Lecture 8 Flowering Plants Flashcards
Summary of heterosporous plants
Heterosporous plants evolved from homosporous ancestors
Sporophyte became larger than gametophyte and nutritionally independent
Gametophyte reduced to a few cells produced in specialised structures within flower
Pollen becomes water independent
Seeds offer long term protection for embryonic sporophyte
Plant timeline
Gymnosperms dominated landscape for 200 MY limited by dependence on wind pollination - animal pollinators more efficient
Permian mass extinction ginkotype die out and conifers take over
Cretaceous angiosperms evolve
Mass extinction of mesozoic period provides space for flowering plants to evolve further
Angiosperms took advantage of surrounding animals that eat fruit and pollinators to spread and reproduce
Angiosperms
Produce flowers and fruit
Male gametophyte is pollen grains
Female gametophyte embryo sac in ovule sporophyte tissue
Double fertilisation - triploid nutritive tissue endosperm unique to angiosperms
Ovule and seed enclosed by carpal (modified leaf that bears the ovule) providing additional protection
Angiosperms also have specialised vessels and fibres in xylem tissue and companion cells in phloem tissue
Angiosperm lifecycle
1) flower:
a) ovary contains ovule containing megasporocyte(2n) that divides by meiosis producing four megaspores (eggs- n) of which only one survives and the other 3 degenerate
b) anther contains microsporocytes that divide by meiosis to form microspores (pollen, n) pollen divides by mitosis forming tube cell and generative cell
2) a) embryo sac develops after surviving megaspore undergoes 3 mitotic divisionS creating 8 haploid cells - 7 take part in double fertilisation and one dissolves where pollen tube joins.
b) pollen grain transferred to stigma and pollen tubule develops towards embryo sac. Generative cell splits mitotically to form 2 haploid sperm cells and pollen tube joins embryo sac
3) Double fertilisation: sperm cells released from pollen tubule. One forms zygote (2n) and other joins the two polar nuclei forming an endosperm (3n) nucleus.
4) endosperm develops to provide nutritional tissue for the embryo. The surrounding ovary develops into fruit
Complete flower
4 concentric groups of organs
Sepals - enclose and protect sexual organs collectively known as the calyx
Petals - aka corolla attract insects w/colours and markings
Stamens - anthers male produce pollen
Carpel- female part style and stigma with ovary at base
Note: multi carpal flowers like buttercup are of a very early group of plants modern flowers have one ovary
Monoecious plants
Have separate male and female flowers e.g. alnus glutinosa - catkins or Holly plants - only females bear berries
Evolution of carpals
Proposed evolution of carpals:
Modified leaf bearing ovules
Leaf edges curl in and fuse
Fused carpal
3 carpal fused together to form multi chamber ovary
Evolution of stamens
Austrobaileya - modified leaf w/sporangia
Magnolia - reduced width of leaf w/sporangia
Lily - anther on filament - leaf reduced until only microsporangia remained
Vascular tissue in angiosperms: xylem
Xylem contains:
Tracheids - single cell wide - small and narrow 1mm length also found in gymnosperms and ferns connected laterally by porous primary cell walls. Being short and narrow help prevent air embolism due to water adhesion.
Vessels - made up of groups of cells large and wide one vessel cell can be 10cm. Connected end to end by perforated end walls that allow efficient water conduction.
Both are tubular with perforated/ absent end walls connecting them. Porous primary cell wall separates adjacent tracheid and vessel elements. End walls of vessel cells disappeared. Conduct water along stem and provide mechanical support.
Vascular tissue in angiosperms: phloem
Sieve tubes are modified plastixs w/lateral sieve areas (pored) sieve plates as end walls also have pores - transport nutrients - primarily sucrose. contain smooth ER, p-protein (phloem specific - obscure function) Have no nuclei are controlled by companion cells.
Companion cells (only in angiosperms)
Contain nucleus, mitochondria, vacuole, chloroplasts have branched plasmodesmata linking to sieve tubes
Amborella trichopoda
Last member of it’s clade (1 specie of 1 family) fleshy waxy flowers that are flat to collect pollen on its surface. The only angiosperm that has only tracheids and no vessels
Basal angiosperm
Water lily, nymphea species - not to be confused with lotus (clear from seed heads)
Core angiosperm - magnolids
Magnolids, largest clade apart from monocots and eudicots 8.5 thousand species including avocado and bay
Core angiosperm - monocots
Flower parts in multiples of 3. Includes all grasses and all starch food crops - wheat oats and rice
From left to lower right: Endosperm, cotyledon, epicotyl, hypocotyl, radicle
Seed coat fused to ovary wall
Hypocotyl sprouts up radicle pushes down. Epicotyl emerges from coleoptile - first leaf
Monocot pollen one pore
Leaf venation: veins parallel 🌾
Stem: complex vasc bundle
Root: fibrous
Flower: multiples of 3
Core angiosperm - eudicot
Eudicots, flower parts in multiples of 5 or larger. No bilateral symmetry e.g. geranium, pea, monkshood (buttercup family)
Two cotyledons, radicle sprouts down forming root, hypocotyl sprouts up, cotyledons shed to release first two leaves
Leaf - net-like veins 🍁
Stem - vasc bundle in ring formation
Root: usually taproot
Flower: petals in multiples of 4 or 5 🌺
