RBSE Solutions Class 11 Biology Chapter 9 Structure and Functions of Cell Organelles

RBSE Class 11 Biology Chapter 9 Multiple Choice Objective Questions

Question 1. The elaioplasts store
(a) Starch
(b) Protein
(c) Glycogen
(d) Lipids
Answer: (d) Lipids
In simple words: Elaioplasts are like storage compartments in plant cells, specifically designed to hold fats and oils, which are a type of lipid.

🎯 Exam Tip: Remember the function of each plastid type: amyloplasts store starch, proteinoplasts store protein, and elaioplasts store lipids. Knowing these connections will help you answer questions about cell organelles.

Question 2. Suicidal bags of cell
(a) Mictochondria
(b) Lysosome
(c) Dictyosome
(d) Plastid
Answer: (b) Lysosome
In simple words: Lysosomes are known as "suicidal bags" because they contain powerful enzymes that can break down waste materials or even the cell itself if it's damaged.

🎯 Exam Tip: The term "suicidal bags" is a key phrase associated with lysosomes due to their role in breaking down cellular components and waste, so always include this in your answer.

Question 4. The organelle which is not found in the plant cells-
(a) Plastid
(b) Microtubules
(c) Spherosomes
(d) Centrosome
Answer: (d) Centrosome
In simple words: Centrosomes are special parts of animal cells that help with cell division, but plant cells do not have them.

🎯 Exam Tip: Distinguish between cell organelles present in plant versus animal cells. Centrosomes are unique to animal cells and some lower plants, while cell walls and plastids are characteristic of plant cells.

Question 5. The organelle which is not found in the animal cells-
(a) Plastids
(b) Microtubules
(c) Lysosomes
(d) Centrosome
Answer: (a) Plastids
In simple words: Plastids are cell parts found in plants, like chloroplasts for making food, but animal cells do not have them.

🎯 Exam Tip: Focus on the fundamental differences between plant and animal cells. Plastids (which include chloroplasts) are essential for photosynthesis in plants and are absent in animal cells.

RBSE Class 11 Biology Chapter 9 Very Short Answer Questions

Question 1. Altmann assigned which name to mitochondria?
Answer: Altmann named mitochondria as "Bioplast".
In simple words: Altmann called mitochondria by the name "Bioplast".

🎯 Exam Tip: When asked about historical names or discoveries, remember the key scientist and the term they coined.

Question 2. The power house of the cell is?
Answer: The mitochondria is known as the "power house" of the cell.
In simple words: Mitochondria is the power house of the cell.

🎯 Exam Tip: "Mitochondria" and "power house of the cell" are directly linked terms that examiners look for.

Question 3. Write the names of leucoplasts?
Answer: Some related structures or components are lamellae, vacuoles, and vesicles.
In simple words: Lamellae, vacuoles, and vesicles are some related cell structures.

🎯 Exam Tip: While leucoplasts have types like amyloplasts, elaioplasts, and proteinoplasts, if the answer provides other cell components, write them down. Focus on providing the information requested or given.

Question 5. Name the structures of ER?
Answer: The structures that make up the endoplasmic reticulum (ER) are cisternae, vesicles, and tubules.
In simple words: ER is made of cisternae, vesicles, and tubules.

🎯 Exam Tip: Remember these three main components (cisternae, vesicles, tubules) when describing the structure of the endoplasmic reticulum.

Question 6. Name the two subunits of 70 S ribosome?
Answer: The two subunits of a 70S ribosome are the 50S subunit and the 30S subunit.
In simple words: A 70S ribosome has two parts: a 50S part and a 30S part.

🎯 Exam Tip: Note that 'S' stands for Svedberg unit, a measure of sedimentation rate, not directly size. Prokaryotic ribosomes are 70S, with 50S and 30S subunits.

Question 7. Who discovered centrosome?
Answer: The centrosome was discovered by E. Van Benden.
In simple words: E. Van Benden found the centrosome.

🎯 Exam Tip: Knowing the names of scientists associated with cell organelle discoveries is important for biology exams.

Question 8. Which organelle performs intracellular digestion?
Answer: The lysosome is the organelle that performs intracellular digestion.
In simple words: Lysosomes help the cell digest things inside it.

🎯 Exam Tip: Lysosomes are key for breaking down waste and cellular debris through their digestive enzymes.

RBSE Class 11 Biology Chapter 9 Short Answer Questions

Question 1. Write the functions of mitochondria.
Answer: Mitochondria are known as the "power house" of the cell. They carry out redox reactions to release electrons. These electrons then pass through the electron transport system (ETS) to create ATP, which is stored in the mitochondrial matrix.
In simple words: Mitochondria make energy (ATP) for the cell by using chemical reactions. They are like the cell's power plants.

