Cell cycle is one of the core concepts in this unit. In teaching, first let students express the definition of cell cycle according to the above picture, and then tell the start and end time and division stage of a cell cycle through map recognition and analysis. Then the teacher summarized the stages of cell cycle division and the ways of cell division in the form of blackboard writing.
Interphase is the preparation stage of cell division. In teaching, students are first prompted to tell the start and end time and duration of the interval according to the diagram of cell cycle; Then, on the basis of reading the text, the metabolic status of interphase cells is sorted out with tables. Finally, students are asked to outline the main characteristics of interphase cells and their position in the cell cycle.
Mitosis is the main division mode of eukaryotic cells, and its knowledge points should include: plant cell mitosis, animal cell mitosis, the characteristics of cell mitosis and the significance of cell mitosis. The standard requires "observing cell mitosis and summarizing its process". According to this requirement, the teaching of plant cell mitosis should first organize students to observe the mitotic slices of plant root tip cells, and identify interphase cells and cells at various stages of mitosis from the microscopic view by comparing pictures. On the basis of students' preliminary perceptual knowledge of plant cell mitosis, teachers explain the mitotic phases of cells in different stages in turn with the help of teaching media such as wall charts, pictures or videos, and then teachers and students summarize the changes of nuclear and cytoplasmic mitotic phases in the process of plant cell mitosis in tabular form. Finally, organize students to make and observe temporary apical compression independently.
To find and identify the mitotic stages of cells in different stages in self-made temporary apical pressing tablets. In order to help students understand the dynamic changes of DNA and chromosomes during mitosis, students can also be organized to model chromosomes with different colors of plastic or rubber mud to simulate the dynamic changes of chromosome behavior and quantity.
In the process of cell mitosis teaching, it is very necessary to organize students to make and observe the mitotic packaging of plant cells. This experimental activity is helpful to improve students' basic skills such as making and packaging, microscopic observation and drawing biological atlas. In teaching, firstly, the procedure of making temporary mitotic slices of onion root tip cells is expounded, and then the method of making slices is demonstrated. Then guide the students to take pictures and observe, and draw a sketch of each period of cell mitosis according to the observation.
When organizing students to make and observe the mitotic slices of plant cells, arrange a certain time for them to observe the mitotic slices of ascaris eggs and identify the centrosome structure and nuclear division at the two poles of cells, so as to lay a foundation for comparing the similarities and differences between animal cell mitosis and plant cell mitosis and summarizing the characteristics of cell mitosis.
Cell mitosis is a continuous process. In order to study and reveal the changes of chromosomes and DNA molecules in the specific process of mitosis, it is artificially divided into different periods. Therefore, in teaching, we should not only make it clear that interphase is the preparation of matter and energy, but also reveal the dynamic changes of chromosomes and spindles during cell division and their relationship, so as to cultivate students' view that things are interrelated, constantly moving and developing. The characteristics of cell mitosis can be summarized as follows: after chromosome is copied once, it is evenly distributed to two daughter cells, thus transmitting the genetic information of parents to future generations. In order to emphasize the significance of cell mitosis, the following figure can be used to summarize the relationship and law between DNA quantity and chromosome dynamics and quantity during cell mitosis.
The most important feature of cell amitosis is that chromosomes and spindles have not changed. In teaching, the process of amitosis is described by combining the amitosis diagram of onion epidermal cells or frog red blood cells. Firstly, it is emphasized that the process of cell division is also divided into nuclear division and cytoplasmic division, and then students are inspired to compare the similarities and differences between mitosis and mitosis, so as to understand the main characteristics of amitosis.
