Human Factors of XR: Using Human Factors to Design XR Systems
Chap. 4 plant reproduction final
1. Chapter 4.
Plant Reproduction
KEY CONCEPT
All plants alternate between two phases in their life
cycles.
AP Biology 2005-2006
2. Plant life cycles alternate between
producing spores and gametes.
A two-phase life cycle is called alternation of
generations.
haploid phase
diploid phase
alternates SPOROPHYTE
PHASE
between fertilization
the two GAMETOPHYTE
meiosis
PHASE
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3. Animal vs. Plant life cycle
Animal Plant
multicellular multicellular
sporophyte
2n
2n
gametes spores
1n 2n
unicellular multicellular
gametes gametophyte
1n 1n
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alternation of generations
6. Gametophytes of seed plants
Gymnosperm Angiosperm
male gametophyte male gametophyte
pollen in male cone pollen in anthers of
flower
female gametophyte female gametophyte
develops in female develops in ovaries
cone of flower
seed seed
naked in cone protected in ovary
ovary wall can
develop into fruit
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7. The sporophyte is the dominant phase for
seed plants.
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8. Gymnosperm life cycle
female
gametophyte
in cone
male
gametophyte
in pollen
sporophyte
in seed
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9. Angiosperm life cycle
male
gametophyte
in pollen
female
gametophyte
in ovary
sporophyte
in seed
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10. Reproduction in angiosperm
Sporophyte plant produces unique reproductive
structure = the flower
male gametophyte = pollen grain
develop within anthers of flower
female gametophyte = embryo sac
develop within ovaries of flower
pollination by wind or animals brings pollen grain to
female gametophyte
fertilization takes place within ovary
double fertilization = embryo & endosperm
seeds contain sporophyte embryo
development of seeds in ovary
ovary develops into fruit around the seed
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14. Parts of flower
Male
stamens = male reproductive organs
stamens have stalks (filament) &
terminal anthers which carry pollen
sacs
pollen sacs produce pollen
pollen grain = gametophyte
sperm-producing structure
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15. Parts of flower
Female
carpels = female reproductive organs
ovary at the base
slender neck = style
within the ovary are 1 or more ovules
within ovules are embryo sacs
female gametophyte = embryo sac
egg-producing structure
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16. Fertilization in Angiosperms
When pollen grain lands on stigma it
begins to grow pollen tube.
Nucleus within pollen grain divides and
forms 2 sperm nuclei
Pollen tube contains tube nucleus and
2 sperm nuclei
Pollen tube grows into style and
eventually reaches ovary and enters
ovule
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17. Fertilization in Angiosperms
Inside embryo sac, two fertilizations
occur
One sperm nuclei fuses with egg nucleus
to produce diploid zygote – grows into
plant embryo
Second sperm nucleus fuses with two
polar nuclei to form triploid (3N) cell –
food tissue known as endosperm.
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19. Fertilization (recap)
Pollination
pollen released from anthers is carried by wind
or animals to land on stigma
pollen grain produces a pollen tube
pollen tube grows down style into ovary & discharges
2 sperm into the embryo sac
1 sperm fertilizes egg = zygote
zygote develops into embryo
ovule develops into a seed
ovary develops into a fruit containing
1 or more seeds
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21. Self-pollination
Why?
Guarantees seeds (no need for mates or
pollinators)
May save resources if flowers are smaller
Maximizes transmission of own genes
Why not?
Inbreeding depression - short-term cost
Loss of genetic diversity - long-term cost
An evolutionary dead end? - very long-term
cost
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22. Preventing self-pollination
Various mechanisms
stamens & carpels may mature at different times
arranged so that animal pollinator won’t transfer
pollen from anthers to stigma of same flower
biochemical self-incompatibility = block pollen
tube growth
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23. Fertilization takes place within the
flower.
Male gametophytes, or pollen grains, are produced in
the anthers.
