Maharashtra Board Class 11 Biology Chapter 5 Cell Structure and Organization Solutions

Cell Structure And Organization Class 11 Exercise Question Answers Solutions Maharashtra Board

Class 11 Biology Chapter 5 Exercise Solutions Maharashtra Board

Biology Class 11 Chapter 5 Exercise Solutions

1. Choose correct option

Question (A)
Growth of cell wall during cell elongation take place by - - - - - - - - - -
(a) Apposition
(b) Intussusception
(c) Both a & b
(d) Super position
Answer: (b) Intussusception
In simple words: Intussusception is the process where new cell wall material is added within the existing wall, causing it to expand. This allows the cell wall to grow in surface area during cell elongation.

🎯 Exam Tip: Understanding the mechanism of cell wall growth is crucial. Intussusception is a key process for plant cell expansion, especially during elongation, differing from apposition which involves adding new layers to the surface.

Question (B)
Cell Membrane is composed of
(a) Proteins and cellulose
(b) Proteins and Phospholipid
(c) Proteins and carbohydrates
(d) Proteins, Phospholipid and some carbohydrates
Answer: (d) Proteins, Phospholipid and some carbohydrates
In simple words: The cell membrane, also known as the plasma membrane, is primarily made up of a phospholipid bilayer and various proteins, with some carbohydrates also present, typically attached to lipids or proteins. This complex composition allows it to regulate what enters and exits the cell.

🎯 Exam Tip: Remember the fluid mosaic model. The cell membrane's structure is essential for its function as a selective barrier, and knowing its components (phospholipids, proteins, carbohydrates) is fundamental.

Question (C)
Plasma membrane is Fluid structure due to presence of
(A) Carbohydrates
(B) Lipid
(C) Glycoprotein
(D) Polysaccharide
Answer: (B) Lipid
In simple words: The fluid nature of the plasma membrane is primarily due to the movement of its lipid components, specifically the phospholipid bilayer, allowing proteins and other molecules to move laterally within the membrane.

🎯 Exam Tip: The lipid bilayer's ability to allow lateral movement of its components is what gives the plasma membrane its characteristic "fluid mosaic" property, which is vital for many cellular functions.

Question (D)
Cell Wall is present in
(a) Plant cell
(b) Prokaryotic cell
(c) Algal cell
(d) All of the above
Answer: (d) All of the above
In simple words: A cell wall provides structural support and protection, and it is a common feature found in plant cells, prokaryotic cells (like bacteria), and algal cells.

🎯 Exam Tip: The presence or absence of a cell wall is a key distinguishing feature between different types of organisms, and its composition varies among kingdoms (e.g., cellulose in plants, peptidoglycan in bacteria).

Question (E)
Plasma membrane is
(a) Selectively permeable
(b) Permeable
(c) Impermeable
(d) Semipermeable
Answer: (a) Selectively permeable
In simple words: The plasma membrane is selectively permeable, meaning it allows certain molecules to pass through while restricting others, playing a crucial role in maintaining the cell's internal environment.

🎯 Exam Tip: "Selectively permeable" accurately describes the plasma membrane's function, as it actively controls the passage of substances, unlike a simple "semipermeable" membrane that only restricts based on size.

Question (F)
Mitochondria DNA is
(a) Naked
(b) Circular
(c) Double stranded
(d) All of the above
Answer: (d) All of the above
In simple words: Mitochondrial DNA is unique because it is naked (not associated with histone proteins), circular in shape, and double-stranded, much like the DNA found in prokaryotic cells.

🎯 Exam Tip: The characteristics of mitochondrial DNA (naked, circular, double-stranded) are strong evidence supporting the endosymbiotic theory, which posits that mitochondria originated from free-living bacteria.

Question (G)
Which of the following set of organelles contain DNA?
(a) Mitochondria, Peroxysome
(b) Plasma membrane, ribosome
(c) Mitochondria, chloroplast
(d) Chloroplast, dictyosome
Answer: (c) Mitochondria, chloroplast
In simple words: Among the given options, both mitochondria and chloroplasts are unique organelles within eukaryotic cells that possess their own genetic material in the form of DNA.

