11.6.3 Alternation of Generations: Gymnosperms

Question 1

Alternation of Generations: Gymnosperms

Answer 1

• Gymnosperms are plants that produce seeds that are not enclosed in a specialized chamber.
• Like all members of the plant kingdom, gymnosperms exhibit alternation of generations. As gymnosperms branch from the seedless vascular plants, we see an increasing dominance of the sporophyte generation over the gametophyte generation.
• In the life cycle of conifers (a type of gymnosperm), greatly reduced male and female gametophytes come together to produce a seed (an enclosed embryo) which will give rise to a sporophyte.

Question 2

note

Answer 2

• The diagram to the left illustrates the life cycle of a pine tree, a common type of gymnosperm.
• Beginning at the far left of the diagram, the mature
  sporophyte (the tree) is the dominant generation in the life cycle of gymnosperms. The sporophyte gives rise to the male and female gametophytes within male and female cones, respectively. The male cone, or pollen cone, contains hundreds of microsporangia held within sporophylls. Cells within microsporangia undergo meiosis to give rise to pollen grains, which are immature male gametophytes.
• The female cone is made up of many scales, each with two ovules. Each ovule contains a single megaspore mother cell that will undergo meiosis to produce a haploid megaspore. The magaspore will grow and divide to become the mature female gametophyte with two to three eggs (typically only one is fertilized).
• The pollen grain lands on the micropyle of the female cone scale and germinates. The pollen grain grows a pollen tube and eventually fertilizes the nucleus of the egg. The fertilized egg then develops into an embryo, which will develop into a tree.

Question 3

Conifers are

Answer 3

• heterosporous

Question 4

True or false?

Some gymnosperms produce cones.

Answer 4

• true

Question 5

True or false?

There are no gymnosperms that can produce flowers.

Answer 5

• true

Question 6

Which statement regarding conifers is correct?

Answer 6

• The male gameteophytes arise from the microspores

Question 7

Which of the following statements regarding gymnosperms is incorrect?

Answer 7

• Gymnosperms are flowering plants.

Question 8

Pollen grains in pine trees

Answer 8

• contain the male gameteophytes.