Cell water absorption teaching plan

Teaching plan of biological metabolism and water metabolism of green plants

Teaching objectives

1. Let students know two ways of water absorption by plant cells; Understand the principle of cell osmotic water absorption; Understand the water metabolism of plants, including the general process of water absorption, transportation, utilization and loss; Understand the effect of transpiration on plants.

2. Through the experiment of cell plasma wall separation and repair, let students understand and explore the method of cell osmotic water absorption, and consolidate the skills of making temporary membrane; By analyzing the principle of cell water absorption and exploring the process of cell water absorption, students can learn scientific methods to explore the principle of cell water absorption and train their scientific thinking. Cultivate students' ability to study problems.

3. Contact with the actual production and life, so that students can understand the practical value of studying this topic and enhance their awareness of caring about production and water resources utilization. At the same time, educate students with the viewpoint of life science compatible with structure and function.

Analysis of key points and difficulties

1. The principle of osmotic water absorption is the focus of this topic. Because:

(1) Osmotic water absorption is the main way for plants to absorb water. Only by understanding the principle of osmotic water absorption can students understand the conditions of cell water absorption, various factors affecting plant cell water absorption, the principle of water transfer between cells in plants and the absorption and loss of water in the whole plant.

(2) Osmotic absorption is not only the main way for plant cells to absorb water, but also for animal cells. Therefore, it is of great significance for students to understand the principle of osmotic absorption to understand the water exchange between animal cells and the external environment and between animal cells and the internal environment.

(3) In the teaching of osmotic water absorption, the idea of the unity of cell structure and function can be well penetrated; Theoretical analysis and experimental verification method of permeability. Cultivate students' ability to study and solve problems.

2. The experiment of plasma wall separation and repair is another key point of this subject. Because:

(1) The experiment of plasma wall separation and repair is the key for students to understand that plant cells are an osmotic system. Only by experimental operation and observing the separation and recovery of plasma wall can students have a perceptual understanding of the relationship between cell water absorption and water loss and environmental solution concentration, and then deeply understand that cells are an osmotic system and the internal and external conditions that affect cell water absorption.

(2) Consolidate students' skills in making films and using microscopes through experiments of separating and repairing plasma walls. Skills need repeated practice to master. Through this experiment, we can consolidate the skills of making films and using microscopes learned in the first chapter.

(3) This experiment is a basic experiment to study the water absorption of cells. It can not only prove that mature plant cells are an osmotic system, but also design a series of physiological experiments using the design idea of this experiment, such as measuring cell water potential, verifying selective permeability of cell membrane, verifying cell life and death, etc. Through this experiment, students' ideas and methods of solving problems can be broadened.

3. The physiological significance of transpiration is also the focus of this teaching. Because:

(1) Transpiration is the main driving force for plants to absorb and transport water, and it is also the main way for plants to use and lose water. Only by guiding students to analyze transpiration pathway, transpiration mode and its relationship with water absorption and transportation can students deeply understand the position of transpiration in water metabolism and its important physiological significance to plants.

(2) Transpiration intensity is an important physiological index of water metabolism in plants. To some extent, it can reflect the water metabolism of plants, and can also judge the water use efficiency of plants. The morphological and structural characteristics of different ecological types of plants adapting to the environment are related to the influence of transpiration, which can be linked here.

4. According to the analysis of osmotic principle, mature plant cells are an osmotic system, which is a difficult point in teaching. Because:

In osmosis, water moves from the side with high density of water molecules to the side with low density. Because water is the solvent of intracellular solution, from the point of view of solution, water permeates from the side with low concentration to the side with high concentration, which is difficult for students to understand. In addition, it is difficult for students to understand the difference between cell wall and cell membrane in permeability and its influence on permeability.

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) Before class, select intact and fresh small herbs and put them in beakers or jars with clean water and 30% sucrose solution respectively. Plants in clear water stand upright, while plants in sucrose solution wither due to lack of water. Put the experimental device on the experimental platform for students to observe.

(2) On the basis of instructing students to observe the wilting phenomenon of normal and water-deficient plants, it is pointed out that plants can maintain normal life only on the basis of water metabolism balance. The lack or excess of water has a great influence on agricultural production, so it is a theoretical topic to study plant water metabolism. How do plants absorb water? What factors affect the water metabolism of plants? This leads to the topic.

