Exercise 27 - Excretory and Reproductive Systems

STUDENT OBJECTIVE

Students observe the structure and function of flame cells in live planarians and nephridia in live earthworms. They dissect the excretory and reproductive systems in the fetal pig and look at prepared slides of the kidney and gonads.

EQUIPMENT AMOUNT (Class of 24 with 8 groups)
Compound microscope 1/student
Dissecting microscope 1/student


MATERIALS

Fetal pigs from previous exercise 1/student
Dissecting pans 1/student
Dissecting instruments set/student
Slides and coverslips 1 box/lab
Petri dishes with clean paraffin 1/student
Live animals
  Planaria (CBS# L210)* 1/student
  Earthworms 1/group
Prepared slides (can be shared to reduce costs)
  Mammalian kidney cortex (CBS#H3510)* 1/student
  Mammalian ovary with graafian follicles (CBS#B701)* 1/student
  Mammalian testis, cross section (CBS#98-9760)* 1/student

SOLUTIONS

10% ethanol
0.8% saline

PREPARATION

Week before Lab

  1. Planaria should be ordered to arrive at this time. Upon arrival, check to be certain cultures are alive. Store at room temperature with loosened lids.

  2. Saline preparation:

    0.8 g NaCl/100 ml water

    Dissolve the salt in water and store in dropper bottles.

  3. All dissecting equipment should be inspected and any missing or dull instruments replaced. Fetal pigs used in previous exercise should be checked for usability.

  4. Alcohol preparation:
    10% ethanol 50 ml 95% ethanol/425 ml water
    Mix and store in two or three dispensing bottles.

NOTES

Glassware for live cultures may need to be acid washed and rinsed well before using to remove polymerized organic material such as paraformaldehyde.

ANSWERS TO CRITICAL THINKING QUESTIONS

  1. Sperm production is temperature sensitive. Viable sperm production requires temperature lower than body temperature. By being outside of the abdominal cavity, the testes are cooled by about 3 ° C (below body temperature of 37 ° C). Other adaptive mechanisms for maintaining proper temperature involve cremaster muscles which elevate the testes when cold, dartos muscle which wrinkles the scrotal skin, also to conserve heat, and a fine network of veins that surrounds the testicular artery and absorbs heat from arterial blood before it arrives at the testes.

  2. Consider the following:
    Bears - metabolic rate maintains body temperature
    - no water intake
    - water is lost through respiration
    - limited bladder capacity
    - no urination
    - nitrogenous wastes must still be removed from circulation
    - possible adaptations
    - decrease protein metabolism, which decreases nitrogenous wastes
    - switch to fat metabolism
    - absorb and `recycle' urine
    Woodchucks - metabolic waste removal
    - no water intake
    - limited bladder capacity
    - no urination
    - possible adaptations - `Hibernation'
    - metabolic activity greatly reduced (body temperature drops)
    - minimal metabolic wastes produced
    - minimal water loss through respiration

SUPPLEMENTAL MATERIALS

Bio Sci II, videodisc--contains pictures of dissected fetal pig and histology photographs. Dubuque, IA: Wm. C. Brown Publishers. See appendix.

Introduction to Excretion, slide set. West Los Angeles, CA: Science Software Systems. #480-0170

Liquid Waste and the Kidney, videocassette. Rochester, NY: Ward's. #193W1097

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