Name_________________________
BOT 101 ALE #6 Sexual life cycles of plants
1.
What is happening in the cell during each phase of the cell cycle?
Interphase:
G1 Growth
S DNA Replication
G2 Growth, preparation for cell division
M phase: Mitosis – division of the nucleus
Cytokinesis – division of the cytoplasm to form 2 cells
2.
Draw a series of cells depicting the stages of mitosis. Label the stages.
Compare your drawings to the drawings of mitosis in your text book or lecture notes
3. What are sister chromatids? How do sister chromatids compare genetically?
Sister chromatids are two molecules of DNA held together at the centromere of one
chromosome. They are genetically identical because one sister chromatid is formed from
the replication of the other chromatid.
4. What are homologous chromosomes?
chromosomes of same size & shape but different genetic origins (one from the “mom
plant,, one from “dad”). Each member of a homologous pair has the same order and
location of genes. However, the two chromosomes are not identical because they can
have slightly different versions of the same gene.
Meiosis
5. a. What is the function of meiosis?
to produce gametes, cells with half the number of chromosomes as their parent
cells. Gametes function in sexual reproduction
b. What kinds of cells are produced by meiosis?_____sex cells (gametes)
c. Are these cells haploid or diploid?
___________________________________haploid___________________
6. Overview of Meiosis…
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a. How do the chromosomes align at metaphase I of meiosis?
With their homologous pairs
b. What separates during anaphase I of meiosis?
Homologous pairs
c. How do the chromosomes align at metaphase II of meiosis?
Individually, randomly
d. What separates during anaphase II of meiosis?
Sister chromatids
e. Are the daughter cells haploid or diploid?
Haploid
7. Compare mitosis and meiosis by completing the table below.
Type of cells involved
Mitosis
All cells of the plant
except those in the
sporangium
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Meiosis
Only the cell of the
sporangium undergo
meiosis, to create spores
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2
4
same
different
diploid
haploid
no
yes
Number of cell divisions involved
Number of daughter cells
How do the daughter cells compare
genetically?
Are the daughter cells diploid (2n) or
haploid (n)?
Involves homologue pairing and cross
over?
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8. Draw and label the generalized diagram of the alternation of generations. Be sure to
label mitosis and meiosis, and indicate which parts of the cycle are haploid and
which are diploid
Item:
Cells:
single
or multi?
#chrom.
sets:
haploid or
diploid?
How form:
mitosis?
meiosis? fert?
What is reproductive job?
spore
Single
Haploid
Meiosis
gametophyte
Multi
Haploid
Mitosis
gamete
Single
Haploid
Mitosis
zygote
Single
Diploid
Fertilization
sporophyte
multi
diploid
mitosis
Divides by mitosis to make the
gametophyte
Divides by mitosis to make
gametes
Are egg and sperm – cells fuse to
form the diploid zygote
Divides by mitosis to create the
sporophyte
Has a region called the
sporangium which divides by
meiosis to make spores
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The moss lifecycle
Step 1. A tiny spore blows in the wind, lands in moist soil, and sprouts into a
leafy plant.
Step 2. At the top of the moss plant, hiding within its leaves, eggs form
within little cups. Neighboring moss plants make sperm inside little sacs.
Step 3. The eggs give off chemicals to beckon the sperm who swim within a
film of rain water.
Step 4. The fertilized egg (zygote) sprouts into a tall stalk, up into the air
currents. At the tip of the stalk is a capsule where spores are made via
meiosis and released into the wind.
B. Moss questions based upon the story above:
1. Does “sprouting” happen via mitosis? yes
2. Are moss gametes (eggs and sperm) made via meiosis as they are in
animals? No, they are made by mitosis
3. The spores are made via meiosis... so are the spores haploid or diploid?
haploid
4. The leafy plants are made from a sprouted spore... so are the leaves
haploid or diploid? haploid
5. How is spore different from a gamete?
Spores are made by meiosis, gametes are made by mitosis. Both spores and
gametes and single-celled and haploid, by spores can grow by mitosis into a
mutlicellular structure (the gametophyte) without fusing to any other cell.
Gametes must fuse together before they can divide by mitosis to make the
sporophyte.
6. How does moss get up onto your roof?
Mosses release their spores into the wind, which travel up to your roof
FERNS ....will represent the SEEDLESS VASCULAR PLANTS
Their story sounds a lot like the moss story... with a few subtle twists.
A. The Fern lifecycle
Step 1. A tiny fern spore blows in the wind, lands in moist soil, and sprouts
into a little heart-shaped flat thing.
Step 2. The heart-shaped thing makes egg cups and sperm sacs on its
surface.
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Step 3. The eggs give off chemicals to beckon the sperm who swim within a
film of rain water (from one “heart” to another).
Step 4. The fertilized egg (zygote) sprouts into a leafy fern plant. On the
surface of the leaves, many spore capsules form. Spores are made via
meiosis and tossed into the wind.
