Taking green flowering plants as an example, the textbook introduces their colorful life phenomena such as flowering, pollination, fertilization, fruiting and seed formation in the process of sexual reproduction. Among them, the double fertilization process of plants and the formation of fruits and seeds are the focus of this lesson, and the double fertilization process of plants is the difficulty of this lesson.
1.2 Analysis of learning situation
Students have a certain understanding of "the structure of pollination, flowers and fruits" in science class in primary school and biology class in grade seven, but they are not clear about the process and fertilization method of "passing on from generation to generation and prolonging life" of green flowering plants. The content of "fertilization process and ovarian development after fertilization" is abstract, which brings some difficulties to teachers' teaching.
2 teaching objectives
2. 1 knowledge objectives
Describe the process of pollen tube germination and double fertilization of green flowering plants; Explain the relationship between flowers and fruits and seed formation.
2.2 Ability objectives
Try to make self-made learning tools to cultivate students' practical ability; Try to express the transformation between pictures and words, so as to improve students' reading ability and language expression ability; In the activities of studying double fertilization and fruit seed formation, students' scientific inquiry ability and analytical inductive thinking ability are cultivated.
2.3 Emotion, Attitude and Values Goals
Understand the significance of flowers, fruits and seeds to the "propagation and longevity" of green flowering plants, and further agree with the biological viewpoint that biological morphological structure and function are compatible; Establish the determination to study hard and realize your dreams.
3 Teaching design ideas
3. 1 Clue teaching runs through.
This lesson takes dreaming of flowers as a clue to teach. The dream of flowers is to form fruits and seeds so that life can continue. Flowers need to go through a series of processes such as flowering, pollination, fertilization, fruiting and seed formation to realize their dreams. This clue links a series of teaching contents, interlocking and natural, so that the teaching contents are not chaotic and full of integrity.
3.2 homemade learning tools to break through difficulties
Teachers instruct students to make simple learning tools of "double fertilization process" by themselves, and demonstrate the process of pollen tube germination and double fertilization with self-made learning tools, which is vivid and effective in breaking through the teaching difficulties. The use of self-made learning tools makes students feel the joy of doing middle school; Let students try the expression mode of graphic conversion, which not only develops students' practical ability, but also improves students' oral expression ability and highlights students' subjectivity.
4 Teaching process
Arrange students to study in groups one day in advance and make a simple learning tool for "double fertilization of plants". Rubber tubes are used to simulate pollen tubes, two black sesame seeds are used to simulate two sperm, and round cardboard is used to simulate pollen grains. Some pistils (only stigma, style and ovary wall) and ovules (embryo sac in eight nuclear is marked with black watercolor pen) are made of cardboard with different colors, which are used to distinguish ovary wall, integument and embryo sac for class (figure 1).
4. 1 Create a situation and review the import.
Play a group of pictures of flowers for students to enjoy and let them feel the breath of spring. Different flowers have different sizes, colors and shapes, but they all have the same basic structure. The teacher shows the Flash courseware of "Structure of Peach Blossom", and asks students to drag the name of the structure to the corresponding part of the flower, and then asks: What structure is the most important for a flower? Why? (stamens, pistils). The related knowledge of flower structure is the teaching content of the second volume of grade seven, and students may forget it to varying degrees after a long time, so it is necessary to review this part to pave the way for later study.
4.2 The dream of flowers is a clue
Although flowers are different in size, color and shape, some are noble and gorgeous, fragrant, some are plain and even smelly, but they all have their own dreams. What are their dreams? How did they realize their dreams? It is difficult to realize your dream, and you need to go through a series of processes. Projection presents a trilogy to realize dreams: (1) flowering and pollination; (2) Pollen tube germination and double fertilization; (3) forming fruits and seeds.
The teacher takes "How Flowers Realize their Dreams" as the main line for clue teaching, and the presentation of "Trilogy of Realizing Dreams" makes students understand the learning content at a glance.
4.3 One Step-Flowering and Pollination
Play the video of "flowering and pollination" to guide students to complete the concept of flowering and pollination with video. Because the students of flowering and pollination have already learned it in primary school science class, they only review the concept of flowering and pollination in the form of filling in the blanks.
② Watch the animation of pollination methods, compare white pollination with cross pollination, and ask: Which pollination method is more common in nature? On what medium does pollen fall on pistil stigma?
③ Summary: Cross-pollination is ubiquitous in nature. Plants with beautiful petals and fragrant smell are mainly pollinated by insects, which are called insect-borne flowers. Plants without beautiful petals and fragrant smell are mainly pollinated by wind, which is called wind-borne flowers.
4.4 Two steps-pollen tube germination and double fertilization
Transitional doubt: after flowering and pollination, flowers have taken the first step to realize their dreams. What wonderful changes will happen to the pollen that falls on the stigma of pistil? Teachers guide students to read the graphic materials on page 12 1 and the relevant contents in the information base, understand the fertilization process of green flowering plants, and show the outline of autonomous learning through projection.
