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 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 image below (Figure below) as you read through the steps.
- The gametophyte produces the gametes, or sperm and egg, by mitosis. Remember, gametes are haploid.
- Then, the sperm fertilizes the egg, producing a diploid zygote that develops into the sporophyte.
- The diploid sporophyte produces haploid spores by meiosis.
- The haploid spores go through mitosis, developing into the gametophyte.
As we will see in additional Plants LS 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.
In ferns, the sporophyte is dominant and produces spores that germinate into a heart-shaped gametophyte.
alternation of generations: Describes how plants alternate between diploid-cell and haploid-cell stages during their life cycle.
diploid: Having two sets of chromosomes.
gametophyte: Haploid generation in the life cycle of a plant.
haploid: Having one set of chromosomes, like sperm and egg.
spore: Reproductive structure; can be adapted for dispersal and survival in unfavorable conditions; found in bacteria, plants, algae, fungi, and some protozoa.
sporophyte: Diploid generation in the life cycle of a plant.
- 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.
Use the resource below to answer the questions that follow.
- When does meiosis occur during a plant's life cycle? Why is this crucial to a successful alternation of generations?
- When does mitosis occur during a plant's life cycle? Why is this crucial to a successful alternation of generations?
- How do gametophytes with both male and female parts avoid self-fertilization?
- How does the fertilization process for an Angiosperm differ from the fertilization process for humans (Homo sapiens)? Be as specific and thorough as possible.
- What is the difference between a haploid and diploid cell?
- What does "alternation of generations" mean?