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Why do some fruits become sweeter after being left for a while, but others do not?

  Everyone should have this kind of experience: Bananas and kiwis need to be stored for a few days after they are bought, and they taste better when they are softened. However, no matter how they are placed, the taste of watermelon, pineapple and other fruits will not change significantly. This is because of their different ripening patterns, with climacteric fruits listed earlier and non-climactic fruits listed later. The main difference between these two types of fruits is the different sensitivity to the plant hormone ethylene. After being picked, the respiration-climbing fruit can still produce a peak respiration rate under the catalysis of ethylene, and convert the large molecules in the body into small molecules-for example, starch is hydrolyzed into sugar, which makes the pulp soft, acidity decreases, and sweetness is reduced. The higher the temperature, the better the flavor. Non-breathing-climate-type fruits will not continue the original development process after picking, the respiration rate will decrease, immature fruits will not continue to mature, and mature fruits will slowly rot.
  Why is it said that Guilin’s landscape is the best in the world?
  Guilin is located in the northeast of Guangxi Zhuang Autonomous Region in China and is a world-famous scenic spot. The mountains in Guilin are very beautiful, some are like elephants, some are like lotus flowers, some are like swords… In the caves of the mountains, there are various shapes of stalactites, stone pillars and stalagmites, exquisitely carved and in different poses and with different expressions. A beautiful Lijiang River flows among the strange peaks standing on pillars. Guilin’s landscape is the best in the world because of its characteristics of beautiful mountains, clear waters, caves and rocks. The reason why Guilin’s landscape is so beautiful and beautiful is because there are many limestones there. Limestone is particularly susceptible to dissolution by rain and river water containing carbon dioxide. After the erosion of rainwater and river water, Guilin has formed the current landscape wonders.
  Why do fish have mucus on their bodies?
  Most of the fish are covered with hard scales, but there are also a few fish, such as eel, catfish, loach, etc., whose whole body is covered with sticky liquid. This is because their scales have degenerated, and there are many special mucus glands in the directly exposed skin, which can secrete a large amount of mucus, forming a mucus layer. Fish scales have a protective effect on fish, and mucus has a similar function. Although it cannot block the impact of hard objects, it can prevent the invasion of poisonous bacteria and prevent harmful substances in the water from entering the body of fish from the skin. In fact, the role of mucus is much more than that. With its presence, the skin of the fish can be impervious to water, which is good for maintaining a constant osmotic pressure in the fish. In particular, some fish that migrate in rivers have mucus on their bodies, which can make them adapt to changes in salinity in the water. Mucus also reduces friction in the water, helping fish swim faster and with less effort. From this point of view, mucus is an indispensable magic weapon for fish to survive.
  Why do sprinters squat to start?
  In track and field competitions, we often see sprinters squat down before starting, with their feet forward and backward, and their rear feet kicking hard to make a preparation position. Why do you want to do this? The reason why a sprinter squats down before starting is actually the same as when a spring compresses. The competition in the sprint competition is fierce, and every second counts. If you are a step slower at the start, it will be too late to catch up. Therefore, athletes squat well before starting, and then start running suddenly after hearing the sound of the starting gun. The muscles will generate a powerful explosive force, which can enable the athletes to rush out at the fastest speed. Therefore, it is necessary for sprinters to adopt a squatting position at the start.

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