(3) Guide students to analyze the causes of plant wilting in the experiment from many aspects. After a brief discussion, the teacher pointed out the experimental treatment. After the students learned that plants withered in high concentration sucrose solution, the teacher further proposed why plants withered due to lack of water in sucrose solution. Plants are composed of cells, and water absorption by plants is the result of water absorption by cells. What happens to cells in clean water and 30% sucrose solution? Therefore, the separation and repair experiments of plasma wall are introduced.

(4) Before the experiment, the teacher introduces the design and operation method of the experiment process. If time permits, students can also have a brief discussion or operation on the basis of watching the experimental guidance. In order to obtain better observation effect, we should pay attention to the following points when preparing and guiding students' experiments:

(1) when using purple onion as experimental material, if the color is too light, put the onion in a sunny place for a period of time, and then use it after the scaly leaves turn dark purple.

② In order to save experimental materials, onion scales can be cut into small pieces and distributed to students. If students don't observe onion epidermal cells, the teacher can use blackboard drawings or slides to explain the method and size of tearing onion epidermis.

③ When observing onion epidermal cells, first find single layer, bubble-free and clear cells under low power microscope, and then observe them under high power microscope. If the cells are very large, there is no need to use a high-power lens.

(4) After observation, students should report the experimental results, analyze the water inside and outside the cells in clear water and sucrose solution, analyze the relationship between water absorption and water loss of cells and environmental conditions, and explain the reasons why plants wither in sucrose solution. Teachers can show pictures of onion epidermal cells (one is normal and the other is in a state of separation of plasma and wall) to illustrate the phenomenon.

(5) On the basis of students' perceptual knowledge that cells will lose water in high concentration sucrose solution and absorb water in clean water, why does the concentration of environmental solution affect the water absorption of cells? What structural characteristics of cells are related to water absorption? The following analysis is based on a cell-like osmotic model. This leads to the infiltration model to guide students to observe and analyze. Here we will introduce the infiltration device and analyze the following problems:

① When introducing the osmotic model device, special attention should be paid to the choice of semi-permeable membrane, in which water molecules can pass freely but sucrose molecules are difficult to pass.

② On the basis of students' observation, ask the following questions to guide students to discuss: a. Why is the sucrose level in the funnel higher than that in the beaker? Guide the students to say that the number of water molecules in unit volume of clean water is more than that in unit volume of sucrose solution, so in unit time, the number of water molecules diffused from beaker to funnel through semi-permeable membrane is more than that from funnel to beaker. Therefore, the liquid level in the funnel rises. It is pointed out that the diffusion of water molecules through semi-permeable membrane is called osmosis. B. what structure maintains this penetration? What happens when the semipermeable membrane is destroyed? It is concluded that the existence of semi-permeable membrane is the key to osmosis. C. If the students have good conditions, it can be further suggested that if the infiltration device is put down again, the liquid level in the funnel will continue to rise. Why? (or: the concentration of sucrose solution in the funnel is always higher than that of clear water in the beaker, so will water continue to enter the funnel? Why? Under the guidance of the teacher, it is concluded that the downward pressure of the liquid column in the funnel can accelerate the water molecules in the funnel to penetrate into the beaker. When the weight of the liquid column is equal to the force of water molecules in the beaker infiltrating into the funnel, the water molecules will balance the two sides of the membrane and the liquid level will stop rising.

③ According to the above analysis, it is concluded that permeation refers to the diffusion of water molecules through a semi-permeable membrane; The conditions of infiltration are: a. the existence of semi-permeable membrane, b. the concentration difference between the two sides of the membrane; The trend of water infiltration is that water molecules permeate from the side with high concentration to the side with low concentration.

(4) After analyzing the osmotic model, it is transferred to the analysis of cell osmotic effect. Ask: Do cells also have the conditions for infiltration? Guide students to analyze that there is cellular fluid in vacuole and extracellular fluid in environment. Is there a semipermeable membrane between cell fluid and environmental solution? The cell loses water in high concentration sucrose solution, and the phenomenon of plasma-wall separation appears, indicating that sucrose molecules have not penetrated the protoplasm layer such as cell membrane, otherwise there will be no concentration difference inside and outside the cell, and water will not penetrate outward. Sucrose molecules penetrate the cell wall, otherwise there will be clear water between the cell membrane and the cell wall, and water molecules will quickly penetrate into the cell, making the cell swell, and there will be no separation between the plasma and the wall. This shows that the cell wall is completely permeable, and the protoplasm layers such as cell membrane, cytoplasm and vacuole membrane are semi-permeable. Therefore, the cell is an osmotic system, which has the conditions of osmotic action.

