Lab 12: Flowers, Fruits & "Grocery Store" Botany

Transcription

1 BIOL 153L General Biology II Lab Black Hills State University Lab 12: Flowers, Fruits & "Grocery Store" Botany FLOWERS: As introduced in Lab 8, the term "flower" refers to sexual reproductive structures of angiosperms. Parts of a simple flower were introduced in Lab 8 but in reality, flowers are highly variable in shape, size, and arrangement and sometimes a "large flower" is many small flowers! The goal today is to learn principles of flower structure and anatomy and then apply this knowledge to a broad diversity of angiosperm species. In addition to assembling plant materials for you to inspect, your instructors have prepared a Supplement PDF with photographs and drawings; throughout this exercise, you'll be referred to pages of this document (e.g., Suppl. 1 = Supplement page no. 1). The "Floral Diversity" display area. Your instructors have arranged and labeled a diversity of flowers in a display area of the lab. Please visit this area, inspect the plant materials, and answer the following questions. 1. Recall from Lab 8 that flowers are in general composed of 4 whorls: sepals, petals, stamens (male), and pistil (female). Stamens are composed of anthers and filaments; pistils are composed of ovary, style, and stigma. Sketch the flower labeled morphology demo and identify these parts. Include the species name with your drawing! 2. Flowers with all four whorls (sepals, petals, stamens, pistil) are called complete. Flowers missing one or more whorls are called incomplete (see Textbook, Chapter 19, p. 463). a. Find one complete flower in the Floral Diversity display area and sketch it. Include the species name and be sure to show (or explain) why it is complete. b. Find one incomplete flower in the Floral Diversity display area and sketch it. Include the species name and be sure to show (or explain) why it is incomplete. Page 1

2 3. Flowers with both stamens and pistils are perfect (= bisexual & hermaphroditic). Flowers with either stamens or pistils but not both are imperfect (= unisexual) (Chapter 19, p. 463). a. Find one perfect flower in the Floral Diversity display area and sketch it. Include the species name and be sure to show (or explain) why it is perfect. b. Find one imperfect flower in the Floral Diversity display area and sketch it. Include the species name and be sure to show (or explain) why it is imperfect. 4. Monoecious (latin, one house ) species have separate male and female flowers on the same plant (i.e. male and female imperfect flowers). Dioecious ( two houses ) species have male and female flowers on different plants (Suppl. 2-5) (Chapter 19, p. 463). a. Sketch the plant identified as monoecious" in the Floral Diversity display area. Include the species name and explain why it is monoecious. Are the flowers perfect or imperfect? b. Sketch the plant identified as dioecious in the Floral Diversity display area. Include the species name and explain why it is dioecious. Are the flowers perfect or imperfect? Page 2

3 5. In flowers with radial symmetry (= regular or actinomorphic), components of a whorl are the same size and shape; any line drawn through the center will divide the flower into identical halves. In flowers with bilateral symmetry (= irregular or zygomorphic), one or more components of a whorl are different shapes; only one line will divide the flower into identical halves (Suppl. 6) (Textbook, Chapter 19, p. 465). a. Find one flower with radial symmetry in the Floral Diversity display area and sketch it. Include the species name and be sure to show (or explain) why it is radially symmetrical. b. Find one flower with bilateral symmetry in the Floral Diversity display area and sketch it. Include the species name and be sure to show (or explain) why it is bilaterally symmetrical. 6. Monocots tend to have flowers that have parts in multiples of 3s while dicots have flower parts in multiples or 4s or 5s. (Recall also that monocots have parallel leaf venation while dicots have net venation, and that there are characteristic differences in root structures and vascular tissues as well.) a. Identify two monocots in the Floral Diversity display area and sketch them (if you've not already sketched them above). How do you know these are monocots? b. Identify two dicots in the Floral Diversity display area and sketch them (if you've not already sketched them above). How do you know these are dicots? Page 3

4 INFLORESCENCES: In addition to the variability in sizes and structures of flowers, there is variation in how flowers are arranged. Some flowers occur singly at the end of the stem and are thus called solitary. However, multiple flowers are often clustered together on a stem, and this is called an inflorescence. Many types of inflorescences occur in angiosperms but here we will introduce just a few common types (Textbook, Chapter 19, p. 461). Solitary: Spike: Raceme: Umbel: Head (capitulum): A single flower attaches to the main stem. Multiple flowers attach directly to the main stem. Multiple flowers attach to the main stem by stalks (= pedicels). Multiple flowers attach by their stalks (= pedicels) to one attachment point on the main stem. Multiple stalk-less small flowers cluster together densely to form a single flower-like structure. The "Inflorescences" display area Your instructors have arranged herbarium sheets and live material showing types of inflorescences in a display area of the lab. Please inspect these plant materials and answer the following questions. 1. Which of the species on display shows a solitary arrangement of flowers? Sketch the arrangement of flowers on the species and then describe it. 2. Look at the example of Queen Anne s Lace and Tansy. Which one has an umbel inflorescence? Sketch the arrangement of flowers for both species and explain why one is an umbel and one is not. Page 4

