RBSE Solutions Class 11 Biology Chapter 34 Amoeba

Multiple Choice Objective Questions

Question 1. The term "Amoebae" means :
(a) Very minute animal
(b) Simplest animal
(c) Changeable animal
(d) Presence of Pseudopodia
Answer: (c) Changeable animal
In simple words: The name "Amoebae" comes from a Greek word meaning to change, which fits because Amoeba can constantly alter its body shape.

🎯 Exam Tip: Understanding the origin of biological terms can help in recalling their key characteristics and definitions.

Question 2. Role of contractile vacuole in Amoeba :
(a) Nutrition
(b) Respiration
(c) Osmoregulation
(d) Reproduction
Answer: (c) Osmoregulation
In simple words: The contractile vacuole works like a tiny pump, pushing out extra water from the Amoeba to keep its internal water balance stable.

🎯 Exam Tip: Remember that osmoregulation is crucial for freshwater organisms like Amoeba to prevent bursting due to water continuously entering their bodies.

Question 4. Type of pseudopodia in Amoeba :
(a) Actopodia
(b) Reticulopodia
(c) Lobopodia
(d) Fillopodia
Answer: (c) Lobopodia
In simple words: Amoeba uses blunt, finger-like extensions of its body, called pseudopodia, for moving and eating. These specific types are known as lobopodia.

🎯 Exam Tip: Distinguish between different types of pseudopodia based on their shape, as they indicate different modes of movement and feeding in various protists.

Question 5. Excretory substance in Amoeba :
(a) Ammonia
(b) Urea
(c) Guanine
(d) Uric acid
Answer: (a) Ammonia
In simple words: Amoeba, like many other animals living in water, gets rid of its waste nitrogen as ammonia, which easily dissolves in water.

🎯 Exam Tip: Aquatic organisms often excrete ammonia because it is highly soluble and can be quickly diluted in water, reducing its toxicity.

Very Short Answer Questions

Question 1. Amoeba belongs to which class?
Answer: Amoeba belongs to the class Rhizopoda.
In simple words: Amoeba is classified under the group called Rhizopoda.

🎯 Exam Tip: Remember the classification of common organisms to answer such direct questions accurately.

Question 2. The posterior end of Amoeba is called as ?
Answer: The posterior end of Amoeba is called Hyman.
In simple words: The back part of an Amoeba is known as Hyman.

🎯 Exam Tip: Be precise with specific anatomical terms when describing parts of an organism.

Question 4. Which structures release enzymes into the food vacuoles?
Answer: Lysosomes are the structures that release enzymes into the food vacuoles.
In simple words: Lysosomes put special chemicals, called enzymes, into the food sacs to help break down food.

🎯 Exam Tip: Remember that lysosomes are often called the "digestive centers" of the cell due to their enzyme content.

Question 5. Give the names of excretory crystals in Amoeba.
Answer: The excretory crystals found in Amoeba are Biurates and Triurates.
In simple words: Amoeba gets rid of waste products in the form of tiny crystals named Biurates and Triurates.

🎯 Exam Tip: List both types of crystals accurately, as they are specific waste products in Amoeba.

Question 6. Where Amoeba is found?
Answer: Amoeba is commonly found in stagnant fresh water.
In simple words: You can find Amoeba in still, fresh water bodies.

🎯 Exam Tip: State the typical habitat of Amoeba clearly and concisely.

Question 7. Name the mode of reproduction in Amoeba that takes place during favourable conditions.
Answer: During favorable conditions, Amoeba primarily reproduces by binary fission.
In simple words: When conditions are good, Amoeba makes copies of itself by splitting into two, which is called binary fission.

🎯 Exam Tip: Differentiate between modes of reproduction in favorable versus unfavorable conditions for Amoeba.

Question 8. Which provides biconvex shape to the nucleus?
Answer: The honey comp lattice provides the biconvex shape to the nucleus.
In simple words: The honey comb lattice helps give the nucleus its biconvex, or lens-like, shape.

🎯 Exam Tip: Identify specific cellular structures responsible for maintaining organelle shapes within an organism.

