Angiosperm reproduction and floral diversification Flashcards
What are flowers?
Reproductive shoots of angiosperm sporophytes
Composed of 4 whorls of modified leaves = floral organs
Determinate shoots
What are the 4 floral organs?
Sepals
Petals
Stamens
Carpels
The evolution of what is a defining feature of angiosperms?
Evolution of the closed carpel
enclosed ovule
What are the 3 variations of ovary positioning?
Hypogynous - above point where sepals + petals join = superior ovary Perigynous - half-superior/half-inferior Epigynous - inferior ovary
What are the 2 types of floral symmetry?
Actinomorphic
= radially symmetrical
Zygomorphic
= bilaterally symmetrical
How do zygomorphic flowers coevolve with their pollinators?
Specialise a petal to provide a landing pad to a specific pollinator
What is the calyx?
What is the corolla?
All the sepals
All the petals
What are the 5 types of flowers?
>Complete = has all 4 floral organs >Incomplete = lacks 1 or more floral organs
>Perfect = hermaphrodite >Imperfect = has either male or female reprod. structures (monoecious + dioecious)
> Inflorescences = clusters of flowers
What does the alternation of generations mean?
Plants have multicellular diploid + haploid phases
Gametophyte produces gametes
Sporophyte produces diploid spores
What is the trend in gametophyte size in evolution?
Reduction in size from moss > ferns > seed plants
What are the key features of the angiosperm life cycle?
Sporophyte = dominant
Gametophytes = reduced + depend of sporophyte for nutrients
Characterised by 3 Fs:
flowers
double fertilisation
fruits
What does double fertilisation produce?
Endosperm
Describe the development of the male gametophyte in pollen grain
Microsporangium contains microsporocytes
-> 4 microspores via meiosis
(joined in a tetrad)
-> male gametophyte via mitosis
(= 3 sperm cells + 1 vegetative cell)
Describe the development of the female gametophyte
Megaspore undergoes meiosis
-> 3 die + 1 megaspore survives
-> female gametophyte via mitosis
(7 cells + 8 nuclei)
What are the 3 pollination syndromes?
Entomophily = insect
Anemophily = wind
Ornithophily = bird
What are the features of entomophily?
> bright petals
strong sweet smell
nectar-producing glands
nectar guides - lead insects to nectar
What are the features of anemophily?
> large stigmas outside flower
little-no smell
large non-sticky pollen
no showy petals
What are the features of ornithophily?
> long tube-shaped flowers
normally bright red/yellow flowers
no smell
nectar
How do pollen tubes grow towards the ovule in order to carry out double fertilisation?
Specific chemical messengers guide the pollen to allow efficient delivery of non-motile sperm to egg
What happens after double fertilisation?
Polarised growth of the embryo within walls of the ovule become the seed
Each ovule develops into a seed
Ovary develops into a fruit
What encloses the embryo + seed?
A hard, protective seed coat
What is the benefit of seed dormancy?
Increases chances of seed germinating at the appropriate time
-> increases chance of survival
What inhibits seed germination?
ABA
What is the purpose of fruit?
Protects seeds
Aids seed dispersal by mitotic + abiotic vectors
What does the diversity of form of fruit depend on?
Shape of ovary from which it’s formed
Extent to which ovary wall (pericarp) expands
What are the 3 layers of pericarp?
Exocarp
Endocarp
Mesocarp
What are the 2 main categories of fruit?
Dry - fruit dries at maturity
Fleshy - ovary becomes thick, soft + sweet at maturity
How can fruits be classified by their type of development?
Simple - single or several fused carpels from 1 flower
Aggregate - single flower w/ multiple separate carpels
Multiple - inflorescence
Accessory fruit - contains other floral parts in addition to ovaries
What are the 4 fruit dispersal mechanisms?
Hydrochory = water
Anemochory = wind
Zoochory = animals
Autochory = by itself e.g. exploding
When is asexual reproduction beneficial?
Why is this?
In a stable environment
Clones are vulnerable to local extinction if environment changes or disease
What does sexual reproduction enable?
Generate genetic variation that makes evolutionary adaptation possible
What are the 3 mechanisms of asexual reproduction?
Fragmentation
Root suckering
Apomixis (agamospermy)
What is fragmentation?
Separation of a parent plant into parts that develop into whole plants
what is root suckering?
Developing adventitious shoots from the root system
-> gives rise to separate plants
What is apomixis?
Asxual production of seeds from a diploid cell
no fusion of sperm + egg
Why does the hermaphrodite flower create an issue?
Potential for inbreeding depression
What are the 3 developmental mechanisms for preventing self-fertilisation?
Dioecy = separate sexes in separate plants
Monoecy = separate sexes in separate flowers on same plant
Dichogamy = sequential hermaphroditism
= stamens + carpels mature at diff times
What is the molecular genetic mechanism for preventing self-fertilisation?
Self-incompatibility
= plant recognises + rejects own pollen
Why are angiosperms so diverse?
> evolution of closed carpel + hermaphrodite flower
-> allowed for diversification in mating systems
> coevolution w/ pollinators + dispersers
> control of mating partner
Why are angiosperms so successful?
> evolution of carpel = protection of ovules + developing embryo
> double fertilisation
-> production of endosperm = food reserve for embryo
> hermaphrodite flower
> adaptations that facilitate genetic diversity via outbreeding
Describe the taxonomy of angiosperms
Floral characteristics take priority over vegetative characteristics when allocating to genera or families
