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Plants. Ch. 29-30, 35-39. Ancestors to Land Plants . Charophyte algae seem to most closely resemble land plants because both charophytes and land plants have: Similar shaped proteins in the cell membrane (rosette shaped) while noncharophyte algae have linear shapes

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Ch. 29-30, 35-39

ancestors to land plants
Ancestors to Land Plants
  • Charophyte algae seem to most closely resemble land plants because both charophytes and land plants have:
    • Similar shaped proteins in the cell membrane (rosette shaped) while noncharophyte algae have linear shapes
    • Peroxisome enzymes that reduce loss of organic products while other algae lack these enzymes
    • Similar structure of flagellated sperm (only in more primitive land plants)
    • Similar events during cell division
    • Similar DNA
adaptations to land
Adaptations to Land
  • Root systems for gaining nutrients and support
  • Shoot systems (stem cells with lignin for support)
  • Cuticle to prevent water loss
  • Vascular systems (xylem and phloem) for transport
  • Haploid to diploid dominance
    • Sporophytes (2n) rather than gametophytes (1n) are dominant
    • Seasonal changes on land
    • Able to survive genetic mutations with 2n
  • Pollen instead of flagellated sperm for easier disperal
  • Seed production in gymnosperms and angiosperms
    • Seeds enclosed in the ovary in angiosperms for protection
alternation of generations
Alternation of Generations
  • All land plants have a 2-part life cycle, each part has a MULTICELLULAR structure
    • Gametophyte (n) – haploid cells make up this structure and divide through mitosis
      • Gametes (egg and sperm) are produced here
      • Gametes fuse (fertilization) to form a diploid zygote = sporophyte
    • Sporophyte (2n) – diploid cells make up this structure and divide through mitosis from the original zygote
      • You see this structure for most plants (except bryophytes)
      • Produce spores/microspore/megaspore (n) through meiosis
additional terrestrial adaptations seen in angiosperms and gymnosperms
Additional terrestrial adaptations seen in angiosperms and gymnosperms
  • Both have reduced gametophytes, ovules, pollen (instead of flagellated sperm), and seeds
  • These adaptations allowed them to cope with drought and UV radiation, and allowed fertilization to occur without water
  • Pollen contain the sperm, and can be carried to the female parts by wind or pollinators
advantages of seeds
Advantages of seeds
  • The entire ovule develops into a seed--the embryo and a food supply are packed within a protective coat
  • The seed can often remain dormant for months or years before germinating
  • The seed uses the enclosed food supply to begin growing until a seedling emerges and photosynthesis begins
  • Insert figure 30.3
benefits of flowers
Benefits of flowers
  • Flower: specialized structure in angiosperms for reproduction
  • Bright colored petals attract pollinators
  • Flower parts:

Pollination: when pollen is transferred from the anthers of one flower to the stigma of another

