Chapter – 5 : Cell | Chapter Solution Class 9

(c) Endoplasm

Explanation:

The endoplasm is the inner granular and less viscous part of the cytoplasm, while the ectoplasm is the outer, more rigid part.

(d) Mitochondria

Explanation:

Mitochondria generate ATP (Adenosine Triphosphate), the energy currency of the cell, through aerobic respiration, which is why they are called the powerhouse of the cell.

(d) Chloroplast

Explanation:

Chloroplasts in plant cells carry out photosynthesis, converting sunlight into glucose, a food source for the cell.

(c) Four

Explanation: The four parts of the nucleus are:

1. Nuclear membrane
2. Nucleoplasm
3. Chromatin fibers
4. Nucleolus

(a) Golgi bodies

Explanation:

The Golgi apparatus is responsible for modifying, packaging, and transporting secretory proteins and lipids.

(b) Animal

Explanation:

Centrosomes help in cell division and are found only in animal cells.

(d) Chloroplast

Explanation:

Chloroplasts contain chlorophyll, which captures sunlight for photosynthesis in plants.

(c) Ribosome

Explanation:

Ribosomes are responsible for assembling amino acids into proteins, making them the site of protein synthesis.

(b) Lysosome

Explanation:

Lysosomes contain hydrolytic enzymes that break down waste materials. If they rupture, they release enzymes that can destroy the cell, hence the name “suicidal bag.”

(b) Ectoplasm

Explanation:

The ectoplasm is the peripheral and narrow part of the cytoplasm, which is more rigid compared to the endoplasm.

(a) Hyaloplasm

Explanation:

Hyaloplasm is the transparent, aqueous, and fluid portion of the cytoplasm.

(c) Both animal and plant cell

Explanation:

The plasma membrane (cell membrane) is present in both animal and plant cells, acting as a selectively permeable barrier that regulates the exchange of substances.

Leucoplasts.

Explanation:

Leucoplasts are plastids that do not contain pigments and are responsible for storing starch, lipids, and proteins in plant cells.

Robert Hooke

Explanation:

In 1665, Robert Hooke observed the structure of cork under a microscope and coined the term “cell” after noticing small compartments resembling monk cells.

Nonliving

Explanation:

Robert Hooke observed dead cork cells, which were nonliving, and noted their honeycomb-like structure.

Inside the nucleus

Explanation:

The nucleolus is a dense, spherical body inside the nucleus, responsible for the production of ribosomal RNA (rRNA).

Chloroplast

Explanation:

Chloroplasts are present only in plant cells and are responsible for photosynthesis.

Centrosome

Explanation: Centrosomes help in cell division and are found only in animal cells, while plant cells lack them.

Vacuole

Explanation:

Cell sap is a liquid stored in the central vacuole of plant cells that contains water, sugars, salts, and enzymes.

Animal Cell

Explanation:

Animal cells lack a cell wall; instead, they have a flexible plasma membrane.

Protoplasm.

Explanation: The protoplasm includes everything inside the cell membrane, comprising the cytoplasm and nucleus.

Plasmodesmata.

Explanation: Plasmodesmata are microscopic channels that connect the cytoplasm of adjacent plant cells, allowing the exchange of materials.

Chlorophyll.

Explanation: Chlorophyll absorbs light energy for photosynthesis and gives plants their green color.

Tonoplast.

Explanation: The tonoplast is the membrane that encloses the vacuole, regulating the movement of substances in and out.

Mitochondria

Explanation: Mitochondria release ATP (energy) and store energy from respiration.

Lysosome

Explanation: Lysosomes contain digestive enzymes that break down waste and foreign substances, functioning like an excretory system for the cell.

Mitochondria

Explanation: Mitochondria are the site of aerobic respiration, producing energy (ATP).

Lysosome

Explanation: Lysosomes digest waste materials, damaged organelles, and harmful substances.

Vacuole

Explanation: Cell sap is the fluid inside the vacuole, rich in water, minerals, and nutrients.

Eukaryotic Cell

Explanation: Eukaryotic cells have a membrane-bound nucleus, unlike prokaryotic cells, which lack a true nucleus.

No.

Explanation: Most cells are microscopic and require a microscope to be seen, except for large cells like the ostrich egg.

Plant Cell

Explanation: Vacuoles and chloroplasts are found only in plant cells and not in animal cells.

Dictyosomes.

Explanation: In plant cells, the Golgi apparatus is called dictyosomes, which perform similar functions.

Prokaryotic Cell

Explanation: Bacterial cells are prokaryotic because they lack a true nucleus and membrane-bound organelles.

