Plant Biology: Structure, Function, and Diversity

Understanding Plant Fundamentals

Plants are multicellular organisms characterized by being anchored to the ground by roots, which absorb water and mineral salts. Chlorophyll, a green pigment, captures light energy. The primary products of photosynthesis are carbohydrates, with oxygen produced as a secondary byproduct.

Plant Transport Systems

Most plants, with the exception of mosses, possess vascular tissues, similar to human blood vessels, through which sap flows. There are two main types of sap:

• Raw sap: A mixture of water and dissolved minerals, it rises from the roots through the xylem.
• Elaborate sap: Containing carbohydrates produced during photosynthesis, it flows through the phloem.

Plant Classification

Plants are broadly categorized into two groups based on the presence or absence of vascular tissues:

Non-Vascular Plants: Mosses

Those without vascular tissues are known as mosses. Although mosses lack true roots, stems, and leaves, they possess structures with similar functions:

• Rhizoids: Resemble roots and anchor the plant.
• Phyllids: Small, scale-like structures similar to leaves that absorb water and carbon dioxide and perform photosynthesis.
• Cauloids: False stems that transport sap.

Mosses exhibit both asexual and sexual reproduction. They can thrive in diverse environments, including tree trunks, bare rocks, and even cold lava. Mosses play a crucial role in preventing soil erosion and desertification of poor soils.

Vascular Plants

Vascular plants include ferns and seed plants.

Ferns

Ferns typically inhabit warm, humid areas, requiring water for reproduction. Unlike many plants, their roots develop along the stem rather than at a single end. Fern stems can be aerial or underground; horizontal underground stems are called rhizomes. Fern leaves are known as fronds, which are often varied in shape and usually divided. On the underside of the fronds, groups of sporangia form, where spores are produced.

Seed Plants

Seed plants possess true roots, stems, and leaves. A true seed consists of a plant embryo, cotyledons, and protective coverings. Cotyledons are small, fleshy structures inside the seed that provide nourishment to the developing plant; a seed can have one or two cotyledons. Seed plants are further divided into two main groups:

Gymnosperms

Gymnosperms have 'naked' seeds, meaning they are not enclosed within a fruit (e.g., unlike an apple). Conifers, such as pines, firs, cedars, cypresses, and junipers, are the most abundant group of gymnosperms.

Angiosperms

Angiosperms, or flowering plants, have seeds protected within a fruit. They also possess roots, stems, leaves, and flowers. Angiosperms are classified based on the number of cotyledons in their seeds:

• Monocotyledons: Have one cotyledon (e.g., lilies, cereals).
• Dicotyledons: Have two cotyledons (e.g., beech, oak).