Plant Structure & Reproduction

Seed Plants & Angiosperms

• Double fertilization — only angiosperms

  • One sperm joins the egg to create a diploid zygote

  • Other sperm fuses with polar nuclei (either of the nuclei in the embryo sac of a flowering plant that form the nutritive endosperm.)

• Wall of ovary thicken and become fruit

  • Botanically no such thing as a vegetable — most “vegetables” are fruit

Seed Plants in the Environment

• Create habitat

• Provide food

• Drive animal evolution

  • Herbivory

  • Pollinators

• Critical members of biogeochemical cycles

  • Phosphorous

  • Carbon

  • Nitrogen

• Importance to humans

  • Food

  • Medicine

  • Building material

  • Clothing

  • Aesthetics

Threats to Plants

• Clearing land — habitat loss

• Invasive species

• Pollution

• Climate change

• Poaching

Plant Form & Physiology

• Plant systems work together

• Two systems

  • Shoot system

  • Root system

• Plant tissues

  • Meristematic — like stem cells in animals

    • Found in zones of growth

    • Apical meristem at tips of roots & stems

    • Lateral meristem — growths in thickness

    • Intercalary meristem — only in monocots

      • At base of lead blades and nodes (allows grass to be grazed and continue growing)

  • Permanent tissues — No longer actively dividing

• Xylem — conducts water & nutrients from roots

  • Dead at functional maturity

  • Flows only one direction

• Phloem — conducts processes of photosynthesis, plant hormones, and other biomoleciles

  • Alive

  • Conducts in both directions

• Transpiration

• Water is constantly moving down a gradient of water potential

  • Difference in potential of any water & pure water

  • Osmosis

• Stomata are key in transpiration

  • Open and close to allow/keep water in

  • Allow for gas exchange

  • Can let water out of the plant

• Stems

  • Modifications: Storage of food, spread of plant, thorns, tendrils

• Roots

  • Tap Roots: One main long root (carrot), good for dryer areas

  • Fibrous Roots: Many smaller roots that spread out, good for moist areas

  • Root hairs: Extension of epidermal cells

  • Modifications

    • Epiphytic Roots: Allow plants to grow on other plants (orchids)

    • Prop Roots: Add support in loose soils

• Photosynthesis Adaptations in fixing carbon

  • C3 is dominant form

    • 3-Carbon molecule produced during calvin cycle

      • Two “turns” required to make one glucose

    • Best suited to cooler or moister conditions

    • In hot and dry conditions C3 can lead to water and energy loss

      • Oxygens starts to interfere with the light-independent reactions preventing creation of glucose

  • In hot, dry conditions

    • C4 Dominant — many grasses

      • Helps to concentrate CO2

      • CO2 is first fixed to form a 4 carbon molecule

      • CO2 is then released to begin the light-independent reactions to produce the C3 precursor to glucose

    • CAM plants — Cacti, pineapple, agave

      • Close their stomata during the day to preserve water

      • Stomata opened at night to preserve CO2

    • Both processes require more energy input than C3, making C3 better under cooler, moister conditions

  • C3 and C4 plants can switch to CAM photosynthesis in stressful situations