Ciclos vitales de animales

El laberinto de los peces.

Un querido alumno me planteó hace ya meses tratar el tema de los Bettas sp. y su

capacidad de respirar aire. Allá vamos.

Branquias

Si, no te preocupes, nadie te ha mentido. Todos los peces cuentan con branquias para respirar. Un órgano que evolucionó para obtener oxígeno disuelto en el agua, no en el aire.

Pero, ¿Por qué las branquias no pueden obtener oxigeno del aire y los pulmones no pueden hacerlo del agua?

Vamos a responder la segunda pregunta primero.

Resulta que la cantidad del oxígeno contenido en el aire es del 21%, mientras que en el agua puede que no llegue al 1% (esto depende de la temperatura y otros factores). El problema no es que un pulmón no pueda obtener oxígeno del agua sino que en el agua hay muy poco oxígeno que obtener.

Los peces se apañan con esa cantidad minúscula gracias a que una branquia es mucho más eficiente obteniendo oxígeno que un pulmón. ¿Cómo lo hace? Básicamente gracias a 3 mecanismos:

• El agua fluye continuamente por las branquias sin cesar. Al contrario que con los pulmones, donde tomamos un poco de aire, lo retenemos unos segundos y lo expulsamos, los peces están tragando continuamente agua y enviándola a presión hacia las branquias a ambos lados de su cabeza, de forma que el suministro de oxígeno es continuo.
• El agua pasa por la branquia a presión, como acabamos de decir. Esto no ocurre con el aire de nuestros pulmones.
• El agua corre por la branquia de alante hacia atrás  (de la boca al opérculo)  pero la sangre corre por el interior de la branquia de atrás hacia delante. Este llamado flujo contra corriente hace que la absorción de oxígeno sea máxima. 

De este modo, aunque en el agua haya muy poco oxígeno, las branquias de los peces son muy eficaces tomando casi cada molécula de este oxígeno. Por contra, nuestros pulmones desperdician la mayor parte del oxígeno del aire que entra, por eso las maniobras de respiración boca a boca sirven para salvar vidas. 

Y de nuevo, ¿Por qué no puede una branquia tomar oxígeno del aire, si tan eficiente es y en el aire hay tanto oxígeno?

La cosa tiene su miga. Una branquia solo puede funcionar en el agua por que:

• El aire no puede enviarse a presión como el agua. El aire, al presionarlo hacia atrás,  se comprimiría, cosa que no le pasa al agua (que es un líquido incompresible). Vaya, se podría enviar comprimido y a presión pero haría falta una fuerza enorme. Demasiado gasto de energía para el pobre pez.
• Las laminillas que forman la branquia se mantienen separadas unas de otras solo cuando flotan en el agua. Fuera del agua se pegan unas a otras como tus pelos cuando sales del mar, y no pueden absorber oxígeno. 

Así que, todo en orden: branquias bajo el agua y pulmones fuera de ella.

Peces respirando aire

Entonces los peces no pueden respirar aire, si los sacas del agua se ahogan y punto pelota.

Pues si, esto es cierto para CASI TODOS los peces. Pero en biología siempre hay excepciones. Hay peces que, además de sus branquias tienen otro órgano para respirar aire. ¡Serán abusones!

Se trata de dos grupos de peces: los pulmonados y los laberíntidos. 

¿Y por qué la naturaleza y la evolución les ha equipado con dos dispositivos, una para respirar agua y otro para respirar aire?

Por que viven en aguas que temporalmente o permanentemente tienen muy poco oxígeno, menos del habitual, que ya es poco. Aguas estancadas donde una intensa putrefacción de restos vegetales esta consumiendo el poco oxígeno disponible, y con altas temperaturas, que hace que menos oxígeno pueda disolverse.

O peor, aguas que se evaporan en el calor del verano y desaparecen para no volver hasta las primeras lluvias de otoño.

En estas condiciones cualquier pez moriría y flotaría panza arriba en la ponzoña o en el fango de la charca seca. Los superpeces de los que hablamos hoy, no, ellos sobreviven.

Pulmones

Ya te estás liando, Píndaro ¿peces con pulmones? .......  Pues si.

Dos grupos de peces africanos cuentan con un rudimentario pulmon: los "saltarines del barro" (Periophthalmus sp.) y el pez pulmonado (Polypterus sp.).
Tienen su vejiga natatoria transformada en un pulmón con el que pueden sobrevivir durante semanas o incluso meses fuera del agua, a condición de permanecer en zonas con suficiente humedad.

Viven en charcas y arroyos que se secan temporalmente. Cuando esto ocurre los saltarines del fango usan sus aletas como torpes patitas, en busca de otra charca en la que vivir. El pez pulmonado, en cambio, se entierra en el fango, dejando una abertura para respirar, y allí espera hasta que las próximas lluvias llenen de nuevo su charca.

Estos peces están emparentados lejanamente con los primeros primitivos anfibios del carbonífero, los laberintodontos, antepasados de todos los vertebrados terrestres pulmonados, incluida nuestra especie.

