Plant Biology and Physiology Notes

Lesson 1: Terrestrial Plant Adaptations

• Environmental Challenges for Land Plants: Transition from aquatic to terrestrial environments poses challenges such as water loss (desiccation).

  • Adaptations:

    • Waxy Cuticle: A protective, waterproof layer covering leaves and stems.

    • Stomata: Pores that open for gas exchange and close to reduce water loss.

• Water Transport: Land plants must transport water absorbed from soil through the plant body.

  • Tracheids: Vascular plants (tracheophytes) have specialized cells called tracheids for transporting water and minerals. These are part of the xylem.

  • Xylem: Conducts water and minerals from roots upward; contains lignin for structural support.

  • Phloem: Transports sugars (produced during photosynthesis in leaves) to other parts of the plant; part of the food-conducting system.

• Sporophyte vs. Gametophyte Generations:

  • Sporophyte: Diploid (2n) generation that produces spores by meiosis.

  • Gametophyte: Haploid generation that produces gametes (eggs and sperm) by mitosis; reproductive structures.

  • Dominant in bryophytes (mosses).

  • Sporophyte dominant in vascular plants (ferns, gymnosperms, angiosperms).

• Evolutionary Adaptations Separating Major Plant Groups:

  • Bryophytes (Non-tracheophytes): Lack tracheids and use other types of water-conducting cells.

    • Limited in size due to reduced water transport and absorption ability.

    • Require water to transport sperm for sexual reproduction.

    • Gametophyte is the dominant photosynthetic stage of the life cycle.

    • Examples: Mosses, liverworts, and hornworts.

  • Vascular Plants (Tracheophytes): Possess vascular tissue for better transport and structural support (xylem and phloem).

    • Waxy cuticle and stomata for water conservation.

    • Sporophyte dominant.

    • Evolution of seeds and pollen leads to less dependence on water.

    • Flowers and fruits enhance reproduction and seed dispersal.

  • Three Subtypes of Tracheophytes:

    • Lycophytes: Have roots but no true leaves and no seeds; water required for fertilization; green leafy sporophytes are the dominant life cycle stage.

    • Pterophytes: No seeds; require water for fertilization; possess vascular tissue, roots, stems, and true leaves; sporophyte dominant (e.g., ferns, horsetails, whisk ferns).

    • Seed Plants: Gymnosperms and angiosperms; most abundant due to evolutionary adaptations.

      • Seeds protect the embryo, provide nutrition, and aid in dispersal.

      • Embryo inside the seed can remain dormant during cold or drought.

• Gametes, Spores, Pollen, and Seeds:

  • Pollen: Multicellular male gametophyte transported by wind or pollinators to the female gametophyte containing the egg; eliminates the need for water during fertilization in seed plants.

  • Gametes (Eggs/Sperm): Fuse during fertilization, leading to sexual reproduction.

  • Seeds (2n): Fertilized ovule containing an embryo and stored food inside a protective coat.

Lesson 2:

• Dermal Tissue:

  • Forms the epidermis, the outer protective layer of the plant.

  • Includes specialized cells like:

    • Pavement cells: for basic protection

    • Guard cells : surround stomata

    • Trichomes : various functions (e.g., protection, reduce water loss)

• Vascular Cambium:

  • Develops between the primary xylem and primary phloem in stems.

  • In dicots, arranged in a ring.

  • In monocots, scattered.

• Cross Section of a Woody Stem:

  • Periderm: Replaces the epidermis; protective outer bark of the stem comprised of cork and phelloderm.

    • Cork: Protective dead cells.

    • Phelloderm: Living cells beneath the cork cambium.

  • Cortex: Parenchyma for storage.

  • Phloem: Part of bark; transports sugars.

  • Secondary Xylem: Wood produced by the vascular cambium.

Lesson 3: Transport Throughout the Plant

• Mechanisms for Water Movement:

  • Cohesion-Tension Mechanism: The main driver of water movement from soil to leaves.

    • Water moves upward in the xylem due to leaves creating negative pressure (tension).

    • Cohesive and adhesive properties of water maintain the pressure.

      • Water molecules stick to each other via hydrogen bonds, forming a continuous water column.

      • Adhesion: Water molecules stick to xylem walls, aiding upward pull.

    • Tension forces pull water column up.

  • Pressure Flow Hypothesis: Explains fluid transport in phloem (translocation).

• Phloem Transport (Translocation):

  • Movement from source to sink.

    • Source: Region producing sugars (e.g., leaves during photosynthesis).

    • Sink: Region using/storing sugars (e.g., roots, fruits, flowers).

  • Most carbohydrates produced in leaves are distributed through the phloem to the rest of the plant.

  • Translocation of solutes provides building blocks for actively growing regions.

  • Plant hormones, mRNA, amino acids, organic acids, proteins, and ions are also transported.

    • This collection of solutes is commonly called Sap and can move both up and down the plant.

• Water Potential Gradients: Constant water potential gradients maintained throughout the plant.

  • Uptake via osmotic pressure in the root.

  • Phloem loading occurs at the source.

  • Highest pressure in the roots, lowest in the leaves.

• Phloem Loading:

  • Carbohydrates or sucrose molecules produced in photosynthetic tissues enter sieve tubes.

  • Sieve cells must be alive to use active transport to load sucrose into the phloem.

  • Companion cells provide much of the ATP needed for active transport.

Lesson 4: Plant Nutrition and Defense

• Soil Composition and Nutrient Extraction:

  • Minerals released by weathering of rocks.

  • Organic matter improves soil structure, aeration, and water retention.

  • Topsoil: Rich in organic matter and nutrients.

  • Minerals and nutrients percolate down through the soil in water.

  • Bedrock: Where water and minerals collect.

• Water and Mineral Availability:

  • Water and dissolved nutrients are essential for root uptake.

  • Hydrogen bonds adhere water to soil particles.

  • Soil composition determines the proportion of air and water.

    • High sand content drains water quickly with a large proportion of air.

    • High silt and clay content drains poorly, leading to too much water and not enough air.

• Nutrient Absorption:

  • Soil particles tend to have a negative charge.

  • Positive ions are attracted to soil particles.

  • H^+ ions displace mineral cations from clay particles.

  • Active transport is required to acquire and maintain K^+ and other positive ions in the root.

• Nutritional Strategies:

  • Symbiosis with Nitrogen-Fixing Bacteria:

    • Ammonia (NH3) and nitrate ( NO3) are usable forms of nitrogen.

    • Plants use nitrogen to build proteins and nucleic acids.

    • Legumes