RBSE SS Agricultural Biology cheat sheet

Photosynthesis summary equation: 6CO2 + 12H2O + light energy → C6H12O6 + 6O2 + 6H2O; light reactions occur in thylakoid membranes, Calvin cycle in the stroma.

Photosystem II splits water (photolysis) and releases O2; electrons flow PSII → plastoquinone → cytochrome b6f → plastocyanin → PSI → ferredoxin → NADP+ reductase.

Calvin cycle has three phases: carboxylation (RuBP + CO2 via RuBisCO), reduction (PGA to PGAL using ATP and NADPH), and regeneration of RuBP; 3 ATP and 2 NADPH are consumed per CO2 fixed.

C3 plants fix CO2 into 3-phosphoglycerate; C4 plants use PEP carboxylase in mesophyll and RuBisCO in bundle-sheath cells; CAM plants fix CO2 at night and decarboxylate by day.

Photorespiration occurs when RuBisCO binds O2 instead of CO2; it consumes ATP and releases CO2 without net sugar gain and is favoured by high temperature and high O2:CO2 ratio.

Respiration: glycolysis (cytoplasm, net 2 ATP + 2 NADH), Krebs cycle (mitochondrial matrix, 2 ATP + 6 NADH + 2 FADH2 per glucose), and oxidative phosphorylation (inner membrane, ~26–28 ATP).

Water potential Ψw = Ψs (solute potential, always negative) + Ψp (pressure potential); water moves from higher to lower Ψw, and turgor pressure arises when Ψp is positive.

Plant hormones: auxin (cell elongation, apical dominance, rooting), gibberellin (stem elongation, seed germination), cytokinin (cell division, delays senescence), ABA (stomatal closure, stress, dormancy), ethylene (ripening, abscission).

Stomatal opening is driven by K+ influx into guard cells, lowering Ψs and raising turgor; ABA triggers K+ efflux and closure; transpiration pull drives xylem sap up under cohesion-tension.

Mendel's laws: segregation (alleles separate in meiosis) and independent assortment (genes on different chromosomes assort independently); monohybrid F2 ratio 3:1, dihybrid F2 ratio 9:3:3:1.

Test cross (cross to homozygous recessive) distinguishes homozygous dominant from heterozygous individuals; backcross is a cross to one of the parents.

Incomplete dominance gives an intermediate phenotype (1:2:1 in F2); codominance expresses both alleles; multiple alleles and epistasis modify standard ratios.

Linkage reduces recombination frequency; recombination frequency (%) = (number of recombinant progeny / total progeny) × 100, and 1% recombination = 1 map unit (centimorgan).

Gene interaction ratios: complementary genes 9:7, duplicate genes 15:1, inhibitory genes 13:3, dominant epistasis 12:3:1, recessive epistasis 9:3:4.

Breeding methods: pureline/selection, hybridization (pedigree, bulk, backcross), heterosis breeding, mutation breeding, and marker-assisted selection using DNA markers linked to traits.

Heritability (broad sense) = VG / VP × 100, where VG = VA + VD + VI; genetic advance depends on selection intensity, heritability, and phenotypic variability.

Cytoplasmic male sterility (CMS) uses sterile cytoplasm (S) with rf rf nuclear genotype; restorer lines carry RfRf and restore fertility in F1 hybrid seed production.

Polyploidy: autopolyploidy arises from chromosome doubling within a species; allopolyploidy follows hybridization plus doubling; haploids have gametic chromosome number (n) and are made diploid by colchicine.

Cropping intensity = (total cropped area / net sown area) × 100; multiple cropping raises this above 100% by growing two or more crops per year on the same land.

Intercropping grows two or more crops simultaneously in distinct rows; mixed cropping lacks a definite row arrangement; sequence cropping follows one crop after another.

Seed rate and plant population: plant population = area / (row spacing × plant spacing); optimum plant density balances intra- and inter-specific competition.

Crop rotation with legumes fixes atmospheric N2 via Rhizobium symbiosis and interrupts pest and disease cycles specific to one crop family.

Irrigation scheduling by critical growth stages: crown root initiation in wheat, flowering and boll formation in cotton, panicle initiation in rice, and flowering in pulses.

Integrated nutrient management combines organic manure, green manure, biofertilizers, and balanced mineral fertilizer, judged by the 4R rule: right source, right rate, right time, right place.

Weed control follows integrated weed management: cultural (crop rotation, stale seedbed), mechanical, biological, and chemical methods; herbicide selectivity depends on dose and crop stage.

Post-harvest losses are reduced by proper moisture at storage (typically around 12–14% for cereals), cleaning, drying, and controlled storage to prevent insect and fungal damage.

Soil texture refers to relative proportions of sand, silt, and clay; soil structure refers to their arrangement into aggregates; loam is a balanced mixture favoured for crops.

Bulk density = oven-dry soil mass / total volume (g/cm³); particle density is about 2.65 g/cm³; porosity = (1 − bulk density / particle density) × 100.

