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How to write 500- 1000 words in the biology test paper of grade one in junior high school?
Junior high school biology composition model essay 1: Why is the trunk round? In the process of observing nature, I happened to find that the shape of the trunk is almost round-an empty cone. Why is the trunk conical? What are the benefits of a conical trunk? In order to discuss these problems, I made more in-depth observation and analysis. With the help of my tutor, I consulted relevant materials and learned that the stems of plants have the functions of supporting plants and transporting water and other nutrients. The stems of trees are mainly composed of vascular bundles. The supporting function of stem is mainly borne by wood fibers in xylem. Although the stems of woody plants will become thicker year by year, in a certain time range, the number of woody fibers in the stems is certain, that is, the cross-sectional area of the stems is certain. Then, based on the assumption that the cross section of the trunk grows into different shapes, we design experiments to explore the reasons and advantages of conical trunk. Through experiments, we find that when the cross-sectional area and length of (1) are fixed, the vertical supporting force of triangular columnar objects is the largest and the lateral bearing capacity is the smallest; The vertical supporting force of cylindrical objects is not as good as that of triangular cylindrical objects, but the lateral bearing force is the largest; (2) For trunks with the same mass and different shapes, the short conical trunk bears the largest wind force; (3) Wind is a natural phenomenon, which affects the cross-sectional shape and height of trees. The approximate cone-shaped trunk has a low center of gravity, and the huge root system is connected with the earth, so the center of gravity drops lower and the stability is greater; (4) The cross section of the trunk is round, which can reduce the damage, has stronger mechanical strength and can resist the wind attack. At the same time, under the action of the wind, the bending degree of the trunk is similar everywhere. No matter which direction the wind blows, the resistance of the trunk is similar, and the trunk is not easy to be damaged. The above experiments reflect the laws of nature, and nature enlightens us: (1) A columnar object with a triangular cross section has the greatest vertical supporting force, and its shape can be used in buildings, such as angle steel; (2) A circular object with a circular cross section has the largest lateral bearing capacity, and similar building materials can be found everywhere, such as TV towers and telephone poles. In the process of observation, experiment and analysis, I gradually explained and revealed the mystery of conical trunk, increased my knowledge, and combined my knowledge with practice, which not only consolidated my knowledge, but also improved my interest in learning, and initially learned the scientific observation and analysis methods. Fan Wener: What effect does vinegar have on flowers? Vinegar is a common condiment in life, while flowers can purify the ecological environment and beautify our life. Have you ever thought about the relationship between vinegar and flowers? We explored the subject with curiosity. According to people who have rich experience in planting flowers, applying some vinegar on potted flowers can improve the growth of potted flowers and increase flowers, which are bright and leafy. We soon confirmed this in the experiment. Do different concentrations of vinegar have different effects on flowers? This is the second stage of our experiment. We select four pots of gypsophila paniculata, primrose and Chinese rose with the same growth and divide them into four groups. Each group (three pots) has three kinds of flowers, which are numbered and labeled respectively. At the same time, we prepared edible white vinegar into three solutions with different concentrations: 1% (pH 2~3), 0.0 1% (pH ≈4) and 0.000 1% (pH ≈6), and sprayed vinegar on three groups of potted flowers once a day, while the fourth group did not. Observe and record the growth of flowers every five days. The results of this experiment are as follows: spraying low concentration vinegar (pH ≈6) has no obvious effect on these flowers; The flowers sprayed with moderate concentration of vinegar (pH ≈4) are obviously better than other groups, with more buds, earlier flowering, richer colors and longer flowering period. Spraying high concentration vinegar with pH value of 2-3 will make the flowers wither prematurely. Through this experiment, we can tell you that spraying vinegar properly when planting flowers can make flowers grow better. But to master the concentration of vinegar, excessive acetic acid will harm flowers.