🎯 Exam Tip: Recognizing which organelles contain their own DNA (mitochondria and chloroplasts) is key, as it highlights their semi-autonomous nature and bacterial origins, crucial for understanding cellular evolution.

2. Answer the following questions

Question (A)
Plants have no circulatory system? Then how cells manage intercellular transport?
Answer:
1. Plant cells show presence of plasmodesmata which are cytoplasmic bridges between neighbouring cells.
2. This open channel through the cell wall connects the cytoplasm of adjacent plant cells and allows water, small solutes, and some larger molecules to pass between the cells.
In this way, though plants have no circulatory system, plant cells manage intercellular transport.
In simple words: Plants use plasmodesmata, tiny channels that connect the cytoplasm of adjacent cells through the cell walls, to allow for the direct exchange of water, nutrients, and other molecules, facilitating intercellular transport without a traditional circulatory system.

🎯 Exam Tip: Plasmodesmata are vital for plant communication and transport; remember their structure as cytoplasmic bridges passing through the cell wall, enabling symplastic transport.

Question (B)
Is nucleolus covered by membrane?
Answer:
A nucleolus is specialized structure present in the nucleus which is not covered by the membrane.
In simple words: The nucleolus is a dense structure within the nucleus that lacks its own surrounding membrane. It is primarily involved in ribosome synthesis.

🎯 Exam Tip: A common misconception is that all organelles are membrane-bound; the nucleolus is a key example of a non-membranous organelle, often a point of distinction in exams.

Question (C)
Fluid mosaic model proposed by Singer and Nicolson replaced Sandwich model proposed by Danielli and Davson? Why?
Answer:
1. The Davson-Danielli model of the plasma membrane of a cell, was proposed in 1935 by Hugh Davson and James Danielli.
2. The model describes a phospholipid bilayer that lies between two layers of globular proteins.
3. This model was also known as a Tipo-protein sandwich', as the lipid layer was sandwiched between two protein layers.
4. But through experimental studies membrane proteins were discovered to be insoluble in water (representing hydrophobic surfaces) and varied in size. Such type of proteins would not be able to form an even and continuous layer around the outer surface of a cell membrane.
5. In case of Fluid-mosaic model, the experimental evidence from research supports every major hypothesis proposed by Singer and Nicolson.
This hypothesis stated that membrane lipids are arranged in a bilayer; the lipid bilayer is fluid; proteins are suspended individually in the bilayer; and the arrangement of both membrane lipids and proteins is asymmetric. Therefore, Fluid mosaic model proposed by Singer and Nicolson replaced Sandwich model proposed by Danielli and Davson.
In simple words: The fluid mosaic model superseded the sandwich model because it better accounted for experimental evidence, showing that membrane proteins are not fixed layers but rather individual, often hydrophobic, components embedded within a dynamic, fluid phospholipid bilayer. The fluid mosaic model recognized the membrane's fluidity and the heterogeneous distribution of proteins.

🎯 Exam Tip: Focus on the key differences: the fluid mosaic model emphasizes fluidity and embedded/transmembrane proteins, while the Davson-Danielli model proposed static protein layers sandwiching the lipid bilayer, which was later disproven by experimental findings on protein mobility and structure.

Question (D)
The RBC surface normally shows glycoprotein molecules. When determining blood group do they
play any role?
Answer:
1. Glycoproteins are protein molecules modified within the Golgi complex by having a short sugar chain (polysaccharide) attached to them.
2. The polysaccharide part of glycoproteins located on the surfaces of red blood cells acts as the antigen responsible for determining the blood group of an individual.
3. Different polysaccharide part of glycoproteins act as different type of antigens that determine the blood groups.
4. Four types of blood groups A, B, AB, and O are recognized on the basis of presence or absence of these antigens.
In simple words: Yes, glycoproteins on the surface of Red Blood Cells (RBCs) play a crucial role in determining an individual's blood group. The specific carbohydrate chains attached to these glycoproteins act as antigens, which define the A, B, AB, or O blood types.

🎯 Exam Tip: Understanding the role of glycoproteins (specifically their carbohydrate components) as antigens on RBCs is fundamental for comprehending blood typing and immunological compatibility.

