1. Reproduction in plants
Topic 9.4

2. U: Flowering involves a change in gene expression in the shoot apex
Stages of a Flowering Plant:
Germination = sprouting of a plant from a seed
Vegetative phase = period of growth between germination & flowering (weeks, months, yrs)
Vegetative structures = roots, stems, leaves
Reproductive phase = shoot apical meristems start producing parts of flowers instead of leaves
Flowers
“reproductive shoot”
allow for sexual reproduction
increase variety

3. Flowering & gene expression
Triggers that cause flowering:
Temp
Day length (main trigger)  it’s really the length of darkness that matters
Short-day plants (flower in autumn)
Long-day plants (flower in summer)
Light plays role in production of inhibitors or activators of genes that control flowering:
LD plants  phytochrome pigment activates flower-time (FT) gene
SD plants  phytochrome pigment inhibits FT gene

4. U: The switch to flowering is a response to the length of light & dark periods in many plants
Phytochrome = pigment in leaves that plants use to measure the length of dark period
Switches between 2 forms:
PR  absorbs red light (660 nm); more stable form
PFR  absorbs far-red light (730 nm); active form
Long-day plants (short nights) = large amount of PFR (promoter), causing transcription of flowering gene
Short-day plants (long nights) = little amount of PFR (inhibitor), so since there’s very little inhibitor, plant will flower

5. App: Methods used to induce short-day plants to flower out of season
Flower-forcing = getting flowers to bloom out of season or at a specific time such as during holidays
Growers manipulate length of days and nights
ghts.html

6. Skill: Drawing of half-views of animal-pollinated flowers

8. U: Most flowering plants use mutualistic relationships w/ pollinators in sexual reproduction
Pollination = transfer of pollen from stamen to stigma
Methods of transfer:
Wind
Water
Animal pollinators (birds like hummingbird, insects like butterflies & bees, bats)
Mutualism = relationship where both organisms benefit
Pollinator gains food (nectar), plant gains mean to transfer pollen

9. U: Success in plant reproduction depends on pollination, fertilization & seed dispersal
Order of events in a flowering plant:
Pollination = transfer of pollen from stamen to stigma
Fertilization
Pollen grain lands on sticky stigma
Pollen tube grows down style; male gametes travel down tube
Male gamete fuses with female gamete (ovule = small egg)
Ovules develop into seeds; ovary develops into fruit
Seed dispersal
Reduces competition between offspring & parent
Spreads the species
Different types of seeds for different methods of dispersal (e.g. feathery to catch wind; hooks to catch animal fur; fleshy to attract animals to eat)
Fertilization:

10. NOS: Paradigm shifts: more than 85% of world’s 250,000 species of flowering plants depends on pollinators for reproduction. This knowledge has led to protecting entire ecosystems rather than individual species
Traditionally, focus of conservation efforts was on single populations & single species
Now, we know the whole ecosystem must be protected!
Why? Mutualistic relationships between pollinators and flowering plants
Example:
Saguaro cactus in Sonoran desert
Cactus provides perching & nesting sites for several species of birds
Bats & several species of birds eat cactus fruit & disperse seeds
Flowers attract different species of bats to their nectar, transferring pollen
One bat (lesser long-nosed bat) is endangered
Invasive grasses, development of desert, and changes in natural fire cycles threaten cactus
Must protect the bats, cactus and seed-dispersing animals  the whole ecosystem!

11. Skill: Drawing internal structure of seeds

12. Cotyledon = seed leaf

13. Skill: Design of experiments to test hypotheses about factors affecting germination
Germination is the process by which a seed emerges from a period of dormancy and starts to sprout
For germination to occur, a seed requires a combination of:
Oxygen:  For aerobic respiration (need ATP in order to grow)
Water:  To metabolically activate the cells
Temperature:  For the optimal function of enzymes
In addition, particular seed species may require other specialised conditions, such as:
• Fire            • Light or darkness            • Freezing            • Prior animal digestion            • Erosion of the seed coat            • Washing (to remove inhibitors)

14. Metabolic process during germination:
Absorption of water, which causes gibberellin (gibberellic acid (GA)) to be produced
Gibberellin causes the synthesis of amylase, which breaks down starch into maltose
Maltose transported to embryo, where it’s either hydrolyzed to glucose (for energy) or condensed to cellulose (for cell wall)
Stored proteins & lipids will also be hydrolyzed to form enzymes, triglycerides and phospholipids
Germination uses food stored in cotyledons as energy source until developing shoot reaches light & begin photosynthesis