PLANT REPRODUCTION QUESTION 1973:			L. PETERSON/AP BIOLOGY

	Seeds that are randomly positioned when planted in a pot of soil placed 
	on a window sill produce seedlings with downward growing roots and 
	upward growing shoots. Above ground, the shoots are oriented toward 
	light. Describe the physiological mechanisms that occur to produce:

	a)  the downward growth of the roots
	b)  the upward growth of the shoots
	c)  the bending of the shoots toward light

STANDARDS:	NOT MORE THAN FIFTEEN TOTAL POINTS WERE GIVEN.

ONE POINT FOR EACH OF THE FOLLOWING:
__  The hormone involved is auxin.
__  In vertical roots or stems, auxin is uniformly distributed.
__  In horizontally placed roots, auxin accumulates on the lower side.
__  The accumulation of auxin on the lower side in roots inhibits cell elongation 
         in the area.
__  In horizontally placed stems, auxin accumulates on lower side.
__  Accumulation of auxin in stems is stimulatory.
__  In a laterally illuminated stem, auxin accumulated on the shady side.
__  There is lateral transport of auxin from the sunny to the shady side, or 
         from top to bottom in horizontally placed stems and roots.

TWO POINTS FOR EACH OF THE FOLLOWING:
__  Auxin is produced in the stem apex.
__  Auxin causes cell elongation in stems.
__  Optimum for root growth is an amount much less than for stem growth.
__  In high concentration, auxin is inhibitory in both stems and roots.
__  Lateral movement of auxin requires energy.
__  Auxin movement is too fast to be explained by diffusion.
__  The perception of auxin in stem tips is light promoted (carotenes or flavenes).
__  Discussion of the perception of gravity.
__  Evidence that the site of perception is the tip.

FIVE POINTS FOR THE FOLLOWING:

The downward growth of roots...the geotropic response of root is dependent on the production of a growth inhibitor or inhibitors produced in the root cap. The inhibitor(s) move from the cap through the apex to the elongating cells. If the root is horizontal, a large part of the substance is transported laterally to the lower side. The difference in concentration produces unequal growth,...the lower side is more inhibited and root therefore turns down.
 














     PLANT REPRODUCTION QUESTION 1982			L. PETERSON/AP BIOLOGY
	In the life cycle of a fern and a flowering plant, compare and contrast each
	of the following:
		A.  The gametophyte generation
		B.  Sperm transport and fertilization
		C.  Embryo protection

STANDARDS:
	A maximum of 10 points was allotted to each of the fern portion and the 
	angiosperm portion of the question. This meant that a student had to include
	correct information on each group of plants in order to achieve a score of 15.
	Within this limit, a single point was given for each valid idea presented. A
	score of more than 15 received a 15. The following outline indicates possible
	responses for which points were awarded.

A.  GAMETOPHYTE GENERATION
	FERN
__ Haploid
__ Reduced in comparison to sporophyte
__ Characterized as a heart-shaped prothallus
__ Eggs formed in archegonia
__ Sperm formed in antheridia
__ Details of archegonial structure
__ Details of antheridial structure
__ Gametophyte is photosynthetic; has rhizoids for anchoring and water absorption

	FLOWERING PLANT
__ Male (micro)gametophyte (or pollen grain is immature microgametophyte)
__ Female (mega)gametophyte or embryo sac
__ Structure of microgametophyte normally two cells, a tube and a generative cell 
		       (sometimes identified as a tube cell and two sperm nuclei)
__ Structure of megagametophyte is 7 cells with 8 nuclei
__ Both gametophytes nutritionally dependent on the sporophyte
__ Haploid
__ Gametophyte develops usually from one type of spore in ferns (homospory), 
      while in the flowering plnats each gametophyte develops from a different type 
      of spore (heterospory).

