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 youto learn and understand what the term “alternation of generations” means, to be able to identify haploid and diploidgenerations 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

AntherStigma

StamenPistil

Style

filament

Ovary

OvuleSepal

  1. What does the sporophyte of an angiosperm plant consist of? (Use general terms for plant parts/organs).

Leaves, stems, roots and shoots.

  1. Which part of the plant is the male gametophyte? _Anther______Female? Ovary______
  1. 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)

  1. What is the ploidy of the male and female gametophyte?

Male sperm = n (haploid)

Female egg = n (haploid)

  1. By which process (meiosis or mitosis) are the sperm cells in the male gametophyte of an angiosperm formed?

meiosis

  1. 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

  1. What is the ploidy of the embryo?

Diploid (2n)

  1. 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

  1. 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.