Cell (कोशिका) - Life का वो basic building blocks जिसे समझे बिना biology को decode करना impossible है! Let's explore discoveries, structures, organelles, and how cells divide. 🧬Cell — life का वो basic building block है जिसे समझे बिना biology को decode करना impossible है! चलो, discoveries, structures, organelles, और how cells divide को explore करते हैं। 🧬
Discovery of the Cell कोशिका की खोज
Goal: After this section you will be able to explain how the cell was discovered and list the main scientists who discovered the cell, the nucleus, and protoplasm.
Honeycomb Analogy (मधुमक्खी का छत्ता)
Think of a honeycomb or a large apartment building built of tiny individual rooms. Just as bricks build a house, microscopic units called cells build every living thing on Earth.
A cell is the basic structural and functional unit of all living organisms (कोशिका — जीवन की सबसे छोटी इकाई जो शरीर को बनाती है और काम चलाती है) [NCERT p.9].
Life originated in water, and the first organisms were unicellular (एककोशिकीय — single cell वाले जीव) such as the thermophilic bacteria living in hot springs like Puga Valley in Ladakh today [NCERT p.8].एक cell सभी living organisms का basic structural और functional unit होता है (यानी शरीर को बनाने और काम चलाने वाली सबसे छोटी इकाई) [NCERT p.9]।
Life की origin पानी में हुई थी, और पहले organisms unicellular थे (यानी single cell वाले जीव) जैसे कि Ladakh की Puga Valley के hot springs में आज भी रहने वाले thermophilic bacteria [NCERT p.8]।
🌟 Key Milestones in Science History
1665: Robert Hooke observed a thin slice of cork under a self-designed microscope. He saw empty honeycomb boxes and named them 'Cells' (Latin word for 'small room') [NCERT p.9].1665: Robert Hooke ने अपने बनाए self-designed microscope के नीचे cork के एक पतले slice को observe किया। उन्होंने खाली honeycomb boxes को देखा और उन्हें 'Cells' नाम दिया (Latin शब्द जिसका मतलब 'small room' होता है) [NCERT p.9]।
1674: Anton van Leeuwenhoek developed improved lenses and observed the first living cells (bacteria and protozoa) in pond water [NCERT p.11].1674: Anton van Leeuwenhoek ने improved lenses develop किए और pond water में पहले living cells (bacteria और protozoa) को observe किया [NCERT p.11]।
1831: Robert Brown discovered a dense sphere in the cell's center, naming it the Nucleus (केंद्रक) [NCERT p.11].1831: Robert Brown ने cell के center में एक dense sphere की खोज की, और इसे Nucleus नाम दिया [NCERT p.11]।
1839: J. E. Purkinje coined the term Protoplasm (जीवद्रव्य) for the living fluid substance inside the cell [NCERT p.11].1839: J. E. Purkinje ने cell के अंदर के living fluid substance के लिए Protoplasm term दिया [NCERT p.11]।
Worked Example: If you peel a thin membrane from an onion skin and place it under a microscope with a drop of water, you will see rows of rectangular chambers. Each chamber is an individual onion cell containing a cell wall, cytoplasm, and a nucleus [NCERT p.9].
Checkpoint (ज्ञान की जाँच)
Q1. Who discovered the first LIVING cell (like bacteria) in pond water?Q1. Pond water में सबसे पहले LIVING cell (जैसे bacteria) की खोज किसने की थी?
Section Summary:
All living organisms are made of cells, which are the basic bricks of life [NCERT p.9].सभी living organisms cells से बने होते हैं, जो life के basic bricks हैं [NCERT p.9]।
Robert Hooke named 'cells' in 1665, and Leeuwenhoek saw living cells in 1674 [NCERT p.9, p.11].Robert Hooke ने 1665 में 'cells' नाम दिया, और Leeuwenhoek ने 1674 में living cells को देखा [NCERT p.9, p.11]।
Robert Brown discovered the nucleus (1831), and Purkinje named the protoplasm (1839) [NCERT p.11].Robert Brown ने nucleus (1831) की खोज की, and Purkinje ने protoplasm (1839) नाम दिया [NCERT p.11]।
Hierarchy of Living Organisms जीवन का संगठन
Goal: After this section you will be able to describe how cells group together to form tissues, organs, organ systems, and complex multicellular organisms.
School Analogy (विद्यालय)
Think of a school. A single student is a cell. A class of similar students is a tissue. A department (like Science) is an organ. All departments running together form the organ system. The entire school is the organism.
In multicellular organisms (बहुकोशिकीय जीव), cells do not work alone. They divide and organize systematically to distribute tasks [NCERT p.9].Multicellular organisms में, cells अकेले काम नहीं करते। वे tasks को distribute करने के लिए systematically divide और organize होते हैं [NCERT p.9]।
Click a node above!
Select any level of the organization flowchart to see how cells build a fully functioning living body.Organization flowchart के किसी भी level को select करें और देखें कि cells मिलकर एक fully functioning living body कैसे बनाते हैं।
Worked Example: Single muscle cells group to build muscle tissue. Muscle tissue builds the heart (an organ). The heart works with blood vessels (circulatory system) to pump blood throughout the human body (organism) [NCERT p.9].