3.2 Teaching of Cell Differentiation, Aging and Apoptosis
As mentioned above, cell proliferation, differentiation, aging and apoptosis are normal life activities of cells, which are the behavior of cells and cannot be mistaken for the four stages of cell development. This is because apoptosis is not the death of aging cells, but both apoptosis and cell proliferation are basic behaviors to maintain the dynamic balance of cells in organisms. Therefore, at the beginning of this unit, we can take the frog's individual development as an example to summarize the complex relationship between cell proliferation, differentiation, aging and apoptosis, as follows:
This knowledge unit contains a series of concepts and is a good material for teaching students to learn concepts. The concept learning methods of senior high school biology are mainly: analyzing typical correct examples, revealing the essential characteristics of a class of things, then expressing them in the form of the following definitions and giving them names, and finally confirming the scope of concept application. Therefore, in the teaching of cell differentiation, firstly, undifferentiated stem cells, differentiated muscle cells, nerve cells, red blood cells and islet secreting cells are displayed through pictures, videos and other media (plant cells can also be taken as an example), so as to guide students to realize the differences between differentiated cells and undifferentiated cells in morphology, structure and function, and thus understand the concept of cell differentiation. Then, examples such as the occurrence of fertilized eggs and human tissues, the formation of cambium, xylem and phloem of plant stems are listed. Then, taking red blood cells and islet cells as examples, it is clarified that red blood cells have hemoglobin that other cells do not have, and islet cells can secrete insulin, which shows that differentiated cells have some special functions, which can be expressed by protein, and protein is the product of gene expression. So as to guide students to draw the conclusion that cell differentiation is the result of selective gene expression under specific conditions.
The original meaning of cell totipotency refers to the differentiation potential of fertilized eggs. One week before class, students should be arranged to collect information about the progress and application of stem cell research. In teaching, taking plant tissue culture or animal cloning as an example, it shows that differentiated cells still maintain their totipotency; In addition, the nuclear transfer technology of animal cells is used to further illustrate the totipotency of nuclear. These examples make students realize that the nucleus of differentiated cells contains all the nuclear genes of this species, so differentiated cells, like fertilized eggs, have the potential to differentiate into various cells and tissues and form complete individuals. In this way, the definition of cell totipotency came into being. On this basis, we can introduce the culture and differentiation of hematopoietic stem cells with charts, organize students to exchange information on the research progress and application of stem cells, and discuss the relationship between stem cells and human health.
Cell aging, also known as cell aging, refers to the irreversible phenomenon that under normal circumstances, with the increase of age, the homeostasis in the body declines, and the tissues and cells of the body degenerate and tend to die. Because of the synchronization of cell aging and individual aging, students should be inspired to describe the facial features of the elderly in a macro way, such as senile plaque, dry skin, wrinkles and so on. Then, let the students read the text and get a preliminary understanding of the structural and functional characteristics of aging cells from a microscopic perspective (as shown in the following table):
Apoptosis is a physiological process of automatically ending life caused by genes during cell development. In teaching, by enumerating the phenomenon of apoptosis in the formation of human nervous system and the phenomenon of apoptosis in the epithelial cells of bone marrow and intestinal mucosa of healthy adults, students can clearly eliminate redundant differentiated cells or complete their mission through apoptosis in the embryonic development stage to ensure the normal development of embryos; In the adult development stage, aging and pathological cells are eliminated by apoptosis to ensure the health of the body. Therefore, apoptosis cannot be confused with cell aging and death. Finally, organize students to discuss how to delay cell aging and pay attention to the health problems of the elderly.
3.3 cell canceration teaching
The teaching of cell canceration can be put in the part of cell differentiation, and can also be put together with cell aging and apoptosis. Students know little about cell canceration, so they are arranged to collect information about malignant tumor and its prevention and treatment before class. Discussion can be used in teaching, so that students can discuss the following questions: What is cancer? What are the main characteristics of cancer cells? What is the root cause of cell canceration? What are the factors inducing proto-oncogene mutation? How to prevent and treat malignant tumors and so on. The discussion activities aimed at the above problems are not only conducive to stimulating students' interest and mobilizing their learning initiative, but also can examine students' learning ability, information processing ability, problem analysis and solving ability, as well as their emotional attitude and values.
The above teaching conception of "cell proliferation, differentiation, aging and apoptosis" is rough and superficial. I hope it can play a role in attracting jade, deeply study and understand the spirit of senior high school biology curriculum standards, promote the reform of senior high school biology teaching and improve the quality of biology teaching.