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9.21: Gymnosperm Life Cycle

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Do pine trees produce flowers?

Of course not. But look closely at these pine cones. Notice the shape. Can you see the "petals?" They do seem oddly similar to flowers. These pine cones have a prominent role in the gymnosperm life cycle. So what is the function of a pine cone?

Life Cycle of Gymnosperms

Gymnosperms are vascular plants that produce seeds in cones . Examples include conifers such as pine and spruce trees. The gymnosperm life cycle has a dominant sporophyte generation. Both gametophytes and the next generation’s new sporophytes develop on the sporophyte parent plant. Figure below is a diagram of a gymnosperm life cycle.

The gymnosperm life cycle follows the general plant life cycle, but with some new adaptations. Can you identify them?

Cones form on a mature sporophyte plant. Inside male cones, male spores develop into male gametophytes. Each male gametophyte consists of several cells enclosed within a grain of pollen . Inside female cones, female spores develop into female gametophytes. Each female gametophyte produces an egg inside an ovule.

Pollination occurs when pollen is transferred from a male to female cone. If sperm then travel from the pollen to an egg so fertilization can occur, a diploid zygote results. The zygote develops into an embryo within a seed, which forms from the ovule inside the female cone. If the seed germinates, it may grow into a mature sporophyte tree, which repeats the cycle.

Summary

  • In gymnosperms, the gametophyte generation takes place in a cone, which forms on the mature sporophyte plant.
  • Each male gametophyte is just a few cells inside a grain of pollen. Each female gametophyte produces an egg inside an ovule.
  • Pollination must occur for fertilization to take place. Zygotes develop into embryos inside seeds, from which the next sporophyte generation grows.

Practice

Use this resource to answer the questions that follow.

  1. Are there male and female cones?
  2. Is the sporangia haploid or diploid?
  3. Are the spores haploid or diploid? How do spores form?
  4. What is pollen? How does it travel to a female gametophyte?
  5. Where is the egg located?
  6. Distinguish between pollination and fertilization.
  7. Where does the embryo form?
  8. Where does the seed come from?
  9. What happens to the seed?

Review

1. Describe how gymnosperms use cones to reproduce.

2. Create your own cycle diagram to represent the life cycle of a gymnosperm.

Vocabulary

conifer

conifer

Examples of gymnosperms, such as pine and spruce trees; cone-bearing seed plants with vascular tissue.
gymnosperm

gymnosperm

Type of seed plant that produces bare seeds in cones.
sporophyte

sporophyte

Diploid generation in the life cycle of a plant; results from sexual reproduction with gametes; produces spores for asexual reproduction.
gametophyte

gametophyte

Haploid generation in the life cycle of a plant that results from asexual reproduction with spores and that produces gametes for sexual reproduction.
pollen

pollen

Tiny grains that bear the male gametes of seed plants and transfer sperm to female reproductive structures.

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At Grade

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Date Created:

Feb 24, 2012

Last Modified:

Sep 15, 2014
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