The Fundamental Unit of Life — NCERT Solutions | Class 9 Science | Academia Aeternum
Ch 5  ·  Q–
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Class 9 Science Exercise NCERT Solutions Olympiad Board Exam
Chapter 5

The Fundamental Unit of Life

Step-by-step NCERT solutions with stress–strain analysis and exam-oriented hints for Boards, JEE & NEET.

10 Questions
20–30 min Ideal time
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Q1
NUMERIC3 marks
Differentiate between Plant Cell and Animal Cell.
📘 Concept & Theory Concept and Theory ›

Cell is the basic structural and functional unit of life. Although both plant and animal cells are eukaryotic cells and possess a nucleus, cytoplasm and cell membrane, they differ in several structural features according to the functions they perform.

Plant cells perform photosynthesis and require additional support and food storage mechanisms. Therefore, they possess a cell wall, chloroplasts and a large central vacuole. Animal cells do not prepare their own food and therefore lack chloroplasts and cell walls. They possess centrioles and numerous lysosomes which help in cell division and intracellular digestion respectively.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the common features of eukaryotic cells.

  2. Identify the structures present only in plant cells.

  3. Identify the structures characteristic of animal cells.

  4. Compare both cells on the basis of structure and function.

  5. Present the differences in a tabular form.

📊 Graph / Figure Graph / Figure ›
Plant Cell Animal Cell Cell Wall Chloroplast Large Vacuole Centrioles Nucleus Mitochondrion Plant cells possess a rigid cell wall, photosynthetic chloroplasts, and a large central vacuole. Animal cells lack a cell wall and chloroplasts, but contain centrioles and smaller, multiple vacuoles.
Plant Cell and Animal Cell Comparison
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  3 steps
  1. Both plant and animal cells are eukaryotic cells. However, they differ in many structural and functional characteristics as shown below.
  2. Features Plant Cell Animal Cell
    Cell Wall Present outside the plasma membrane and provides rigidity, shape and mechanical support to the cell. Absent. The outer boundary is formed only by the plasma membrane.
    Shape Generally larger and rectangular, polygonal or hexagonal in shape due to the presence of the rigid cell wall. Generally smaller and irregular, spherical or rounded in shape.
    Chloroplast Present. Chloroplasts contain chlorophyll and carry out photosynthesis to prepare food. Absent because animals cannot synthesize their own food by photosynthesis.
    Vacuoles One large, permanent central vacuole is generally present for storage of water, minerals and cell sap. Vacuoles are usually small, temporary and may even be absent.
    Centrioles Generally absent in higher plant cells. Present and play an important role in spindle formation during cell division.
    Food Storage Food is generally stored in the form of starch and oils. Food is generally stored in the form of glycogen and fats.
    Lysosomes Usually absent or present in smaller numbers. Present in larger numbers and perform intracellular digestion.
  3. Why do these Differences Exist?
    • Plant cells need rigid support to remain upright; therefore, they possess a cell wall.
    • Plants manufacture food through photosynthesis; hence chloroplasts are present.
    • Large vacuoles maintain turgidity and store cell sap in plants.
    • Animals require greater flexibility and movement; therefore, their cells lack a rigid cell wall.
    • Animal cells possess centrioles and numerous lysosomes to facilitate rapid cell division and intracellular digestion.
🎯 Exam Significance Exam Significance ›
  • This question is one of the most frequently asked three-mark and five-mark questions in CBSE and State Board examinations.
  • Comparative features of plant and animal cells are regularly tested in school practical examinations and viva voce.
  • Questions based on cell wall, chloroplast, vacuoles, centrioles and lysosomes are commonly asked in scholarship examinations, Olympiads and foundation examinations for NEET and other competitive entrance tests.
  • Understanding these differences forms the basis for studying tissues, photosynthesis, cell division and physiology in higher classes.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. Both plant and animal cells are eukaryotic cells.

  2. Plant cells possess a cell wall, chloroplasts and a large central vacuole.

  3. Animal cells generally possess centrioles and numerous lysosomes.

  4. Plant cells are usually larger and more regular in shape than animal cells.

  5. Structural differences between plant and animal cells are adaptations to their different modes of nutrition and functions.
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NUMERIC3 marks
How is a Prokaryotic Cell Different from a Eukaryotic Cell?
📘 Concept & Theory Concept and Theory ›

Living organisms are made up of cells that can broadly be classified into two categories: prokaryotic cells and eukaryotic cells.

The term prokaryotic means "before nucleus". These cells are primitive and do not possess a true, membrane-bound nucleus or membrane-bound cell organelles. Their genetic material lies freely in the cytoplasm in a region called the nucleoid.

The term eukaryotic means "true nucleus". These cells possess a well-organized, membrane-bound nucleus and several membrane-bound organelles such as mitochondria, endoplasmic reticulum, Golgi apparatus and lysosomes. Their cellular organization is therefore more complex and efficient.

Prokaryotic cells are considered evolutionarily older and simpler, whereas eukaryotic cells are structurally advanced and highly organized.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the meaning of prokaryotic and eukaryotic cells.