Checkpoint (ज्ञान की जाँच)
Q1. What level of biological hierarchy is formed when a group of similar cells work together to do a specific job?Q1. जब similar cells का एक group मिलकर कोई specific job करता है, तो biological hierarchy का कौन सा level बनता है?
Section Summary:
Multicellular organisms divide labor across organized levels of cells [NCERT p.9].Multicellular organisms अपने cells के organized levels में labor को divide करते हैं [NCERT p.9]।
The structural order is: Cell → Tissue → Organ → Organ System → Organism [NCERT p.9].Structural order यह है: Cell → Tissue → Organ → Organ System → Organism [NCERT p.9]।
Grouping similar cells together allows the body to run complex life processes efficiently.Similar cells को एक साथ group करने से body के complex life processes efficiently चलते हैं।
Prokaryotes vs Eukaryotes प्रोकैरियोट और यूकैरियोट
Goal: After this section you will be able to distinguish between primitive prokaryotic cells and advanced eukaryotic cells based on size, nucleus, and organelles.
Apartment Analogy (अपार्टमेंट)
A prokaryotic cell is like a studio apartment—it has no walls separating the kitchen, bedroom, or living space. Everything floats in one open space. A eukaryotic cell is like a multi-room flat—it has clear walls dividing the rooms (membrane-bound organelles).
Cells are divided into two categories based on whether they contain a well-defined nucleus bound by a membrane [NCERT p.15].इस basis पर कि cell में membrane से घिरा हुआ well-defined nucleus है या नहीं, cells को दो categories में divide किया गया है [NCERT p.15]।
Daily Life Analogy (सोचने का नज़रिया)
Prokaryotic Cell (जैसे Bacteria) एक Studio Apartment की तरह है. यहाँ अलग बेडरूम, किचन या हॉल नहीं होता; सब कुछ एक ही बड़े कमरे (Cytoplasm) में खुला पड़ा रहता.
Nucleoid (अविकसित केंद्रक)
No nuclear membrane (nuclear region points directly to cytoplasm).कोई nuclear membrane नहीं होती (nuclear region सीधे cytoplasm में खुला होता है)।
Contain a single, circular chromosome [NCERT p.15].इसमें एक single, circular chromosome होता है [NCERT p.15]।
Organelles & Size
No membrane-bound organelles (like Mitochondria or Golgi).कोई membrane-bound organelles (जैसे Mitochondria या Golgi) नहीं होते।
Generally very small size (1-10 micrometers) [NCERT p.15].आमतौर पर बहुत small size (1-10 micrometers) होता है [NCERT p.15]।
Daily Life Analogy
Eukaryotic Cell (जैसे Human cell or Plant cell) एक Multistory Luxury Villa की तरह है, जिसमें अलग-अलग कमरों (compartments) में रसोई, स्टडी रूम, और वॉशरूम होते हैं—यानी विशिष्ट कार्य के लिए अलग-अलग Organelles होते हैं!
Well-defined Nucleus
Surrounded by a double-layered nuclear membrane [NCERT p.15].यह एक double-layered nuclear membrane से घिरा होता है [NCERT p.15]।
Multiple linear chromosomes containing DNA.इसमें DNA वाले multiple linear chromosomes होते हैं।
Organelles & Size
Contains highly specialized organelles (Mitochondria, ER, Plastids) [NCERT p.16].इसमें highly specialized organelles (जैसे Mitochondria, ER, Plastids) होते हैं [NCERT p.16]।
Larger size (5-100 micrometers) [NCERT p.15].आकार में बड़े (5-100 micrometers) होते हैं [NCERT p.15]।
Worked Example: A bacterial cell is prokaryotic. It has circular DNA floating in an undefined region called the nucleoid (केन्द्रकाभ). A human cheek cell is eukaryotic. It has multiple linear chromosomes bound inside a nuclear envelope [NCERT p.15].
Checkpoint (ज्ञान की जाँच)
Q1. What is the undefined genetic region of a prokaryotic cell called?Q1. Prokaryotic cell के undefined genetic region को क्या कहते हैं?
Section Summary:
Prokaryotes are small, primitive cells lacking a nuclear membrane [NCERT p.15].Prokaryotes छोटे, primitive cells होते हैं जिनमें nuclear membrane नहीं होती [NCERT p.15]।
Eukaryotes are larger, complex cells with a well-defined nucleus and membrane organelles [NCERT p.15].Eukaryotes बड़े, complex cells होते हैं जिनमें well-defined nucleus और membrane organelles होते हैं [NCERT p.15]।
Bacteria are prokaryotes; plant and animal cells are eukaryotes [NCERT p.15].Bacteria prokaryotes हैं; plant और animal cells eukaryotes हैं [NCERT p.15]।
Interactive 3D Eukaryotic Cell Model 3D कोशिका मॉडल
Goal: After this section you will be able to visualize the three-dimensional layout of an animal cell and describe the positions of its organelles.
Water Balloon Analogy (पानी का गुब्बारा)
Imagine a water balloon filled with gelatin and floating spheres inside. The balloon is the cell membrane, the water is the cytoplasm, and the floating items are the organelles.
An animal cell is a eukaryotic structure bounded by a flexible plasma membrane (कोशिका झिल्ली) that controls what enters and exits the cell [NCERT p.14].
