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Plant Reproductive Cycle

Plant Reproductive Cycle

Have you ever tried planting a seed from a fruit you've eaten? Think about it: you can plant the seed, and if it grows, you can eventually get more fruits and, with it, more seeds. It's a cycle! In Biology, we call this a reproductive cycle, and it is generally observed in sexually reproducing living organisms--including plants - although with different variations.

Read on to learn more about the plant reproductive cycle.

  • First, we'll distinguish between the two modes of reproduction in plants.
  • Then, we'll have an overview of the plant reproductive cycle.
  • Finally, we'll discuss the reproductive cycle of two plant groups: flowering plants and nonvascular plants.

Modes of Reproduction in Plants

Let's start by looking at the definition of the two modes of reproduction in plants: asexual and sexual.

Asexual reproduction is when offspring, or new living organisms, are produced by a single parent. Offspring produced asexually inherit all the genetic material from the single parent, so the offspring are genetically identical clones of the parent.

For example, the plant Kalanchoe pinnata can reproduce asexually by forming miniature plantlets along the edges of its leaves, with each one able to fall off, grow roots, and become a new plant identical to its parent.

Sexual reproduction is when offspring, or new living organisms, are produced through the combination of genetic material from two different parents. Offspring produced sexually are genetically different from its parent.

For example, when a tomato plant produces seeds, each seed grows into a plant that is slightly different from the parent: maybe it is taller, or perhaps it is more resistant to diseases.

Plants reproduce sexually, asexually, or both!

Plant Reproductive Cycle Figure 1: Kalanchoe leaves with plantlets | StudySmarter

Plant Reproductive Cycle Figure 2: Tomato Seedlings | StudySmarter

Figures 1-2. Kalanchoe producing plantlets asexually (left) and tomato seedlings (right).

Plant Reproductive Cycle in Biology

Two distinct multicellular stages characterize a plant's reproductive cycle: haploid gametophyte and diploid sporophyte, one giving rise to the other, a phenomenon known as alternation of generations.

The alternation of generations sets plants apart from animals, which only have one multicellular stage. Whereas an animal's diploid cells divide by mitosis, starting from the zygote, to produce its diploid body, its haploid cells do not undergo mitosis--they simply become single-celled haploid gametes.

On the other hand, in plants both haploid and diploid cells undergo mitosis, which means that plants produce two kinds of multicellular bodies. This is what we mean by two multicellular stages.

Before we go into detail about this reproductive cycle, let's go over the definition of some terms you'll be encountering throughout the article:

Haploid (denoted as 'n') means having one set of chromosomes, while diploid (denoted as '2n') means having two sets of chromosomes (one set from each parent).

Gametophytes are haploid plants that produce gametes by mitosis.

Sporophytes are diploid plants that produce spores by meiosis.

A gamete is a mature haploid germ cell that, when fused with another gamete of the opposite sex, forms a diploid zygote (or fertilized egg).

Spores are small, typically haploid, single-celled (unicellular) reproductive units (units of asexual reproduction) that can give rise to a new individual without sexual fusion.

Plant Reproductive Cycle Diagram

The plant life cycle (also called reproductive cycle) is generalized in the diagram below. First, we'll go over the different stages in this diagram, and then later we will get into detail as to how this cycle varies among different plant groups.

  1. The ovary contains the ovules.

    • Each ovule contains a megasporangium, which holds the megasporocytes.

      • When a megasporocyte undergoes meiosis, it produces four megaspores, but only one survives. It then undergoes mitosis to become the embryo sac. The embryo sac is the female gametophyte.

  2. The style brings up the stigma over the ovary and other flower parts.

  3. The stigma is a structure with a sticky surface that traps pollen.

The stamen represents the male reproductive parts of the flower. It is made up of anther and filament.

  1. The anther is made up of microsporangia, which contain microsporocytes.

    • Microsporocytes divide by meiosis to produce microspores that develop into pollen.

    • Each pollen grain is a sperm-producing male gametophyte. It contains a generative cell and a tube cell.