  2. Compare the presence or absence of a true nucleus.

  3. Compare the presence of membrane-bound cell organelles.

  4. Compare their level of organization and examples.

  5. Present the differences systematically in tabular form.

📊 Graph / Figure Graph / Figure ›
PROKARYOTIC CELL EUKARYOTIC CELL Nucleoid (Free DNA) True Nucleus Membrane-boundOrganelles Structure Features: • Lacks a nuclear envelope and nuclear membrane. • Simple internal design completely lacking organelles. Structure Features: • DNA enclosed safely inside a double-membrane nucleus. • High complexity with specialized cellular machinery.
Type of Cells
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  3 steps
  1. Prokaryotic and eukaryotic cells differ in their structure, organization and complexity. The major differences are given below.
  2. Features Prokaryotic Cells Eukaryotic Cells
    Nucleus A true, membrane-bound nucleus is absent. Genetic material is present in a nucleoid region. A well-defined, membrane-bound nucleus is present.
    Cell Organelles Membrane-bound organelles are absent. Only ribosomes are present. Membrane-bound organelles such as mitochondria, Golgi apparatus, endoplasmic reticulum and lysosomes are present.
    Size and Complexity Cells are generally smaller and structurally simple. Cells are generally larger and structurally more complex.
    Cell Organisation Organisms are usually unicellular. Organisms are generally multicellular but may also be unicellular.
    Chromosomes Usually possess a single circular chromosome without a nuclear membrane. Possess multiple linear chromosomes enclosed within the nucleus.
    Mode of Cell Division Divide mainly by binary fission. Divide by mitosis and meiosis.
    Examples Bacteria and cyanobacteria. Plants, animals, fungi and protists.
  3. Why are Eukaryotic Cells More Advanced?
    • The presence of a true nucleus protects and regulates genetic material.
    • Membrane-bound organelles divide cellular functions among different structures, making the cell more efficient.
    • Specialized organelles allow eukaryotic organisms to develop tissues, organs and complex body systems.
    • Prokaryotic cells are simpler and perform all activities within a single compartment of cytoplasm.
🎯 Exam Significance Exam Significance ›
  • This is one of the most important comparison-based questions frequently asked in CBSE and State Board examinations.
  • The differences between prokaryotic and eukaryotic cells are often asked as three-mark and five-mark questions.
  • Questions related to nucleoid, membrane-bound organelles and examples of prokaryotes and eukaryotes are commonly asked in Olympiads, NTSE and foundation examinations for NEET.
  • Understanding this topic forms the basis for advanced concepts such as cell division, genetics, microbiology and evolution.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. Prokaryotic cells do not possess a true nucleus, whereas eukaryotic cells have a membrane-bound nucleus.

  2. Membrane-bound organelles are absent in prokaryotic cells but present in eukaryotic cells.

  3. Prokaryotic cells are generally smaller and simpler, while eukaryotic cells are larger and more complex.

  4. Prokaryotic organisms are usually unicellular, whereas eukaryotic organisms may be unicellular or multicellular.

  5. Bacteria are examples of prokaryotes, while plants, animals and fungi are examples of eukaryotes.
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NUMERIC3 marks
What would happen if the plasma membrane ruptures or breaks down?
📘 Concept & Theory Concept and Theory ›

The plasma membrane, also called the cell membrane, is the outer living boundary of the cell. It separates the contents of the cell from the external environment and maintains the integrity of the cell.

The plasma membrane is selectively permeable, which means that it permits only certain substances to enter or leave the cell. It regulates the movement of water, nutrients, gases and waste products and thereby maintains a stable internal environment essential for the survival of the cell.

Since all cell organelles and cytoplasm are enclosed by the plasma membrane, any damage to this membrane severely affects the normal functioning of the cell.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the functions of the plasma membrane.

  2. Understand its role in enclosing cell contents.

  3. Consider what happens when the membrane loses its integrity.

  4. Explain the consequences of leakage of cellular materials.

  5. Conclude the effect on the survival of the cell.

📊 Graph / Figure Graph / Figure ›
Healthy Cell Ruptured Cell Leakage of Cell Contents Plasma membrane maintains cellular integrity Rupture causes leakage and ultimately cell death
Effect of Rupture of Plasma Membrane
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  8 steps
  1. If the plasma membrane ruptures or breaks down, the cell can no longer maintain its boundary with the external environment.
  2. The plasma membrane loses its ability to enclose the cytoplasm and cell organelles.
  3. The cellular contents, such as cytoplasm, enzymes and essential molecules, begin to leak out of the cell.
  4. Harmful substances and unwanted materials from the surroundings may enter the cell uncontrollably.
  5. The selective permeability of the membrane is lost, and the cell can no longer regulate the movement of substances.
  6. Normal metabolic activities stop because the internal environment of the cell is disturbed.
  7. Therefore, when the plasma membrane ruptures or breaks down, the cell loses its contents, fails to regulate the exchange of materials and ultimately dies.
  8. Why Does the Cell Die?
    • The plasma membrane acts as a protective barrier around the cell.
    • It maintains the proper concentration of water, ions and nutrients inside the cell.
    • Rupture of the membrane destroys this controlled environment.
    • Essential enzymes and biomolecules leak out, and cellular activities cease.
    • Consequently, the cell cannot survive and undergoes death.
🎯 Exam Significance Exam Significance ›
  • This question tests the understanding of the structure and functions of the plasma membrane and is frequently asked in CBSE and State Board examinations.
  • The concept of selective permeability is important for short-answer and competency-based questions.
  • Similar concepts are asked in Olympiads, NTSE and foundation examinations for NEET.
  • Understanding the role of the plasma membrane forms the basis for studying diffusion, osmosis, transport mechanisms and cell physiology in higher classes.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. The plasma membrane is the living outer boundary of the cell.

