ICSE Class 10 Biology Essentials

Cheatsheet Content

1. Cell Cycle and Division Cell Cycle: Interphase ($G_1$, S, $G_2$) $\rightarrow$ Mitotic Phase (M). Mitosis: Growth, repair, asexual reproduction. Produces 2 diploid ($2n$) identical daughter cells. Stages: Prophase, Metaphase, Anaphase, Telophase. Meiosis: Reduction division (produces haploid cells, $n$). Sexual reproduction. Produces 4 haploid ($n$) genetically diverse daughter cells. Homologous Chromosomes: Pair of chromosomes (one maternal, one paternal) with similar genes. Crossing Over: Exchange of genetic material between homologous chromosomes during meiosis, leading to variation. Significance: Mitosis: Growth, repair, replacement of cells. Maintains chromosome number. Meiosis: Produces gametes, maintains chromosome number across generations, introduces variation. 2. Structure of Chromosome & Genetics Chromosome: Contains DNA. Made of: Chromatin: DNA + proteins (histones). Chromatid: One of two identical halves of a duplicated chromosome. Centromere: Constricted region joining chromatids. Gene: Segment of DNA that codes for a specific trait. Mendel's Laws: Law of Dominance: In a cross of parents differing in one trait, only one form (dominant) appears in $F_1$. Law of Segregation: Alleles for a trait separate during gamete formation. Law of Independent Assortment: Alleles for different traits assort independently. Terms: Gene: Unit of heredity. Allele: Alternative form of a gene. Homozygous: Two identical alleles (e.g., AA, aa). Heterozygous: Two different alleles (e.g., Aa). Dominant: Trait expressed in heterozygous state. Recessive: Trait masked in heterozygous state. Mutation: Sudden heritable change in genetic material. Variation: Differences among individuals of a species. Phenotype: Observable characteristics. Genotype: Genetic makeup. Monohybrid Cross: Cross involving one trait. $F_2$ Phenotypic Ratio: $3:1$ (e.g., Tall:Dwarf) $F_2$ Genotypic Ratio: $1:2:1$ (e.g., TT:Tt:tt) Dihybrid Cross: Cross involving two traits. $F_2$ Phenotypic Ratio: $9:3:3:1$ Sex Determination (Humans): XX (female), XY (male). Father determines sex. Sex-linked Inheritance (X-linked): Diseases like Haemophilia, Colour Blindness. More common in males as they have only one X chromosome. 3. Plant Physiology Absorption by Roots Processes: Imbibition, Diffusion, Osmosis, Active Transport, Passive Transport. Osmosis: Movement of water from higher water potential to lower water potential across semi-permeable membrane. Turgidity: Cell firm due to water intake. Flaccidity: Cell soft due to water loss. Plasmolysis: Cell membrane pulls away from cell wall due to water loss. Deplasmolysis: Reverse of plasmolysis. Forces for Ascent of Sap: Root pressure, Transpiration pull, Cohesion-adhesion forces. Transpiration Definition: Loss of water vapor from aerial parts of plants. Significance: Creates transpiration pull, cools plant, helps in mineral absorption. Factors Affecting Rate: Temperature, Humidity, Wind speed, Light intensity. Stomatal Mechanism (Potassium Ion Exchange Theory): Day: $K^+$ ions enter guard cells $\rightarrow$ water enters by osmosis $\rightarrow$ guard cells become turgid $\rightarrow$ stomata open. Night: $K^+$ ions leave guard cells $\rightarrow$ water leaves $\rightarrow$ guard cells become flaccid $\rightarrow$ stomata close. Guttation: Loss of water droplets from leaf margins (hydathodes) when transpiration is low and root pressure is high. Photosynthesis Definition: Process by which green plants convert light energy into chemical energy (glucose). Equation: $6CO_2 + 12H_2O \xrightarrow{\text{Light, Chlorophyll}} C_6H_{12}O_6 + 6H_2O + 6O_2$ Site: Chloroplasts (Thylakoids for light