In the context of the new curriculum reform, various new teaching methods have emerged one after another, and the situational teaching method has gradually gained the attention of front-line teachers. Situational teaching can give full play to the strengthening and regulating effect of individual emotions on students' cognitive activities, and at the same time, it can also improve the intuitiveness of knowledge, help students generate more inspiration, and let students learn consciously. In the creation of situations, teachers need to reprocess the teaching content, turn the complex teaching content into concrete and perceptible things, substitute students into the situation, and improve the learning effect of students. Normally, the teaching situations created by teachers are specific scenes with images as the main body, which have a certain mood or emotional color, which can optimize students' learning experience, allow students to understand the content of the textbook more smoothly, and improve the learning effect. In the teaching of biology at the high school level, teachers should not only let students understand subject knowledge, but also cultivate students' ability to think rationally, let students realize that experiments are an important method to learn biology, guide students to learn in specific situations, and use biological knowledge to solve practical problems. Taking the "law of gene segregation" in high school biology as an example, the situational teaching method is used to combine the problem situation, the experimental situation, and the game situation, which gives full play to the advantages of situational teaching and achieves good teaching results.
1. Teaching Basics
1) Analysis of teaching materials.
The Law of Gene Segregation" is the content of the first section of the first chapter of the second compulsory course of high school biology in the People's Education Edition. From the perspective of the arrangement of the textbook, the textbook first introduces Mendel's hybridization experimental methods and experimental phenomena, and then expresses Mendel's analysis of experimental phenomena with "genetic factors", explains the causes of segregation phenomena, and summarizes the essence of the law of gene segregation. This section covers a large number of biological concepts, including dominant traits, recessive traits, trait segregation, etc. In teaching, teachers should pay attention to the fundamental position of the law of gene segregation in the whole textbook, strengthen the education of the history of science and the education of science methods, and improve the learning effect of students.
2) Teaching objectives of the lesson.
1.An overview of Mendel's experiments on the hybridization of a pair of relative traits;
2.Determine whether the given trait is relative;
3.Explain the causes of the phenomenon of separation;
4.Summarize and analyze experimental data, explain genetic phenomena, and try to design hybridization experiments
5.Improve the ability to innovate and create, and learn Mendel's quality of daring to question and challenge.
3) Analysis of the learning situation.
High school students already have a certain biological foundation, cognitive ability, and ability have been greatly improved, but the motivation of students in the problem is mainly curiosity about related questions, which is an interest-oriented nature, lacking a clear purpose, and logical thinking is not clear enough. High school students do not understand the essential mechanism of heredity and variation, and can only understand some superficial phenomena of heredity from life experience. To this end, teachers can create rich classroom teaching situations based on teaching content to improve students' intuitiveness of learning.
Second, the teaching process
1) Create problem situations to stimulate students' thinking.
In daily life, people often say that a child looks like his father or mother, or that a child's personality is the same as that of his father or mother. The teacher asks the students, "What does this mean?"”
Based on the prompts given by the teacher, students answer "heredity" based on their life experiences.
In order to further provoke reflection and be close to the content of the lesson, the teacher continued to ask the question: "In life, some parents have double eyelids, but the children born have single eyelids;Some mothers have curly hair, and children have curly hair. What determines heredity?”
Heredity is an important part of biology, when learning this section, many students will feel that the knowledge is too difficult, learning pressure, through the connection with real life, students can look at heredity from the perspective of life, improve their interest in learning, associate common genetic phenomena, and think about heredity-related issues.
2) Build an activity situation and guide students to practice.
Activity 1: Collect information and carry out cooperative learning.
Students in each group collected Mendel's information before class, made all the collected materials into a PPT, and then exchanged reports in class to explain Mendel's life and deeds.
In the process of collecting information and exchanging reports, the students in each group were able to summarize Mendel's education process, experience Mendel's love for science, feel Mendel's perseverance and dedication in the 8-year pea experiment, and be moved by Mendel's life deeds.
Activity 2: Hands-on experience of core concepts.
