Plant Anatomy: Xylem Structure and Function

Study Notes

Xylem fibers are elongated, lignified, and pointed at both ends.
Xylem functions include conducting water and nutrients from roots to leaves and providing mechanical support.
Xylem parenchyma consists of living, thin-walled cells primarily involved in storing starch and fatty substances.

Phloem consists of four main elements: sieve tubes, companion cells, phloem fibers, and phloem parenchyma.
Sieve tubes are elongated, tubular cells with perforated walls and facilitate food translocation from leaves to storage organs.
Companion cells, which are elongated, support the function of sieve tubes, predominantly found in angiosperms.
Phloem parenchyma consists of living cells and is responsible for storing food materials.
Phloem fibers are long and lignified, providing additional mechanical strength.

Dermal tissue acts as the outer covering of plants, forming a protective barrier and controlling environmental interactions.
The epidermis is typically one layer thick and covers all primary plant structures, lacking chloroplasts.
Periderm refers to tissues that replace the epidermis in woody plants, particularly in older stems.

A fruit, characteristic of angiosperms, develops from a mature ovary post-fertilization; parthenocarpic fruits form without fertilization.
Fruits consist of pericarp (the fruit wall) and seeds, with pericarp varying between dry and fleshy types.
Seeds develop from ovules post-fertilization and consist of a seed coat and an embryo, which comprises radicle, embryonal axis, and cotyledons.
Dicotyledonous seeds have a seed coat made of two layers, hilum (attachment point), micropyle (small opening), and food-storing endosperm.

Roots may undergo modifications for various functions:
- Food storage: roots become swollen to store nutrients.
- Support: prop roots and stilt roots provide stability for plants.
- Respiration: pneumatophores facilitate oxygen intake for plants in swampy areas.

Plant tissues are organized into three systems: epidermis (outer surface), ground tissue (nutrient manufacture and storage), and vascular tissue (xylem and phloem for nutrient transport).
Tissues are further divided into meristematic (actively dividing) and permanent tissues (specialized functions).

Meristems, located at growing tips (apical), sides (lateral), and base (intercalary), contribute to primary and secondary plant growth.
Apical meristems lead to vertical growth, while lateral meristems increase the girth of plants.

Permanent tissues arise from meristematic tissues and can be simple (uniform cells) or complex (mixed cell types).
Simple permanent tissues include parenchyma (storage and photosynthesis), collenchyma (structural support), and sclerenchyma (strength).

Parenchyma is found in various plant parts, storing substances like starch and oils and participating in photosynthesis.
It facilitates wound repair and renews meristematic activity and aids in gas exchange (aerenchyma) for aquatic plants.

Collenchyma cells offer structural support in young plant parts, characterized by thickened primary walls.
Sclerenchyma provides rigidity throughout the plant body, composed of thickened cell walls to withstand mechanical stress.