  2. It is selectively permeable and regulates the movement of substances.

  3. It keeps the cytoplasm and cell organelles enclosed within the cell.

  4. Rupture of the plasma membrane causes leakage of cellular contents.

  5. The loss of membrane integrity ultimately results in the death of the cell.
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NUMERIC3 marks
What would happen to the life of a cell if there was no Golgi apparatus?
📘 Concept & Theory Concept and Theory ›

The Golgi apparatus is a membrane-bound cell organelle discovered by Camillo Golgi. It consists of a stack of flattened, membrane-bound sacs called cisternae.

The Golgi apparatus acts as the packaging, processing and dispatching centre of the cell. Proteins synthesized by ribosomes and lipids synthesized by the endoplasmic reticulum are transported to the Golgi apparatus, where they are modified, sorted, packaged and transported to different parts of the cell or secreted outside the cell.

The Golgi apparatus also plays an important role in the formation of lysosomes and contributes to the synthesis and maintenance of the plasma membrane.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the major functions of the Golgi apparatus.

  2. Consider the role of Golgi apparatus in processing proteins and lipids.

  3. Understand its role in lysosome formation.

  4. Examine its contribution to plasma membrane formation and maintenance.

  5. Conclude how the absence of Golgi apparatus affects the survival of the cell.

📊 Graph / Figure Graph / Figure ›
GOLGI APPARATUS THE CELLULAR PACKAGING & DISPATCHING CENTRE CIS FACE RECEIVING SIDE TRANS FACE SHIPPING SIDE Incoming Cargo PROTEINS & LIPIDS FROM ER Secretory Vesicles PROTEIN EXOCYTOSIS Lysosome Formation HYDROLYTIC ENZYMES Membrane Integration LIPID & PROTEIN REPAIR CRITICAL PATHOLOGY & CELLULAR IMPACT Absence or dysfunction of the Golgi apparatus completely disrupts cellular macromolecule processing, metabolic packaging, intracellular protein sorting, and vital lysosome formation.
Golgi Apparatus: Packaging and Dispatching Centre of the Cell
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  8 steps
  1. If there were no Golgi apparatus in a cell, several essential cellular functions would be disrupted.
  2. Proteins and lipids synthesized in the endoplasmic reticulum would not be properly modified and processed.
  3. The cell would fail to sort and package these substances into vesicles for transport to their proper destinations.
  4. Lysosomes would not be formed properly because the Golgi apparatus is responsible for packaging digestive enzymes into lysosomal vesicles.
  5. Intracellular digestion and removal of worn-out cell components would be severely affected due to the absence of lysosomes.
  6. Formation and maintenance of the plasma membrane would also be impaired because the Golgi apparatus contributes membrane materials to the cell surface.
  7. Therefore, in the absence of the Golgi apparatus, the cell would not be able to properly process, package and transport proteins and lipids. Lysosome formation and plasma membrane maintenance would fail, causing severe disruption of cellular activities and ultimately affecting the survival of the cell.
  8. Why is Golgi Apparatus Called the Packaging Factory of the Cell?
    • It receives proteins and lipids from the endoplasmic reticulum.
    • It chemically modifies these substances according to the needs of the cell.
    • It packages them into membrane-bound vesicles.
    • It transports these packaged materials to different cellular locations or outside the cell.
    • It forms lysosomes and contributes to membrane synthesis and secretion.
🎯 Exam Significance Exam Significance ›
  • This is an important application-based question frequently asked in CBSE and State Board examinations.
  • The functions of the Golgi apparatus and lysosome formation are common topics in competency-based and short-answer questions.
  • Questions on cell organelles and their functions are frequently asked in NTSE, Olympiads and foundation examinations for NEET.
  • Understanding the role of the Golgi apparatus forms the basis for studying secretion, intracellular transport and cell physiology in higher classes.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. The Golgi apparatus acts as the packaging and dispatching centre of the cell.

