Plant Structure and Water Absorption

Larrel: The Root Structure

Larrel is a structure that has the dual mission to fix the plant in the soil and absorb water and mineral salts. In some cases, it serves as a reserve substance.

Parts of Larrel

They are morphologically and functionally different:

• Zone of Growth

  Formed by meristematic tissue, the apex is protected by the calyptra, composed of dead cells.

• Zone of Elongation

  Meristematic cells are transformed to become adult tissues. Elongation of cells is responsible for growth in length of the root.

• Piliferous Zone

  This is the closest to the stem. Here are found absorbent hairs.

Layers of Cells in Larrel

• The Cortical Cylinder

  • Epidermis: Its cells are absorptive hairs.
  • Cortical Parenchyma: Cells in which the plant stores food.
  • Endodermis: A monolayer of cells. The Casparian strip, which includes a waterproof substance, selects nutrients before they enter the xylem.

• Vascular Cylinder

  Constituted by vascular tissues, xylem and phloem, surrounded by meristematic cells of the pericycle.

Types of Stem

• Air Stems

  These are the most common, can be straight or adapt to a given surface. They are variable in height and thickness.

• Water Stems

  They remain below the water level at the nodes and usually have very spaced nodes.

• Underground Stems

  These are the hardest to observe, related to human nutrition. Several types are distinguished: tubers, like potatoes, bulbs like onions, and rhizomes.

How Leaves Survive Drought

• Decrease of the surface area of the leaf.
• Stomata hosted in epidermal depressions.
• Thickened epidermal hairs.
• Leaves with sclerenchyma, which prevents excessive water loss.
• Ability to be curved or rolled up.

Cellular respiration is a process of degradation of organic molecules that are stored energy to release and transform it into a form of energy that cells may use.

Inorganic Molecules for Plants from the Environment

Plants lose by evaporation from 98% to 99% of the water they absorb through the root.

Plants in arid regions may quickly lose all the water they absorb unless they have a special protective cover, a waterproof cuticle.

The opening and closure of stomata depends on environmental conditions and the needs of the plant.

The availability of water restricts plant growth, even more than the deficiency of some minerals.

Water and minerals penetrate the root. They can do so through two mechanisms: passive transport (diffusion) or active transport.

Water enters the root and is fetched by absorbent hairs and intermediate cell layers, to reach the xylem vessels.

In the case of plant cells, the existence of the cell wall adds a second factor: pressure. The combined effect of solute concentration and pressure is what we know as water potential.

Water moves from the area with higher water potential to a dissolution with lower water potential.