Click & Drag to Rotate in 3D
Eukaryotic Cell Structure
The cell is bounded by a plasma membrane, filled with cytoplasm containing various floating membrane-bound organelles that run metabolic actions [NCERT p.16].
Checkpoint (ज्ञान की जाँच)
Q1. Which of the following defines the outer flexible boundary of an animal cell?Q1. इनमें से कौन animal cell की outer flexible boundary को define करता है?
Section Summary:
Animal cells are eukaryotic and lack a cell wall [NCERT p.14].Animal cells eukaryotic होते हैं और इनमें cell wall नहीं होती [NCERT p.14]।
The plasma membrane is the selectively permeable outer envelope [NCERT p.14].Plasma membrane एक selectively permeable outer envelope है [NCERT p.14]।
Organelles float inside the fluid cytoplasm to execute metabolic reactions [NCERT p.16].Organelles fluid cytoplasm के अंदर float करते हैं ताकि metabolic reactions को execute कर सकें [NCERT p.16]।
Interactive Plant Cell Structure पादप कोशिका संरचना
Goal: After this section you will be able to identify plant cell parts on a diagram and describe the roles of the cell wall, vacuole, and plastids.
Concrete Fence Analogy (कंक्रीट की दीवार)
A plant cell has a plaster wall (cell membrane) inside, and a thick concrete security fence (cell wall) outside. This rigid wall keeps the cell stiff, supporting the plant structure since it has no bones.
Plant cells contain cell walls (कोशिका भित्ति), large central vacuoles (रसधानी), and plastids (लवक) like chloroplasts [NCERT p.14, p.19].
Click on any organelle or membrane structure in the plant cell illustration to load its structural properties and textbook descriptions.
Checkpoint (ज्ञान की जाँच)
Q1. Which of the following is found in plant cells but completely absent in animal cells?Q1. इनमें से कौन सा structure plant cells में पाया जाता है लेकिन animal cells में बिल्कुल absent होता है?
Section Summary:
Plant cells have a cellulose cell wall outside the membrane for rigidity [NCERT p.14].Plant cells में rigidity के लिए membrane के बाहर cellulose से बनी cell wall होती है [NCERT p.14]।
Plastids (like chloroplasts) manufacture and store food [NCERT p.19].Plastids (जैसे chloroplasts) food manufacture और store करते हैं [NCERT p.19]।
A large central vacuole provides turgidity and occupies up to 90% of the cell volume [NCERT p.19].एक बड़ी central vacuole cell को turgidity देती है और cell volume का 90% तक occupy करती है [NCERT p.19]।
Goal: After this section you will be able to explain how to focus a microscope slide to view onion or cheek cells.
Camera Tuning Analogy (कैमरा फोकस)
Focusing a microscope is like tuning a camera lens. You turn the dial slowly until the blurry outlines disappear, and the details (like nuclei) snap into focus.
When preparing onion peel or cheek cell slides, we view them under a compound microscope by adjusting the coarse and fine focus knobs [NCERT p.10].
Specimen & Adjustments नमूना एवं फोकस
1. Select the slide you want to view:1. वो slide select करें जिसे आप देखना चाहते हैं:
2. Slide the knob to focus the microscope:2. Microscope को focus करने के लिए knob को slide करें:
Focus Status:Unfocused (धुंधला)
The specimen slide is far from the lens. Increase focus to see cells.Specimen slide lens से बहुत दूर है। Cells को देखने के लिए focus बढ़ाएं।
Checkpoint (ज्ञान की जाँच)
Q1. Why does an onion peel cell slide show a regular brick-like pattern under a microscope?Q1. Microscope के नीचे onion peel cell slide में एक regular brick-like pattern क्यों दिखता है?
Section Summary:
Microscope focus adjustments bring the specimen slide into the focal plane [NCERT p.10].
Onion cells show organized brick-like shapes; animal cheek cells show irregular shapes [NCERT p.10].
Organelle Atlas — Internal Structure अंगक की आंतरिक संरचना
Goal: After this section you will be able to describe the internal foldings and micro-structures of the cell wall, nucleus, mitochondria, endoplasmic reticulum, and Golgi apparatus.
Machine Blueprint Analogy (मशीन का नक्शा)
This atlas is like a sliced blueprint of a machine. By looking inside, you see the membranes, folds, and channels that allow the organelle to carry out reactions.
Organelles (कोशिकांग) possess highly specialized internal structures to isolate chemical reactions from each other [NCERT p.16].
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Cell Wall — Double-layered Organic Boundary
👆 Click a part👆 Part पर click करें
Click the green walls, purple lamella, orange channel or blue membrane to learn about each layer of the plant cell boundary.
Fig. Cell Wall cross-section. Adapted from NCERT p.14.
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Nucleus — Command Center with Chromatin
👆 Click a part👆 Part पर click करें
Click the orange pores, purple nucleolus, chromatin threads, or the double membrane to explore the nucleus.
Fig. Nucleus cross-section with nuclear pores. Adapted from NCERT p.15.
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Mitochondria — Cristae & Inner Structure
👆 Click a part👆 Part पर click करें
Click the orange cristae folds, matrix (with circular mtDNA), or membranes to explore the powerhouse's inner workings.
