1. Plant Science Topic 9

2. Reproduction in Angiospermophytes Topic 9.3

3. Assessment Statements

4. Variety in Flowers • Reproductive structure of angiosperms • Smallest Flower • Largest Flower

5. Flower Structure and Function

7. Flower Structure and Function • Meiosis occurs in: • Carpel/Pistil = Female part of the flower • Stamen = Male part of the flower • Flower Variety: • Complete flowers contain all four basic flower parts • Sepals, petals, stamen, carpel • Incomplete flowers lack at least one of these parts • Staminate flowers have only stamen, not carpels • Carpellate flowers have only carpels

8. Flower Structure and Function Staminate Carpellate

9. Pollination and Fertilization • Alternation of Generations • Generations are named according to the reproductive cells made • Life Cycles of Plants: • Gametophyte generation: haploid • Gametes produced by mitosis • Sporophyte generation: diploid • Spores produced by meiosis • Flowering Plant  sporophyte generation • Grew from zygote, new cells made through mitosis • Flowers gametophytes are made through haploid spores • Sperm in pollen • Eggs in ovary

10. Pollination • Pollination: • Pollen (containing make sex cells) is places on the female stigma • First step towards fertlization • Pollen Vectors • Wind • Insects • Fossil evidence that angiosperms and insects coevolved • Birds • Water • Animals • Attractive Flowers • Red flowers are conspicuous to birds • Yellow and orange flowers are noticed by bees • Heavily scented flowers are easily found by nocturnal animals • Plants that rely on wind have inconspicuous, odorless flowers

11. Pollination • Two types of pollination • Self-pollination • Pollen from anther of the same plant falls onto its own stigma • Form of inbreeding • Results in less genetic variation within a species • Cross-pollination • Pollen is carried from the anther of one plant to the stigma of a different plant • Increases variation  offspring with better fitness • Problem: female stigma may not receive male pollen due to distance travelled

12. Fertilization • Fertilization • Male and female sex cells unite to form a diploid zygote • Process: • Pollen germinates to produce a pollen tube • The pollen tube grows down the style of the carpel • Within the growing pollen tube is the nucleus that will produce the sperm • The pollen tube completes its growth by entering an opening at the bottom of the ovary • The sperm moves from the tube to combine with the egg of the ovule to form a zygote • Zygote develops with the surrounding tissue into the seed • As seed develops, the ovary around the ovule matures into a fruit • Fruit encloses and helps to protect the seed

13. The Seed • Seed: • Means by which an embryo can be dispersed to distant locations • Protective structure

15. The Seed • Maturation • Involves dehydration until H2O content is 10-15% of its weight • Dormancy period • Very low metabolism, no growth or development • Variable for different seeds • Adaptation to overcome hard environmental conditions • Germination • Development of the seed into functional plant • Conditions • Water is needed to rehydrate the dried seed tissues • Oxygen is needed to allow aerobic respiration to produce ATP • An appropriate temperature for the seed is necessary • Enzyme action

16. The Seed • Germination continued • Conditions • Testa must be disrupted/scarified before water uptake can occur, or • Fire or smoke is needed • Emerging seedling is fragile • Exposed to harsh weather, parasites, predators, many other hazards

18. Seed Metabolism during Germination • Seed absorbs water • Gibberellin, aka gibberellic acid, is released after the uptake of water • Gibberellin is a growth substance (plant growth hormone) and it triggers the production of the enzyme amylase • Amylase causes the hydrolysis of a starch into maltose. • The starch is present in the seed’s endosperm or food reserve • Maltose is pivotal compound • Used to produce a number of different compounds, depending on seeds needs • Meristematic regions

19. Seed Metabolism during Germination • Maltose is then further hydrolyzed into glucose that can be used for cellular respiration or may be converted into cellulose by condensation reactions • The cellulose is necessary to produce the cell walls of new cells being produced

20. Control of Flowering in Angiosperms • Light • Required for photosynthesis • Controls many aspects of plant growth and development • Plants are able to detect presence of light, its direction, wavelength, and intensity • Photoperiodism • Plants response to light involving the relative lengths

21. Control of Flowering in Angiosperms * Actually length of night controls flowering process in plants

22. Control of Flowering in Angiosperms • Control by Light • Blue-green pigments  phytochrome • Inactive = Pr • Active = Pfr • Red light (660nm)  inactive phytochromePr converted to Pfr  able to absorb far red light (730nm)  converted back to Pr • In darkness, the conversion back to Pr is much slower • Controlling factor for flowering • Long-day • Remaining Pfr at the end of short night stimulates the plant to flower • Acts as a promoter • Short-day • Remaining Pfr appears to act as an inhibitor • Pfrhas been converted to Pr to allow flowering to occur

23. Control of Flowering in Angiosperms