B.  SPERM TRANSPORT AND FERTILIZATION
	FERN
__ Swim to archegonium and require dew, moisture, etc., for transport
__ The neck canal cells and ventral canal cell of the archegonium disintegrate
__ Disintegration of cells may form a chemical that attracts sperm
__ Fertilization occurs in venter of the archegonium

	FLOWERING PLANT
__ Pollen transport from anther to stigma of the pistil
__ Pollination agent (example)
__ Pollen grain germinates and grows through the style
__ Pollen tube penetrates the ovule (usually through the micropyle)
__ Double fertilization occurs (is characteristic of the angiosperms)
__ Details of double fertilization






	C.  EMBRYO PROTECTION
FERN
__ Embryo develops in center of archegonium
__ Embryo is surrounded by and protected by cells of the archegonium
__ Embryo dependent upon gametophyte for nutrition until the third or 
      fourth leaf forms
__ Gametophyte ultimately dies

	FLOWERING PLANT
__ Embryo protected within a seed (which forms from the ovule)
__ Integuments of ovule become a hardened seed coat
__ Nucellus of the ovule withers and dies
__ Endosperm provides nutrition for the developing embryo
__ The seed is enclosed within a fruit which develops from the ovary wall 
      and sometimes includes accessory tissue of the flower.
__ Ovary wall forms the pericarp of the mature fruit
__ Pericarp has three layers: endocarp, mesocarp, and exocarp 









































     PLANT REPRODUCTION QUESTION 1984:			L. PETERSON/AP BIOLOGY

	Define the following plant responses and explain the mechanism of 
	control for each. Cite experimental evidence as part of your discussion.
	a)  Phototropism
	b)  Photoperiodism

STANDARDS:
PHOTOTROPISM:	
	Max. = 9 points if experimental evidence is given
	Max. = 7 points if experimental evidence is lacking

__  Definition - movement in response to light (involving growth) - 2 points
__  Possibility of negative response

Mechanism
__  Auxins
__  Distribution (apex -> stem or lateral)
__  elongation of cells
__  stem tip or coleoptile

Evidence (2 points for any of the following)
__  Darwin - covered coleoptiles
__  Paal - cut coleoptiles - agar, uneven placement
__  Boysen-Jensen - mica
__  Went - bioassay

PHOTOPERIODISM:
	Max. = 9 points if experimental evidence is given
	Max. = 7 points if experimental evidence is lacking
__  Definition - response to light/dark periods
__  flowering (or other response)

Mechanism
__  Categories of plants (LDP, SDP)
__  Receptor in leaf
__  LDP (if night shorter than minimum)
__  SDP (if night longer than minimum)
__  night not day
__  existence of phytochrome in two forms
__  PFR/PR  interconvertible
__  PFR active form
__  ratio (PR/PFR) important
__  possible hormonal involvement

Evidence
__  light flash in dark
__  grafting
__  ratio of PR/PFR 







     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




     PLANT REPRODUCTION QUESTION 1987:			L. PETERSON/AP BIOLOGY

	Describe the effects of plant hormones on plant growth and development.
	Design an experiment to demonstrate the effect of one of these plant 
	hormones on plant growth and development.

STANDARDS:
PART I. EFFECTS:				Max. = 7 points
__  For identifying a plant hormone
__  For correctly defining a plant hormone
For correctly describing the effects of a plant hormone (most frequently mentioned hormones and effects given below, but see addendum for a more complete master list):
AUXINS
__  Promote cellular elongation
__  Promote softening of cell walls
__  Involved in phototropism
__  Involved in geotropism
__  Involved in apical dominance
GIBERELLINS
__  Stimulate cell elongation
__  Produce bolting in biennials
__  Stimulate production of starch digestion enzymes in some seeds
__  Reverse effects of genetic dwarfism
CYTOKINETINS
__  Promote growth in size of leaf cells
__  Stimulate cell division
__  Release buds from apical dominance
ETHYLENE
__  Promotes ripening of fruit
ABSCISIC ACID
__  Promotes stomatal closure
__  Promotes resistence to water stress
__  Promotes seed and bud dormancy
__  formerly thought to promote abscission
FLORIGEN
__  May induce flowering
Extra points, up to two, awarded for each association of a hormone with a correct, specific effect. In order for two points to be awarded, two different hormones must 
be associated with their specific effects.
PART II.  EXPERIMENTAL DESIGN		Max. = 7 points
Appropriate understanding or indication of:
__  Basing design on past observations or the literature
__  Problem, statement, or question posed
__  Hypothesis
__  Use of adequate sample size or replicates
__  Maintaining uniform conditions
__  Control or understanding of the concept of control
__  Treatment of experimental group
__  Taking of data
__  Evidence supports or refutes the hypothesis
One extra point awarded for a particularly innovative experimental design and another for especially well organized and detailed description of the experiment.  
							Max. = 2 points





