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The Green Machine
Understanding the Seed Plants (Gymnosperms)
22
To the Instructor
The gymnosperms are more obvious to students than the nonvascular and seedless vascular plants. A stroll across
campus should yield several species of gymnosperms, from pine trees to junipers. In this chapter, attempt to anchor
the gymnosperms to students’ existing schema of these plants by using meaningful and interesting examples. This
chapter can easily be modified to teach along with other chapters on plant diversity. The instructor can pick and
choose activities from these chapters to meet the needs of the students.
Topics for Discussion
77 At the beginning of this lab, review the objectives to the chapter. If this chapter is taught with other plant diversity
chapters, cover the objectives and material for the other chapters.
77 Discuss the classification and basic evolution of the gymnosperms.
77 Discuss the phyla of the gymnosperms included in this chapter, providing specific examples, natural history, uses, life
history, and anatomical information.
77 Discuss and bring in local specimens or photographs of the plants discussed in this chapter.
77 Discuss the environmental, industrial, and medical importance of the gymnosperms.
Total Estimated Completion Time: 3 hours, 30 minutes
1
Exercise
22.1
Phylum Cycadophyta
Estimated Exercise 22.1 Completion Time: 30 minutes
Procedure 1
Macroanatomy of Cycas
Estimated Procedure 1 Completion Time: 15 minutes
Materials
❏❏ Dissecting microscope
❏❏ Leaf, pollen cone, microsporophyll, megasporophyll, and a seed from a living or preserved specimen of cycad
❏❏ Colored pencils
Procedure 2
Microanatomy of Cycas
Estimated Procedure 2 Completion Time: 15 minutes
Materials
❏❏ Compound microscope
❏❏ Transverse or cross section of a microsporangiate cone (Triarch Microslides #10-8C-D), transverse or cross section of a
megasporangiate cone (Triarch Microslides #10-8E-EE), unfertilized ovule, and fertilized ovule from a living or preserved specimen
of cycad
❏❏ Prepared slides of a typical cycad species such as Cycas revoluta (Triarch Microslides #10-2A-D) or Zamia pumila (Triarch
Microslides #10-8A-H)
❏❏ Colored pencils
Check Your Understanding
1.1 What is the major means of pollinating cycads?
Thrips and beetles serve as insect pollinators in cycads.
1.2 Describe the dioecious nature of cycads.
Cycads are dioecious (having separate sexes) and produce distinct male pollen cones and female seed cones. The
male pollen cones usually are elongated, and the female seed cones are rounded and may contain dozens of large
seeds.
1.3 Why should one not eat cycad seeds?
Although they are a rich source of starch, cycads should not be consumed because they contain large amounts of
carcinogenic and neurotoxic chemicals.
Chapter 22 | The Green Machine: Understanding the Seed Plants (Gymnosperms)
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Exercise
22.2
Phylum Ginkgophyta
Estimated Exercise 22.2 Completion Time: 30 minutes
Procedure 1
Macroanatomy of Ginkgo biloba
Estimated Procedure 1 Completion Time: 15 minutes
Materials
❏❏ Dissecting microscope
❏❏ Fresh or preserved stems and leaves of Ginkgo biloba
❏❏ Colored pencils
Procedure 2
Microanatomy of Ginkgo biloba
Estimated Procedure 2 Completion Time: 15 minutes
Materials
❏❏ Compound microscope
❏❏ Prepared slides of Ginkgo biloba: a transverse or cross section of a short branch (Triarch Microslides #10-4AAAA), a
microsporangiate strobilus (Triarch Microslides #10-4C), a longitudinal section of an ovule (Triarch Microslides #10-4EF), a
longitudinal section of a seed with the seed coat removed (Triarch Microslides #10-4K), and a section of the ovule
❏❏ Colored pencils
Check Your Understanding
2.1 Why are female ginkgo trees considered undesirable in urban areas?
Female ginkgo trees are called stink bomb trees because their fruit is extremely foul smelling.
2.2 Sketch and describe a ginkgo leaf.
Sketches will vary, but the leaves of Ginkgo biloba do not
possess a midrib (central vein) and have dichotomous
(forked) venation.
Chapter 22 | The Green Machine: Understanding the Seed Plants (Gymnosperms)
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Exercise
23.3
Phylum Coniferophyta
Estimated Exercise 23.3 Completion Time: 2 hours, 30 minutes
Procedure 1
Macroanatomy of Conifers
Estimated Procedure 1 Completion Time: 20 minutes
Materials
❏❏ Dissecting microscope or hand lens
❏❏ Specimens of select conifers, such as pine, bald cypress, cedar, spruce, juniper, arborvitae, fir,
and other specimens provided by the instructor
❏❏ Colored pencils
Procedure 2
Macroanatomy of Conifer Cones
Estimated Procedure 2 Completion Time: 20 minutes
Materials
❏❏ Dissecting microscope
❏❏ Colored pencils
❏❏ White paper
❏❏ Sterile microscope slides
❏❏ Dropper
❏❏ Water
❏❏ Coverslip
❏❏ Pollen cones (male/staminate) from select conifers
❏❏ Seed cones (female/ovulate) from select conifers
❏❏ Seeds from select conifers
Answers to Procedural Questions
6 Drop a seed from Pinus sp. from above your head. Describe the action as it falls.
It falls to the ground in a twirling, helicopter blade type motion.
