Amoeba

Introduction
The Amoebidae is more than 80 µm in length. Not all species of amoeba reproduce the same way. They are found in a wide range of habitats. They use their pseudopodia for movement. Amoeba are made of many different parts. The Plasma Membrane, Protoplasm, Cytoplasm, Ectoplasm, Endoplasm, Nucleus, Pseudopodia, Contractile Vacuole, Food Vacuole, Water Vacuole, Golgi bodies, and Mitochondria are some of the structures that make up and amoeba. The amoeba is a large,single-celled protozoan that belongs to the genus Protozoa and phylum Sarcodina. The largest organism can grow to 1 mm. They grow best in moist habitats.

Body Design


The length of the Amoebidae is more than 80 µm in length. It has cylindrical pseudopodia with hyaline (glassy translucent appearance) caps. Most species of Amoebidae are polypodial but a few are monopodial. They have many cytoplasmic crystals. Their nuclear material is often in tiny fragments.

Specifically Amoeba's lack a specific shape since their pseudopodia change their shape with movement. Amoeba's have a condition called asymmetry meaning that the Amoeba's body can be divided into two parts. The Amoeba's body can be divided in two, the Plasmalema and Protoplasm. Plasmalema, the combination of protein and lipid which is thin, semi-permeable, and elastic, covers the Amoeba's surface. The Plasmalema, also known as the Plasma membrane, serves the Amoeba in many ways. It gives the Amoeba its shape, holds various organelles in the protoplasm, and helps the Amoeba attach to any solid surfaces. Since the membrane is elastic it easily produces pseudopodia, takes in oxygen and water through diffusion, as well as expels carbon dioxide and other excretory materials through the membrane.

The protoplasm is a thick jelly like substance surrounding the Plasma membrane. The protoplasm can be divided into the Cytoplasm and the Nucleus. The Cytoplasm can be divided into Ectoplasm and Endoplasm. Ectoplasm, the cytoplasm that is directly behind the plasma membrane, is thick, transparent, and contractile. It also serves protection for the organelles in the Amoeba's body. It aids the Amoeba in the production of pseudopodia. The endoplasm is surrounded by the ectoplasm. It is less thick and only semi-permanent. The plasmagel is the thick outer portion of the endoplasm. The plasmasol is the inner liquid portion of the endoplasm. Plasmagel and plasmasol can transform into each other. Endoplasm contains the organelles of the cell, aids in different physiological functions, and the changing of the plasmagel and plasmasol assist in the production of pseudopodia.

There is only one nucleus in an Amoeba, and it is located in the center of the Amoeba's body. Covering the nucleus is the nuclear membrane made of protein and lipid. The nucleus manages all of the cell body's functions, and takes part in reproduction. Pseudopodia are made of plasmalema, ectoplasm, and endoplasm. Pseudopodia aid in obtaining food, as well as play a major role in movement.

The three types of vacuoles in Amoeba are: contractile, food, and water vacoules. Contractile vacoules are found in the Amoeba's endoplasm. They are transparent, fast growing, and can be contracted or expanded constantly. They store the body's watery substances, help expel excess water and excretion, and help expel the carbon dioxide that is produced during the process of respiration. The food vacuole is materialized around the food. The size, shape, and number of possible food materials decides the size, shape, and number of food vacuoles. They store food, aid in the Amoeba's digestion and in excretion. The water vacuole is round and filled with water. It is noncontractile and there can be more than one. This vacuole stores water and keeps the water balance constant in the Amoeba.

The Golgi bodies look like small tubules and vesicles. Golgi bodies aid in secretion and excretion of food. The mitochondria are located near the contractile vacuoles, and the aid in respiration and energy generation.

Life Cycle
Not all species of Amoeba reproduce the same way. Some reproduce through spores, some through binary fission, multiple fission, etc. In preperation for reproduction, A. proteus withdraws its pseudopodia to make a more spherical shape. In the nucleus, mitosis occurs, pinching the cytoplasm in the middle of the original cell forming two daughter cells. Since A. proteus reproduces asexually, the cell division results in two identical cells. The original cell just copies its genetic code into the second cell. The homologous chromosomes do not cross over at all.

Asexual reproduction in an Amoeba is carried out in a process known as binary fission. The first step in binary fission is for the amoeba to attain a spherical shape by pulling its pseudopodia in. Two daughter cells are formed by mitotic cell divison where the nucleus and cytoplasm are pinched, creating two identical copies of genetic information. If there are perfect conditions, binary fission can be as quick as 30-60 minutes.

Another way that amoeba can reproduce is by multiple fission. The only reason multiple fission is undergone is if the surrounding environment lacks the nutrients necessary for binary fission. This process has the same beginning as binary fission. The amoeba begins by pulling its pseudopodia in so that it creates a spherical shape. If the amoeba finds itself in harsh or hostile conditions, it covers itself in a protective coating called a cyst. This cyst is capable of surviving conditions which would be harmful and/or potentially harmful to an amoeba without the cyst covering. Multiple mitosis occurs inside the cyst, creating several daughter cells. Once this cyst reaches survivable/better conditions, it bursts, releasing all of the daughter cells into the environment.

Ecology
Amoeba are found from the Antarctica to the Arctic. They can be found in caves, mines, and also in some deep aquifer systems, but not in all. Marine amoeba can be found in coastal-rock pools, on the fronds of seaweed, and in the open ocean. They are particularly abundant in soil. The more moist a soil is, the more likely it is contain a larger amount of active amoeba.