes 33.47kJ of energy to generate 38 mol of ATP.1mol of ADP, so 38 mol of TP needs 38×33.47= 1272kJ of energy. The total energy released by each oxidation of 1mol glucose is 2870kJ, of which only 1272kJ remains in ATP.
The process of anaerobic respiration
In addition to the above aerobic respiration, plants can also carry out another kind of respiration, namely anaerobic respiration. Anaerobic respiration does not need oxygen in the atmosphere, and some tissues can also breathe anaerobically under aerobic conditions. The basic difference between these two kinds of breathing is that some stages of aerobic breathing need oxygen in the atmosphere as a reactant, while strict anaerobic breathing does not need oxygen at any stage. Anaerobic respiration also includes many types. But they have a common feature, that is, oxygen is not the ultimate receptor of H+ and E, and the respiratory substrate is only partially oxidized, so the final products are alcohol, lactic acid and so on. Anaerobic respiration, sometimes called fermentation, is not an exact synonym. This is because some fermentation, such as acetic acid fermentation, is actually aerobic oxidation.
1. Alcohol-fermented yeast and some other microorganisms, even some higher plants, perform anaerobic respiration in the form of alcohol fermentation under anoxic conditions. Because the cells of yeast and higher plants not only contain alcohol dehydrogenase, but also contain a small amount of lactic acid, a small amount of lactic acid will also be produced during alcohol fermentation. Because alcohol fermentation is the main form of general anaerobic respiration, the way of anaerobic respiration is often described by alcohol fermentation process.
The previous stage of alcohol fermentation is exactly the same as all the steps of glycolysis. Under anoxic conditions, pyruvate is decarboxylated to acetaldehyde by pyruvate carboxylase. However, acetaldehyde does not react with acetyl coenzyme A and does not participate in the tricarboxylic acid cycle, but NADH2 produced by glycolysis is reduced to ethanol (ethanol) under the action of ethanol dehydrogenase.
2CH3COCOOH→2CH3CHO+2CO2
2CH3CHO+2NADH2→2C2H5OH+2NAD
The total reaction formula of alcohol fermentation is:
c6h 12o 6+2 ADP+2Pi→2 C2 H5 oh+2 CO2+2 ATP
The available energy provided by alcohol fermentation is only two molecules of ATP obtained in glycolysis stage. Most of the original bonds of glucose molecules can remain in alcohol and cannot be used by yeast or higher plants. Therefore, anaerobic respiration is an inefficient way to produce ATP. However, alcohol fermentation products play a very important role in industrial and agricultural production. For example, beer, fruit wine and industrial alcohol are all fermented by yeasts from different sources.
2. Lactic acid fermentation Lactic acid fermentation does not need the participation of oxygen, but only relies on the action of enzymes to decompose one molecule of glucose into two molecules of lactic acid and produce two molecules of ATP.
The steps of decomposing glucose into pyruvate are the same as those of alcohol fermentation, except that pyruvate is reduced by lactate dehydrogenase to produce lactic acid, and reduced coenzyme I(NADH2) is oxidized to oxidized coenzyme I(NAD), thus ensuring the continuous fermentation of lactic acid.
2ch 3 cocooh+2 NADH 2→2ch 3 chohcooh+2 nad
The total reaction formula of lactic acid fermentation is:
c6h 12o 6+2 ADP+2Pi→2 C3 h6 o 3+2 ATP
Lactic acid bacteria can ferment milk into cheese and yogurt. Pickles, sauerkraut and silage can be preserved for a long time because lactic acid fermentation accumulates lactic acid and inhibits the activities of other microorganisms.