Mitosis, Meiosis & Echinoidea

Grade Level: 7th Grade Life Science

California Science Content Standards: Cell biology ~ All living organisms are composed of cells, from just one to many trillions, whose details usually are visible only through a microscope. Genetics ~a typical cell of any organism contains genetic instructions that specify its traits. Those traits may be modified by environmental influences. Investigation and experimentation ~ scientific progress is made by asking meaningful questions and conducting careful investigations.

Objective: In this lesson students will observe the process of mitosis in sea urchins

Time: Two class periods; 15 minute observations 3 - 5 subsequent days

Overview: In the study of cell biology and genetics students learn about the process of mitosis and meiosis as cells divide to increase their number or produce of sex cells. Sea urchins provide an excellent opportunity for students to observe the mitotic process in the classroom. Sea urchin eggs are large enough to allow microscopic observation. Sea urchin gametes (sperm and egg) may be induced to spawn by injecting potassium chloride (KCL). The gametes may be fertilized and develop externally in seawater. This activity allows first hand observation by students as the developmental stages move from initial fertilization to the pluteal stage in the developmental cycle of a sea urchin. Prior Knowledge ~ Students will have studied and illustrated the cell cycle, mitosis and meiosis. Students will demonstrate understanding of the terms and concepts of meiosis and mitosis in their Science Log (lab notes). Vocabulary: Cell cycle, eukaryotic cell, mitosis, chromosome, chromosome duplication, homologous chromosomes, centromere, chromatids, the six steps of mitosis (interphase, prophase, metaphase, anaphase, telophase, cytokinesis Heredity, meiosis, genes, alleles, genotype, phenotype, probability, sex cells, sex chromosomes

Materials: WARNING: due to safety concerns only teachers should handle the syringe with KCL soln 0.05M potassium chloride solution – KCL (3.73g KCL + 100ml distilled water) Sea water Adult sea urchins (10-12 to ensure at least one male or female) 5cc syringe pipettes or eyedroppers tubes for sperm storage beaker smaller that the diameter of the female urchin graduated cylinder or beakers for spawning microscopes (10x and 40x objective) glass depression slides Video microscope if available

Grouping: Whole class and dyads or triads depending upon the number of microscopes available

Procedure:  Note: If possible, spawn a culture prior to class in the event that spawning during class is unsuccessful  Introduce topic and procedure.  Inject KCL (0.1-0.2 ml per inch of urchin width). A total of two injections with a small gauge needle at an angle past the teeth into the body cavity.  Gently rotate the urchin for a few seconds. Place the male mouth side down on a small dish (should not be underwater). In a few minutes, collect sperm with a pipette and place in tube for storage. Sperm is milky white color. Place female mouth side up on a beaker full of sea water. Eggs shed into the sea water and collect at the bottom of the beaker. Pour egg suspension into a 100ml graduated cylinder and fill with seawater.  Fertilize by placing a drop of egg suspension on a glass depression slide under the microscope, have students focus on the eggs, then add a drop of sperm and have students watch for the fertilization membrane to rise.  Maintain dilute cultures of embryos in seawater for further student observation on subsequent days.  Observations by student to continue for 3 - 5 days. Each day, observations must be recorded by the student in their Science Log.  NOTE: if a Video Microscope is available it enhances the student experience as well as serving as a whole class visual aid

Closure: What were the stages of mitosis that were observed? What was the cellular process that occurred to enable spawning? How do organisms develop from the size of a sperm and egg to the adult? Students will write a summary of the lab to include the cell cycle, mitosis and meiosis.

Lesson adapted from Stanford University Education website

Resources:

One cell to Urchin Anatomy and Physiology of the Sea Urchin How to Spawn an Urchin Normal Fertilization