Practical Botany: Laboratory Techniques, Experiments, Field Study and Record Work
Practical questions test procedure order and reagent purpose, plus one small calculation from quadrat or transpiration data. Knowing exactly what each stain and each apparatus actually measures is what separates full marks from partial marks.
Core rules
- Microscope: total magnification = eyepiece × objective; focus on low power first; mount in water or glycerine.
- Staining: safranin stains lignified walls red; fast green is the counterstain; acetocarmine is used for chromosomes; iodine detects starch.
- Onion root-tip mitosis: grow roots, fix in Carnoy's fixative, hydrolyse in 1 N HCl, stain with acetocarmine, squash and score stages.
- Osmosis: potato osmoscope - a rise of level in the cavity or a gain in weight shows endosmosis.
- Transpiration: Ganong's potometer measures water uptake, not transpiration itself; cobalt chloride paper turns pink on absorbing water.
- Photosynthesis: variegated-leaf starch test - only the green areas turn blue-black with iodine.
- Respiration: germinating seeds release CO₂, turning lime water milky.
- Quadrat sampling (species in 8 of 20 quadrats, 1 m² each, 40 individuals): frequency = 8/20 × 100 = 40%; density = 40/20 = 2 plants per m²; abundance = 40/8 = 5 plants per occupied quadrat.
- Herbarium sheet standard size is 29 × 41 cm, with a label giving locality, date, collector and determination.
Worked example
A quadrat survey records species A in 8 of 20 quadrats of 1 m², with 40 individuals in those quadrats. Frequency = 8/20 × 100 = 40%. Density = total individuals ÷ total area = 40/20 = 2 plants m⁻². Abundance = total individuals ÷ number of occupied quadrats = 40/8 = 5 plants per occupied quadrat. Note that abundance uses occupied quadrats only.
Traps that cost marks
Reporting potometer readings as transpiration instead of water uptake; using fast green as the primary stain for lignified tissue; calculating abundance over all quadrats rather than occupied ones; confusing frequency with density.