Before studying the Mendelian pair of relative trait hybridization experiments, students first need to understand what relative traits are, at this point, the teacher can explain relative traits with a simple action: "Students stretch out their hands, then cross their hands together, keep this position still, everyone looks at each other, what is the difference in the position of each person's hands?".”
In the absence of a clear rule, the student's gesture is presented in two states, one with the right thumb on top and the other with the left thumb on top. The teacher summarized in a timely manner: "Students, these two states of the hand can essentially be understood as a pair of relative traits, and relative traits are different types of manifestations of the same trait of the same creature. ”
Activity 3: Analyze and judge, and strengthen explanation exercises.
After understanding the concept of relative traits, teachers need to carry out classroom exercises and ask students to judge whether the descriptions in the questions are relative traits.
1.Short hair for cats and curly hair for dogs;
2.The long hair of rabbits and the short hair of dogs;
3.Long and short hair of rabbits;
4.Short-haired and long-haired cats;
5.Short-haired and gray-haired cats;
6.Human cheeks with and without dimples;
7.Single and double eyelids in humans.
After students have completed a series of true/false questions, the teacher can invite students to give examples of people, animals, and plants and list some relative traits. In the process of students giving examples, the teacher conducts timely evaluation, and summarizes and generalizes, emphasizing "the same species", "the same trait" and "different types of expression".
3) Create experimental situations to exercise students' thinking.
1.**Simulation experiment**, summarize the experimental procedure.
The teacher asks the question: "How can I change the pea trait?"Then Mendel's hybridization experiment was introduced, in which Mendel chose a pair of relative traits of peas—purple and white flowers. Combined with the problem, the teacher created a real experimental situation for the students through the simulation experiment of artificial cross-pollination with multiple equipment.
Students observe the content of the simulation experiment, summarize the steps of the simulation experiment, and complete the following fill-in-the-blank questions:
1) Remove all stamens of the immature flowers of the female parent;
2) Bagging isolation: use paper bags to isolate the interference of pollen from the outside world;
3) When the pistil is ripe, collect pollen from another plant and sprinkle it on the stigma of the pistil;
4) Isolate pollen from the outside world to ensure that the seeds obtained from the hybridization are entirely hand-pollinated.
After completing the lab questions, the teacher can ask the question of "Why do you want to go to the male?"What are the functions of scissors and brushes in the simulation experiment?”
2.Combined with experimental design problems, break through the key points and difficulties.
Simulation experiment 1: The purple pea was maleed as the female parent, and the white pea was used as the male parent to provide pollen.
Question: What were the results of the experiments on purple peas and white peas?
Based on what they have learned and real-life experience, some students believe that the hybrid F1 peas are white flowers, some students think that the hybrid F1 peas are purple flowers, and some students think that they are light purple.
The teacher simulates the experiment and presents the process and results of the experiment. In the experiment**, all the hybrid F1 peas were purple flowers. At this time, students will wonder why only purple flowers are inherited, so they will continue to think about follow-up experiments and conduct in-depth research on this phenomenon.
Some students suggested that it was possible that all purple flowers were caused by the emasculation of purple peas as the female parent in this experiment, and the teacher invited the students to design the experiment.
Simulation experiment 2: White-flowered pea was used to de-male as the female parent, and purple-flowered pea provided pollen as the male parent for crossing. Teacher**simulation experiment**, some students thought that the hybrid F1 peas were all white flowers, **The results were unexpected, and the offspring were still all purple flowers.
The teacher summarizes the results of the experiment and introduces the students to the concepts of dominant traits, recessive traits, orthogonal traits, and reverse crossings.
Simulation experiment 3: Teacher**Simulation experiment**, let the offspring of purple flowers self-inbred, showing that the experimental results are: there are both purple flowers and white flowers.
The teacher used multi-** equipment to explain the concept of trait separation, and counted the data of purple flowers and white flowers, and after data statistics, the proportion of purple flowers and white flowers in the second generation was 3 1. Ask the question: "Is the ratio of purple flowers to white flowers in the second generation a coincidence?"The students combined the data of the hybridization experiments with the relative traits of other peas to carry out inductive statistics and calculations, and finally came to a conclusion.