⑤ Summarize the principle of cell osmotic water absorption. Mature plant cells have osmotic conditions: a. They have semi-permeable membrane (protoplasm layer). B. There are solutions inside and outside the membrane, that is, cell fluid and environmental solution. C. When the cell fluid is greater than the concentration of the environmental solution, the cells will absorb water from the environment, otherwise the cells will lose water.

(6) According to the principle of cell water absorption, contact the related content in daily life. If you have time, properly analyze the factors that affect the concentration of cell fluid and environmental solution under natural conditions.

Third, the second category:

1. The design idea of teaching process;

■ Reviewing the conditions of cell osmotic water absorption principle leads to how vacuole-free cells absorb water? What factors are affected?

Observe the water absorption experiment of dry seeds and analyze the difference between cell imbibition and osmotic water absorption.

The water absorption of plants comes from the water absorption of cells. The transport, utilization and loss of water in plants are discussed.

Summarize the whole process of water metabolism, guide students to complete the textbook review questions, and make students consolidate their knowledge.

2. About teaching design:

(1) One day before class, weigh two soybean seeds and two peanut seeds with the same weight, soak one of them in water, and then weigh them after the seeds fully absorb water, and calculate their water absorption (the water absorption of soybean seeds will be significantly higher than that of peanut seeds) for later use.

(2) At the beginning of the second class, students can review the contents of the first class about cell osmotic water absorption. Why do mature plant cells absorb water mainly through osmosis? What are the conditions for infiltration? What factors affect the absorption of water by cells from environmental solutions? So, how do some plant cells absorb water without big vacuoles, such as cells in dry seeds, cells in plant roots, stems and meristems? What factors are affected? This led to the water absorption experiment observed in seeds.

(3) Show dried soybean and peanut seeds. The teacher can briefly introduce them. These dried seeds have strong vitality and almost the same water content. They can absorb water quickly when put in water. So, do the two seeds have the same water absorption capacity? Let the students discuss. Then take out another group of soaked seeds, guide students to observe the results and compare the differences of water absorption between the two seeds. What is the main method to analyze the water absorption of seeds? Why soybean seeds absorb more water than peanut seeds. Through discussion, students can make the following points clear: ① Macromolecules such as protein, starch and cellulose in seeds have strong hydrophilic ability. In the cells of dried seeds and plant meristems, the hydrophilic ability of these substances is not saturated, so the cells mainly absorb water in this way, that is, imbibition and water absorption. ② The content of hydrophilic substances such as protein in soybean seeds is higher than that in peanut seeds, while the content of hydrophobic substances such as fat in peanut seeds is higher than that in soybean seeds. Therefore, soybean seeds have stronger swelling and water absorption ability than peanut seeds. ③ In general mature cells, the water-binding capacity of macromolecular hydrophilic substances has been exhausted, and a large amount of water is stored in vacuoles. Therefore, the water absorption mode is changed to osmotic water absorption.

(4) With regard to the process of transportation, utilization and loss of water by plants, the following points can be analyzed by using the pictures in the textbook:

① The concentration of soil solution is generally lower than the concentration of cell sap in root hair (mature) area of root tip, so that the water in soil solution enters the epidermal cells in root hair area through osmosis. According to the principle of osmosis, water in epidermal cells can penetrate into inner cells layer by layer and finally enter the catheter. Here we should contact some practical problems about agricultural production, such as why plants in saline-alkali land are more prone to water shortage, why it is not appropriate to apply too much fertilizer at one time, and so on.

② Roots, stems, leaves and other ducts are connected, and the water in the ducts will penetrate into cells in other parts of the plant. Part of water participates in various physiological activities such as photosynthesis and stays in plants; Most of the water is lost by transpiration, such as leaves, thus forming a metabolic pathway of water absorption, transportation, utilization and loss.

