2101 - Fertilisation Flashcards
State meaning of Fertilisation
The union of a male gamete from pollen with the female gamete in the ovule to produce a zygote.
Pollen recognition
Chemical recognition signals are sent when the pollen lands on the stigma.
Full recognition usually only takes place between male/female gametes of the same species.
Pollen Tubes
After Full Recognition a pollen tube grows from the pollen grain down through the Style into the Ovule.
Nuclei of the male cell will travel along the pollen tube and join with the female nucleus in the female cell.
Fruit - meaning
a Fruit is formed from the Ovary after fertilisation
Seed - meaning
a Seed is formed from the Ovule after fertilisation
Parts of the Ovule
Main Parts:
Integuments - forming its outer layers (eventually forms Testa)
Embryo Sac - an egg cell for the purpose of fertilisation
Hilum - attached to the ovary wall like an umbilical cord. Provides nutrients and sugars.
Micropyle - allows pollen tube access
After fertilisation, the ovule develops into a seed.
Seed parts
Embyro - develops from the embryo sac
Testa - seed coat, develops from the integuments
Micropyle - weak spot on the testa, develops from the micropyle from the integuments
Hilum - point of attachment of the seed to the ovary as it develops
Seed develops from…
A seed is…
A seed develops from the fertilised ovule
A seed is an embryonic plant enclosed in a protective outer covering known as the testa.
Seed functions
Gives rise to new plants Contains the Embryo during development Protect the embryo during distribution and dormancy May impose dormancy on the embryo May help with distribution of the embryo
Seed / Embryo parts
Radicle - the embryonic root
Hypocotyl - shoot between the radicle and Cotyledons
Cotyledon - seed leaves, storage or protection of epicotyl and plumule
Epicotyl - shoot above the cotyledons
Plumule - The growing tips of the epicotyl, including first true leaves
Endosperm - storage tissue in several (but not all) angiosperm seeds.
Cotyledons
Cotyledons can be photosynthetic, and are functionally similar to leaves. However they are developmentally distinct.
Seed is Viable if…
- It is Healthy and not diseased
- Capable of germination (under suitable environmental conditions)
- Dormancy has been broken
Length of time a seed can remain viable…
Large seeds - Recalcitrant seeds 6 months
Small seeds - Orthodox number of years
Respire at a very low rate to remain dormant without using up food supply. (used for germination)
Requirements for Germinisation
Water
Oxygen
Temperature appropriate for species (most 18-21c)
Light appropriate for species
(most seeds will germinate in light or dark, some seeds need light to germinate - Primula vulgaris)
Epigeal germination
Hypocotyl emerges first (hypocotyl extension)
Cotyledons appear, may be used for photosynthesis
French Bean - Phaseolus vulgaris
Hypogeal germination
Epicotyl emerges first (epicotyl extension)
Cotyledons stay below ground, used as a food source.
Broad Beans - Vicia faba
Process of germination
- Seed absorbs water through the micropyle
- Cotyledons absorb water and swell
- Testa absorbs water and softens
- Testa will tear as Cotyledons swell
- Cotyledons break down starch into glucose
- Rate of Respiration increases, creates new cells for emerging plant (roots, stems, buds, leaves)
- Radicle emerges from Testa, grow lateral roots and absorbs water/nutrients from soil
- Plumule emerges, grows up through the soil and unfurls
- Begins to Photosynthesise
Seed Dormancy - Physical
Hard seed coat. Requires physical scarification to allow moisture and oxygen through the seed coat. Abrasion by rocks, thaw/freeze cycle.
Can break artificially, light sanding, nicking or dipping in acid.
Lathyrus odoratus - Sweet Pea
Seed Dormancy - Physiological
Chemically inhibited. May require specific water, temperature, light conditions to germinate.
Place seeds in refrigerator (stratification)
Rosa spp. (Rosa canina)
Seed Dormancy - Morphological
Immature embryo. Still requires development after release. (after-ripening)
Fraxinus excelsior - Ash
Seeds are from…
Fruits are from… revisited
Seeds form from fertilised Ovule
Fruits form from the fertilised Ovary
FRUITS
A fruit is formed from the Ovary after fertilisation
The fruit contains the seeds
Fruit Functions
- Provides seeds with Protection
- Aids in dispersal and distribution of the seed
- May impose dormancy on the seed prior to dispersal
Types of fruit
Succulent - Fleshy
Dry - Hard
Seed Dispersal - Wind
Parachute - Taraxacum Officinale
Winged - Acer pseudoplatanus
Censer - Papaver spp.
Seed Dispersal - Water
Coconut - Cocos nucifera
Seed Dispersal - Explosvie / self dispersed
Geranium macrorhizum
Impatiens glandulifera (Himalayan balsam)
Ceanothus spp.
Euphorbia
Seed Dispersal - Animal (usually with fruit)
Frugivory (fruit eaters)
- Ilex aquifolium
- Rubus fruticosus (blackberry)
- Rubus idaeus (raspberry)
Attachment
- Galium aparine (cleavers)
Scatter Hoarding (squirrels burying) - Quercus robur
