Biology and Classification of Plant Species

Characteristics of Plants

Plants are living things and multicellular eukaryotes (cells with nuclei). Plants have tissues formed by clusters of specialized cells that perform the same function. These associated tissues form their bodies. They are autotrophs that perform photosynthesis, since they produce their own organic matter from inorganic substances using light as an energy source. They are green because they contain chlorophyll and live fixed to the soil.

Evolution and Adaptation

We classify plants into those without flowers or seeds (mosses and ferns) and flowering plants with seeds (gymnosperms and angiosperms). All samples appeared some 500 million years ago, evolving from certain species of algae. They spread across the continents thanks to the development of:

• Epidermal tissue: To prevent the loss of water from the body.
• Maintenance tissue: Allowing them to grow and stay upright.
• Vascular (driver) tissue: Carrying water and nutrients through their interior.
• Flowers and seeds: To reproduce without the need for water.

The Process of Photosynthesis

Photosynthesis is the process by which the plant obtains organic matter (glucose) from inorganic substances (water, carbon dioxide, and mineral salts), thanks to the energy that chlorophyll absorbs from sunlight.

Plant Nutrition Phases

The nutrition of a plant involves the following phases:

• Absorption: Absorbent root hairs soak up water and mineral salts, forming gross sap.
• Transport: Gross sap moves upwards to the leaves through woody vessels.
• Photosynthesis: In the leaves, photosynthesis takes place, producing organic matter (glucose) and oxygen, which is released into the atmosphere through the stomata.
• Distribution: Glucose produced in photosynthesis dissolves in water to form elaborated sap, which is distributed throughout the plant via Liberian vessels.

Classification of Plant Species

Mosses and Ferns

Mosses are the least evolved group since they lack vascular (driver) tissue. They do not have true roots, stems, or leaves. They need water to reproduce so that the male gametes can swim to reach and fertilize the female gametes.

Ferns possess vascular (driver) tissue. They have true roots, stems, and leaves. Like mosses, they still need water for reproduction so that male gametes can swim to reach and fertilize the female gametes.

Flowering and Seed-Bearing Plants

Flowering plants and seeds have all tissues well developed, including true roots, stems, and leaves. They have succeeded in achieving reproductive independence from water because male gametes move through the air inside grains of pollen. They are classified as:

• Gymnosperms: Plants with "naked" seeds; that is, seeds are not enclosed within a fruit. They have unattractive flowers without petals or sepals.
• Angiosperms: Plants with seeds enclosed in a protective fruit. They generally present very showy flowers with petals and sepals.