Cell Biology and Biotechnology — Maharashtra (SSC) Class 10 Science Solutions (Free)

Cell membrane (plasma membrane): Structure - (1) Fluid mosaic model: phospholipid bilayer with embedded proteins. (2) Selective permeability: hydrophilic heads face outward, hydrophobic tails face inward. (3) Proteins serve as channels, receptors, and enzymes. (4) Cholesterol maintains fluidity. (5) Carbohydrates form glycoproteins and glycolipids. Functions - (1) Controls substance entry and exit. (2) Protects cell contents. (3) Cell recognition and signaling. (4) Maintains osmotic balance.

Prokaryotic cells (bacteria): (1) No membrane-bound nucleus. (2) No mitochondria or endoplasmic reticulum. (3) Single circular DNA in nucleoid region. (4) Cell wall present (peptidoglycan in bacteria). (5) Smaller - 1-5 micrometers. (6) Reproduce by binary fission. Eukaryotic cells (animals, plants, fungi): (1) Membrane-bound nucleus containing DNA. (2) Mitochondria, endoplasmic reticulum, Golgi apparatus. (3) Linear DNA organized into chromosomes. (4) Cell wall in plants (cellulose) and fungi (chitin). (5) Larger - 10-100 micrometers. (6) Reproduce by mitosis or meiosis.

Mitochondria functions: (1) Powerhouse of the cell - produces ATP through cellular respiration. (2) Process: Glucose oxidation releases energy captured in ATP bonds. (3) Inner membrane has cristae increasing surface area for enzyme activity. (4) Matrix contains enzymes for Krebs cycle. (5) Electron transport chain on inner membrane produces 30-32 ATP per glucose. (6) Regulate calcium levels in cytoplasm. (7) Initiate apoptosis (programmed cell death) when necessary. (8) Have own DNA (mitochondrial DNA) inherited maternally.

Genetic engineering - modification of organism's DNA to introduce desired traits: Process - (1) Isolate gene of interest from source organism. (2) Use restriction enzymes to cut target DNA. (3) Insert gene into plasmid or viral vector. (4) Introduce into host cell. (5) Incorporate into genome. Applications - (1) Insulin production: Human insulin gene inserted into E. coli bacteria, producing pharmaceutical insulin at scale. (2) Disease-resistant crops: Bt cotton with insecticidal protein kills pests, reducing pesticide use. (3) Golden Rice: Vitamin A gene inserted to prevent blindness. (4) Gene therapy: Correcting genetic disorders by replacing faulty genes.

Protein synthesis occurs in two stages: Transcription - (1) Occurs in nucleus. (2) RNA polymerase unwinds DNA double helix. (3) mRNA synthesized complementary to DNA template strand. (4) mRNA leaves nucleus through nuclear pores. Translation - (1) Occurs on ribosomes in cytoplasm. (2) mRNA codons read by tRNA anticodons. (3) Each codon specifies an amino acid. (4) Amino acids bond forming polypeptide chain. (5) Stop codon signals termination. (6) Protein released and folds into functional shape. (7) tRNA recycled for reuse.

Agricultural biotechnology benefits: (1) Crop improvement - increasing yield, nutritional content, drought tolerance. (2) Pest resistance - inserting Bt gene for insecticidal proteins, reducing pesticide use. (3) Disease resistance - developing crops resistant to fungal and bacterial pathogens. (4) Herbicide tolerance - Roundup Ready crops allow easier weed control. (5) Enhanced nutrition - Golden Rice, biofortified crops with increased vitamins. (6) Stress tolerance - plants withstanding salinity, waterlogging, extreme temperatures. (7) Faster breeding - marker-assisted selection accelerates desirable trait development. (8) Reduced environmental impact through lower chemical inputs.

Cloning - creation of genetically identical organism: Process - (1) Remove nucleus from somatic cell (donor). (2) Remove nucleus from egg cell. (3) Insert somatic nucleus into enucleated egg. (4) Stimulate cell division via electrical or chemical shock. (5) Implant into surrogate mother. (6) Gestation produces genetically identical offspring. Ethical implications - (1) Benefits: Creating organs for transplant (xenotransplantation), preserving endangered species. (2) Concerns: Human cloning violates human dignity and genetic diversity. (3) Psychological harm to clone from identity confusion. (4) Unknown long-term health effects. (5) Unequal access creates social inequality. (6) Religious and moral objections in many cultures. (7) Legal bans on human reproductive cloning in most countries.