How do weeds spread? Detailed answer

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How do weeds spread? Detailed answer

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How do weeds spread?

When they say the word "weed", they mean some kind of useless plant. However, from the point of view of nature, all plants bring the same benefit. Another thing is that people select and cultivate only those that have valuable qualities for the person himself, and all the rest, growing in cultivated fields and gardens, are called weeds! The damage caused by weeds can be different. Some of them are poisonous to cows and horses grazing in the meadows. Others damage valuable crops by robbing them of sunlight, moisture, and soil nutrients. Still others are parasites, serve as sources of disease, or attract insects that harm crops.

It is known how difficult it is to fight weeds: every year they have to be weeded out again. This is because the ways weeds spread are very diverse and difficult to control by humans. A certain proportion of weeds are carried from one place to another along with livestock feed, dust, garbage or manure. However, most of those that cause especially a lot of trouble and trouble do not at all need the services of human carelessness or carelessness. They have plenty of their own means for distribution and reproduction.

For example, weeds such as nightflower, nightshade, dodder, and many grasses produce such a huge amount of seeds that some of them survive in almost any conditions. Other weeds on seeds or fruits have processes in the form of hairs or wings. With their help, the seeds manage to move downwind for considerable distances. This is how sorrel, oxalis and dandelion spread. There are also weeds that, instead of hairs on seeds or fruits, grow thorns or small hooks that cling to animal hair or people's clothes. This method is used by the well-known thistle.

However, the most elusive of weeds are not propagated by seeds at all. They grow branched underground stems, and what we see on the surface is just small vertical shoots. If the underground stem is cut, then these shoots, instead of dying, become simply separate plants!

Author: Likum A.

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We can learn about what is happening inside the brain with the help of functional magnetic resonance imaging (fMRI) - it allows you to see activity in certain parts of the nervous tissue and quite accurately compare this activity with the performance of a particular task. But we will not be able to learn everything about the brain if we do not penetrate to the cellular level, to the level of neurons and interneuronal contacts - synapses, to the level of auxiliary glial cells, which not only nourish neurons, but also interfere with the conduction of a neurochemical signal. And it should be remembered that there are many neural varieties. For example, if we carefully examine the cerebral cortex, we will find six layers in it, differing from each other in the ratio of neurons of different types. To understand how the higher cognitive functions are realized at the molecular-cellular level (namely, the cortex is engaged in them), we need to understand the structure and the relationship of its layers to each other to the subtleties.

Something, of course, can be studied on the brains of rodents and primates. In addition, the interaction of neurons is often studied in cell culture: cells live in a nutrient medium at the bottom of some laboratory vessel, and neuroscientists monitor how, for example, the strength of their synapses changes in response to certain stimuli. As a result, some conclusions can be drawn about the causes of schizophrenia, autism, and other cognitive impairments - after all, in the case of such pathologies, it is the neural architecture, the interconnection of neurons with each other, that is violated. But a flat layer of cell culture is still not a bark with its six layers. Another way is to analyze samples taken from deceased people. Needless to say, here one must always remember about post-mortem changes in the cellular structure, and it is impossible to study signal conduction in such samples. Ideally, we would like to have in our hands a three-dimensional cellular model that completely recreates one or another element of the brain structure, if not the entire brain. The experiments of researchers from Stanford University bring us closer to this ideal.

Of course, the matter was not without stem cells - Sergiu Pasca (Sergiu Pasca) and his colleagues received induced stem cells from human skin and then turned them into neurons. Now this is almost a standard procedure: differentiated cells are forced to "remember their youth", when they were stem cells and could not do anything but divide. But they can be turned into any other cell type, you just need to direct them along the right path using molecular signals. At first, everything went as usual: artificial stem cells grew flat in a culture dish. But then they were separated from the bottom and transplanted into a special new "place of residence", where they could no longer firmly attach to the walls or to the bottom. Within a few hours, the cells united into microballoons, in which they continued to divide. And here they started turning into cells of nervous tissue.

After seven weeks, 80% of the cells, by molecular and other characteristics, became similar to nerve cells. Moreover, 7% turned not into neurons, but into glial astrocytes, which support and nourish neurons, protect them from the penetration of harmful substances from the blood, and also regulate neuronal activity. Until now, it was not possible to grow both neurons and the cells that support them from the same stem material, you had to use third-party astrocytes obtained from a different stem cell line, which meant that genetically both turned out to be different - whereas in the brain all cells carry the same genes . Now, apparently, this difficulty will disappear.

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