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BSC 2011L – Principles of Biology 2 Lab
Lab Topic 15
Plant Diversity II: Seed Plants
Lab Topic 15: Plant Diversity II
• After completing this lab topic, you should be able
to:
– (1) Identify examples of the phyla of seed plants
– (2) Describe the life cycle of a gymnosperm (pine tree) and
an angiosperm
– (3) Describe the features of flowers that ensure pollination
by insects, birds, bats, and wind
– (4) Describe factors influencing pollen germination
– (5) Identify types of fruits, recognize examples, and
describe dispersal mechanisms
– (6) Relate the structures of seed plants to their functions
in the land environment
– (7) Compare the significant features of life cycles for
various land plants and state their evolutionary
importance
– (8) Summarize major trends in the evolution of land plants
and provide evidence from your laboratory investigations
Plant Diversity
• There are four major periods of plant evolution:
• (1) Origin of plants from aquatic ancestors
–
–
–
–
Ancestors were green algae (charophytes)
First adaptation was gametangia
Earliest examples are bryophytes (mosses)
Vascular tissue for conducting water and nutrients
(not all plants are vascular)
• (2) Diversification of plants with vascular tissues
– Conducting tissues allow plants to grow larger as
opposed to growing out in mats like the mosses
– Earliest forms lacked seeds (similar to present-day
ferns)
Plant Diversity
• (3) Origin of the seed
– Seeds further protect plant embryos
– Consist of embryo and packaged food with a
protective covering to prevent dessication
– Gymnosperms = plants with naked seeds
• Modern examples are conifers (pine trees)
• (4) Emergence of flowering plants
– Angiosperms = “contained seed”
– Flower is a complex reproductive structure
• Bears seeds within protective chambers or ovaries
Highlights of Plant Evolution
Highlights of Plant Evolution
Protected Embryo of a Plant
PLANT GROUP
Mosses and other
nonvascular plants
Gametophyte Dominant
Sporophyte
Ferns and other seedless
vascular plants
Seed plants (gymnosperms and angiosperms)
Reduced, independent
(photosynthetic and
free-living)
Reduced (usually microscopic), dependent on surrounding
sporophyte tissue for nutrition
Reduced, dependent on
Dominant
gametophyte for nutrition
Dominant
Gymnosperm
Sporophyte
(2n)
Microscopic female
gametophytes (n) inside
ovulate cone
Sporophyte
(2n)
Gametophyte
(n)
Angiosperm
Microscopic
female
gametophytes
(n) inside
these parts
of flowers
Example
Microscopic male
gametophytes (n)
inside pollen
cone
Sporophyte (2n)
Gametophyte
(n)
Microscopic
male
gametophytes
(n) inside
these parts
of flowers
Sporophyte (2n)
Exercise 15.1 - Gymnosperms
• Gymnosperms are a diverse group of seed plants
that do not produce flowers
• Represented by four phyla
• Compared to ferns, gymnosperms have additional
adaptations
• Further reduction of the gametophyte
– Greater development of diploid sporophyte
– Pine tree = sporophyte + tiny gametophytes living in the
cones
– Gametophytes are dependent on and protected by the
parent sporophyte
• Evolution of pollen
– Pollen grain = much-reduced male gametophyte
– Houses cells that will develop into sperm
– Wind carries pollen from male to female cones
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms
Gymnosperms (700 species)
• Vascular seed plants (no flowers)
• Conifers or cone-bearing plants
– Pines, firs, spruces, junipers, cedars
• Among the tallest (up to 360 feet), largest
and oldest (4,600 years) organisms on
Earth
• Nearly all are evergreens
– Retain leaves throughout the year
• Thick cuticle covers the leaf
• Stomata located in pits – helps to prevent
water loss
Coniferous Forest in Canada
A Pine Tree
From ovule to seed in a gymnosperm
Integument
Female
gametophyte (n)
Seed coat
(derived from
integument)
Spore wall
Egg nucleus (n)
Immature
female cone
Megasporangium
(2n)
Megaspore (n)
(a) Unfertilized ovule
Male gametophyte
(within a germinated
pollen grain) (n)
Micropyle
(b) Fertilized ovule
Food supply
(female
gametophyte
tissue) (n)
Discharged
sperm nucleus (n)
Pollen grain (n)
Embryo (2n)
(new sporophyte)
(c) Gymnosperm seed
Lab Study A. Phyla of Gymnosperms
• Materials
– Living or pressed examples of conifers, ginkgos,
cycads and Mormon tea
• Introduction
– Coniferophyta (pines and other cone-bearing trees
and shrubs)
– Cycadophyta (cycads)
– Ginkgophyta (ginkgos)
– Gnetophyta (gnetums, Welwitschia, Mormon tea)
• Procedures
– Observe the demonstration phyla and also refer to
the slides in the lab topic outline.