Question 9. What is meaning of term “Proteus"?
Answer: The term "Proteus" means the ability to change shape frequently. Amoeba is often referred to as Proteus animalcule because of its constantly changing form.
In simple words: "Proteus" means something that can change its shape often. Amoeba is like this because it keeps changing its body form.

🎯 Exam Tip: Link the term "Proteus" to the characteristic of shape-changing, which is key to Amoeba's biology.

Question 11. Concern to nutrition, Amoeba is?
Answer: Regarding nutrition, Amoeba is omnivorous and holozoic. This means it eats both plant and animal matter, and it engulfs its food whole.
In simple words: Amoeba eats all kinds of food, including both plants and animals. It takes in food by swallowing it completely.

🎯 Exam Tip: Define both 'omnivorous' and 'holozoic' in the context of Amoeba's feeding habits to provide a complete answer.

Question 12. Where food is digested in Amoeba?
Answer: Food is digested inside the food vacuoles in Amoeba. These are temporary sacs formed around the engulfed food particles.
In simple words: Amoeba digests its food inside special temporary sacs called food vacuoles.

🎯 Exam Tip: Clearly state the specific organelle responsible for digestion in Amoeba.

Question 13. What is the mode of respiration in Amoeba.
Answer: Amoeba performs aerobic respiration. This means it uses oxygen to break down food and release energy.
In simple words: Amoeba breathes using oxygen, which is called aerobic respiration, to get energy from its food.

🎯 Exam Tip: Distinguish between aerobic and anaerobic respiration and explain why Amoeba utilizes the former.

Question 14. In what form, stored food is found in Amoeba.
Answer: Stored food in Amoeba is primarily found in the form of Glycogen and Fat.
In simple words: Amoeba keeps its extra food as glycogen and fat for future use.

🎯 Exam Tip: List the major forms of stored energy in Amoeba accurately.

Question 15. Taking in of solid food by Amoeba is called as?
Answer: The process of taking in solid food by Amoeba is called Phagocytosis. It involves engulfing the food particle using its pseudopodia.
In simple words: When Amoeba eats solid food, it's called phagocytosis. This means it swallows the food particle whole.

🎯 Exam Tip: Use the correct scientific term 'Phagocytosis' for the engulfment of solid food by cells.

Short Answer Questions

Question 1. How the terms systole and diastole are related to Amoeba?
Answer: Amoeba is a freshwater animal. Due to its semipermeable membrane, water continuously flows into its body through a process called endosmosis. To manage this, Amoeba constantly expels out the excess water using its contractile vacuole. This process where the contractile vacuole suddenly contracts to release water is called systole. The filling of the contractile vacuole with water is called diastole. This action helps in osmoregulation and also plays a role in respiration and excretion, preventing the Amoeba from swelling and bursting.
In simple words: Water keeps entering Amoeba because it lives in fresh water. To get rid of this extra water, a special sac called a contractile vacuole pushes it out (systole). The filling of this sac is diastole. This helps Amoeba control its water balance and also helps with breathing and waste removal.

🎯 Exam Tip: Explain both systole and diastole in the context of the contractile vacuole's function in osmoregulation, respiration, and excretion.

Question 3. What is cryptomitosis?
Answer: Cryptomitosis is a special type of mitosis (cell division). It is characterized by the formation of a modified achromatic spindle and the absence of clearly differentiated chromosomes.
In simple words: Cryptomitosis is a kind of cell division. It's different because the spindle that pulls chromosomes apart is changed, and the chromosomes don't look distinct like they normally do.

🎯 Exam Tip: Define cryptomitosis by highlighting its key distinguishing features compared to typical mitosis.

Question 4. What is encystment? How it benefits Amoeba?
Answer: Encystment is a process where Amoeba develops a three-layered protective cyst around itself during unfavorable environmental conditions. This cyst acts as a protective covering, helping the Amoeba survive until conditions become favorable again.
In simple words: When things are bad (like no food or too hot), Amoeba forms a tough, protective wall around itself, called a cyst. This helps it stay alive until conditions get better.

🎯 Exam Tip: Explain both what encystment is and its crucial adaptive advantage for Amoeba's survival.