Question (E)
How cytoplasm differs from nucleoplasm in chemical composition?
Answer:
1. A thick liquid enclosed by cell membrane which surrounds the central nucleus in eukaryotes or nucleoid region in prokaryotes is known as cytoplasm.
2. The cytoplasm shows presence of minerals, sugars, amino acids, t-RNA, nucleotides, vitamins, proteins and enzymes.
3. The liquid or semiliquid substance within the nucleus is called the nucleoplasm.
4. Nucleoplasm shows presence of various substances like nucleic acid, protein molecules, minerals and salts.
In simple words: Cytoplasm, found outside the nucleus, is a complex mixture containing organelles, minerals, sugars, amino acids, and various proteins and enzymes for metabolic activities. Nucleoplasm, inside the nucleus, is more specialized, containing nucleic acids (DNA, RNA), specific proteins (like histones), minerals, and salts, essential for genetic functions and gene expression.

🎯 Exam Tip: While both are viscous fluids, the key distinction lies in their primary components and functions: cytoplasm is the site of many metabolic pathways and organelle activity, whereas nucleoplasm is specialized for genetic material organization and transcription.

3. Answer the following questions

Question (A)
Distinguish between smooth and rough endoplasmic reticulum.
Answer:
Smooth endoplasmic reticulum (SER):
1. Depending on cell type, it helps in synthesis of lipids for e.g. Steroid secreting cells of cortical region of adrenal gland, testes and ovaries.
2. Smooth endoplasmic reticulum plays a role in detoxification in the liver and storage of calcium ions (muscle cells).
Rough Endoplasmic Reticulum (RER):
1. Rough ER is primarily involved in protein synthesis. For e.g. Pancreatic cells synthesize the protein insulin in the ER.
2. These proteins are secreted by ribosomes attached to rough ER and are called secretory proteins. These proteins get wrapped in membrane that buds off from transitional region of ER. Such membrane bound proteins depart from ER as transport vesicles.
3. Rough ER is also involved in formation of membrane for the cell.
The ER membrane grows in place by addition of membrane proteins and phospholipids to its own membrane. Portions of this expanded membrane are transferred to other components of endomembrane system.
In simple words: Rough Endoplasmic Reticulum (RER) is characterized by ribosomes on its surface and is primarily involved in protein synthesis and modification for secretion or insertion into membranes. Smooth Endoplasmic Reticulum (SER) lacks ribosomes and is crucial for lipid synthesis, detoxification, and calcium ion storage.

🎯 Exam Tip: The presence or absence of ribosomes is the defining structural difference; remember that RER's function is protein-centric (synthesis, folding), while SER's is lipid-centric (synthesis, detoxification, Ca²⁺ storage).

Question (B)
Why do we call mitochondria as power house of cell? Explain in detail.
(Hint: Refer chapter Cellular Respiration.)
OR
Mitochondria are power house of the cell. Give reasons.
Answer:
a. Mitochondria possess oxysomes on its inner membrane. These oxysomes take active part in synthesis of ATP molecules.
b. During cellular respiration, ATP molecules are produced and get accumulated in the mitochondria. They play an important role in cellular activities.
c. only mitochondria can convert pyruvic acid to carbon dioxide and water during cell respiration. Therefore, mitochondria are called 'power house of the cell'.
In simple words: Mitochondria are called the "powerhouse of the cell" because they are the primary sites where cellular respiration occurs, converting nutrients like pyruvic acid into ATP (adenosine triphosphate) molecules. ATP is the main energy currency that fuels almost all cellular activities, making mitochondria essential for the cell's energy supply.

🎯 Exam Tip: To score well, emphasize the role of oxysomes (F₀F₁ particles) in ATP synthesis on the inner mitochondrial membrane, and mention the complete oxidation of glucose derivatives (like pyruvic acid) to yield significant energy for the cell.

