Teaching objectives of plant hormone regulation biology 1
1. Make students understand the regulation mode of life activities and its significance to organisms; Understand the concept of hormones; Understand the main physiological functions and characteristics of auxin, and preliminarily understand the characteristics of hormones through the understanding of auxin; Understand the interaction between plant hormones.
2. Through the discovery process of auxin, students can understand the experimental methods of studying plant hormones, stimulate their interest in learning life science and cultivate their logical thinking ability.
3. In the teaching of auxin physiological function, through the application of plant growth regulators in agricultural production, cultivate students' awareness of integrating theory with practice and educate students' values of life science.
Analysis of key points and difficulties
1. The regulation mode of life activities and its influence on biological life activities are one of the focuses of this teaching. Because: this topic is the teaching content after the topics of cell, biological metabolism, biological reproduction and development. Combining with students' existing knowledge, analyzing various metabolic activities and strict and orderly growth and development process in organisms requires the coordination of various life structures and metabolic activities, which is realized through the adjustment function of life activities; On the other hand, creatures living in the environment always respond to the changes of various factors in the environment, and the unity of this biological organism and the external environment is also completed through the adjustment of life activities. Through the study of this topic, students can understand the regulation mode of life activities and its role in biological life activities, and further understand that life is an extremely complex self-regulation system.
2. The physiological function of auxin is another focus of this teaching. On the one hand, students can understand the characteristics of plant hormones and the way plants regulate life activities through the understanding of plant auxin. On the other hand, auxin analogues are widely used in agricultural production, so it can be better combined with practice in the teaching of this content, which is conducive to stimulating students' interest in learning and educating students on the values of life science.
3. The discovery process of auxin is also the focus of this teaching. Although the discovery history of auxin does not necessarily require students to focus on memory, students can understand the cognitive process and scientific experimental methods of scientists by analyzing the discovery process of auxin, which embodies the characteristics of scientists' logical thinking. Therefore, some attention should be paid to this aspect of teaching.
4. The characteristics of plant hormones are one of the difficulties in this teaching. Although students have a certain understanding of hormones in junior high school biology class, they also have a certain perceptual knowledge of hormones in life, but they lack specific perceptual knowledge of the characteristics of hormone production, transportation and function, so this part of the content is the difficulty of teaching.
5. The interaction between plant hormones is another difficulty in this teaching. According to the requirements of teaching syllabus and teaching materials, the interaction between plant hormones is not the focus of this topic, so it is not appropriate to take up more time to talk about the functions and relationships of various hormones in teaching. However, it is very important for students to understand the interaction between plant hormones and fully understand the regulation mode of plant life activities. Therefore, it is a difficult point in teaching how to deal with it well in less time and let students understand the interaction between plant hormones.
Teaching process design
First, the reference classes of this question are two classes.
Second, the first class:
1. The design idea of teaching process;
2. Description of teaching process:
(1) By reviewing the coordination and strict sequence of various metabolism in the process of biological growth and development, it is pointed out that the coordination and unification of internal activities of organisms are realized through the adjustment mechanism of organisms. Here you can list one or two specific activities for further explanation, such as the coordination of breathing, circulation, digestion and other activities in the process of human body from calm to strenuous exercise, page 4, current page 1, page 1234 and adaptive response; Another example is the continuous development of plants from seed germination, organ differentiation and construction, flowering, fruiting, maturity and senescence. On the other hand, creatures living in the environment will make adaptive responses to the changes of various external factors, and the unity of such creatures and the environment is also the result of biological automatic adjustment. Here, it is best to give some examples to illustrate, such as the adaptive response of the human body from a warm environment to a cold environment; Phototropism of plants; Geotropism of roots, etc. On the basis of discussion, it is concluded that life is a self-regulating system, which maintains the unity of organism, organism and environment through regulation. After summarizing the significance of regulating life activities, it is pointed out that there are many ways to regulate life activities. Here, taking auxin of plants as an example, we will learn about hormone regulation of plants. Therefore, the subject of plant auxin is introduced.
