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Lab #6: Plant Reproduction Objectives: Observe the parts of the flower and their variations. Learn the functions of the parts of a flower (petal, sepal, carpel, stamen, anther, filament, stigma, style, ovary, ovule). Identify types of fruits and how they are dispersed, and observe how they are formed Identify the difference between gymnosperm seed cones and pollen cones Identify different parts of a seed. General Information Angiosperms have two characteristics that set them apart from the other plants: flowers and fruits. Flowers are structure specialized for sexual reproduction. Fruits are structures that help protect the seed and aid in dispersal of the seed. Seed dispersal is the movement of a seed to a new location. Plants that are able to disperse their seeds over a broad area have a greater chance of any one seed finding a good location to grow. Flower Structure Flowers consist of 4 whorls (or layers) of modified leaves: sepals, petals, stamens and carpels. Sepals are the outer whorl. They cover the flower before it is open, helping to protect it. They are often green, but may also be brightly colored, similar to the petals. Petals are the next whorl. They are often brightly colored. The coloration of both the petals and sepals functions to attract pollinators. Pollinators are organisms (typically insects, but some mammals) that move pollen from one flower to another flower. Flowers that are wind pollinated, like grasses, typically are not brightly colored. Stamens are the third whorl in, and are the male reproductive structures. They produce the pollen, which contains the male gametophyte which will produce the sperm. The pollen is formed in the anthers, and the filament attaches the anthers to the flower. The carpel is the female reproductive structure, found at the center of the flower, or the innermost whorl. There may be one or many carpels. (This structure is also referred to as the pistol.). The top of the carpel is the stigma. This is the structure that receives the pollen. The style connects the stigma to the ovary. The ovary contains the ovules, which contain the female gametophyte, which produce the eggs. An ovary may have one or many ovules (so one or many eggs). Lab #8: Plant Reproduction 1 When pollen lands on the stigma, the process is called pollination. Once the pollen lands, the sperm matures and burrows down the style, into the ovary and ovule to reach the egg. When the sperm and egg fuse, the process is called fertilization. Once the egg has been fertilized, the egg will go through several rounds of mitosis, forming the multicellular embryo, which is the developing plant. The seed will then begin to develop. A seed is the embryo and a food supply wrapped in a protective covering called a seed coat. The seed protects the embryo from drying out and provides food until the embryo is able to grow its first true leaves and start photosynthesizing to produce its own food. In angiosperms, the seed is enclosed in a fruit. A fruit is the ripened ovary of a flower. It functions to protect the seed and to aid in dispersal of the seed. Remember that gymnosperms also form seeds, but they are found naked on cones, not in a fruit. Part I: Flower Observations In order to identify angiosperms, botanists focus on flower and fruit structure. Leaf morphology can display plasticity and may change in response to environmental conditions, whereas flowers and fruits are more conservative. In order to understand the structure of a flower it helps to take it apart and examine each of its structures individually. Procedure: You will use your fingers and a razor blade to dissect the flowers. Use a watch glass to hold your specimen and examine it using the dissecting microscope. You will begin by removing the outermost segments and work your way inward. Make sure you examine each part of the flower under the dissecting scope. Record your observations in your notebook. Materials: • “Model” flower – Alstroemeria sp. • Second flower – your choice from the various specimens • Dissecting needle, razor blade, watch glass, dissecting scope A. Make a quick sketch of the intact flower, showing each part and their spatial relationships to one another. Identify each of the whorls (layers). B. Now observe each part separately under the dissecting scope. Use your fingers to remove the outermost layer (4th whorl) - this will be the sepals. After recording your observations, continue removing the layers (whorls) until you are done. Make sure you examine each part of the flower under the dissecting scope. You may place the table below in your notebook and use it to make a drawing and answer the questions. Lab #8: Plant Reproduction 2 Drawings/descriptions Sepals: Remove the sepals. How many are there? Color? Markings? Hairs? Function Petals: Remove the petals. How many are there? Color? Markings? Hairs? Stamens: Examine the stamens. How many are there? Shape of the anther? Where are the anthers located in relation to the stigma (higher or lower)? Is there pollen visible on the anthers? If yes, what color is the pollen? Carpels: Examine the carpel. Does the flower have a single carpel or multiple carpels? Describe the stigma. Is it branched? If so, how many branches? Ovary: Make a cross-section of the ovary at its widest point and exam it under the dissecting scope. How many chambers are present? Are there ovules present? How many? Lab #8: Plant Reproduction 3 Questions: 1. Identify each specimen as either a monocot or eudicot and explain how you determined that designation. 2. What do you think are the selective pressures for flower morphology? Hypothesize how these selective pressures may have affected the different flower types observed in lab (or on the greenhouse tour). Part 2: Demonstration stations Procedure: There are several demonstrations set up around the room. Go to each station and examine the specimens and answer the questions in your lab notebook. Make any additional drawings or notes necessary for you to remember the material and to be able to answer the questions. Part 3: Gymnosperm Reproduction After finishing with this station you should be familiar with: • Determining the difference between a mature seed cone and a mature pollen cone. • Identifying pollen, sporophylls, microsporangium and microspores. Demonstration slides: Pinus staminate cones Pinus pollen grains Identify sporophyll, microsporangium, microspores Identify pollen Questions: 3. How would you describe the difference between a seed cone and a pollen cone of a typical conifer? 4. How are seeds of conifers dispersed? Lab #8: Plant Reproduction 4