Question (C)
What are the types of plastids?
Answer:
1. Plastids are classified according to the pigments present in it. Three main types of plastids are - leucoplasts, chromoplasts and chloroplasts.
2. Leucoplasts do not contain any photosynthetic pigments they are of various shapes and sizes. These are meant for storage of nutrients:
a. Amyloplasts store starch.
b. Elaioplasts store oils.
c. Aleuroplasts store proteins.
3. Chromoplasts contain pigments like carotene and xanthophyll etc.
a. They impart yellow, orange or red colour to flowers and fruits.
b. These plastids are found in the coloured parts of flowers and fruits.
4. Chloroplasts are plastids containing green pigment chlorophyll along with other enzymes that help in production of sugar by photosynthesis. They are present in plants, algae and few protists like Euglena.
In simple words: Plastids are categorized into three main types based on their pigments and functions: chloroplasts (green, for photosynthesis), chromoplasts (colorful, for pigmentation in fruits and flowers), and leucoplasts (colorless, for storing various nutrients like starch, oils, or proteins).

🎯 Exam Tip: When distinguishing plastids, focus on their characteristic pigment (or lack thereof) and primary storage/synthesis function; remember that leucoplasts have sub-types like amyloplasts, elaioplasts, and aleuroplasts.

Question 4.
Label the diagrams and write down the details of concept in your words.
ℹ️ चित्र व्याख्या (Diagram Explanation):
**Diagram A:** यह एक माइटोकॉन्ड्रियन की त्रि-आयामी संरचना को दर्शाता है, जिसमें बाहरी और भीतरी झिल्ली, क्रिस्टी, मैट्रिक्स और DNA जैसे घटक दिखाई देते हैं। यह कोशिका में ऊर्जा उत्पादन का मुख्य केंद्र है।
**Diagram B:** यह एक क्लोरोप्लास्ट की संरचना को दर्शाता है, जिसमें बाहरी और भीतरी झिल्ली, ग्रैनम (थायलाकोइड के ढेर), स्ट्रोमा और क्लोरोप्लास्ट DNA जैसे घटक दिखाई देते हैं। यह पौधों में प्रकाश संश्लेषण के लिए जिम्मेदार है।
**Diagram C:** यह गॉल्जी कॉम्प्लेक्स (गॉल्जी उपकरण) की संरचना को दर्शाता है, जिसमें सिस्टर्न, सिस्ट्रांस और नवगठित वेसिकल्स दिखाई देते हैं। यह प्रोटीन और लिपिड के संशोधन, छँटाई और पैकेजिंग में भूमिका निभाता है।
**Diagram D:** यह एंडोप्लाज्मिक रेटिकुलम (ER) की संरचना को दर्शाता है, जिसमें खुरदुरी (राइबोसोम युक्त) और चिकनी (राइबोसोम रहित) ER दोनों ही नाभिकीय आवरण से जुड़े हुए दिखाई देते हैं। यह प्रोटीन संश्लेषण, लिपिड चयापचय और डिटॉक्सीफिकेशन में शामिल है।
Answer:
*Note: The source document provides detailed labeled diagrams for Mitochondrion (A), Chloroplast (B), Golgi complex (C), and Endoplasmic reticulum (D) as part of the solution. As per instructions, these complex diagrams are not rendered in HTML. The following text provides additional conceptual details for chloroplasts.*
Structure of chloroplast:
1. In plants, chloroplast is found mainly in mesophyll of leaf.
2. Chloroplast is lens shaped but it can also be oval, spherical, discoid or ribbon like.
3. A cell may contain single large chloroplast as in Chlamydomonas or there can be 20 to 40 chloroplasts per cell as seen in mesophyll cells.
4. Chloroplasts contain green pigment called chlorophyll along with other enzymes that help in production of sugar by photosynthesis.
5. Inner membrane of double membraned chloroplast is comparatively less permeable.
6. Inside the cavity of inner membrane, there is another set of membranous sacs called thylakoids.
7. Thylakoids are arranged in the form of stacks called grana (singular: granum).
8. The grana are connected to each other by means of membranous tubules called stroma lamellae.
9. Space outside thylakoids is filled with stroma.
10. The stroma and the space inside thylakoids contain various enzymes essential for photosynthesis.
11. Stroma of chloroplast contains DNA and ribosomes (70S).
In simple words: Question 4 asks to label provided diagrams (Mitochondrion, Chloroplast, Golgi Complex, Endoplasmic Reticulum) and explain the concepts. The chloroplast, for instance, is typically lens-shaped, contains chlorophyll for photosynthesis, and has an internal structure of thylakoids stacked into grana, all enclosed within a double membrane. The stroma fills the inner space, containing enzymes, DNA, and ribosomes.