Fig. Mitochondria cross-section with cristae. Adapted from NCERT p.18.
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Endoplasmic Reticulum — Rough & Smooth
👆 Click a part👆 Part पर click करें
Click the blue sheets (Rough ER with yellow ribosomes), green tubes (Smooth ER for lipids), or the nucleus to understand this membrane network.
Fig. ER showing rough (ribosome-studded) and smooth (tubular) regions. Adapted from NCERT p.17.
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Golgi Apparatus — Stacked Cisternae
👆 Click a part👆 Part पर click करें
Click each green layer (cisterna), the blue incoming vesicles, or the secretory vesicles to explore how Golgi processes proteins.
Q1. Why does the inner membrane of mitochondria have deep folds called cristae?Q1. Mitochondria की inner membrane में deep folds क्यों होते हैं जिन्हें cristae कहा जाता है?
Section Summary:
Mitochondria have double membranes; the inner membrane is folded into cristae [NCERT p.18].Mitochondria में double membranes होती हैं; inner membrane cristae में folded होती है [NCERT p.18]।
The nucleus envelope has pores to allow communication with the cytoplasm [NCERT p.15].Nucleus envelope में pores होते हैं ताकि cytoplasm के साथ communication हो सके [NCERT p.15]।
The Golgi apparatus consists of flattened cisternae that package cell materials [NCERT p.18].
Key Cell Organelles कोशिका के अंग
Goal: After this section you will be able to list the functions of the main cell organelles, including mitochondria, lysosomes, and plastids.
Factory City Analogy (फैक्ट्री शहर)
The cell is like a factory city:
• Mitochondria = Power plant (produces energy)
• Lysosomes = Waste disposal trucks (digests waste)
• Endoplasmic Reticulum (ER) = Assembly line (makes lipids and proteins)
• Golgi Apparatus = Shipping department (packages and delivers products)
Cell Division कोशिका विभाजन
Goal: After this section you will be able to visualize and compare mitosis and meiosis in terms of cell steps, chromosome numbers, and biological functions.
Photocopy vs Dealing Cards Analogy
• Mitosis is like photocopying—you make a perfect replica of the original document.
• Meiosis is like dealing cards—you split the deck in half, giving a unique hand with half the cards to each player.
New cells are continuously formed in organisms in order to grow, to replace old, dead and injured cells, and to form gametes required for reproduction. The process by which new cells are made is called cell division (कोशिका विभाजन) [NCERT p.21].
1. Mitosis (समसूत्री विभाजन)
The process of cell division by which most of the cells divide for growth and tissue repair is called mitosis [NCERT p.21].
Key features: In this process, each cell—called parent cell—divides to form two identical daughter cells [NCERT p.21]. The daughter cells have the same number of chromosomes as the parent cell (diploid, 2n). This helps in growth, repair, and cell replacement.
2. Meiosis (अर्धसूत्री विभाजन)
Specific cells of reproductive organs divide to form gametes, which after fertilization give rise to offspring. They divide by meiosis [NCERT p.22].
Key features: Meiosis involves two consecutive divisions instead of one [NCERT p.22]. When a cell divides by meiosis, it produces four new cells (gametes). The new cells have only half the number of chromosomes as the parent cell (haploid, n).
Worked Example: If a human cell (46 chromosomes) divides by mitosis, it yields two cells with 46 chromosomes each. If it divides by meiosis (to form sperm or eggs), it yields four cells with 23 chromosomes each [NCERT p.21, p.22].
Checkpoint (ज्ञान की जाँच)
Q1. Which type of cell division produces gametes with half the parent cell's chromosome number?
Section Summary:
Mitosis divides a cell once to create 2 identical diploid cells for growth and repair [NCERT p.21].
Meiosis divides a cell twice to create 4 haploid gamete cells for reproduction [NCERT p.22].
Halving chromosomes in meiosis ensures the offspring restores the 2n diploid count upon fertilization [NCERT p.22].
Cell Theory कोशिका सिद्धांत
Goal: After this section you will be able to state the three core tenets of cell theory and name the scientists who proposed them.
Element Analogy (मूल तत्व)
Cell theory is like stating "all matter is made of atoms." It states that no matter how different a blue whale, an onion, and a human look, they are all made of the exact same basic Lego brick: the cell.
The cell theory (कोशिका सिद्धांत) is the core principle of cell biology [NCERT p.23]:
All living organisms are composed of one or more cells [NCERT p.23].
The cell is the basic structural and functional unit of life [NCERT p.23].
All cells arise from pre-existing cells (proposed by Rudolf Virchow in 1855: "Omnis cellula-e cellula") [NCERT p.23].
Worked Example: If a new plant shoot grows, it doesn't appear out of nowhere. Existing plant cells divide by mitosis to make new cells, proving Virchow's rule that all cells arise from pre-existing cells [NCERT p.23].
Checkpoint (ज्ञान की जाँच)
Q1. Who added the tenet that "all cells arise from pre-existing cells" to the cell theory in 1855?
Section Summary:
Cell theory was formulated by Schleiden, Schwann, and Virchow [NCERT p.23].