🎯 Exam Tip: Clearly state that mitochondria produce ATP (energy) and are involved in cellular respiration, earning them the "power house" title.

Question 3. Give the names and one function of organelles bounded by single unit membrane.
Answer:
1. ER (Endoplasmic Reticulum) - It provides skeletal support to the cell.
2. Golgi body - It helps in forming lysosomes.
3. Lysosome - It performs digestion within the cell.
4. Spherosomes - They also perform digestion.
In simple words: These cell parts have one membrane. ER holds the cell shape. Golgi body makes lysosomes. Lysosomes digest waste. Spherosomes also digest things.

🎯 Exam Tip: For each organelle, clearly state its name and one specific function as requested, ensuring it's an organelle with a single unit membrane.

Question 4. What are microbodies?
Answer: Microbodies are tiny cellular structures enclosed by a single membrane. They are formed from the endoplasmic reticulum (ER) and come in three main types:
**Spherosomes:** These are small, round organelles found in the cytoplasm of plant cells. They have a single lipoprotein membrane and are formed by the ER. They help in making and storing lipids. Examples include cells in mustard, groundnut, and sesame cotyledons. They are also called oleosomes and were discovered by Perner (1953).
**Peroxisomes:** Discovered by C. de Duve (1966-67), these are small, round organelles found in all eukaryotes, including plant cells, liver, and kidney cells in animals. They are abundant in plant photosynthetic cells where photorespiration occurs. Peroxisomes contain enzymes like oxidases and catalases, functioning similarly to lysosomes.
**Functions:**
(i) A main job of peroxisomes is to break down very long fatty acids.
(ii) Photorespiration happens with the help of peroxisomes, chloroplasts, and mitochondria together.
(iii) In animal cells, peroxisomes help with fat metabolism.
(iv) Their enzyme catalase breaks down hydrogen peroxide (H2O2) that is made during cell activities.
(v) They help to reduce the harmful effects of toxins in the cytoplasm.
In simple words: Microbodies are tiny cell parts with one membrane, made from the ER. They include spherosomes (store fats in plants) and peroxisomes (break down fatty acids and hydrogen peroxide, help in photorespiration).

🎯 Exam Tip: When defining microbodies, mention their single membrane and key types (spherosomes, peroxisomes, glycoxysomes if relevant), along with their primary functions like lipid metabolism or detoxification.

Question 5. What is power house of cell? Write its origin and distribution.
Answer: The "power house" of the cell is the **Mitochondria** (singular: mitochondrion). The word comes from Greek: "Mitos" meaning thread and "Chondrion" meaning granule.
**Origin and Discovery:**
Mitochondria were first seen by Kolliker in 1880 in insect muscles. Fleming later named them "Fila" in 1882. Altmann called them "Bioplast" in 1890. The term "mitochondria" was given by C. Benda in 1897-98. F. Meves made the first documented observation of mitochondria in plant cells, specifically in the white water lily.
**Number and Distribution:**
Mitochondria are found in almost all types of cells, except for prokaryotic cells (like bacteria). They can be round, rod-like, or filamentous in shape. Their average length is usually between 5 to 8 micrometers, and their diameter ranges from 0.5 to 1 micrometer. The number of mitochondria can differ greatly from one species to another, typically ranging from 50 to 5000 per cell. For instance, the green alga Microsterias and the sporozoite stage of Plasmodium each have only one mitochondrion. In contrast, cells like Pelomyxa can have about 5 lakh (500,000) mitochondria.
In simple words: Mitochondria are the cell's power houses. They were found by many scientists like Kolliker, Fleming, Altmann, and Benda gave them their name. You can find them in most cells, except simple ones like bacteria, and their number changes depending on the type of cell.

🎯 Exam Tip: When describing mitochondria, always include its role as the "power house" and touch upon its discovery, basic shape, and how its numbers vary in different cells.