Soil pH affects nutrient availability; most crops grow best in pH 6.0–7.5, and lime raises pH on acid soils while gypsum or elemental sulfur lowers pH on alkaline soils.

Cation exchange capacity (CEC) is the total exchangeable cations a soil can hold, expressed in cmol(+)/kg; clay and organic matter raise CEC; base saturation = (exchangeable bases / CEC) × 100.

Essential macronutrients: N, P, K, Ca, Mg, S; micronutrients: Fe, Mn, Zn, Cu, B, Mo, Cl, Ni; a deficiency is confirmed by soil and plant tissue testing.

Nitrogen cycle steps: fixation, ammonification, nitrification (NH4+ → NO2− → NO3−), immobilization, denitrification, and volatilization of ammonia.

Fertilizer grade N-P2O5-K2O expresses nutrient content; to convert P2O5 to P multiply by 0.44, and K2O to K multiply by 0.83; urea (46-0-0) is the commonest N source.

Soil erosion by water follows the universal soil loss equation factors: rainfall erosivity, soil erodibility, slope length and steepness, cover management, and support practice.

Insect mouthparts determine control: chewing insects (caterpillars, beetles) respond to stomach poisons; sucking insects (aphids, whiteflies, hoppers) require systemic or contact insecticides.

Insect development: complete metamorphosis is egg–larva–pupa–adult (holometabolous); incomplete metamorphosis is egg–nymph–adult (hemimetabolous); economic threshold guides spray decisions.

Integrated pest management hierarchy: monitoring and scouting, cultural control, mechanical and physical control, biological control, then judicious chemical control as last resort.

Key disease agents: fungi (powdery mildew, rust, blight), bacteria (wilt, blight, canker), viruses (mosaic, leaf curl, transmitted by vectors such as aphids and whiteflies), and nematodes (root-knot).

Disease triangle: a disease develops only when a susceptible host, a virulent pathogen, and favourable environment coincide; disease control targets one or more of these factors.

Koch's postulates establish pathogenicity: the organism must be consistently associated with disease, isolated in pure culture, reproduce disease when inoculated, and be re-isolated.

Pesticide formulation codes: EC (emulsifiable concentrate), WP (wettable powder), SC (suspension concentrate), G (granule); pre-harvest interval and label dose must be respected to limit residues.

Resistance management: rotate insecticide and fungicide modes of action, avoid repeated use of a single active ingredient, and combine chemical control with resistant varieties.

Farm cost concepts: fixed cost does not vary with output; variable cost changes with output; total cost = fixed + variable; gross margin = gross return − variable cost.

Net return (profit) = gross return − total cost; benefit-cost ratio = gross return / total cost; a ratio above 1 indicates a profitable enterprise.

Cost of cultivation per hectare = total expenses (inputs, labour, machinery, interest) divided by area; cost of production per unit = total cost / total output.

Demand and supply: price rises when demand exceeds supply and falls when supply exceeds demand; price elasticity of demand = percentage change in quantity demanded / percentage change in price.

Extension teaching methods: individual (farm visit, telephone), group (demonstration, field day, farmer field school), and mass (radio, television, print, digital media).

Diffusion of innovations: innovators, early adopters, early majority, late majority, laggards; adoption is faster when the innovation has relative advantage, compatibility, simplicity, trialability, and observability.

Technology assessment uses partial budget analysis: compare added returns and reduced costs against added costs and reduced returns to decide whether a change is worthwhile.

Agricultural credit and insurance reduce risk: crop insurance covers yield loss from weather or pests; credit repayment capacity depends on net farm income and cash flow timing.

Soil pH is measured with a pH meter in a 1:2.5 soil:water suspension; calibrate the meter with standard buffer solutions at pH 4.0, 7.0, and 9.2 before use.

Soil organic carbon is estimated by the Walkley–Black wet oxidation method; organic matter ≈ organic carbon × 1.724.

Seed germination test: germination % = (number of normal seedlings / total seeds sown) × 100; purity and moisture tests complete a seed quality analysis.

Plant height, leaf area, and dry matter are measured at defined growth stages; leaf area index (LAI) = total leaf area / ground area, and dry weight is recorded after oven drying at about 70 °C to constant weight.

Field layout for a replicated trial uses randomization and replication; a randomized complete block design controls field variation, and analysis of variance tests treatment differences.

Pest and disease scouting records incidence (percentage of plants affected) and severity (percentage of plant area affected); sweep-net and light traps sample insect populations.

Fertilizer recommendation calculation: nutrient required (kg/ha) = recommended dose; fertilizer needed = nutrient required / fraction of nutrient in fertilizer, e.g. urea for 60 kg N = 60 / 0.46 ≈ 130 kg/ha.

Water use efficiency = crop yield / water used (kg per mm or kg per m³); irrigation depth (mm) = irrigation water volume (m³) / area (m²) × 1000.