  2. The filament links the anther to the flower.

Flowering Plant Reproduction

So, how does a flowering plant (angiosperm) reproduce? Let's start from pollination.

The movement of pollen from the anther to the stigma, and eventually to the ovule, is called pollination.

When pollination occurs under the right conditions, the pollen grain germinates, causing the tube cell to grow within the style. The generative cell then enters the tube and undergoes mitosis, forming two sperm cells. The pollen tube passes through the micropyle, which is an opening in the ovule.

One sperm cell fertilizes the egg cell, forming a diploid zygote. The other sperm cell fertilizes two polar nuclei in the embryo sac, forming a triploid cell, which later develops into the endosperm that will nourish the embryo.

These two fertilization events are collectively called double fertilization, and it is a process that is unique to angiosperms!

The fertilized ovule now forms the seed, while the ovary forms the fruit that surrounds the seed. When the seed germinates, the embryo develops into a new sporophyte individual.

The angiosperm sporophyte generation is more dominant than its gametophyte generation: the gametophyte is attached to and is dependent on the sporophyte.

The angiosperm reproductive cycle is illustrated in the diagram below.

Like angiosperms, gymnosperms (like conifers and ginkgos) also have a dominant sporophyte generation. The difference between them is that gymnosperms do not have flowers or fruits; instead, they have "naked" seeds. They also do not undergo double fertilization.

Reproductive Cycle of Nonvascular Plants

Let's move on to another plant group: nonvascular plants.

Nonvascular plants are those that do not have specialized vascular tissues, as well as true roots, stems, and leaves. These include liverworts, hornworts, and mosses.

Unlike angiosperms and gymnosperms, nonvascular plants have a dominant haploid gametophyte stage in their reproductive cycle.

During its gametophyte phase, a nonvascular plant develops several gametangia (multicellular sex organs). Female gametangia are called archegonia, while male gametangia are called antheridia. A mature archegonium contains one egg cell, while a mature antheridium produces many sperm cells.

The fusion of these gametes leads to the diploid sporophyte phase. For fertilization to take place, most nonvascular plants require moisture as the sperm typically travels on a layer of water (like rainwater or dew) to reach the egg.

The egg is usually fertilized within the archegonium so that the young developing sporophyte is protected and fed by gametophytic tissue. For most of their life cycle, the sporophyte remains attached to the parent gametophyte, depending on the parent for water, sugars, and other nutrients.

There are exceptions to this nonvascular plant life cycle: some ferns have been found to have no ability to produce sporophytes! These interesting species exist only as gametophytes.

Plant Reproductive Cycle - Key takeaways

  • There are two modes of reproduction in plants: asexual and sexual.
  • The plant reproductive cycle is characterized by alternation of generations: gametophyte and sporophyte.
    • Gametophytes are haploid plants that produce gametes.
    • Sporophytes are diploid plants that produce spores.
  • One of the two generations can be dominant, meaning that the individual in the dominant generation lives longer and grows larger than the less dominant generation.

References

  1. Figure 1: Kalanchoe leaves (https://commons.wikimedia.org/wiki/File:Kalanchoe_laetivirens_with_viviparous_plantlets_-_Thailand_-_close-up.jpg) by User:Mattes (https://commons.wikimedia.org/wiki/User:Mattes). Licensed by CC BY-SA 4.0 (https://creativecommons.org/licenses/by-sa/4.0/deed.en).
  2. Figure 2: Tomato seedlings (https://commons.wikimedia.org/wiki/File:Tomato_plants_grown_from_seeds_near_window.JPG) by Tomwsulcer. Licensed by CC0 1.0 Universal (https://creativecommons.org/publicdomain/zero/1.0/deed.en).
  3. Jane B. Reece et al. Campbell Biology. Eleventh ed., Pearson Higher Education, 2016.
  4. Georgia Tech Biological Sciences, Plant Reproduction, accessed 4 December 2022.
  5. CK-12 Foundation, Plant Life Cycles, 6 March 2021.
  6. Gar W. Rothwell et al, “Plant - Characteristics of Plants and Nonvascular Plants,” Encyclopedia Britannica, 15 Jun 2021.
  7. John Yopp, "Plant", Encyclopedia Britannica, 15 June 2021.
  8. UC Davis, Life Cycles and the Alternation of Generations, accessed 4 December 2022.

