9.4: REPRODUCTION IN PLANTS

Angiosperms Can be divided into two groups, monocotyledonous (monocots) and dicotyledonous (dicots) plants. MonocotsDicots Parallel venation in leavesNetlike venation 3 flower parts4 or 5 flower parts Seeds with one seed leaf (cotyledon) Two cotyledon’s Vascular bundles throughout stem Vascular bundles in a ring Fibrous rootsTap root Pollen grain with one openingPollen grain with three openings

Reproductive phase Flowers allow for sexual reproduction in plants. This increase variety of flowers available. Whether a shoot becomes a leaf or a flower is determined by temperature as well as day length (dark period).

What is photoperiodism? A plants response to day/night cycles Plant typeFloweringDark periode.g. Long-dayMidsummerShorter dark period Radishes, spinach, lettuce Short-dayLate springLonger dark period Poinsettias, chrysanthem ums, asters Day-neutralAnytimeRoses, dandelions, tomatoes

Phytochrome (blue-green pigment) controls flowering in plants. There are two forms, inactive phytochrome (P r ) or active phytochrome (P fr ) PrPr P fr 660nm red light 730nm far-red light P fr changes to P r in the dark, very slowly. Growth response

Reproduction in Angiosperms

Flower partFunction SepalsProtect developing flower while it’s a bud PetalsColourful to attract pollinators AntherPart of the stamen, produces male sex cells, pollen FilamentStalk of stamen, holding up anther StigmaSticky top of the carpel, pollen lands here StyleSupports the stigma OvaryBase of carpel, female sex cells develop here

Plants can self-pollinate. Results in in- breeding – limited genetic variation Plants can also cross-pollinate. Pollen carried from one plant to another, creates genetic variation but is risky! Why? Pollination can be controlled by scientists, but it’s very tricky.

Remember… Pollen is male Stigma is female How many vectors of pollination can you think of? -Wind -Water -Insects -Birds -Animals

Male sex cell fuses with female sex cell. Diploid zygote formed. How does the genetic material in the pollen reach the egg cells in the ovules (inside the ovary)? POLLEN TUBES! Once fertilized, the growing zygote will grow and eventually become a seed.

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Seed partFunction TestaProtective outer layer CotyledonsSeed leaves, nutrient store MicrophyleScar left where pollen tube entered Embryo root and embryo shoot New plant after germination

For a seed to be dormant, how much water should it contain? 10 – 15% Are there advantages of dormancy? If so what are they? What conditions are needed for germination? Water ( rehydration ) Oxygen (respiration to produce ATP ) Temperature ( enzymes )

Germination

1.Water absorbed by seed. Osmosis 2.Gibberellin (gibberellic acid) released  growth hormone. Amylase released 3.Amylase causes hydrolysis of starch  maltose 4.Maltose hydrolysed  glucose ( cellular respiration or condensed  cellulose) 5.Cellulose forms cell walls Maltose really important until leaves are produced, then photosynthesis takes over.

26ft Sunflower?!!