11.6.1 Alternation of Generations: Mosses

Question 1

Alternation of Generations: Mosses

Answer 1

• Tracing the reproductive evolution of plants is a critical component in studying plant phylogeny.
• Mosses (division Bryophyta) are thought to have arisen from charophyte-like ancestors nearly 475 million years ago. Mosses have no vascular tissues or seeds, but do have protected gametes, allowing them to live on land.
• Mosses exhibit alternation of generations. The male gametophyte generation gives rise to gametes that swim through moisture in order to reach the female gametophyte.

Question 2

note

Answer 2

• Review: The diagram to the left is a general representation of alternation of generations, a feature present in all plants.
• A diploid sporophyte gives rise to haploid spores. These spores undergo mitosis to form the multicellular haploid gametophyte.
• The gametophyte will produce haploid gametes. Two gametes will undergo fertilization to eventually form the diploid sporophyte.
• Like all plants, the life cycle of the moss exhibits alternation of generations.
• Beginning at the bottom left-hand corner, the sporophyte, a long stalk-like structure, releases spores.
• Spores undergo mitosis, eventually producing male and female gametophytes. The male and female gametophytes give rise to sperm and eggs, respectively.
• The sperm are released from a structure called an
  antheridium and then swim through moisture to reach the egg found within the archegonium.
• After fertilization, a diploid zygote undergoes mitosis and becomes a long stalk-like sporophyte that grows out of the archegonium of the female gametophyte. And the cycle continues…

Question 3

The archegonium is the structure that encloses the

Answer 3

• egg

Question 4

True or false?

Most mosses produce two different types of spores which will develop into the male and female gametophyte, respectively.

Answer 4

• true

Question 5

In mosses, the zygote divides to become the

Answer 5

• diploid sporophyte

Question 6

In bryophytes, the sperm are released from a structure called a ______________ and then swim through moisture to reach an egg found within the ______________.

Answer 6

• antheridium; archegonium

Question 7

Bryophytes have all of the following characteristics except

Answer 7

• vascular tissue

Question 8

In mosses, the ______________ is diploid, while the _______________ is haploid.

Answer 8

• sporophyte; gametophyte