Laberintos

El llamado "laberinto" es un órgano único que aparece en los laberíntidos, también llamados anabátidos, un grupo de peces de África y Asia que incluye a los Bettas sp., los "peces del paraiso" y la "perca trepadora".

Este órgano es una estructura rígida bajo el opérculo de la branquia, con la que pueden tomar oxígeno del aire. Como si una parte de la branquia hubiera evolucionado para convertirse en "pulmón".
Cuando el animal cuenta con suficiente oxígeno en el agua donde vive, usa su branquia como cualquier otro pez. Cuando el oxígeno del agua se agota o la charca se seca, el animal toma una bocanada de aire, lo retiene bajo su opérculo unos segundos,  y lo libera después abriendo los opérculos de las branquias en forma de burbujas de aire cargadas de CO2; exactamente igual a como trabaja un pulmón.

De este modo sobreviven respirando aire o emprenden la búsqueda de mejores aguas. La perca trepadora, como su nombre indica, puede incluso trepar sobre troncos inclinados en esa búsqueda.

En algunas especies el laberinto a crecido tanto, a expensas de la branquia, que no pueden vivir respirando solo agua. Necesitan, si o si, aire para respirar.

Bibliografía

• https://www.sdpnoticias.com/sorprendente/2014/02/18/no-es-tan-obvia-la-razon-por-la-que-no-podemos-respirar-bajo-el-agua
• https://naturalmenteciencias.wordpress.com/2011/04/05/respiracion-branquial-por-que-los-peces-se-ahogan-fuera-del-agua-y-dentro-tambien/
• 
  

Scientific Aquariophilia, an eTwinning project

General details  

Name of project: Scientific aquariophilia
For:

• 4 ESO (age 15-16)
• Groups of 15-30 students
• Work teams of 4-6 students from 2 or 3of the partner schools participants
• No limit of total partners participants (the more, the best). 

Curricula subjects:

Biology: ecosystems, biotic and abiotic components and factors, energy and biomass flow.
Mathematics: statistics

Objectives

• Learn about ecosystem ecology through an aquiarium maintenance
• Use the scientific method and propose hypothesis  
• Let students get control of their own learning process.
• Get involved and cowork in citizen science projects.

Process 

Students will maintain an aquiarium and recolect data from survival, grouth and various factors mesures (hours of light, temperature, pH of water, food given, ...) to study their ecology.
Teachers will decide the species to use, in order to use common species and have data from each partner concerning the same species. Any aquarium and any number of species used could be usefull, from the simplest (copepoda in a bottle) to the more complex and biggest aquarium with fish, invertebrates and algae species.
All data will be upload to a common data base.
Students will use the data base to work with figures, search correlations and make hypothesis.

Activity 1: setting the plan.

Teachers of each partner school will introduce the project to their pupils.
In class group they will decide temporary which species will get on their aquarium and which factors could they control and note. Biology teachers will guide this discussion to avoid making decitions difficult or impossible to  implement.

Class group will choose one of the students as spokesperson. Teachers and student spokepersons of all the partner schools taking part in the project  will agree for good and for all the partners the species and factors to use in the project, using the "Chat room" or the "Video Conference" tool of their TwinSpace, trying to unify the species used more than the factors chosen.
This commision of students and teachers will also agree a hashtag of the project which will be used to share their progress in the social networks.

After that, spokespersons will communicate all the decisions taken to their classes.

Finally each class group of each partner school will organise in groups of four students. Each four-student group, following the common decisions taken, will write a plan to obtain the specimens, maintain their aquiarium and recolect data from survival, grouth and the factors chosen.
Finally students, with the supervision of Biology teachers, will choose the better plan.

Evaluation of activity 1

Teachers will use the next evaluation rubric, using the values "improvable", "good" and "excellent":

• Quality and clarity of the plan wrote
• Involvement in group decisions

In the delay asigned all student teams will be able to improve their plans in order to get better values.

Share it! (Activity 1)

Teachers and students will use social networks of their election to share their ideas and progress in the activity, and the plan finally chosen, using the project hashtag.

Activity 2: Data collect

Following their own plan, students of each partner school will organise to maintain their aquiarium and recolect data from survival, grouth and the factors chosen.
They will organise in groups of three studets.

Each three-student group will keep a lab notebook where they will record data, observations or any other notes, and a diary of activities, described in sufficient detail to allow another student group to replicate the steps.

All the data will be upload to a common data base using an on line form of Google Forms, set by their teachers.

Evaluation of activity 2

Teachers will use the next evaluation rubric, using the values "improvable", "good" and "excellent":

• Quality and clarity of the lab notebook
• Detail of the descriptions of the activities recorded in the lab notebook
• Accuracy of the data provided
• Involvement in group work and maintenance of the aquarium
• Collaborative work with the other students

Share it! (Activity 2)

Teachers and students will use social networks of their election to share their ideas, progress of the activity and pictures of their aquarium and the specimens, using the project hashtag.

Activity 3: Thinking about results.

Teachers will set the students in teams of 4 from 2 different partner schools.
Each team will be asigned with an enviromental factor (hours of light, temperature, pH of water, food given, ...) and one or more of the species used in the schools aquariums in previous fases of the project.
The number of species asigned will depend on the number of total species used, the number of pupils and the number of partner schools involved.

