algi

Algae are a diverse group of photosynthetic organisms that live in aquatic environments, ranging from microscopic phytoplankton to large seaweeds. They are not a single coherent lineage but a collection of several taxonomic groups that together perform primary production in many ecosystems. Commonly studied groups include green algae (Chlorophyta), brown algae (Phaeophyceae), red algae (Rhodophyta), diatoms, and dinoflagellates. Cyanobacteria, historically called blue-green algae, are photosynthetic bacteria that are sometimes grouped with algae in informal contexts but belong to a different domain of life.

Physiology and morphology vary widely among algae. Some are unicellular and free-living, others form complex multicellular colonies or thalli. They contain chlorophylls and accessory pigments that give them green, brown, or red hues. Algae use light energy to convert carbon dioxide and water into organic matter, releasing oxygen in the process. They occupy diverse habitats, including oceans, rivers, lakes, wetlands, and moist soils, and they support many food webs as primary producers.

Ecology and environmental impact are central to algae. They form the base of many aquatic ecosystems and contribute significantly to global carbon and nutrient cycles. Algal blooms can occur when nutrients are abundant, sometimes producing toxins that affect wildlife and human health or creating dead zones by depleting oxygen. Climate factors, nutrient loading, and water chemistry influence bloom dynamics and distribution.

Humans use algae in various ways, from dietary staples and supplements (for example, certain edible seaweeds and spirulina) to industrial applications such as biofuels, wastewater treatment, cosmetic products, and agar or carrageenan production. The study of algae remains foundational in ecology, phycology, and environmental science.