The Beginning of Life

 

Reproduction occurs when an organism (living thing) makes a copy of DNA and produces an offspring. 

All living things on Earth are a process of reproduction.

To better understand the reproduction of living things, click the image above.

 

Introduction

You have learned that parents pass on their traits to their offspring. But how does that happen?

In this unit, you will explore how plants and animals reproduce differently. You will see how some organisms form new offspring from one parent while others create new offspring from two parents—and some can do both. 

        

Life on Earth is possible because plants, animals, and other organisms can reproduce. But what does it mean to reproduce?

Reproduction is the ability to make a copy of something. In biology, it is the process of forming new offspring. Reproduction is one of the basic characteristics of life, and it is why new life is possible.

There are two ways to reproduce:

In your science journal, watch the video above and answer the questions.

1.  Why do offspring sometimes look similar to their parents and sometimes look different?

2.   What is the difference between sexual and asexual reproduction?

3.   What are some examples of animal adaptations for improving their chances of reproduction and offspring survival?

 

Asexual Reproduction

 

In most organisms that reproduce asexually, the single parent passes on its genetic material to its offspring to make an exact copy of itself. That can be a problem if the parent has a gene that causes a particular disease because the offspring will also have that gene.

Only one parent is needed for asexual reproduction. The offspring are copies, or genetic clones, of their parents.

Asexual reproduction is common in simple organisms such as one-celled bacteria. Some many-celled organisms can also reproduce asexually. For example, Komodo dragons usually reproduce sexually, but they can reproduce asexually if needed, such as when conditions are not ideal, or they cannot find a mate.

 

Asexual Reproduction (Budding)

 

Most cells reproduce asexually by making copies of the chromosomes within them and then splitting one cell in half to produce two cells. This simple process is called mitosis, which refers to the division of cells.

Through mitosis, the two resulting cells have the same genetic information as the original cell. These are diploid cells, meaning they have the organism's full set of chromosomes.

Mitosis also helps you stay healthy! As some cells in your body age and stop working well, new cells created through mitosis replace them. If you have ever watched a cut or wound heal, you have seen mitosis. Your skin cells use mitosis to replace damaged or lost cells with healthy ones.

         Mitosis

·     Produces genetically identical cells

·     Results in diploid cells

·     Take place throughout an organism's lifetime

·     Involved in asexual reproduction

Watch the video below, then answer the questions in your science journal.

 

In your science journal, answer the following questions.

1.  Reproduction is the process of __________.

2.  Sexual reproduction requires _____ parent(s).

3.  Asexual reproduction requires _____ parent(s).

4.  Through _____, a cell splits in half to produce two exact copies of itself. 

5.  _____ is a good example of how mitosis helps you stay healthy.

 

Let's Practice

Watch the video below, then complete the Let's Practice.

 

 

 

 

Sexual Reproduction

 

You know that with asexual reproduction, offspring are copies of their parents. Their genes are the same. With sexual reproduction, this is not the case. Because of sexual reproduction, many different genes of plants and animals mix, creating genetic variation.

Sexual reproduction happens when the genes of two different parents unite to create unique offspring. Each parent puts in one sex cell—an egg from the female parent or sperm from the male parent—and each sex cell gives half the genetic material the offspring needs. 

Female and male sex cells are called gametes. Gametes are haploid cells because they have only half the number of chromosomes needed for a complete organism. In sexual reproduction, two haploid gametes join to make one zygote with the right number of chromosomes to grow into a new organism. Because a zygote has two sets of chromosomes, it is called a diploid cell. This process of two haploid gametes coming together into one diploid zygote is fertilization.

Fertilization Process

 

Where do haploid gametes come from? The answer is meiosis, a special kind of cell division.

Meiosis is similar to mitosis because cells divide, but it is more complicated—with nine phases instead of five.

         Meiosis

·     Produces genetically unique cells

·     Results in haploid cells

·     It takes place only at certain times in an organism's life cycle

·     Involved in sexual reproduction

In your science journal, answer these questions.

1.  Sexual reproduction takes _____ parent(s).

2.  A _____ from the male joins with the _____ from the female.

3.  _____ % of the offspring's genes come from each parent.

4.  The joining of reproductive cells is called _____.

5.  When an egg is fertilized inside the body, it is called _____ fertilization.

6.  When an egg is fertilized outside the body, it is called _____ fertilization.

7.  Sexual reproduction creates genetically _____ offspring.

 

Let's Practice

 

 

 

Let's Practice