– Sketch the overall structure of the plants and label
structures where appropriate.
Lab Study A. Phyla of Gymnosperms
• Results
– 1. Complete Table 15.2 in your lab manual
– 2. Are there any reproductive structures present for
these plants? If so, make notes in the margin of your
lab manual.
• Discussion
– 1. What are the key characteristics shared by all
gymnosperms? (produce pollen and seeds, but no
flowers or fruits)
– 2. What is the ecological role of conifers in forest
ecosystems? (primary producers, important in
secondary succession)
– 3. What economically important products are
provided by conifers? (resins, turpentine, wood and
paper products, disposable diapers)
European larch
Cycas revoluta
Ginkgo biloba
pollen-producing tree
Ephedra
Lab Study B. Pine Life Cycle
• Materials
– Living or preserved pine branch
– Male and female pine cones
– Fresh or dried pine pollen and preserved slide of pine
pollen
– Prepared slides of male and female pine cones
– Slides, cover slips, and colored pencils
• Introduction
– All gymnosperms are wind-pollinated trees or shrubs
– Most bear unisexual male and female reproductive
structures on different parts of the same plant
– Gymnosperms are heterosporous
• Male microspores develop into pollen
• Female megaspores, which develops into the female
gametophyte
Lab Study B. Pine Life Cycle
• Procedure
– 1. Pine sporophyte (see Figure 16.1)
• a. Examine the pine branch and notice the arrangement of leaves. Is this
•
plant haploid or diploid? (diploid)
b. Examine the small cones. What important process occurs in the
sporangia? (meiosis)
c. Locate an ovulate cone and a pollen cone.
•
– 2. Male gametophyte – development in pollen cones
• a. Examine a longitudinal section of a pollen cone and identify its parts.
•
Observe that pollen cones are composed of radiating scales, each of which
carries two elongated sacs (microsporangia). Microspore mother cells within
microsporangia divide by meiosis and each produces four haploid
microspores, which develop into pollen grains.
b. Observe a slide of pine pollen. Note the wings on either side of the grain.
Remember that the pollen grain is the male gametophyte.
– 3. Female gametophyte – development in ovulate cones
• a. Examine a longitudinal section of a young ovulate cone. Note the ovule
•
•
(containing the megasporangium) on the upper surface of the scales. Diploid
megasporocytes produce megaspores.
b. Observe a second-year cone.
c. Observe a mature cone.
Lab Study B. Pine Life Cycle
• Results
– 1. Review the structures and processes observed.
– Using colored pencils, indicate the structures of the pine life cycle
in Figure 15.2 that are haploid or diploid, and circle the processes
of mitosis, meiosis, and fertilization.
