Topic 9.4~ Reproduction in Plants

Essential idea: Reproduction in flowering plants is influenced by the biotic and abiotic environment. Most flowering plants use mutualistic relationships with pollinators in sexual reproduction.

The Noble, Under-appreciated Bee Nature of science: Paradigm shift—more than 85% of the world’s 250,000 species of flowering plant depend on pollinators for reproduction. This knowledge has led to protecting entire ecosystems rather than individual species. (2.3) Utilization: The University of Göttingen, in Germany, conducted an extensive review of scientific studies from 200 countries for 115 of the leading global crops in 2005. They found that 87 of the crop plants depend to some degree upon animal pollination, including bees. This accounts for one-third of crop production globally. The Noble, Under-appreciated Bee

Draw and Label: A dicotyledonous animal-pollinated flower Skill: Drawing of half-views of animal-pollinated flowers. Floral organs: Sepals petals stamens (male ) Anther filament carpel/ pistil (female) Stigma Style ovary •complete: all 4 floral organs •incomplete: lacking 1 or more floral organs •perfect: both stamens and carpels on 1 flower •imperfect: lacking either a stamen or carpel •monoecious: staminate and carpellate flowers on 1 plant) •dioecious: staminate and carpellate flowers on separate plants

Plant Reproduction Basics Pollination = transfer of pollen from anther to stigma Pollen contains male gametes (sperm) Fertilization = fusion of sperm and egg to make a zygote. Seed dispersal- how?

The fruit From ovary…. Fruit protects seeds and aids in their dispersal Pericarp (thickened wall of fruit from ovary wall) Pericarp: Three layers

The seed (draw and label a named example) From fertilized ovule….. The mature seed: •seed coat (testa)-- function =protection •micropyle= small hole in testa that the root grows out of. cotyledons (seed leaves)= also food reserves The embryo is found between the cotyledons. It consists of: •radicle (embryonic root) plumule (embryonic shoot) Phaseolus vulgaris

Seed dormancy low metabolic rate and growth suspension Fun Fact:. Some lotus seeds which were 10,000 years old started to germinate when planted in suitable conditions by scientists! Source: http://www.saburchill.com/chapters/chap0047.html

Seed germination Germination: To begin to sprout or grow, (emergence of the radicle through the seed coat) Conditions for germination: Water (to rehydrate seed tissues) Oxygen (for respiration) Suitable temperatures (for enzymes) Light may influence some seeds as well. Radicle 1st, then shoot tip (hypocotyl); My be stimulated by light

Metabolism of Germination Water absorption activates metabolism Gibberellins (a class of plant growth hormone) is produced. Stimulates production of amylase breaks down starch to make maltose Transported throughout seedling and converted to glucose Used for energy and growth

Skill: Design of experiments to test hypotheses about factors affecting germination.

Control of Flowering Flowering involves a change in gene expression in the shoot apex. (response to photoperiod in many plants) PHOTOPERIODISM :The biological measurement of the relative lengths of day and night Phytochrome: Plant pigment that measures length of darkness in a photoperiod Two interchangeable forms: Pr (red absorbing) 660nm Pfr (far-red absorbing) 730nm http://glencoe.mcgraw-hill.com/sites/0003292010/student_view0/chapter41/animations_and_videos.html#

Control of Flowering: Long-day vs. short day plants. Long-day plant: Flower when days are long and nights are short. Short-day plant: Flower when days are short and nights are long. Important Note: Flowering in short-day plants such as chrysanthemums, is stimulated by long nights rather than short days. Critical night length

Think Application: Methods used to induce short-day plants to flower out of season. How could this be done?

End of IB stuff

Sexual Reproduction Alternation of generations: haploid (n) and diploid (2n) generations take turns producing each other Sporophyte (2n): produces haploid spores by meiosis; these spores divide by mitosis giving rise to male and female haploid plants called…. Gametophytes (n): develop and produce gametes by mitosis!

Gametophyte development Male gametophyte: microsporocyte (in pollen sacs of anther) divides by meiosis into 4-1N microspores; mitosis produces a generative cell (sperm) and a tube cell (pollen tube)= a pollen grain Female gametophyte: megasporocyte (in ovule) divides by meiosis to 4 cells, only 1 survives to a 1-N megaspore; 3 mitotic divisions forms the embryo sac; includes: 1 egg cell (female gamete) and 2 polar nuclei (synergids)

Double fertilization Pollination (pollen grain lands on a receptive stigma) Tube cell (pollen tube produced down the style) Generative cell forms 2 sperm by mitosis Enters ovary through micropyle 1 sperm fertilizes egg to form zygote; other sperm combines with 2 polar nuclei to form 3n endosperm (food-storing tissue)