11.7.2 Alternation of Generations: Angiosperms

Question 1

Alternation of Generations: Angiosperms

Answer 1

• During alternation of generations in angiosperms (and gymnosperms), the game-tophyte is greatly reduced to several mobile cells that do not rely on water for dispersal.
• In angiosperms, the immature male gametophyte, a pollen grain, consists of two cells, while the female gametophyte, the embryo sac consists of seven cells (one of which has a double nucleus).
• During fertilization, the male gametophyte will produce two sperm cells, which will double fertilize the female gametophyte creating both an embryo and a food source (the endosperm); this phenomenon is referred to as double fertilization.

Question 2

note

Answer 2

• The sporophyte generation (the flower at the top of the
  diagram) will give rise to the male and female gametophytes within male and female reproductive organs, respectively.
• A pollen grain (the male gametophyte), will attach to the stigma of the carpel and germinate. The pollen grain will extend a pollen tube down the style to the ovary. Once at the ovary, the tube will penetrate the ovule (at a pore called the micropyle) and deposit two sperm to the female gametophyte, the embryo sac.
• In a process called double fertilization, one sperm will
  fertilize the egg cell to form the zygote and the other sperm will fertilize the polar nuclei to form the triploid endosperm. Endosperm serves as a nutrient-rich material that will nourish the zygote.
• Once the egg cell is fertilized, the resulting zygote develops into the embryo, which is packaged in a seed.
• Haploid cells called microspores will undergo mitosis to form pollen grains, the male gametophyte. A pollen grain consists of two cells: the tube cell will form the pollen tube and the generative cell will give rise to two sperm.
• A haploid cell called a megaspore will develop into the
  embryo sac, which is the female gametophyte. The embryo sac consists of seven cells including the egg cell and a double-nucleated cell called the polar nuclei.

Question 3

True or false?

After the megasporocyte undergoes meiosis only one megaspore results.

Answer 3

• true

Question 4

The letter that points to the egg in the diagram is

Answer 4

• C

Question 5

The letter that points to the endosperm in the diagram is

Answer 5

• E

Question 6

After fertilization the ____________ develops into a seed and the ____________ develops into a fruit.

Answer 6

• ovule; ovary

Question 7

In angiosperms, the endosperm forms due to

Answer 7

• double fertilization of the female gametophyte

Question 8

Which statement regarding the male gametophyte in flowering plants is correct?

Answer 8

• The male gametophyte is the pollen grain.