③ The relationship between plant water requirement and transpiration was cited, which indicated that transpiration was the main driving force for plants to absorb and transport water. The role of transpiration in reducing plant body temperature and the significance of adapting to the environment are explained by associating the way of animal heat dissipation. Here, the characteristics of plants in arid environment can be linked.

(5) Finally, the metabolism of water can be summarized as shown in the following figure (Figure 2-2):

Fourth, the problems that should be paid attention to in the teaching of this topic:

1. If the verification experiment of plasma wall separation and repair is changed into exploratory experiment, and combined with the principle of cell osmotic water absorption, students should master the skills of making slices and using microscope in the first chapter of observing plant cell mitosis experiment. We can arrange an experiment to observe onion epidermal cells, and cooperate with the teaching of cell structure to lay a good foundation for students to observe mitosis and this experiment.

2. Don't take up too much time in the teaching of cell imbibition and water absorption. The focus of the second class should be to analyze the relationship between transpiration and plant water absorption.

Small data

First, the relationship between plant water demand and transpiration loss:

The lifetime water demand of plants is amazing. It is estimated that a sunflower will consume about 30 kilograms of water in its lifetime. An acre of paddy field consumes about 300,000 kilograms of water during the whole growing period. Obviously, the water used to form the plant itself is extremely limited, estimated to be only about 0. 15% ~ 0.2%, and the rest is lost through transpiration. It can also be said that the difference of water consumption of different ecological types of plants in a lifetime is mainly caused by the difference of transpiration and water loss.

The grams of dry matter formed by plant transpiration loss 1 kg is called transpiration efficiency. The higher the transpiration efficiency, the more economical the water use for plants. The transpiration efficiency of different plants is different.

Second, the transpiration site:

When plants are young, almost all the surface of the aboveground parts have transpiration. With the growth of plants, the trunk and branches are corked, and the stem can only evaporate and lose water through the lenticels, but the amount is very small and can generally be ignored. Therefore, transpiration is mostly carried out on leaves, and there are two ways of leaf transpiration: one is through the cuticle of leaf epidermis, which is called cutin transpiration; The other is transpiration through stomata on the surface of leaves, which is called stomatal transpiration. Comparison of two transpiration rates of different plants;

(Unit: mg of water 0.0 1 decimeter 0. 1 hour)

Floriculture.

Maximum transpiration of stomata (a)

Maximum transpiration of cutin (b)

A/B

Total transpiration a+b

Sedum erythraeum

654

36

18

690

Black pine

423

seven

60

430

Duck toe grass

920

360

2.5

1280

wheat

985

420

2.3

1405

broad bean

640

600

1. 1

1240

As can be seen from the above table, the ratio of stomatal transpiration to cutin transpiration of different plants is significantly different. Sedum alfredii and Pinus thunbergii with strong drought resistance are quite different from Vicia faba with weak drought resistance. In addition, under the same leaf volume, the larger the leaf area, the greater the transpiration per unit area, and vice versa.

Three, transpiration and water absorption:

Leaf transpiration water loss, first of all, is the water loss of cells close to leaf epidermis and guard cells, which leads to the poor water absorption between these cells and adjacent mesophyll cells, which leads to the water absorption of adjacent cells and drags the water column in the stem and root canal upward. Finally, root cells are short of water, and their water absorption capacity is enhanced, which promotes root cells to absorb water from soil.

Generally speaking, water absorption of plants mainly comes from the tension of transpiration. The right picture (Figure 2-3) shows the diurnal variation of transpiration and water absorption of sunflower, from which it can be seen that transpiration and water absorption are roughly parallel, and water absorption always lags behind transpiration slightly.

Four, transpiration and photosynthesis:

Some people experimented that after cutting leaves from plants, they were immediately placed in containers with high humidity and sufficient light (leaves kept alive), and the water content of leaves gradually decreased due to transpiration. Then, the relative photosynthetic intensity of leaves was measured under the condition of water deficiency. Therefore, leaf water shortage has obvious influence on photosynthesis (see Figure 2-4). The main reason may be that the lack of water leads to the closure of stomata, which reduces the absorption of carbon dioxide and thus affects photosynthesis. In addition, different plants have different effects on photosynthesis due to water shortage.

(No.2 Middle School Attached to Caobei Normal University)