Do you know viruses (病毒) and bacteria (细菌)? Both of them are very small, we can't see them with our eyes, and many people know nothing about them, In fact, there are a number of differences between viruses and bacteria. Bacterium, the singular form of the word bacteria, is a one-celled (单细胞) living thing, with complete sets of both RNA and DNA genetic codes (遗传密码). For viruses, some are sections of RNA, and the others are sections of DNA. So, bacterium is at least a hundred times larger than a typical virus.
One main difference between viruses and bacteria is the method of reproduction. A bacterium is a completely independent and self-reproducing unit. When the time is right, bacterium will divide its DNA and RNA genetic material in two. This is how bacteria live in almost every environment on Earth, including non-living things like rocks or plastic.
A virus, on the other hand, cannot reproduce without a living host. A virus may lie for thousands of years before finally coming into a suitable host. Once it enters the body of a host, a virus will get in the ling cell. Once inside a living cell, a virus takes the place of the living cell's DNA or RNA genetic instructions with its own. Those instructions are usually to make as many copies of the virus as possible.
Ninety-nine percent of all known bacteria are considered useful to humans, or at least have no bad influence. But most viruses, on the other hand, serve no good purpose. Their only purpose is to create more viruses in order to make themselves continue to live.
Bacteria are alive, which means they can be killed by some form of chemical things. Antibiotics (抗生素) can kill bacteria. Viruses, by comparison, are not considered living things. They cannot be 'killed' in the same way as antibiotics kill bacteria. In fact, any medicine is useless for virus' infections. The disease must run its course until the body can make a successful protection on its own.
Viruses and Bacteria | |||
Similarity | Both are too small 1. with our eyes. | ||
Differences | Viruses | Bacteria | |
What they're like | ● They are not living things. | ● They are living things. | |
● A virus is a section of 2. RNA 3. DNA. | ● A bacterium has complete sets of both RNA and DNA genetic codes. | ||
● A virus is much smaller than a bacterium. | |||
How they reproduce | A virus can not copy without a living host | A bacterium can reproduce 4. in almost every environment on Earth. | |
How they influence humans | Most of them do 5.humans. | Most of them are considered useful to humans, or at least have no bad influence. | |
6.for viruses and bacteria | We can use antibiotics to kill bacteria while for viruses it only depends on if our body can make a successful protection on its own. |
九年级英语填空中等难度题
Do you know viruses (病毒) and bacteria (细菌)? Both of them are very small, we can't see them with our eyes, and many people know nothing about them, In fact, there are a number of differences between viruses and bacteria. Bacterium, the singular form of the word bacteria, is a one-celled (单细胞) living thing, with complete sets of both RNA and DNA genetic codes (遗传密码). For viruses, some are sections of RNA, and the others are sections of DNA. So, bacterium is at least a hundred times larger than a typical virus.
One main difference between viruses and bacteria is the method of reproduction. A bacterium is a completely independent and self-reproducing unit. When the time is right, bacterium will divide its DNA and RNA genetic material in two. This is how bacteria live in almost every environment on Earth, including non-living things like rocks or plastic.
A virus, on the other hand, cannot reproduce without a living host. A virus may lie for thousands of years before finally coming into a suitable host. Once it enters the body of a host, a virus will get in the ling cell. Once inside a living cell, a virus takes the place of the living cell's DNA or RNA genetic instructions with its own. Those instructions are usually to make as many copies of the virus as possible.
Ninety-nine percent of all known bacteria are considered useful to humans, or at least have no bad influence. But most viruses, on the other hand, serve no good purpose. Their only purpose is to create more viruses in order to make themselves continue to live.
Bacteria are alive, which means they can be killed by some form of chemical things. Antibiotics (抗生素) can kill bacteria. Viruses, by comparison, are not considered living things. They cannot be 'killed' in the same way as antibiotics kill bacteria. In fact, any medicine is useless for virus' infections. The disease must run its course until the body can make a successful protection on its own.
