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Protozoa, also known as single-celled eukaryotes, are microscopic organisms that lack the complex tissues and organs found in multicellular organisms. They are classified under the kingdom Protista and are characterized by several key features:
**General Characteristics:**
* **Unicellular:** They consist of a single cell that performs all the functions necessary for survival.
* **Eukaryotic:** They have a nucleus containing genetic material (DNA) and other membrane-bound organelles.
* **Microscopic:** They are generally too small to be seen with the naked eye and require a microscope for observation.
* **Heterotrophic:** They obtain their food by ingesting other organisms or organic matter.
* **Diverse:** Protozoa exhibit a wide range of shapes, sizes, and lifestyles.
**Classification:**
Protozoa are classified into four major subphyla based on their mode of locomotion and other characteristics:
**1. Sarcomastigophora:**
* **Locomotion:** These protozoa move using pseudopodia (false feet) or flagella (whip-like structures).
* **Examples:** Amoeba, Euglena, Trypanosoma
**2. Sporozoa:**
* **Locomotion:** These protozoa are non-motile in their adult stage and reproduce through spores.
* **Examples:** Plasmodium (causes malaria), Toxoplasma gondii
**3. Cnidospora:**
* **Locomotion:** These protozoa are also non-motile and are characterized by the presence of cnidocysts (stinging cells).
* **Examples:** Myxosporidia, Microsporidia
**4. Ciliophora:**
* **Locomotion:** These protozoa move using cilia (hair-like structures).
* **Examples:** Paramecium, Stentor
**Details about each subphylum:**
**1. Sarcomastigophora:**
* **Pseudopodia:** These are temporary extensions of the cell membrane that allow the protozoan to engulf food particles.
* **Flagella:** These are long, whip-like structures that propel the protozoan through its environment.
* **Examples:**
* **Amoeba:** A common freshwater protozoan that moves using pseudopodia and engulfs food by phagocytosis.
* **Euglena:** A photosynthetic protozoan that possesses both plant-like and animal-like characteristics. It can move using a flagellum and can also produce its own food through photosynthesis.
* **Trypanosoma:** A parasitic protozoan that is transmitted by insects and causes diseases such as African trypanosomiasis (sleeping sickness) and Chagas disease.
**2. Sporozoa:**
* **Spores:** These are resistant structures that contain the protozoan's genetic material and are capable of surviving harsh conditions.
* **Examples:**
* **Plasmodium:** The causative agent of malaria, a serious disease that is transmitted by mosquitoes. It has a complex life cycle that involves both sexual and asexual reproduction.
* **Toxoplasma gondii:** A parasitic protozoan that can infect a variety of animals, including humans. It is most commonly transmitted through undercooked meat or contact with cat feces.
**3. Cnidospora:**
* **Cnidocysts:** These specialized cells contain a stinging apparatus that is used to capture prey or defend against predators.
* **Examples:**
* **Myxosporidia:** Parasitic protozoa that infect fish and other aquatic animals.
* **Microsporidia:** Obligate intracellular parasites that infect a wide range of hosts, including humans.
**4. Ciliophora:**
* **Cilia:** These tiny hair-like structures cover the surface of the protozoan and help it move and capture food.
* **Examples:**
* **Paramecium:** A common freshwater protozoan that is characterized by its slipper-shaped body and cilia. It is a predator that feeds on bacteria and other small organisms.
* **Stentor:** A large, trumpet-shaped protozoan that is often found in ponds and lakes. It is a filter feeder that uses its cilia to sweep food particles into its mouth.
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