• Discussion
– 1. What is the function of the wings on the pollen grain? (wind
dispersal)
– 2. Why is wind-dispersed pollen an important phenomenon in the
evolution of plants? (plants were no longer dependent on water for
sexual reproduction)
– 3. Are microspores and megaspores produced by mitosis or
meiosis? (meiosis)
– 4. Can you think of at least two ways in which pine seeds are
dispersed? (wind and various animals like squirrels)
– 5. One of the major trends in plant evolution is the reduction in size
of the gametophytes. Describe the male and female gametophyte in
terms of size and location. (male gametophyte is the pollen grain
with two nucleii and is wind dispersed, while the female
gametophyte never leaves the sporophyte and is composed of a
multicellular structure inside the ovule)
Key
Haploid (n)
Diploid (2n)
Ovule
Ovulate
cone
Pollen
cone
Megasporocyte (2n)
Integument
Microsporocytes
(2n)
Megasporangium
Pollen (2n)
Pollen grain
grains (n) MEIOSIS
MEIOSIS
Mature
sporophyte
(2n)
Microsporangia
Microsporangium (2n)
Seedling
Archegonium
Female
gametophyte
Seeds
Food
reserves
(n)
Seed coat
(2n)
Embryo
(2n)
Sperm
nucleus (n)
Pollen
tube
FERTILIZATION
Egg nucleus (n)
Surviving
megaspore (n)
Nonvascular plants (bryophytes)
Seedless vascular plants
Gymnosperms
Angiosperms
Exercise 15.2 - Angiosperms
• Flowering plants classified in the phylum
Anthophyta
• Supply nearly all of our food and much of our fiber
for textiles
• Adaptations include refinements in vascular tissue
and FLOWERS
• Unique characteristic is the carpel – a vessel in
which ovules are enclosed
– After fertilization, the ovule develops into a seed and the
carpel matures into a fruit
• Flowers
– Display of a plant’s sex organs
– Helps to attract insects and other animals that transfer
pollen
– More reliable than wind-blown transfer
Lab Study A. Flower Morphology
• Materials – living flowers
• Introduction – we will investigate the structure
•
of the flower
Procedure
– 1. Examine fresh flowers of four different species
– 2. Identify the parts of the flower using Figure 15.2 as
a guide
– 3. Record observations in Table 15.3
• Discussion
– What structures or characteristics did you observe in
your investigations that you predict are important to
pollination?
Lab Study A. Flower Morphology
• Short stem with 4 whorls of modified leaves
– Sepals
• Bottom of the flower, usually green, and enclose the flower
before it opens
– Petals
• Above the sepals and usually the showiest part of the flower
used to attract pollinators
– Stamens
• Consists of a stalk (filament) bearing a sac (anther) in which
the pollen grains develop
– Carpals
• Consists of a stalk (style) with an ovary at the base and a
sticky tip (stigma) for trapping pollen
• Ovary is a protective chamber with one or more ovules in
which the eggs develop
Lab Study B. Pollinators
• Materials – living flowers
• Introduction
– Flowers with inconspicuous sepals and petals are
usually pollinated by wind
– Most showy flowers are pollinated by animals
• Procedure – use the key to pollination in your
•
manual, then classify the flowers used in lab
Results
– 1. Record your results in Table 15.3
• Discussion
– 1. Review the key to pollination and describe the
characteristics of flowers that are adapted for
pollination by each of the following agents:
Lab Study B. Pollinators
• Discussion
– 1. Review the key to pollination and describe the
characteristics of flowers that are adapted for
pollination by each of the following agents:
• a. wind – inconspicuous sepals and petals, feathery stigma,
no odor
• b. hummingbird – red tubular flowers with little or no odor
• c. bat – white flowers that smell like fruit, strong flower parts
– 2. Discuss other ways in which keys are used in
biology. (primarily in the form of taxonomic keys used
to identify species)
Stigma
Stamen
Anther
Carpel
Style
Filament
Ovary
Petal
Sepal
Ovule
Lab Study C. Angiosperm Life Cycle
• Materials
• Introduction
– Here we will study the life cycle of flowering plants
• Procedure
–
–
–
–
1. Pollen grain – the male gametophyte
2. Development of the female gametophyte
3. Pollination and fertilization
4. Seed and fruit development
• Results
– 1. Review the structures and processes observed in
the angiosperm life cycle (Figure 16.3). Indicate the
haploid and diploid structures in the life cycle.
Lab Study C. Angiosperm Life Cycle
• Results
– 2. Sketch observations of slides in the margin of your
lab manual
– 3. Record the results of pollen germination studies in
Table 15.4
• Discussion
– 1. What part of the life cycle is represented by the
mature pollen grain? (male gametophyte)
– 2. How does the female gametophyte in angiosperms
differ from the female gametophyte in gymnosperms?