🎯 Exam Tip: For diagram-based questions, accurately identifying and labeling key structures of organelles is crucial. Additionally, a concise description of the primary function of each identified part, especially for chloroplasts in photosynthesis, will fetch full marks.

Question 5.
Complete the flow chart.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह एक प्रवाह चार्ट है जो सेलुलर प्रक्रिया को दर्शाता है। इसमें "ट्रांसपोर्ट वेसिकल" और "गॉल्जी उपकरण" के साथ एक अधूरा पथ है, जो "ऑटोफेगी" के रूप में समाप्त होता है। छात्रों को इस मार्ग को पूरा करना है।
Answer:

🎯 Exam Tip: Accurately mapping the endomembrane system components (ER, Golgi, vesicles, lysosomes) and their sequence in cellular processes like protein modification, transport, and autophagy is vital for flowchart completion questions.

Question 6.
Identify labels A, B, C in the given diagram. Explain how lysosomes perform intracellular and extracellular digestion.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह एक पादप कोशिका या यूकेरियोटिक कोशिका का आरेखीय प्रतिनिधित्व है, जिसमें विभिन्न अंग, जैसे कि भोजन रिक्तिका (A), गॉल्जी कॉम्प्लेक्स (B), लाइसोसोम (C), और संभवतः एक और संरचना (D) लेबल करने के लिए दर्शाई गई है। छात्रों को इन अंगों की पहचान करनी है और लाइसोसोम के कार्यों की व्याख्या करनी है।
Answer:
1. A: Food vacuole
B: Golgi complex
C: Lysosome
2. Intracellular digestion:
The intracellular digestion is brought about by autophagic vesicle or secondary lysosomes which contain foreign materials brought in by processes like phagocytosis. E.g. Food vacuole in amoeba or macrophages in human blood that engulf and destroy harmful microbes that enter the body.
3. Extracellular digestion:
Extracellular digestion is brought about by release of lysosomal enzymes outside the cell. E.g. acrosome, a cap like structure in human sperm is a modified lysosome which contain various enzymes like Hyaluronidase. These enzymes bring about fertilization by dissolving protective layers of ovum.
In simple words: In the given diagram, A is the Food vacuole, B is the Golgi complex, and C is the Lysosome. Lysosomes perform intracellular digestion by breaking down waste materials and cellular debris within the cell, and extracellular digestion by releasing enzymes outside the cell to break down external substances, such as the acrosome of sperm dissolving egg layers during fertilization.

🎯 Exam Tip: Clearly identify the labeled organelles. For lysosomes, differentiate between their intracellular role (autophagy, breaking down engulfed particles) and extracellular role (enzyme release for external digestion), providing specific examples for each.

Question 7.
Identify each cell structures or organelle from its description below.
1. Manufactures ribosomes
2. Carries out photosynthesis
3. Manufactures ATP in animal and plant cells.
4. Selectively permeable.
Answer:
1. Nucleolus
2. Chloroplast
3. Mitochondria
4. Plasma membrane
In simple words: The nucleolus makes ribosomes, chloroplasts conduct photosynthesis, mitochondria produce ATP in both animal and plant cells, and the plasma membrane regulates cell entry and exit as it is selectively permeable.

🎯 Exam Tip: For this type of question, focus on the unique, primary function of each organelle. Ribosome manufacturing, photosynthesis, ATP production, and selective permeability are defining characteristics that help identify these specific cell structures.

Question 8.
Onion cells have no chloroplast. How can we tell they are plants?
Answer:
1. The bulb of an onion is a modified form of leaves.
2. While photosynthesis takes place in the leaves (present above the ground) of an onion containing chloroplast, the little glucose that is produced from this process is converted in to starch (starch granules) and stored in the bulb.
3. Starch act as reserved food material in plants.
4. Using an iodine solution, we can test for the presence of starch in onion cells. If starch is present, the iodine changes from brown to blue-black or purple. Hence, we can say that though onion cells have no chloroplast they are considered as plants.
In simple words: Even though onion bulb cells lack chloroplasts and don't photosynthesize, they are identified as plant cells because they contain starch, a common energy storage molecule in plants, which can be detected by an iodine test, turning it blue-black or purple. Also, they possess a cell wall, a characteristic feature of plant cells.