(2) The discovery of auxin began with the study of phototropism of plants, which was completed after more than 50 years of research by several generations of scientists. According to this clue, we can discuss with students according to the following process (Figure 4- 1). The experimental discussion and analysis show that unilateral illumination will cause the light to bend, and the growth to the light side is slower than that to the backlight side. What structure is this phenomenon related to? What changes have light caused internally? After cutting off the top of the coleoptile, the coleoptile will no longer bend to light and stop growing. This phenomenon indicates that phototropism is related to the top of coleoptile. It can be inferred that the tip can feel the stimulation of light. This phenomenon shows that phototropism is really caused by the stimulation of unilateral light felt by the tip. It is speculated that something may be produced at the top of the coleoptile. The phenomenon confirmed the conjecture. It is further speculated that this substance may affect the growth of coleoptile. This phenomenon shows that the top of the coleoptile does produce some substances, which can be transported downwards. The side with more distribution of this substance grows fast, and the side with less distribution grows slowly, which leads to the curvature of coleoptile. Through the following experiments, the discussion and analysis of the phenomenon are further verified, and it is confirmed that the top of the coleoptile does produce substances that promote growth, and these substances can be transported downward from the top to promote the growth of the lower part. Finally, this substance was isolated and proved to be indoleacetic acid, named auxin. In order to save time, teachers should make slides before class, show the experimental treatment and phenomena one by one, and discuss and analyze them with teachers and students.
(3) The characteristics of auxin production location and transportation can be obtained by analyzing the following data (Figure 4-2).
According to this information, the following points are explained:
① The most active part of auxin synthesis is meristem, which is mainly distributed in the parts with vigorous growth. Such as stem tip, root tip, young leaves, fertilized ovary, etc.
② Auxin has the characteristics of polar transportation (from the top to the bottom of plant morphology).
Third, the second category:
1. The design idea of teaching process;
2. Description of teaching process:
Every physiological effect of (1) on auxin can be started with the introduction of related experiments or plant growth phenomena, and the corresponding physiological effects are summarized on the basis of analysis, and then the application in production practice is expounded.
(2) About promoting plant growth. By analyzing the response data of different organs of plants to auxin (Figure 4-3), the following points can be explained:
① The effect of auxin on plant growth is related to its concentration. Generally, low concentration promotes plant growth, while high concentration inhibits plant growth.
② The optimum concentration of auxin for promoting the growth of different organs is different. Sensitivity to auxin: root > bud > stem.
③ Explain the phenomenon of plant apical dominance and introduce some application examples in production practice.
(3) Auxin can promote fruit development and rooting of cuttings. Let the students read the relevant contents in the textbook and finally summarize the conclusion. Here, the teacher can introduce some application examples in production practice.
(4) About the interaction between plant hormones. Teachers can briefly introduce the main functions of several hormones, such as cytokinin, abscisic acid and ethylene * * * Page 4, currently Page 2 1234. On this basis, it is pointed out that any physiological activity of plants is not controlled by a single hormone, such as plant growth, but is influenced by auxin and cytokinin at the same time. Another example is that abscisic acid has antagonistic effect on auxin and cytokinin, which strongly inhibits growth and accelerates plant aging; Auxin promotes the growth of plants and induces the formation of ethylene. When the concentration of auxin exceeds the optimum concentration, the ethylene content increases and the plant growth is inhibited. By introducing the interaction between hormones, students can understand the coordination and unity of various physiological activities in plants and the adaptive response of plants to the environment, which is the result of simultaneous regulation of multiple hormones.
Fourth, the problems that should be paid attention to in the teaching of this topic:
1. In the teaching of auxin discovery, the main purpose is to let students know the methods of studying plant hormones and cultivate their ability to explore problems. Therefore, we should give full play to students' initiative, guide them to analyze the experimental design and results, and let them draw conclusions through their own analysis.
2. Attention should be paid to the regulation of plant hormones on life activities in teaching. For example, the concentration of auxin can promote and inhibit different organs, so that different organs can grow harmoniously; Such as the interaction between various hormones and the regulation of growth and development process.
3. In the teaching of this topic, whether it is the discovery process of auxin or the physiological function of auxin, we should pay attention to connecting with practice, so that students can analyze practical problems and form a theory about auxin. In addition, we should pay attention to the knowledge in the third chapter, such as auxin promoting fruit ripening, which should be related to the content of plant embryo and endosperm development process; Auxin promotes the rooting of cuttings, so it should be related to the content of vegetative propagation.
