Why is cotton in everything? - Michael R. Stiff
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Cotton that we grow today is descended from wild ancestors that humans found useful. The process of adapting wild plants for human use is called domestication. This occurs when humans keep the seed of plants that possess traits they like, for example long, fluffy fibers. This passes the genes from the parent plants that had the longer fibers to the offspring. Over time, domestication led to longer, stronger fibers than the wild ancestors.
Cotton fiber is so useful that four cotton species were domesticated by civilizations in different regions of the world. Gossypium hirsutum, also called Upland cotton, was domesticated in Central America. Today, this species accounts for over 90% of the land used for cotton production. It produces good quality cotton for making fabric for things like t-shirts and blue jeans. G. barbadense was domesticated in South America. Cotton fiber from this species is often labeled “Pima” or “Egyptian” cotton. The longer fibers from G. barbadense make softer, higher quality fabrics used for making pricier clothes and bedsheets. G. herbaceum and G. arboreum were domesticated in the Levant and South Asia, respectively, and both produce relatively shorter and coarser fiber than G. hirsutum and G. barbadense. Check out more about cotton genetics and domestication.
Cotton fiber shape
When most people think of a plant cell, they think of a rectangular box with a cell pushing against the inside of the cell wall. In fact, plant cells come in many shapes, and there are complex mechanisms that the plant cell uses to make those shapes. The cotton fiber is an example of an extremely long and thin plant cell. Other long plant cells include pollen tubes. Arabidopsis, a tiny mustard species, makes leaf trichomes that are single cells that project from the leaf surface to split into three pointy spikes at the end. Cells that make up the surface of the leaf look like interlocking puzzle pieces.
One way for the plant cell to control its shape is to stiffen parts of the wall that it wants to keep in place while maintaining softer parts of new wall to mold the shape of the cell. Turgor pressure pushes the soft part of the wall until the plant cell achieves its target shape. Next, it stiffens all the cell wall. It can do this by adding more cellulose and altering other polysaccharides to the wall. Many other factors involved in plant signaling and parts of the cytoskeleton are also important for determining plant cell shape. This video shows a pollen tube growing from its soft-walled tip while the sides of the cell behind the tip have strengthened walls.
Cotton and sustainability
Brian Resnick reports synthetic fibers in our clothing contribute a large proportion of microplastic pollution to our waterways. Microplastics are tiny pieces of plastic, less than 5 millimeters long, that are found in our environment. They can be toxic to wildlife and end up in fish we eat. One response to the challenge of microplastics from clothing could be to choose clothing made from natural, potentially renewable cotton fiber. Cotton fabrics, however, can come with their own set of environmental and ethical challenges. In the case of a t-shirt, these challenges include the sustainability of how cotton is farmed and the treatment of workers who make the t-shirt.
Watch this TED-Ed Lesson about the life cycle of a t-shirt to learn more. Go here to learn about one example program that aims to encourage sustainable cotton production.
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