Chapter 22 | The Green Machine: Understanding the Seed Plants (Gymnosperms)
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Procedure 3
Microanatomy of Conifer Cones
Estimated Procedure 3 Completion Time: 20 minutes
Materials
❏❏ Compound microscope
❏❏ Microscope slides of longitudinal section through the tip of a microsporangiae cone of Pinus sp., pollen from Pinus sp.,
transverse and longitudinal sections of the seed cones of Pinus sp., and ovule of Pinus sp.
❏❏ Colored pencils
Procedure 4
Conifer Seed Germination
Estimated Procedure 4 Completion Time: 30 minutes
Materials
❏❏ Pine seeds
❏❏ Pine seedlings
❏❏ Sand
❏❏ Sectioned potting container with drains
❏❏ Potting soil
❏❏ Small pot
❏❏ Pencil with eraser
Procedure 5
Macroanatomy of Conifer Needles and Leaves
Estimated Procedure 5 Completion Time: 10 minutes
Materials
❏❏ Dissecting microscope
❏❏ Selected specimens of conifer needles and leaves
❏❏ Colored pencils
Answers to Procedural Questions
3 If your conifer needle is fresh, smell your specimen. Describe the smell. What is responsible for the distinct smell?
Conifers have an intense, sharp, fruity smell. The smell is described by many as a clean smell and is caused by
terpines.
Chapter 22 | The Green Machine: Understanding the Seed Plants (Gymnosperms)
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Procedure 6
Microanatomy of Conifer Needles and Leaves
Estimated Procedure 6 Completion Time: 10 minutes
Materials
❏❏ Compound microscope
❏❏ Prepared microscope slide of the transverse section of a needle from Pinus sp.
❏❏ Colored pencils
Procedure 7
Microanatomy of Conifer Stems
Estimated Procedure 7 Completion Time: 25 minutes
Materials
❏❏ Compound microscope
❏❏ Prepared microscope slide of transverse section through the stem of a young conifer, transverse section through the stem of Pinus
sp. (Triarch Microslides #10-6A-DM), radial longitudinal section through the phloem of Pinus sp., and radial longitudinal section
through the xylem of Pinus sp.
❏❏ Colored pencils
Procedure 8
Conifer Stem Aging
Estimated Procedure 8 Completion Time: 15 minutes
Materials
❏❏ Cross section of a tree trunk
Answers to Procedural Questions
3 Determine the age of your specimen.
Answers will vary depending on specimen.
4
Examine the annual rings. Was the tree exposed to any interesting conditions? How do you know, and when in the
life of the tree did it occur?
Answers will vary depending on specimen.
Chapter 22 | The Green Machine: Understanding the Seed Plants (Gymnosperms)
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Check Your Understanding
3.1 Compare and contrast softwood and hardwood, and provide examples of each.
The wood of conifers is considered softwood, and the wood of angiosperms is considered hardwood. Softwood is
composed primarily of tracheids and rays (lateral conduction structures), whereas hardwoods have tracheids, rays,
and vessel elements. Softwoods are relatively light and usually less dense than hardwoods, with the exceptions
of balsa and basswood. Softwoods contain vertical resin canals that occur either naturally or as a result of injury.
Generally, softwoods are easier to work with in the building and furniture industry. Softwoods also are used in the
production of paper, medium density fiberboard (MDF), and the majority of plywood. Hardwood is used in fine
­furniture and flooring and typically is more expensive and durable than softwood.
3.2 What is the function of the cork cambium?
The cork cambium found in gymnosperms and angiosperms is responsible for secondary growth that becomes the
epidermis in roots and stems.
3.3 Compare and contrast springwood and summerwood.
Springwood is lighter in color, with larger cells. Summerwood is darker in color, with smaller cells. In many species,
the age of a tree can be determined by counting the summerwood bands.
3.4 What is the function of the heartwood?
Heartwood is the darker inner xylem tissue, which serves primarily as a reservoir for gum, resin, and tannin.
3.5 Describe the location of the xylem and phloem in your specimen.
Answers will vary, but xylem is found between the pith and cambium, and phloem is found between the cambium
and cortex.
3.6 List several uses of softwood and hardwood.
Softwood: paper, fiberboard, plywood
Hardwood: flooring and fine furniture
Chapter 22 | The Green Machine: Understanding the Seed Plants (Gymnosperms)
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Chapter 22 Review
1
Compare and contrast the seeds of gymnosperms and angiosperms.
Gymnosperm and angiosperm seeds are distinctly different. The term gymnosperm literally means “naked seed
leaf.” In these plants, the seeds are not enclosed in an ovule, and they mature on the surface of a cone scale, such
as that of a pine cone. The nutritive material in gymnosperms accumulates prior to fertilization. In angiosperms, the
nutritive material is stored only after fertilization. In angiosperms, double fertilization occurs, producing an embryo
and a nutritive endosperm. The seeds of angiosperms are encased in a fruit. In both cases, the parental sporophyte
generation provides nutrition to potential offspring, giving them a distinct advantage over seedless plants.