Question 5. Give the phillotaxic responses of Amoeba.
Answer: Phillotaxis refers to the positive response of Amoeba to external stimuli. Amoeba shows positive responses to various stimuli such as food contact, dim to moderate light, gravity, water current, and the cathode (negative electrode).
In simple words: Phillotaxis means Amoeba moves towards certain things it likes. It moves towards food, dim light, gravity, water flow, and the negative pole of electricity.

🎯 Exam Tip: List a few diverse examples of positive phillotaxic responses to demonstrate understanding.

Question 6. What will be the effect on contractile vacuole, if Amoeba is place in marine water?
Answer: If Amoeba is placed in marine (salt) water, the contractile vacuole will soon disappear. This happens because marine water is hypertonic, meaning water will leave the Amoeba's body instead of entering. Therefore, the contractile vacuole is no longer needed to expel excess water.
In simple words: If Amoeba is put in salty ocean water, its contractile vacuole will vanish. This is because water will leave the Amoeba, so it won't need the vacuole to pump water out anymore.

🎯 Exam Tip: Relate the function of the contractile vacuole to the osmotic environment (freshwater vs. saltwater) to explain its disappearance.

Question 7. Explain folding unfolding theory of locomotion in Amoeba.
Answer: The Molecular Folding and Unfolding Theory, proposed by Goldacre and Lorsch in 1950, explains how Amoeba moves based on changes in its cytoplasm. According to this theory, the inner part of the endoplasm, called plasma sol, has folded protein molecules. The outer part of the endoplasm, called plasma gel, contains unfolded protein molecules. The movement (gelation) involves the unfolding of these microfilaments, while the fluid state (solation) involves their folding. This continuous folding and unfolding of proteins helps the cytoplasm change its state, allowing Amoeba to form pseudopodia and move.
In simple words: This theory explains how Amoeba moves. It says that the inner liquid part of Amoeba's body has folded proteins, and the outer gel-like part has unfolded proteins. Amoeba moves by these proteins constantly folding and unfolding, which makes its body change between a liquid and a gel, helping it create its false feet to crawl.

🎯 Exam Tip: Clearly describe how the change in state (sol to gel and vice-versa) of the cytoplasm, driven by protein changes, facilitates pseudopodial movement.

Question 9. Write the features of class-sarcodina.
Answer: Key features of the class Sarcodina include the presence of blunt pseudopodia and the absence of a pellicle (a thin, flexible outer layer).
In simple words: Sarcodina, the group Amoeba belongs to, has false feet that are blunt and does not have a thin outer skin or covering.

🎯 Exam Tip: Identify the two primary distinguishing characteristics of organisms in the class Sarcodina.

Question 10. Why the pseudopodia in amoeba are called as lobopodia?
Answer: The pseudopodia in Amoeba are called lobopodia because they are blunt and finger-like extensions of the cytoplasm.
In simple words: Amoeba's false feet are called lobopodia because they are thick, blunt, and shaped like fingers.

🎯 Exam Tip: Connect the term 'lobopodia' directly to the physical description of Amoeba's pseudopodia.

Question 11. Explain egestion in Amoeba.
Answer: Egestion in Amoeba is the process of removing undigested food from its body. This typically occurs through exocytosis, where the waste material is expelled from the posterior end by a temporary opening in the plasmalemma.
In simple words: Egestion is how Amoeba gets rid of food it couldn't digest. It pushes out the waste from its back end through a temporary opening.

🎯 Exam Tip: Define egestion and specify how and where it occurs in Amoeba.

Question 12. Why it is more correct to called amoeba as a cellular.
Answer: It is more correct to call Amoeba "a cellular" rather than "unicellular" because, structurally, it consists of only one cell. However, this single cell performs all the vital activities necessary for life, making it a complete functional entity on its own, not just a component of a larger organism.
In simple words: Amoeba is called "a cellular" because even though it's just one cell, that single cell does everything needed to live, like eating and moving, making it a complete organism by itself.

🎯 Exam Tip: Explain the distinction between 'unicellular' and 'a cellular' in the context of an organism like Amoeba performing all life functions within a single cell.