  2. It modifies, sorts and packages proteins and lipids.

  3. It plays an essential role in the formation of lysosomes.

  4. It contributes to the synthesis and maintenance of the plasma membrane.

  5. In the absence of the Golgi apparatus, transport, secretion and intracellular digestion would be severely affected, threatening cell survival.
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NUMERIC3 marks
Which organelle is known as the powerhouse of the cell? Why?
📘 Concept & Theory Concept and Theory ›

Cells require energy to perform various life processes such as growth, movement, transport of substances, synthesis of biomolecules, cell division and repair. This energy is obtained from food and released through the process of cellular respiration.

The organelle responsible for cellular respiration is the mitochondrion. Mitochondria are double membrane-bound organelles found in the cytoplasm of eukaryotic cells. They contain their own DNA and ribosomes and can synthesize some of their own proteins.

During cellular respiration, food molecules such as glucose are oxidized in the mitochondria, and the released energy is stored in the form of Adenosine Triphosphate (ATP). ATP acts as the energy currency of the cell and supplies energy for all cellular activities.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the function of mitochondria.

  2. Understand the process of cellular respiration.

  3. Identify the role of ATP in providing energy.

  4. Relate ATP production to the term "powerhouse of the cell".

  5. Conclude why mitochondria are essential for cell survival.

📊 Graph / Figure Graph / Figure ›
MITOCHONDRION THE POWERHOUSE OF THE CELL ATP ATP ATP Outer Membrane SMOOTH BARRIER Intermembrane Space PROTON ACCUMULATION Inner Membrane ELECTRON TRANSPORT CHAIN Ribosomes ORGANELLE PROTEIN SYNTHESIS Cristae Folds MAXIMIZED SURFACE AREA Matrix Fluid KREBS CYCLE ENZYMES Circular DNA (mtDNA) SELF-REPLICATING GENOME ATP Synthase ROTARY ATP GENERATOR FUNCTIONAL SIGNIFICANCE & ATP SYNTHESIS Mitochondria convert nutrients into adenosine triphosphate (ATP) via cellular respiration. Dysfunction halts energy production, leading to multi-system failure, neuromuscular disorders, and is a primary driver in aging, metabolic syndrome, and cellular apoptosis.
Mitochondrion – Powerhouse of the Cell
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  10 steps
  1. Mitochondria are the sites of cellular respiration in eukaryotic cells.
  2. During cellular respiration, food molecules are broken down and oxidized, releasing energy.
  3. The released energy is used to synthesize Adenosine Triphosphate (ATP).
  4. ATP stores energy in its high-energy phosphate bonds.
  5. When ATP breaks down,
  6. \[\mathrm{ATP \rightarrow ADP + P_i + Energy}\]
  7. the released energy is utilized by cells to perform various metabolic activities.
  8. Therefore, mitochondrion is known as the powerhouse of the cell because it produces ATP, which provides the energy required for all cellular activities and sustains life processes.
  9. Why is ATP Called the Energy Currency of the Cell?
    • ATP stores chemical energy in its phosphate bonds.
    • It can be broken down rapidly whenever energy is required.
    • The energy released is used for active transport, biosynthesis, movement and cell division.
    • Since almost all cellular activities depend upon ATP, it is called the energy currency of the cell.
  11. Additional Facts about Mitochondria
    • Mitochondria possess a double membrane consisting of an outer membrane and a highly folded inner membrane.
    • The folds of the inner membrane are called cristae, which increase the surface area for ATP production.
    • Mitochondria contain their own DNA and ribosomes and are therefore called semi-autonomous organelles.
    • Cells that require large amounts of energy, such as muscle cells, contain a large number of mitochondria.
🎯 Exam Significance Exam Significance ›
  • This is one of the most frequently asked short-answer questions in CBSE and State Board examinations.
  • The terms mitochondria, cellular respiration and ATP are important for one-mark and competency-based questions.
  • Questions related to ATP production, cristae and the semi-autonomous nature of mitochondria are commonly asked in Olympiads, NTSE and foundation examinations for NEET.
  • Understanding the role of mitochondria forms the basis for advanced topics such as respiration, metabolism and bioenergetics in higher classes.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. Mitochondrion is called the powerhouse of the cell.

  2. It is the site of cellular respiration.

  3. Food molecules are oxidized in mitochondria to release energy.

  4. The released energy is stored in the form of ATP.

  5. ATP provides energy for all essential cellular activities and is therefore called the energy currency of the cell.
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NUMERIC3 marks
Where do the lipids and proteins constituting the cell membrane get synthesised?
📘 Concept & Theory Concept and Theory ›

The plasma membrane is primarily composed of lipids and proteins. According to the fluid mosaic model, the membrane consists of a phospholipid bilayer with proteins embedded within it. These components are synthesized by the Endoplasmic Reticulum (ER), an extensive network of membrane-bound tubules and sacs present in the cytoplasm.

The Endoplasmic Reticulum is of two types:

  • Rough Endoplasmic Reticulum (RER): It bears ribosomes on its surface and is mainly involved in protein synthesis.
  • Smooth Endoplasmic Reticulum (SER): It lacks ribosomes and is responsible for the synthesis of lipids and fats.

