CBSE Class 11 Biotechnology — NCERT Solutions

Given/Concept: The term 'Biotechnology' combines 'biology' and 'technology'. It refers to the use of living organisms, cells, or their components to develop products and processes for human welfare.

Definition:
Biotechnology is defined as the integration of natural sciences and engineering sciences in order to achieve the application of organisms, cells, parts thereof, and molecular analogues for products and services. (European Federation of Biotechnology, EFB)

In simpler terms, biotechnology involves the use of biological systems (microorganisms, plants, animals, or their components) to develop useful products and processes.

Key aspects of Biotechnology:

1. It uses living organisms or their derivatives.
2. It involves manipulation at the molecular, cellular, or organismal level.
3. It aims at producing useful products or solving problems.

Examples:

Conclusion: Biotechnology is a broad, multidisciplinary field that harnesses biological knowledge and engineering principles to benefit agriculture, medicine, industry, and the environment.

Given/Concept: Biotechnology has been practised by humans for thousands of years, but the nature and scale of its application have changed dramatically with advances in science.

Comparative Account:

Key Distinction:

• Ancient biotechnology relied on naturally occurring biological processes without understanding the underlying mechanisms.
• Modern biotechnology deliberately manipulates genetic material (DNA) to achieve desired outcomes with precision and predictability.

Conclusion: While ancient biotechnology laid the foundation by demonstrating the utility of microorganisms and selective breeding, modern biotechnology has revolutionised the field by enabling precise genetic manipulation, leading to products and solutions that were previously unimaginable.

Correct Option: (d) Singer and Nicolson

The Fluid Mosaic Model of the plasma membrane was proposed by S.J. Singer and G.L. Nicolson in 1972. According to this model, the membrane is a fluid phospholipid bilayer in which proteins are embedded (like a mosaic), and both lipids and proteins can move laterally. Robert Brown discovered the nucleus; Schleiden and Schwann proposed the Cell Theory; Virchow proposed 'Omnis cellula e cellula'.

Correct Option: (b) rRNA and proteins

Ribosomes are ribonucleoprotein particles composed of ribosomal RNA (rRNA) and proteins. They do not contain DNA or lipids. Each ribosome consists of two subunits (large and small), both made of rRNA molecules associated with specific ribosomal proteins. They are the sites of protein synthesis in the cell.

Given/Concept: Carbohydrates are polyhydroxy aldehydes or ketones. They are classified on the basis of the number of sugar units they contain.

Classification of Carbohydrates:

1. Monosaccharides (Simple sugars):

• Cannot be hydrolysed further into simpler sugars.
• General formula: $(CH_2O)_n$ where $n = 3$ to $7$.
• Classified by number of carbon atoms:
• Trioses ($n=3$): e.g., Glyceraldehyde, Dihydroxyacetone
• Tetroses ($n=4$): e.g., Erythrose
• Pentoses ($n=5$): e.g., Ribose, Deoxyribose
• Hexoses ($n=6$): e.g., Glucose, Fructose, Galactose
• Heptoses ($n=7$): e.g., Sedoheptulose
• Further classified as aldoses (contain aldehyde group, $-CHO$) or ketoses (contain ketone group, $C=O$).

2. Oligosaccharides:

• Contain 2–10 monosaccharide units joined by glycosidic bonds.
• Sub-classified as:
• Disaccharides (2 units): e.g., Sucrose (glucose + fructose), Maltose (glucose + glucose), Lactose (glucose + galactose)
• Trisaccharides (3 units): e.g., Raffinose
• Tetrasaccharides (4 units): e.g., Stachyose

3. Polysaccharides:

• Contain more than 10 (often hundreds to thousands) monosaccharide units.
• Two types:
• Homopolysaccharides: Made of one type of monosaccharide. e.g., Starch, Glycogen, Cellulose (all made of glucose)
• Heteropolysaccharides: Made of two or more types of monosaccharides. e.g., Hyaluronic acid, Heparin

Conclusion: Carbohydrates are broadly classified into monosaccharides, oligosaccharides, and polysaccharides based on the degree of polymerisation.