5 3. Which of the species on display shows a raceme inflorescence? Sketch the arrangement of flowers on this species and then describe it. 4. Bring a dandelion back to your lab table and dissect it. (See also Suppl. 7-8.) Flowers such as dandelions and sunflowers have composite flowers each unit on the head is an individual flower. Look at the dandelion image in the Supplement PDF to understand the parts. Note that the anthers are fused and the style/stigma grows through the ring of fused anthers. The green leafy parts at the bottom of the flower head are not sepals they are bracts. Sepals are found at the base of individual flowers and is a modified feathery structure called the pappus. The corolla (petals) is fused at the base. Dissect the dandelion flower head and draw an individual flower. FRUITS: A fruit is the ripened ovary of a plant doesn t that sound appetizing? The seeds inside are the ripened ovules. Sometimes, accessory tissues will unite with the ovary as it matures. The primary functions of fruits are protecting seeds and aiding dispersal. Animals may eat fleshy fruits and deposit seeds with feces fertilizer or hooked, almost velcro-like fruits may stick to fur and be carried unintentionally. Some fruits have cottony or winged extensions that allow them to be carried by the wind. There are many fruit types we will describe only a subset in today s lab. Simple fruits form from one flower that has one pistil (with a single carpel or multiple fused carpels). Aggregate fruits form from one flower that has multiple free pistils. Multiple fruits come from the fusion of the ovaries from multiple flowers in an inflorescence. Accessory fruits contain accessory tissue (not ovary), and can be simple, aggregate, or multiple. Label the petals and pistils/ovaries on these images: Page 5

6 Apple (Malus) Pick up an apple flower, apple cross section, and apple longitudinal section from the front of the room (Suppl. 9). This link provides good information for interpreting the apple fruit: 1. Examine apple flowers a. Sketch sepals, petals, stamens, pistil(s), hypanthium (structure to which whorls attach), and pedicel (stem that attaches flower to tree). Count the number of each. If there are too many to easily to count, say >10. Do not destroy flowers they need to be used by multiple lab! b. Is the apple flower perfect or imperfect? Explain. c. Is the apple flower complete or incomplete? Explain. d. Does an apple have an inferior or superior ovary (see lab 8)? Explain. 2. Examine the apple cross section. In apple fruits, the hypanthium becomes the part that we eat. The core of the apple is the ovary, and the ovary wall is roughly equivalent to a circle that touches the tips of the five locules. Seeds, which develop in ovules, are in each locule. (Interesting note, apple seeds contain cyanide!) The ten vascular bundles of the calyx and corolla are in the hypanthium they look like small circles. This shows that the corolla and calyx were once attached to the hypanthium. Apples are fivemerous, meaning their flower parts occur in multiples of five. Look at Fig on page 464 and notice the apple flower has five petals. Dicots tend to have their flower parts in multiples of 4 or 5, while monocots have their flower parts in multiples of 3 (see also lab 8, Alstroemeria dissection). a. What are the calyx and corolla (see lab 8)? b. Sketch the apple cross section. Label hypanthium, ovary wall, locules, seeds, and vascular bundles (Suppl. 9). Page 6

7 3. Examine the apple longitudinal section. Sketch the apple longitudinal section. Label pedicel, sepals, hypanthium, ovary, style(s), and stamens. 4. Explain why an apple is considered a simple, accessory fruit. Blackberry (Rubus): Pick up a blackberry. Each tiny ball that composes a blackberry is a fruit with a fleshy outside and one seed inside (similar to a very small cherry). The little fruits are stuck to a receptacle that creates a hollow center when it is removed. A blackberry flower has many separate pistils; the ovaries of each develop into separate small fruits. (An apple flower looks similar to a blackberry flower but has just one pistil that produces the fruit.) (See Supplementary PDF page 11.) a. Explain why a blackberry is considered an aggregate fruit. b. Explain why a blackberry is a simple rather than an accessory fruit. Strawberry (Fragaria): Pick up a strawberry. The tasty red part is not ovary it is actually receptacle, which is a structure at the base of some flowers. The actual fruits are the seeds on the outside (these dry fruits are technically called achenes). Strawberry flowers have multiple unfused pistils which mature into multiple achenes. The receptacle grows as the fruit ripens, and achenes wind up stuck to its surface (see Supplementary PDF page 12). a. On the strawberry flower line drawing below, label the sepals, petals, stamens, pistils, ovaries, receptacle, and pedicel. Page 7