	ADDENDUM TO STANDARDS / MASTER LIST OF PLANT HORMONAL EFFECTS:
AUXINS						GIBBERELLINS

promote cellular elongation.				stimulate cell elongation in stem.
promote phototropism in stems.			promote bolting and flowering in promote softening of cell walls.			  	biennials.
promote growth of branch or adventitious roots.		promote production of starch. promote renewed cell division in cambium.			digesting enzymes in grass seeds.
promote differentiation of vascular tissue.		promote pollen germination.
promote joining of vascular tissue of leaves		increase size of grapes and loosen     
  with that of stems.					  clusters.
affect transcription of at least ten genes			break seed and bud dormancy.
 involved with growth.					stimulate leaf growth in monocots.
inhibit growth of main roots.				inhibit root formation.
inhibit production of abscission layer. 			stimulate development of "male" 
 act as a herbicide for dicots.			              	  flower parts.
exert apical dominance by inhibition of cell		stimulate auxin production.
 elongation.						stimulate cell division at the stem
artificially promotes parthenocarpy.		  	  apex.											may stimulate the production of 
							  auxins.
							stimulate fruit-set in some species.
							stimulate vascular cambium to 
							  produce secondary phloem.
							stimulate protein synthesis.
CYTOKININS						ABSCISIC ACID (ABA)
promote growth in size of leaf cells.			promote stomatal closure.
stimulate cell division.					promote seed and bud dormancy.
promote conversion of immature plastids		promote resistance to water stress.
 to chloroplasts.					counters effects of auxin.
inhibit senescence of leaves.				induces apical meristem to stop 
help break dormancy in some seeds.		 	  mitosis and cytokinesis.
enhance flowering in some plants.			induces leaf primordia to form 
promote fruit development in some species.	  	protective bud scales.
release lateral buds from apical dominance.		keeps twigs dormant until leaching 
							  occurs.
							involved in root geotropism by 
							  inhibiting elongation of cells on 
							  lower side.
ETHYLENE						FLORIGEN   (hypothetical)
promotes ripening of fruit.				may induce flowering.
promotes radial growth in stems and roots.
contributes to leaf drop.
produces horizontal growth of stems.
affects sex expression in some monoecious species.
promotes wound healing.










     PLANT REPRODUCTION QUESTION 1990:			L. PETERSON/AP BIOLOGY

	Discuss the adaptations that have enabled flowering plants to overcome the
	following problems associated with life on land.

	a.  The absence of an aquatic environment for reproduction
	b.  The absence of an aquatic environment to support the plant body
	c.  Dehydration of the plant
	
STANDARDS:

A.  ABSENCE OF AN AQUATIC ENVIRONMENT FOR REPRODUCTION:	Max. = 4 points
__  Flowers - attraction for insects - shape, color, smell, chemical, nectar.
	          Mimicry for pollination (coevolution)
__  Timing of reproduction
Male
__  Microspores - pollen / Reduced Gametophyte
__  Lack of motility of gamete - pollen grain modification for transport
				e.g. light weight/structure
__  Pollination - transport of male gametes, wind, insects (self-pollination)
Female
__  Reduced gametophyte (in megaspore or megasporangium)
__  Protected gametophyte - embryo inside ovary, carpel, pistil
__  Evolution of seed
__  Fertilization - internal - pollen tube, endosperm
__  Fruit and seed dispersal
__  Seed dormancy

