KINGDOM PLANTAE
Introduction. Plants can be defined as living organisms that carry on photosynthesis, they are autotrophic (can make their
own food through photosynthesis) and multicellular. We will start off this kingdom by looking at the the green algae. The
unicellular green algae are classified as Protists and the multicellular green algae are placed in the Plant kingdom. We are
going to study both the unicellular, colonial and multicellular algae. Two major themes will be investigated: (a) the
evolution of multicellular body forms and (b) the evolution of sexual reproduction. The Algae, mosses, ferns,
gymnosperms, and angiosperms will be our study specimens
GREEN ALGAE
With over 700 species green algae show more diversity than other algal groups. Most species live in freshwater, you can
find them on the surface of ponds and oceans, and just below the surface of soil and marine sediment, on rocks, on tree
bark as well as other organisms, even on snow! Sink your feet in white, powdery beach in the tropics, it is largely the
work of countless green alga cells that formed calcified cell walls then went on to die and disintegrate. Green algae go on
space flight, to give off oxygen; space-traveling algae would take up carbon dioxide exhaled by the aerobically respiring
crew! The green algae are aquatic and photosynthetic. We will look at the (a) unicellular algae; (b) filamentous algae; (c)
colonial algae, and the multicellular algae.
Chlamydomonas-Unicellular Green Algae
Features
•
Single celled, egg shaped.
•
Two flagella for movement.
•
Eyespot, light sensitive, searches out light for photosynthesis.
•
Cell wall not made up of cellulose unlike most plants.
•
Chlamydomonas spends most of its time in haploid stage.
Asexual Reproduction. Interior cells of adult Chlamydomonas divides by mitosis producing many cells asexually called
zoospores which are motile and resemble the adult. Since the adult was (n) haploid, the asexually produced offspring will
be haploid or (n). With disintegration of the cell wall, the zoospores are released into the water and some become adult
cells like the parent.
Sexual Reproduction. Conditions are usually unfavorable, Chlamydomonas switches to sexual reproduction. The adult
haploid Chlamydomonas divides repeatedly to produce isogametes (gametes that look alike and are both motile). The
isogametes are released, fuse together by their flagella, fertilization occurs to form a fertilized egg or a diploid (2n)
zygote. Process called isogamy.
Survival and Adaption: A heavy wall forms around the zygote, and it becomes a resistant body able to survive until
conditions are favorable, at which time the zygote germinates and produces four zoospores by meiosis. Chlamydomonas
produces zoospores, or flagellated spores, in both the sexual and asexual life cycle.
Importance of Sexual Reproduction. Sexual reproduction aids the process of evolution because concurrent
recombination of genes may produce a product more suited to the environment than either parent. Two Chlamydomonas
strains fuse their genetic material to form a zygote which is diploid or 2n, having two sets of chromosomes, one set from
one adult strain and one from another strain.
Summary Chlamydomonas is a unicellular green aquatic alga that demonstrates isogamy, a method of sexual
reproduction. It can photosynthesize, store starch, and move through the water, it is motile with its flagella.
Spirogyra-Filamentous Green Algae
Features: Spirogyra is a filamentous form of green algae found in green masses on the surface of ponds and streams. It is
a chain of cells lined up end to end to form a filament. In Spirogyra the chloroplasts are ribbon- like and spiral within the
cell, the chloroplast, which looks like a coiled spring. Embedded within the chloroplast are pyrenoids which store starch
and the chloroplast produces glucose and stores it as starch in the pyrenoids, typical of green land plants, more evidence
for evolutionary relationship between the alga and the green land plants.
Asexual Reproduction: Occurs when a filament is broken into two and each piece begins to produce new cells which
grow into filaments by mitosis.
Sexual Reproduction: Occurs when two adult haploid filaments line up next to one another, and conjugation tubes form
between their respective cells. The contents of the cells of one haploid filament move into the cells of another filament,
forming a 2n zygote. This fusion results in a diploid zygote, the only diploid cell in the life cycle which forms a heavy
wall and as a zygospore remain dormant over the winter until spring when the zygospore undergoes meiosis to produce
new haploid filaments.
Significance: Spirogyra is filamentous, it has a nucleus, chloroplast, pyrenoids and cytoplasm. The conjugation method
of sexual reproduction is unique feature of Spirogyra.