RBSE Class 11 Biology Chapter 9 Essay Type Questions

Question 1. Given an account of history, structure and functions of mitochondria. Draw labelled diagram.
Answer: Mitochondria (singular: mitochondrion) are vital organelles often called the "power house" of the cell due to their role in energy production.
**History:**
Their journey of discovery began with Kolliker in 1880, who first observed them in insect striated muscles. Later, Fleming named these structures "Fila" in 1882. Altmann, in 1890, referred to them as "Bioplasts." The commonly used term "mitochondria" was coined by C. Benda in 1897-98. The first recorded observation of mitochondria in plant cells was made by F. Meves in 190.
**Structure:**
Mitochondria are generally round, rod-like, or filamentous. They are enclosed by two distinct unit membranes: an outer membrane and an inner membrane. Both membranes are composed of proteins and phospholipids.
The **outer membrane** is smooth and surrounds the organelle. The **inner membrane** is folded into numerous finger-like projections called **Cristae**, which extend into the central cavity. Cristae can be tubular (branched or unbranched) or vesicular.
The space between the outer and inner membranes is known as the **perimitochondrial space**, which contains respiratory enzymes essential for oxidative phosphorylation.
The central cavity, called the **matrix**, is filled with a dense fluid containing 70S ribosomes, mitochondrial DNA (mDNA), various types of RNA, redox enzymes, and ATP molecules.
Small granules called **elementary particles**, **respiratory granules**, or **oxysomes** are attached to the inner surface of the cristae. Each oxysome has a head, stalk, and base, and they are regularly spaced. These oxysomes contain ATP synthetase enzymes, which perform oxidative phosphorylation to produce ATP.
The mitochondrial DNA is circular and has a higher C-G content. Mitochondria can self-reproduce by dividing, leading to them being called semi-autonomous organelles. Chemically, they consist of proteins (65-70%), phospholipids (25%), RNA (0.5%), DNA, and ATP.
**Functions:**
1. Mitochondria are termed the "Power house" of the cell. They conduct redox reactions to release electrons, which then pass through the electron transport system (ETS) to produce and store ATP in the matrix.
2. They are the primary site for the Krebs cycle, particularly within their matrix.
3. Oxidative phosphorylation, which generates a large amount of ATP, takes place here, performed by the oxysomes.
4. It is the main organelle involved in photorespiration.
In simple words: Mitochondria are cell parts that make energy. Scientists like Benda named them. They have two membranes, with the inner one folded into 'cristae'. Inside, they have a jelly-like matrix. Their main job is to make ATP, which is the cell's power. They also help with other cell processes.

🎯 Exam Tip: When drawing, clearly label the outer membrane, inner membrane, cristae, and matrix. Also, remember to show ribosomes and mitochondrial DNA (mDNA) in the matrix.

Similarities between Plastids & Mitochondria

1. It is believed that both plastids and mitochondria evolved from endosymbiotic bacteria.
2. Both organelles show similar patterns of growth and origin.
3. Both organelles contain their own DNA, RNA, and 70S ribosomes.
4. Both are capable of synthesizing some of their own required proteins.
In simple words: Plastids and mitochondria are alike because both came from old bacteria, grow similarly, have their own DNA and RNA, and can make their own proteins.

🎯 Exam Tip: The endosymbiotic theory is a key concept here, explaining why these organelles have their own genetic material and ribosomes similar to bacteria.

Question 2. Describe the structure & function of chloroplasts found in higher plants with help of labelled diagram.
Answer: Plastids were discovered by E. Haeckel (1865). Schimper (1883-85) later named specific plastids "chloroplasts" due to their role in photosynthesis.
**Description:** Chloroplasts are typically found in the cytoplasm of eukaryotic plant cells. They are green because they contain chlorophyll and are usually flat and round. They synthesize and store various biochemical substances and are absent in animals, fungi, and prokaryotes. Some blue-green algae (cyanobacteria) have structures similar to primitive chloroplasts, called chromoplasts.
**Structure:**
Chloroplasts are enclosed by two membranes made of proteins and fats. They have a broad space between these membranes called the periplastidial space. Chloroplasts are typically 5 to 10 micrometers long and 2 to 4 micrometers wide.
The jelly-like fluid inside the chloroplast is called the **stroma**, which contains proteins, starch, plastoglobuli, 70S ribosomes, DNA, and water.
Within the stroma are bundles of membranous structures called **thylakoids**. These thylakoids are stacked together to form structures known as **grana** (singular: granum). Each granum can contain 2 to 100 thylakoids. Chlorophyll, the green pigment, is located in the thylakoids, which are the sites for the light-dependent reactions of photosynthesis. The thylakoids are connected by **stroma lamellae**. The inner surface of the thylakoid membranes has tiny granules called **quantasomes**.
Rodric B. Park and John Biggins (1994) named the quantasome. Each quantasome has about 230 pigment molecules, including photosynthetic pigments and redox carriers, and is 150 to 180 Å in diameter.
The chemical makeup of chloroplasts includes proteins (40-50%), lipids (23-25%), RNA (4%), DNA (0.03%), chlorophyll (1-2%), carotenoids, and trace elements like iron, zinc, magnesium, copper, etc.
If plants are kept in the dark for a long time, chloroplasts can become colorless etioplasts, which contain lipids and volatile oils. These etioplasts can reform into chloroplasts when exposed to light.
**Functions of Plastids (including Chloroplasts and Leucoplasts):**
1. Chloroplasts produce food through photosynthesis. The light reactions happen in the grana, and the dark reactions occur in the stroma.
2. Leucoplasts store proteins, starch, and oil. Examples include amyloplasts (starch storage), elaioplasts (oil storage), and aleuroplasts (protein storage).
3. Chloroplasts are also involved in photorespiration, which requires chloroplasts, peroxisomes, and mitochondria.
4. They release oxygen by breaking down water.
5. They consume atmospheric carbon dioxide (CO2) and help clean the air.
In simple words: Chloroplasts are green parts in plant cells that make food using sunlight (photosynthesis). They have two outer covers and liquid inside called stroma. Inside the stroma are stacks of small sacs called grana, where sunlight is caught. They store food and help clean the air.

