Crop Biology: Classification, Structure and Function
What you must understand
Crop biology supplies the vocabulary for every later topic. Know the difference between monocotyledons (one seed leaf, parallel veins, fibrous roots, scattered vascular bundles, e.g. maize, sorghum, millet) and dicotyledons (two seed leaves, net veins, taproot, ringed vascular bundles, e.g. beans, groundnuts, sunflower). Be able to label a plant: root, stem, node, internode, leaf blade, petiole, flower parts, and the parts of a seed (testa, cotyledon, endosperm, radicle, plumule).
Understand the processes: photosynthesis (light + carbon dioxide + water → sugar + oxygen, in chloroplasts), respiration (sugar + oxygen → energy + carbon dioxide + water), transpiration (water loss through stomata, pulling water up the xylem), and translocation (sugars moved in the phloem). Know that legumes fix nitrogen through Rhizobium in root nodules, and that C4 crops such as maize and sorghum photosynthesise efficiently in heat.
Traps in questions
- Xylem carries water and minerals up; phloem carries sugars both ways. Reversing these is the commonest error.
- Monocots have scattered bundles, not a ring.
- Respiration happens all day and night; photosynthesis only in light.
- A taproot is a dicot feature; fibrous roots are monocot.
- Epigeal germination (bean) lifts cotyledons above soil; hypogeal (maize, groundnut) keeps them below.
Rule of thumb
If a plant has parallel veins, fibrous roots and one seed leaf, treat it as a monocot and expect a grass-type cereal or pasture.
Worked example
A question asks why maize leaves wilt at midday even when soil is moist. Reasoning: high temperature and light open stomata, transpiration exceeds uptake, so cells lose turgor. Answer: transpiration pull outruns water absorption, not a soil-moisture shortage.