Flower fruit seed lab domb reworked 10.12
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Flower fruit seed lab domb reworked 10.12 Document Transcript

  • 1. Second Form Science; Domb; 10/12/2012 Name: _________________________________Sexual Reproduction in Flowering Plants: PLANT REPRODUCTION AND PLANT PARENTINGScientific QuestionsLook for patterns in nature, and always ask“WHY?” Why do some plants produce flowers andfruits? Why do some plants produce flowers with no petals while others produce flowerswith beautiful petals? And what about the different petal colors and shapes? Why do plantsproduce yummy fruits? And why are some fruits not so yummy? Always ask “WHY?”Carrying CapacityAs you’ve learned, populations of organisms can grow at exponentialrates, but available resources limit the number of individuals in apopulation (Darwin’s Postulate #1; Carrying Capacity). Similarly,remember the trophic pyramids? One trophic level can only supporta limited number of organisms at the next trophic level. Allpopulations are constrained (in terms of numbers) by their access toenergy at the lower trophic level. Only so many individuals can grow,maintain and reproduce themselves at each trophic level because of the limitation of available resources.With that thought in mind, individuals that accomplish their tasks (of growth, maintenanceand reproduction) most efficiently – with the least amount of energy – will grow, surviveand produce more babies than those that require more resources to accomplish the sametasks. These more efficient individualspass on more genes than less efficient individuals;they will be “selected for”.Strategies So, why would any organism – plant or animal - put its valuable energy resources into what appear to be extravagant, expensive (requiring lots of energy) structures, like flowers and fruits? Why would a plant put its precious glucose it produced in photosynthesis into nectar, petals or sweet fruit?Perhaps these plant strategies – these adaptations - pay off. Perhaps those organisms that put theirprecious resources into the construction of flowers and fruits pass on more genes than those that do not, incertain environments.We will be exploring these plant strategies – these adaptations – in the following pages and in the followingactivities.Adaptation: a feature that has become prevalent in a population because of a selective advantageconveyed by that feature in the improvement in some function. 1
  • 2. PART 1: FINDING A PARTNER Sexual Reproduction In sexual reproduction, a new individual is produced by the combining of material from two parents. In sexually reproducing plants, as in animals, a sperm moves towards an egg. Fertilization occurs when the egg and sperm unite to start the development of theoffspring. All living things that reproduce sexually take some features from each parent. Next year’sflowers will resemble this year’s flowers because they inherit features from both of their parents.The flower is the structure that makes sexual reproduction in flowering plants possible.Flower anatomyThe stamen – contains the male part of the flower. Itproduces pollen, a yellow powdery substance. Pollen isproduced in the top of the stamen, in a structure called theanther. The female part of the flower includes the stigma,style and ovary. The top of the carpel is called the stigma.When a pollen grain reaches the carpel, it sticks to thesurface of the stigma and makes its way down through thestyle, allowing delivery of the sperm down to the ovary.This is the enlarged part of the carpel where the female sex cells (eggs or ovules) are produced. The transfer of the pollen from an anther to a stigma is called pollination. Most plants have strategies to guard against self-fertilization, and strategies to get their pollen to other plants. Grasses, oaks, pines, and willows are all wind-pollinated plants. They have simplified flowers without petals that release lots of pollen for the wind to carry.Wind-pollinated species produce lightweight, small and smooth pollen grains.Some plants produce flowers with petals; these are animal-pollinated plants.The petalsof the flower, andsometimes the scent of the flower, attract insects, birds or mammals that carry the pollen from one plantto another. These pollinators are rewarded with nectar (and/or anedible – non-reproductive form ofpollen), which they consume. As they are dining, the real pollen sticks to their faces or bodies. When theyfinish dining at one flower, they move off to another flower, and in the process drop the pollen from oneflower onto the stigma of another flower. 2
  • 3. PollinatorsThe color and shape of the petals are clues to which animal the plant is trying to attract.Animal pollinatedspecies have sticky or barbedpollen grains.Why would flowers that are designed to attract nocturnal pollinators (animals that are active at night) mostoften be white? The flowers of Carrion plants (image on left) smell strongly of rotting meat. What kind of insect do you think pollinates carrion flowers? Why?Can you think of any other ways pollen could be transferred from plant to plant? 3
