In this video we're looking at stem cells. So we're going to explain what they are and why they're so important and then take a closer look at some examples. Namely, embryonic stem cells and adult stem cells, which are found in animals, and then plant stem cells, which are found in meristem tissue in plants. Let's start with what stem cells are. And there are really two key features that you need to know.
The first is that stem cells are able to divide by mitosis to form more cells. So one can divide into two, then they can divide into four, and so on. The second is that stem cells are able to differentiate into specialised cells. So one stem cell could differentiate into a specialised nerve cell, for example, whilst another could differentiate into a skin cell.
To understand why this is important, let's consider how human life starts. When a sperm cell fertilizes an egg cell, it forms a single cell called a zygote. This cell is now its own organism, and during the following few days, it will divide by mitosis over and over again to form a small group of cells, called an embryo.
We call these cells embryonic stem cells. And importantly, these ones can differentiate into absolutely any type of cell. For example, a nerve cell, skin cell, or blood cell.
Over time, these cells continue to divide, and also differentiate into all of the other important cells that we need. And after 9 months or so, we end up with a baby. Now, if we fast forward a bit to an adult.
There are no longer stem cells that can differentiate into absolutely anything, like the embryonic stem cells can. Instead, we have other types of stem cells that have already specialised a bit, meaning that they can now only differentiate into a narrow range of cells. For example, in the middle of some large bones, there's a jelly-like substance called bone marrow, which contains adult stem cells. These cells can divide by mitosis as much as they like. but they can only differentiate into different types of blood cells, like red blood cells, white blood cells, or platelets.
The idea with stem cells like this is that they can replace damaged cells to keep us alive, but they don't form any new tissues like the embryonic stem cells did. Now, the last thing we need to cover are plant stem cells. Plant stem cells are found in plant tissues called meristems.
which are found in areas of the plant that are continually growing, like the very tips of the roots and shoots. As the plant grows, these unspecialised stem cells will differentiate into all of the cells and tissues that the plant needs, like the palisade cells that do photosynthesis, phloem and xylem cells that transport sugars and water, or root hair cells that absorb water and mineral ions. Importantly, plant stem cells persist for the plant's entire life, unlike embryonic stem cells which disappear by the time we're fully developed.
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