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Biology 1114 – Midterm #2 Lecture Notes
2/13/15 -

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Seed Plants
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Step 3: origin of seeds
o Bryophytes and ferns are homosporous; each spore produces bisexual gametophyte
Some ferns are heterosporous; spores produced come in 2 sizes with unisexual gametophyte
o Megaspores produce megagametophytes (female)
o Microspores produce microgametophytes (male)
Heterspory improves allocation of reproductive resources
o Megagametophyte can protect and nourish developing embryo, thus increases survival
chance/life reproductive success
Seed plants use heterospory
o Sporophyte (2N) retains megaspore in megasporangium
o 1 megasporangium, 1 spore
o Reversal of bryophyte condition
Integement tissues from sporophyte, develop female megagametophyte
Tissue from 3 generations in a seed
o Benefits because of nourishment
 Free water no longer needed
Seed plants analogous to “truly” terrestrial animals, the amniotes of plants
Evolution of seed allows reproduction in terrestrial environment (no free water needed)
Gymnosperm seed is analogous to amniotic egg

*Exctinction gave rise to gymnosperms, then radiation of angiosperms

Gymnosperms
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Ovary open to air (microphyte)
Seeds take more energy to produce than spores
Relatively long life cycle
Wind-born pollen
o Angiosperms have animal pollen relationship; key distinction from gymnosperms

Angiosperms (flowering plants)
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Most successful in terms of number of species
Have evolved fruit, and therefore unique seed type
o Angiosperm name comes from ‘seed in a container’
o Seeds develop from ripened ovary in the base of the flower
Leaf distinctions - veins and number of points
Mono most important for crops/food (rice, corn)

Flowers & Reproductive Cycle
 4 kinds of leaves
o 2 are sterile; not involved in reproduction (seeples)
 Petals (taxonomic differences between flowers)
o 2 are reproductive
 Filaments
 Carpels (female)
 Distinctions from gymnosperms – seed buried within flower, not exposed to air like
gymnosperms; double fertilization, as opposed to single in gymnosperms; survival of all male
microsporocytes; zygote growth happens in ovial; 3 generations in seed, same; triploid rather
than haploid in gymnosperms
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Possible for self-fertilization because both parts are present in the plant
o Angiosperms more at risk than gymnosperms because the gymnosperms had
female/male cones for seeds
o Sometimes angiosperms allow self-fertilization…why might that happen?
o Most of the time plants avoid self-fertilization to prevent inbred offspring
 Genetic diversity
o Prevention Methods:
 Antlers and carpels often mature at different times in a flower
 Chemical recognition, female plant won’t accept it

Success of Angiosperms
 Can have relatively short reproductive cycle (gymnosperms take 1-3 years, fairly long)
 Many can reproduce asexually (vegetatively)
o Avoidance of polyploidy advantage????
o Ex: Aspen tree clones (roots to shoots, genetically identical to parent)
 Differences when they shed their leaves
 Animal relationships
o Delivery of pollen
o Function of bright colors, nectar, shelter, and/or scent to entice animals
o Plants take advantage of animals; animals don’t always get anything in return
o Have evolved reflection of short wavelengths that mammals can’t see but insects can
o Those pollenated by moths/bats tend to be white or use scent to appeal in the dark
 Echolocation helps bats find flowers
 Star orchid; Darwin suggested that moth existed capable of reaching down its
long nectar tube (hawk moth)
 Tongues too long or too short to get pollen or reach nectar; natural
selection plays on that

Transportation across Plasma Membranes
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Osmosis determines net uptake or water loss by a cell and is affected by:
o Solute concentration
o Pressure
Water potential combines effects of solute concentration and pressure and refers to the
capacity to perform work

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Pure water at sea level and room temp is 0 water potential
Solute potential is always negative (there is less water available to move across the membrane
because they’re bound to the dissolved molecules)
Pressure potential is pressure exerted on solution
Negative pressure in leaves that pulls water from the roots
The greater the negative, the more osmolarity
o The cell with -
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7 will draw water out of the cell
Long distance transport of fluid requires bulk flow, driven by pressure
Most absorption occurs near root tips, where root hairs located and epidermis permeable to
water
Concentration of essential minerals is great in roots than soil due to ACTIVE TRANSPORT
Endodermis is final barrier that needs to be crossed; cylinder of cells surrounding vascular
cylinder; final barrier to any mineral taken up
o If it’s recognized, the selective transport takes up the molecules
Casparian strip; selective lining, part of the endodermis
Water droplets in the morning haven’t evaporated; it’s from the root uptake
Xylem sap – water + dissolved minerals
Transpiration – evaporation of water from a plants surface
Cohesion-tension hypothesis – transpiration and water cohesion pull water from shoots to roots
o Xylem sap is normally under negative pressure or tension from transpiration pulling
water out of leaves, and that pulls water up
o Positive charges on one molecule attracted to negative on another
o Adhesive hydrogen bonds allow water to pull other water molecules up
Guard cells with stoma affect how the plant interacts with environment to create potential
difference
Guard cells use electrochemical gradient (H+ out, K+ in)
K+ channel regulation determines flaccid/turgidity
Stomata closed at night
Less CO2, light act as cues for stomata

3/4/15
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Animal body plans are normally talked about in respect to tissue layers
o Tissues are normally separated from the rest of the body by membrane
o 3 germ layers (animals may have different combinations of them) in early embryonic
development
 Ectoderm - outer
 Endoderm – innermost, lines digestive tube
 Mesoderm – middle layer
o Not all animals have all 3 germ layers

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Sponges don’t have germ layers, so the developing sponge doesn’t share the
same development process that others may have
Dipoblastic – no mesoderm
 Cnidarians, jellies
Triploblastic – have additional mesoderm
 Bilaterian (flat worms, arthropods, vertebrates, us)
 Most of them have body cavities, which result from the layers
 Coelomates have true coelom; these are cavities derived from the
MESODERM
o Ex: worm
 Psuedocoelomates – have cavity not derived from mesoderm
Some triploblastic animals are aceolomates – lack the cavity; flat worm
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(cell cleavage differences)
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Protostomes vs

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