RBSE Solutions Class 11 Biology Chapter 10 Nucleus and Chromosomes

RBSE Class 11 Biology Chapter 10 Multiple Choice Objective Questions

Question 1. Solenoid structure is associated with-
(a) Nucleus
(b) Nucleolous
(c) Chromatin
(d) Nucleoid
Answer: (c) Chromatin
In simple words: The solenoid structure is a way DNA and proteins (chromatin) are tightly packed inside the cell's nucleus. It helps organize the long DNA molecule efficiently.

🎯 Exam Tip: Remember that chromatin condensation is crucial for fitting DNA into the small nucleus, and the solenoid structure is a key part of this packing.

Question 2. The suitable dye for chromatin is-
(a) Safrenin
(b) Acetocarmine
(c) Light green
(d) Aniline blue
Answer: (b) Acetocarmine
In simple words: Acetocarmine is a special color used by scientists to clearly see chromatin under a microscope. It makes the chromatin stand out, so it's easy to study.

🎯 Exam Tip: Know common stains used in microscopy, as different stains highlight different cell structures, which can be a tricky area.

Question 4. Example of coenocyte is-
(a) Vaucheria algae
(b) Straited muscle cells
(c) Epithelium of Ascaris
(d) All of the options
Answer: (d) All of the options
In simple words: A coenocyte is a cell that has many nuclei but no dividing walls between them, acting like one large, shared cell. All the listed examples, including certain algae, muscle cells, and some worm tissues, show this feature.

🎯 Exam Tip: Distinguish between coenocyte (multiple nuclei from nuclear division without cytokinesis) and syncytium (multiple nuclei from cell fusion), as they are related but distinct concepts.

Question 5. Nuclear membrane originates from which of the following-
(a) Mitochondria
(b) Golgi body
(c) ER
(d) Lysosome
Answer: (c) ER
In simple words: The nuclear membrane, which surrounds the nucleus, grows from the endoplasmic reticulum (ER). The ER is like a network of sacs and tubules within the cell. This connection helps to form the nucleus after cell division.

🎯 Exam Tip: Understand the origin and interrelationship of cell organelles, as the ER plays a crucial role in forming several other membrane-bound structures.

Question 6. Ribosomes originate from
(a) Nucleolous
(b) Chromosome
(c) Nuclear membrane
(d) Nucleoplasm
Answer: (a) Nucleolous
In simple words: Ribosomes, which are responsible for making proteins, are put together in a special part of the nucleus called the nucleolus. The nucleolus acts like a factory for these protein-making machines.

🎯 Exam Tip: Remember the nucleolus's primary role in ribosome synthesis, as it's a key function of this nuclear component.

Question 7. Genetically more active part is-
(a) Chromatin
(b) Euchromatin
(c) Heterochromatin
(d) None of the options
Answer: (b) Euchromatin
In simple words: Euchromatin is the part of the chromosome that is loosely packed, allowing the genes there to be easily read and used to make proteins. This makes it the most active part for genetic functions.

🎯 Exam Tip: Differentiate between euchromatin and heterochromatin based on their condensation levels and genetic activity; euchromatin is open for transcription, while heterochromatin is mostly silent.

Question 9. The diploid number of chromosomes in wheat is-
(a) 42
(b) 07
(c) 21
(d) 14
Answer: (a) 42
In simple words: Wheat plants typically have a total of 42 chromosomes in their regular body cells. This is a characteristic number for the common bread wheat species.

🎯 Exam Tip: Specific chromosome numbers for important organisms like wheat are common knowledge points in biology and worth memorizing.

Question 10. Number of DNA molecule in one chromatid-
(a) One
(b) Two
(c) Four
(d) Many
Answer: (a) One
In simple words: Each chromatid, which is one half of a duplicated chromosome, contains a single, long molecule of DNA. This DNA molecule is tightly coiled to fit within the structure.

🎯 Exam Tip: Understand the structure of a chromosome before and after replication; a single chromatid is a single DNA molecule, while a duplicated chromosome has two sister chromatids, each with one DNA molecule.