After their synthesis, lipids and proteins are transported to the Golgi apparatus, where they are modified, packaged and sent to the plasma membrane.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the major constituents of the plasma membrane.

  2. Identify the cell organelle responsible for their synthesis.

  3. Differentiate between the functions of rough ER and smooth ER.

  4. Explain how these molecules become components of the plasma membrane.

  5. State the final answer clearly.

📊 Graph / Figure Graph / Figure ›
MEMBRANE SYNTHESIS PATHWAY SYNTHESIS & TRANSPORT OF LIPIDS AND PROTEINS FOR PLASMA MEMBRANE Rough ER PROTEIN SYNTHESIS Smooth ER LIPID SYNTHESIS Transport Vesicle SHUTTLE CARGO Golgi Apparatus CARGO PROCESSING Secretory Vesicle TARGETED TRANSIT Plasma Membrane LIPID BILAYER TARGET Membrane Fusion VESICLE INTEGRATION 01 | ER SYNTHESIS Rough ER ribosome sheets synthesize membrane proteins, while Smooth ER synthesizes phospholipids & lipids. 02 | VESICLE TRANSIT Newly synthesized lipids and proteins are packaged into transport vesicles which bud off and travel to the Golgi. 03 | GOLGI PROCESSING Golgi cisternae modify the cargo (e.g., glycosylation), sort them, and package them into outgoing secretory vesicles. 04 | MEMBRANE FUSION Vesicles fuse with the lipid bilayer during exocytosis, integrating lipids & proteins into the plasma membrane.
Synthesis of Cell Membrane Components
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  9 steps
  1. The plasma membrane is mainly composed of lipids and proteins.
  2. Lipids constituting the cell membrane are synthesized in the Smooth Endoplasmic Reticulum (SER).
  3. Proteins constituting the cell membrane are synthesized in the Rough Endoplasmic Reticulum (RER) by the ribosomes attached to its surface.
  4. These newly synthesized lipids and proteins are transported to the Golgi apparatus, where they undergo modification and packaging.
  5. The packaged materials are then transported to the plasma membrane and become its structural components.
  6. Therefore, lipids and proteins constituting the cell membrane are synthesized in the Endoplasmic Reticulum (ER). Lipids are produced in the Smooth Endoplasmic Reticulum (SER), whereas proteins are synthesized in the Rough Endoplasmic Reticulum (RER) by the attached ribosomes.
  7. Flow of Cell Membrane Component Formation
  8. The process may be summarized as:
  9. Smooth ER → Lipid Synthesis
    Rough ER + Ribosomes → Protein Synthesis
    Golgi Apparatus → Modification and Packaging
    Plasma Membrane → Incorporation of Lipids and Proteins
  10. Why are ER and Golgi Apparatus Functionally Related?
    • The Endoplasmic Reticulum synthesizes proteins and lipids.
    • The Golgi apparatus modifies and packages these substances.
    • Vesicles transport the packaged materials to their final destinations.
    • Together, these organelles maintain membrane formation and cellular activities.
🎯 Exam Significance Exam Significance ›
  • This is an important short-answer question frequently asked in CBSE and State Board examinations.
  • The distinction between Smooth ER and Rough ER is commonly tested in competency-based and objective questions.
  • Questions related to ribosomes, protein synthesis and membrane biogenesis are frequently asked in NTSE, Olympiads and foundation examinations for NEET.
  • This concept forms the basis for understanding protein synthesis, secretion, membrane transport and cell physiology in higher classes.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. The plasma membrane is mainly composed of lipids and proteins.

  2. The Endoplasmic Reticulum is the site of synthesis of these components.

  3. Smooth Endoplasmic Reticulum synthesizes lipids.

  4. Rough Endoplasmic Reticulum synthesizes proteins with the help of ribosomes.

  5. The Golgi apparatus modifies and packages these substances before they become part of the plasma membrane.
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NUMERIC3 marks
How does an Amoeba obtain its food?
📘 Concept & Theory Concept and Theory ›

Amoeba is a unicellular, microscopic organism that does not possess a fixed shape. It continuously changes its shape by forming temporary finger-like projections called pseudopodia, which means "false feet".

Amoeba obtains its food by a process known as endocytosis. Endocytosis is the process in which the plasma membrane folds inward and engulfs substances from the external environment, forming a food vacuole inside the cell.

Since Amoeba lacks specialized organs for feeding, digestion occurs inside the cell. The ingested food is enclosed in a food vacuole where digestive enzymes act upon it.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Identify the feeding organ of Amoeba.