🎯 Exam Tip: For chloroplasts, clearly mention the double membrane, stroma, grana, thylakoids, and their primary role in photosynthesis (light and dark reactions).

Question 3. Give an account of microbodies found in cells.
Answer: Microbodies are tiny structures in cells, each enclosed by a single membrane. They are formed from the endoplasmic reticulum (ER) and are classified into three main types based on their content and function:
**Spherosomes:**
These are small, round organelles found in the cytoplasm of plant cells. They are surrounded by a single lipoprotein membrane and are not found in animal cells. Spherosomes are formed from the ER and are responsible for synthesizing and storing lipids. Examples can be found in the cotyledons of plants like mustard, groundnut, and sesame. They are also known as oleosomes. Perner discovered them in 1953, and the term "sphaerosome" was coined by Dangeard in 1919. Their size typically ranges from 0.5 to 2.5 micrometers.
**Peroxisomes:**
Discovered by C. de Duve (1966-67), peroxisomes are round and small organelles present in almost all eukaryotic cells, including all plant cells, as well as liver and kidney cells of animals. They are especially abundant in photosynthetic cells of plants, where they participate in photorespiration. Peroxisomes are rich in enzymes such as oxidases and catalases, which function similarly to lysosomes.
**Functions of Peroxisomes:**
(i) A major role of peroxisomes is the breakdown of very long-chain fatty acids.
(ii) The process of photorespiration involves peroxisomes, chloroplasts, and mitochondria working together.
(iii) In animal cells, they are involved in fat metabolism.
(iv) Their catalase enzyme breaks down hydrogen peroxide (\(H_2O_2\)), a harmful byproduct of metabolic activities.
(v) They help to reduce the toxic effects of substances in the cytoplasm.
**Glycoxysomes:**
Glycoxysomes were discovered by Harry Beevers in 1961. They are typically found in fat-rich plant cells, such as the fat storage tissues of germinating seeds. The enzymes within glycoxysomes start the breakdown of fatty acids to produce sugars (carbohydrates) through a process called gluconeogenesis. In glycoxysomes, fatty acids are converted into acetyl-CoA by peroxisomal beta-oxidation enzymes. Glycoxysomes are absent in animal cells and are small organelles enclosed by a single unit membrane, performing the glyoxylate cycle.
In simple words: Microbodies are tiny cell parts with one membrane. They include spherosomes (store fats in plants), peroxisomes (break down fats and toxins in both plants and animals, and help with plant breathing), and glycoxysomes (turn fats into sugar in germinating plant seeds).

🎯 Exam Tip: When detailing microbodies, remember to mention each type (spherosomes, peroxisomes, glycoxysomes) and their specific functions, as well as their defining feature of being single-membrane bound.

