2 ... 9 - Alternation of generation / early plant development Flashcards
Percentage of plant species classified as angiosperms?
75 - 80%
Define angiosperms.
Flowering plants that produce seeds enclosed in a fruit
Define flower
a determinate shoot of the sporophyte bearing modified leaves for reproduction
Angiosperms are divided into what groups, based largely on what?
Two groups, based on cotyledon number:
- Monocots - one
- Eudicots - two
Five key differences between monocots and eudicots?
- Embryos
- Leaf venation
- Stems
- Roots
- Flowers
5 key characteristics of monocots
- One cotyledon
- Parallel venation
- Complex arrangement of vascular bundles
- Fibrous root system
- Floral parts in multiples of three
5 key characteristics of eudicots
- Two cotyledons
- Netlike venation
- Ring arrangment of vascular bundles
- Taproot present in root system
- Floral parts in multiples of four or five
Briefly decribe alternation of generations.
Sporophyte generation (2n- diploid) ALTERNATES with gametophyte generation (1n- haploid).
Gametophyte generation produces sperm/eggs… haploid sperm + haploid egg = 2n zygote… zygote begins sporophyte generation.
Reproduction in angiosperms takes place in …
the flower!
Male gametophyte development involves…
male gametophyte develops in the anther.
Spores -> meiosis -> haploid spores become single pollen grains.
Female gametophyte development involves…
female gametophyte developes in the ovules (inside ovary).
embryo sac (contains 8 nuclei from single divided cells) -> become eggs
Define microsporogenesis.
Formation of spores within microsporangia (pollen sacs).
Inside anther, sporogenous cells become microsporocytes which divide to produce 4 single-celled microspores.
Define microgametogenesis.
Development of the male gametophyte… or microspores into microgametophytes (pollen grains)
Microspore -> mitosis -> two cells: 1. tube cell, 2. generative cell
Define megasporogenesis.
Formation of megaspores within the megasporangium
Single megasporocyte -> meiosis -> four haploid megaspores… three disintegrate, one functional megaspore
Define megagametogenesis.
Development of female gametophyte.
Process continues when one functional megaspore -> mitosis (3x) -> eight nuclei … arranged in embryo sac (megagametophyte)
Arrangement of eight nuclei in embryo sac?
3 remain at micropylar end … 1 egg, 2 synergids
3 remain at chalazal (opposite) end… antipodals
2 at center… polar nuclei, usually fused
Double fertilization in angiosperms gives rise to ___ and the ___.
zygote, endosperm
Describe the proces of double fertilization.
Pollen lands on stigma, produces pollen tube… pollen tube reaches embryo sac. Two fertilizations take place:
- Zygote: 1n sperm + 1n egg = 2n zygote
- Double fertilization: other sperm fuses with polar cells = 3n endosperm
General purpose of endosperm and pattern of development?
Provides nutrients for developing embryo, after undergoing many nuclear divisions -> multinucleate “supercell” -> cytokinesis -> multicellular.
Endosperm in monocots…
stores nutrients for use by seedling after germination.
Endosperm in eudicots…
Reserves of endosperm exported to cotyledons.
Initial divisions of embryo…
Mitotic.
- Apical (terminal) cell divides to form spherical embryo
- Large basal cell forms suspensor
Define suspensor.
an extension at the base of the embryo that anchors it in the embryo sac.
involved in nutrient or hormone transfer between embryo and parent
Define cotyledon
embryonic or seed leaf involved in nutrient storage or absorption.
Define hypocotyl
part of the embryo or seedling between cotyledon(s) and radicle.
Define radicle.
embryonic root
Differences in monocot development?
Scutellum, embryonic sheaths (coleoptile and coleorhiza)
Define scutellum
specialized cotyledon with large surface area to absorb nutrients from endosperm during germination.
Define coleoptile.
monocot embryonic sheath, protects shoot
Define coleorhiza
monocot embryonic sheath, protects root
