ch. 38 Flashcards
how to flowers reproduce with physically distant members of their own species?
insect
- Rhizanthese flower emits foul odor that attracts female blowflies to lay eggs on flower and deposit sticky pollen grains in process - pollinator doesn’t benefit, no food for hatched larva
how to most angiosperms lure insects
with nectar or pollen
mutualistic associations
both plant and pollinator benefit
symbiotic
living together
angiosperm reproduction is characterized by:
- flowers
- double fertilization
- fruit
flowers
reproductive shoots of angiosperm sporophyte
where do flowers attach to stem
receptacle
4 floral organs of flowers
- carpels - sporophyll
- stamens - sporophyll
- petals - sterile modified leaves
- sepals - sterile modified leaves
carpel
megapsporophyll with long style and sticky stigma to capture pollen
- base of style: ovary with 1+ ovules
what do fertilized ovules produce
seeds
pistil
single carpel or group of fused carpels
stamen
microsporophyll
- filament topped by an anther
- anther contains microsporangia (pollen sacs) that produce pollen
sepals
structures that resemble leaves
- enclose/protect unopened floral buds
petals
typically brightly colored to attract pollinators
complete flowers
contain all 4 floral organs
incomplete flowers
lack 1 or more floral organs
- petals or stamens
sterile flowers
lack stamens and carpels
unisexual flowers
lack either stamen or carpel
inflorescences
clusters of flowers
pollination
transfer of pollen from anthers to stigma
how can pollination occur?
wind, water, animals
what do most angiosperm species depend on for pollination?
animal pollinators
wind-pollinated species
- produced large amounts of pollen
- 20% of angiosperms
- grasses and many trees
- small, inconspicuous flowers that lack nectar/scent
pollination by bees
- 65% of angiosperms require insects, bees most important
- brightly-colored flowers w/ sweet fragrance
- nectar guides - UV markings that direct bees/insects to nectar-producing glands
pollination by moths/butterflies
- flowers have sweet fragrances
- butterfly flowers: brightly colored
- moth flowers: white or yellow
pollination by bats
- flowers are light and aromatic
pollination by flies
- flowers look/smell like rotten meat
pollination by bids
- flowers large and bright red/yellow, have little odor, produce large quantities of nectar
- petals often fused into floral tube
what does angiosperm life cycle include
- gametophyte development
- sperm delivery by pollen tubes
- double fertilization
- seed development
androecium
all stamens of flower
gynoecium
female part of flower, consisting of. one or more carpels (pistil)
where does the embryo sac develop
(female gametophyte) within ovule
what is in an ovule
2 integuments surround a megasporangium, except at micropyle
What happens to the four megaspores in the ovule?
- only 1 survives
- divides w/o cytokinesis to produce 1 large cell w/ 8 haploid nuclei
- cell is partitioned into multicellular female gametophyte (embryo sac)
what cells does the megaspore form
- 3 antipodal cells
- 2 polar nuclei in central cell
- 2 synergids
- 1 egg
what happens to the microspores
each undergoes mitosis to produce 2 cells: generative and tube cell
pollen grain composition
2-celled male gametophyte and spore wall
how many sperm does the pollen tube discharge into the ovary
2
what happens during fertilization
- 1 sperm fertilizes egg
- 1 sperm combines w/ 2 polar nuclei to give rise to triploid food-storing endosperm
what does double fertilization ensure
that the endosperm only develops in ovules containing fertilized eggs
what happens after double fertilization
- each ovule develops into a seed
- ovary develops into fruit enclosing the seed
- when seed germinates, embryo develops into new sporophyte
what does a mature seed consist of
dormant embryo surrounded by stores food and protective layers
does endosperm develop before or after embryo development
before
what does the endosperm store
nutrients that can be used by seedling
first mitotic division of the zygote
asymmetrical, splits the fertilized egg into a basal cell and terminal cell
basal cell of embryo
produces suspensor which anchors embryo to parent plant and aids in nutrient transfer to embryo
terminal cell of embryo
gives rise to most of the embryo
what encloses the embryo and its food supply?
hard, protective seed coat
what happens after the seed coat forms
seed dehydrates and enters a state of dormancy
water composition of mature seed
5-15% water
embryo in eudicots (like common garden bean)
consists of embryonic axis attached to 2 fleshy cotyledons
- embryonic axis below cotyledons: hypocotyl, terminates in radicle
- above cotyledons: epicotyl
what does the plumule comprise
epicotyl, young leaves, shoot apical meristem
monocot embryo
- 1 cotyledon
scutellum
special cotyledon in grasses (maize/wheat)
2 sheaths that enclose embryo of a grass seed
- coleoptile - covers young shoot
- coleorhiza - covers young root
what does seed dormancy increase the chances of
germination occurring at time and place most advantageous to seedling
what does the breaking of seed dormancy require
specific environmental cute
- temperature, lighting changes
how long do seeds remain viable?
- year or two, days, or centuries
what is seed germination followed by
growth of stems, leaves, roots, and flowering
imbibition
uptake of water due to low water potential of the dry seed
- germination depends on it
what emerges from the seed first?
radicle (embryonic root)
- developing root system anchors the plant and provides water for cell expansion
- then shoot tip breaks through soil surface
hook in eudicots
- hook forms in hypocotyl and growth pushes hook above ground
- light causes hook to straighten and pull cotyledons and shoot tip up
how does shoot tip grow through seed in some monocots
- coleoptile pushes up through soil and creates tunnel for shoot tip to growth through
why are flowers of certain species synchronized to appear at a specific time of year?
to promote outbreeding
what is flowering triggered by
combination of environmental cues and internal signals
function of fruit
encloses seeds and aids in seed dispersal by wind or animals
dry fruit
soybean pods
fleshy fruit
grapes
different developmental classifications of fruits
- simple
- aggregate
- multiple
- accessory
simple fruits
develop from single/several fused carpels
aggregate fruits
single flower with multiple separate carpels
multiple fruits
develop from group of flowers (inflorescence)
accessory fruits
contain other floral parts in addition to ovaries
how are fruits dispersed
wind, water, animals
- ensures seeds germinate away from competitive influence of parent plant
asexual reproduction
produces offspring without fusion of egg and sperm
offspring of asexual reproduction
clone of parent
where is asexual reproduction common?
in angiosperms and other plants
methods of asexual reproduction
- fragmentation
- parent root system gives rise to adventitious shoots that become separate shoot systems
fragmentation
separation of parent plant into parts that develop whole plants
apomixis
asexual production of seeds from a diploid cell
what is asexual reproduction also called
vegetative reproduction - progeny arise from mature vegetative fragments
- progeny more resilient than seedlings produced by sexual reproduction
self-fertilize
some flowers self-fertilize to ensure that every ovule will develop into a seed - reduces genetic diversity
mechanisms to prevent selfing
- dioecious
- stamens/carpels that mature at different times
- different spacial arrangements
- self-incompatibility
dioecious species
staminate flowers (lacking carpels) and carpellate flowers (lacking stamens) on separate plants
self-incompability
plant rejects its own pollen
what is recognition of self pollen based on?
S genes
- some plants reject pollen that has an S-gene matching an allele in the stigma cells