RBSE Class 11 Biology Chapter 10 Very Short Answer Questions

Question 1. Who discovered nucleus ?
Answer: Robert Brown.
In simple words: The cell nucleus was first found by a scientist named Robert Brown. He made this discovery while studying plant cells.

🎯 Exam Tip: Remember key scientists and their discoveries, especially for fundamental cell structures like the nucleus.

Question 2. Which part of chromosomes form nucleolous?
Answer: Nucleolar organizer.
In simple words: A special region on certain chromosomes, known as the nucleolar organizer region (NOR), is responsible for making the nucleolus. This area contains genes for ribosomal RNA.

🎯 Exam Tip: Focus on the specific function of the nucleolar organizer region in ribosome synthesis and nucleolus formation.

Question 3. Who propound the names enchromatin and heterochromatin ?
Answer: Emil Heitz.
In simple words: Emil Heitz was the scientist who first described and gave the names euchromatin and heterochromatin to the different types of chromatin packaging in the nucleus. This distinction is important for gene activity.

🎯 Exam Tip: While Strasberger and Waldeyer contributed to chromosome understanding, Emil Heitz specifically defined euchromatin and heterochromatin.

Question 5. What is the maximum number of haploid chromosomes in organisms?
Answer: Aulocantha.
In simple words: Among known organisms, the protozoan Aulocantha has the highest number of haploid chromosomes, reaching up to 1600. This organism is notable for its incredibly large chromosome count.

🎯 Exam Tip: While humans have 23 haploid chromosomes, be aware that other organisms can have vastly different numbers, and some can be very high.

Question 6. Which shapes of chromosomes are formed during metaphase?
Answer: V, L, J, I shapes.
In simple words: During metaphase, chromosomes take on different shapes depending on where their centromere is located. These can be V-shape (metacentric), L-shape (submetacentric), J-shape (acrocentric), or I-shape (telocentric).

🎯 Exam Tip: Relate each shape to the specific position of the centromere (e.g., V for central, I for terminal) as this is a common examination point.

Question 7. Name the acidic proteins found in the chromosomes.
Answer: Non-histone.
In simple words: Besides histones, which are basic proteins, chromosomes also contain other proteins that are acidic. These are called non-histone proteins and play a role in gene regulation and chromosome structure.

🎯 Exam Tip: Recognize that chromosomes are complex structures made of both DNA and various proteins, not just histones, and non-histone proteins are vital for their function.

Question 8. Which histone protein is absent in the core particle of nucleosome.
Answer: H1.
In simple words: The H1 histone protein is not part of the main core of the nucleosome, which is made of other histones (H2A, H2B, H3, H4). Instead, H1 acts as a linker, binding where the DNA enters and exits the nucleosome.

🎯 Exam Tip: Differentiate between the core histones and the linker histone (H1) and understand their respective roles in DNA packaging.

Question 9. Number of nucleosomes in a solenoid coil.
Answer: 3-6.
In simple words: A solenoid coil is a higher level of DNA packing where nucleosomes are further condensed. Each turn or coil of this solenoid structure usually contains about 3 to 6 nucleosomes.

🎯 Exam Tip: Understand the hierarchical organization of DNA packaging, from the double helix to nucleosomes, then to the solenoid, and finally to metaphase chromosomes.

Question 10. Which cell division forms polytene chromosome.
Answer: Endomitosis.
In simple words: Polytene chromosomes are very large chromosomes that form during a special type of cell division called endomitosis. In endomitosis, the chromosomes replicate many times but the cell does not divide, leading to giant chromosomes.

🎯 Exam Tip: Polytene chromosomes are a unique feature in certain insect salivary glands, and their formation through endomitosis is a key concept.

RBSE Class 11 Biology Chapter 10 Short Answer Questions

Question 2. Give the main functions of nucleus.
Answer: The nucleus is a very important part of eukaryotic cells. It holds the cell's DNA, which has all the instructions for how the cell works and grows. Because of its DNA content, the nucleus controls all the metabolic activities of the cell. It also directs protein synthesis by sending messenger RNA to the cytoplasm.
In simple words: The nucleus is the control center of the cell. It stores the cell's genetic material (DNA) and manages all cell activities, including growth and protein production.