(angiosperm is reduced to eight nuclei and lacks and
archegonium)
– 3. Do you think that all pollen germinates on all
stigmas? How might pollen germination and growth
be controlled? (this is basically a chemical
recognition problem)
Angiosperm Life Cycle
Angiosperm Life Cycle
• (1) The flower is a part of the sporophyte
plant
– Pollen grain is the male gametophyte
– Female gametophyte is the embryo sac
located within an ovule
• (2) Pollen grain lands on sticky stigma of a
carpel
– Pollen grain travels down a tube to the ovule
• (3) Pollen grain deposits two (2) sperm
nuclei within the embryo sac
– Double fertilization
• (4) Fertilization produces a zygote
Angiosperm Life Cycle
• (5) Zygote develops into an embryo
• Second sperm fertilizes another female
gametophyte cell
– Develops into endosperm – nutrient storing
tissue
– Nourishes developing embryo
• Whole ovule develops into a seed
• Fruit = ripened ovary of a flower
– Pea pod is an example of a fruit
– Seeds are the mature ovules (peas) encased
in the ripened ovary (the pod)
Key
Haploid (n)
Diploid (2n)
Mature flower on
sporophyte plant
(2n)
Microsporangium
Microsporocytes (2n)
Anther
MEIOSIS
Ovule (2n) Microspore
(n)
Ovary
Germinating
seed
MEIOSIS
Megasporangium
(2n)
Embryo (2n)
Endosperm (3n)
Seed
Seed coat (2n)
Nucleus of
developing
endosperm
(3n)
Male gametophyte
(in pollen grain)
Pollen
(n)
grains
Stigma
Pollen
tube
Megaspore
(n)
Antipodal cells
Female gametophyte Central cell
(embryo sac)
Synergids
Egg (n)
Generative cell
Tube cell
Sperm
Style
Pollen
tube
Sperm
(n)
FERTILIZATION
Zygote (2n)
Egg
nucleus (n)
Discharged sperm nuclei (n)
Lab Study D. Fruits and Dispersal
• Materials – variety of fruits
• Introduction
– Seed develops from the ovule and the fruit develops
from the ovary or from other tissues in the flower
– Fruits provide protection for seeds and may be
involved in dispersal of the sporophyte embryo
• Procedure – examine the fruits and seeds on
•
demonstration
Results
– 1. Record in Table 15.5 the fruit type for each of the
fruits keyed.
– 2. For each fruit, indicate the probable method of
dispersal (wind, water, gravity, animal ingestion,
adhesion)
– 3. Indicate in Table 15.5 if the seeds have structures
to enhance dispersal.
Lab Study D. Fruits and Dispersal
• Discussion
– 1. How might dry fruits be dispersed? Fleshy fruits?
(some dry fruits open when mature and seeds from
these might be dispersed by wind or gravity. Other
dry fruits may be eaten by animals. Fleshy fruits do
not open and may be eaten.)
– 2. Describe the characteristics of an achene, drupe,
and berry.
• Achene: dry, one-seeded fruit with the ovary and seed fused
• Drupe: fleshy, one-seeded fruit with a stone covering around
the seed
• Berry: is a fleshy, many-seeded fruit
Tomato
Ruby grapefruit
Nectarine
Hazelnut
Milkweed
Fruits and Seed
Dispersal
Reviewing Your Knowledge
• 1. Complete Table 15.6. Compare mosses, ferns,
•
conifers, and flowering plants relative to sexual
life cycles and adaptations to the land
environment.
Answer questions 2-6 on pages 419-420.
Reviewing Your Knowledge
• 2. Identify the function of each of the following
structures found in seed plants. Consider their
function in the land environment.
– Pollen grain: male gametophyte, transports sperm to
egg without water, produced in large numbers with
dessication-resistant coat
– Microsporangium: sterile jacket of cells protecting
spore production (meiosis)
– Flower: attracts pollinator to enhance movement of
pollen
– Carpel: protects the ovule and developing embryo
plants
– Seed: can be dispersed to new areas, pre-packaged
embryonic plant
– Fruit: enhances seed dispersal, protects seeds
– Endosperm: nutrient source for embryonic plant in
developing seed
Reviewing Your Knowledge
• 3. Plants have evolved a number of
•
characteristics that attract animals and ensure
pollination, but what are the benefits to animals
in this relationship? (plants provide pollen and
nectar, which are energy-rich food sources for
animals)
4. Why is internal fertilization essential for true
terrestrial living? (results in protection of the
sperm or sperm nuclei from drying out; water is
therefore not required for reproduction to occur)
Applying Your Knowledge
• Answer questions 1-5 on pages 420-422
• Be sure to complete Table 15.7