Seeds Flashcards
Steps of seed germination
pollination
fertilization
embryogenesis
mature seed
apomixis
seeds produced without pollination
apomictic
seeds produced with pollination
seeds are alive
respiration
finite lifespan
General features of seeds
embryonic axis -root and shoot in mini form food reserves -allows seeds to grow before it is capable of performing photosynthesis seed coat -provides protection
Two groups based on seed structure, monocots and dicots (difference)
dicot - two seed leaves
monocot - one seed leaf
Dicot characteristics
two cotyledons web veins in leaves ring of vascular bundles in stems 4/5 petals on flowers pollen has three pores
Monocot characteristics
one cotyledon parallel veins in leaves scattered vascular bundles in leaves usually 3 petals on flowers pollen had one pore
Typical seed of a dicot plant
embryonic axis plumule - first true leaves hypocotyl/epicotyl - embryonic stem (H/E) radicle - embryonic root cotyledons (seed leaves) - for storage of food reserves -proteins -starch, carbohydrates -lipids, oils *think bean seed
Exterior structure of a dicot plant
seed coat - protection
hilum - botanical belly button
micropyle - where tube that carried pollen to the egg was attached
*think bean seed
Typical seed of a monocot plant
embryonic axis
plumule - first true leaves
radicle - embryonic root
coleoptile - protective cap over plumule
cotyledons (scutellum) - transfer of food from endosperm to seedling
endosperm - food storage and reserve
-proteins, starch and , oils
Diversity in seeds
size
adaptation
method of distribution
germination requirements
Steps of seed germination
uptake of water
utilization of stored reserves
expansion of the embryonic axis
establishment of an autotrophic seedling
Germination requires
water
temperature
oxygen
Utilization of stored reserves in cotyledons or endosperm tissue
during germination, enzymes are produced that convert stored reserves (large molecules) into compounds that can be used by the seedling (smaller molecules)
starches -> sugars
lipids, fats -> sugars
proteins -> amino acids
Transport of these small molecules during germination have two functions
support respiration in the embryo because the seedling is not yet able to perform photosynthesis
provide a source of building blocks for growth of the seedling
Expansion and growth of the seedling
root radicle elongates down and hypocotyl expands up
establishment of root system
cotyledons emerge above the soil surface
Seed dormancy
a mechanism to delay germination until environmental conditions are favorable
Seed dormancy can be broken by various natural conditions
temperature (some seeds requires period of low temps)
exposure to sunlight
exposure to dry heat
heavy rainfall
Artificial treatments to break seed dormancy
manipulating environment
scarification - physical disruption of hard seed coat
Seedling establishment
shoot emerges and is exposed to light
chlorophyll is produced and seedling startes to perform photosynthesis
seedling is autotrophic, no longer depends on reserves from the seed
*if stored reserves are consumed before the plant performs photosynthesis, the seedling will die