🎯 Exam Tip: When listing functions, start with the most critical role (housing genetic material and control) and then elaborate on key processes like metabolism and gene expression.

Question 3. What is satellite chromosome.
Answer: A satellite chromosome is one where the end part is separated from the main body of the chromosome by a narrow, constricted region. This secondary constriction is often called the nucleolar organizing region. The chromosome that has this satellite portion is known as a SAT chromosome. These satellites play a role in forming the nucleolus.
In simple words: A satellite chromosome has a small, distinct part at its end, separated by a thinner segment. This special part helps to create the nucleolus inside the cell's nucleus.

🎯 Exam Tip: Understand that not all chromosomes have satellites, and their presence indicates a specific role in nucleolus organization.

Question 4. What is chromatids ?
Answer: During the metaphase stage of cell division, each chromosome is made up of two identical halves called chromatids. These two sister chromatids are joined together at a central point called the centromere. They are essentially identical copies of a chromosome, ready to be separated into new daughter cells.
In simple words: Chromatids are the two identical halves of a chromosome after it has copied itself. They stay connected at the center until the cell divides.

🎯 Exam Tip: Clearly define "chromatid" in the context of a duplicated chromosome and its role in cell division, especially metaphase.

Question 5. Give the names & functions of two giant chromosomes.
Answer: The two main types of giant chromosomes are:
1. Polytene Chromosome: This type allows for very high levels of gene expression. Its multiple DNA copies help the cell quickly produce large amounts of specific proteins, which is useful in cells like insect salivary glands.
2. Lampbrush Chromosome: This chromosome is involved in the synthesis of RNA, yolk, and proteins. It has loops that extend out, which are sites of active gene transcription, especially important during the development of eggs.
In simple words: Giant chromosomes are extra-large. Polytene chromosomes help cells make many copies of genes and proteins quickly. Lampbrush chromosomes are busy making RNA, yolk, and proteins, especially for developing eggs.

🎯 Exam Tip: Remember the specific functions and unique structures (puffs in polytene, loops in lampbrush) that make these chromosomes "giant" and biologically significant.

Question 6. Differentiate coenocyte and syncytium.
Answer:
Coenocyte: A coenocyte is a cell or organism that contains multiple nuclei within a single cytoplasm, but without distinct cell walls or membranes separating them. This condition arises from repeated nuclear divisions without the accompanying division of the cytoplasm (cytokinesis). A common example is found in some fungi and algae, where nutrients can move freely throughout the structure.
Syncytium: A syncytium is also a multinucleated cell, but it forms when multiple individual cells fuse together. This fusion results in a large cell with shared cytoplasm and many nuclei. Striated muscle cells in animals are a classic example of syncytia, formed from the fusion of many myoblasts during development.
In simple words: Both coenocytes and syncytia have many nuclei in one cell. A coenocyte forms when a cell's nucleus divides many times without the cell itself splitting. A syncytium forms when several separate cells join together into one big cell.

🎯 Exam Tip: The key difference lies in their formation: coenocytes result from incomplete cell division, while syncytia result from cell fusion.

Question 8. Write in short about nucleosome.
Answer: Nucleosomes look like small beads. Each nucleosome has a central core and a piece of DNA that links it to the next bead. The central core is made of eight histone proteins: one pair each of H2A, H2B, H3, and H4. This core is wrapped by two coils of DNA. This structure helps DNA fit neatly into the cell's nucleus.
In simple words: Nucleosomes are like tiny beads where DNA is wrapped around special proteins.

🎯 Exam Tip: Remember that nucleosomes are the basic units of DNA packaging, helping to condense the long DNA molecule into a compact form.

Question 9. What is heteropycnosis? Give its types.
Answer: Heteropycnosis describes how different parts of a chromosome stain. Tightly coiled areas take up more stain, while less coiled areas take less stain. This difference helps scientists see how packed the DNA is.
In simple words: Heteropycnosis is when parts of chromosomes stain differently because some parts are tightly packed and others are loose.

