Why do people have different blood types? Scientists don’t know why humans have different blood types, but a good hypothesis is that they protect us as a species against different diseases. We have approximately 4.5 to 6 liters of blood, depending on our size. Blood is generally about 10% of our body weight. Blood is […]
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Why can we eat lettuce and spinach, but we can’t eat leaves and grass? We can’t eat leaves and grass because of the cellulose and silica they contain. There are several different ways of getting energy. Plants photosynthesize and make energy, which they store in their cells. Herbivores eat the plants to get the energy
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How does antibiotic resistance happen? Bacteria develop the ability to survive an antibiotic, which is then passed on to future generations. The antibacterial power of some moulds has been known about since 1874, possibly even earlier. In 1897, Ernest Duchesne published a paper about the ability of moulds to kill bacteria. Alexander Fleming noticed that
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How do reflexes work? They work by using a reflex arc that bypasses the brain. There are many different types of reflex, but they are generally meant to protect us and to allow us to move around without having to think about everything. Our brains have a limited amount of processing space and if we
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How do amphibians breathe underwater? They breathe through their skin. The word “amphibian” comes from the Greek amphi, meaning both and bios, meaning life. The word was first used in the 1630s and it was used to mean animals that “have two modes of existence”. There are about 7,000 different types of amphibians in the
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What causes brain damage? There are several things that cause brain damage. These can be traumatic injury, poison, stroke, tumor, or lack of oxygen. The brain weighs about 1.5 kg on average and contains over 100 billion nerve cells. It uses 20% of the body’s energy, which is more than any other organ. Obviously, without
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How did the Black Death change society? It ended serfdom and slavery, improved worker conditions, brought a recession, harmed religion, increased antisemitism, improved medical practice, improved women’s rights, and changed the world of art and fashion. There were three major plagues, but let’s look at the middle one, the one that is most famous. It
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How did the Black Death spread? It was spread by people along trade routes. The Black Death is another name for bubonic plague, which is caused by a bacteria called Yersinia pestis. Y. pestis generally lives in fleas that feed on rats. When the flea bites the rat, the bacteria passes into the rat’s blood.
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How much blood can you lose? Well, obviously all of it. How much blood can you lose and still function? Depending on your body size, from between 15 to 30%. We have approximately 5 liters of blood in our bodies, but that varies by size. An average-sized female of 165 cm will have about 4.3
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Why is PM 2.5 dangerous? They are particles that are too small for our nose to catch. PM stands for Particle Matter and they are microscopic solid or liquid particles that are small enough and light enough to be suspended in the air. There are many sources of these particles. In some countries, one of
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