In this post, I’m going to discuss a topic that I thought about a lot when I was younger. Have you ever wondered why, exactly, saltwater fish can’t live in fresh water and freshwater fish can’t live in salt water? When I was creating my Insta-pets kit and watching the little guys swimming around in their saltwater tank, I decided to find out why the amount of salt in their water was so critical to their well being.

As most of us know, there are two main types of fish: saltwater and freshwater. Saltwater fish can’t survive in fresh water, and freshwater fish can’t survive in salt water. In nature, they live in different environments (the ocean vs. a stream, for example) and in captivity we keep them in different types of aquariums. If a saltwater fish somehow makes its way into a freshwater aquarium, it will die after only a few hours. Most fish can survive in just one type of water. These are referred to by scientists as stenohaline. There are also euryhaline fish, like salmon, that can survive in salt water OR fresh water. Why are fish so picky about what kind of water they live in? Read on to find out.

The key to the answer is osmosis. To explain osmosis, let’s start with a cell – the building block of life. Cells are responsible for the vital functions of all living things. We’re made of them, plants are made of them, and so are fish. Before I talk about osmosis, let’s take a look at two important parts of a cell: the cell membrane and the cytosol.

Think of the cell membrane as the “skin” that surrounds a cell and think of the cytosol as the substance that fills the cell and surrounds its contents. The cell membrane’s job is to keep everything inside safe, and to keep a balance between the levels of chemicals (mostly salts) in the cell and in the surrounding environment. It’s made up of water and lots of different kinds of dissolved chemicals that a cell needs to work properly. Cells like to keep the concentration of chemicals on the inside the same as on the outside. For example, if a cell that was previously surrounded by a fairly diluted solution (like fresh water) is suddenly exposed to a salty solution, the cell membrane will allow most of the water inside the cell to leave. This makes the cell shrink, and increases the concentration of salts in the cytosol so that the concentration inside the cell becomes equal to the concentration outside the cell again.

Confusing? Think of it this way – the cell membrane lets water move through it from areas of low concentration (less chemicals, more water) to areas of high concentration (more chemicals, less water). This helps keep the concentration of chemicals the same on the inside and outside of a cell.

Check out the illustration below to get a better idea of how osmosis works:

An example of osmosis – water is moving from an area of low concentration of salt, outside the cell, (notice the cell is smaller) to an area of high concentration of salt, inside the cell. Once the process is finished, the concentration of salt is the same on the outside and inside of the cell (now the cell is larger because there is more water in it). Before is on the left and after is on the right.

Fish need a certain amount of salt in their bodies to stay healthy. Too much or too little can cause problems. Since fish’s natural habitats are always changing due to weather and other forces, they have to be able to adapt to small changes in salinity by controlling how much salt is present in their bodies. This is called osmoregulation, and it’s one of the functions of the kidneys – for both fish and people. The gills and kidneys of saltwater fish get rid of salt because they live in such a salty environment. Freshwater fish concentrate salt in their bodies because they live in an environment where salt is harder to come by.

Saltwater fish’s cells naturally contain a very high concentration of chemicals so that they don’t shrink when exposed to the salt water they live in. When a saltwater fish is exposed to fresh water, all of that water floods into their cells in order to dilute the chemicals inside and keep a balance with the surrounding environment. Two things can happen when water floods in. Some cells fill up with so much water that they burst (scientists call this cytolysis), while others just stop working because the chemicals inside them are too diluted. Both of these things will kill the fish. The opposite happens to freshwater fish in a saltwater environment – water flows out of their cells, dehydrating the fish and disrupting cell function.

Here’s how osmosis can affect the size of blood cells:

An example of osmosis in blood cells. On the left are cells in a solution with more salt in it than there is inside the cells (a hypertonic solution); in the middle are the cells in a solution with the same amount of salt in it as there is inside the cells (an isotonic solution); on the right are cells in a solution with less salt in it than there is inside the cells (a hypotonic solution).

Most fish are stenohaline, and will die when exposed to the wrong environment (salt water vs. fresh water). But what about euryhaline fish like salmon, eels, and some trout? Salmon, for example, have evolved to survive in both fresh and salt water because of their life cycle. Salmon are born in freshwater streams, but then migrate into the ocean where they mature and spend about 1-5 years. After that, they migrate back to the same freshwater streams they were born in so they can reproduce. Their bodies have adapted to use osmoregulation to either retain or get rid of salt depending on their surroundings.

