Download Reproduction with Cones and Flowers

Reproduction with Cones and
Flowers
Chapter 22
Alternation of Generations
All plants have a diploid sporophyte
generation and a haploid gametophyte
generation
 Gametophyte plants produce sperm and
eggs
 Fertilization begins the sporophyte
generation

Generations cont.
Actual plant is the diploid sporophyte
generation
 Gametophytes are found in cones or flowers

Pollen cones and seed cones

Pollen cones (male) produce male
gametophytes or pollen grains
– One haploid nuclei will develop into 2 sperm

Seed cones (female) produce female
gametophytes contained in the ovules
– Each ovule contains a few eggs for fertilization
Pollination
Gymnosperm life cycle takes 2 years for
completion
 Male cones release pollen which is carried
by wind to female cones

Fertilization and development
Pollen grains stuck to female cones will
develop a pollen tube containing the 2
sperm
 One sperm disintegrates, the other fertilizes
the egg to make a diploid zygote
 Zygote grows into an embryo which is
enclosed in a seed

Flower structure
Flowers are reproductive structures
 Have four parts

–
–
–
–
Sepals
Petals
Stamens
Carpels (pistils)
Sepals and petals

Sepals
– Outermost circle of parts (green)
– Protect the bud before it opens

Petals
– Usually brightly colored
– Found inside the sepals
– Attract pollinators
Stamens and carpels

Stamen
– Filament-long, thin stalk that supports anther
– Anther-sac at end of filament that contains pollen
grains

Carpel (pistils)
– Ovary-broad base containing one or more ovules
– Style-narrow stalk extending from top of ovary
– Stigma-sticky section on top of style that collects pollen
Complete and incomplete flowers

Complete flowers
– Contain all flower parts: sepals, petals, stamen,
carpel

Incomplete flowers
– Missing one or more flower parts
– Often seen in plants that produce separate male
and female plants
– Or in plants that have separate male and female
flowers (on same plant)
Angiosperm life cycle
Flowers are produced
 Meiosis occurs in the anther to produce
pollen grains
 Meiosis occurs in the ovary to produce the
embryo sac which contains the egg and
endosperm nuclei

Pollination
Pollen picked up by pollinator and carried
to stigma
 Some wind pollinated
 More efficient pollination by insects or
animals

Fertilization
Once pollen reaches a stigma, pollen tube
develops and grows into the ovule
 2 sperm nuclei develop
 Double fertilization occurs

– One sperm fertilizes the egg to make the zygote
– One sperm fertilizes the endosperm to make a
triploid cell or endosperm (food for the
embryo)
Seed development
After fertilization, nutrients flow into flower
tissue to support development of embryo
and seed
 Ovary walls thicken to make fruit to protect
the seeds
 Ovule toughens to become seed coat
 FRUIT-is any seed enclosed within the
embryo wall; includes common fruits,
vegetables, nuts

Seed dispersal

Animals
– Seeds usually found in fleshy fruits; can pass
through digestive tracts unharmed
– Deposited in new areas with animal feces

Wind and water
– Usually light weight seeds
– Can float on air currents or in water
– Carried to far places or remote places (islands)
Seed dormancy
Embryo is alive but not growing
 Length of dormancy varies in each plant
 Allows for long-distance dispersal
 Environmental factors cause seeds to end
dormancy and germinate

Seed germination
Early growth stage of embryo
 Seeds must absorb water to crack seed coat
 Root emerges first
 Shoots emerge next

– Can be protected by a sheath (monocots)
– Can be protected by the cotyledons or a “shoot
arch” (dicots)
Vegetative reproduction
Asexual form of reproduction
 Produce many plants from horizontal stems
(stolons), plantlets, or underground roots
 No pollination or seeds
 New plants are genetically identical to
parent plant

Plant propagation
Use cuttings or grafting or budding from
original plant to produce offspring from
seedless plants
 Avoids genetic variation
 Preserves wanted characteristics

Cuttings
Pieces of stem with buds containing
meristematic tissue
 Stem is partially buried in soil
 Usually use rooting powders to stimulate
root growth

Grafting and budding

Grafting
– Plants with poor roots grown on plants with
strong roots
– Stem is cut (scion) and attached to another plant
(stock)
– Words bests when plants are dormant
– Vascular tissues of scion / stock must connect

Budding
– Using buds for scions instead of stems
Plant hormones and responses

Hormone- chemical messenger that
stimulates or suppresses activity of cells in
another area
– Released in response to environmental ques
– Released in response to internal changes of the
plant as part of the life cycle
Gibberellins
Hormones that produce dramatic increase in
size
 End seed dormancy
 Start germination
 Promote rapid growth of the seedling
 Increase the size of fruits
 Elongate stems/stalks

Ethylene
Hormone that causes ripening
 Naturally produced by fruits

Cytokinins
Hormones that stimulate cytokinesis (final
part of cell division)
 Produced in growing roots and developing
seeds and fruits
 Involved in the “width” growth or lateral
growth of stems and branches
 Slows the aging process of plant organs

Auxins
Hormones involved in lengthening plant
cells of the apical meristem
 Stimulate growth of primary stem
 Prevents growth of new branches
 Prevent root growth

Phototropism

Tendency of a plant to grow toward light
Thigmotropism

Response to touch
– Coiling around trellises or other stems when in
contact
– Curling up when touched by other organisms
Gravitropism
Positive - is growing down toward gravity
(roots, stimulated by low levels of auxins)
 Negative – growing up away from gravity
(stems stimulated by high levels of auxins)

Photoperiodism
Plant responses to changing lengths of
day/night
 Longer days trigger flowering
 Shorter days trigger change in leaf colors
and dropping of leaves in deciduous plants