Frequently Asked Questions about Plant Reproductive Cycle

The reproductive cycle of a plant is characterized by an alternation of generations--gametophyte and sporophyte--where one gives rise to the other. 

The plant reproductive cycle can be summarized in 6 stages:

  • A mature diploid sporophyte produces haploid spores through meiosis. 

  • These haploid spores undergo mitosis and develop into a mature multicellular haploid individual called a gametophyte.

  • The gametophyte produces male and/or female gametes (sperm and egg, respectively) through mitosis.

  • Fertilization, or the fusion of male and female gametes, forms a diploid zygote. 

  • The zygote undergoes mitosis, developing into a multicellular diploid sporophyte.

  • …and the cycle begins again!

The gametophyte stage in a plant's life cycle is when they need to reproduce. 

The life cycle of a flowering plant can be summarized as follows:

  • The pollen grain germinates.
  • The generative cell of the pollen grain forms two sperm cells.
  • One sperm fertilizes the egg cell and the other fertilizes two polar nuclei in the embryo sac. 
  • The fertilized ovule forms the seed while the ovary forms the fruit. 
  • Under the right conditions, the seed germinates and forms a new plant individual.
  • The mature individual produces flowers and the cycle begins again.

There are two modes of reproduction in plants: sexual and asexual. Sexual reproduction is when offspring, or new living organisms, are produced through the combination of genetic material from two different parents. Offspring produced sexually are genetically different from its parent. On the other hand, asexual reproduction is when offspring, or new living organisms, are produced by a single parent. Offspring produced asexually inherit all the genetic material from the single parent, so the offspring are genetically identical clones of the parent.

Learning about the plant life cycle is important because it helps us understand how plants grow, develop, and produce new individuals.

Final Plant Reproductive Cycle Quiz

Question

What are the two modes of reproduction in plants?

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Answer

Sexual and asexual reproduction

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Question

____  is when offspring, or new living organisms, are produced by a single parent. 

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Answer

Asexual reproduction

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Question

Offspring produced ____ inherit all the genetic material from the single parent, so the offspring are genetically identical clones of the parent.

Show answer

Answer

asexually

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Question

What is sexual reproduction?

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Answer

Sexual reproduction is when offspring, or new living organisms, are produced through the combination of genetic material from two different parents. 

Show question

Question

What are the two multicellular stages in a plant reproductive cycle?

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Answer

Diploid sporophyte and haploid gametophyte

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Question

What is the alternation of generations?

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Answer

Alternation of generations is where two multicellular stages of the plant reproductive cycle--sporophyte and gametophyte--give rise to each other.

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Question

Distinguish between the plant and animal reproductive cycle.

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Answer

Whereas an animal's diploid cells divide mitotically starting from the zygote to produce its diploid body, its haploid cells do not undergo mitosis--they simply become single-celled haploid gametes. 


On the other hand, in plants both haploid and diploid cells undergo mitosis, which means that plants produce two kinds of multicellular bodies.

Show question

Question

_______ are haploid plants that produce gametes

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Answer

Gametophytes

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Question

A mature diploid sporophyte produces haploid spores through ____.

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Answer

meiosis

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Question

Haploid spores undergo _____ and develop into a mature multicellular haploid individual called a gametophyte.

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Answer

mitosis

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Question

______, or the fusion of male and female gametes, forms a diploid zygote. 

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Answer

fertilization

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Question

What is pollination?

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Answer

Pollination refers to the movement of pollen from the anther to the stigma.

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Question

What do we mean by double fertilization?

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Answer

Double fertilization is where one sperm cell fertilizes the egg cell, forming a diploid zygote. The other sperm cell fertilizes two polar nuclei in the embryo sac, forming a triploid cell. 

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Question

The ____ generation is dominant in the angiosperm reproductive cycle.

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Answer

sporophyte

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Question

What is the male gametophyte of a flowering plant?

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Answer

pollen grain

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