chapter 38: angiosperm reproduction Flashcards
How is a plant cycle characterized?
Alternation between sporophyte (spore-producing) and gametophyte (gamete-producing)
What does the angiosperm lifecycle entitle?
- Flowers
- Double fertilization
- Fruits
What are flowers?
They are reproductive shoots of angiosperm attached at receptacle.
What are the four floral organs?
- carpels
- stamens
- petals
- sepals
What is a pistil?
group of fused carpels
What is the anther?
Has pollen sacs that produce pollen
What is the difference between a simple pistil and a compound pistil?
simple: unfused carpels
compound: fused carpels
What is the difference between complete and incomplete flowers?
complete flowers have all four floral organs while incomplete flowers lack 1 or more organ (usually stamen or carpel)
What are a cluster of flowers called?
Inflorescence
What is pollination?
transfer of pollen from an anther to a stigma.
When landed, pollen grain produces pollen tube, grows down to ovary and discharges two sperm cells.
What are the main methods of pollination?
- Animals (bees- 65% of all flowering plants are pollinated by insects)
- Wind (abiotic pollination (20% of angiosperms)
- Water
What is coevolution?
Joint evolution of interacting species in response to selection imposed by each other.
What is the male gametophytes mechanism?
- pollen develops from microspore in microsporangia (pollen sac)
- microspore undergoes mitosis, producing
i. generative cell
ii. tube cell
What is the female gametophytes mechanism?
- embryo sac develops within ovule
- In an ovule, 2 integuments surrond a megasporangium
- One cell undergoes meiosis, producing 4 megaspores, where only 1 survives
- Megaspore divides without cytokinesis, producing 1 large cell with 8 nuclei
- This cell is partitioned into embryo sac
What does a pollen grain consist of?
two-celled male gametophytes and spore wall
What is fertilization
fusion of gametes occurs after the two sperm reach female gametophyte
What is an endosperm?
One sperm fertilizes the egg and the other combines with the two polar nuclei
Why is double fertilization crutial?
Ensures endosperm only develops in ovules containing fertilized eggs
What happens after double fertilization?
each ovule develops into a seed
What does the ovary develop into?
A fruit, enclosing the seeds
What happens when seed germinates?
Embryo develops into a new sporophyte
How does endosperm development happen?
It precedes embryo development, stores nutrients used by seedling.
What happens during embryo development?
the first miotic division of zygote splits fertilized egg into
1. basal cell: that produces multicellular suspensor (anchors embryo to parent plant)
- terminal cell: gives rise to most of embryo
What is the structure of a mature seed?
embryo and food supply enclosed by hard protective seed coat, with cotyledon inside
What is a cotyledon?
seed leaf that retains food in their endosperm and absorb nutrients from endosperm to transfer during germination.
monocots: have 1 cotyledon
eudicots: have 2 cotyledons
What is the embryonic axis called?
hypocotyl and it terminates in the radicle.
What is a scutellum?
special cotyledon in grasses (maize and wheat)
Why is seed dormancy important?
It increases the chances germination occurs at a time/place most advantageous to seedling.
What breaks seed dormancy?
Environmental cues, like temperature changes and lighting changes
What does germination depend on?
Inhibition, which is the uptake of water due to low water potential of a dry seed.
What is the seeding development of the eudicot seed germination?
- the hook forms in hypocotyl the growth then pushes hook above ground.
- light causes hook to straighten, pulling cotyledons and shoot tip up.
What is the seeding development of the monocot seed germination?
- coleoptile pushes through soil, creating tunnel for shoot tip.
What is the development of flowering?
- germinated seed starts to photosynthesize
- resources are devoted to stem, leaves and roots
- flowers are synchronized to appear to promote outbreeding by environmental cues and internal signals.
What is a fruit?
mature ovary of a flower
It protects enclosed seeds and helps seed dispersal
What are the 4 different types of fruits?
- Simple fruits: develop from single/several fused carpels
ex: pea flower and pea fruit - Aggregate fruits: result from single flower with multiple separate carpels
ex: raspberry flower and fruit - Multiple fruits: develop from a group of flowers called an inflorescence
ex: pineapple inflorescence and fruit - Accessory fruits: contains other floral parts in addition to ovaries
ex: apple flower and fruit
What are the two types of reproduction?
- sexual reproduction: offspring that are genetically different from parents
- asexual reproduction: results in clone of genetically identical organisms.
What is fragmentation?
The seperation of parent plant into parts that develop into whole plants
What is apomixis?
asexual production of seeds from a diploid cell (without fertilization)
What are the advantages and disadvantages of asexual reproduction?
Advantages:
1. vegetative reproduction: progeny arises from mature vegetative fragments.
2. stable environment, gives a beneficial and successful asexual reproduction.
Disadvantages:
1. environmental change causes vulnerability of a clone of plants to local extinction.
What are the advantages and disadvantages of sexual reproduction?
Advantages:
1. generates genetic variation making evolutionary adaptation possible
2. some flowers self-fertilize; ensuring every ovule will develop into a seed
3. mechanisms evolved to prevent selfing
Disadvantages:
1. only fraction of seedlings survive
What are the mechanisms that prevent self-fertilization?
- Dioecious species have staminate and carpellate flowers on separate plants.
- Some arrange so that stamen and carpels mature at different times
- Self-incompatibility: plants ability to reject its own pollen. (recognition of self blocks pollen tube growth.
