TOPIC 9.4 REPRODUCTION OF PLANTS

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1 TOPIC 9.4 REPRODUCTION OF PLANTS

2 INTRO IB BIO Flowers are reproductive structures found in flowering plants. Their function is to effect reproduction by providing a mechanism for the fertilization of eggs by sperm.

3 IB BIO 9.4 Understandings U1: Flowering involves a change in gene express in the shoot apex. Flowering is the process by which plants produce flowers. This is typically triggered by external stimuli such as length of day or environmental temperatures. 3 Flowering

4 IB BIO Understandings U1: Flowering involves a change in gene express in the shoot apex. When the reproductive phase of a plant is triggered, it begins to flower. This results when apical shoot meristems begin to produce flower parts instead of leaves. Flowering These parts then proliferate and differentiate into mature flower structures.

5 IB BIO Understandings U1: Flowering involves a change in gene express in the shoot apex. This flowering is the result of a change in gene expression in the shoot apex. As shown in the diagram below, gene expression in parts of the plant change during reproductive development. Flowering

6 IB BIO Flower Diagram Skills S2: Drawing of half-views of animalpollinated flowers. The following is a cross-section diagram of an animal-pollinated flower. You should be able to draw this from memory.

7 IB BIO 9.4 Sepal protect the flower 7 Skills S2: Drawing of half-views of animalpollinated flowers. Petals - help pollinators find the flower Anthers produce pollen bud during development and at night.

8 IB BIO 9.4 Stigma sticky and captures 8 Skills S2: Drawing of half-views of animalpollinated flowers. Filaments hold anthers in position to promote pollen brushing off. pollen from pollinators

9 IB BIO 9.4 Carpel female part of the 9 Skills S2: Drawing of half-views of animalpollinated flowers. Style holds up the stigma Ovary female reproductive structure flower consisting of stigma, style and ovary.

10 IB BIO Understandings U2: The switch to flowering is a response to the length of light and dark periods in many plants. Do Now: Research the following: 1. What is florigen? 2. What is a pigment? 3. What is mrna? Photoperiodism 4. What is an biological promotor and what is a biological inhibitor?

11 IB BIO Understandings U2: The switch to flowering is a response to the length of light and dark periods in many plants. In most plants, the switch to flowering is a response to the length of the day (photoperiodism). Long-day plants flower in the summer when nights are short Short-day plants flower in the fall when nights are longer Photoperiodism

12 IB BIO Understandings U2: The switch to flowering is a response to the length of light and dark periods in many plants. Experiments have shown that plants are sensitive to the length of darkness rather than the light. It was found that plants use a pigment, phytochrome, to measure this. Photoperiodism Phytochrome Phytochrome can switch between two states, P r and P fr : When P r absorbs red light it is converted to P fr When P fr absorbs far red light, it is converted back to P r

13 IB BIO Understandings U2: The switch to flowering is a response to the length of light and dark periods in many plants. Photoperiodism Phytochrome Sunlight contains more red light, so during the day P r is rapidly converted to P fr. However, P r is more stable. So, during the night, P fr gradually converts back to P r. As a result, plants can detect the length of the day by the levels of P fr.

14 IB BIO Understandings U2: The switch to flowering is a response to the length of light and dark periods in many plants. In long-day plants, large amounts of P fr promote the gene expression needed for flowering. Since the night is short, there is less time for P fr to break down. Phytochrome ursera.org/learn /plantknows/lec ture/ome9g/2-4-phytochrome- In short-day plants, P fr acts as an inhibitor for flowering. After a long night, little P fr remains, which allows the plant to flower.

15 ntknows/lecture/ome9g/2-4- phytochrome-a-light-activatedswitch

16 IB BIO Applications A1: Methods used to induce short-day plants to flower out of season. Short-day plants can be induced to flower out of season with flower forcing. Growers do this by manipulating the length of day and amount of light plants are exposed to. Flower Forcing This is used to make the plants flower at certain times (i.e. out of season, holidays, etc.)

17 IB BIO After flowering, success in plant reproduction depends on pollination, fertilization and seed dispersal. Understandings U3: Success in plant reproduction depends on pollination, fertilization and seed dispersal. Pollination occurs when a pollen reaches the stigma. The pollen can come from the same plant (self-fertilization) or a different one. Pollination Fertilization

18 IB BIO Understandings U4: Most flowering plants use mutualistic relationships with pollinators in sexual reproduction. Most flowering plants have formed mutualistic relationships with pollinators (animals). This promotes the transfer of pollen to the stigma of another plant (and thus genetic diversity). Pollination Fertilization Seed Dispersal Pollinators (bees, bats, insects, etc.) gain food from nectar while the plant gains a means of transferring pollen to other plants.

19 IB BIO After flowering, success in plant reproduction depends on pollination, fertilization and seed dispersal. Understandings U3: Success in plant reproduction depends on pollination, fertilization and seed dispersal. Pollination Fertilization In fertilization, a pollen grain on the stigma grows down the style and reaches the ovary. Each fertilized ovule is diploid and develops into a seed. The ovary develops into a fruit, which protects and provides nutrients for seeds.

20 IB BIO Seed Diagram Skills S1: Drawing internal structure of seeds. The following is a diagram of the internal structure of a seed. You should be able to draw/label one from memory.

21 IB BIO 9.4 Cotyledon embryo leaves 21 Skills S1: Drawing internal structure of seeds. Radicle embryo root Epicotyl embryo shoot Seed Coat aka testa with initial food stores. Hypocotyl becomes stem

22 IB BIO Understandings U3: Success in plant reproduction depends on pollination, fertilization and seed dispersal. After flowering, success in plant reproduction depends on pollination, fertilization and seed dispersal. Finally, seed dispersal involves seeds being carried away by the wind or animals. This prevents competition with the parent plant. Pollination Fertilization Seed Dispersal

23 IB BIO Skills S3: Design of experiments to test hypotheses about factors affecting germination. Germination is the early growth of a seed that occurs when the favorable conditions are met. Requirements include: Water availability Oxygen supply Warmth to catalyze metabolic reactions Germination ** The photo here shows a germinating pea sead.

24 IB BIO Skills S3: Design of experiments to test hypotheses about factors affecting germination. At the start of germination, giberellin hormone is produced. This stimulates cell division and the production of amylase, which is needed to break down stored starches. Germination The resulting sugars are used by the developing seed as an energy source until leaves form.

25 REVIEW IB BIO Outline the role of gene expression in flowering Draw a diagram of an animal-pollinated flower. 3. Outline photoperiodism as seenbin long-day and short-day plants. 4. Define flower forcing. 5. Outline a plant s reproductive success in terms of pollination, fertilization and seed dispersal. 6. Draw a diagram showing the internal structure of a seed. 7. Define germination and its necessary conditions.

26 VIDEOS IB BIO 9.4 CrashCourse: Plant Reproduction 26 Khan Academy: Photoperiodism Pollination: Trading Food for Fertilization Seed Disperal: The Great Escape Mung Bean Germination Timelapse