Oedogonium-Filamentous Green Algae
Features: Oedogonium is a filamentous algae in which the cells have cylindrical and netlike chloroplasts. They live in
fresh water and attach to the bottom of the pond by a specialized cell called a holdfast.
Sexual Reproduction: Occurs when an enlarged specialized cell in the adult filament produces an egg protected within a
structure, and other short, disk-like cells (called the antheridia, sing. antheridium) each produce two sperm. The sperm,
which look like small zoospore, escape and swim to an egg a structure called the oogonium. One sperm enters the
oogonium through a funnel end and fertilizes the egg to form a zygote which is deployed (2 sets of chromosomes), the
only diploid structure in the life cycle. The zygote is released and enters a period of dormancy. Upon germination, the
zygote produces 4 zoospores, each of which may grow into a filament. This form of sexual reproduction is called
heterogamy like Volvox. The zygote is the ONLY diploid structure of the Oedogonium life cycle, the adult filamentous
Oedogonium is haploid.
Asexual Reproduction: Vegetative cells may produce a zoospore asexually and this may develop directly into a filament.
Significance: Another form of aquatic green algae, a filamentous form with Heterogamy, the method of sexual
reproduction demonstrated by land plants. The dominant or conspicuous generation is the haploid Oedogonium and the
only diploid structure is a zygote.
Volvox-Colonial Algae
Features. Volvox forms a loose association of cells forming colonies consisting of 500 to 50,000 cells embedded in a
transparent, gelatinous hollow green sphere. The hollow sphere has thousands of cells arranged in a single layer
surrounding a watery interior. Each cell resembles a Chlamydomonas cell.
Evidence for a colonial design. Volvox is a colony with many cells working together in a group. What evidence is their
for this? (a) All of the individual cells inside the sphere work together in a coordinated way; (b) the cells on the outside of
the sphere are motile cells with beating cilia so the colony can move; (c) other cells in the colony has specialized functions
such as reproduction (reproductive cells) where they divide asexually to form a new daughter colony and many other
vegetative cells.
Division of labor. This cell specialization illustrates what we call division of labor where the functions of the colony are
performed by different cells. This is an advance over the unicellular Chlamydomonas and has no division of labor.
Asexual Reproduction: The daughter colony resides for a time within the parent colony. A daughter colony leaves the
parent colony by releasing an enzyme that dissolves away a portion of the matrix of the parent colony, allowing it to
escape and grow into a parent.
Sexual Reproduction: During sexual reproduction the Volvox produces heterogametes by meiosis, a large nonmotile egg
and small flagellated sperm. The motile sperm swims to and fertilizes a nonmotile egg within a protective structure in the
colony, this is isogamy. Upon germination the initial meiotic divisions give rise to one to four haploid (n) zoospores,
which by mitosis form a new colonial, haploid colony.
Significance of Volvox because:
a.
Colonial design as already explained, the “evolutionary bridge” between unicellular form and multicellular form.
b.
Heterogamous. Volvox also demonstrate the evolution of heterogamy, a motile sperm swimming to a enclosed
egg, the method of sexual reproduction found in green multicellular land plants where the egg is protected.
Ulva-A multicellular Green Algae
Form: Ulva (sea Lettuce) is a multicellular marine green alga that grows attached to the rocks in the intertidal pools along
beach areas. There is usually an alternation of similar haploid and diploid generations which have a flat sheet form of only
two cells in thickness. Any cell of the Thallus (leafy body), except those which make up the holdfast that Ulva attaches
itself to rocks, may become fertile and produce gametes or zoospores, depending on the chromosome number of the
thallus.
The life cycle of Ulva is an alternation of generation life cycle. Alternation occurs between a sexual and asexual cycle
stage, a diploid (2n) and haploid (n) generation. The change from the other algae here is that their is an adult form in the
Ulva’s life cycle in both the diploid and haploid generation. This is different from Chlamydomonas, Volvox, spirogyra,
and Oedogonium.
Sexual Reproduction: The sexual cycle starts with the 2n adult Ulva producing haploid isogametes which escape through
a pore in the cell wall. Syngamy or fertilization occurs and a 2n zygote results (isogamy). The diploid zygote germinates
by mitotic division and forms a multicellular Ulva filament. The Ulva is flat and thallus-like and is called the sporophyte
because it produces spores by meiosis.
