BIOL1030 Chap.5 Plant Growth, Meristems and Plasticity
Plant Growth, Meristems and Plasticity
Plant Growth, Meristems and Plasticity follows Lecture 3 of Unit 6, on how plants keep remodelling themselves. Plants grow indeterminately from meristems: apical meristems drive primary growth in length, producing roots, stems and leaves, while the vascular cambium and cork cambium drive secondary growth in width, producing wood and bark.
The chapter follows the root tip through protoderm, ground meristem and procambium, explains how lateral roots arise from the pericycle, contrasts eudicot and monocot anatomy, and shows how tree rings record growing conditions. It closes on phenotypic plasticity: phenotype depends on genotype, environment and their interaction, as sun and shade leaves on the same species demonstrate.
What this chapter covers
- 01
Indeterminate growth and apical meristems
- 02
Protoderm, ground meristem and procambium in the root
- 03
Lateral roots from the pericycle and nutrient patches
- 04
Eudicot and monocot roots, stems and intercalary meristems
- 05
Primary versus secondary growth, cambia, wood and rings
- 06
Genotype, environment and phenotypic plasticity
Worked example · free
Classify three genotype by environment experiments
- 1Experiment 1: both genotypes rise by 60 in the same way, so the trait is plastic but shows no genotypic variation.
- 1Experiment 2: each genotype keeps one value in both environments, so genotypes differ but neither is plastic.
- 1Experiment 3: genotype 1 rises by 60 while genotype 2 falls by 40, so the lines cross: a genotype by environment interaction.
Key terms
- Apical meristem
- A zone of dividing cells at a root or shoot tip that adds length through primary growth.
- Vascular cambium
- A lateral meristem that adds secondary xylem and phloem, thickening stems and roots.
- Pericycle
- The outermost layer of the root vascular cylinder, which keeps dividing and gives rise to lateral roots.
- Phenotypic plasticity
- The range of phenotypes one genotype can express across different environments.
Plant Growth, Meristems and Plasticity FAQ
What is the difference between primary and secondary growth?
Primary growth comes from apical meristems and makes roots, stems and leaves longer; every vascular plant has it. Secondary growth comes from the vascular cambium and cork cambium, adds wood and bark and makes organs wider, stronger and longer-lived, and it is characteristic of woody plants.
Where do lateral roots come from?
They start deep inside the root, in the pericycle at the edge of the vascular cylinder. Environmental and hormonal signals reactivate cell division there, a primordium forms and pushes out through the cortex, which is why lateral roots multiply where soil patches are rich in nutrients.
Why can grass be mowed without killing it?
Grasses are monocots, which often keep meristems at the base of leaves and intercalary meristems at nodes. Cutting removes leaf tips but leaves those growing zones in place, so growth resumes after grazing or mowing. The same arrangement lets pasture grasses recover quickly after animals graze them down.
Why can grasses keep growing after they are mown or grazed?
Many monocots, grasses included, keep meristems at the base of their leaves and intercalary meristems at nodes. Cutting or grazing removes the tips but leaves those dividing zones intact, so the leaves regrow from below, unlike a eudicot shoot whose growing apex sits at the very tip of the stem.
Exam move
Draw two timelines side by side: a herbaceous annual that grows mostly by primary growth and a long-lived tree that adds secondary growth every year, and label which meristem acts at each stage. Practise tracing the three primary meristems into the tissues they form, then compare eudicot and monocot roots and stems from memory.
For plasticity, invent pairs of genotypes and environments, sketch their reaction lines and name the pattern, because exam questions often give results as a small table rather than a graph. Keep the tree-ring idea ready too: wider rings usually mean a favourable year, not a better genotype.
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