1. 9.4 Reproduction in plants AHL
The commonly held view is that flowering is influenced by abiotic factors such as day length. The importance of biotic factors such as pollination (e.g. by bats), and seed dispersal is being increasingly realized. All factors influence flowering by introducing a selective pressure, which in turn influences the genetics of a population.
Essential idea: Reproduction in flowering plants is influenced by the biotic and abiotic environment.
By Chris Paine

2. Understandings, Applications and Skills
Statement
Guidance
9.4.U1
Flowering involves a change in gene expression in the shoot apex.
9.4.U2
The switch to flowering is a response to the length of light and dark periods in many plants.
9.4.U3
Success in plant reproduction depends on pollination, fertilization and seed dispersal.
Students should understand the differences between pollination, fertilization and seed dispersal but are not required to know the details of each process.
9.4.U4
Most flowering plants use mutualistic relationships with pollinators in sexual reproduction.
9.4.A1
Methods used to induce short-day plants to flower out of season.
Flowering in so-called short-day plants such as chrysanthemums, is stimulated by long nights rather than short days.
9.4.S1
Drawing internal structure of seeds.
9.4.S2
Drawing of half-views of animal-pollinated flowers.
9.4.S3
Design of experiments to test hypotheses about factors affecting germination.

3. 9.4.S2 Drawing of half-views of animal-pollinated flowers.

4. 9.4.S2 Drawing of half-views of animal-pollinated flowers.

5. 9.4.S2 Drawing of half-views of animal-pollinated flowers.

6. Reproduction is dependent on the success of each process
9.4.U3 Success in plant reproduction depends on pollination, fertilization and seed dispersal.
Reproduction is dependent on the success of each process

7. Pollination is the transfer of pollen from the anther to the stigma.
9.4.U4 Most flowering plants use mutualistic relationships with pollinators in sexual reproduction.
Pollination is the transfer of pollen from the anther to the stigma.
Cross-pollination (transfer of pollen between different flowers) is preferred as it leads to greater variation in the next generation.
Some flowering plants, e.g. grasses, rely on wind or water for pollination, but most use animals to transfer pollen.
Common types of pollinator include:
birds
bats
Insects, e.g. bees
Mutualism is a close association between two organisms where both organisms benefit from the relationship: the animal is rewarded with food in the form of nectar, the plant with successful pollination.

8. 9.4.U1 Flowering involves a change in gene expression in the shoot apex.
Floral initiation is caused by the growth and differentiation of apical cells.
Cells in the shoot apex change how they divide and differentiate due to changes in their gene expression.
The triggers for the change in gene expression vary between plants, but the most common one is day length (photoperiod)

9. 9.4.U2 The switch to flowering is a response to the length of light and dark periods in many plants.

10. 9.4.U2 The switch to flowering is a response to the length of light and dark periods in many plants.

11. 9.4.U2 The switch to flowering is a response to the length of light and dark periods in many plants.

12. 9.4.U2 The switch to flowering is a response to the length of light and dark periods in many plants.

13. 9.4.U2 The switch to flowering is a response to the length of light and dark periods in many plants.

14. Chrysanthemum is short-day plant
9.4.A1 Methods used to induce short-day plants to flower out of season.
Chrysanthemum is short-day plant
For most varieties day length needs to be less than 13 hours for flowers to develop and open
During the summer months (April to September) in temperature countries chrysanthemum will not naturally flower.
This is accomplished by covering the plant with opaque black cloth for hours per day. For example place the cover at 5pm and then remove it again at 8am.
Plants need to be covered daily until flower buds begin to show colour.

15. 9.4.S1 Drawing internal structure of seeds.

16. 9.4.S3 Design of experiments to test hypotheses about factors affecting germination.

17. 9.4.S3 Design of experiments to test hypotheses about factors affecting germination.

18. 9.4.S3 Design of experiments to test hypotheses about factors affecting germination.

19. 9.4.S3 Design of experiments to test hypotheses about factors affecting germination.

20. 9.4.S3 Design of experiments to test hypotheses about factors affecting germination.
Design an investigation to test how a chosen factor affects germination in a particular species of plant.
Which species of plant/type of seed will you use? It is best to avoid seeds that have long dormancy periods
How will you collect your results, how will you assess whether germination has happened (dependent variable)? How often will you observe your seeds?
Which factors will you investigate (independent variables)? Which need to be kept constant (controlled variables)?
Factors affecting germination are numerous, some are specific to particular species such as the Lodgepole pine (Pinus contorta) needs exposure to fire to germinate. A few of the more important factors include:
(soil) temperature
age of the seeds
Hydration / water availability
Level of light, e.g. some seeds need to be buried and therefore require low light levels