Lesson 13 of 13 · 11 min
Chapter review
Watch a class
The whole chapter on YouTube
Loading the full lesson
Must-know facts
17 facts
- 01Growth: irreversible, permanent increase in size, needing energy. Development = growth + differentiation.
- 02Open form of growth: meristems keep adding cells throughout life.
- 03Primary growth: root and shoot apical meristems (length). Secondary growth: vascular cambium and cork cambium (girth), in dicots and gymnosperms.
- 04Parameters: fresh weight, dry weight, length, area, volume, cell number. Maize root apical meristem: over 17,500 new cells per hour; watermelon cells: up to 3,50,000 times larger.
- 05Three phases of growth: meristematic, elongation, maturation.
- 06Arithmetic growth: one daughter divides; Lt = L0 + rt; straight line.
- 07Geometric growth: both daughters divide; lag, log (exponential), stationary; sigmoid curve; W1 = W0 e^rt; r = relative growth rate = efficiency index.
- 08Absolute growth rate: total growth per unit time. Relative growth rate: growth per unit time per unit initial size.
- 09Dedifferentiation examples: interfascicular cambium and cork cambium from parenchyma.
- 10Heterophylly (plasticity): cotton, coriander, larkspur (phase of life); buttercup (air against water).
- 11PGR chemistry: IAA indole; kinetin adenine derivative; ABA carotenoid derivative; GA₃ terpene; ethylene gas.
- 12Discoverers: Darwins (coleoptile tip, canary grass), Went (auxin, oat), Kurosawa (bakanae, Gibberella fujikuroi), Skoog and Miller (kinetin), three groups (inhibitor-B, abscission II, dormin = ABA), Cousins (ethylene, oranges and bananas).
- 13Auxin: rooting of cuttings, apical dominance, parthenocarpy in tomato, 2,4-D herbicide for dicot weeds, xylem differentiation.
- 14Gibberellin: grape stalk length, apple shape, delays senescence, malting, sugarcane stem (up to 20 tonnes per acre), bolting in rosette plants.
- 15Cytokinin: cytokinesis, overcomes apical dominance, delays leaf senescence; kinetin from herring sperm DNA, zeatin from corn kernels and coconut milk.
- 16Ethylene: fruit ripening, respiratory climacteric, apical hook, deep-water rice elongation, ethephon, female flowers in cucumber.
- 17ABA: stomatal closure, stress hormone, seed dormancy, inhibits germination, antagonist of GAs.
Common traps
Where marks are lost
Key terms
20 terms
- Growth
- An irreversible, permanent increase in size of a cell, organ or organism, usually needing energy.
- Meristem
- A group of cells that keep dividing and perpetuating themselves, adding new cells to the plant body.
- Open form of growth
- Growth in which meristems keep adding new cells to the body throughout life.
- Arithmetic growth
- Growth in which only one daughter cell of each division keeps dividing; length rises in a straight line with time.
- Geometric growth
- Growth in which both daughter cells keep dividing; gives lag, log and stationary phases.
- Sigmoid curve
- The S-shaped curve of growth against time, with lag, exponential and stationary phases.
- Efficiency index
- The relative growth rate r in W1 = W0 e^rt, measuring a plant's ability to produce new material.
- Absolute growth rate
- Total growth per unit time.
- Relative growth rate
- Growth per unit time expressed per unit of initial size.
- Differentiation
- Maturation of cells from meristems to perform specific functions, with changes to walls and protoplasm.
- Dedifferentiation
- A differentiated cell regaining the ability to divide, as when parenchyma forms cork cambium.
- Redifferentiation
- Cells from dedifferentiated tissue losing the ability to divide again and maturing for a function.
- Plasticity
- The ability of a plant to form different structures in response to environment or phase of life.
- Heterophylly
- Different leaf shapes on the same plant, by life phase (larkspur) or environment (buttercup).
- Apical dominance
- Suppression of lateral bud growth by the growing apical bud.
- Parthenocarpy
- Development of fruit without fertilisation; induced by auxins in tomato.
- Bolting
- Internode elongation just before flowering in rosette plants, promoted by gibberellins.
- Respiratory climacteric
- The rise in respiration rate during fruit ripening, enhanced by ethylene.
- Ethephon
- A compound that releases ethylene slowly inside the plant; the usual commercial source of ethylene.
- Stress hormone
- Abscisic acid, which closes stomata and raises tolerance to many stresses.