Asexual Reproduction: Asexual spores are motile zoospores which are haploid or n. They escape into the water and
germinate by mitosis to form the haploid thallus or Ulva called the gametophyte.
Evolutionary Trend: This life cycle is different from Chlamydomonas, Volvox, Spirogyra, and Oedogonium because of
its dominant adult in both the sporophyte and gametophyte generations. It foreshadows what is going to happen on land
because of its multicellular structure and placing cells inside so they will not dry out.
SIGNIFICANCE OF THE GREEN ALGAE
Sexual Reproduction: Was advantageous because it provided these green algae with a means to survive unfavorable
conditions and offspring that had a new combination of genes. The protective coat of the zygote allows it to survive the
winter. Upon germination, the offspring has a new combination of genes that may be more suited to different
environmental conditions. We also note that while some forms carry out isogamy (Chlamydomonas and Ulva) others do
heterogamy (Volvox and Oedogonium).
Dominant generation: Chlamydomonas, Volvox, Oedogonium, and Spirogyra have a dominant haploid generation as an
adult, the zygote undergoes meiosis immediately. In Ulva, the zygote grows into an adult sporophyte generation. This is
also the pattern in land plants.
Body Form: The green alga studied so far demonstrate the evolution of a multicellular green alga (Ulva) from a
unicellular green alga (Chlamydomonas) where all activities were carried out in one cell to a colonial alga (Volvox) where
we saw some division of labor, some cells were for motility and others vegetative inside the colony. Cells within Volvox
(some 50,000) were similar to the vegetative cells of Chlamydomonas and arranged in a single layer in the peripheral
gelatinous matrix. The center of the sphere is filled with water. Cytoplasmic strand connect the individual cells in some
species. The fact that some cells take part in reproduction indicates a degree of cell differentiation in the colony. We have
a multicellular body form in Ulva which is an important form for land plants.
Significance of sexual reproduction in algae.
a.
Brings about change and diversity in offspring.
b.
Foreshadows heterogamy found in green multicellular land plants.
c.
Evolution of multicellular body form (Ulva) from gene shuffling and change.
NAME:
BLOCK
LAB WRITE UP
Your task today, is to observe the following algae species: Chlamydomonas, Oedogonium, Spirogyra, Volvox, and
Ulva. For each of these species you must:
o
View them using a light microscope
o
Draw one of two cells at the most appropriate magnification
o
Answer the questions regarding each algae
o
Calculate:
o
The actual size of the algae or part of it (indicate on picture)
o
The magnification of your drawing compared to the actual size
INRODUCTION & CONCLUSION TO BE WRITTEN ON A SEPARATE SHEET
DRAWING OF CHLAMYDOMONA
OBSERVATIONS:
CALCULATIONS:
Actual Size:
Magnification of drawing:
Magnification of Image :
DRAWING OF SPRIROGYRA
OBSERVATIONS:
CALCULATIONS:
Actual Size:
Magnification of drawing:
Magnification of Image :
DRAWING OF VOLVOX
OBSERVATIONS:
CALCULATIONS:
Actual Size:
Magnification of drawing:
Magnification of Image :
DRAWING OF OEDOGONIUM
OBSERVATIONS:
CALCULATIONS:
Actual Size:
Magnification of drawing:
Magnification of Image :
DRAWING OF ULVA
OBSERVATIONS:
CALCULATIONS:
Actual Size:
Magnification of drawing:
Magnification of Image :
QUESTIONS:
1.
WHAT EVIDENCE DID YOU SEE IN TODAYS LAB THAT DEMONSTRATES THE EVOLUTIONARY TREND
FROM UNICELLULARITY TO MULTICELLULARITY? EXPLAIN YOUR ANSWER AND GIVE EXAMPLES.
2.
ALL OF THE ORGANISMS YOU LOOKED AT IN THIS LAB LIVE IN AQUATIC ENVIRONMENTS. WHAT DO
YOU THINK ARE SOME ADVANTAGES, AND DISADVANTAGES OF LIVING IN AQUATIC
ENVIRONMENTS? (p434-435 in text)
3.
EVOLUTION IS DRIVEN BY SURVIVAL OF THE FITTEST WHERE BY NATURAL SELECTION RESULTS IN
ADNVATAGOUS TRAITS EVOLVING. WHAT DO THINK ARE THE ADVANTAGES TO DEVELOPING
MULTICELLULARITY?