Viruses and Bacteria | |||
Similarity | Both are too small 1. with our eyes. | ||
Differences | Viruses | Bacteria | |
What they're like | ● They are not living things. | ● They are living things. | |
● A virus is a section of 2. RNA 3. DNA. | ● A bacterium has complete sets of both RNA and DNA genetic codes. | ||
● A virus is much smaller than a bacterium. | |||
How they reproduce | A virus can not copy without a living host | A bacterium can reproduce 4. in almost every environment on Earth. | |
How they influence humans | Most of them do 5.humans. | Most of them are considered useful to humans, or at least have no bad influence. | |
6.for viruses and bacteria | We can use antibiotics to kill bacteria while for viruses it only depends on if our body can make a successful protection on its own. |
九年级英语填空中等难度题查看答案及解析
Harmful microbes (微生物) like bacteria (细菌), viruses (病毒) and other germs (病菌) are pathogens (病原体). They may enter your bodies and make you ill. The immune system (免疫系统) is the body’s defence (防卫) system that protects you from illness and disease caused by the pathogens.
The immune system is made up of non-specialized defences such as skin, tears and the acidic juice produced by the stomach, keeping you from the pathogens. It also has some highly specialized defences, which are different kinds of immune cells (细胞), grouped into phagocytes (噬菌细胞) and lymphocytes (淋巴细胞). Phagocytes are a type of white blood cell. They are swimming around in your blood stream, always on the lookout for antigens (抗原) —the pathogens that have entered your bodies. Whenever they see one, they will eat it. However, some antigens are hard to find and kill. Then lymphocytes, which are also white blood cells and the main types are B cells, T helper cells and T killer cells, will be the killers of the sneaky antigens. B cells, T helper and T killer cells work together to find and kill these antigens. B cells produce substances, called antibodies, which stick to the antigen. When that happens, it will tell the T helper cells to come over and either: 1. help the B cells kill the antigen, or 2. call the phagocytes or T killer cells to move in for the kill. Once a B cell or a T cell attacks an antigen, they create cells to “remember” it. Those “memory cells” hang out in your blood and if they see the same antigen again, they quickly recognize (识别) it so your immune system can act faster at killing it.
The immune system is more powerful than you probably imagine. Scientists from the University of Pennsylvania recently took immune cells from three patients with leukemia (白血病), then genetically changed them into “serial killer” cells to attack cancer cells. The study was small but the results were ground-breaking. The modified immune cells increased at least 1,000 times in the body and killed all the cancer cells. Therefore, more “memory cells” were created.
The immune system can be developed. Eating lean protein food (beef, beans) and food rich in vitamins A, C and E (sweet potatoes, carrots),taking a 30-minute walk every day and reducing your stress levels, will help you achieve it.
1.The immune system can _________.
A. keep you from antibodies. B. protect you against antigens.
C. make your bodies weak and sick. D. help microbes enter your bodies.
2.How are the sneaky antigens found and killed
A. B cells produce antibodies to tell T helper and T killer cells.
B. B cells create “memory cells” to swim around in the blood.
C. Skin, tears, acidic juice and immune cells work together.
D. Phagocytes, B cells, T helper and T killer cells work together.
3.After a B cell or a T cell attacks an antigen, they create _________.
A. phagocytes B. lymphocytes C. memory cells D. serial killer
4.The underlined word “it” in the last paragraph refers to _________.
A. Less antigens can be killed by the immune system
B. The immune system can be changed into the “serial killer”
C. White blood cells act less quickly in the immune system
D. The immune system can be made more powerful
5.This article is mainly about _________.
A. the types of white blood cells B. an introduction to the immune system
C. a research report about human health D. the cause of illness and disease
九年级英语阅读理解困难题查看答案及解析
---Which film do you like best?
--- ________ of them. They are both long and boring.
A. Neither B. All C. Either D. None
九年级英语单选题困难题查看答案及解析
---Which film do you like best?
--- ________ of them. They are both long and boring.
A.Neither B.All C.Either D.None
九年级英语单选题困难题查看答案及解析
根据句子意思及所给的词首字母或汉语提示,完成下列单词。(5分)
1.Both of them are nice and cheap. I really don’t know which one I should c________.