2
How have seed plants influenced the development of humans?
Seed plants provide food for animals and humans. Neolithic human societies approximately 12,000 years ago used
seed plants, such as wheat, figs, corn, and squash, and shaped their destinies through artificial selection.
3
What are the general characteristics of gymnosperms?
The gymnosperms are generally characterized by lacking flowers and fruits; the seed develops in association with a
scale that exists on a cone.
4
List and give examples of each phylum of gymnosperms.
Cycadophyta—sago palms
Ginkgophyta—ginkgo trees
Gnetophyta—Ephedra spp.
Coniferophyta—pine trees and bald cypress
5
What are some unique characteristics and facts about Ginkgo biloba?
The leaves of ginkgos do not possess a midrib (central vein) and have dichotomous (forked) venation. The tree
is deciduous (shedding leaves yearly), and the leaves turn bright yellow before abscission (shedding) in the fall.
Ginkgo trees have two types of shoots: short shoots, or spurs, appear knobby and feature clusters of leaves and
immature ovules. The leaves of slow-growing short shoots usually are unlobed or slightly bilobed. The leaves of
fast-growing long shoots usually are deeply bilobed. Ginkgo trees are dioecious, having separate sexes. After
­fertilization, embryos form and the integument develops into an extremely bad-smelling, fleshy seed coat.
6
What is unique about Welwitschia sp.?
The genus Welwitschia is represented by one member, Welwitschia mirabilis, native to the extremely dry Namib
and Mossamedes deserts of southwestern Africa. It is rather strange in appearance, possessing a long taproot along
with a short stem that usually supports two permanent strap-like leaves. Welwitschia mirabilis may live for more
than 1,000 years.
7
What characteristic do members of phylum Gnetophyta have in common with angiosperms?
The gnetophytes are unique gymnosperms because their wood contains conducting cells, known as vessel elements,
similar to the angiosperms, or flowering plants. In addition, gnetophytes such as angiosperms undergo double
­fertilization. It is thought that the gnetophytes perhaps are ancestral to the angiosperms.
8
Describe reproduction in cycads.
Cycads are dioecious (having separate sexes) and produce distinct male pollen cones and female seed cones. The
male pollen cones usually are elongated, and the female seed cones are rounded and may contain dozens of large
seeds. The sperm of cycads are the largest living in the world and may possess more than 10,000 flagella. The
scales surrounding the sometimes colorful seeds may be covered by feltlike hairs that can be highly irritating to
the skin. Thrips and beetles serve as insect pollinators in cycads.
Chapter 22 | The Green Machine: Understanding the Seed Plants (Gymnosperms)
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9
Sketch and label a transverse section of a tree trunk.
Sketches will vary, but refer to Fig. 22.56 (p. 369) of the lab manual. Make sure students include bark, heartwood,
springwood, summerwood, vascular cambium, and pith.
10 Discuss the economic importance of conifers.
Some conifer species are sources of lumber, paper, wood alcohol, turpentine, and resin. Several species, such
as juniper and yew, are ornamentals. In this regard, bonsai conifer plants are popular, along with spruce and fir
Christmas trees. Oils from conifers are used in soaps and air fresheners. Humans eat some seeds, such as pine
nuts. Some conifer products, such as taxol (a cancer treatment), are used in medicine.
11 Trace the life cycle of a pine tree.
Sketches will vary. Most conifers,
including pine, produce two distinct
types of cones as a sporophyte, the
micro­sporangiate pollen cone (male)
and the ovulate seed cone (female).
Pollen develops within the microsporangia of the pollen cone. In
the seed cone, the megasporangia
produce eggs in the archegonia,
forming the ovule. Pollen enters
the mature seed cone and forms
sperm cells ultimately delivered
to the waiting egg by means of
a pollen tube. The egg is fertilized
and forms a zygote. The seed
cone closes and increases in size
as the seeds develop.
Microsporangiate
(male) cone
Young
sporophyte (2n)
(seedling)
Mature
sporophyte (2n)
Seed coat
Embryo
(2n)
Ovulate
(female)
cone
Megagametophyte (n)
Fertilized egg
(zygote) (2n)
Longitudinal
section through
microsporangiate
cone
Meiosis
Meiosis
Microsporophyll
Microsporophyll
Microsporangium
Microsporangium
Fertilization
Germinating
pollen
Germinating
pollen
grain
(mature
male
grain
(mature
male
gameophyte)
gametophyte)
Sperm
Sperm(n)(n)
Functional
Functional
megaspore
megaspore (n)
(n)
Ovule
Ovule with
with
megasporocyte
megasporocyte (2n)
(2n)
Meiosis
Microspore
Microspore
tetrad
tetrad(n)
(n)
Mature pollen
pollen grain
grain (n)
(n)
Mature
(immature male
male gametophyte)
gametophyte)
(immature
Chapter 22 | The Green Machine: Understanding the Seed Plants (Gymnosperms)
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