🎯 Exam Tip: Note that heteropycnosis is a feature of heterochromatin, which is highly condensed and usually genetically inactive.

Question 10. Differentiate the following.
(i) Eukaryotic & prokaryotic nuclei
(ii) Enchromatin & heterochromatin
(iii) Chromosome & chromatid
Answer:
(i) Eukaryotic and prokaryotic nuclei have key differences. A prokaryotic nucleus does not have a nuclear membrane around it. In contrast, a eukaryotic nucleus is surrounded by a clear nuclear membrane. This membrane protects the genetic material.
(ii) Euchromatin and heterochromatin are two forms of chromatin. Euchromatin is less coiled and stains lightly, meaning its genes are often active. Heterochromatin is more tightly coiled and stains darkly, and its genes are usually inactive. This coiling affects how genes are used.
(iii) A chromosome is a whole package of DNA, carrying genetic information. A chromatid is one of the two identical halves of a duplicated chromosome, joined together at the centromere. These are formed when a cell prepares to divide.
In simple words: (i) Prokaryotic cells have no membrane around their DNA, but eukaryotic cells do. (ii) Euchromatin is loose and active, while heterochromatin is packed tight and usually quiet. (iii) A chromatid is half of a duplicated chromosome, created before cell division.

🎯 Exam Tip: Remember that the presence of a nuclear membrane is a defining characteristic distinguishing eukaryotes from prokaryotes. Also, relate chromosome coiling to gene activity and understand that chromatids are formed during DNA replication before cell division.

RBSE Class 11 Biology Chapter 10 Essay Type Questions

Question 1. Describe structure of nucleus. Give suitable diagram.
Answer: The nucleus is a vital part of eukaryotic cells. It contains the cell's genetic material and controls its activities. The nucleus is made of several key parts: 1. **Nuclear Membrane:** This is a double-layered cover, about 85 Angstroms thick, around the nucleus. It has small openings called nuclear pores, which are 300 to 400 Angstroms wide. These pores allow substances to move in and out. The outer membrane is connected to ribosomes and the Endoplasmic Reticulum (ER). The nuclear membrane helps protect the genetic material inside. 2. **Nucleolus:** This is a small, round body inside the nucleus, usually one or two per nucleus. It was discovered by Fontana (1781) and named by Bowman (1840). It is not surrounded by a membrane. The nucleolus helps make ribosomes and disappears during cell division phases like prophase, reappearing in telophase. It is structurally made of: * **Fibrilar part:** Contains thin fibers of ribonucleoproteins (50-80 Angstroms long). * **Granular part:** Contains small granules of RNA and proteins (150-200 Angstroms wide). * **Amorphous part:** This is a smooth, liquid part, also called the matrix, mainly made of proteins, where the fibers and granules float. 3. **Nucleoplasm:** This is a clear, semi-liquid, and granular fluid found within the nucleus. It is also known as nuclear sap or karyolymph. The nucleoplasm holds the nucleolus and chromatin suspended in it. It contains important substances like proteins, DNA, RNA, and nuclear enzymes. 4. **Chromatin Material/Chromosomes:** During the normal interphase of a cell, the nucleus contains a network of fine threads called chromatin. These threads condense and form distinct structures called chromosomes during cell division. Chromatin can be stained with acetocarmine. Emil Heitz (1928-1935) found that chromatin has two types: euchromatin (genetically active) and heterochromatin (genetically inactive).
In simple words: The nucleus has a double membrane, a nucleolus for making ribosomes, a fluid called nucleoplasm, and chromatin (DNA and proteins) which forms chromosomes during cell division.

🎯 Exam Tip: When describing the nucleus, remember to mention its key components and their basic functions, emphasizing the nuclear membrane, nucleolus, and chromatin as main parts.