Concept: The D- and L- designation of glucose is based on the configuration of the asymmetric carbon atom farthest from the carbonyl (aldehyde) group, i.e., C-5 in glucose. This is compared to the reference molecule glyceraldehyde.

Note: The D/L designation refers to the spatial configuration at the reference carbon, not to the direction of optical rotation.

Conclusion: D- and L-glucose are enantiomers differing in the orientation of the $-OH$ group at C-5. D-glucose is the biologically important form.

Correct Option: (b) decrease the activation energy

Justification: Enzymes are biological catalysts. They function by lowering the activation energy (energy barrier) required for a reaction to proceed, thereby increasing the rate of the reaction. Enzymes do not alter the equilibrium constant of a reaction, nor do they need to be saturated with substrate to catalyse a reaction. They certainly do not increase the activation energy.

Apoptosis vs. Necrosis

Conclusion: Apoptosis is a physiologically regulated process essential for normal development and homeostasis, whereas necrosis is a pathological process resulting from acute cellular injury.

(a) Genotype and Phenotype

(b) Dominant and Recessive Characters

(c) Hybrid and Pure Individuals

(d) Heterozygous and Homozygous Progeny

(e) Monohybrid and Dihybrid Cross

(f) Gene and Allele

(g) Incomplete Dominance and Codominance

Given / Concept: Gene expression is the process by which the information encoded in a gene is used to synthesize a functional gene product (usually a protein).

Importance of Gene Expression:

1. It converts the genetic information stored in DNA into functional proteins that carry out all biological activities of a cell.
2. It regulates growth, development, differentiation, and metabolism of an organism.
3. It allows cells to respond to environmental changes by switching genes on or off.
4. It determines the phenotype of an organism.
5. It is essential for maintaining cellular homeostasis.

Steps Involved in Gene Expression:

Step 1 — Transcription:

• The DNA double helix unwinds at the gene locus.
• RNA polymerase binds to the promoter region and reads the template (antisense) strand in the $3' \rightarrow 5'$ direction.
• A complementary mRNA strand is synthesized in the $5' \rightarrow 3'$ direction.
• In eukaryotes, the primary transcript (pre-mRNA) undergoes post-transcriptional modifications: addition of 5' cap, 3' poly-A tail, and splicing out of introns to produce mature mRNA.

Step 2 — Translation:

• The mature mRNA moves to the ribosome.
• The ribosome reads the mRNA codons (triplets of bases) in the $5' \rightarrow 3'$ direction.
• tRNA molecules carry specific amino acids; their anticodons pair with the mRNA codons.
• Peptide bonds form between successive amino acids, elongating the polypeptide chain.
• Translation ends at a stop codon (UAA, UAG, or UGA).
• The polypeptide is released and folds into a functional protein (sometimes requiring post-translational modifications).

Summary equation:
$$\text{DNA} \xrightarrow{\text{Transcription}} \text{mRNA} \xrightarrow{\text{Translation}} \text{Protein}$$

Final Answer: Gene expression is vital for converting genetic information into functional proteins. It involves two main steps: transcription (DNA → mRNA) and translation (mRNA → Protein).

Given: A set of fundamental genetic terms to be defined.

Definitions:

(i) Dominant:
A dominant allele is one that expresses its effect (trait) in the phenotype even when only one copy is present (i.e., in heterozygous condition). It masks the effect of the recessive allele. It is conventionally represented by a capital letter (e.g., $A$).

(ii) Recessive:
A recessive allele is one whose effect is masked by the dominant allele when both are present together. It expresses itself only when present in homozygous condition (i.e., two copies of the recessive allele are present). It is represented by a lowercase letter (e.g., $a$).

(iii) Homozygous:
An organism is said to be homozygous for a particular gene locus when it carries two identical alleles at that locus on homologous chromosomes. It can be homozygous dominant ($AA$) or homozygous recessive ($aa$). Homozygous organisms breed true for that trait.

(iv) Heterozygous:
An organism is said to be heterozygous for a particular gene locus when it carries two different alleles at that locus on homologous chromosomes (e.g., $Aa$). The dominant allele is expressed in the phenotype, while the recessive allele remains hidden. Such organisms are also called carriers.