A little information 1. Action mechanism of auxin:
At present, there are various explanations for the mechanism of hormone action, which can be summarized into two types:
One is that hormones act on nucleic acid metabolism, which may be at the level of dna transcription. It activates some genes, forms some new mrna and protein (mainly enzymes), and then affects intracellular metabolism, causing changes in growth and development. On the other hand, hormones act on the cell membrane, that is, the plasma membrane is first affected by hormones, and a series of changes in membrane structure and function occur, so that many enzymes or prozymes attached to some organelles or plasma membranes change correspondingly, or are inactivated or activated. The change of enzyme system changes metabolism and the growth and development of the whole cell. In addition, some people think that hormones have an effect on both nuclear and plasma membranes; In other words, the action of hormones first passes through plasma membrane, then cytoplasm, and finally reaches the nucleus. Although there are different explanations for the mechanism of action of hormones, no matter which explanation, it is believed that hormones must first specifically bind to a substance in cells in order to produce effective regulation. This substance is a hormone receptor.
1. Hormone receptor: Plant hormone receptor refers to substances that can specifically bind plant hormones. This substance can combine with corresponding substances, recognize hormone signals, and transform the signals into a series of physiological and biochemical reactions, and finally show different biological effects. Receptors are the places where hormones initially act. Therefore, understanding the nature of hormone receptor and its existing position in cells is one of the important contents to study the mechanism of hormone action. Hormone receptor is a kind of protein, which may be located in plasma membrane, nucleus or cytoplasm. Because there are many kinds of hormones in plants, there must be many kinds of hormone receptors, which exist in different parts of cells.
2. The basic function of auxin is to promote cell elongation and growth, which is especially obvious in some isolated organs such as coleoptiles or etiolated stem segments. Why can auxin promote cell elongation and growth, and by what means? The outermost part of a plant cell is the cell wall. If a cell wants to elongate and grow, that is, to increase its volume, its cell wall must be enlarged accordingly. Fine ***4 pages, the current page 3 1234 to expand the cell wall, first of all, it needs to soften and relax to increase the plasticity of the cell wall, at the same time, synthesize new cell wall substances and increase protoplasm. The experiment shows that treating oat coleoptile with auxin can increase the plasticity of cell wall. Under the influence of different concentrations of auxin, the plasticity change and growth increase range are very close, indicating that auxin-induced growth is realized by increasing the plasticity of cell wall. Auxin promotes the increase of cell wall plasticity, which is not a simple physical change, but the result of metabolic activities. Because auxin has no effect on the plasticity of dead cells; In the presence of hypoxia or respiratory inhibitors, the changes of cell wall plasticity induced by auxin can be inhibited.
Second, the interaction between plant hormones:
In the process of plant growth and development, any physiological activity is not controlled by a single hormone, but the result of the interaction of multiple hormones. In other words, the process of plant growth is controlled by the interaction of various hormones. For example, cytokinin promotes cell proliferation, and auxin promotes daughter cell proliferation. For another example, abscisic acid strongly inhibits growth and accelerates the aging process, but these effects will be alleviated by cytokinins. Another example is that when the auxin concentration is appropriate, it can promote plant growth and induce the formation of ethylene at the same time. When the concentration of auxin exceeds the optimum concentration, the growth will be inhibited. It is of great significance to study the relationship between hormones in production practice.
