Looking at the onion root tip under the microscope you can see large, rectangular cells with visible distinct cell walls surrounding it (cells have a more regular shape because of the wall). Inside the cells, you can notice darkly stained nucleus, large vacuoles at the center and sometimes small granules within the cytoplasm. Looking the onion root tip under the microscope is often the way to observe mitosis. Usually, you cannot see organelles such as mitochondria, ribosomes, rough and smooth endoplasmic reticulum, centrioles and Golgi body as they appear translucent and because are too small to be seen under the light microscope (electron microscope required). Also, chloroplasts are not present in an onion cell because it is not a photosynthetic cell.
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Because flu viruses evolve so quickly, last year's vaccine may not protect you from this year's viruses. New flu vaccines are released every year to keep up with rapidly adapting flu viruses.
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Fossils are the sources to learn the changes on the earth and how much it changed in these years. Its provides us with information about the existence of plant and animals in the past.
Actually, the fossils we found till the date are the ancestors of the plants and animals that live today. Moreover, some fossils of animals are easily identifiable since they exist till the date.
But there are fossils of animals that exist no longer in the earth. By studying and analyzing the fossils, one can tell how life on the earth has changed.
Also, we can learn about the ancestors of the plants and animals and how their long life existed on earth.
In other words, one can learn where and how those organisms were lived. So that we can know about our ancient environments.
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