Want to learn more?

http://www.ca.uky.edu/wkrec/vertebratefishevolution.pdf

http://www.scientificamerican.com/article.cfm?id=why-do-some-fish-normally

Want an Insta-pets kit? Click here!

Courtesy of the CDC

Once the infection goes away, the antibodies required to fight off the disease stay in our bodies so if we ever catch the disease again, our immune systems are prepared. Unfortunately, antibodies are antigen-specific. That means we need a different sets of antibodies for each different virus or bacterial infection.

This is where vaccines come in handy. When you get a vaccine,  a very small amount of a specific antigen is introduced to your body – enough for your immune system to recognize the virus and develop antibodies to fight it off, but not enough to get you sick. That way, when you get the virus or infection for real, your body already has antibodies to fight it off, and you don’t get sick. Neat, huh?

If you want to learn more about vaccines, check out the following sites:

• http://www.wisegeek.com/how-do-vaccines-work.htm
• http://health.howstuffworks.com/vaccine.htm
• http://www.chop.edu/service/vaccine-education-center/vaccine-science/how-are-vaccines-made.html

First, he found a study by Chinese scientists on Google that showed how a mixture of soil and chicken manure broke down 25% more oil than if it was just plain soil. He wanted to prove this for himself, so he filled 10 jars with two cups of dirt and two tablespoons of motor oil. He then added 3 tablespoons of chicken manure to half of the jars and three more tablespoons of dirt in the remaining jars as a control. He let all ten jars incubate for two weeks and then filled the jars with water, forcing the oil to the top. 31.2% of the oil broke down in the jars with manure, whereas the jars with only dirt only broke down 7% of the oil.

Like dispersants, this method has its pros and cons but hey, this might be just what BP needs. They’re looking for help after their most recent attempts at stopping the spill have failed (they’re now taking suggestions from the public of ways to clean up/stop the oil).

Read more about Nick’s experiment here:

• http://www.newsobserver.com/2010/06/03/512661/boy-has-a-crude-solution-chicken.html

Here’s a a video of me in a North Carolina kindergarten classroom. We’re working on a Connor in the Classroom page for my website, so stay tuned for more photos and videos!

Do you know a teacher in a struggling US school district? Leave a comment or send me an email!

A C-130 Dropping Oil Dispersant into the Gulf on May 5th, 2010. Image from Wikipedia.

We’ve all been hearing a lot about the massive oil spill in the Gulf lately – and the attempts to stop it. One of the methods currently employed by BP to try to get rid of some of the oil is the use of oil dispersants. What are oil dispersants, and how do they work?

Dispersants are made up of two main parts: a surfactant, and a solvent. These two parts work together to pull small drops of oil off the main slick – the same way you can use soap to clean grease off a dirty pan.

Oil is biodegradable. The problem is, it takes a long time for the naturally occurring bacteria and microorganisms in the water to break down the oil when it’s in one large slick so it first has to be slowly broken up into smaller pieces by waves and turbulence in the ocean. The goal of a dispersant is to speed up this process so the oil-eating microorganisms in the water can break it down quickly. Another advantage to having small drops of oil instead of one large slick is that the smaller drops don’t rise to the surface as quickly, therefore keeping the oil out of delicate coastal wetlands.

Dispersants have never been used at this scale before. So far, BP has applied over 840,000 gallons of the stuff and the environmental consequences of both the dispersant and the dispersed oil are largely unknown. Scientists believe that dispersants are the best option for now, but that may change in the future.

For more information, check out the following sites:

• ITOPF – Spill Response – Dispersants
• Dispersants – A Guided Tour
• How Do Oil Dispersants Work? | Popular Science

A picture of the International Space Station, photographed by a crew member on the space shuttle Discovery. Image from NASA.

On Sunday, the space shuttle Atlantis undocked from the International Space Station (ISS) to head back home – completing what will probably be its final mission. Atlantis will land back on Earth Wednesday.

Now that the ISS is almost completely finished, NASA only has two more shuttle missions to wrap up its share of construction. Check out the photo below – the Space Station weighs over 816,000 pounds and is about 98% complete in terms of living space.

To learn more, you can read here: http://www.msnbc.msn.com/id/37301258/ns/technology_and_science-space/