3. Plant hormone analogues;
With the research on plant hormones, people constantly make some analogues with plant hormone activity through artificial synthesis. These plant hormone analogues are often called plant growth regulators. There are many kinds of plant growth regulators. According to different functions, it can be divided into three categories: plant growth promoters (such as NAA, 2,4-D, etc. ), plant growth inhibitors (such as triiodobenzoic acid, cyano, etc. ) and plant growth retardants (such as metformin and paclobutrazol). ). The following examples briefly introduce their functions and applications. Indobutyric acid: iba for short. Pure product is white or yellowish crystal, slightly smelly, insoluble in water, soluble in organic solvents such as ethanol and acetone. When in use, it can be dissolved in a small amount of alcohol first, and then diluted to the required concentration by adding water. It is mainly used to promote the rooting of plant cuttings, especially to promote rooting. However, the roots induced by indolebutyric acid are thin and long, and those induced by acetic acid are thick. Therefore, these two plant growth regulators are often mixed in production. Triiodobenzoic acid: triiodobenzoic acid is abbreviated as tiba. Pure product is white powder, insoluble in water, soluble in organic solvents such as ethanol and ether. Triiodobenzoic acid can hinder the transport of auxin in plants, inhibit the growth of stem tips and promote the germination of lateral buds, thus dwarfing plants, increasing branches and increasing the number of flowers and seeds. Triiodobenzoic acid has been widely used in soybean production. Spraying its solution on soybean plants can make the plants shorter, increase branches and increase pod setting rate, thus increasing soybean yield. Chlormequat chloride: ccc for short, and its chemical name is 2- chloroethyl trimethyl ammonium chloride. Pure product is white crystal, easily soluble in water. Contrary to gibberellin, it can inhibit cell elongation, but not cell division, so it can shorten plants and thicken stems. Chlormequat chloride has obvious effect on preventing rice and wheat from lodging and cotton buds from falling off, and increasing yield. Because chlormequat chloride is not easy to be fixed by soil and decomposed by microorganisms in soil, it is effective to apply it directly to soil. Paclobutrazol: Paclobutrazol is abbreviated as pp333. Paclobutrazol can inhibit gibberellin biosynthesis, slow down plant cell division and elongation, and inhibit stem elongation. Paclobutrazol is widely used in fruit trees, flowers, vegetables and field crops with remarkable results. For example, after spraying paclobutrazol on tomato seedlings, the seedlings can be stocky and have many branches. It is worth noting that plant growth regulators belong to pesticides. Although their toxicity is generally low or slightly toxic, it is still necessary to strictly abide by the safety operation rules in use to ensure the safety of people and animals. * * * Page 4, now Page 4 1234
Design idea of teaching plan 2 of plant hormone regulation biology;
1, design main line
The teaching activities focus on the discovery experiment of auxin, the physiological function of auxin and its application in agricultural production, and the regulation mechanism of plant hormones. In this process, the education of scientific history, scientific methods, scientific spirit and scientific values should be infiltrated in time; Cultivate students' participation consciousness, and cultivate students' observation ability, design experiment ability and hands-on operation ability.
2. Class plan:
Using interactive teaching mode, it is completed in three classes. Teachers provide discussion materials, organize and guide students' discussions and activities, and finally teachers and students conduct them in the form of summary.
The first class: in the first stage, the teacher asks questions or presents materials about the olfactory movement and sexual movement of plants to inspire students to think and discuss; Practice, put forward hypothesis, and design experiments to verify hypothesis; In the second stage, the teacher introduced Darwin's experiment and his hypothesis based on experimental observation.
The second class: in the first stage, teachers provide experimental materials for testing Darwin's hypothesis, organize students to discuss and analyze the experimental materials, guide students to get the experimental results for testing Darwin's hypothesis, and summarize the specific experimental methods for studying hormones; In the second stage, organize students to practice experimental design.
The third class: provide materials to enable students to understand the physiological function of auxin and the relationship between various plant hormones, understand the mechanism of plant hormone regulation, and how to apply the knowledge about auxin in production practice.
3. Analysis of key points and difficulties
Key points:
Three experiments in the process of (1) auxin discovery and analysis of experimental results.
In the historical process of scientific research and discovery, observation (including experimental observation), analysis based on the problems found in the observation process, and hypotheses put forward according to the analysis and verification activities of hypotheses continue to occur. The three experiments in the history of auxin discovery introduced in this paper completely reproduce the process of putting forward and verifying a hypothesis, and are excellent materials for educating students on the history of science. If we can make good use of these materials, it can also be an excellent opportunity to train students in scientific methods.
(2) Physiological function of auxin and its application in agricultural production.
Scientific research results can only benefit mankind if they are transformed into social productive forces through technology. Through teaching activities, students can understand the physiological function of auxin and its application in production practice, which not only helps students understand that scientific research should serve social production, but also helps students understand the mechanism of hormone regulation.