  • Germination: when a pollen grain (containing 2 sperm) begins growing down the style, forming a pollen tube that will deliver the sperm to the ovule
  • Double fertilization: the egg is fertilized, and the polar nuclei are fertilized, becoming the endosperm (a nutritive tissue that is 3n)
angiosperms the 3 f s
Angiosperms: The 3 F’s
  • Flowers, double Fertilization, and Fruits are unique to the angiosperms, and each provides an adaptive advantage
    • Flowers provide bright, colorful petals and sweet nectar to attract pollinators
    • Double fertilization allows 1 sperm to fertilize the egg (becoming the embryo), and 1 sperm to fertilize the endosperm (3n tissue)
    • Fruits: the ovary develops into a fruit (often a bright and sweet fleshy fruit) which protects the seeds and aids in dispersal by wind and animals
seed germination
Seed germination
  • Seeds germinate after they:
    • take in water
    • begin breaking down the 3n nutritive endosperm
    • Roots begin to grow down into the soil
    • Shoots begin to grow up, and the first leaves emerge
genetically modified plants
Genetically Modified Plants
  • Plant biotechnologists use genetic engineering to insert genes from one species to a plant species to give desirable traits
  • A few examples include:
    • Crops such as cotton, maize, and potatoes that contain genes from the bacterium Bacillus thuringiensis—the plants make a protein (Bttoxin) that is toxic to insect pests, reducing the need for chemical insecticides
    • Many crops that contain genes making them resistant to herbicides (Round-up ready soybeans and others)—crops can be sprayed but only weeds die
genetically modified plants cont d
Genetically Modified Plants (cont’d.)
  • “Golden rice”—rice grains that produce beta-carotene (vitamin A), preventing blindness in the poor who have vitamin A deficiencies
dermal tissue
Dermal Tissue
  • Epidermal cells that cover plants, guard cells around the stomata, specialized surface cells like hair cells, glandular cells, and cuticle
    • Root hairs greatly increase the surface area of the root, leading to more absorption of water
vascular tissue
Vascular Tissue
  • Functions to distribute substances throughout the plant
  • A vascular bundle is made of:
    • Xylem – moves water and minerals absorbed from soil up the plant against gravity; made of:
      • Vessel members – short cells, joined end to end to form a vessel (dead)
      • Tracheids – long cells with tapered ends with perforations (holes) between cells that water moves through (dead)
    • Phloem – moves sugar and other solutes throughout the plant after photosynthesis; made of…
      • Sieve tube members – form columns called sieve tubes (living)
      • Companion cells – adjacent to sieve tube members and help to load and unload sugars from the leaves to root/storage regions (living)
water potential review
Water potential review

ψ = ψP + ψS(ψS) = – iCRT

C= molar concentration of solution

R = 0.0831 L bars/mol K

T=temperature in K

  • Water ALWAYS moves from high water potential (where there is more water) to lower water potential (where there is less water)—remember this means less negative to more negative water potential
  • The transpiration-cohesion-tension mechanism for moving water from roots to leaves through plants—again water is moving from HIGH to LOW ψ
the nitrogen cycle
The Nitrogen Cycle
  • Plants can use nitrogen in the following forms:
  • NH4+ and NO3-
nitrogen fixing rhizobium on root nodules
Nitrogen fixing Rhizobium on root nodules
  • Rhizobiumbacteria living in nodules on plant roots convert N2 gas into NH3 –the first step in converting atmospheric nitrogen into forms the plants can use
  • Mutualism between fungi and plants roots—the fungus helps increase the surface area for water uptake (and some minerals absorbed from soil), fungi receive food from the plant
  • They can be endo- or ecto- mycorrhizae (spanning into the roots or mainly on the outside)
  • These are found in most plant species
  • The extensions of fungi that form a dense network are called hyphae
  • Any growth response that results in plant organs curving toward or away from stimuli; the hormone auxin in plants is responsible for the curvature
  • Phototropism: growth of shoots toward light, roots away from light
  • Auxin is distributed to the side that is AWAY from the light, and stimulates cell elongation, allowing the stem to bend toward

the light

more tropisms
More Tropisms
  • Gravitropism: shoots grow against gravity, roots grow down with gravity
    • Even plants placed on their side in the dark will show shoots curve up and grow against gravity, roots down with gravity
  • Thigmotropism: directional growth in

response to touch--usually a coiling

response--seen in vines/climbing

plants that have tendrils

circadian rhythms
Circadian rhythms
  • The 24-hour cycle of day and night—which all eukaryotic organisms respond to
  • Plant opening and closing of stomata and the production of many photosynthetic enzymes oscillate within a 24 hour period (its Circadian rhythm)—and continues at about the same timing even if plants are kept in constant light or dark
  • Short day plants require a long night (and short day) in order to flower (think spring/fall plants)
  • Long day plants require a short night (and long day) in order to flower—summer plants
  • Some plants are day-neutral, and can flower regardless once they reach maturity