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.
The major causes of the greenhouse effect is excessive carbon dioxide gas in the atmosphere. The greenhouse effect is a process that warms the Earth's surface. When the Sun's energy reaches the Earth's atmosphere, some of it is reflected back to space and the rest is absorbed and re-radiated by green house gases, such as carbon dioxide, water vapor, metahne, nitrous oxide, and ozone. The absorbed energy warms the atmosphere and the surface of the Earth.
I think that the answer is c, i’m not completely sure
<span>The primary evidence that supports the theory that an asteroid strike approximately 65 million years ago caused a mass extinction is a thin layer of clay containing iridium, an element that is common in space, but not on earth being of that age and found in many different places in the world, indicating a large-scale event..</span>