reaction, Stroma for dark reaction). Phases: Light Dependent (Photochemical): Occurs in thylakoids. Light energy $\rightarrow$ ATP, NADPH. Photolysis of water ($H_2O \rightarrow H^+, O_2, e^-$). Light Independent (Biosynthetic/Dark): Occurs in stroma. ATP and NADPH used to fix $CO_2$ into glucose (Calvin Cycle). Experiments: Necessity of light, $CO_2$, chlorophyll, starch formation, $O_2$ release. Destarching is crucial first step. Chemical Coordination in Plants Plant Hormones (Growth Regulators): Auxins: Cell elongation, apical dominance. Gibberellins: Stem elongation, seed germination, dormancy breaking. Cytokinins: Cell division, delay senescence. Abscisic Acid (ABA): Growth inhibitor, dormancy, stomatal closure. Ethylene: Fruit ripening. Tropic Movements (Directional growth in response to stimuli): Phototropism: Towards light (stems positive, roots negative). Geotropism: Towards gravity (roots positive, stems negative). Hydrotropism: Towards water (roots positive). Thigmotropism: Towards touch (tendrils coiling). Chemotropism: Towards chemicals (pollen tube growth towards ovule). 4. Human Anatomy and Physiology Circulatory System Blood Components: Plasma, RBCs (no nucleus/mitochondria for more $O_2$ transport), WBCs (immunity), Platelets (clotting). Heart: 4-chambered. Double circulation (pulmonary & systemic). Systole: Contraction. Diastole: Relaxation. Main vessels: Aorta, Vena Cava, Pulmonary Artery/Vein, Renal Artery/Vein, Hepatic Artery/Vein. Blood Vessels: Arteries: Thick, muscular, carry oxygenated blood away from heart (except pulmonary artery). Veins: Thin, less muscular, valves, carry deoxygenated blood to heart (except pulmonary vein). Capillaries: One-cell thick, site of exchange. Lymphatic System: Lymph, lymph vessels, lymph nodes, spleen, tonsils. Returns tissue fluid to blood, immunity. Blood Groups: ABO system (A, B, AB, O), Rh factor. Hepatic Portal System: Vein carries nutrient-rich blood from digestive organs to liver for processing. Excretory System Organs: Kidneys, Ureters, Urinary Bladder, Urethra. Skin, Lungs, Liver are also excretory. Kidney Structure: Cortex, Medulla, Pelvis. Nephron: Functional unit of kidney. Bowman's capsule, Glomerulus, PCT, Loop of Henle, DCT, Collecting Duct. Urine Formation: Ultrafiltration: In glomerulus/Bowman's capsule. Filters blood plasma (except proteins, blood cells). Selective Reabsorption: In tubules. Reabsorbs useful substances (glucose, amino acids, salts, water). Tubular Secretion: In tubules. Secretes waste products (urea, creatinine, $H^+$, $K^+$). Nervous System Neuron: Basic unit. Dendrites (receive), Cell Body (soma), Axon (transmit), Synapse. Brain: Cerebrum: Largest part, thought, memory, voluntary actions. Cerebellum: Balance, coordination, muscle tone. Medulla Oblongata: Involuntary actions (heartbeat, breathing, digestion). Thalamus, Hypothalamus, Pons. Spinal Cord: Connects brain to peripheral nerves, controls reflex actions. Reflex Action: Automatic, involuntary response to a stimulus. Pathway: Sensory neuron $\rightarrow$ Spinal cord $\rightarrow$ Motor neuron. Voluntary Action: Involves brain, conscious control. Eye: Cornea, Lens, Retina (rods/cones), Optic Nerve. Accommodation (focusing), Adaptation (light intensity). Defects: Myopia (nearsightedness, concave lens), Hyperopia (farsightedness, convex lens), Astigmatism, Cataract. Ear: Outer (pinna, ear canal), Middle (ossicles: malleus, incus, stapes), Inner (cochlea for hearing, semicircular canals for balance). Endocrine System (Hormones) Endocrine Glands: Ductless, secrete hormones directly into blood. Exocrine Glands: Have ducts (e.g., salivary glands). Glands & Hormones: Pancreas: Insulin (lowers blood