Question 2. Describe structure of chromosome with the help of diagram.
Answer: Chromosomes are important structures that carry genetic information. Their structure is best seen during the metaphase stage of cell division (mitosis). At this time, chromosomes become thick, condensed, and clearly visible.
**Structure of Chromosome:** * **Chromatids and Centromere:** During metaphase, each chromosome has two identical halves called chromatids. These chromatids are joined together at a central point called the centromere. During anaphase, the centromere divides, and the two chromatids separate, becoming individual daughter chromosomes. * **Chromonemata and Chromomeres:** Before division, in interphase, each chromatid is made of a coiled thread called chromonemata. Parts of chromonemata that are more tightly coiled are called chromomeres. These chromomeres are where many genes are located. * **Centromere (Primary Constriction):** This is the uncoiled region of the chromosome where spindle fibers attach during cell division. It is essential for chromosome movement. * **Secondary Constrictions:** These are other less-coiled regions on the chromonemata. One specific secondary constriction is known as the nucleolar organizer, which helps form the nucleolus. These constrictions are always found in the same place. * **Satellite and SAT Chromosomes:** Some chromosomes have a small, distinct end-part separated by a secondary constriction, called a satellite. A chromosome with a satellite is called a SAT chromosome. These satellites appear connected by a thin thread of chromatin during metaphase. Each diploid nucleus usually has at least two SAT-chromosomes. * **Telomere:** These are protective segments at both ends of a chromosome. Telomeres consist of repeating DNA sequences (like TTAGGG in vertebrates) that can be up to 15,000 base pairs long. They prevent the loss of genetic information during replication. Each time a cell divides, a small portion of the telomere is lost (25-200 base pairs). This shortening of telomeres is linked to the aging process in humans.
**Chemical Composition of Chromosomes:** Chromosomes are mainly made of: 1. **Nucleic Acids:** These include DNA (Deoxyribonucleic acid) and RNA (Ribonucleic acid). 2. **Proteins:** There are two main types: * **Histones:** These are basic proteins that DNA wraps around to form nucleosomes. * **Non-histones:** These are acidic proteins. 3. **Mineral Ions and Salts:** Such as calcium (Ca), magnesium (Mg), and sodium (Na). DNA and histone proteins make up about 90-92% of the chromosome, while RNA and non-histone proteins form the remaining 8-10%. The table below shows details of histone proteins:

In simple words: Chromosomes are structures holding our DNA. They become visible during cell division, showing two identical chromatids joined at a centromere. Other parts like telomeres protect the ends. They are mostly made of DNA, RNA, and histone proteins.

🎯 Exam Tip: For chromosome structure, focus on clearly defining chromatids, centromere, telomere, and the chemical composition. Visualizing these parts during cell division helps understanding.

Question 3. What is polytene chromosome? Give its structure & function.
Answer: Polytene chromosomes are special, very large chromosomes. They were first discovered by Balbiani in 1881. These giant chromosomes are typically found in the salivary gland cells of insect larvae, like those of Drosophila (fruit flies), Chironomus, and mosquitoes.
**Structure:** * **Formation:** Polytene chromosomes are formed through a process called endomitosis. In this process, the chromosome replicates many times without the cell actually dividing. This results in numerous identical chromatids remaining joined together. * **Appearance:** These chromosomes have many puffed and unpuffed regions along their length. * **Puffed Regions (Balbiani Rings):** The puffed areas are known as Balbiani rings. These regions are very active in gene expression, meaning they are busy making RNA and proteins. * **Unpuffed Regions:** These areas consist of alternating bands and interbands. The bands are more tightly coiled parts, while the interbands are less condensed. * **Chromocentre:** Many chromatids remain attached to a common central part called the chromocentre.
**Function:** The main function of polytene chromosomes comes from having multiple copies of genes. This allows for a very high level of gene expression, which is a metabolic advantage for these cells. This high activity helps produce the large amounts of proteins and RNA needed for the rapid growth and development of the larvae.
In simple words: Polytene chromosomes are huge chromosomes found in insect larvae. They are formed when DNA copies itself many times but the cell doesn't divide. They have puffy parts called Balbiani rings that are very active in making proteins, helping the larva grow quickly.

🎯 Exam Tip: Remember that polytene chromosomes are characterized by their large size, presence in specific insect cells, formation by endomitosis, and high gene expression due to multiple DNA copies.