Plant Reproduction and Life Cycle

Jessica Harwood Douglas Wilkin, Ph.D.

Say Thanks to the Authors Click http://www.ck12.org/saythanks (No sign in required) AUTHORS Jessica Harwood To access a customizable version of this book, as well as other Douglas Wilkin, Ph.D. interactive content, visit www.ck12.org EDITOR Douglas Wilkin, Ph.D.

CONTRIBUTORS CK-12 Foundation is a non-proﬁt organization with a mission to Doris Kraus, Ph.D. reduce the cost of textbook materials for the K-12 market both Niamh Gray-Wilson in the U.S. and worldwide. Using an open-content, web-based Jean Brainard, Ph.D. collaborative model termed the FlexBook®, CK-12 intends to Sarah Johnson pioneer the generation and distribution of high-quality educational Jane Willan content that will serve both as core text as well as provide an Corliss Karasov adaptive environment for learning, powered through the FlexBook Platform®.

The names “CK-12” and “CK12” and associated logos and the terms “FlexBook®” and “FlexBook Platform®” (collectively “CK-12 Marks”) are trademarks and service marks of CK-12 Foundation and are protected by federal, state, and international laws.

Any form of reproduction of this book in any format or medium, in whole or in sections must include the referral attribution link http://www.ck12.org/saythanks (placed in a visible location) in addition to the following terms.

Except as otherwise noted, all CK-12 Content (including CK-12 Curriculum Material) is made available to Users in accordance with the Creative Commons Attribution-Non-Commercial 3.0 Unported (CC BY-NC 3.0) License (http://creativecommons.org/ licenses/by-nc/3.0/), as amended and updated by Creative Com- mons from time to time (the “CC License”), which is incorporated herein by this reference.

Complete terms can be found at http://www.ck12.org/terms.

Printed: January 27, 2015 www.ck12.org Chapter 1. Plant Reproduction and Life Cycle

CHAPTER 1 Plant Reproduction and Life Cycle

• Deﬁne alternation of generations. • Outline plants’ reproductive cycle. • Distinguish a sporophyte from a gametophyte.

Do all plants have flowers? No, plants do not all have flowers. For example, the mosses and ferns pictured here are both types of plants. However, they never produce flowers. They don’t produce seeds, either. They do, however, make tiny spores to reproduce.

Plant Reproduction and Life Cycle

The life cycle of a plant is very different from the life cycle of an animal. Humans are made entirely of diploid cells (cells with two sets of chromosomes). Our only cells that are haploid cells (cells with one set of chromosomes) are sperm and egg cells. Plants, however, can live when they are are at the stage of having haploid cells or diploid cells. Plants alternate between diploid-cell plants and haploid-cell plants. This is called alternation of generations, because the plant type alternates from generation to generation. In alternation of generations, the plant alternates between a sporophyte that has diploid cells and a gametophyte that has haploid cells. Alternation of generations can be summarized in the following four steps: follow along in the Figure 1.1 as you read through the steps.

1 www.ck12.org

1. The gametophyte produces the gametes, or sperm and egg, by mitosis. Remember, gametes are haploid, having one set of chromosomes. 2. Then, the sperm fertilizes the egg, producing a diploid zygote that develops into the sporophyte. 3. The diploid sporophyte produces haploid spores by meiosis. 4. The haploid spores go through mitosis, developing into the haploid gametophyte.

As we will see in additional Plants concepts, the generation in which the plant spends most of its life cycle is different between various plants. In the plants that ﬁrst evolved, the gametophyte takes up the majority of the life cycle of the plant. During the course of evolution, the sporophyte became the major stage of the life cycle of the plant.

FIGURE 1.1 In ferns, the sporophyte is dominant and produces spores that germinate into a heart-shaped gametophyte.

Summary

• Plants undergo alternation of generations, meaning they alternate between diploid-cell plants and haploid-cell plants. • During the course of evolution, the sporophyte (diploid) became the major stage of the life cycle of the plant.

Explore More

Use the resource below to answer the questions that follow.

• Plant Reproduction at http://www.youtube.com/watch?v=ZvBMQIrlhYw (2:23)

2 www.ck12.org Chapter 1. Plant Reproduction and Life Cycle

MEDIA Click image to the left or use the URL below. URL: http://www.ck12.org/ﬂx/render/embeddedobject/57431

1. When does meiosis occur during a plant’s life cycle? 2. When does mitosis occur during a plant’s life cycle? 3. How do gametophytes with both male and female parts avoid self-fertilization? 4. Describe the fertilization process for an Angiosperm.

Review

1. What is the difference between a haploid and diploid cell? 2. What does "alternation of generations" mean? 3. What part of the plant life cycle is made of haploid cells, the sporophyte or the gametophyte? 4. What process is used by the sporophyte to produce spores?

References

1. Zachary Wilson. Alternation of generations on ferns . CC BY-NC 3.0