  2. Recall the role of pseudopodia.

  3. Understand the process of endocytosis.

  4. Explain the formation of food vacuole.

  5. Describe digestion and absorption of nutrients.

📊 Graph / Figure Graph / Figure ›
NUTRITION IN AMOEBA MECHANISM OF ENDOCYTOSIS (PHAGOCYTOSIS) 01 | INGESTION / SENSING Amoeba detects a nearby food particle (prey). It begins to project flexible pseudopodia towards it. 02 | PSEUDOPODIA EXTENSION Pseudopodia ("false feet") extend and wrap around the food particle, creating a cup-like engulfment cavity. 03 | VACUOLE FORMATION Membranes fuse, trapping the food inside a food vacuole. Lysosomes inject digestive enzymes to break it down. 04 | ABSORPTION & WASTE Nutrients are absorbed into the cytoplasm. Undigested waste is expelled through membrane fusion (exocytosis).
Nutrition in Amoeba by Endocytosis
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  10 steps
  1. Amoeba obtains its food by the process of endocytosis.
  2. When Amoeba encounters a food particle, it extends finger-like projections called pseudopodia towards the food.
  3. The pseudopodia gradually surround and engulf the food particle.
  4. The plasma membrane encloses the food particle and forms a food vacuole inside the cytoplasm.
  5. Digestive enzymes are secreted into the food vacuole and digest the food into simpler substances.
  6. The digested nutrients diffuse into the cytoplasm and are utilized by the cell for energy, growth and other metabolic activities.
  7. The undigested material is expelled outside the cell through the plasma membrane.
  8. Therefore, Amoeba obtains its food by endocytosis, in which the flexible plasma membrane forms pseudopodia that engulf the food particle and enclose it in a food vacuole for digestion.
  9. Sequence of Nutrition in Amoeba
  10. Food Particle → Formation of Pseudopodia → Engulfment of Food → Food Vacuole Formation → Digestion → Absorption → Egestion of Undigested Matter
  11. Why is Endocytosis Important in Amoeba?
    • Amoeba has no mouth or digestive system.
    • Its flexible plasma membrane enables it to engulf food particles.
    • Endocytosis allows ingestion of solid food particles.
    • Formation of a food vacuole ensures intracellular digestion.
    • This process enables Amoeba to survive and obtain nutrients necessary for life.
🎯 Exam Significance Exam Significance ›
  • This is a frequently asked short-answer question in CBSE and State Board examinations.
  • Terms such as pseudopodia, endocytosis and food vacuole are important for one-mark and competency-based questions.
  • The process of nutrition in Amoeba is commonly asked in Olympiads, NTSE and foundation examinations for NEET.
  • Understanding endocytosis forms the basis for advanced concepts of membrane transport, intracellular digestion and cellular physiology.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. Amoeba is a unicellular organism with no fixed shape.

  2. It captures food using temporary projections called pseudopodia.

  3. The process of engulfing food is called endocytosis.

  4. Food is digested inside a food vacuole by digestive enzymes.

  5. Digested nutrients are absorbed by the cytoplasm, and undigested matter is expelled outside the cell.
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NUMERIC3 marks
What is osmosis?
📘 Concept & Theory Concept and Theory ›

Cells continuously exchange substances with their surroundings. One of the most important processes involved in this exchange is osmosis.

Osmosis is a special type of diffusion that involves only the movement of solvent molecules, usually water, through a selectively permeable (semi-permeable) membrane.

During osmosis, water molecules move from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration) until equilibrium is established.

In simple words, water moves from a dilute solution to a concentrated solution through a selectively permeable membrane.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the meaning of diffusion.

  2. Understand that osmosis involves only solvent molecules.

  3. Identify the role of a selectively permeable membrane.

  4. Determine the direction of movement of water molecules.

  5. State the definition of osmosis clearly.

📊 Graph / Figure Graph / Figure ›
OSMOSIS SELECTIVELY PERMEABLE MEMBRANE DYNAMICS NET WATER FLOW Hypotonic Solution HIGH WATER POTENTIAL Free Water (Solvent) HIGH FREE CONCENTRATION Selectively Permeable Membrane RESTRICTS LARGE SOLUTES Hypertonic Solution LOW WATER POTENTIAL Solute Particles LARGE IMPERMEABLE MOLECULES PHYSICAL DYNAMICS & CELLULAR IMPORTANCE Water moves down its concentration gradient (from high to low water potential) to achieve equilibrium. This process is critical for cellular turgor pressure in plants, nutrient absorption in kidneys, and maintaining osmotic homeostasis in red blood cells to prevent lysis or crenation.
Osmosis Through a Selectively Permeable Membrane
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  7 steps
  1. Consider two solutions separated by a selectively permeable membrane.
  2. One solution has a lower solute concentration and therefore contains a higher concentration of water molecules.
  3. The other solution has a higher solute concentration and therefore contains a lower concentration of water molecules.
  4. Water molecules pass through the selectively permeable membrane from the region of higher water concentration to the region of lower water concentration.
  5. Therefore, osmosis is the process in which solvent molecules, usually water, move from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration) through a selectively permeable membrane.
  6. Important Conditions for Osmosis
    • A selectively permeable membrane must be present.
    • There should be a difference in concentration between the two solutions.
    • Only solvent molecules move through the membrane.
    • The movement continues until equilibrium is attained.
  8. Examples of Osmosis
    • Absorption of water by plant roots from the soil.
    • Swelling of raisins when kept in water.
    • Shrinking of red blood cells in a concentrated salt solution.
    • Movement of water into plant cells, making them turgid.
🎯 Exam Significance Exam Significance ›
  • Osmosis is one of the most frequently asked concepts in CBSE and State Board examinations.
  • Questions based on hypotonic, hypertonic and isotonic solutions commonly appear in competency-based and application-oriented questions.
  • Osmosis is an important topic in Olympiads, NTSE and foundation examinations for NEET.
  • Understanding osmosis is essential for studying transport mechanisms, plant physiology and cell biology in higher classes.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. Osmosis is a special type of diffusion involving only solvent molecules.