It establishes cells as the basic unit of life and says all living things have cells [NCERT p.23].यह cells को life की basic unit के रूप में establish करती है और कहती है कि सभी living things में cells होते हैं [NCERT p.23]।
Virchow proved that cells can only come from older cells that divided [NCERT p.23].
Checkpoint Quiz ज्ञान की परीक्षा
Question 1 of 15Score: 0/15
Question: Which of the following cell organelles is called the "suicide bag" of a cell and why? [NCERT p.18]
What You Can Now Do अब आप ये कर सकते हैं
Verify your understanding of this chapter by checking off these skills. You should be able to:इन skills को check करके verify करें कि आपने इस chapter को समझ लिया है। आपको यह आना चाहिए:
NCERT Solutions अभ्यास प्रश्नोत्तर
Below are the official exercise solutions for Class 9 Science Chapter 2: Cell — The Building Block of Life based on the new NEP curriculum. Click the button above to print or download these solutions as a clean PDF document.
Q1. Differentiate between the following pairs of terms based on the clues given in parentheses:
(i) Cell membrane and cell wall (permeability)
(ii) RER and SER (structure)
(iii) Chloroplasts and chromoplasts (pigments)
Chloroplasts: Contain green chlorophyll pigment and carotenoids; active in photosynthesis [NCERT p.19].
Chromoplasts: Contain yellow, orange, or red carotenoid pigments; give colour to flowers and fruits [NCERT p.19].
Q2. Two similar animal cells are placed in two different solutions:
• Cell X is placed in pure water.
• Cell Y is placed in a concentrated salt solution.
Cells are observed after some time. Cell X swells, and Cell Y shrinks. Which statement provides the correct explanation for the above observations?
(i) Salt molecules moved into Cell Y, causing it to shrink.
(ii) Water moved into Cell X and more water moved out of Cell Y than the salt solution entered in it.
(iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.
(iv) Solute movement caused osmosis in both cells.
Ans:(iii) Water moved into Cell X and moved out of Cell Y through the cell membrane.
Explanation:
Cell X undergoes endosmosis (water moves from outside high concentration into the cell) because pure water is a hypotonic solution.
Cell Y undergoes exosmosis (water moves from inside the cell into the concentrated salt solution) because the salt solution is hypertonic relative to the cell's cytoplasm. Both happen through the selectively permeable cell membrane [NCERT p.14].
Q3. Look at the diagram of a cell in Fig. 2.20. Identify the parts labelled from (a) to (g) and correctly match them with their functions given below:
(i) Controlling all the activities of a cell.
(ii) Site of cellular respiration.
(iii) Storage organelle that also provides rigidity to the cell.
(iv) Separates the cell contents from surroundings.
(v) Provides structural rigidity to the cell.
(vi) Packs and stores materials received from ER.
(vii) Helps in manufacturing food.
Ans: Based on the functional descriptions in the textbook, we identify and match the parts as follows:
(i) Controlling all activities of the cell → Nucleus (केंद्रक) [NCERT p.15].
(ii) Site of cellular respiration → Mitochondria (सूत्रकणिका / ऊर्जाघर) [NCERT p.18].
Q4. Which of the following option(s) of the pairs of cell organelles are correctly placed under the given categories? Option | Present in the plant cells | Absent in the animal cells
(i) Leucoplast | Cell wall
(ii) Mitochondria | Ribosome
(iii) Cell wall | Golgi apparatus
(iv) Lysosome | Endoplasmic reticulum
Ans:(i) Leucoplast | Cell wall
Justification:
Leucoplasts (plastids) are present in plant cells, and cell walls are absent in animal cells. Mitochondria, ribosomes, Golgi apparatus, and endoplasmic reticulum are present in both plant and animal cells, making other choices incorrect [NCERT p.14, p.19].
Q5. Two students, Renu and Rohit, were having a discussion on the plastids. Renu emphasised that all parts of the plants, even roots, contain plastids. However, Rohit did not agree with the statement and told her that plastids are absent in plant roots since the roots are underground and do not need to perform photosynthesis. Who is correct? Justify your answer.
Ans:Renu is correct.
Justification: Plastids are not just chloroplasts for photosynthesis. There are multiple types of plastids, including Leucoplasts (colorless/white plastids) which store starch, oils, and protein granules. Underground parts like roots and tubers contain leucoplasts for food storage [NCERT p.19]. Therefore, roots do contain plastids.
Q6. Mitochondria and chloroplasts are two important organelles in a plant cell. Discuss how these two organelles are structurally and functionally similar to each other, and different from each other.
Ans:
Similarities (समानताएं):
Structure: Both are bound by a double membrane and contain inner membrane foldings (cristae in mitochondria, thylakoids/grana in chloroplasts) [NCERT p.18, p.19].
Semi-autonomous: Both possess their own DNA and ribosomes, allowing them to synthesize some of their own proteins [NCERT p.18, p.19].
Differences (अंतर):
Feature
Mitochondria
Chloroplasts
Function
Site of cellular respiration; breaks down glucose to generate ATP power [NCERT p.18].
Site of photosynthesis; uses solar energy to synthesize glucose food [NCERT p.19].
Pigments
Contain no metabolic pigments.
Contain green chlorophyll and yellow-orange pigments [NCERT p.19].
Presence
Found in both animal and plant cells.
Found only in plant cells [NCERT p.19].
