How do you write a 500 word expository essay after speaking in science class?

Today, we had a science lab class in the lab. This is the third time our class has been in the lab, and the students are very excited.

When I came to the lab, I saw a large fish tank filled with water on every other desk. I thought about it for a long time and didn't know what lesson the science teacher was going to give us today.

The class started, and the teacher asked everyone to follow the steps to do the experiment. First blow a lot of breath in a large bag, blow the bag to a bulging one, and then tie a dead knot in the mouth of the bag and set it aside. Then he took out two more pieces of glass and two cups, filled one of the cups with water and poured it out, and immediately covered the glass pieces.

In this way, a cup of fresh air is loaded. Then, he took out the straw and the large puffed bag, plunged the straw into the bag at one end, and put the other end into the mouth of the cup in the water, and while grabbing the bottom of the cup, he asked a classmate to squeeze the gas from the bag into the cup, and then poured out the water and covered the glass sheet. In this way, it is a cup full of exhaust gases.

At this time, the teacher lights two matches, puts two cups in them at the same time, and asks us to observe which cup will extinguish the match first. We looked closely, widening our eyes, and found that it was the matches in the cup filled with exhaust gases that went out first, and the matches that burned in the cup filled with fresh air went out later.

It turns out that what the science teacher is telling us today is that a burning fire lasts longer in the fresh air with oxygen.

Generally, technical explanatory texts are manuals.

Human blood. The red osmotic mass flowing in the human body is whole blood composed of red blood cells, white blood cells, platelets, plasma and other components. At present, advanced medical technology emphasizes the transfusion of blood components, and in many cases of clinical use, whole blood is not required, and only one or several blood components are used.

Therefore, artificial blood does not need to be exactly the same as whole blood composition. Plasma substitutes are now available on the market, platelet substitutes have been studied, and many countries are currently focusing on the development of erythrocyte substitutes. The main function of red blood cells in the blood is that the hemoglobin in red blood cells carries oxygen.

If hemoglobin, which is responsible for transporting oxygen molecules, can be synthesized, the key problem of artificial blood will be solved.

Since it is life-saving blood, safety is naturally the first need. Because of the virus removal or inactivation process incorporated into the artificial blood preparation process, the infusion of artificial blood can avoid the spread of disease due to blood-contaminated sources. In addition, the transfusion of artificial blood eliminates the need to consider the matching of different blood types.

When we talk about blood type, we generally refer to ABO blood group, which is classified according to the antigen contained in the red blood cell membrane. Because artificial blood composed of hemoglobin does not have a red blood cell membrane, there is no antigen and will not cross-react with the existing antibodies in the body, so artificial blood is suitable for any blood type, and the human body will not reject it, and it can truly achieve "one blood universal". Especially in the case of emergency rescue, doctors only need to directly transfuse artificial blood for the patient, instead of having to test the patient's blood type first, and then spend time searching for the matching blood, saving a lot of valuable time.

The advantage of artificial blood is that it can be produced in large quantities to ensure the sufficiency of blood for medical use**. Artificial blood, which uses animal hemoglobin as a raw material for hematopoiesis, is rich in raw materials**. The artificial blood currently developed in China is made from bovine hemoglobin, and researchers in France recently discovered that the blood of a beach worm called the sea earthworm is also suitable for making artificial blood.

Another advantage of artificial blood is its ability to be stored for a long time. According to the current technical conditions, ordinary blood can only be kept fresh for 42 days under special storage conditions, and if this time is exceeded, the blood may deteriorate, while artificial blood can be stored for several years. Artificial blood based on hemoglobin is a red solution that is lyophilized as a red or dark red powder.

If necessary, the dry powdered artificial blood can be dissolved in a specific liquid to be infused into the patient. Because it does not require blood type matching and is easy to carry and store, artificial blood is particularly suitable for emergency medical rescue in the event of war or large-scale disasters.