– male spores produced in
anthers by meiosis
– each spore divides by
mitosis to form two
haploid cells
– two cells form a
single pollen grain
pollen grain
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24. One female gametophyte can form in each ovule of a
flower’s ovary.
four female spores produced in ovule by
meiosis
one spore develops into female
gametophyte
female gametophyte contains seven
cells
one cell has two nuclei, or polar nuclei
one cell will develop into an egg
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25. Pollination occurs when a pollen grain lands
on a stigma.
pollen tube
sperm
stigma
– one cell from pollen grain forms pollen tube
– other cell forms two sperm that travel down tube
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26. Flowering plants go through the process of
double fertilization.
female
gametophyte
egg
sperm
polar nuclei
ovule
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27. Flowering plants go through the process of double
fertilization.
endosperm
– one sperm fertilizes
the egg seed coat
– other sperm unites
with polar nuclei,
forming endosperm
– endosperm provides
food supply for
embryo
embryo
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28. Each ovule becomes a seed.
The surrounding ovary grows into a fruit.
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29. Fertilization in flowering
plants
Double fertilization
2 sperm from pollen
1 sperm fertilizes
egg = diploid zygote
1 sperm fuses with
2 polar nuclei to
form 3n endosperm
endosperm = food
tissue in seed
coconut milk
grains
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32. Fruit
Fruit is a mature ovary
seeds develop from ovules
wall of ovary thickens to form fruit
fruits protect dormant seeds &
aid in their dispersal
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34. Seed dispersal
• Why disperse?
• sample more (better?) sites for
germination/growth
• avoid predation or disease
• avoid competition
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35. Seed dispersal
Plants produce enormous numbers of seeds to
compensate for low survival rate
a lot of genetic variation for natural selection to screen
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39. Dormancy
Metabolism falls
Number of organelles per cell falls
Dehydration – water content falls
Vacuoles in cells deflate
Food reserves become dense
crystalline bodies
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40. Maintaining dormancy
Physical barriers
The seed coat (testa) is waxy =
waterproof and impermeable to oxygen
Physical state – dehydrated
Chemical inhibitors present e.g. salts,
mustard oils, organic acids, alkaloids
Growth promoters absent
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41. Seed viability
Viability: When a seed is capable of
germinating after all the necessary
environmental conditions are met.
Average life span of a seed 10 to 15 years.
Some are very short-lived e.g. willow (< 1
week)
Some are very long-lived e.g. mimosa 221
years
Conditions are very important for longevity
Cold, dry, anaerobic conditions
These are the conditions which are
maintained in seed banks
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42. Germination: The breaking of dormancy
The growth of the embryo and its penetration of the seed
coat
Break down of barriers
Abrasion of seed coat
(soil particles)
Decomposition of seed
coat (soil microbes, gut
enzymes)
Cracking of seed coat Change in physical
(fire) state - rehydration
Destruction and dilution
of inhibitors
Light, temperature, water
Production of growth
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43. Seeds begin to grow when
environmental conditions are favorable.
Seed dormancy is a state in which the
embryo has stopped growing.
– Dormancy may end
when conditions
are favorable.
– While dormant,
embryo can
withstand extreme
conditions.
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45. Germination begins the growth of an embryo
into a seedling.
– water causes seed to swell and crack coat
– embryonic root, radicle, is first to emerge
– water activates enzymes that help send sugars to
embryo
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46. Germination begins the growth of an
embryo into a seedling.
water causes seed to swell and crack coat
embryonic root, radicle, is first to emerge
water activates enzymes that help send
sugars to embryo
– embryonic shoot, plumule, emerges next
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47. Germination begins the growth of an
embryo into a seedling.
water causes seed to swell and crack coat
embryonic root, radicle, is first to emerge
water activates enzymes that help send
sugars to embryo
embryonic shoot, plumule, emerges next
– leaves emerge last
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49. Germination
STAGE EVENTS
PREGERMINATION (a) Rehydration – imbibition of water.
(b) RNA & protein synthesis stimulated.
(c) Increased metabolism – increased respiration.
(d) Hydrolysis (digestion) of food reserves by
enzymes.
(e) Changes in cell ultra structure.
(f) Induction of cell division & cell growth.
GERMINATION (a) Rupture of seed coat.
• Emergence of seedling, usually radicle first.
POST GERMINATION (a) Controlled growth of root and shoot axis.
(b) Controlled transport of materials from food stores
to growing axis.
(c) Senescence (aging) of food storage tissues.
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