FOR SEA Institute of Marine Science
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FOR SEA Grade 3
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How Hot Is Too Hot?


Key Concepts
  1. Brine shrimp have unique structural and behavioral adaptation which allow tham to tolerate dramatic changes in the temperature and salinity of their environment.

  2. Environmental factors (eg. temperature) affect the development and life of marine organisms.



Background
Living things must deal with changes in their environment. Many environmental factors, including temperature, may vary a great deal over time. Changes in temperature affect the rate of development of brine shrimp eggs.

Brine shrimp are remarkable little animals. They can live in evaporating salt ponds where salinity and temperature increase dramatically. When all of the water in the pond disappears, the brine shrimp populations survive by producing eggs in a sort of state of suspended animation called "diapause". Brine shrimp eggs have adapted to a lack of water because many of the ponds where they live dry up during the summer. Eggs can lie dormant for up to 13 years! Dried-out eggs will hatch when rain water carries the "beached" eggs into the water. The dried up salt along the pond's edge dissolves into the water and provides a ready-made supply of saltwater for the eggs to hatch.

The life cycle of the brine shrimp has three stages: egg, larva, and adult. The larva shrimp has a round body and two legs by its head. The legs help it swim. Even as an adult the brine shrimp is less than one inch long. They are often sold in pet stores as fish food.


Materials
For the class:
  • refrigerator
  • premixed, saltwater solution made from Instant Ocean or a similar product
  • water to make saltwater solution (distilled water works best)
  • containers to mix saltwater
For each group of three to four students:
  • copies of student activity sheet, "How Hot is Too Hot?"
  • brine shrimp eggs (Ask for the species that will grow the largest.)
  • 3 baby food jars or similar containers
  • marking pencil or labels
  • thermometer
  • hand lens or dissecting microscope
  • coffee stirring stick

Teaching Hints
In "How Hot is Too Hot," students hatch brine shrimp eggs. Students investigate the effect of changing one variable (temperature, in this case) on the development of brine shrimp eggs.
   Planning Ahead
It is important to start the investigation when you are sure the class will meet for four consecutive days so that the necessary observations can be made. Brine shrimp eggs are easily obtained at tropical fish stores for a small sum. Likewise, products like Instant Ocean are available in pet stores that sell fish. Read the instructions on the container for making the salt solution needed. About a 3% salt solution is ideal. The shrimp will hatch in solutions from 1% to saturation.

Jar size, for hatching, is not critical. Baby food jars are usually readily available for the asking. It is important that each group of students doing the exercise have three jars of similar size. Groups of 3 students work well.

Jars should be filled to the same level. The number of eggs fitting on the end of a coffee stirrer is about the correct number to place in the jar. The eggs will float, so try to keep them from all sticking to the side of the container.

Observations should be made at the same time each day. The observations can be made in about 15 minutes. The students will take the temperature of the water and count the number of shrimp larva, during these daily observations. The absolute numbers are not critical.


Key Words
  • adult - a fully grown, mature organism
  • brine shrimp - a small, slender crustacean that lives in very salty water
  • dissecting microscope - microscope with two eyepieces which can view objects as three dimensional
  • environment - living and non-living factors surrounding an organism; surroundings
  • experiment - a process undertaken to discover something not yet known or to demonstrate something known
  • hand lens - a small magnifying lens held in the hand
  • hatching - to come forth from an egg
  • label - to name
  • larva - the early form of any animal that metamorphoses (changes structurally) when it becomes an adult
  • life cycle - the series of changes from an animal's earliest stage of development to the same stage in the next generation
  • observe - to watch or notice
  • record - to set down, as in writing
  • relatives - individuals connected by blood
  • scale - a series of marks along a line
  • solution - a liquid in which another substance has been dissolved
  • temperature - the degree of hotness or coldness of anything
  • thermometer - an instrument for measuring temperatures
Extensions
Brine shrimp eggs are remarkable. Try freezing the eggs or boiling the eggs. Then place the eggs in saltwater at a normal temperature. Do they hatch?
Answer Key
  1. 2.  3.   The answers depend on the results. Usually the room temperature works the best, the refrigerator has the fewest. Discuss the possible reasons for the results obtained. This is a good opportunity for creative hypothesizing by your students.

  2. Again, depends on the results. But usually high and low temperatures will have fewer hatching.

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