It’s a matter of dimension
A January govt order by President Donald Trump designates individuals as feminine in the event that they make the “massive” reproductive cell (the egg) and male in the event that they make the “small” one (the sperm). However the human sexes don’t match neatly right into a male–feminine binary because of components equivalent to genetics and hormones, senior molecular biology author Tina Hesman Saey reported in “The actual biology of intercourse.”
Reader Root Gorelick, a biologist at Carleton College in Ottawa, appreciated the function and wrote in so as to add some nuanced factors.
Reproductive cells change all through growth, so a intercourse definition primarily based on dimension is difficult. For example, in creating embryos, the progenitors of eggs and sperm, generally known as primordial germ cells, sometimes type earlier than ovaries and testes do. PGCs migrate to the gonads later in growth. These cells are enormous, and so they begin off roughly the identical dimension, no matter the kind of gonad an embryo kinds, Gorelick notes.
After gonads type, meiosis, the method of cell division that produces sperm and eggs, additional complicates issues. In human females, meiosis produces one massive egg cell and two small infertile cells known as polar our bodies. “Issues are weirder in males,” Gorelick continues. Earlier than meiosis in males, a PGC replicates its genome a number of instances with out splitting up into product cells. So one enormous cell with a number of nuclei is produced, Gorelick says. That vast cell then jettisons a number of tiny sperm cells, and the remaining cytoplasm is left as a big “residual physique” cell with out nuclei.
Roughly talking
A research of practically 100 human mind samples exhibits that micro- and nanoplastics, or MNPs, within the mind have elevated considerably over time, senior neuroscience author Laura Sanders reported in “Plastic shards permeate human brains.”
The story acknowledged: “From 2016 to 2024, the median focus of MNPs elevated by about 50 %, from 3,345 micrograms per gram to 4,917 micrograms per gram — roughly three bottle caps value of plastic.”
A few readers had been confused about what the bottle cap comparability referred to.
The “roughly three bottle caps value of plastic” refers back to the whole quantity of plastic estimated to be current in a whole human mind. That’s about 4,917 micrograms multiplied by the typical weight of a mind in grams, Sanders says.
However this comparability comes with caveats. Brains range in weight, as do bottle caps. Additionally, the research measured MNPs in samples from the mind’s frontal cortex, Sanders says. It’s not clear whether or not plastic masses differ relying on mind area.
Tip of the hat
Reader Diana Lutz drastically loved the April difficulty’s three options, which lined the talk across the revival of nuclear weapon testing, the complexity of organic intercourse and the unsure guarantees of the carbon credit score market. “All three articles are on essential matters which can be hardly ever examined at such depth,” Lutz wrote. “In every case, I had lingering questions the articles resolved. Kudos!”
Correction
April’s “Spooky lights could possibly be earthquake farts” mistakenly described radon as a flammable fuel. Certainly, it’s an inert fuel.