(3) Interaction between plant hormones.
Other plant hormones and the interaction between plant hormones are also a key point that should be dealt with emphatically in teaching. Only by letting students know about other hormones in plants can they understand that plant life activities are regulated by many hormones.
Difficulties: duality of physiological function of auxin and duality analysis of its application.
"Different organs (stem tips and root tips) have different concentrations of auxin that cause cell growth". If students do not master this feature well, they will be confused when analyzing practical problems by using the duality of auxin physiological function, so this part is the difficulty for students to master knowledge. Therefore, teachers must try to make two points clear in the teaching process: first, auxin has the characteristics of low concentration to promote growth and high concentration to inhibit the growth of various organs; Secondly, the optimum concentration of auxin to promote the growth of different organs is different.
4. Teaching process:
Introducing a new lesson: through the presentation of language statements, color pictures in textbooks, or the presentation of plant tropism experimental devices prepared by teachers in advance, we must first contact the content of the introduction lesson and make it clear that what happened is the expression of plant stress. Question: Why? Arouse students' interest and attract their attention.
Main teaching process: Introduce a series of experiments to discover auxin through animated media, introduce the general process of scientific research, and cultivate students' ability to analyze problems, put forward hypotheses, verify hypotheses and draw conclusions according to experimental results.
first kind
Analysis and discussion of experimental results;
"Why do plants show sexual movement? Darwin experimented with this phenomenon as early as 1880. " (You can introduce Darwin's experiment in two parts with animation courseware to guide students to learn to analyze the experimental results. ) "according to the results of the first part of the experiment, where do you think the part that produces light movement is in the plant?" "-at the top of the coleoptile." Students will naturally come to this conclusion.
"According to the results of the second part of the experiment, can you know what factors affect the tip of the coleoptile? Which direction is its influence? " "-The top of coleoptile is only stimulated by unilateral light." But it should be concluded that "the direction of its influence is from the top to the bottom of coleoptile." This conclusion requires the teacher to further guide the students to observe that the coleoptile tip moves towards light because it bends below the embryo tip. At this point, we can introduce Darwin's hypothesis based on the experimental results-the tip has a downward influence.
Scientific method training:
To cultivate and train students' scientific quality, we should not only introduce the general process of scientific research into the teaching process of biological knowledge, but also pay attention to summarizing the specific experimental (operational) methods of predecessors' work for students in time.
"Looking back at the discovery history of auxin, we can find that scientists from different countries have made unremitting efforts to uncover the mystery of plant life activities during the decades from 1880 to 1934. We can also try to analyze the specific experimental methods used by some scientists. " "What did Darwin do to the coleoptile in the first part of the experiment?" "-a part of the top of the coleoptile was cut off." "This is the experimental method used by Darwin." "When cutting off the top of this coleoptile, do you only observe the seedlings at the top of the coleoptile?" "This is a comparative observation of seedlings with coleoptile tips removed and seedlings without coleoptile tips removed." "This is a comparative experimental method that must be established in the experiment."
Second lesson
Analysis and discussion of experimental results;
"1928, Dutch scientist Winter conducted further experiments with coleoptiles. On the basis of Darwin's experiment, he made technical improvements to the operation of the experiment. " (Introduce Winter's experiment with animation courseware) "What conclusions can we draw from Winter's experimental results?" -"Confirmed Darwin's hypothesis about the reason why plants move towards the light-there is indeed a substance that causes the germ tip to move towards the light".
1934, Dutch scientist Guo Ge and others isolated this substance from plants and determined that it was indoleacetic acid, which really confirmed Darwin's hypothesis from the perspective of chemical substances.
Scientific method training:
"Winter's experiment not only confirmed Darwin's hypothesis about the reason why plants move towards light-there is indeed a substance that causes the tip of coleoptile to bend towards the light source, but also made further improvement on the experimental method-and managed to add the hypothetical substance back to the excised plants, and then made a comparative observation. This became the experimental method of' excision-addition' commonly used by botanists to study hormones later. "
The third category
Scientific method training:
Only when students understand the specific operation methods of learning plant hormones can they spread their wings of thinking and make it possible for teachers to train students to expand their thinking.
