Kingdom Prokaryotae Bacteria and Cyanobacteria FSc Part 1, Chapter 6, with 100 MCQs for MDCAT

Bacteria
Definition:
Bacteria are microscopic, single-celled organisms that belong to the domain Bacteria. They are among the most diverse and abundant organisms on Earth, found in virtually every environment, from soil and water to extreme environments like hot springs and deep-sea vents.
Characteristics:
Size and Shape: Bacteria typically range in size from 0.5 to 5 micrometers and come in various shapes, including rods (bacilli), spheres (cocci), and spirals (spirilla).
Cell Structure: Bacterial cells lack a nucleus and membrane-bound organelles. Their genetic material is a single circular chromosome located in a region called the nucleoid.
Cell Wall: Most bacteria have a rigid cell wall composed of peptidoglycan, which provides structural support and protection. The composition of the cell wall varies between Gram-positive and Gram-negative bacteria, which can be distinguished by the Gram stain technique.
Reproduction: Bacteria primarily reproduce asexually through binary fission, a process where a single cell divides into two identical daughter cells.
Metabolism: Bacteria exhibit diverse metabolic pathways and can be classified based on their energy and carbon sources. They can be autotrophic (producing their own food) or heterotrophic (relying on external organic matter).
Roles and Functions: Bacteria play essential roles in various ecological processes, including nutrient cycling, decomposition, and symbiotic relationships with other organisms. Some bacteria are pathogenic and can cause diseases in humans, animals, and plants.
Cyanobacteria
Definition:
Cyanobacteria, also known as blue-green algae, are a phylum of bacteria that obtain their energy through photosynthesis. Despite their name, cyanobacteria are not true algae but share some similarities, such as the ability to perform photosynthesis.
Characteristics:
Size and Shape: Cyanobacteria vary widely in size and shape, ranging from unicellular forms to multicellular filaments and colonies.
Cell Structure: Like other bacteria, cyanobacteria lack a nucleus and membrane-bound organelles. They possess thylakoid membranes, where photosynthesis occurs, similar to the chloroplasts of plants and algae.
Pigmentation: Cyanobacteria contain pigments such as chlorophyll a, phycocyanin, and phycoerythrin, which give them their characteristic blue-green color and enable them to capture light energy for photosynthesis.
Nitrogen Fixation: Many cyanobacteria have the ability to fix atmospheric nitrogen into usable forms like ammonia, playing a crucial role in nitrogen cycling. This process is facilitated by specialized cells called heterocysts in some filamentous cyanobacteria.
Habitat: Cyanobacteria are found in diverse environments, including freshwater, marine, and terrestrial ecosystems. They can thrive in extreme conditions, such as hot springs, salt flats, and polar regions.
Ecological Importance: Cyanobacteria are primary producers in many ecosystems, forming the base of the food web. They also contribute to the formation of oxygen in the atmosphere through photosynthesis. Some cyanobacteria form harmful algal blooms in aquatic systems, releasing toxins that can negatively impact water quality and aquatic life