  • 4. PART 2: THE BABYOnce pollen from one flower makes its way to the egg ofanother flower, fertilization occurs. A fertilized egg thendevelops into a SEED (the new baby!). All seeds are babies! Acorns are babies! Oak trees produce many babies!The problem for the parent plant is that its seeds – its babies:1) need food to grow;2) are vulnerable to the elements;and3) often have a better chance of survival away from the parent plant. Embryo = Seed leavesParents take up a lot of light, water and other resources. Babies will have abetter chance of survival where there is less competition from other plants. + shoot and rootSo parent plants do the following:1) depositstored chemical potential energy (lots of glucose in the form ofstarch = endosperm) around the embryo (thefertilized egg that has begun Shootto divide and grow); Root2) construct a protective covering (seed coat);3) develop ways to move the babies away from the parent plant.Seed dispersalUnlike animals, plants are limited in their ability to seek out favorable conditions for life andgrowth. As a result, plants have evolved many ways to disperse their offspring by dispersing their seeds. Aseed must somehow "arrive" at a location and be there at a time favorable for germination and growth. By wind Dandelion seeds (left) can be carried long distances by the wind. A milkweed seed pod opens up when the seeds are mature and the seedshave a wing that aids in wind dispersal. SO, WHAT IS A FRUIT? 4
  • 5. A fruit is extra packaging for the seed(s). Some fruit are very fancy and expensive for plants to make;others are simple and relatively cheap. This packaging helps seeds survive and sometimes the fruit helpsthe seed(s)move away from the parent plant.By waterSome plants producebuoyant seeds that can float in rivers to the oceans and wash up on beaches. Othersproduce buoyant fruits around their seeds that can survive water journeys.By animals Seeds with fruits that consist of barbs or hooks are useful because they attach to animal fur or feathers, and then drop off later. Seeds with fruit that consist of a fleshy covering (e.g. apple, cherry, juniper) are eaten by animals (birds, mammals, reptiles, fish) which then disperse these seeds in their droppings. Nuts (e.g. acorns, hazelnut, walnut) are fruits which consist of a hard outer wall that cover the seed coat. Nuts are usually packed with a great deal of storable food resources for the seed. This is why they are so attractive to animals that store their food, like squirrels. Plants that produce nuts typically produce a great number of them per season so that some of the nuts that are stored by animals like squirrels are stored some distance from the parent plant, and some will escape being eaten if the animal forgets them. Diagram of the anatomy of an acorn: A.)Cupule B.) Pericarp (fruit wall) C.) Seed coat (testa) D.) Cotyledons (2) E.) Plumule F.)Radicle G.) Remains of style. Together D., E., and F. make up the embryo. 5
  • 6. Prelab Questions1) What is a flower? A seed? A fruit?2) What are some roles fruit play in insuring seed dispersal? 6
  • 7. In labSeveral types of seeds have been soaking overnight. Choose 3 types and carefully dissect them. Draw yourobservations in the space below, noting the type of seed and labeling the seed coat, endosperm, andembryo for each. 7
  • 8. Consider the seeds and fruit below (provided in lab), and pictured as flowers. For each, make a fewobservations about the structure and infer how that can be useful to the embryo. Be sure to note whichportion is the seed and which portion is the fruit for each. Milkweed podreleasing seeds Mango fruit, seed exposed Raspberry fruit Horse chestnuts Coconut fruit and seed (they float!) 8
  • 9. Postlab QuestionsExplain the importance of the endosperm to the embryo, making reference to potential and kinetic energyin your answer.If you could follow every seed releasedfrom a single plant, chances are highthe placement of those seeds wouldresemble the diagram of a seedshadow (at right – this is not a literalshadow, it’s a metaphorical one).However, not every seed wouldgerminate and, of those that did, notevery embryo would grow into amature plant.Describe the graph in words. distance from parent plantWhy does a seed shadow take this shape? 9
  • 10. Which of the seeds pictured in the diagram below do you predict will have the best chances of producingmature plants? Explain.Name three different seed dispersal strategies plants use, and describe the adaptations that allow theseeds to disperse in these ways.Mistletoe plants are parasitic on other plants, that is, they grow on another plant’s branch and drive theirroots into the branch to get nourishment. Consider the following:The mistletoebird (Dicaeumhirundinaceum) of Australia isdependent on the fruits of mistletoe for its survival. Thoughquite common, mistletoebirds are inconspicuous and rarelyseen by untrained observers. They are effective dispersalagents for mistletoe because, although the fruits are eaten,the seed and its sticky coating pass through the birdundigested. Seeds pass out in the droppings and some aredeposited on tree branches where their sticky coating helps them to attach and 10
  • 11. grow. Mistletoebirds are credited with perching sideways on branches thus facilitating placement of theseed. In all, 33 bird species have been recorded feeding on mistletoe berries but the behavior and digestiveprocess of most do not aid mistletoe dispersal.1What does the mistletoe bird get from the mistletoe plant?What does the plant get from the bird?What kinds of traits have been selected for in the mistletoe plant population?1 http://www.dpi.vic.gov.au/dpi/nreninf.nsf/childdocs/-9599F8E44B161F63CA256BC800079622-738D5F5AA8EE28A2CA256BC800090A63-6F1B33D2E88612BE4A256DEA002933B4-B2A6433E6844F1D2CA256BCF00088823?open 11