🎯 Exam Tip: When identifying plant cells without chloroplasts, remember to mention other key plant characteristics, such as the presence of a cell wall and the ability to store starch, which can be chemically tested using iodine.

Project/ Practical:

Question 1.
Observe the cells of onion root tip under microscope.
Answer:
The cells of onion root tip will show various stages of cell division when observed under micrscope.
ℹ️ चित्र व्याख्या (Diagram Explanation): यह प्याज के जड़ के सिरे की कोशिकाओं में कोशिका विभाजन (माइटोसिस) के विभिन्न चरणों को दर्शाने वाले चार सूक्ष्मदर्शीय चित्र प्रस्तुत करता है: प्रोफेज, मेटाफेज, एनाफेज और टेलोफेज। प्रत्येक चित्र कोशिका के भीतर गुणसूत्रों की विशिष्ट व्यवस्था और गति को प्रदर्शित करता है।
In simple words: When observing onion root tip cells under a microscope, one can see various stages of cell division, including prophase, metaphase, anaphase, and telophase, which are crucial for plant growth.

🎯 Exam Tip: In practical observations of onion root tips, the focus should be on correctly identifying and differentiating the distinct chromosomal changes characteristic of each mitotic phase (prophase, metaphase, anaphase, telophase).

Question 2.
Observe the cells from buccal epithelium stained with Giemsa under microscope.
Answer:
The following observations are made when cells from buccal epithelium stained with Giemsa:
1. Cheek cells are flat and irregular in shape.
2. These cells lack cell wall. A distinct blue nucleus can be observed on viewing the cells under the microscope after Geimsa staining.
In simple words: When observing Giemsa-stained buccal epithelial cells under a microscope, you will see flat, irregularly shaped cells that lack a cell wall, each containing a distinct blue-stained nucleus.

🎯 Exam Tip: For observing buccal epithelial cells, focus on their characteristic irregular shape, the absence of a cell wall, and the ability to clearly identify the nucleus (stained blue with Giemsa) under the microscope.

11th Biology Digest Chapter 5 Cell Structure And Organization Intext Questions And Answers

Can You Recall? (Textbook Page No. 44)

Question (i) Who observed cells under the microscope for the first time?
Answer:
Robert Hooke observed cells under the microscope for the first time.
[Note. Cell walls were first observed by Robert Hooke (1665) as he looked through a microscope at dead cells from the bark of an oak tree. But Anton van Leeuwenhoek was first to visualize living cells using a single-lens microscope of his own construction.]
In simple words: Robert Hooke was the first to observe cells, specifically cell walls in cork, using a microscope in 1665, while Anton van Leeuwenhoek later observed living cells.

🎯 Exam Tip: Distinguish between Robert Hooke's observation of dead cells (cell walls) and Anton van Leeuwenhoek's observation of living cells; both are pioneers in microscopy.

Question (ii) Who made the first microscope?
Answer:
The first microscope was made by two Dutch spectacle makers Hans and Zacharias Janssen.
[Note: The Dutch scientist Anton van Leeuwenhoek made microscopes capable of magnifying single-celled organisms in a drop of pond water.]
In simple words: The first compound microscope is credited to Hans and Zacharias Janssen, Dutch spectacle makers, though Anton van Leeuwenhoek later developed more powerful single-lens microscopes.

🎯 Exam Tip: Remember Hans and Zacharias Janssen for the invention of the compound microscope, a foundational achievement in biology. Anton van Leeuwenhoek's contributions were also significant for observing microscopic life.