The teacher explains the important concepts: dominant traits, dominant genes, recessive traits, recessive genes, and trait segregation.
4) Design game situations to strengthen the application of knowledge.
The teacher asks the question: "In the previous experiment, the genetic trait was separated by 3 1 in F2, why is this ratio?".Why not 2 1 or 1 1?”
Student Game: Small colored balls simulate trait separation.
1.Game paraphernalia.
Two plastic kegs marked with A and B, 20 red balls, 20 blue balls (the two balls are only different in color), paper, and a pen.
2.Steps of the game.
1) Mark D on the red ball, mark D on the blue ball, prepare the keg with A and B written on it, and use these two kegs to simulate the female and male *** officer.
2) Put two kinds of colored balls in two small buckets A and B, and put 10 colored balls in each small bucket to simulate the equal number of two gametes produced by the female and the two gametes produced by the male with the same number.
3) Shake the two small kegs of A and B to fully mix the two colored balls in the keg.
4) Students close their eyes, put their left and right hands into the two plastic buckets of A and B respectively, grab a random colored ball, and then combine the ball caught by the left hand and the ball caught by the right hand together to simulate the random combination of female and male gametes, and record the combination of letters on the paper.
5) Repeat the catch game, students put the caught colored balls back into the original bucket, shake them well, and then repeat the catch session of (4) at least 30 times, the more times the ball is caught, the better.
6) Students will count the results of the catch record, accurately record the number of times dd, dd, and dd occurrences, and draw conclusions to calculate the probability of these three situations.
By creating game situations, students can fully participate in classroom activities, understand the quantitative relationship between the separation of genetic factors and the random combination of gametes and traits in the process of observing game phenomena and counting game data, so as to experience Mendelian's hypothesis.
3. Reflection on teaching
1) Use questions to guide students' thinking.
In this practical teaching, the teacher made full use of the situational teaching method to create a lot of problem situations for students, and guided students' thinking through questions, which effectively promoted the development of students' thinking. Throughout the teaching process, teachers first use common phenomena in life to stimulate students' interest, use questions to guide students to pay attention to genetic-related phenomena in life, establish a relationship between biological knowledge and students' life, and reduce students' psychological burden. In the follow-up teaching, teachers have been using questions to promote the development of classroom teaching activities, communicate with students, and the value of problem situations has been fully reflected. In the creation of problem situations, teachers need to grasp the difficulty and density of questions, ensure that the questions develop with the development of classroom teaching rhythm, and assist the development of teaching activities.
2) Enhance the student experience with activities.
When explaining complex biological knowledge, teachers guide students to collect information, so that students have more opportunities to participate, broaden their knowledge horizons, and improve their interest in learning. In addition, the teacher allows students to use their hands to cross their hands to feel a pair of relative traits, so that complex knowledge is easy to understand, and improves students' sense of participation and experience in the classroom. High school students have difficulties in understanding subject concepts, so teachers can actively work in small groups to strengthen students' understanding of knowledge in an all-round way.
3) Visualize the content with experiments.
In this teaching practice, the teacher presented three simulation experiments for students, and the three experiments progressed layer by layer, and the content presented was continuously deepened, so that students could understand important knowledge points. In the process of simulation experiments, teachers continue to ask questions, so that students can boldly guess the results according to the existing experience and the content of the experiment, which mobilizes the curiosity of students, and some unexpected results can stimulate students' desire and help students deeply remember knowledge. In addition, teachers also guide students to design experiments independently in the teaching process, so that they can master the methods of first-class problems and strengthen knowledge transfer.
4) Use games to arouse students' interest.
Game situations can fully mobilize students' interest in learning and allow students to participate in classroom activities. In this teaching practice, in order to let students understand that genetic traits are separated by 3 1 in F2, the teacher designed a game of catching colored balls, and students can repeatedly catch the ball, record data repeatedly, simulate the process of hybridization, and make statistics and induction of data to improve the learning effect. In the future teaching, teachers can appropriately introduce game situations based on teaching content and students' interests and hobbies, so as to make classroom activities more colorful and deepen students' understanding and application of knowledge. (Author: Wang Shirong).
*: New Curriculum Magazine.