B.  ABSENCE OF AN AQUATIC ENVIRONMENT TO SUPPORT THE PLANT BODY:  Max. = 4 points
__  Stem - support
__  Root - anchorage
__  Vascular tissue - xylem fibers, tracheids, vessels, heartwood, dead tissues, phloem 
         fibers or Vascularization
__  Vines, Tendrils
__  Cell wall - lignin, cell wall support, cellulose
__  Cambium - secondary thickening
__  Sclerenchyma - whole wall support
__  Collenchyma - corner wall support
__  Prop, buttressed roots
__  Turgor pressure

C.  DEHYDRATION OF THE PLANT:					  Max. = 4 points
__  Root hair, absorption
__  Cuticle, wax, acellular
__  Bark - suberin, cork
       Scales - bud protection
       Sepal/petals - floral part protection
__  Seed coat / Pollen grain wall
__  Stomates - function to control water movement
__  Xylem - water transport






__  Leaf/stem/root modifications (2 points max.) 
	surface area reduction in desert plants/succulents
	stomates under surface
	leaf rolling
	hairs and trichomes
	interlocked epidermal cells
	hypodermis
	cortex - water storage or retention
	loss of leaves / abscission layer
__  CAM/C4 plants - modified stomate functions
__  seed dormancy (if not mentioned in part A)














































 
     PLANT REPRODUCTION QUESTION1992:		 	L. PETERSON/AP BIOLOGY

	Survival depends on the ability of an organism to respond to changes in its 
	environment. Some plants flower in response to changes in day length. Some 
	mammals may run or fight when frightened. For both of these examples, 
	describe the physiological mechanism involved in the response.

STANDARDS:
    FLOWERING RESPONSE 
ADAPTIVE  (1 point MAX)
__	Value to plant - in balance with pollinators - greater reproductive efficiency
	- controls distribution - or Day/night length less variable than temperature 
	- to set photoperiod response, etc.
MECHANISM
__	Minimum size to flower (ripeness to flower)
__	Photoperiodism - basic explanation = relative lengths of day/night
__	Importance of dark period over light period (controversy of what is measured)
__	Statement of short day, long, day, day-neutral plants
__	Plants vary as to response to light/dark intervals - contrasting categories
	   a.  short-day    b.  long-day   c.  day-neutral
__	Detailed information, such as:
	   Short day - (explanation) Flower in late summer, fall or winter or example
	   Chrysanthemums, poinsettias, soybean, strawberry, primrose, cocklebur,
	   goldenrod, ragweed
__	   Long day - (explanation) Flower in late spring or early summer or example
	   Petunias, iris, lettuce spinach, henbane, wheat, potatoes, clover, tobacco
__	   Day neutral - (explanation) Unaffected by photoperiods or example
	   Tomatoes, dandelions, garden peas, rice, gorse, rose, snapdragons
__	Phytochrome - Pr and Pfr
__	Phytochrome = Blue-green pigment
__	Absorption at 660 nm converts Pr to Pfr. Absorption at 730 nm converts 
	   Pfr to Pr
__	Slowly decays back to Pr in darkness
__	Phytochrome located in plasma membrane
__	Pfr - biologically active form - or the ratios of Pr and Pfr
__	Description of phytochrome
__	Internal (biological) clock - circadian rhythm interaction with phytochrome to
	trigger physiological change

EFFECT
__	Evidence that effect is transported throughout plant - grafts - etc.
__	"Florigen" - (hormones) much debate and remains in doubt
__	Other possibilities than "florigen" - balance between gibberellins/cytokinins 
	or gibberellins/auxins or giberellins alone

MAXIMUM OF 7 points - one point must be about phytochrome