Plant Cell

Explanation: Plant cells have a cell wall and plastids (chloroplast, chromoplast, leucoplast), while animal cells lack them.

Protoplasm

Explanation: Protoplasm, the living content of a cell, was described by J. Huxley as the physical basis of life.

Chromatin Fibers

Explanation: Chromatin fibers contain DNA and proteins that form chromosomes during cell division.

Tonoplast

Explanation: The tonoplast is a selectively permeable membrane that surrounds the vacuole.

Plasmalemma.

Explanation: The plasma membrane is also known as the plasmalemma, which surrounds the cell and regulates material exchange.

A prokaryotic cell is a simple, primitive cell that lacks a true nucleus and membrane-bound organelles. The genetic material (DNA) is present in a region called the nucleoid instead of being enclosed within a nuclear membrane.

Example: Bacteria and cyanobacteria.

A eukaryotic cell is a complex cell that contains a true nucleus enclosed by a nuclear membrane and has membrane-bound organelles like mitochondria, Golgi bodies, and the endoplasmic reticulum.

Example: Plant and animal cells.

The cell wall of prokaryotic cells is primarily composed of peptidoglycan (murein) in bacteria. In archaea, the cell wall may contain pseudopeptidoglycan, polysaccharides, glycoproteins, or proteins.

Location: Present in the cytoplasm of animal cells.

Function: Lysosomes contain digestive enzymes that break down worn-out organelles, waste materials, and foreign invaders like bacteria.

A nucleoid is an irregularly shaped region in a prokaryotic cell that contains genetic material (DNA) but is not enclosed by a nuclear membrane.

The nucleus is a membrane-bound organelle in eukaryotic cells that contains chromatin (DNA + proteins) and controls cell growth, reproduction, and gene expression.

Location: Present in the cytoplasm of eukaryotic cells near the endoplasmic reticulum.

Function: Modifies, packages, and transports proteins and lipids for secretion and use within the cell.

The two functions of vacuoles are:

1. Storage of water, nutrients, and waste products.
2. Maintaining turgor pressure in plant cells, keeping them firm.

The two functions of Golgi bodies are:

1. Processing and packaging of proteins and lipids.
2. Formation of lysosomes and secretion of enzymes and hormones.

Robertson proposed the unit membrane model, describing the plasma membrane as a trilaminar structure (protein-lipid-protein, P-L-P) with an inner lipid layer sandwiched between two protein layers.

Plasmodesmata are microscopic channels that connect adjacent plant cells, allowing the exchange of substances and communication between them.

• Without a nucleus, the cell cannot control its functions, grow, or reproduce.
• Without mitochondria, the cell will lack ATP (energy) and will die.

If lysosomes are absent, the cell will fail to digest waste and harmful materials, leading to toxicity and cell death.

Without chloroplasts, plants cannot perform photosynthesis, leading to no food production.

Without centrosomes, animal cells will have difficulty in cell division.

• Pigment: Chlorophyll
• Function: Absorbs sunlight and converts it into chemical energy during photosynthesis.

• The exposed root may start photosynthesizing if chlorophyll is present.
• However, roots lack stomata, so they cannot carry out full photosynthesis.

Smooth ER (SER): Lacks ribosomes, synthesizes lipids and hormones.

Rough ER (RER): Has ribosomes, synthesizes proteins.

The nucleus is called the brain because it controls all cell activities, including growth, metabolism, and reproduction, by regulating gene expression.

• Cell wall: Fully permeable, found in plants.
• Cell membrane: Selectively permeable, found in both plants and animals.

Ergastic substances are non-living materials in the cytoplasm, such as starch, crystals, and oils, used for storage and defense.

The functions of cytoplasm are:

1. Holds and supports organelles.
2. Acts as a medium for metabolic reactions.

The functions of centrosome are:

• Helps in cell division by forming spindle fibers.
• Assists in the formation of cilia and flagella.

Primordial refers to the earliest or original stage of development in a cell or organism.

• Robert Hooke first discovered the cell in 1665.
• He used a simple microscope to observe thin slices of cork (bark of a tree).
• He noticed small compartments resembling honeycomb structures, which he named “cells.”

• Ribosomes are small, non-membranous organelles found in both prokaryotic and eukaryotic cells.
• They are made up of ribosomal RNA (rRNA) and proteins.
• Their primary function is protein synthesis.
• They are either free-floating in the cytoplasm or attached to the rough endoplasmic reticulum (RER) in eukaryotic cells.
• Prokaryotic ribosomes are 70S (50S + 30S subunits), while eukaryotic ribosomes are 80S (60S + 40S subunits).

Ergastic substances are non-living materials found in the cytoplasm of plant and animal cells. These substances may be organic or inorganic in nature.