4.4. The structure of1ovary is the basis.
The teacher showed the "vertical structure diagram of ovary" to explain the ovary. Ovary consists of ovary wall and ovule. The outer part of ovule is called integument and the inner part is called embryo sac. There is an egg cell and two polar nuclei in the embryo sac. On this basis, students are required to take out their own learning tools to identify ovary, ovary wall, ovule, integument, egg cell and polar nucleus. Although the structure of ovary is not the focus of this lesson, the study of this part of knowledge will help students understand the following contents, especially the study of fruit and seed formation, which needs to be based on the structure of ovary.
4.4.2 Take you into the microscopic world.
① Show pictures and texts about pollen, inspire students to tell the characteristics (small and light) that pollen is suitable for spreading, and carry out biological viewpoint education that adapts to morphology and function.
(2) Play the Flash courseware of pollen tube germination and double fertilization, emphasizing that there are many pollen falling on the stigma of pistil, but only one can germinate completely and grow a pollen tube. There are two sperm in a pollen tube. One sperm combines with the egg to form a fertilized egg, and the other sperm combines with the polar nucleus to form the polar nucleus of the fertilized egg.
4.4.3 Use self-made learning tools to carry out group activities.
In groups of four, describe the process of pollen tube germination and double fertilization while demonstrating with self-made learning tools. The teacher reminds students to use verbs such as "grow out, cross, enter, combine" to help them remember. Then ask the group representatives to come on stage and demonstrate on the physical projector. Summary: What is fertilization? What is double fertilization? The teacher emphasized that double fertilization is a unique fertilization method for green flowering plants and wrote it on the blackboard.
Q: Is this reproduction sexual or asexual?
4.5 Transitional doubts
Teacher: When the flowers finish the task of pollination and fertilization, the beautiful parts such as petals will wither immediately. People often grieve for the fleeting flowers. In fact, flowers bloom only to bear seeds, and the day when flowers fail is the time to celebrate the birthday of new life. Do you know which structures of flowers will wither? What structure will continue to develop?
The teacher plays the Flash courseware of "Flowers Fall after Fertilization". After reading the courseware, students come to the conclusion that petals, stamens, stigmas and styles fall off, and the ovary continues to develop and bear fruit.
4.6 Trilogy-The Formation of Fruits and Seeds
① Question: How does the ovary develop and bear fruit? First, review the structure of fruit with pictures. Show a group of pictures of fruits and seeds. What are fruits? What is a seed? Peanuts, watermelons and peaches are fruits, and peach kernels among peanuts, watermelons and peach kernels are seeds. )
(2) After students learn to distinguish between fruits and seeds, teachers guide students to observe the pictures of peach houses and peach fruits, infer the development of various parts of the ovary, and correspond them one by one in the form of lines.
(3) Play the Flash animation of ovarian development to verify the hypothesis. Teachers and students summarize and present the conclusion on the blackboard in the form of network diagram. Students develop a scientific way of thinking and a scientific attitude of seeking truth from facts by observing, putting forward and verifying the hypothesis and experiencing the process and method of inquiry.
4.7 Contact with life and broaden your horizons.
Some plants have only one seed, such as peaches, some plants have two or three seeds, such as peanuts and broad beans, and some plants have many seeds, such as watermelons. What happened? Teachers guide students to analyze some common phenomena, link knowledge with life, walk out of textbooks and into life, and exercise students' thinking ability.
4.8 emotional sublimation, the end of the new lesson
The teacher plays the video "Sexual Reproduction Process of Green Flowering Plants" to reproduce the process of flowering, pollination, fertilization, fruiting and seed formation.
Teacher: The dream of flowering, fruiting and seeds has finally come true. Each of our classmates has his own dream. Today's dream may be tomorrow's reality. For the dream in our hearts, let's adjust the direction of the ship of life, aim at the goal and embrace the dream!
Finally, the teacher designed a poem about dreams to encourage students.
5 Teaching reflection
The theoretical knowledge of this lesson is numerous and fragmentary, and it is also boring and abstract. How to make more knowledge not confusing and turn abstract boring into vivid images? This poses a great challenge to teachers' teaching. First of all, the author takes "Flowers in a Dream" as a clue to link the complicated life phenomena in the process of sexual reproduction in an orderly way, so that the teaching content is not messy but full of a sense of integrity, permeating the education of emotional attitudes and values, and inspiring students' determination to study hard to realize their dreams; Secondly, guiding students to make and use learning tools, "learning by doing" fully embodies the combination of learning and doing, and students' observation ability, operation ability, oral expression ability and cooperation ability are effectively exercised. Using multimedia animation and video-assisted teaching, students can see life phenomena that they can't see at ordinary times, combine static and dynamic, make macro and micro vivid, highlight key points and break through difficulties. Teaching is no longer boring, but lively. The whole teaching process is oriented to all students and pays attention to the guidance of learning methods, so that students can construct new knowledge, improve their biological science literacy and implement the new curriculum concept in the process of active participation, active thinking and cooperative inquiry.