quiz tmw

Protists

A diverse group of eukaryotic organisms, meaning their cells contain a nucleus and other complex organelles. Protists are not plants, animals, or fungi, and they vary widely in size, shape, and ecological role.

Endosymbiosis hypothesis

The leading evolutionary theory that explains the origin of mitochondria and chloroplasts, two major organelles in eukaryotic cells. It proposes that these organelles were once free-living prokaryotic cells that were engulfed by a host cell, leading to a symbiotic relationship.

Protist diversity

Protists exhibit a wide range of structural and functional diversity. They can be unicellular or multicellular, with examples including microscopic algae, giant kelp (a large, multicellular alga), colonial species like Volvox, and filamentous forms such as Spirogyra.

Contractile vacuole

A specialized organelle found in some freshwater protists, like amoeboids and ciliates. Its primary function is osmoregulation, helping the cell expel excess water to maintain osmotic balance and prevent lysis.

Photosynthetic

Describes protists, such as algae, that contain chloroplasts and can perform photosynthesis. These organisms use sunlight to convert carbon dioxide and water into organic compounds, producing oxygen as a byproduct.

Heterotrophic

Describes protists that cannot produce their own food through photosynthesis and must obtain nutrients by consuming other organisms or organic matter. This can occur through phagocytosis or absorption.

Endocytosis

A cellular process used by some heterotrophic protists to ingest food. The cell membrane surrounds a particle or small organism, forming a vesicle or vacuole that brings the food inside the cell for digestion.

Asexual reproduction

A common mode of reproduction in protists, typically involving mitosis (cell division). This process results in offspring that are genetically identical to the parent cell, allowing for rapid population growth under favorable conditions.

Sexual reproduction

A less frequent mode of reproduction in protists, involving meiosis (reduction division) and the fusion of gametes. This process leads to genetic recombination and increased genetic variation, which can be advantageous in stressful or changing environments.

Cysts

A dormant, resistant stage formed by some protists to survive unfavorable conditions. Cysts have a protective outer covering that allows them to withstand desiccation, temperature extremes, and other environmental stresses, facilitating dispersal and transmission to new hosts.

Ecological importance of protists

Protists play vital roles in various ecosystems. Photosynthetic protists, such as algae and phytoplankton, produce a significant portion of the Earth's oxygen and form the base of many aquatic food webs. Other protists serve as decomposers or consumers, contributing to nutrient cycling and energy flow.

Symbiosis

A close and prolonged interaction between two or more different species. Symbiotic relationships can be mutualistic (both organisms benefit), commensalistic (one organism benefits, and the other is not affected), or parasitic (one organism benefits, and the other is harmed).

Phylum Chlorophyta

A major division of green algae, comprising approximately 7,500 species. Green algae share many characteristics with plants, including the presence of chlorophyll a and b, and they are found in a variety of aquatic and terrestrial habitats.

Chlamydomonas

A genus of unicellular green algae commonly found in freshwater environments. Chlamydomonas cells are characterized by their flagella (for motility), a cup-shaped chloroplast (for photosynthesis), and a simple cell structure, making them a model organism for studying cellular processes.

Spirogyra

A genus of filamentous green algae characterized by its spiral-shaped chloroplasts. Spirogyra reproduces sexually through conjugation, a process in which two adjacent filaments form a bridge for the transfer of genetic material.

Ulva

A genus of multicellular green algae, commonly known as sea lettuce. Ulva has a flattened, sheet-like thallus (body) that is typically two cells thick, allowing for efficient nutrient uptake and gas exchange. It is often found in intertidal zones.

Phylum Rhodophyta

A diverse group of red algae, comprising over 5,000 species. Red algae are primarily marine organisms, with a high concentration found in warmer tropical waters. They contain unique photosynthetic pigments called phycobilins, which give them their characteristic red color and allow them to absorb blue light in deeper waters.

Coralline algae

A type of red algae that incorporates calcium carbonate into their cell walls, making them hard and rigid. Coralline algae play a crucial role in the formation and stabilization of coral reefs, as they help to cement coral skeletons together and provide habitat for other reef organisms.

Diatoms

A major group of unicellular algae characterized by their unique silica (glass) cell walls, called frustules. Diatoms are a major component of phytoplankton in both freshwater and marine environments, and they are responsible for a significant portion of global photosynthesis. Their intricate frustules are widely used in various industrial applications.

Dinoflagellates

A phylum of unicellular aquatic protists, many of which are photosynthetic. Dinoflagellates are characterized by their two flagella (one encircling the cell and the other trailing behind) and their cellulose plates. Some species produce potent toxins that can cause harmful algal blooms, such as red tides.

Euglena

A genus of euglenoid protists that can function as both autotrophs (producing food through photosynthesis) and heterotrophs (ingesting food particles). Euglena cells are characterized by their flagellum (for motility), a flexible pellicle (for shape maintenance), and a stigma (eyespot) that detects light for photosynthesis.

Kingdom Fungi

A kingdom of eukaryotic organisms that includes yeasts, molds, and mushrooms. Fungi are heterotrophic, obtaining nutrients by absorbing organic matter from their environment. They play crucial roles as decomposers, symbionts, and pathogens in various ecosystems.

Mycelium

The vegetative part of a fungus, consisting of a network of thread-like filaments called hyphae. The mycelium grows within or on a substrate, such as soil or decaying organic matter, and it is responsible for nutrient absorption and fungal growth.

Chitin

A tough, structural polysaccharide that forms the main component of fungal cell walls. Chitin provides rigidity and support to fungal cells, similar to the role of cellulose in plant cell walls. It is also found in the exoskeletons of insects and other arthropods.

Mycorrhizae

A mutualistic symbiotic association between a fungus and the roots of a plant. The fungus helps the plant absorb water and nutrients from the soil, while the plant provides the fungus with carbohydrates produced through photosynthesis. Mycorrhizae are essential for the health and productivity of many plant species.

Lichens

A composite organism formed by a symbiotic association between a fungus and a photosynthetic partner, such as cyanobacteria or green algae. The fungus provides structure and protection, while the photosynthetic partner provides the fungus with carbohydrates. Lichens are highly resilient and can colonize harsh environments, such as rocks and tree bark.