Examples include starch grains, crystals, tannins, latex, resins, and oils.

They are involved in storage, defense, and metabolic processes.

The function of the centrosome are:

• The centrosome is an organelle found in animal cells, near the nucleus.
• It contains centrioles, which help in the formation of spindle fibers during cell division (mitosis and meiosis).
• It plays a crucial role in the formation of cilia and flagella in certain cells.

Golgi bodies (Golgi apparatus) are membrane-bound organelles that modify, package, and transport proteins and lipids.

• They play a key role in secretion, lysosome formation, and production of cell wall components.
• In plant cells, the Golgi apparatus is called Dictyosomes.

Vacuoles are membrane-bound fluid-filled organelles present in both plant and animal cells but are larger in plant cells. They are surrounded by a membrane called Tonoplast.

Functions:

1. Storage of water, nutrients, waste products, and enzymes.
2. Maintains turgor pressure in plant cells, helping to maintain shape.
3. Stores pigments and defensive compounds like alkaloids.

1. Chlorophyll (Green pigment) – Found in leaves, responsible for photosynthesis.
2. Carotenoids (Yellow, orange, red pigments) – Found in flowers and fruits, aiding in attracting pollinators.
3. Anthocyanins (Red, purple, blue pigments) – Found in flowers, fruits, and some leaves, providing color.
4. Betalains (Red and yellow pigments) – Found in some roots (e.g., beetroot).

Plastids are double-membrane-bound organelles found in plant cells and some protists. They are classified into three types:

1. Chloroplasts – Found in the green parts of plants, mainly in leaves and young stems.
2. Chromoplasts – Found in colored plant parts such as flowers and fruits.
3. Leucoplasts – Found in non-photosynthetic parts of plants, such as roots and underground stems.

Green-colored plastids (Chloroplasts):

1. Perform photosynthesis by absorbing sunlight and converting it into chemical energy.
2. Contain chlorophyll, which gives plants their green color.
3. Synthesize carbohydrates, fatty acids, and some amino acids.

Colorless plastids (Leucoplasts):

1. Store starch, lipids, and proteins.
2. Help in biosynthesis of oils and essential compounds.
3. Found in roots and underground parts of plants.

A cell is the basic structural and functional unit of all living organisms. It consists of the following parts:

1. Cell Membrane : The outer boundary that regulates the movement of substances.
2. Cytoplasm : A jelly-like fluid that holds organelles.
3. Nucleus : The control center containing DNA.
4. Organelles : Include mitochondria, ribosomes, Golgi bodies, endoplasmic reticulum, and lysosomes.

Prokaryotic cells: Simple cells without a nucleus or membrane-bound organelles.

• Examples: Bacteria (E. coli) and Cyanobacteria (Nostoc).

Eukaryotic cells: Complex cells with a nucleus and membrane-bound organelles.

• Found in plants, animals, fungi, and protists.

A bacterial cell consists of:

• Cell Wall – Made of peptidoglycan, provides shape and protection.
• Plasma Membrane – Regulates exchange of substances.
• Cytoplasm – Contains ribosomes and enzymes.
• Nucleoid – Region containing circular DNA.
• Flagella – Used for movement.
• Pili/Fimbriae – Help in attachment.

Cell Wall:

• Found in plant, fungal, and bacterial cells.
• Composed of cellulose in plants, chitin in fungi, and peptidoglycan in bacteria.
• Function: Provides rigidity, support, and protection.

Cell Membrane:

• Present in all cells.
• Made of lipid bilayer with embedded proteins.
• Function: Controls transport of substances and cell communication.

The nucleus is the control center of the cell and is responsible for regulating all cellular activities, including growth, metabolism, and reproduction.

Structure of the Nucleus:

Nuclear Membrane:

• The double-layered membrane that surrounds the nucleus.
• Contains nuclear pores for the exchange of materials between the nucleus and the cytoplasm.

Nucleoplasm:

• The gel-like fluid inside the nucleus.
• Contains enzymes, nucleotides, and chromatin fibers.

Chromatin:

• Thread-like structures made of DNA and proteins.
• During cell division, chromatin condenses to form chromosomes.

Nucleolus:

• A dense, spherical body inside the nucleus.
• Responsible for the synthesis of ribosomal RNA (rRNA) and the formation of ribosomes.

Functions of the Nucleus:

1. Controls all cellular activities, including metabolism and growth.
2. Stores and transmits genetic information in the form of DNA.
3. Regulates protein synthesis by controlling mRNA production.
4. Plays a role in cell division through the replication of DNA.
5. Produces ribosomes in the nucleolus.