Smoking, smoking is harmful to health, but everyone knows it, but there are still so many people smoking? Some people think smoking is a bit handsome, while others do it to relieve their worries. How intoxicated they are when they see others smoking! I'm in a bad mood recently, and I smoke! It seems that smoking can eliminate my sadness and make me less depressed. But I found myself even sadder! Not only did it not eliminate my sadness, but it intensified in a movie! Friend, please don't smoke for your health and for people who care about you! Smoking does a lot of harm. It not only devours the health and life of smokers, but also pollutes the air and harms others. 1. Lung diseases: 38 kinds of toxic chemicals are released when cigarettes are burned, among which tar, carbon monoxide, nicotine, dioxins and irritating smoke are harmful components. Tar is harmful to the mouth, throat, trachea and lungs. Tar in tobacco smoke is deposited on lung villi, which destroys the function of villi, increases phlegm and causes chronic bronchial diseases, such as tracheitis, emphysema, pulmonary heart disease and lung cancer. According to statistics, the proportion of smokers suffering from lung disease after 60 years old is 74%, while the proportion of non-smokers suffering from lung disease after 60 years old is only 4%, which is a shocking figure. Second, cardiovascular diseases: carbon monoxide in cigarettes reduces the oxygen content in the blood, causing hypertension and other related diseases. Smoking will contract coronary artery, reduce or block supply, and lead to myocardial infarction. Smoking can increase adrenaline, make the heart beat faster, increase the heart load, affect blood circulation, and lead to more than 20 diseases such as cardiovascular and cerebrovascular diseases, diabetes, sudden death syndrome, decreased respiratory function and stroke. Third, smoking causes cancer: The study found that smoking is the fastest and most free radical generation method, and each cigarette will produce at least 654.38 million free radicals, which will lead to cancer and many chronic diseases. Recently, a 50-year study was conducted on 35,000 smokers at Tidcliffe Hospital in Oxford, England. The results show that lung cancer, gastric cancer, pancreatic cancer, bladder cancer, liver cancer, oral cancer and sinus cancer are "significantly related" to smoking. Why smokers catch a cold easily is because the activity of lymphocytes in the human body decreases, leading to cancer. In view of the three major factors leading to smoking and cancer, the sooner you quit smoking, the better. Fourth, smoking can also lead to osteoporosis and early menopause. Smoking can make men lose their sexual and reproductive functions. Smoking in pregnant women will lead to premature delivery and underweight of the fetus, and the probability of miscarriage will increase. Smoking makes teeth yellow, which makes bad breath easy. Smoking harms people, and the harm of passive smokers is five times that of smokers. For the health of you and your family, you should quit smoking as soon as possible. Fifth, the harm of smoking to intelligence. Smoking will affect people's attention. Some people think that smoking can refresh the mind, eliminate fatigue and inspire, which is totally unreasonable. Experiments show that smoking seriously affects people's intelligence and memory, thus reducing the efficiency of work and study. Smoking is harmful to nothing. 53% of children in China smoke passively, which is even more harmful and prone to pneumonia, bronchitis, severe asthma and other diseases. If the current smoking situation continues, children's intellectual development, families and individuals who smoke will pay a huge price.

Campus energy conservation and environmental protection paper: energy conservation and environmental protection paper (hint: 100 words is just enough to write an argument! What does the environmental change of the earth remind us of? Earth Day is a day to repent to Mother Earth. Let's think about what kind of disaster has been caused to the earth by excessive consumption of resources and environmental pollution; Think about it, in such a disaster, each of us has an unshirkable responsibility. When the fragile ecology is difficult to maintain, how will human consumption continue; When the earth is terminally ill, how long can humans live? Earth Day is also a day for human beings to save themselves. Human beings are not only the makers of environmental disasters, but also the victims and managers of environmental disasters. Each of us can participate in environmental protection by choosing a green lifestyle: saving resources and reducing pollution; Green consumption, environmental protection procurement; Reuse and reuse; Garbage sorting and recycling; Save species and protect nature. Green life is the information of the new century, which guides enterprises to develop green technology and clean production; Green life is the requirement of the new century, which urges politicians to assume the responsibility of sustainable development of mankind; Green life is the fashion of the new century, which embodies a person's civilization and accomplishment, and also marks the quality and strength of a nation. China is a country with the most fragile ecosystem in history, but it bears the largest population and the greatest development pressure in history. Patriotic people, let us first cherish the foundation on which this nation depends, and let us start with bit by bit environmental protection behavior.