8 b. Sketch a strawberry fruit. Label the pedicel, sepals, petals and stamens (if present), receptacle, achenes, and styles (protruding from achenes). c. Do strawberries have inferior or superior ovaries? Explain. d. Explain why a strawberry is considered an aggregate accessory fruit. Pineapple (Ananas): Examine a pineapple. Pineapples form when multiple flowers in an inflorescence fuse together. The fused ovaries of the pineapple are the outer ring, while the core is the fleshy axis. Pineapple contains enzymes that can be used to tenderize meat. If you eat too much fresh pineapple especially the core, which is extra rich in enzymes it can actually tenderize (digest) your mouth! Sepals and bracts are visible on the outer surface. Seeds reduce the value of pineapple fruit, so growers do not allow them to be pollinated (Suppl ). a. Sketch the pineapple, showing ovaries, fleshy axis, and sepals. b. Explain why a pineapple is considered a multiple fruit. TOUR OF FRUITS & VEGETABLES ("GROCERY STORE BOTANY") In general usage, the term fruit applies to plant foods that are sweet, juicy, and dessert-like, while vegetable refers to plant foods that are less sweet and used for more savory purposes. From the botanical perspective, fruit is the ripened ovary while vegetable is not defined. Many foods that we consider vegetable are actually fruits! The tomato is the most famous example. It is definitely a fruit (=ripened ovary), but it is treated legally and in a nutritional context as a vegetable the U.S. Supreme Court even ruled the tomato was a vegetable in the late 1800s. Oddly, in Europe, the carrot a root rather than a ripened ovary has been legally defined as a fruit to justify its inclusion in jam. So, ignoring science and accepting popular opinion is not a new phenomenon! Vegetables are generally roots, stems, leaves, or flowers. Examine the foods displayed in lab and note whether they are fruit, root, stem, leaf, or flower. Be warned, some of the answers will be unexpected. Be sure to tell your friends during the next visit to the dining center, to impress everybody with your new-found botanical knowledge! Page 8

9 For each of the items on the following pages, sketch the object and label edible parts as fruit, root, stem, leaf, or flower some will have more than one answer! BANANA (see also Suppl. 15) Interesting trivia: bananas as we know them are on the verge of extinction. Watch the video at the following link for more information: a. Where are the seeds in the banana? b. Why are Cavendish bananas at risk of extinction? BROCCOLI (see also Suppl. 16) Interesting trivia: Broccoli (Brassica oleracea) is the same species as cabbage, Brussels sprouts, cauliflower, kale, collard greens, and kohlrabi. Read the link below to learn how artificial selection has generated the great phenotypic diversity found in this species. Artificial selection on the following plant parts in Brassica oleracea led to which types of vegetables? (e.g., kale, collard greens, Chinese broccoli, cauliflower, etc.) Leaves: Terminal bud: Lateral (axillary) buds: Stem: Inflorescences (flowers & buds): Page 9

10 BRUSSELS SPROUTS: (see also Suppl. 17) TOMATO: What are the leafy green appendages at the top of the tomato? ONION: The onion on display contains leaf, stem, and root. Identify each part on the onion. What are the concentric rings that make up an onion (i.e., what we eat)? Page 10

11 CARROT: Examine the dissected carrot. Locate the cortex and the endodermis, and note the protrusion of lateral roots from the pericycle into the cortex. Sketch the relevant parts below. POTATO: One of the potatoes on display sat in the bag too long. Note the white structures emerging from eyes of the potato. What structure on a winter tree branch is comparable? KALE or COLLARD: What other vegetable(s) shown in lab today are the same species as kale? Page 11

12 BELL PEPPER: a. In hot peppers, the most fiery (spicy) part is the membrane (not the seeds). Structurally, what does this membrane represent? b. What advantage does the pepper plant gain by production of this fiery spice? GREEN BEAN or SNAP PEA: When you trim fresh green beans, what structures are you removing? TURNIP: Page 12

13 CORN: (see also Suppl ) Where is the embryo in the corn kernel? Where is the endosperm? Compare the corn to the germinating bean seeds. How do beans and corn differ? Interesting trivia: In some areas of the U.S., detasseling corn is a lucrative (and challenging) summer job for young people. Read the following article for information about corn detasseling. - b a. What is the tassle at the top of the stalk (hint, this is where pollen is produced)? b. What flower structure is the corn silk (hint, it is part of the female flower)? c. Is corn monoecious, dioecious, or hermaphroditic? d. Why do growers of hybrid corn remove the tassels from most corn plants in a field? CELERY: a. One end of a celery stalk has been placed colored water. What structure is the dye illuminating in the celery (hint, it is not stem )? b. To better understand celery structure, compare it to rhubarb. What is the edible stalk of both celery and rhubarb? Page 13

14 Fruit & Vegetable summary table: Fill in the table below to assist with studying! Demo Name Cultural Name/ Category (Do you call it fruit or vegetable.) Botanical Category (Vegetative or reproductive part) Botanical Term for Edible Part (Stem, root, leaf, seed, fruit, flower) Tomato Vegetable Reproductive Part Fruit & Seeds Banana Broccoli Brussels Sprouts Tomato Onion Carrot Potato Kale/Collard Bell Pepper Green Bean Turnip Corn Celery Rhubarb Page 14