B. Questions based upon the life cycle story
1. Is the flat heart-shaped thing diploid or haploid?
haploid
2. Are the fern leaves haploid or diploid?
diploid
4. Where would you find fern zygotes?
Within the archegonia, which is a part of the fern gametophyte ( the tiny
heart-shaped thing
5. What is the “job” of a fern spore?
To disperse on the wind or water, finding a suitable place to begin growing by
mitosis into a new fern gametophyte.
6. What is the technical name for the heart-shaped thing?
The gametophyte
7. What is the technical name for the stage when ferns have roots, stems,
leaves and spore capsules?
The sporophyte
8. What is the technical name for spore capsules?
Sporangium
PINES will represent the Gymnosperms
The general steps are the same in pines as they are in moss and ferns but
many of the stages are very small and happen inside cones. The scales of the
cones are modified leaves. On the surface of each leaf are sporangia.
A. The Pine Lifecycle
Step 1. Spores are made via meiosis within tiny male cones and tiny female
cones. The spores do not go anywhere.
Step 2. : In the male cones, the spores divide a few times then get coated
with a hard material. They have become pollen grains. They are sperm in a
capsule! They are the male gametophytes. They blow in the wind and the
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male cones shrivel up and fall off. In the female cones’ sporangia, all the
spores die except one. That remaining spore divides many times, making an
egg or two within sacs, surrounded by nutritious tissue.
Step 3. The pollen lands on the female cones (usually before they are even
done making the eggs) and starts growing a tube towards the eggs. The
sperm nucleus slides down the tube and fertilizes the egg.
Step 4. The fertilized egg (zygote) divides to form an embryo surrounded
by nutritious female gametophyte tissue. The sporangium sac hardens into a
seed coat. The seed falls out and grows into a new tree.
B. Questions based upon the life cycle story
1. Why is it adaptive for the sperm to be wrapped in a hard coat and travel
in the air?
It’s wrapped in a hard coat c to protect it from dessication (drying out). It
travels in the air so that the sperm can travel far enough to reach the
female cones of another tree. This means that the trees don’t have to rely
on water for fertilization. The sperm of these trees don’t have flagellated
sperm, like mosses and ferns do.
2. Why is it adaptive for the embryo to be wrapped inside a seed?
When the seed it below the ground, it is covered by soil and so there is not
enough sunlight for photosynthesis. The tissues of the seed will nourish the
germinating plant until it has leaves that can photosynthesize. The tissues
of the seed also prevent the embryo from drying out.
FLOWERING PLANTS
Flower Lifecycle- : Fill in the blanks
Step 1. A plant has matured and formed a young flower.
Step 2. Within the sporangia sacs of the anthers, spores are made via
meiosis___. The spores each divide a few times to form pollen grains (the
male gametophytes).
Step 3. Meanwhile, in the ovules, spores are made via meiosis and only one
survives. The survivor divides three times to make 8 nuclei in communal cell.
One of these is the egg. These 8 nuclei are the female gametophyte______.
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Step 4. Pollination: Pollen lands on the female’s stigma and grows a
pollen____ tube___.
Step 5. Fertilization: the tube reaches the egg, and one sperm cell slides
down the tube and unites with the egg. Then a second sperm slides down
and unites with TWO other female nuclei to make a triploid (3n) cell in a
unique process called “double fertilization______”.
Step 6. The embryo grows. The triploid tissue grows also and is future food
for the baby. It is called “endosperm” and is a milky white fluid. The ovule
wall becomes a seed coat. The ovary (and sometimes other parts like the
receptacle) will mature to become the fruit____.
9. Compare and contrast Monocots & Dicots. What characteristics would you use to
identify a plant as one or the other?
Monocots are defined as having one seed leaf; Dicots have two seed leaves. This
characteristic is impossible to know without dissecting the seed. In order to decide
whether the plant is a monocot or dicot, it may be easier to look at other
characteristics. Monocots typically have parallel leaf veins and flower parts in
threes. Dicots typically have netlike leaf veins and flower parts in fours or fives.
10. Describe the move of plants onto land. What challenges did plants need to
overcome in order to successfully live & reproduce on land? What adaptations
allowed them to overcome these challenges?
Plants evolved from freshwater and marine algae that obtained mutations that
allowed them to live successfully on land. On land, these ancient plants needed to
obtain water (to avoid dessication), protect themselves against UV radiation, and
resist new pathogens and herbivores (much later in time). Plant acquired mutations
that allowed them to successfully photosynthesize (obtain food) and reproduce under
these new environmental conditions. The 5 adaptations that all members of
Kingdom Plantae share include apical meristems, alternation of generations, walled
spores produced in sporangia, multicellular gametangia, and multicellular, dependent
embryos. Additional adaptations that some (most) members of Kingdom Plantae
acquired include, cuticles, roots, shoots, secondary compounds, stomata, lignin in
cell walls, vascular system.
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