1
Q
seed
A
- Consists of an embryo and its food supply, surrounded by a protective coat.
- When mature, seeds are dispersed from their parent by wind or other means.
- B/c it nourishes and protects the embryo, yet can move away from the mother plant, a seed is analogous to a detachable and mobile version of a pregnant women’s uterus.
2
Q
In addition to seeds, the following are comon to all seed plants:
A
reduced gameotphytes, heterospory, ovules, and pollen.
3
Q
The miniaturization of gametophytes of seed plants allowed for an impiortant evolutionary innovation in seed plants:
A
- Their tiny gametophytes can develop from spores retained within the sporangia of the parental sporophyte. This arrangement protects the gametophytes from environmental stress.
- The moist reproductive tissues of the sporophyte shield the gametophytes from UV radiation and protect them from drying out. This relationship also enables the dependent gametophytes to obtain nutrients from the sporophyte.
- In contrast, the free-living gametophytes of seedless plants must fend for themselves.
4
Q
Heterospory: the rule among seed plants
A
- Ferns and other close relatives of seeds plants are homosporous, suggesting that seed plants had homosporous ancestors.
- At some point, seed plants or their ancestors became heterosporous, producing two kinds of spores: megasporangia produce megaspores that give rise to female gametophytes, and microsporangia produce microspores that give rise to male gametophytes.
- Each megasporangium has a single functional megaspore, whereas each microsporangium contains vast numbers of microspores.
5
Q
integument
A
- Although a few species of seedless plants are heterosporous, seed plants are unique in retaining the megasporangium within the parent sporophyte.
- A layer of sporophyte tissue called integument envelops and protects the megasporangium.
- Gymnosperm megasporangia are surrounded by one integument, whereas those in angiosperms usually have 2 integuments.
6
Q
ovule
A
- Megasporangium + megaspore + their integuments
- Inside each ovule, a female gametophyte develops from a megaspore and produces one or more eggs.
7
Q
pollen grain
A
- A microspore develops into a pollen grain that consists of a male gametophyte enclosed within the pollen wall. (The outer layer of the pollen wall is composed of molecules secreted by sporophyte cells; hence, we refer to the male gametophyte as being in the pollen grain, not equivalent to the pollen grain.)
- The tough pollen wall, which contains the polymer SPOROPOLLENIN, protects a pollen grain as it is transported from the parent plant.
8
Q
pollination
A
- The transfer or pollen to the part of a seed plant that contains the ovules.
- Pollen grain may be transported by wind or by hitchhiking on the body of an animal.
- If a pollen grain germinates (begins growing), it gives rise to a pollen tube that discharges sperm into the female gametophyte within the ovule.
9
Q
sperm: vascular vs nonvascular
A
- In nonvasculars and seedless vasculars, freeliving gametophytes release flagellated sperm that swim thru a film of water to reach eggs. (Distance for sperm transport rarely exceeds a few centimeters)
- Seed vasculars: a sperm-producing male gametophyte inside a pollen grain can be carried long distances by wind or by animals, eliminating the dependence on water for sperm transport.
- The sperm of seed plants also don’t require motility b/c sperm are carried directly to the eggs by pollen tubes.
- Living gymnosperms provide evidence of the evolutionary transition to nonmotile sperm.
10
Q
advantages of seeds over spores
A
- Spore are usually single-celled; seeds are multicellular, consisting of an embryo protected by a layer of tissue, the seed coat.
- Seeds can remain dormant for days, months, even years after being released; spores have shorter lifetimes.
- Unlike spores, seeds have a supply of stored food. Under favorable conditions, the seed can emerge from dormancy and germinate with its stored food providing critical support for growth as the sporophyte embryo emerges as a seedling.
11
Q
progymnosperm
A
- An extinct “transitional” seedless vascular plant that may be ancestral to seed plants.
- Ex: Archaeopteris – heterosporous tree w/ a woody stem; did not bear seeds.
12
Q
gymnosperm evolution
A
- The earliest gymnosperms lived in Carboniferous ecosystems still dominated by seedless vascular plants. As the Carboniferous period gave way to the Permian, markedly drier climatic conditions favored the spread of gymnosperms.
- Gymnosperms were particularly well-suited to arid conditions b/c of the thick cuticles and relatively small surface areas of their needle-shaped leaves.
- Gymnosperms dominated throughout the Mesozoic. Toward the end of the Mesozoic, angiosperms appeared; they were dominating by the mid-Cretaceous.
13
Q
conifer
A
- Member of the largest gymnosperm phylum. Most of these are cone-bearing trees, such as pines, firs, spruces, and redwoods dominate vast forests in northern latitudes.
- In conifers, the 2 types of spores are produced by separate cones: small pollen cones and large ovulate cones.
14
Q
flower
A
- Angiosperm structure specialized for sexual reproduction.
- A specialized shoot that can have up to 4 rings of modified leaves (sporophylls) called floral organs: sepals, petals, stamens, carpels.
15
Q
sepals
A
Starting at the base of the flower are the sepals, which are usually green and enclose the flower before it opens.
16
Q
petals
A
- Interior to the sepals.
- Brightly colored, but flowers that are wind-pollinated generally lack brightly colored parts.
17
Q
stamens
A
- Produce microspores that develop into pollen grains containing male gametophytes.
- Consists of a stalk called the filament + a terminal sac, the anther, where pollen is produced.
18
Q
carpels
A
- Make megaspores and their products, female gametophytes.
- Some flowers have a single carpel; others have multiple carpels, which may be separate or fused together.
19
Q
stigma
A
- At the tip of the carpel.
- Sticky; receives pollen.
20
Q
style
A
- Leads from the stigma to the ovary at the base of the carpel.
- Ovary contains one or more ovules. If fertilized, ovule develops into a seed.
21
Q
fruit
A
- Typically consists of a mature ovary; can also include other flower parts. As seeds develop from ovules after fertilization, the ovary wall thickens.
- Protect dormant seeds and aid in their dispersal.
22
Q
fleshy fruits
A
In which the wall (PERICARP) of the ovary becomes soft during ripening.
23
Q
fossil angiosperms
A
- 125mill y/o angiosperms: Archaefructus liaoningensis and Archaefructus sinensis.
- Most researchers agree that the angiosperm common ancestor was woody.
24
Q
cotyledons
A
- Until the late 1990s, most systematists divided flowering plants into 2 groups, based partly on the number of cotyledons, or seed leaves, in the embryo.
- Species w/ 1 cotyledon were called monocots; those w/ 2 were called dicots.
- Recent DNA studies indicate that the monocot-dicot distinction doesn’t completely reflect evolutionary relationships.
25
new angiosperm classification
- The vast majority of species once categorized as dicots form a large clade, now known as eudicots.
- The rest of the former dicots are now grouped into 4 small lineages. 3 of these lineages are informally called basal angiosperms b/c they appear to include the flowering plants belonging to the oldest lineages. A 4th lineage, called the magnoliids, evolved later.
