WBBSE Madhyamik Life Science (English Adaptation) cheat sheet

Tropisms are slow, directional growth responses to a one-sided stimulus; nasties (e.g. Mimosa leaf folding) are rapid, non-directional movements independent of stimulus direction.

Auxin (IAA) produced at the shoot apex moves basally; it promotes cell elongation in shoots but inhibits elongation in roots, so the same hormone bends shoot up and root down in response to gravity.

Phototropism: unilateral light drives lateral auxin shift to the shaded side, causing greater elongation there and curvature toward light; roots are negatively phototropic.

Geotropism: statoliths (amyloplasts) settle in root cap columella cells, redirecting auxin to the lower side; root curvature is downward because root cells are auxin-sensitive.

Reflex action path: receptor → sensory neuron → spinal cord (relay neuron) → motor neuron → effector muscle/gland; the reflex arc bypasses conscious brain control for speed.

Synapse transmission is chemical: an impulse arriving at the axon terminal releases neurotransmitter into the synaptic cleft, which depolarises the next neuron's dendrite; transmission is one-way.

Human brain divisions: cerebrum (thought, memory, voluntary movement), cerebellum (balance, posture, coordination of muscle activity), medulla oblongata (respiration, heart rate, blood pressure).

Endocrine vs nervous control: hormones travel in blood, act slowly and last longer; nerve impulses travel along neurons, act fast and are short-lived.

Thyroxine from the thyroid regulates basal metabolic rate and growth; insulin from pancreatic beta cells lowers blood glucose, glucagon from alpha cells raises it.

Mitosis: one parent cell yields two genetically identical diploid daughter cells; occurs in somatic cells for growth, repair and asexual reproduction; chromosome number conserved (2n → 2n).

Meiosis: two successive divisions from one diploid cell yield four haploid cells that are genetically different due to crossing over and independent assortment; basis of gamete formation.

Prophase: chromosomes condense, nuclear membrane breaks down, spindle forms; metaphase: chromosomes align at the equator; anaphase: chromatids separate to poles; telophase: nuclei reform.

DNA replication occurs in S phase of interphase, before mitosis begins; cytokinesis in animal cells uses a cleavage furrow, in plant cells a cell plate.

Crossing over occurs in prophase I between non-sister chromatids of homologous chromosomes at chiasmata; it produces new allele combinations.

Asexual reproduction (binary fission, budding, fragmentation, vegetative propagation) gives genetically uniform offspring; sexual reproduction generates variation through gamete fusion.

Mendel's law of segregation: two alleles of a gene separate during gamete formation so each gamete carries only one allele.

Monohybrid cross Tt × Tt gives phenotypic ratio 3:1 and genotypic ratio 1:2:1; test cross with recessive parent distinguishes homozygous dominant from heterozygous.

Human sex determination: female XX, male XY; the father's gamete (X or Y) determines the child's sex, giving a 1:1 ratio.

Autosomal dominant trait appears in every generation and affects both sexes equally; autosomal recessive may skip generations and appears when both parents are carriers.

Thalassaemia is an autosomal recessive disorder of haemoglobin chain synthesis; carriers are usually symptom-free but can pass the allele on.

Haemophilia A is X-linked recessive: males (XY) express it with one allele, females need two; affected fathers pass the allele to all daughters, none to sons.

Colour blindness is X-linked recessive; carrier mothers transmit it to about half their sons; affected females are rare.

Sickle cell anaemia results from a point mutation (glutamic acid replaced by valine at position 6 of beta-globin), causing HbS and distorted red cells under low oxygen.

Down syndrome (trisomy 21) arises from non-disjunction during meiosis, giving 47 chromosomes; risk rises with maternal age.

Pedigree rules: an affected child from unaffected parents indicates recessive inheritance; an affected father with an unaffected daughter rules out X-linked dominant.

Punnett square method: write parental gametes along both axes, fill the four boxes with combined alleles, then count genotype and phenotype frequencies.

Karyotype analysis detects numerical and large structural chromosome abnormalities; it cannot detect single-gene point mutations.

Adaptation categories: morphological (shape, size), physiological (osmoregulation, temperature tolerance), behavioural (migration, hibernation); all are heritable and improve survival.