glucose), Glucagon (raises blood glucose). Thyroid: Thyroxine (metabolism). Adrenal: Adrenaline (fight or flight), Cortical hormones. Pituitary (Master Gland): Growth Hormone, Tropic hormones (TSH, ACTH, FSH, LH), ADH (water reabsorption), Oxytocin (uterine contraction, milk ejection). Hypo/Hypersecretion: GH: Gigantism/Dwarfism. Thyroxine: Cretinism/Myxedema (hypo), Goitre/Exophthalmic goitre (hyper). Insulin: Diabetes Mellitus (hypo). Feedback Mechanism: Regulates hormone levels (e.g., TSH release from pituitary stimulates thyroid, high thyroxine inhibits TSH). Reproductive System Male Organs: Testes (sperm, testosterone), Vas deferens, Epididymis, Prostate, Seminal Vesicles. Female Organs: Ovaries (ova, estrogen, progesterone), Oviducts (fallopian tubes), Uterus, Vagina. Fertilization: Fusion of sperm and egg (in oviduct). Implantation: Embryo attaches to uterine wall. Placenta: Connects fetus to uterine wall. Functions: Nutrition, Respiration, Excretion for fetus. Endocrine (produces hormones). Gestation: Period of development in uterus. Parturition: Childbirth. Menstrual Cycle: Monthly cycle in females involving changes in uterus and ovary, preparing for pregnancy. Hormones: Estrogen, Progesterone. Foetal Membranes: Amnion (amniotic fluid for protection), Chorion. Twins: Identical (monozygotic - from one zygote), Fraternal (dizygotic - from two zygotes). 5. Population Terms: Demography: Study of population. Population Density: Number of individuals per unit area. Birth Rate (Natality): Number of live births per 1000 individuals per year. Death Rate (Mortality): Number of deaths per 1000 individuals per year. Growth Rate: (Birth Rate - Death Rate). Population Explosion Causes: Reduced death rate, increased birth rate due to better health, food. Problems: Unemployment, resource depletion, pollution, low per capita income. Control Measures: Education, family planning, surgical methods (Tubectomy, Vasectomy). 6. Human Evolution & Theories Human Ancestors (Brief): Australopithecus, Homo habilis, Homo erectus, Neanderthals, Cro-Magnon, Homo sapiens sapiens. Key changes: Bipedalism, increased cranial capacity, reduced canine teeth, forehead development, chin, reduced body hair, posture. Lamarck's Theory (Inheritance of Acquired Characteristics): Organisms develop traits during their lifetime by use/disuse of organs, and these traits are passed to offspring (e.g., giraffe neck). (Generally disproven). Darwin's Theory (Natural Selection): Survival of the Fittest: Individuals with advantageous traits for their environment are more likely to survive and reproduce. Adaptation: Traits that help an organism survive in its environment. Example: Peppered moth (melanic and light forms) adapting to industrial pollution. 7. Pollution Types & Sources: Air: Vehicular, industrial, burning garbage. Pollutants: $CO_2, CO, SO_2, NO_x$, Particulates. Water: Sewage, industrial waste, detergents, oil spills. Soil: Industrial, urban waste, chemical fertilizers, pesticides. Thermal: Increase in water temperature from power plants. Radiation: X-rays, nuclear waste. Noise: Vehicles, industry, loudspeakers. Biodegradable Waste: Decomposed by microbes (e.g., paper, vegetable peels). Non-biodegradable Waste: Not decomposed by microbes (e.g., plastics, glass, DDT). Effects & Control: Greenhouse Effect & Global Warming: Trapping of heat by greenhouse gases ($CO_2, CH_4$). Leads to climate change. Acid Rain: $SO_2, NO_x$ react with water to form acids. Damages buildings, forests, aquatic life. Ozone Layer Depletion: CFCs deplete ozone ($O_3$) layer, increasing UV radiation. Control Measures: Unleaded petrol, CNG, sewage treatment, ban on plastics, organic farming, social forestry.