Teachers will provide the "Materials" section of the TwinSpace of each team with a database file with all the data collected in the previous activity concerning the grouth and survival of the specie/s and factor of breeding asigned.

Student teams have to study their data, using Google Spreadsheet to make charts and statistical calculations of their election in order to find any correlation among the figures. Students will talk each other and make decisions about their work using the "Chat room" or the "Video Conference" tool of their TwinSpace.
This work will be done under the supervision of Mathematics teachers, although the students should feel free to work with their data as they would prefer.

After that, students teams will discuss and make together hypothesis that may explain the results and charts, using as well the "Chat room" or the "Video Conference" tool of their TwinSpace.
This work will be done under the supervision of Biology teachers, although the students should be encouraged to be creative.

Finally students teams will use Google Docs to write a collaborative paper explaining their results, adding their charts and presenting their hypothesis.

Evaluation of activity 3

Teachers will use the next evaluation rubric, using the values "improvable", "good" and "excellent":

• Quality and clarity of the charts
• Coherence of the charts and staticstic results
• Coherence of the hypothesis
• Power of the hypothesis to explain the results
• Quality and clarity of the paper
• Collaborative work with the other partner school students

In the delay asigned all student teams will be able to improve their works in order to get better values.

Share it! (Activity 3)

Teachers and students will use social networks of their election to share their ideas, hypothesis and their conclusions of the project, using the project hashtag.

Final products:

• Plans to obtain the specimens, maintain their aquiarium and recolect data from survival, grouth and the emviroment factors.
• Lab notebooks.
• Charts and statistical calculations based on data recolected.
• Hypothesis explaining the results and charts.
• Papers explaining their results, adding their charts and presenting their hypothesis.
• Progress and conclutions of the project shared in the social networks using the hashtag of the project. 

 

 

A collaborative activity

Thinking about results.

This activity is part of the project draft Scientific Aquariophilia. To know more about this project enter here.

Activity

Teachers will set the students in teams of 4 from 2 different partner schools.
Each team will be asigned with an enviromental factor (hours of light, temperature, pH of water, food given, ...) and one or more of the species used in the schools aquariums in previous fases of the project.
The number of species asigned will depend on the number of total species used, the number of pupils and the number of partner schools involved.

Teachers will provide the "Materials" section of the TwinSpace of each team with a database file with all the data collected in previous fases of the project concerning the grouth and survival of the specie/s and factor of breeding asigned.

Student teams have to study their data, using Google Spreadsheet to make charts and statistical calculations of their election in order to find any correlation among the figures. Students will talk each other and make decisions about their work using the "Chat room" or the "Video Conference" tool of their TwinSpace.
This work will be done under the supervision of Mathematics teachers, although the students should feel free to work with their data as they would prefer.

After that, students teams will discuss and make together hypothesis that may explain the results and charts, using as well the "Chat room" or the "Video Conference" tool of their TwinSpace.
This work will be done under the supervision of Biology teachers, although the students should be encouraged to be creative.

Finally students teams will use Google Docs to write a collaborative paper explaining their results, adding their charts and presenting their hypothesis.

Evaluation

Teachers will use the next evaluation rubric, using the values "improvable", "good" and "excellent":

• Quality and clarity of the charts
• Coherence of the charts and staticstic results
• Coherence of the hypothesis
• Power of the hypothesis to explain the results
• Quality and clarity of the paper
• Collaborative work with the other partner school students

In the delay asigned all student teams will be able to improve their works in order to get better values.

Share it!

eTwinning project scheme

General details  

Name of project: Scientific aquariophilia
For:

• 4 ESO (age 15-16)
• Groups of 15-30 students
• Work teams of 4-6 students from 2 or 3of the partner schools participants
• No limit of total partners participants (the more, the best). 

Curricula subjects:

Biology: ecosystems, biotic and abiotic components and factors, energy and biomass flow.
Mathematics: statistics

Objectives

• Learn about ecosystem ecology through an aquiarium maintenance
• Use the scientific method and propose hypothesis  
• Let students get control of their own learning process.
• Get involved and cowork in citizen science projects.

Process 

Students will maintain an aquiarium and recolect data from survival, grouth and various factors mesures (hours of light, temperature, pH of water, food given, ...) to study their ecology.
Teachers will decide the species to use, in order to use common species and have data from each partner concerning the same species. Any aquarium and any number of species used could be usefull, from the simplest (copepoda in a bottle) to the more complex and biggest aquarium with fish, invertebrates and algae species.
All data will be upload to a common data base.
Students will use the data base to work with figures, search correlations and make hypothesis.

ICT tools used: Google Forms, Google Spreadsheet and Google Docs.
communication tools among partners used: TwinSpace

Final product:
papers about ecology of the aquarium species used and the influence of some biotic or abiotic factors.
more final products: ?

Evaluation 

• Students shoud provide data of their observation and mesures to a common data base
• Student collaborative work teams shoud write a paper explaining their works, results, data from common data base used and hypothesis issued.