Notes to Instructors
Chapter 29 Plant Diversity I: How Plants Colonized Land
Chapter 30 Plant Diversity II: The Evolution of Seed Plants
What is the focus of these activities?
By about 500 million years ago, increasing amounts of oxygen led to the formation of an
What are the particular activities designed to do?
Activity 29.1/30.1 What major events occurred in the evolution of the plant
kingdom?
Activity 29.2/30.2 What can a study of extant species tell us about the evolution of
form and function in the plant kingdom?
Activity 29.3/30.3 How are the events in plant evolution related?
Answers
Activity 29.1/30.1 What major events occurred in the evolution
of the plant kingdom?
Construct a concept map that describes the early evolution of plant life on Earth. Be sure
to include relationships among all the organisms and factors in the list on the next page.
Keep in mind that there are many ways to construct a concept map.
208 Notes to Instructors
Here is an example:
If you are doing this activity in small groups in class, explain your map to another group
of students when you finish it.
Terms
bryophytes
pteridophytes
lycophytes
endosymbiont
anaerobic bacteria
alternation of generations
megaspore
microspore
nonvascular plants
seedless
spore
gametophyte
sporophyte
egg
gametangia
Activity 29.1/30.1 209
t
hat became
that becam
e
chloroplasts
mitochondria
210 Activity 29.2/30.2
Use the understanding you gained from constructing the concept map to answer the
questions.
1. Describe the major problems ancestral land plants had to overcome before they
could make the transition from water to land.
Water was less available on land, and most of the available water was not on the
2. Describe the major solutions to the problems in question 1 that can be found in
today’s land plants. In other words, what mutations occurred that allowed organisms
to make the transition to land?
To reduce evaporative loss, a waxy cuticle covers the surface of cells in contact with
the environment.
Activity 29.2/30.2 What can a study of extant species tell us
about the evolution of form and function in the plant kingdom?
Fill in the chart on the next pages to compare the major features of key groups of land
plants with one another and with the charophyceans.
Plant Group
Feature Bryophytes Lycophytes Pterophytes Gymnosperms Angiosperms
Charophyceans
(green algae)
Peroxisomes Yes Yes Yes Yes Yes Yes
Chlorophylls
aand bYes Yes Yes Yes Yes Yes
Jacketed
gametangia Yes Yes Yes Yes Yes No
Cuticle Yes Ye s Yes Yes Yes No
True leaves
(contain vascular
tissue)
No No Yes Ye s Ye s No
Plant Group
Feature Bryophytes Lycophytes Pterophytes Gymnosperms Angiosperms
Charophyceans
(green algae)
Gametophyte
dominant
Yes No No No No Ye s
Sporophyte
dominant
No Yes Ye s Ye s Yes No
Use the information in the chart you have completed to answer the questions.
1. Some of the major plant groups are listed in the following table from most primitive
to most advanced. For each group, indicate what major characteristics make it more
advanced than the preceding group. For example, how are ferns more advanced than
mosses?
Plant group
Charophyceans Bryophytes Lycophytes Pterophytes Gymnosperms Angiosperms
Advance(s)
over
preceding
group
Peroxisomes
help reduce
photores-
piration, and
Jacketed
gametangia
(archegonia
and
Dominance
of
sporophyte
generation
Rhizomes
increase the
ability to
pick up
Pollen grain
removes the
need for water
for transport of
Flower
attracts
animal
pollinators
2. How do the bryophytes differ from the seedless vascular plants? How are they
similar?
Refer to the previous table. Differences between bryophytes and the seedless
vascular plants are:
3. The life cycle of all land plants includes an alternation of generations between a
multicellular gametophyte phase and a multicellular sporophyte phase.
Diagram the life cycle of a seed plant.
Refer to Figures 30.6 and 30.10 in Campbell Biology, 9th edition. See also Figure 13.6
on page 252.
a. What cellular division process always precedes formation of the gametophyte
generation?
b. What cellular process always precedes formation of the sporophyte generation?
c. If the sexual generation gives rise to the gametes, what part of an angiosperm is
sexual?
d. If the sexual generation gives rise to the gametes, what part of a bryophyte moss
is sexual?
The gametophyte, or green, leaflike moss structures, give rise to the gametes in
archegonia and antheridia.
214 Activity 29.2/30.2
4. Until the evolution of the seed plants, land plants were dependent on the availability
of water for reproduction. Explain why this was true. Explain how seed plants
overcame the need for water in reproduction.
