AP Biology Plant Reproduction Questions and Standards

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1973 1982 1984 1985 1990

PLANT REPRODUCTION QUESTION 1973: L. PETERSON/ECHS   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 sub- stance 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/ECHS 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 venter 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/ECHS   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/ECHS 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/ECHS Describe the effects of plant hormones on plant growth and development. Deisgn 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 biennials promote softening of cell walls promote production of starch digesting enzymes promote growth of branch or adventitious roots in grass seeds promote renewed cell division in cambium promote pollen germination promote differentiation of vascular tissue increase size of grapes and loosen clusters promote joining of vascular tissue of leaves break seed and bud dormancy with that of stems stimulate leaf growth in monocots affect transcription of at least ten genes inhibit root formation involved with growth stimulate development of "male" flower parts inhibit growth of main roots stimulate auxin production inhibit production of abscission layer stimulate cell division at the stem apex act as a herbicide for dicots may stimulate the production of auxins exert apical dominance by inhibition of cell stimulate fruit-set in some species elongation stimulate vascular cambium to produce artificially promotes parthenocarpy 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 mitosis help break dormancy in some seeds and cytokinesis enhance flowering in some plants induces leaf primordia to form protective promote fruit development in some species 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/ECHS   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)