Name _________________________________________________
AP Bio Review for Sexual Life Cycle for Plants and Animals
This worksheet is designed to familiarize you with the fundamental differences between the life
cycles of a) vertebrates (you - as a reference), b) early land plants (e.g. mosses as an example of
a phylum with easily distinguishable alternating generations), and c) seed plants). The main goal
of this excercise is for you to learn and understand what the term “alternation of generations”
means, to be able to identify haploid and diploid generations in seed plants, to be familiar with
the terms “ sporophyte” and “gametophyte” and to have an understanding of the principle of
“double fertilization” in angiosperms. Please use chapters 13, 31, 38 of your Campbell Biology
textbook for assistance and/or see me for help.
A
B
Answer the following questions: (see Figures A and B above and your textbook for help)
1. What does the term “ploidy” refer to?
The number of sets of chromosomes in a cell (haploid, diploid, triploid, etc)
2. What is the ploidy of the gametes of a normally diploid organism?
Haploid – one copy of each chromosome (gene) because they are sex cells.
3. Which biological process is required for a cell to go from diploid to haploid state?
Meiosis – reduction division
4. What is the function of haploid cells in humans?
Gametes – used for reproduction (sperm and egg)
5. What other functions can haploid cells have in fungi, algae, and plants?
In these organisms the haploid form is multicellular and produces sperm and egg by mitosis. Remember,
gametophyte – makes gametes.
Over evolutionary time, different phyla have developed different strategies of reproduction, each
changing the way the two alternating generations contribute to development. Figure C shows these
differences for bryophytes (mosses), pteridophtes (ferns) and angiosperms (seed plants).
C
D
Figure D reviews the life cycle of angiosperms and shows where “double fertilization”, which is
unique to angiosperms, occurs. (In simplified terms, angiosperms are all “flowers” and trees that
you see around you, except for needle trees (conifers), ginkgos, and cycads, which collectively
are called gymnosperms.)
Double fertilization refers to the fact that each pollen contains 2 sperm. Both sperm fertilize
nuclei in the female gametophyte. During fertilization, sperm #1 fuses with the egg (one of the
seven cells) to form the zygote/embryo, sperm #2 fuses with the two nuclei in the central cell to
form the “endosperm”, which becomes a nutritive tissue used to nurture the embryo in the seed.
Answer the following questions:
1. Label the parts of the complete flower below
Petal
Anther
Stigma
Stamen
Pistil
Style
filament
Ovary
Ovule
Sepal
2. What does the sporophyte of an angiosperm plant consist of? (Use general terms for plant
parts/organs).
Leaves, stems, roots and shoots.
3.
Which part of the plant is the male gametophyte? _Anther______ Female? Ovary_______
4. Define “microsporogenesis” and “megasporogenesis”. In what portion(s) of the flower does
each of these processes occur? What is the end product of each process?
Microsporogenesis – production of the pollen containing haploid sperm
Megasporogenesis – production of the ovule by meiosis, forming the female gamete (egg)
5. What is the ploidy of the male and female gametophyte?
Male sperm = n (haploid)
Female egg = n (haploid)
6. By which process (meiosis or mitosis) are the sperm cells in the male gametophyte of an
angiosperm formed?
meiosis
7. What is pollination? How does it differ from fertilization?
Pollination is the transfer of pollen containing sperm to the female organs of seed plants.
Fertilization is the actual direct union of the sperm contained within the pollen and the egg
8.
What is the ploidy of the embryo?
Diploid (2n)
9. What is the ploidy of the endosperm? Why?
3n. The endosperm is formed from tissue that is already 2n, but then upon fertilization the
endosperm receives a set of chromosomes from the sperm so it becomes 3n
10. Why don’t humans undergo alteration of generations? Is one generation more prevalent than
the other? Which one? Explain.
The haploid form in humans is unicellular (sperm or egg) and cannot survive on its own as a
functioning organism. Diploid is of course the prevalent form in humans and is the only
viable form.