  2. It occurs through a selectively permeable membrane.

  3. Water moves from a region of higher water concentration to a region of lower water concentration.

  4. Equivalently, water moves from a dilute solution to a concentrated solution.

  5. smosis plays an essential role in maintaining water balance in living organisms.
← Q7
8 / 10  ·  80%
Q9 →
Q9
NUMERIC3 marks
Carry out the following osmosis experiment:
• Take four peeled potato halves and scoos each one out to make potato cups.
One of these potato cups should be made from a boiled potato.
Put each potato cup in a trough containing water. Now,
(a) Keep cup A empty
(b) Put one teaspoon sugar in cup B
(c) Put one teaspoon salt in cup C
(d) Put one teaspoon sugar in the boiled potato cup D.
Keep these for two hours. Then observe the four potato cups and answer the following:
(i) Explain why water gathers in the hollowed portion of B and C.
(ii) Why is potato A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed out portions of A and D.
📘 Concept & Theory Concept and Theory ›

This experiment demonstrates the process of osmosis. Osmosis is the movement of water molecules from a region of higher water concentration (lower solute concentration) to a region of lower water concentration (higher solute concentration) through a selectively permeable membrane.

The cells of a fresh potato possess living plasma membranes that act as selectively permeable membranes. When sugar or salt is placed inside the hollow of the potato cup, the concentration inside the cavity becomes greater than that of the surrounding water. Consequently, water moves into the cavity by osmosis.

In a boiled potato, the cells are dead and the plasma membrane loses its selectively permeable nature. Therefore, osmosis does not occur.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the definition of osmosis.

  2. Identify which potato cups contain concentrated solutions.

  3. Determine the direction of movement of water molecules.

  4. Understand the purpose of the control setup.

  5. Explain why osmosis does not occur in the boiled potato cup.

📊 Graph / Figure Graph / Figure ›
Potato Osmosis Experiment Demonstration A deep-sea blue themed animation showing water accumulating in potato hollows due to osmosis. Potato Osmosis Experiment Cup A (No Solute) Sugar Cup B (Sugar) Salt Cup C (Salt) Sugar Cup D (Sugar + Boiled) Observation: Water accumulates in cups B and C through living potato membranes. In Cup D, boiling has destroyed the cell membrane's selectivity.
Potato Osmosis Experiment
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  12 steps
  2. Potato Cup Contents Observation After Two Hours Reason
    A Empty No water accumulates in the cavity. No concentration difference is created.
    B Sugar Water collects inside the cavity. Water enters due to osmosis.
    C Salt Water collects inside the cavity. Water enters due to osmosis.
    D Sugar in boiled potato cup No water accumulates in the cavity. Boiling destroys the selectively permeable membranes.
  3. Explain why water gathers in the hollowed portions of B and C
  4. Sugar in cup B and salt in cup C dissolve and form concentrated solutions.
  5. The water surrounding the potato cups has a higher concentration of water molecules than the solution inside the cavities.
  6. The plasma membrane of the potato cells acts as a selectively permeable membrane.
  7. Water moves from the surrounding trough into the cavities by osmosis.
  8. Therefore, water gathers in the hollowed portions of cups B and C because water enters the cavities through the selectively permeable membranes of the potato cells by the process of osmosis.
  9. Why is potato A necessary for this experiment?
  10. Potato cup A is kept empty and serves as a control setup.
  11. Since no sugar or salt is present, no concentration gradient is established and water does not accumulate inside the cavity.
  12. The observation in cup A confirms that the accumulation of water in cups B and C occurs because of the presence of concentrated solutions and not due to any other factor.
  13. Explain why water does not gather in the hollowed portions of A and D.
  14. In cup A, the cavity is empty and therefore no concentration difference exists between the inside of the cavity and the surrounding water. Hence, osmosis does not occur and water does not accumulate.
  15. In cup D, although sugar is present, the potato has been boiled. Boiling kills the potato cells and destroys the selectively permeable nature of their plasma membranes. Since osmosis requires a living selectively permeable membrane, water cannot enter the cavity and therefore does not accumulate.
🎯 Exam Significance Exam Significance ›
  • This is one of the most important activity-based questions from the chapter and is frequently asked in CBSE examinations.
  • The experiment tests understanding of osmosis, concentration gradient and selectively permeable membranes.
  • Questions based on control experiments and boiled potato cups are common in competency-based and case-study questions.
  • Similar concepts are asked in Olympiads, NTSE and foundation examinations for NEET.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. Osmosis requires a selectively permeable membrane.

