Review for Plant Test

1. Water Uptake and Transport in Plants

  • Water is absorbed by root hairs through osmosis.

  • It moves through the cortex via the apoplastic (cell wall) and symplastic (cytoplasm) pathways.

  • The Casparian strip in the endodermis forces water into the symplast pathway.

  • Water enters the xylem and is transported upward due to transpiration pull, cohesion, and adhesion (cohesion-tension theory).

  • Water exits through the stomata in leaves by transpiration.

2. Properties of Water for Xylem Transport

  • Cohesion: Water molecules stick to each other due to hydrogen bonding, creating a continuous column.

  • Adhesion: Water sticks to xylem walls, preventing the column from breaking.

  • Capillary Action: Helps water move up narrow xylem vessels.

  • High Surface Tension: Aids in maintaining the column under negative pressure.

3. Transport of Organic Compounds in Plants

  • Phloem transports sugars (sucrose) and other organic compounds via translocation.

  • Source to Sink Movement:

    • Source: Where sugar is made (e.g., leaves).

    • Sink: Where sugar is used/stored (e.g., roots, fruits).

  • Pressure-Flow Hypothesis:

    • Sugar is actively loaded into phloem at the source, lowering water potential.

    • Water enters by osmosis, creating hydrostatic pressure.

    • This pressure pushes sugar toward sinks, where it is unloaded, and water leaves the phloem.

4. Xylem vs. Phloem

Feature

Xylem

Phloem

Function

Transports water and minerals

Transports sugars and organic molecules

Direction

Upward only

Bidirectional

Structure

Dead cells, thick walls, lignified

Living cells, sieve plates

Mechanism

Transpiration pull, cohesion-tension

Pressure-flow hypothesis

5. Micrographs of Vascular Tissue

  • Xylem: Large, hollow, thick-walled cells.

  • Phloem: Smaller cells with sieve plates and companion cells.

  • Root vs. Stem:

    • In roots, xylem is central (X-shape in dicots).

    • In stems, xylem and phloem form a ring (vascular bundles).

6. Role of the Shoot Apex

  • Contains apical meristem, responsible for primary growth.

  • Produces new leaves and stems.

  • Cell division and elongation drive upward growth.

  • Influenced by auxin for phototropism and gravitropism.

7. Auxin’s Effect on Plant Cells

  • Auxin (IAA) promotes cell elongation in shoots.

  • Accumulates on the shaded side of a plant, causing asymmetric growth (phototropism).

  • In roots, inhibits elongation, leading to gravitropism.

  • Activates proton pumps, lowering pH in cell walls, making them more flexible for expansion.

8. Annotated Diagram of a Flower

Include:

  • Sepals (protect bud)

  • Petals (attract pollinators)

  • Stamens (male reproductive part, includes anther & filament)

  • Carpel (Pistil) (female reproductive part, includes stigma, style, ovary)

9. Pollination and Seed Dispersal

  • Pollination: Transfer of pollen from anther to stigma.

  • Fertilization: Fusion of male and female gametes.

  • Seed Dispersal: Spreading seeds away from the parent plant (wind, animals, water).

10. Advantages of Wind Pollination

  • No reliance on pollinators.

  • Large amounts of pollen increase fertilization chances.

  • Can reach isolated plants.

11. Advantage of Seed Production in Fruits

  • Protects seeds from predators/environment.

  • Aids in seed dispersal (via animals, wind, or water).

  • Provides nutrients to the developing embryo.