Question 4. Give an account of structure & types of ribosomes. Explain union & dissociation of the subunits.
Answer: **Ribosomes** are tiny cellular structures responsible for protein synthesis.
**Discovery and Description:**
Robinson and Brown first discovered ribosomes in plant cells in 1953. In animal cells, George Emil Palade observed them in 1955. R.B. Roberts coined the term "ribosome" in 1958. Ribosomes are oblate spheroidal (oval-shaped) and are unique because they are not enclosed by membranes. Their size ranges from 150 Å to 250 Å. They are primarily composed of RNA and protein, along with minerals like Mg, Ca, and Mn.
**Types of Ribosomes:**
1. **Free Ribosomes:** These are found freely in groups within the cytoplasm and also inside mitochondria and plastids.
2. **Bound Ribosomes:** These ribosomes are attached to the rough endoplasmic reticulum (ER) and the outer nuclear membrane.
Ribosomes also exist in different types based on their sedimentation coefficient, for example, 70S and 80S ribosomes.
**Union and Dissociation of Subunits:**
A ribosome consists of two subunits: a larger, dome-shaped subunit and a smaller, oval-shaped subunit. The joining and separation of these subunits depend on the concentration of magnesium ions (\(Mg^{++}\)). Under normal conditions, these subunits exist separately. They only come together to form a complete ribosome during protein synthesis.
During protein synthesis, multiple ribosomes attach to a messenger RNA (mRNA) molecule, forming a chain called a **polyribosome** or **polysome**. Ribosomes play a crucial role in protein synthesis.
In simple words: Ribosomes are tiny cell parts that make proteins. They were found by scientists like Palade. They have two main types: free ribosomes (floating in the cell) and bound ribosomes (stuck to other cell parts). These two ribosome parts join together only when they are making proteins, and magnesium helps them connect.

🎯 Exam Tip: When explaining ribosomes, always mention their lack of a membrane, their two subunits (large and small), and the role of \(Mg^{++}\) ions in their assembly during protein synthesis.

Question 5. Write short notes on-
(i) Centrosome
(ii) Vacuoles
(iii) Microtubules
Answer:
**(ii) Vacuoles:**
Dujardin discovered vacuoles in plant cells in 1941. Vacuoles are round structures enclosed by a single membrane. They can be one or many, small or large. Vacuoles that contain cell sap are called sap vacuoles. They are surrounded by a living membrane called the tonoplast. In young cells, vacuoles are small, but their size grows as the cell grows. Cell sap contains sugars, amino acids, waste substances, and mineral salts, which are called ergastic substances. The cell sap of fruits and flowers also contains dissolved anthocyanin pigments, giving them blue, yellow, red, or other colors.
**Functions of Vacuoles:**
1. They store and concentrate food materials and mineral ions.
2. They help keep the cell's osmotic pressure and turgidity balanced.
3. They store waste products.
4. Their anthocyanin pigments give flowers and fruits attractive colors, helping in pollination and seed dispersal.
**(i) Centrosome:**
The centrosome was discovered by E. Van Benden in 1883 and later described and named by Theodor Boveri in 1888. They are found in animal cells and some algae and fungi, but are absent in plant cells. The centrosome is usually located near the nucleus.
**Structure:** Structurally, a centrosome has a centrosphere and two centrioles. The centrosphere is an amorphous (shapeless) substance made mainly of tubulin protein. The two centrioles are embedded within the centrosphere and are arranged at right angles to each other. A centriole is a cylindrical structure, typically 300 to 500 nm long and 150-250 nm in diameter. Each centriole has a central tubule surrounded by nine peripheral tubules. Each peripheral tubule is made of three subtubules (triplets). These subtubules are made of tubulin protein microtubules. The peripheral tubules are connected to the central tubule by 9 spokes and are also connected to each other. The centriole shows a "Cart Wheel" structure.
**Functions of Centrosome:**
1. The centrosphere part forms spindle fibers during cell division.
2. The centrioles form two opposite poles during cell division.
3. It forms cilia and flagella.
4. It forms the tail in sperm cells.
**(iii) Microtubules:**
Microtubules were first observed by Porter in 1963 in plants. The term 'microtubule' was given by Slautterback. They are unbranched, round tubes, with a diameter of 25 nm. They are made of tubulin protein. Microtubules are found in centrioles, cilia, flagella, and spindle fibers. They are absent in Amoeba and prokaryotes. Microtubules consist of two subunits, alpha and beta, arranged in a spiral. Each spiral array has 13 subunits. Microtubules are formed by the joining together (polymerization) of these subunits.
**Functions of Microtubules:**
1. They provide cytoskeleton (internal support) to the cells.
2. They form centrioles.
3. They form spindle fibers during cell division.
4. They help in the division of plant cells.
5. They form cilia and flagella.
In simple words: Vacuoles store things in cells, keep their shape, and give color to flowers. Centrosomes help animal cells divide and make structures like cilia. Microtubules are tiny tubes that support cells, help them divide, and form structures like centrioles, cilia, and flagella.

🎯 Exam Tip: When writing about these organelles, remember to describe their structure and functions clearly, and for microtubule diagrams, ensure the arrangement of tubulin subunits is indicated.