You may remember the process of osmosis from science class at school. Osmosis occurs across a semi-permeable barrier (our cell membranes). That barrier allows water molecules to pass in certain directions, depending on the concentration of water solutions on each side (imagine different concentrations of salt water).
In normal circumstances, the saltiness of water in your cells is the same as the saltiness outside your cells. This is called an isotonic state. But when your cells consume water, the solution becomes more concentrated, and the natural process of osmosis allows water from outside your cells to pass into your cells to achieve equilibrium (this is called osmoregulation). That’s how we absorb water as it’s needed; it’s a natural process. Your cells are isotonic to about 0.9% saline solution. If the salinity of the solution outside the cells decreases, your cells absorb more water to get back to an isotonic state. When marathon runners and other endurance athletes drink too much fresh water, the solution outside their cells drops rapidly in salinity, so osmosis allows water to pass into the cells as a part of osmoregulation. If they absorb too much water, the cells will swell and burst, which can lead to a quick death. This is why runners drink sports drinks that contain sodium and potassium, to help maintain an isotonic state (and it’s why they’re called isotonic sports drinks). The opposite happens when drinking sea (salt) water. The salinity outside your cells increases rapidly, so osmoregulation effects a movement of water from in your cells, to outside your cells, to achieve an isotonic state. So even though you may be dehydrated, your cells will actually release, rather than absorb, the water around them.
But why would your dehydrated body expel water when death is imminent? Well, this isn’t a conscious decision by your body. It’s simply molecular physics and osmosis at work. And in osmosis, water passes from low saline concentrations to high saline concentrations, end of story. So, you should absolutely not drink sea or salt water when dehydrated. It’s not just an issue of not absorbing the water, but an issue of osmosis accelerating the release of water and dehydration.
I said in the introduction, “You’ll die if you don’t drink something soon, so what’s the worst that can happen?” Well, what’s worse than dying? Dying much sooner, potentially before help arrives.
Astronomers can use telescopes to look at very distant galaxies. This is how they see what the Universe looked like a long time ago. This is because the light from distant parts of the Universe takes a very long time to reach us. From these observations, it seems the physical laws and constants of the Universe have not changed.
Physicists are currently unsure if anything existed before the Big Bang. They are also unsure whether the size of the Universe is infinite.
The Mid-Atlantic Ridge (MAR) is a mid-ocean ridge, a divergent or constructive plate boundary located along the floor of the Atlantic Ocean, and part of the longest mountain range in the world. ... The ridge has an average spreading rate of about 2.5 centimetres (1 in) per year.
In this case, researchers observed a trade-off between the ability to tolerate harsh dry conditions and the ability to colonize deeper water. This type of trade-off can increase the fitness of only one phenotypic trait.
An evolutionary trade-off can be defined as an evolutionary mechanism where a trait can increase its adaptive fitness in the detriment of decreased adaptive fitness in another phenotypic trait.
In trade-offs, the evolutionary adaptive processes cannot optimize a given trait without compromising another.
A well-known example of an evolutionary trade-off is the balance between the number of eggs that a bird can produce in a determined clutch.
