PLSC Lab six
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Microsporangiate or pollen cone
Smaller of the two kinds of cone. Each microsporangiate cone has whorls of microsporocytes (microspore mother cells) which undergo meiosis to produce haploid microspores, or pollen grains
pollen grains have these to increase the surface area of the grain and to aid in wind dispersal. The challenge is for grain to drift on the wind until it contacts a larger, megasporangiate or ovulate cone. The majority of pollen grains released fall to the ground and never pollinate an ovulate cone
The female cones have wholrs of seed scales surrounding a woody axis. Seed scales consist of a ovuliferous scale and sometimes a visible bract. On the surface of the woody ovuliferous scale are two seeds with membranous wings that aid in wind dispersal
Each ovuliferous scale bears 2 ovules, and each ovule contains a megasporangium (surrounded by a nucellus) which produces a megasporocyte or megaspore mother cell which is surrounded by a layer of cells called the integument (becomes the seed coat). Meiosis occurs to give rise to 4 megaspores three of which disintegrate. The remaining megaspore develops into a megagametophyte which contains one or more archegonia. The egg cell is located inside the archegonia
When pollen lands, it develops a tube that enters an opening to where the egg is enclosed. Sperm then moves down the tube to the egg, where fertilization occurs. The delay between pollination when pollen lands on the scale, until fertilization when the sperm and egg fuse, may be more than one year. The developing conifer seed contains an embryo representing genetic information of both parents, but most is composed of an energy-rich megagemetophyte that is entirely from the megaspore parent
Refers to the tightly-packed ovuliferous scales and resin-coated condition of megasporangiate cones in some conifers. Both lodgepole pine and jack pine have serotinous cones that prevent the release of seed until sufficient heat melts the resin and allows the scales to separate.
seeds of conifers large enough to be people food. They are harvested from the cones of limber pine (pinus Flexilis); a species that grows in the foothills of Alberta!
Not all gymnosperms bear their seeds in cones. The junipers have both micro and megaspores contain in fleshy berries
A fleshy cup that the yew bears a single seed within
6CO2 + 12 H2O + solar energy = C6H12O6 + 6 O2 + 6 H2O
Is the corollary of photosynthesis, because it involves the breakdown of glucose and other compounds to obtain the stored energy for use in growth and metabolism of both plants and all heterotrophic life.
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