Test: Amoeba - 1 (Old NCERT) - NEET MCQ

The structures presents in Amoeba are pseudopod plasma lemma, nucleus, contractile vacuole, Food vacuole, water globules, endoplasmic reticulum, ribosomes, golgi bodies, mitochondria, lysosomes and microtubules.

Since amoeboid movement involves crawling, it needs contact of body with a solid substratum. Adhesion with substratum is facilitated by glycocalyx and also by traces of inorganic ions such as Ca⁺⁺, Mg+2 and K⁺, that are present in the surrounding water.

Vacoules in amoeba are generally used for digestion while excretion takes place through body surface.

Amoeba is an unicellular organism also known as amoeboid, which has the capacity to modify its body by expanding and revoking pseudopods. Carbon dioxide and ammonia are the main waste products of amoeba and they are excreted out through the body by the process called diffusion with the help of contractile vacuole.

Amoebas "breathe" by allowing oxygen from their aquatic environments to diffuse through their cell membranes. Hence, if it is placed in an oxygen-less atmosphere, it might die. However, there are amoebae, which do not have mitochondria (the organelle responsible for generating cellular energy) because they live in environments lacking in oxygen, or "anoxic conditions. "

By removing the nucleus, the "blueprints" of cell function are missing. The cell will not die immediately is that there was still enough mRNA to allow production of the necessary enzymes. If too much time goes by, the mRNA is all used up, no more enzymes are made, and the chemical reactions required for life stop.

Contractile vacuoles, common in freshwater Protozoa, eliminate water that moves into the cells by osmosis. The contractile vacuole is present in amoeba but absent in Entamoeba because Amoeba lives in water and needs osmotic regulation. The contractile vacuole is basically a water bubble within the endoplasm of A. proteus. Its function is to regulate the water content of the cell. It is also a means of excreting its waste from the cell (out through the cell membrane) via diffusion. E. histolytica doesn't need to have a contractile vacuole as it lives in an isotonic environment. Since the osmotic concentration of its body remains equal to its surroundings entry of water through osmosis will not happen. Therefore, there is no need of contractile vacuole. Thus, the correct answer is C.

The protoplasm of an amoeba is made up of an outer layer termed the ectoplasm which surrounds an inner portion called the endoplasm. Locomotion of an amoeba is thought to occur due to the sol-gel conversion of the protoplasm within its cell.

Reproduction in Amoeba under unfavourable conditions:

• A method known as multiple fission is adopted by the unicellular organism Amoeba to survive and reproduce under unfavourable conditions.
• When the conditions are unfavourable, Amoeba withdraws its pseudopodia and becomes almost round.
• It secretes a hard covering called cyst. The cyst forms a thick protective coat around it.
• Inside the cyst, the nucleus undergoes repeated divisions to form many nuclei.
• Nuclear division is followed by the division of cytoplasm. 

It would likely lyse. Freshwater amoebae contain a specialized vacuole for expelling water. Since freshwater is a hypotonic solution, osmosis will continually transfer water into the amoeba. Without a way to counteract this, the amoeba will swell to the point it bursts. To that extent, freshwater species have developed contractile vacuoles. These will swell with water, and when close to bursting, will move to the outer edge of the cell membrane. They will then contract, releasing water to the external environment of the cell. It’s a continual process, and marine amoebae likely don’t have the ability to produce contractile vacuoles since they reside in hypertonic environments. This will lead to them swelling and eventually lysing.

Nucleus is the major organelle of the Amoeba, located centrally; it controls reproduction and many other important functions like eating and growth.

Amoeba, also spelled ameba, plural amoebas or amoebae, any of the microscopic unicellular protozoans of the rhizopodan order Amoebida. The well-known type species, Amoeba proteus, is found on decaying bottom vegetation of freshwater streams and ponds.

Digestion in amoeba is intracellular taking place within the cell. The food taken in remains in a food vacuole formed by the cell membrane and small part of the cytoplasm. The vacuoles are transported deeper into the cells by cytoplasmic movements. Here they fuse with lysosomes that contains enzymes.

Circumvallation: With the help of pseudopodia food cup form to engulf active prey like Paramecium

Binary fission in Amoeba.

Amoeba reproduces by the common asexual reproduction method called binary fission. After replicating its genetic material through mitotic division, the cell divides into two equal sized daughter cells.

In the cytoplasm, food vacuole fuses with lysosomes containing digestive enzymes. In this, the complex and non-diffusible nutrients are changed into simple and diffusible nutrients. Medium inside the food vacuole is first acidic but later becomes alkaline (as in the alimentary canal of man).