Sea Urchins Project
Hello dear Reader,
We are the Sea Urchinies team. The global aim of the our one-week project was to compare chemical gradients on a biological sensor and on an electronic one in different salty environment. But what is a chemical gradient ? A chemical gradient is a difference of concentration of molecular entities. An example of that could be sirop in water. When you add water after having put sirop at the bottom of the glass the sirop will take time to diffuse and the bottom of the glass will have much more sirop than the top !
Therefore, we realized two different experiments. The electronic experiment was made thanks to a Grove Water Sensor. We will later explain what it is. For the biological experiment, we used sea urchins’ gametes (ovum and sperm cell). The goal was to observe gametes movement according to the salt concentration. The gametes of sea urchins follow chemotaxis to mate. But what is chemotaxis ? It is the movement of an organism in response to a gradient of concentration. In our case, the ovums - thanks to their hormones creating the gradient of concentration - attracted the sperms to them. We choose to focus on :
Is chemotaxis in sea urchin a better indicator of salinity then the grove water sensor ?
We first started by the electronic experiment. So what is the Grove Water Sensor ? Thanks to the data it collects the sensor indicates whether he is dry, damp or completely immersed in water by measuring conductivity (capacity to conduct electrical current). We chose this device because the more ions there are in water (represented here by the concentration of salt) the more conductive the water will be. To launch it, we created different salt concentration of 0 g/L, 31 g/L, 35 g/L, 39 g/L. The 0g/L was there as a reference to see if the sensor worked well while the other concentrations belongs to the range of salt concentration that can be found in the ocean. Thanks to a Grove water sensor, we obtained salt concentration of our solutions in arbitrary unit.
We then did the biological experiment. We started by extracting the eggs and sperms cells of sea urchins. To do it, we put the top of the sea urchin facing down on a jam jar full a salty water. This position make them released their gametes. To identify whether it was a female or a male, we looked at the color of the ejaculation. If it looked orange-ish, it was a female and if it was whitish, it was a male. After differentiating the gametes, we put a drop of sperm and a drop of ova on opposite sides of a microscope slide in different saltwater concentration (same salt concentrations as the electronic experiment but without the 0 g/L).
We collected our data and for a better visualization, we decided to represent them on a histograms. For all the concentrations, we represented the average of all the data that we have collected.
 |  |
Figure 2 : Data of the electronic experiment
|
Figure 3 : Data of the biological experiment
|
Interpreting the data
For the electronic experiment, we expected an increase of the conductivity with the increase of the concentration of minerals. However, this is not what our electronic sensor showed us. Indeed, there is no link between the concentration of salt and the conductivity of the water. Some possible options to these strange results are that we did not used normal salt but aquarium salt or we might not have programmed the sensor the right way.
For the biological experiment, we can see that as the salt concentration is increasing the time for sperms to meet increases. This is also not what we expected but we had no precise idea of what we shall expect. Plus, we made an experimental mistake as we have found fertilized eggs before introducing eggs on the slide. For this reason we can’t know if the sperm we saw were coming from the opposite side of the slide or directly from the egg solution. We thought that we should have take the sexuals cells at the beginning before mixing the urchin in the aquarium.
To conclude, we could say that none of our sensors were precised enough and no conclusion can be given on the impact of salinity on the mating of sea urchin. So, we can not know what will be the impact of an increase in salinity of the ocean.
Now you might want to know how sea urchins have kids in real life ?! And you will find that by clicking on video. And for more scientific contain on sperm chemotaxis you can read this article.
Have a nice day and see you soon !
Written by : Lucile Szpiro, Pauline Gasquet, Floriane Coulmance--Gayrard & Alexandra Perron
No comments:
Post a Comment