(1) "According to Winter's experiment, can an experiment be designed to prove that auxin produced at the top of coleoptile can only be transported downwards, but not upwards?" Asking questions in this way can stimulate students' interest and inspire their thinking.
(2) "If you want to know, in plants, except the top of coleoptile, which parts of cells can produce auxin? What kind of cells do you think should be selected for testing? " After this question, it can inspire students to think, and it can also be transferred to the teaching activities of the location and distribution of auxin.
(3) "After auxin can be separated and extracted from plants, it is necessary to know:' What effect does auxin have on plant organs besides making plants bright?' What method can you use to do the experiment? "Through this question, we can not only inspire students to think, but also smoothly transfer to the teaching activities about the physiological functions of auxin.
Solution to the difficult problem: duality of auxin function
Disclaimer: When scientists can separate and extract auxin, it is possible to do further experiments with auxin.
Guiding analysis: What can we find from the description of the experimental results? Variation curve of difficulty of three auxins
Teacher-student discussion: As can be seen from the figure, the growth rate of plant organs does not always increase with the increase of auxin concentration. However, when the concentration exceeds a certain value, the growth rate of plant organs decreases with the increase of auxin concentration. This leads scientists to the conclusion that "the physiological function of auxin in promoting growth is twofold ―― low concentration promotes growth and high concentration inhibits growth".
Further analysis: "So, is the auxin concentration that promotes or inhibits growth the same for all organs of plants?" From the experimental results, it can be seen that the concentrations of auxin required by roots, buds and stems are different, and the concentrations of auxin inhibiting them are also different. For example, this concentration can inhibit the growth of roots and buds, but can promote the growth of stems.
Create a problem scenario: put a sprouting broad bean seed horizontally, and constantly provide the conditions needed for growth, so that the embryo of broad bean grows upward and the radicle grows downward. What is the concentration distribution of auxin in the embryo and radicle transition? Animation fragment
Further discussion and analysis: the underground essence of stem is that higher concentration of auxin promotes the growth of near-surface cells. The geotropism of roots is that higher concentration of auxin inhibits the growth of near-surface cells. Roots and stems all show stress under the action of auxin, but the action mechanism of auxin on them is different The main reason is that different organs have different sensitivities to auxin concentration.
Summary and improvement: Whether it is the physiological function of auxin or the regulatory function of other plant hormones, there are two processes of promoting or inhibiting some plant life activities. These two contradictory processes regulate the life activities of plants.
Biology teaching plan of plant hormone regulation III. The discovery process of auxin;
1. Darwin put forward the hypothesis through comparative observation: something was produced at the tip and affected the lower part under the stimulation of light.
2. Winter confirmed Darwin's hypothesis through experiments: something really exists.
3. Pueraria lobata isolated and identified an influential substance: indoleacetic acid, that is, auxin.
Second, the synthesis and distribution of auxin:
Synthesis site: cells and meristems with vigorous growth.
Distribution: 1, the light side is smaller than the backlight side.
2. It is produced at the top and transported downwards.
Third, the physiological function of auxin:
1, low concentration promotes growth and high concentration inhibits growth. Example: Top Advantage.
2. The concentration of auxin promoting the growth of different organs of plants is different.
Fourth, the application of auxin in production:
1, promoting rooting of cuttings.
2. Promote fruit development
3. Prevent falling flowers and fruits
Five, other plant hormones:
1, gibberellin
2, abscisic acid
3. Cytokinin
4. Ethylene
Investigation activities
Exploring the sexual movement of flower buds
In the design experiment to verify the sexual movement of plants, students can be prompted to put garlic, onion, radish and other plants upside down or sideways to observe the sexual movement of flower buds.
Explore the direction of auxin transportation in plant stems
Can the stems of plants transport auxin upward? This question aims to guide students to explore from material selection to experimental design and implementation. The specific implementation method is: in spring (March), select leafless poplar, bend several branches, make its terminal buds downward, and observe the growth and development phenomenon. After the experimental setup is completed, the possible experimental results should be expected, observed and recorded. When all the leaves on the branches grow out, summarize the observation records, make a summary report and analyze the experimental results.