Seed plants produce pollen rather than flagellated sperm. Pollen do not require water
5. Pollen, seeds, flowers, and fruits are considered among the most advanced
characteristics in the plant kingdom. What evolutionary advantage(s) does each of
these offer (relative to what existed before)?
Pollen: As noted in question 4, pollen no longer requires free water for transport.
Activity 29.2/30.2 215
Activity 29.3/30.3 How are the events in plant evolution related?
1. Working in groups of three or four, assign each student in the group one of the
following events in plant evolution to research. Then give each student 5 minutes to
report the results of his or her review to the other members of the group.
Events in Plant Evolution
I. Evolution of vascular tissue
Mutations in some land plants gave rise to vascular tissue. What advantage(s) did these
plants have compared with land plants that did not contain any vascular tissue?
The evolution of vascular tissue provided plants with support against the force of gravity.
II. Evolution of roots and leaves
Mutations in some land plants gave rise to roots, leaves, or both. What advantage(s) did
these plants have compared with plants that did not contain roots or leaves?
Roots increased a plant’s surface area for water absorption from the soil. Leaves with
III. The trend toward reduction of the gametophyte generation
Mutations in some land plants gave rise to life cycles in which the gametophyte
generation was reduced. What advantage(s) did these plants have compared with plants
that did not have a reduced gametophyte generation?
Reduction and enclosure of the gametophyte generation within the sporophyte helped
216 Activity 29.3/30.3
Activity 29.3/30.3 217
IV. Evolution of the seed
Mutations in some land plants gave rise to the seed. What advantages did these plants
have compared with plants that did not have seeds?
The seed contains a partially developed 2nembryo (the product of fertilization of the egg
by a sperm from the pollen tube), a food store for its early development, and a protective
2. Work together as a group to determine how these events in plant evolution (I to IV)
might be related. For example, which would have to come first (in evolution), which
next, and so on? Another way to look at this question is to consider which of these
events paved the way (or made it possible) for the other events to occur.
Be sure to state evidence for your proposed evolutionary scheme. To do this, it is
useful to ask yourself questions like these: Would it have been possible for the seed
to evolve without vascular tissue first having evolved? Leaves? And so on. If yes,
how could this have occurred? If no, why not?
Because roots and leaves contain vascular tissue, vascular tissue must have evolved
before roots and leaves. When we look at the evolution of dominance of the
3. Incorporate the following true observations into your analysis of how the events in
evolution (I to IV) could be related.
a. The fossil record (spore evidence and so on) indicates that the first plants on
Earth were similar to modern-day bryophytes.
b. The very large marine brown algae (for example, giant kelp) can grow to heights
of 30 feet or more. These algae have both leaflike and stemlike structures and
are held to the bottom of the sea by a holdfast. When examined microscopically,
the algae are found to contain transport vessels that are similar to phloem in
function. These giant kelp do not contain any xylemlike vessels, however, nor do
they have roots.
This provides evidence for the coevolution of transport systems. In the ocean, a
c. The first land plants with xylem and phloem had no leaves or roots.
This indicates that there was a selective advantage to having xylem and phloem
d. Some seedless vascular sporophyte plants do not release megaspores. Instead, the
megaspore divides on the sporophyte (in the old sporangium) to produce the
female gametophyte. This female gametophyte produces eggs in archegonia,
which are fertilized by sperm produced in antheridia of this or other plants.
Neither the female gametophyte (once formed) nor the developing embryo
receives nutrition from the old sporophyte plant.
This information allows us to recognize how the stage could have been set for
4. Write an analysis of how events a through d could be related.
Each change in evolution builds on what already exists. Observations a, c, and d
218 Activity 29.3/30.3
Consider a puddle of water in which mosses, ferns, and an angiosperm are growing. In a
drop of water taken from the puddle, you observe flagellated sperm.
Which of the following statements concerning the sperm could be true and which
are definitely false?
Consider each statement separately and explain your answers.
1. (T/F) The sperm could have been produced by an antheridium on the moss
sporophyte.
2. (T/F) The sperm could later stop swimming and develop into the male gametophyte
of the fern.
3. (T/F) The sperm may be swimming to the archegonium of the fern.
4. (T/F) The sperm could have been released from a pollen tube of an angiosperm.
29.3/30.3 Test Your Understanding