2. F________ the doctor’s advice, and you will get better soon.
3.Our Chinese teacher wants us to write a d________ every day to improve our writing.
4.That baby has only three ________(牙齿) . He can’t eat that apple.
5.Tan Jiexi’s song “Run, Run, Run” is very ________(流行的) among young people.
九年级英语单词拼写简单题查看答案及解析
—What do you think of the two mobile phones?
— of them are very nice.
A. Either B. Both C. Each D. All
九年级英语单选题简单题查看答案及解析
---- Could you lend me a pen ?
---- Of course . Here are two and you can take ______ of them .
A. both B. all C. any D. either
九年级英语单项填空中等难度题查看答案及解析
How much do you know about the North Pole(北极) and the South Pole? They are both places with very cold temperatures and few people live there. However, the North and South Poles are not much alike as people may imagine.
The North Pole has no land, only thick ice. Temperatures seldom go above 32°F, at which water turns into ice. Most of the time, it stays below zero. In winter temperatures are usually as low as-30°F.
Although conditions were very poor, people tried for many centuries to reach the North Pole. Over 100 years ago, two men, Robert Peary and Mathew Henson, were able to get to this environment full of troubles and difficulties. They reached the North Pole on March 8th, 1909. It was really a hard trip for them.
There are few things more dangerous than crossing the Arctic(北极圈) on foot. People who stayed there may face many problems: very cold temperatures, sudden storms, and even hunger. Most of the area is uninhabited, few people can live in such a difficult place.
People might think that with such low temperatures for most of the year, the ice would be thick and hard. However, this is not true in the Arctic. The movement of the ocean water under the ice may often cause many different changes on the surface. Sometimes the ice breaks into two opening lanes of water(水道) called "leads". Anyone who falls into a lead can be frozen to death in a few minutes.
1.This passage is probably from ___________________.
A.a book review
B.a science book
C.a school report
D.a computer magazine
2.According to the passage, what happened over 100 years ago ?
A.Two men succeeded in getting to the North Pole.
B.Temperatures in the North Pole went above 32°F.
C.The environment in the North Pole suddenly became worse.
D.The North Pole changed into thick ice because of the temperatures.
3.What does the underlined word "uninhabited" mean in Chinese?
A.气候恶劣的
B.充满危险的
C.困难重重的
D.无人居住的
4.The reason for the ice to break into two opening lanes of water is that __________________.
A.the temperature suddenly drops
B.the water under the ice is frozen
C.the ocean water under the ice moves
D.the surface is covered with lots of ice
5.What does this passage mainly talk about?
A.The thick ice in the North Pole
B.A difficult trip to the North Pole
C.The real situation in the North Pole
D.The differences between the North Pole and the South Pole
九年级英语阅读单选中等难度题查看答案及解析
---May I borrow your pencil, please? -of course, here are two and you can use __of them.
A. both B. every C. any D. either
九年级英语单项填空简单题查看答案及解析
根据短文内容,填写表格。(所填内容可能是单词,短语或句子)
There are many kinds of vegetables. Do you know some of them? Do you like eating them? It is good for our health to eat some every day. Let’s see what vegetables help what parts of our body!
A slice of carrot looks like human eyes. And the science now shows carrots greatly help the blood go to the eyes. Often eating them is good for our eyes.
A tomato has four parts and is red. The heart has four parts and is red, too. All of the research shows tomatoes are really the best food for the blood and the heart.
Celery looks more like bones. It specifically makes bones strong. Bones are 23% Ca. If you don’t have enough Ca in your diet, the bones will be weak.
Onions look like the body’s cells. Today’s research shows onions help take away waste things from all of the body cells.
You see, how important vegetables are! Maybe some of them don’t taste good. But if you want to be healthy, you should eat as many as you can. You should have a balanced diet!
Eating1.___________is good for our health | |
Names of the vegetables | Functions(作用) of vegetables |
Carrots | to help the blood2.__________ |
3.______ | to be the best food for the blood and the heart |
Celery | to 4._________ |
Onions | to help5.____from all of the body cells |
九年级英语其他题中等难度题查看答案及解析