Water makes up 71% of our planet while only around 3.5% of the total water on. Earth is fresh. While there is plenty of water around, many animals can’t even drink it. For humans, consuming salt water disrupts cellular processes. Cells try to balance osmotic pressure, and end up losing more water, leading to dehydration. Our kidneys also work to filter out the excess salts, but the high rapid intake of seawater overwhelms our body’s ability to eliminate it. However, marine animals, like the sea turtle, have evolved to live in salty environments. Although sea turtles can process and get rid of the salt from their bodies, they are not too different from humans when it comes to the intake of salt water. You may think how is a sea turtle similar to us? Well Sea turtles have less salt inside their bodies than the ocean around them, and their kidneys can’t make saltier urine than their blood. In order to survive they need less salt in their bodies than their surroundings. The turtles are able to keep the salt from going through its skin because their skin is so tough. Some marine animals are able to regulate their water intake through the food they eat, like in the case of whales, but this does not work for the sea turtle. The main food source for many sea turtles are jellyfish. If you think about the jellyfish, they really dont have much to them. If you had to guess that sea turtles have to eat a lot of jellyfish to get the energy they need you would be right. Jellyfish are 96% water, and 4% salt, which makes them salty just like the ocean. Less than 1% of the jellyfish is used for food. This causes the sea turtle to take in a lot of salt along with its meal. Imagine having more salt than food on your plate! How would you handle the intake of all that salt?

Chelonia mydas and bubbles

Sea turtles use salt glands to shed out the salt they intake. The salt glands take up a large part of the head region, primarily around its eyes. The glands transport the salt from the turtle’s bloodstream and concentrate it into a salty solution, which is then excreted through the turtle’s tear ducts. Specifically the leatherback sea turtle cries around 8 liters (2 gallons) of tears every hour. Yes, it sounds sad, but sea turtles cry out salt everyday. This process is very important in maintaining sea turtles internal salt balance and allows them to survive in salty environments.

In our AP Biology class, we learned about osmosis which is, the movement of water across a permeable membrane to equalize solute concentrations. The process of a  turtle’s regulation of its bodys salt concentration is related to the topic of osmosis. In the case of sea turtles, their bodies must manage the osmotic challenge of living in a salty ocean environment. The process of the turtle using its salt glands involves the movement of water. This process involves moving water to dilute the excess salt, and is a form of osmosis that helps the turtles maintain their internal salt balance despite the high-salt surroundings. As we learned, animals can not have salt water surrounding their cells because it will cause the cells to become severely hypertonic, meaning the cell will completely shrivel up since the water went from a high concentration of water inside the cell to the low concentration of water surrounding it.

Osmosis diagram

Process of osmosis: water going from high to low concentration


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