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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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Plants

Plants

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


4 groups of plants

4 groups of plants


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


Alternation of generations1

Alternation of Generations


Figure 30 2

Figure 30.2


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:


Angiosperm life cycle

Angiosperm Life Cycle


Plants

  • 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)


Plants

Flaccid, turgid, and plasmolysis:


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


Proton pumps and cotransport

Proton pumps and cotransport


Plasmodesmata aquaporins

Plasmodesmata & aquaporins


Transpiration

Transpiration

  • 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


Mycorrhizae

Mycorrhizae

  • 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


Tropisms

Tropisms

  • 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


Photoperiodism

Photoperiodism

  • 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


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