Q7. Which of the following pairs of cell organelles contains DNA?
(i) Chloroplasts, Ribosomes
(ii) Mitochondria, Nucleus
(iii) Golgi bodies, Ribosomes
(iv) Nucleus, Lysosomes
Ans:(ii) Mitochondria, Nucleus
Explanation: The nucleus houses the cell's main genomic DNA [NCERT p.15]. Mitochondria (and chloroplasts in plants) also contain their own independent loops of DNA [NCERT p.18]. Ribosomes, lysosomes, and Golgi bodies do not contain DNA.
Q8. A researcher carried out an experiment in which she took two carrots of similar size. She placed one carrot in plain water and the other carrot in concentrated salt solution (Fig. 2.21). After 24 hours she recorded her observations.
(i) What hypothesis does she want to test through this experiment?
(ii) What would you suggest for the improvement of this experiment?
(iii) Why does the carrot in plain water stay stiff and crunchy, but the carrot in concentrated salt solution become rubbery and limp?
Ans:
(i) Hypothesis: She wants to test the effect of hypertonic vs. hypotonic surrounding environments on water movement in living plant tissues via osmosis [NCERT p.14].
(ii) Improvement: To improve accuracy, she should peel the carrots to expose the cells directly, measure the weight and dimensions of the carrots before and after the 24-hour period, and perform multiple trials to average the results.
(iii) Mechanism:
• In plain water: The external environment is hypotonic. Water enters the carrot cells by endosmosis, causing them to become turgid, stiff, and crunchy.
• In concentrated salt solution: The external environment is hypertonic. Water leaves the carrot cells by exosmosis (plasmolysis), causing cells to lose turgor pressure and shrink, making the carrot rubbery and limp [NCERT p.14].
Q9. Indicate the presence or absence of following structures in bacterial and animal cells: Structures | Bacterial cell | Animal cell
Chromosome, Nucleus, Mitochondria, Golgi complex, Chromoplasts
Ans:
Cell Structure
Bacterial Cell (Prokaryotic)
Animal Cell (Eukaryotic)
Chromosome
Present (single, circular DNA in nucleoid) [NCERT p.15]
Present (multiple, linear DNA in nucleus) [NCERT p.15]
Nucleus
Absent (has no nuclear membrane) [NCERT p.15]
Present (membrane-bound nucleus) [NCERT p.15]
Mitochondria
Absent [NCERT p.15]
Present [NCERT p.18]
Golgi complex
Absent [NCERT p.15]
Present [NCERT p.18]
Chromoplasts
Absent [NCERT p.15]
Absent (found in plants/fruits only) [NCERT p.19]
Q10. Carry out the following potato cup experiment. Observe the four potato cups at least two hours and answer:
(i) Explain why water gathers in the hollowed portion of Cup B and Cup C.
(ii) Why is Cup A necessary for this experiment?
(iii) Explain why water does not gather in the hollowed portions of Cups A and D.
Ans:
(i) Water accumulation in B and C: Cups B (sugar) and C (salt) contain solutes in their hollow cavity. When placed in water, the cell sap of potato cells acts as a selectively permeable membrane. Water moves from the outside beaker (low solute concentration) into the hollow cavity (high solute concentration) by osmosis [NCERT p.14].
(ii) Importance of Cup A: Cup A is a control experiment (नियंत्रण प्रयोग). It demonstrates that water does not move into the hollow cavity without a concentration gradient (since no solute is present inside).
(iii) No water in A and D:
• Cup A: Has no solutes, so there is no concentration difference to drive osmosis.
• Cup D (Boiled Potato): Boiling denatures/kills the proteins in the cell membranes, destroying their selective permeability. Since the cells are dead, osmosis cannot occur, and water cannot cross into the cavity [NCERT p.14].
Q11. Identify the pair that incorrectly matches the cell organelle with its function.
(i) Ribosome — Protein synthesis
(ii) SER — Lipid and cellulose synthesis
(iii) Lysosome — Digestion of foreign agents
Ans:(ii) SER — Lipid and cellulose synthesis is an incorrect match.
Explanation: While the Smooth Endoplasmic Reticulum (SER) is indeed responsible for lipid synthesis [NCERT p.16], cellulose (which makes up the plant cell wall) is synthesized by cellulose synthase enzymes at the plasma membrane, not by the SER.
Q12. What outcome do you expect, if all the mitochondria are removed from a eukaryotic cell?
Ans:
Mitochondria are the "powerhouses" of the cell, responsible for converting carbohydrates into chemical energy in the form of ATP through cellular respiration [NCERT p.18]. If all mitochondria are removed:
1. The cell will fail to generate ATP energy for active transport and synthesis.
2. Metabolic functions will shut down immediately.
3. The cell will starve of energy and undergo cell death (necrosis).
Q13. Which phenomenon inhibits the formation of tumors in the human body? Can plants also develop tumors? Explain.
Ans:
1. Tumor Inhibition: The phenomenon that prevents tumor formation is Apoptosis (programmed cell death) and tight cell-cycle check-points. Normal cells divide in a highly regulated manner and self-destruct when damaged. If cells lose control, they divide uncontrollably to form a tumor/cancer [NCERT p.21].
