Investigating Reproductive Strategies

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Objective

SWBAT to compare and contrast both asexual and sexual reproduction.

Big Idea

There are advantages and disadvantages to both sexual and asexual reproduction.

NGSS

1 minutes

This is lesson 3 in a 3 lesson series on reproduction. 

Lesson 1 - Asexual Reproduction

Lesson 2 - Sexual Reproduction

Lesson 3 - Investigating Reproductive Strategies

 

The first two lessons provide the background knowledge for lesson 3 which address the following:

NGSS standard:

MS-LS3-2. Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation. 

Cross Cutting Concept:

Cause and Effect

Cause and effect relationships may be used to predict phenomena in natural systems. 

Science and Engineering Practices:

Developing and Using Models

Develop and use a model to describe phenomena

Engage

10 minutes

To engage students in this lesson I show a video that answers a question that will surely grab that attention of middle school students, "Why Sex?" 

The video introduces the following topics:

1.  Fundamental need for reproduction (asexual/sexual), to continue species (avoid extinction).

2.  Percentage of organisms that sexually reproduce.

3.  Organisms that can reproduce either sexually or asexually.

4.  Sexual reproduction

5.  Asexual reproduction

  • Binary Fission
  • Budding
  • Vegetative
  • Parthenogenesis
  • Fragmentation

7.  Gene variation

As students watch the video they are required to write down definitions and make sketches of each the reproductive strategies described in video.

Explore

30 minutes

In this section of lesson students complete a Reproductive Strategies Lab(MS-LS3-2 Develop and use a model to describe why asexual reproduction results in offspring with identical genetic information and sexual reproduction results in offspring with genetic variation./SP2 Developing and using Models/CCC Cause and Effect) 

Students work in pairs to compare five aspects of an organism that reproduces sexually with one that reproduces asexually. As a class, students share their comparisons and generate a list of general characteristics for each mode of reproduction, and discuss the advantages and disadvantages of both.

Learning Objectives

  • There are two modes of reproduction; sexual and asexual. 
  • There are advantages and disadvantages to both sexual and asexual reproduction. 

Classroom Implementation

1. Divide students into pairs.

2. Hand each pair:

  • The Investigating Reproductive Strategies worksheet (page S-1).
  • Two organism descriptions - one for an organism that reproduces sexually and one for an organism that reproduces either asexually or using both strategies (see chart below).

Reproductive strategies used by organisms described in this activity:

Sexual

   Asexual

       Both Sexual and Asexual

Blue-headed wrasse

   Amoeba

       Brittle star

Duck leech

   Salmonella

       Meadow garlic

Grizzly bear

   Whiptail lizard

       Spiny water fleas

Leafy seadragon

 

 

Red kangaroo

 

 

Sand scorpion

 

 

3. Instruct each pair to read about their assigned organisms and complete the comparison table on the Investigating Reproductive Strategies worksheet.

4. When all pairs have completed the comparison table, have them post their tables around the room.

5. Ask students to walk around the room and read the comparison tables with the goal of creating a list of general characteristics for organisms that reproduce sexually and one for organisms that reproduce asexually.

6. As a class, compile lists of general characteristics for organisms that reproduce sexually and asexually on the board. Learning objectives and discussion points for each category on the Investigating Reproductive Strategies worksheet are listed on pages 2-4 to help you guide the discussion.

7. Ask students to discuss the advantages and disadvantages of each mode of reproduction in their pairs. Have them prepared to support their reasoning.

8. Add advantages and disadvantages to the list of general characteristics for each mode of reproduction.

9. Lead a discussion on the types of situations or conditions in which each mode of reproduction would be most advantageous or disadvantageous. Do students think one reproductive mode is generally better? Why? 

Explain

10 minutes

In this section of lesson students visit cK-12 to read the article Asexual vs. Sexual Reproduction.

Topics Covered in the text are:

1.  Asexual Reproduction

  • Binary Fission
  • Fragmentation
  • Parthenogenesis

2.  Sexual Reproduction

Once students have finished reading, they answer the following text-dependent questions:

Review

  1. What is asexual reproduction?
  2. What is the advantage of sexual reproduction?
  3. Describe two types of asexual reproduction.
  4. What is a zygote?
  5. How many chromosomes are in a human zygote? How many chromosomes are in a human gamete?

(RST-6.8.1 - Cite specific textual evidence to support analysis of science and technical texts.)

Elaborate

10 minutes

In this section of lesson students read an article in Nature Magazine titled Virgin births seen in wild vipers.

This article elaborates on parthenogenesis, which is one of the asexual reproductive strategies discussed before.

It Doesn't Always Take Two

I am sure you are familiar with males and females, and how you need both to make a baby. But did you know that isn't always the case? Well, it's not. There is a process called parthenogenesis which scientists are finding is far more widespread than most of them thought.

As you know now, parthenogenesis is not only found in snakes. Watch this video and find out more:

After watching the videos, students read an article on Komodo Dragons and then complete the follow questions:

  • Considering what is essential for an animal's survival...
    • How do conditions in the wild differ from conditions in captivity?
    • Why might these conditions make scientists think that parthenogenesis was an artifact of captivity?
    • Why is it significant that virgin births are seen in the wild and not just captivity?
  • What percentage of wild births of copperheads Agkistrodon contortrix does Professor Booth estimate are from parthenogenesis? Do you think this percentage is significant? Why or why not?
  • How does the way sex chromosomes determine sex (male or female) differ in snakes from humans?
  • What was so unusual about the babies of the captive boa that gave birth through parthenogenesis? How do you think this could affect the survival of the species?
  • Why is parthenogenesis in Komodo Dragons (Varanus komodoensis) a concern in captive breeding programs? Do you think this concern may be unfounded given what was documented with the captive boa? Why or why not? Explain your reasoning as fully as you can.

Evaluate

10 minutes

Students complete an Exit Slip.  This exit slip requires students to develop an evidence based argument to answer the question "Why Sex?".(SP7 - Engaging in Argument from Evidence/W.7.1- Write arguments focused on discipline-specific content.)