Find Out (Textbook Page No. 44)

Question (i) How do a combination of lenses help in higher magnification?
Answer:
a. In a light microscope, visible light is passed through the specimen and then through two glass lenses.
b. The first lens focuses the magnified image of the object on the second lens, which magnifies it again and focuses it on the back of the eye.
c. The glass lenses bend (refract) the light in such a way that the image of the specimen is magnified.
In this way, a combination of lenses helps in higher magnification.
In simple words: A combination of lenses, as in a compound microscope, works by having an objective lens create a magnified intermediate image, which is then further magnified by an eyepiece lens, resulting in a much higher total magnification than a single lens could achieve.

🎯 Exam Tip: Explain the two-stage magnification process: the objective lens provides initial magnification, and the eyepiece then magnifies that image further, effectively multiplying their individual magnifications for a clearer, larger view.

Can You Recall? (Textbook Page No. 44)

Question (i). Why bacterial nucleus is said to be primitive?
Answer:1. The DNA-containing central region of bacterial nucleus (prokaryotic cells) i.e. nucleoid, has no nuclear membrane separating it from the cytoplasm. Therefore, bacterial nucleus is said to be primitive.
In simple words: Bacterial nuclei are considered primitive because their genetic material (nucleoid) is not enclosed by a membrane and directly floats in the cytoplasm, unlike the well-defined nucleus in eukaryotic cells.

🎯 Exam Tip: Understanding the absence of a nuclear membrane is key to explaining why a bacterial nucleus is primitive. Compare with eukaryotic cell structure for clarity.

Question (ii). Draw neat and labelled diagram of Prokaryotic cell.
Answer:
ℹ️ चित्र व्याख्या (Diagram Explanation): यह चित्र एक सामान्य प्रोकैरियोटिक कोशिका को दर्शाता है, जिसमें कोशिका भित्ति, प्लाज्मा झिल्ली, साइटोप्लाज्म और एक न्यूक्लियोइड क्षेत्र (गुणसूत्र के साथ) शामिल हैं। इसमें राइबोसोम, प्लास्मिड (डीएनए), पिली और फ्लेजेलम जैसी अन्य संरचनाएं भी दिखाई गई हैं जो गति और आसंजन में मदद करती हैं, साथ ही एक कैप्सूल या स्लाइम लेयर और फूड ग्रेन्यूल भी हैं।
In simple words: A prokaryotic cell diagram shows a simple cell structure lacking a membrane-bound nucleus and other organelles, typically featuring a cell wall, plasma membrane, cytoplasm, nucleoid, ribosomes, and sometimes flagella or pili.

🎯 Exam Tip: When drawing, focus on clearly labeling the key structures like the cell wall, plasma membrane, nucleoid (without a membrane), ribosomes, and flagellum. Precision in drawing and labeling is crucial for scoring.

Find Out (Textbook Page No. 46)

Question. Why do basal body of bacterial flagella considered as smallest motor in the world?
Answer:1. The bacterial flagellum is an organelle for motility made up of three parts:
a. The basal body that spans the cell envelope and works as a rotary motor;
b. The helical filament that acts as a propeller;
c. The hook that acts as a universal joint connecting these two to transmit motor torque to the propeller. 2. The motor i.e. basal body drives the rotation of the long, helical filamentous propeller at hundreds of hertz to produce thrust that allows bacteria to swim in liquid environments. Therefore, basal body of bacterial flagella considered as smallest motor in the world.
In simple words: The basal body of bacterial flagella is considered the smallest motor because it's a microscopic, intricate molecular machine that rapidly rotates, functioning like a propeller to enable bacterial movement.

🎯 Exam Tip: Highlight the three main components of the flagellum and specifically explain how the basal body generates rotary motion to produce thrust, justifying its 'smallest motor' title.

Use Your Brainpower (Textbook Page No. 46)

Question. Describe major differences between prokaryotic and eukaryotic cells.
Answer:

🎯 Exam Tip: When comparing, always highlight the presence/absence of a nuclear membrane and membrane-bound organelles, as these are fundamental distinctions. Use a table format for clarity and easy comparison.