Xerophytic adaptations: thick cuticle, sunken stomata, reduced leaves/spines, succulent water-storage tissue, deep or widespread roots.

Hydrophytic adaptations: air spaces (aerenchyma) for buoyancy and gas diffusion, poorly developed cuticle, stomata on upper leaf surface.

Analogous organs (bird wing vs insect wing) share function but differ in origin; homologous organs (forelimbs of human, whale, bat) share basic structure and origin.

Darwin's natural selection: heritable variation exists, more offspring are produced than survive, favourable variants reproduce more, and allele frequencies shift over generations.

Evidence for evolution: fossils in rock strata, homologous structures, vestigial organs (human appendix, vermiform), embryological similarities, molecular (DNA/protein) comparisons.

Biodiversity levels: genetic, species and ecosystem diversity; hotspots are regions of high endemism and high habitat loss.

Binomial nomenclature: genus name capitalised, species name lower case, both italicised or underlined; e.g. Homo sapiens.

Five-kingdom classification: Monera, Protista, Fungi, Plantae, Animalia; viruses are excluded as they are acellular obligate parasites.

Food chain transfer: producers → primary consumers → secondary consumers; energy decreases about 90% at each step (10% law), so chains rarely exceed 4-5 trophic levels.

Ecological pyramid of energy is always upright; pyramid of numbers can be inverted (e.g. many insects on one tree).

Carbon cycle: photosynthesis fixes CO2, respiration and combustion release it; deforestation and fossil fuel burning raise atmospheric CO2.

Nitrogen cycle steps: nitrogen fixation (Rhizobium, Azotobacter), nitrification (Nitrosomonas, Nitrobacter), assimilation, ammonification, denitrification.

Greenhouse gases: CO2, methane, nitrous oxide, CFCs, water vapour; they absorb outgoing infrared radiation and warm the lower atmosphere.

Ozone depletion by CFCs releasing chlorine radicals in the stratosphere reduces UV absorption, raising skin cancer and cataract risk.

In-situ conservation: national parks, sanctuaries, biosphere reserves; ex-situ: zoos, botanical gardens, seed and gene banks.

Renewable resources (solar, wind, biogas, hydel) replenish naturally; non-renewable (coal, petroleum, minerals) are finite and cause pollution on burning.

Biomagnification: non-degradable pollutants such as DDT and mercury increase in concentration at each higher trophic level.

Photosynthesis overall: 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O in the presence of chlorophyll and light; light reactions in thylakoids, Calvin cycle in stroma.

Light reaction products: ATP and NADPH, plus oxygen from photolysis of water; photosystems I and II absorb mainly red and blue light.

Essential macronutrients for plants: N, P, K, Ca, Mg, S; micronutrients include Fe, Mn, Zn, Cu, B, Mo.

Nitrogen deficiency causes chlorosis and stunted growth; magnesium deficiency causes chlorosis because Mg is central to chlorophyll.

Insectivorous plants (Nepenthes, Drosera) trap insects mainly to obtain nitrogen in nitrogen-poor soils; they still photosynthesise.

Human digestion sequence: mouth (salivary amylase, starch → maltose) → stomach (pepsin, protein) → duodenum (bile emulsifies fat, pancreatic amylase, trypsin, lipase) → ileum (absorption via villi) → colon (water absorption).

Bile is produced by the liver, stored in the gall bladder, and contains no enzymes; it neutralises acidic chyme and emulsifies fats.

Villi adaptations: large surface area, thin epithelium, dense capillary network and lacteals for fat absorption.

Dental formula of an adult human: 2/2 incisors, 1/1 canines, 2/2 premolars, 3/3 molars per side, total 32 teeth.

Aerobic respiration: C6H12O6 + 6O2 → 6CO2 + 6H2O + 38 ATP (about 686 kcal released); glycolysis in cytoplasm, Krebs cycle in mitochondria.

Anaerobic respiration in muscle: glucose → lactic acid + 2 ATP; in yeast: glucose → ethanol + CO2 + 2 ATP.