Question 13. What is assimilation?
Answer: Assimilation is the process where the digested food is absorbed by the surrounding cytoplasm and distributed to all parts of the Amoeba. This distribution happens through the cyclic movement of the cytoplasm, known as cyclosis. These absorbed nutrients are then used to build new protoplasm and for energy.
In simple words: Assimilation is when Amoeba's body takes in the digested food and uses it to grow and get energy. The food moves around inside the Amoeba's body to reach all parts.

🎯 Exam Tip: Define assimilation in Amoeba and mention the role of cyclosis in nutrient distribution.

Question 14. Give an account of vacuoles found in Amoeba.
Answer: The endoplasm of Amoeba primarily contains three types of vacuoles: food vacuoles, contractile vacuoles, and water vacuoles. Food vacuoles help in digestion, contractile vacuoles regulate water balance (osmoregulation), and water vacuoles store water.
In simple words: Amoeba has three main types of small sacs called vacuoles: food vacuoles for digestion, contractile vacuoles for removing extra water, and water vacuoles for storing water.

🎯 Exam Tip: List and briefly describe the function of each type of vacuole found in Amoeba.

Question 15. What is the role of food vacuole in Amoeba.
Answer: The food vacuole in Amoeba is where intracellular digestion takes place. Amoeba engulfs food particles, forming a food vacuole around them. Lysosomal enzymes are then released into this vacuole to break down the food.
In simple words: The food vacuole in Amoeba acts like a stomach. It holds the food that Amoeba eats, and special enzymes are added to it to break down the food inside the cell.

🎯 Exam Tip: Explain that food vacuoles are sites of intracellular digestion and highlight the role of lysosomal enzymes.

Essay Type Questions

Question 1. Describe ultra structure of Amoeba. Give labelled diagram.
Answer: Amoeba is a microscopic and a cellular organism. Structurally, it is unicellular, performing all vital life activities within its single cell. Its size typically ranges from 0.2 to 0.3 mm, though some species can be larger. The shape of Amoeba is irregular as it lacks a rigid cell wall, being covered only by a flexible plasma membrane. Thus, it has no definite anterior or posterior ends. Amoeba is generally colorless, translucent, and jelly-like. It is polypodial, meaning it forms one to many blunt, finger-like pseudopodia, known as lobopodia, which aid in locomotion and food ingestion. The largest pseudopodium is considered the anterior end, while the opposite end is the posterior or uroid end. The entire organism is enclosed by a selectively permeable plasma membrane, about 1 µ thick.

Internally, Amoeba consists of cytoplasm and a nucleus. The cytoplasm is divided into two main parts: the outer ectoplasm (or ectosarc) and the inner endoplasm. The ectoplasm is transparent, homogeneous, and lacks cell organelles. It is widest at the anterior end of the main pseudopodium, forming a structure called the hyaline cap. The endoplasm, in contrast, contains various organelles such as food vacuoles, contractile vacuoles, and a biconvex nucleus. The nucleus has a honey-comb lattice structure.
In simple words: Amoeba is a tiny, single-celled creature with an irregular shape because it doesn't have a hard outer wall. It moves and eats using finger-like extensions called pseudopodia. Inside, it has a main liquid part (cytoplasm) divided into clear outer and grainy inner parts, along with a nucleus and tiny sacs for food and water balance.

🎯 Exam Tip: When describing ultrastructure, cover key external features (size, shape, membrane, pseudopodia) and internal components (cytoplasm divisions, nucleus, vacuoles), explaining their roles. Diagrams are crucial for such questions.

Question 2. What is food of Amoeba? Give an account of methods of ingestion's in Amoeba.
Answer:
**Nutrition:** Amoeba is omnivorous and holozoic. Its diet includes bacteria, diatoms, algae, dead organic material, and other small protozoans. It takes in food by engulfing it whole.