Use Your Brain Power! (Textbook Page No. 52)

Question. Are mitochondria present in all eukaryotic cells?
Answer:
a. Mitochondria are found in nearly all eukaryotic cells, including plants, animals, fungi, and most unicellular eukaryotes.
b. Some of the cells have a single large mitochondrion, but frequently a cell has hundreds of mitochondria.
c. The number of mitochondria correlates with the cell's level of metabolic activity. For e.g. cells that move or contract have proportionally more mitochondria than metabolically less active cells.
d. However, mature red blood cells in humans lack mitochondria.
In simple words: Mitochondria are present in most eukaryotic cells as they are vital for energy production, but mature red blood cells in humans are a notable exception, lacking them to maximize space for hemoglobin.

🎯 Exam Tip: Remember the general rule that mitochondria are found in most eukaryotes, but critically note the exception of mature mammalian red blood cells and explain the reason for this exception.

Can You Recall? (Textbook Page No. 54)

Question (i). Consider the following cells and comment about the position, shape and number of nuclei in a eukaryotic cell. Add more examples from your previous knowledge about cell and nucleus. Cuboidal epithelial cell, different types of blood corpuscles, skeletal muscle fibre, adipocyte.
Answer:

🎯 Exam Tip: Focus on linking the cell type to the specific nuclear characteristics. For example, mention why skeletal muscle fibers are multinucleate or why adipocytes have a peripherally located nucleus.

Question (ii). Why nucleus is considered as control unit of a cell?
Answer:
a. Nucleus contains the genetic material of an organism.
b. This genetic material is present in the form of Deoxyribonucleic Acid (DNA) which is responsible for synthesis of various proteins and enzymes.
c. These proteins and enzymes in turn regulate metabolic activities of the cells. Therefore, nucleus is considered as control unit of a cell.
In simple words: The nucleus is the cell's control unit because it houses the DNA, which contains all genetic instructions for protein and enzyme synthesis, thereby directing all metabolic activities and overall cell function.

🎯 Exam Tip: Emphasize DNA's role as the blueprint and its control over protein synthesis, which ultimately dictates cellular functions, to clearly explain why the nucleus is the control center.

Question (iii). Can cells like Xylem or mature human RBCs called living?
Answer:
a. Xylem is a complex tissue consists of tracheids, vessels, xylem parenchyma and xylem fibres. From these components of xylem, tracheids are dead cells and xylem parenchyma is the only living tissue,
b. RBCs do not possess nuclei once they reach maturity as they have to accommodate haemoglobin in them. They do not require a nucleus to function as they do not reproduce but only serve as a vehicle for the transport of oxygen and carbon dioxide in the blood.
In simple words: Mature human RBCs are not considered fully "living" as they lack a nucleus and organelles, while in xylem, only xylem parenchyma cells are living; tracheids and vessels are dead, forming water-conducting tubes.

🎯 Exam Tip: For xylem, specify which components are living and which are dead. For RBCs, explain the functional reason (hemoglobin accommodation) for lacking a nucleus and other organelles, which leads to their "non-living" classification.

Question (iv). What is a syncytium and coenocyte?
Answer:Syncytium: It refers to mass of cells formed by fusion of multiple uninuclear cells and followed by dissolution of the cell membrane. Coenocyte: It is a multinucleate cell resulted from multiple nuclear divisions without undergoing cytokinesis.
In simple words: A syncytium is a single large cell formed by the fusion of multiple individual cells, while a coenocyte is a single cell containing multiple nuclei due to repeated nuclear divisions without cytoplasmic division.

🎯 Exam Tip: Clearly differentiate between the formation mechanisms: syncytium (cell fusion) vs. coenocyte (nuclear division without cytokinesis). Provide examples if remembered, like skeletal muscle fibers for syncytium or certain fungi/algae for coenocyte.

Can You Recall? (Textbook Page No. 44)

Question. How do onion peel cells and our body cells differ?
Answer:1 – (a, b, d, e,f g)
In simple words: Onion peel cells (plant cells) have a rigid cell wall, a large central vacuole, and chloroplasts (in green parts), whereas human body cells (animal cells) lack a cell wall and chloroplasts, have smaller or no vacuoles, and possess centrioles.

🎯 Exam Tip: Focus on the key distinguishing features between plant and animal cells: presence/absence of cell wall, chloroplasts, central vacuole, and centrioles. Listing these differences directly helps in scoring.