Stomata open when guard cells become turgid (K+ influx, water entry); CO2 enters and O2 leaves through stomata; lenticels serve woody stems.

Human breathing mechanics: diaphragm contracts and flattens, external intercostals lift ribs, thoracic volume rises, pressure falls, air enters.

Blood composition: plasma, RBCs (haemoglobin, oxygen transport), WBCs (immunity), platelets (clotting); RBCs lack a nucleus in mammals.

Double circulation: pulmonary circuit (right ventricle → lungs → left atrium) and systemic circuit (left ventricle → body → right atrium); prevents mixing and maintains pressure.

Arteries carry blood away from the heart, thick muscular walls, no valves; veins carry blood to the heart, thin walls, valves prevent backflow.

Cardiac cycle: SA node initiates the impulse (pacemaker), causing atrial systole, then ventricular systole; normal rate about 72 beats per minute.

Transpiration pull and root pressure drive water up the xylem; translocation of food occurs through phloem in both directions.

Nephron sequence: glomerular filtration in Bowman's capsule → selective reabsorption in proximal tubule → concentration in loop of Henle → secretion in distal tubule → urine via collecting duct.

Glucose and amino acids are fully reabsorbed in the proximal tubule; their appearance in urine indicates diabetes mellitus or kidney damage.

ADH from the posterior pituitary increases collecting-duct water permeability; low water intake means more ADH and concentrated urine.

Homeostasis definition: maintenance of a stable internal environment (temperature, pH, glucose, water, ions) despite external change, using negative feedback.

Human normal body temperature is about 37 °C; sweating and vasodilation cool the body, shivering and vasoconstriction conserve heat.

Liver functions: glycogen storage, urea formation from excess amino acids (deamination), detoxification, bile production, plasma protein synthesis.

Skin excretes water, salts and traces of urea via sweat; lungs excrete CO2 and water vapour; kidneys are the main excretory organs.

Dialysis removes urea and excess salts by diffusion across a semipermeable membrane when kidneys fail.

Human skeleton functions: support, protection of organs, muscle attachment, mineral storage, blood cell formation in bone marrow.

Number of bones in an adult human is 206; the vertebral column has 33 vertebrae in the child, fused to 26 in the adult.

Types of joints: ball and socket (shoulder, hip), hinge (elbow, knee), pivot (atlas-axis), gliding (carpals), immovable sutures (skull).

Sliding filament theory: actin filaments slide over myosin, sarcomere shortens; myosin heads bind actin, pivot using ATP, then detach.

Muscle contraction requires ATP, calcium ions and acetylcholine released at the neuromuscular junction.

Antagonistic muscle pairs: biceps flexes the forearm while triceps extends it; one contracts as the other relaxes.

Bone composition: about one-third organic matter (collagen, ossein) and two-thirds inorganic salts (calcium phosphate) giving strength and flexibility.

Locomotion in lower organisms: Amoeba by pseudopodia, Paramecium by cilia, earthworm by setae and circular-longitudinal muscle waves, fish by myotomes and fins.

Disorders: arthritis is joint inflammation, osteoporosis is loss of bone density, scoliosis is lateral curvature of the spine.

Biological drawings must use a sharp pencil, single continuous lines, no shading, correct proportions, and a title plus labels with straight horizontal leader lines.

Magnification = size of drawing ÷ actual size of object; convert both to the same unit before dividing.

Controls in an experiment are the parts kept unchanged; only the independent variable is altered, and the dependent variable is measured.

Test for starch: iodine solution turns blue-black; for glucose: Benedict's solution turns brick-red on heating; for protein: Biuret turns violet; for CO2: lime water turns milky.

Destarching a leaf before a photosynthesis experiment requires keeping the plant in the dark for 24-48 hours.

To test that light is needed, cover part of a destarched leaf with black paper, expose to sunlight, then boil in alcohol and add iodine; only the exposed region turns blue-black.

Observation vs inference: an observation is what is directly sensed or measured, an inference is a conclusion drawn from it.

Reading a graph: identify axes and units, state the trend, note plateaus or peaks, and quote numerical values to support the description.

Tables of data: independent variable in the first column, dependent variable in the second, units in the column heading, replicates averaged.