**Ingestion:** The process of taking in food is called ingestion, and it can occur at any point on the Amoeba's surface. Amoeba exhibits four primary methods of ingestion:
1. **Circumvallation:** This method is used to ingest active or motile food. Amoeba forms a large food cup with its pseudopodia, trapping the food, and then creates a food vacuole around it.
2. **Circumfluence:** This method is used to ingest inactive or non-motile food. Amoeba surrounds the food with its pseudopodia, forming a food cup, which then develops into a food vacuole.
3. **Import:** In this method, food, such as algae, directly enters the cytoplasm upon contact with the plasmalemma (cell membrane). A food vacuole then forms around the food inside the cytoplasm.
4. **Invagination:** Here, the plasmalemma indents at the point of food contact, forming a tube-like structure into the cytoplasm. The food enters through this tube, and a food vacuole develops at the inner end of the tube.
In simple words: Amoeba eats many kinds of tiny things like bacteria and algae. It takes in food in different ways: it can surround moving food (circumvallation), surround still food (circumfluence), absorb food directly through its skin (import), or make a small pocket to pull food inside (invagination).

🎯 Exam Tip: Clearly state Amoeba's diet and then explain each ingestion method with a brief description to differentiate them.

Question. What is osmoregulation? Explain its process in Amoeba.
Answer: **Osmoregulation** is the process by which an organism maintains a stable balance of water and dissolved salts in its body. In Amoeba, which is a freshwater animal, water constantly enters the body through endosmosis. To prevent excess water from building up and potentially causing the cell to burst, Amoeba uses a contractile vacuole to expel this water. The process involves the formation of a small contractile vacuole near the nucleus, which grows as water droplets fuse with it (diastole). Once it reaches its full size, the vacuole moves towards the plasmalemma and suddenly bursts, releasing the water outside (systole). This continuous cycle of filling and expelling water is how Amoeba performs osmoregulation.
In simple words: Osmoregulation is how Amoeba keeps the right amount of water inside its body. Because it lives in fresh water, water always tries to enter. So, Amoeba has a special sac called a contractile vacuole that fills up with water and then squeezes it out to keep the water balance steady.

🎯 Exam Tip: Define osmoregulation and then detail the two phases (diastole and systole) of the contractile vacuole's action in Amoeba.

Question 5. Describe modes of reproduction in Amoeba with the help of diagrams.
Answer: Amoeba primarily exhibits asexual reproduction through several methods:
1. **Binary Fission:** This is the most common mode of reproduction in Amoeba under favorable conditions. In this method, the parent Amoeba divides into two daughter Amoebae. First, the nucleus divides, followed by the cytoplasm, resulting in two identical offspring. This ensures rapid multiplication when resources are plentiful.
2. **Multiple Fission:** During unfavorable conditions, Amoeba forms a three-layered protective cyst wall around itself. Inside this cyst, the nucleus divides repeatedly by mitosis, forming 500 to 600 daughter nuclei. Each nucleus gets surrounded by a small amount of cytoplasm and develops into a cell membrane, forming structures called amoebullae. When conditions become favorable, the cyst absorbs water, swells, and bursts to release these amoebullae, each developing into a young Amoeba.
3. **Sporulation:** According to Taylor, Amoeba also undergoes sporulation during unfavorable conditions. The nuclear membrane bursts, releasing chromatin granules into the cytoplasm. These granules form groups of 2 to 3, becoming a "polyenergid nucleus." Each group then gets a bit of cytoplasm and a cell membrane, eventually forming a spore sheath. These resulting structures are called pseudopodiospores. The parent Amoeba eventually breaks down to release these spores, which develop into young Amoebae under favorable conditions.
4. **Regeneration:** While not a primary reproductive method, Amoeba possesses a remarkable power of regeneration. A small fragment of an Amoeba, provided it contains a piece of the nucleus, can regenerate into a complete, new Amoeba.
In simple words: Amoeba mainly reproduces without a partner (asexually). In good conditions, it just splits into two (binary fission). In bad conditions, it can form a protective cover (cyst) and divide into many tiny Amoebae inside (multiple fission), or it can make special spores (sporulation) that grow into new Amoebae later. Also, if a piece of Amoeba has part of its control center (nucleus), it can grow into a whole new Amoeba (regeneration).

🎯 Exam Tip: For each reproductive mode, explain the process and state the conditions (favorable/unfavorable) under which it occurs. While diagrams are requested, a clear textual description is also essential.