2. Tumors in Plants: Yes, plants can also develop tumors. An example is Crown Gall disease, caused by the bacterium Agrobacterium tumefaciens. The bacterium inserts a piece of its plasmid DNA into plant cells, transforming them to divide uncontrollably and form woody tumor-like galls.
Q14. The cell membrane of a cell is made up of proteins and lipids. Which cell organelles help in the synthesis of cell membrane? Write the path of these compounds from their site of synthesis to the cell membrane.
Ans:
The synthesis of the cell membrane is called membrane biogenesis [NCERT p.16]. It involves:
• Lipids: Synthesized by the Smooth Endoplasmic Reticulum (SER) [NCERT p.16].
• Proteins: Synthesized by the Rough Endoplasmic Reticulum (RER) via ribosomes [NCERT p.16].
Pathway:
Synthesis: Lipids are synthesized in SER, and proteins in RER.
Transport 1: Transport vesicles bud off from the ER and carry these lipids and proteins to the cis face of the Golgi apparatus [NCERT p.18].
Processing & Packaging: In the Golgi apparatus, proteins and lipids are modified, sorted, and packed into secretory vesicles [NCERT p.18].
Transport 2: Vesicles migrate from the trans face of the Golgi to the plasma membrane.
Fusion: The vesicles fuse with the cell membrane, inserting the new lipids and proteins to expand the membrane.
Q15. What would happen if gametes are formed by mitotic divisions?
Ans:
Gametes (sperm and egg cells) must be haploid (n)—having half the chromosome count of somatic cells—so that when they fuse during fertilization, the diploid count (2n) is restored [NCERT p.22].
If gametes were formed by mitotic division (which maintains diploid count, 2n):
The gametes would be diploid (2n).तो gametes diploid (2n) होते।
Upon fertilization, the zygote would be tetraploid (4n) (2n + 2n).Fertilization पर, zygote tetraploid (4n) हो जाता (2n + 2n)।
In the next generation, chromosome numbers would double to octaploid (8n), then 16n, and so on.अगली generation में, chromosome numbers double होकर octaploid (8n), फिर 16n, और ऐसे ही बढ़ते जाते।
This exponential increase in chromosomes would disrupt the cell's genetic balance, leading to cellular instability, systemic failure, and the extinction of the species. Thus, meiosis is essential [NCERT p.22].
Q16. Based on the passage about Deepa preserving amla and lemons, answer:
(i) Which scientific concept has the farmer applied in the preservation?
(ii) How does the addition of high concentrations of salt and sugar prevent spoilage?
(iii) Suggest a healthy recipe of this kind.
(iv) What are the scientific values addressed in this case?
Ans:
(i) Scientific Concept: The farmer applied the concept of plasmolysis / osmosis [NCERT p.14].
(ii) Protection Mechanism: High concentration of salt or sugar surrounding the fruits forms a hypertonic environment. When bacteria or fungi attempt to settle on the fruit, water is drawn out of the microbial cells by exosmosis (plasmolysis). This dehydration shrinks the microbes and inhibits their metabolic activity, preventing reproduction and spoilage [NCERT p.14].
(iii) Healthy Recipe: A traditional salted amla preserve (dry amla pickles). Slice amla, mix with turmeric and sea salt, and solar-dry in sterilized glass jars. The salt acts as a dehydrator and preservative.
(iv) Scientific Values: The values addressed include resourcefulness, utilizing local produce to cut post-harvest waste, sustainability, applying simple biological principles (osmosis) for food preservation, and economic self-reliance.
Solved Previous Years' Questions (PYQs) गत वर्षों के हल प्रश्न
Goal: After reviewing these questions, you will know exactly how to structure your answers for 1, 2, 3, and 5 marks to score full marks in your exams.
Below are actual questions from previous years' school and CBSE board-style exams. Answers are structured point-wise as per the board marking scheme.
Group A: 1-Mark Questions (VSA - Very Short Answer)
Q1. Where are proteins synthesized inside the cell? [CBSE 2018, 2020] [1 Mark]
Ans: Proteins are synthesized on the Ribosomes (commonly known as the protein factories of the cell) [NCERT p.16]. These ribosomes are either attached to the Rough Endoplasmic Reticulum (RER) or float freely in the cytoplasm.
Q2. Which cell organelle is called the 'Powerhouse of the Cell' and why? [CBSE 2017, 2022] [1 Mark]
Ans:Mitochondria is called the powerhouse of the cell because it generates energy in the form of ATP (Adenosine Triphosphate) molecules through cellular respiration, which the cell uses to perform metabolic activities [NCERT p.18].
Q3. Name the process by which cell membranes are synthesized. Which organelle is primarily involved? [CBSE 2019] [1 Mark]
Ans: The process is called membrane biogenesis [NCERT p.16]. The Endoplasmic Reticulum (ER) is primarily involved—lipids are synthesized by the Smooth ER (SER) and proteins by the Rough ER (RER).
Group B: 2-Mark Questions (SA-I - Short Answer Type I)
Q4. Why is the cell called the structural and functional unit of life? [CBSE 2015, 2021] [2 Marks]
Structural Unit: All plants and animals are composed of cells. A cell provides the basic physical framework and shape to the body of an organism [NCERT p.9].