(v) Phenotype:
Phenotype refers to the observable physical, biochemical, or physiological characteristics of an organism that result from the interaction of its genotype with the environment. Examples include height, eye colour, blood group, and skin colour. Two organisms with different genotypes may have the same phenotype (e.g., $AA$ and $Aa$ both show the dominant phenotype).

(vi) Genotype:
Genotype refers to the complete genetic constitution (allelic composition) of an organism for a particular trait or for all traits. It represents the actual set of alleles present in the organism's genome. For example, for a gene with alleles $A$ and $a$, possible genotypes are $AA$, $Aa$, or $aa$. The genotype determines the potential phenotype of the organism.

Given: A question about the two modalities of analysis that follow sequencing.

Answer:

The two modalities of analysis following sequencing are:

1. De novo assembly – In this approach, the sequenced reads are assembled without the use of a reference genome. It is used when no reference genome is available for the organism under study.

2. Reference-guided (Genome-guided) assembly/mapping – In this approach, the sequenced reads are aligned or mapped to an already available reference genome. It is used when a well-annotated reference genome exists for the organism.

Given/Concept: Information technology (IT) provides computational tools and databases that allow scientists to analyse protein sequences and structures without performing every experiment in the laboratory.

Answer:

Information technology plays a crucial role in the determination of protein properties in the following ways:

1. Sequence Analysis: IT tools allow rapid analysis of amino acid sequences to determine physicochemical properties such as molecular weight, isoelectric point (pI), instability index, aliphatic index, and GRAVY (Grand Average of Hydropathy) value. Servers like ProtParam (ExPASy) perform these calculations automatically from raw sequence data.

2. Secondary Structure Prediction: Tools such as APSSP, CPSSP, SOPMA, and GOR predict the secondary structural elements (α-helices, β-sheets, coils) of a protein from its primary sequence.

3. Domain and Motif Prediction: IT-based tools (e.g., PROSITE, Pfam, InterPro) identify functional domains and conserved motifs within a protein sequence.

4. 3D Structure Prediction: Computational methods like homology modelling, fold prediction, and de novo prediction use IT to build three-dimensional models of proteins whose structures have not been experimentally determined.

5. Database Management: Large biological databases (UniProt, PDB, NCBI) store and organise vast amounts of protein data, making it accessible for analysis worldwide.

Conclusion: Thus, information technology accelerates protein characterisation, reduces experimental cost and time, and enables large-scale proteomics studies.

Given / Context: Modern biology generates enormous volumes of data (genomic sequences, proteomics data, metabolic networks, etc.) that cannot be handled manually.

Answer:

Programming languages are considered a boon for biologists for the following reasons:

1. Handling large datasets: Biological experiments (e.g., genome sequencing, microarray analysis) produce massive datasets. Programming languages such as Python, R, and Perl allow biologists to store, retrieve, and process these datasets efficiently.

2. Statistical analysis: Programming languages provide built-in and third-party statistical libraries (e.g., NumPy, SciPy in Python; statistical packages in R) that help biologists perform complex statistical analyses without requiring deep mathematical expertise.

3. Automation: Repetitive tasks such as sequence alignment, BLAST searches, and data formatting can be automated using scripts, saving enormous time and reducing human error.

4. Visualisation: Libraries like Matplotlib (Python) and ggplot2 (R) allow biologists to create publication-quality graphs and visual representations of biological data.

5. Bioinformatics tools: Most bioinformatics applications (e.g., BLAST, ClustalW, genome browsers) are built on programming platforms, and knowledge of programming helps biologists customise and extend these tools.

6. Modelling and simulation: Programming languages enable the construction of computational models of metabolic pathways, signalling networks, and gene regulatory networks, which is central to systems biology.

Conclusion: Thus, programming languages bridge the gap between raw biological data and meaningful biological insight, making them indispensable tools for modern biologists.

Correct Option: (b) visualise the DNA molecules

Justification: Ethidium bromide (EtBr) is a fluorescent intercalating dye that inserts itself between the stacked base pairs of DNA. When exposed to UV light, it fluoresces bright orange, making the DNA bands visible on the agarose gel. It does not separate DNA, provide charge, or track electrophoresis progression (that is done by tracking dyes like bromophenol blue).