  2. Water moves from a dilute solution to a concentrated solution.

  3. Sugar and salt create a concentration gradient that causes water movement.

  4. Potato cup A acts as the control setup.

  5. Boiling destroys the selectively permeable nature of potato cell membranes, preventing osmosis.
← Q8
9 / 10  ·  90%
Q10 →
Q10
NUMERIC2 marks
Which type of cell division is required for the growth and repair of the body, and which type is involved in the formation of gametes?
📘 Concept & Theory Concept and Theory ›

Cell division is the process by which a parent cell divides to produce new cells. In multicellular organisms, cell division is essential for growth, repair and reproduction. There are two main types of cell division:

  • Mitosis: A type of cell division in which one parent cell produces two genetically identical daughter cells having the same number of chromosomes as the parent cell.
  • Meiosis: A type of cell division in which one parent cell undergoes two successive divisions to produce four daughter cells, each having half the number of chromosomes. These daughter cells develop into gametes.

Mitosis maintains chromosome number and helps in body growth and repair, whereas meiosis reduces chromosome number and enables sexual reproduction.

🗺️ Solution Roadmap Step-by-step Plan ›

  1. Recall the two major types of cell division.

  2. Identify the purpose of mitosis.

  3. Identify the purpose of meiosis.

  4. Compare the number of daughter cells formed.

  5. State which type of division is responsible for growth and which forms gametes.

📊 Graph / Figure Graph / Figure ›
Mitosis vs. Meiosis Comparison A deep-sea blue themed animation comparing Mitosis (somatic cell division) and Meiosis (gamete production). Mitosis Meiosis One Division Two Identical Daughter Cells (2n) Two Divisions Four Unique Haploid Cells (n)
Mitosis and Meiosis
✏️ Solution Complete Solution ›
Step-by-step Solution  ·  8 steps
  1. During growth and repair, damaged or worn-out cells must be replaced by new cells that are identical to the original cells.
  2. In mitosis, one parent cell divides only once and forms two genetically identical daughter cells.
  3. Since the daughter cells have the same chromosome number and genetic information as the parent cell, mitosis is responsible for growth and repair of body tissues.
  4. In meiosis, one parent cell undergoes two successive divisions and produces four daughter cells.
  5. Each daughter cell contains half the number of chromosomes and functions as a gamete or develops into a gamete.
  6. Therefore, mitosis is the type of cell division required for the growth and repair of the body, whereas meiosis is the type of cell division involved in the formation of gametes.
  7. Comparison Between Mitosis and Meiosis
  8. Feature Mitosis Meiosis
    Number of Divisions One division Two successive divisions
    Number of Daughter Cells Formed Two daughter cells Four daughter cells
    Chromosome Number Remains unchanged Reduced to half
    Nature of Daughter Cells Genetically identical Genetically different
    Function Growth and repair Formation of gametes
    Occurrence Somatic (body) cells Reproductive cells
  9. Why is Meiosis Necessary?
    10. <`li> It produces gametes containing half the chromosome number.
    • It prevents doubling of chromosome number in every generation.
    • It introduces genetic variation among offspring.
    • It is essential for sexual reproduction and evolution.
🎯 Exam Significance Exam Significance ›
  • This is one of the most important conceptual questions from the chapter and is frequently asked in CBSE and State Board examinations.
  • Differences between mitosis and meiosis are commonly tested in short-answer, long-answer and competency-based questions.
  • The concepts of chromosome number, gamete formation and genetic variation are frequently asked in Olympiads, NTSE and foundation examinations for NEET.
  • Understanding cell division forms the foundation for advanced topics such as genetics, heredity, reproduction and evolution.
🔑 Key Takeaways Key Takeaways ›
Key Takeaways  ·  5 points

  1. Mitosis produces two genetically identical daughter cells.

  2. Mitosis is responsible for growth and repair of body tissues.

  3. Meiosis produces four daughter cells with half the chromosome number.

  4. Meiosis is involved in the formation of gametes.

  5. Meiosis introduces genetic variation and maintains chromosome number across generations.
← Q9
10 / 10  ·  100%
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    Frequently Asked Questions

    Diffusion is the free movement of molecules from a region of high concentration to low concentration.

    Osmosis is the movement of water molecules through a semipermeable membrane from lower to higher solute concentration.

    Plasmolysis occurs when a plant cell loses water and the cytoplasm shrinks away from the cell wall.

    Water enters the cell, causing it to swell.

    Water leaves the cell, causing it to shrink.

    There is no net movement of water; the cell retains its size and shape.

    Cell division is the process by which one cell divides into two or more cells for growth and repair.

    The types are mitosis and meiosis.

    Mitosis is the division of a somatic cell resulting in two identical daughter cells.

    Meiosis is reduction division occurring in sex cells, producing four haploid gametes.

    Cells are small to increase surface area to volume ratio for efficient transport of materials.

    Specialized cells form tissues, organs, and organ systems to perform coordinated activities.

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