The centrosome is a specialized region in animal cells that plays a crucial role in cell division and the formation of cytoskeletal structures.

Structure of the Centrosome:

Centrioles:

• Two tiny cylindrical structures arranged at right angles to each other.
• Made of microtubules.

Centrosphere:

• A dense, clear zone of cytoplasm surrounding the centrioles.
• Helps organize microtubules during cell division.

Functions of the Centrosome:

1. Plays an important role in animal cell division by organizing the mitotic spindle.
2. Forms spindle fibers that help in the movement of chromosomes.
3. Aids in the formation of cilia and flagella, which help in cell movement.

The mitochondrion is known as the “powerhouse of the cell” because it generates ATP (energy) through cellular respiration.

Structure of Mitochondria:

Mitochondria are double-membrane-bound organelles in eukaryotic cells, essential for cellular respiration and ATP production. The outer membrane is smooth and permeable, while the inner membrane is folded into cristae, increasing the surface area for energy production. The intermembrane space lies between the two membranes, and the matrix, the inner fluid-filled compartment, contains enzymes, ribosomes, and circular DNA, allowing mitochondria to replicate independently. Their structure and function support the endosymbiotic theory, suggesting they evolved from ancient prokaryotic cells.

Functions of Mitochondria:

1. Produces ATP through aerobic respiration.
2. Regulates cellular metabolism by breaking down glucose and fatty acids.
3. Contains its own DNA and ribosomes, allowing it to replicate independently.

Plastids are double-membrane-bound organelles found in plant cells. Two important plastids are:

Chloroplast

• Structure: Contains thylakoids, grana, and stroma. The thylakoids contain chlorophyll, which captures sunlight for photosynthesis.
• Function: Performs photosynthesis, converting solar energy into chemical energy.

Chromoplast

• Structure: Contains pigments like carotenoids but lacks chlorophyll.
• Function: Provides colors to flowers, fruits, and roots, helping in pollination and seed dispersal.

Structure of Golgi Body:

The Golgi bodies consist of four to eight thin membrane-bound flattened sacs, stacked upon each other like a pile of dishes with expanded areas at their ends. The stacked elements are called cisternae.

In the peripheral part of the cisternae, small droplet-like sacs, known as vesicles, bulge out. They also possess vacuoles.

Functions of the Golgi Body:

1. Golgi bodies are associated with the secretory activity of the cell.
2. They help in the formation of plant cell walls, plasma membrane, and secretory vesicles.

On the basis of its association with ribosomes, ER is divided into two types:

1. Granular (rough) ER (RER or GER) – Studded with ribosomes. Ribosomes are attached to the membrane of RER by a protein called ribophorin.
2. Agranular (smooth) ER (SER) – Lacks ribosomes and is synthesized from granular ER.

Each type of endoplasmic reticulum consists of inter-communicating narrow tubes, called tubules, small spherical or oval sac-like structures, known as vesicles, and large flat sacs, called cisternae.

All these structures are filled with fluid called the endoplasmic matrix and are surrounded by a single lipoprotein membrane.

Functions:

1. Proteins are synthesized by ribosomes attached to the membranes of granular ER (RER).
2. Agranular ER (SER) synthesizes sterols, fats, and phospholipids.
3. ER is involved in intracellular exchange of materials between the nucleus and the cytoplasm.

Lysosomes are single-membrane-bound vesicles that contain digestive enzymes.

Structure of Lysosome:

1. Membrane-bound sac that contains hydrolytic enzymes.
2. Present in animal cells but absent in plant cells.

Functions of Lysosome:

1. Breaks down waste materials and cellular debris.
2. Digests foreign invaders like bacteria.
3. Recycles old organelles (autophagy).

• Vacuoles are fluid-filled sacs enclosed by a membrane called the tonoplast.
• Formation: They form by the fusion of vesicles from the Golgi apparatus and endoplasmic reticulum.

Functions of Vacuoles:

1. Stores nutrients, waste products, and pigments.
2. Regulates turgor pressure, keeping plant cells firm.
3. Provides structural support to plant cells.

Structure of Ribosomes:

Ribosomes are non-membranous organelles responsible for protein synthesis.

Made up of two sub-units:

• Eukaryotic Ribosomes: 60S + 40S = 80S
• Prokaryotic Ribosomes: 50S + 30S = 70S

Can be free-floating in the cytoplasm or attached to the rough ER.

Functions of Ribosomes:

1. Translate mRNA into proteins.
2. Facilitate peptide bond formation during protein synthesis.
3. Help in enzyme production for metabolism.

Structure of cell membrane

Structure of cell wall

Diagrams of a chloroplast

Diagrams of a mitochondrion