Functional Unit: All life-supporting processes (like respiration, nutrition, excretion, and protein synthesis) occur at the cellular level. Each cell can perform these jobs independently [NCERT p.11].
Q5. What will happen if the plasma membrane of a cell gets ruptured or broken down? [CBSE 2016, 2020] [2 Marks]
If the plasma membrane ruptures:
The cell will lose its selective permeability, meaning it can no longer control what goes in and out [NCERT p.13].
The protoplasmic contents (cytoplasm, organelles) will leak out into the surroundings.
Chemical balance is lost, metabolic activity stops, and the cell will die.
Q6. Define plasmolysis. What happens when a plant cell undergoes this process? [CBSE 2018, 2022] [2 Marks]
Definition: Plasmolysis (जीवद्रव्य संकुचन) occurs when a living plant cell loses water through osmosis, causing the cytoplasm and central vacuole to shrink and draw away from the rigid cell wall [NCERT p.14].
Outcome: The cell membrane shrinks away from the cell wall, and the cell loses turgidity, causing the plant tissue to become limp and wilt.
Group C: 3-Mark Questions (SA-II - Short Answer Type II)
Q7. Differentiate between Prokaryotic and Eukaryotic cells. [CBSE 2014, 2019] [3 Marks]
Feature
Prokaryotic Cell (प्रोकैरियोटिक)
Eukaryotic Cell (यूकैरियोटिक)
Size
Generally very small (1-10 µm) [NCERT p.12].
Generally larger (5-100 µm) [NCERT p.12].
Nucleus
Undefined nuclear region (nucleoid) lacking a nuclear membrane [NCERT p.12].
Well-defined nuclear region surrounded by a double nuclear membrane [NCERT p.12].
Organelles
Membrane-bound organelles (like mitochondria, plastids, Golgi) are absent [NCERT p.12].
Membrane-bound organelles (mitochondria, ER, Golgi) are present [NCERT p.12].
Q8. How does chromatin differ from chromosomes? What are their functions? [CBSE 2016, 2021] [3 Marks]
Differences:
Chromatin: Appears as an entangled mass of thread-like structures inside the nucleus when the cell is not dividing [NCERT p.15].
Chromosomes: Formed when chromatin threads condense into thick, rod-like structures when the cell is about to divide [NCERT p.15].
Composition & Function: Chromosomes are composed of DNA and proteins. They contain genetic information (genes) which carries hereditary instructions from parents to offspring, regulating all cell functions [NCERT p.15].
Group D: 5-Mark Questions (LA - Long Answer)
Q9. Describe what happens when a red blood cell (RBC) and a plant cell are placed separately in hypotonic, isotonic, and hypertonic solutions. Explain the difference in their behaviors. [CBSE 2017, 2020] [5 Marks]
When placed in different solutions, water moves across the cell membrane by osmosis:
Hypotonic Solution (Dilute/Pure water): Water enters the cell by endosmosis [NCERT p.14].
Animal Cell (RBC): Swells up and eventually bursts because it lacks a protective cell wall.
Plant Cell: Swells and becomes turgid. It does not burst because the rigid cellulose cell wall exerts an equal wall pressure opposing the swelling [NCERT p.14].
Isotonic Solution (Same concentration as cytoplasm): No net movement of water. Both RBC and plant cell sizes remain unchanged.
Hypertonic Solution (Concentrated salt/sugar solution): Water leaves the cell by exosmosis [NCERT p.14].
Animal Cell (RBC): Loses water, shrinks, and becomes wrinkled (crenated).
Plant Cell: Undergoes plasmolysis—the protoplast and vacuole shrink and pull away from the rigid cell wall [NCERT p.14].
Exam Tip: Plant cells survive extreme environment changes better than animal cells because their rigid cell walls prevent bursting in hypotonic solutions and provide mechanical support during plasmolysis.
Q10. Compare Mitosis and Meiosis under the following parameters: Site of occurrence, Number of divisions, Number of daughter cells formed, Chromosome count in daughter cells, and Biological purpose. [CBSE 2018, 2022] [5 Marks]
Here is a detailed comparison of the two processes of cell division:यहाँ cell division के दोनों processes का detailed comparison दिया गया है:
Parameter
Mitosis (समसूत्री विभाजन)
Meiosis (अर्धसूत्री विभाजन)
1. Site of Occurrence
Occurs in somatic (body) cells [NCERT p.21].
Occurs in germ cells of reproductive organs [NCERT p.22].
2. Number of Divisions
A single cell divides once [NCERT p.21].
A single cell divides twice consecutively [NCERT p.22].
3. Daughter Cells Formed
Yields 2 identical daughter cells [NCERT p.21].
Yields 4 non-identical gamete cells [NCERT p.22].
4. Chromosome Count
Same as parent cell (Diploid, 2n) [NCERT p.21].
Halved from parent cell (Haploid, n) [NCERT p.22].
5. Biological Purpose
Used for vegetative growth, healing, and tissue repair [NCERT p.21].
Used for producing gametes (sperm/egg) for sexual reproduction [NCERT p.22].
Exam Tip: Remember: Meiosis reduces chromosomes by half, ensuring that when the sperm (n) and egg (n) fuse at fertilization, the offspring's chromosome count is restored to diploid (2n) [NCERT p.22].
