PLANT REPRODUCTION QUESTION 1985:			L. PETERSON/AP BIOLOGY

	Describe the structure of a bean seed and discuss its germination 
	to the seedling stage. Include in your essay hormonal controls, 
	structural changes, and tissue differentiation.

  
  
  STANDARDS:
  
  STRUCTURE:             Max. = 8 points
  __  Seed coat (protection)
  __  Embryo (new plant)
  __  Cotyledons (store food)
  __  Epicotyl (new shoot)
  __  Hypocotyl (new stem/root)
  __  Radicle (1st root)
  __  Plumule (1st leaves)
  __  Hilum scar (attachment)
  __  Micropyle (pollen tube entry)
  
  GERMINATION DISCUSSION:     Max. = 12 points
  __  Imbibition of water (increases metabolism)
  __  Correct temperature (enzymes)
  __  Oxygen (for respiration)
  __  Radicle emerges 1st (establishes root)
  __  Subsequent shoot (photosynthesis when stored food gone)
  __  Formation of hook/arch (pulls epicotyl)
  __  Epigeal germination
  
  a.  Hormonal Control
     --  Auxin in geotropism (+ or -)
     --  More auxin, lower 1/2 axis
     --  Stem/root affected differently
     --  Gibberellins stimulate length growth
     --  Cytokinins stimulate cell division
     --  Abscisic acid inhibits root cell elongation
  
  b.  Structural Changes (Note: some germination discussion is structural change)
     --  Formation of root cap
     --  Dropping spent cotyledons
     --  Change, dark-to-light-growth
     --  Branch root production
     --  Leaf primordia
     --  Two different foliage leaves
  
  c.  Tissue differentiation
     --  Cell division, elongation, maturation
     --  Xylem, phloem (elaboration)
     --  Apical meristem
     --  Protoderm, ground meristem, procambium
     --  Several vascular strands, stem; one, roots
     --  Collenchyma, sclerenchyma
     --  Mesophyll, epidermis, guard cells
     --  Endodermis pericycle
     --  Root hair formation