Unit A Lesson 7:  Sexual Reproduction

 Learning Targets

Inquiry Question: Sexual Reproduction - What's it all about?
Most plants and animals use sexual reproduction to reproduce. This type of reproduction has both advantages and disadvantages.

At the end of this inquiry, you should be able to answer the following questions:

  • What is sexual reproduction?
  • How does sexual reproduction occur in animals and humans?
  • What are gametes?
  • What is a zygote?
  • What is an embryo?
Page 32 in your textbook will help you answer these questions about sexual reproduction.


Introduction

As a mammal, a purple cow could not be produced through any of the four types of asexual reproduction. Mammals cannot undergo asexual reproduction.

Perhaps the next method of reproduction will hold the key to our quest to produce a purple cow.

Sexual reproduction requires the union of male and female sex cells.  The offspring inherits genetic material from both parents. That means that a purple calf would get its 'purpleness' from one, or both, of its parents. It also means that there must be genetic material in the calf's cells that result in it being purple.

Can sexual reproduction do all that? Let's find out.


Watch

The video "Sexual Reproduction" introduces the basicconcepts of fertilization.

Sexual Reproduction Sexual reproduction relies on specialized cells called gametes.


The female sex cell is called the egg and/or ovum , and the male sex cell is called the sperm.  When they unite, fertilization occurs.  Fertilization is the same in humans as it is for most animals. 

In Figure 2.10 on page 32 of your textbook, you can see the male and female gametes, which combine to form the zygote .  Then, the cells divide many times in a process called cleavage; at that time, they form the embryo, which eventually becomes the offspring.

The genetic combinations that occur when the sperm and egg unite are incredible.  Siblings often have similar features, but they have their own looks, too.  They have their own unique combination of genetic makeup.  Identical twins are an exception to the rule.  Their genetic material or DNA is exactly the same. 


Try It!

Practice Worksheet: Fertilization in Animals

  1. DOWNLOAD this practice worksheet "S9_UA_S2_L7_fertilization". If you prefer to use a Google Drive or PDF version of the worksheet, click here.

  2. Complete the questions. You will find page 32 in your textbook is a useful reference if you get stuck.

  3. When you are satisfied with your responses you can check your work by clicking on the "SUGGESTED ANSWERS" button below.

Wait! Don't view the suggested answers first. This practice work is not for marks, it is meant to help you check your understanding. Check the answers AFTER doing the questions! Keep the practice worksheet for study purposes. If you don't understand something, contact your teacher!

  1. a) egg and ovum
    b) sperm
  1. When the sperm and egg meet, they fuse to form a zygote. This joining involves combining the genetic material of the egg and sperm. The name of the process is fertilization.
  2. After the zygote is formed, it divides into two cells. This dividing continues in a process known as cleavage. the cell division continues into a ball of cells – the cells then begin to specialize, and a multicellular embryo forms.


Figure 1 – Birds lay eggs that have been fertilized internally.

Figure 2 – Cows are fertilized internally, carry their babies to term, and care for the young after they are born.

I nternal Fertilization

Fertilization that occurs inside the body is called internal fertilization.  This process relies on the male and female gametes being present at the same time and place.  Mammals, birds, and reptiles rely on internal fertilization.

Figure 3 – Female frogs lay eggs that males fertilize later.

Figure 4 – A frog's eggs hatch into tadpoles, which survive on their own until they develop into frogs.

External Fertilization

External fertilization occurs in fish and amphibians, such as frogs.  For external fertilization, the male and female organisms do not have to be present at the same time, but the gametes must unite in the same place – outside the body.  External fertilization occurs in shallow water.

Watch

Reptiles use internal fertilization to reproduce, which the video "Reptile Exam: Internal Fertilization in Reptiles" explains.

 
 
Watch "Habitats, frog: External Fertilization" to see how external fertilization works with amphibians like frogs.




Coral Reefs
 
Coral reefs are amazing collections of living and non-living things, all co-existing in some of the most complex ecosystem on Earth.


Some coral reef species can undergo both external and internal fertilization. To learn about coral reefs, watch the video “Exploring the Coral Reef”.






Banana Slugs: Boys or Girls or Both?

Banana slugs are very interesting because they are hermaphrodites — organisms that have male and female reproductive organs.  If the banana slug does not find a mate, it has the ability to mate with itself because it has both sperm and eggs. 

Where do purple cows come from?

A cow is a mammal.  Therefore, a purple cow would be produced through sexual reproduction.  Would it be through internal or external fertilization? 

Internal fertilization. Cows are mammals, and mammals reproduce by internal fertilization.