FOCUS-Chapter 3.pdf

TOPIC 3 Passing It On Everywhere you look there are examples of organisms that look more or less like...

TOPIC 3 Passing It On Everywhere you look there are examples of organisms that look more or less like their parents. How are these characteris- tics passed on from generation to genera- tion? You have already learned that the characteristics of organisms vary greatly within a species. How does reproduction allow for variation? Not only do the physical traits of organ- isms vary, but the ways in which organisms reproduce show variation as well. The plant shown in Figure 1.20 reproduces sex- ually (see page 32) and uses the wind to disperse its seeds. When a seed germinates Figure 1.20 This plant the new plant will have characteristics of both its parents. Whether you reproduces sexually and examine reproduction in bacteria, maple trees, or elephants, you will produces wind-borne seeds. notice characteristics that are passed on from parent to offspring. These traits are said to be inherited or heritable. Such traits are passed on in the genetic material, a subject you will learn more about in Topic 5. Living organisms display a wide variety of methods or reproductive strategies for passing on their genetic information to their offspring. Asexual Reproduction binary fission Reproductive strategies may be classified into two major types: asexual and sexual. Asexual reproduc- tion occurs when only one parent supplies the infor- spores mation to the offspring. The genetic material of the offspring, and thus their inherited characteristics, are identical to those of the parent. This type of reproduction is common among bacteria and fungi. vegetative growth in plants One advantage of asexual reproduction is that there is no need for an organism to find a mate. Also, reproduction can occur quite rapidly. As long as budding the environment does not change much, offspring produced by asexual reproduction will be able to survive Figure 1.21 Here are some of the diverse forms of and reproduce as their parents did. asexual reproduction we will look at in this Topic. Organisms pass on their traits in various ways. How would the use of wind-borne seeds increase variation in the plant species shown in Figure 1.20? Record your thoughts on this question in your Science Log as you read through Topic 3. 26 MHR Biological Diversity Binary Fission Many one-celled organisms such as the amoeba reproduce asexually using How many microscopic a form of cell division called binary fission. The cell first duplicates its spores do you think contents, including its nucleus and other organelles. After the amoeba might be produced by divides, each new cell has one mushroom? In one a copy of the genetic mate- species, each of the rial, as well as half of the gills underneath the cap of a single mushroom cytoplasm. As a result, the produces about 13 550 offspring are identical. spores on one side of Figure 1.22 Binary fission in an one gill. Keep in mind amoeba results in two “daughter” cells. that each cap of this species of mushroom Asexual Spores has about 150 gills. Some fungi, such as mushrooms, can reproduce asexually by forming Calculate the approximate single-celled, reproductive structures called spores. When asexual number of spores spores are formed, only one parent organism supplies the genetic produced by the cap of one mushroom. (Hint: material. Many spores are produced to ensure that at least some of them Remember that each gill survive. Some fungi and algae, such as the green algae Chlamydomonas has two sides.) and Ulva, produce zoospores, which move using tail-like flagella. Interestingly, fungi can also reproduce sexually — a process we will look at in more detail shortly. spores (cap) gill pileus Figure 1.23 The Earth star fungus releases millions of tiny spores. Suppose you get on a bus to go to school. At 8:20 A.M., you yawn and a single Streptococcus bacterium drifts into your open mouth and settles in your throat. Under ideal conditions, a single bacterium can reproduce by binary fission in 20 min. So, by the time the bus drops you off at school at 8:40 A.M., there are two bacteria in your throat. When your homeroom period starts at 9:00 A.M., there are four. Figure 1.24 Chlamydomonas is a unicellular 1. Assume that the bacteria continue to reproduce asexually every 20 green alga (magnification: 500x). It can min and your body does not fight them off. How many bacteria will reproduce asexually by forming zoospores. be in your throat by: (a) lunchtime (12:00 noon); (b) by the time you Why do you think zoospores have flagella? get the bus in the afternoon (3:20 P.M.); (c) suppertime (6:00 P.M.); (d) bedtime (10:00 P.M.)? 2. Make a graph showing the growth of the Streptococcus population in your throat over the 14 h period. You may create your graph using a computer. Why are relatively few mushrooms seen growing in our yards when the 3. Do you think bacteria can keep multiplying in this way indefinitely? number of spores produced is so high? Explain. Write a possible reason in your 4. At what time do you think your throat may feel sore? How many Science Log. bacteria will be present in your throat? Passing It On MHR 27  Asexual Reproduction in Plants You may remember that asexual, or vegetative, reproduction in plants can occur without the formation of special cells such as spores. Unlike many Research the African violet and make a sketch animals, plants continue to grow throughout their lives. The growing in your Science Log of a tips of roots and stems contain areas of rapidly reproducing cells called technique that could be meristem. At a certain point in the plant’s growth, meristematic cells used to grow several specialize into the cells that make up the roots, stems, and leaves of the African violets asexually plant. If any of these structures are later damaged, the meristem function from a leaf. is activated. Meristematic cells are then able to make repairs to damaged roots, leaves, or the stem of the plant. Asexual reproduction can occur in plants by activating the meristematic cells in different plant structures. Look up the origin of the You can make use of the meristem function by taking a cutting and word “clone.” Write a planting it. Cuttings from a parent stem may be used to produce new science fiction story that plants that are clones (exact copies) of the parents. features a clone! Find Out Asexual Reproduction in Duckweed Duckweed is a very small aquatic plant with 4. Over the next two weeks, count and record leaf-like structures called fronds. Duckweed the number of separate plants in each con- reproduces asexually by producing two or three tainer. Construct a table to show your results. daughter fronds from each parent plant. As the daughter fronds grow larger, they break away 5. At the end of two weeks, construct a line from the parent frond. Under suitable conditions, graph showing the number of plants that a new plant with a genetic program identical to were growing each day. Use two separate that of the parent may form within 24 h. lines to compare the numbers of plants growing in the two solutions. Materials daughter two small jars or fronds What Did You Find Out? Analyzing and Interpreting culture dishes 1. Describe the difference between the parent 100 mL distilled water mother and offspring plants. 100 mL Knop’s solution fronds rootlet 8 duckweed plants 2. How do you think the genetic material in the wax pencil offspring compares with that of the parent? Procedure Performing and Recording 3. What was the purpose of setting up one 1. Examine a duckweed plant. Identify the container with distilled water? fronds, rootlet, and daughter fronds. 4. Which container showed the greatest Sketch the duckweed in your notebook. number of new plants? Why? What does 2. Label two jars or culture dishes: A. Knop’s Knop’s solution contain? solution and B. distilled water. Place 5. Why do you think that the other dish 50 mL of the appropriate solution into displayed relatively less growth? each container. 3. Place four duckweed plants into each container and place them in a well-lit area. For tips on drawing graphs, turn to Skill Focus 10. Wash your hands when you are finished. 28 MHR Biological Diversity  S K I L L C H E C K Initiating and Planning Performing and Recording 1-D Analyzing and Interpreting Communication and Teamwork The Cloning Controversy Think About It their development is normal. This is important in You may have heard of Dolly the sheep. Dolly is a order to know whether or not human cloning clone, an identical copy of another sheep. She is the would be safe. first artificially cloned mammal. Cloning has many Procedure applications in the fields of agriculture, medicine, and forestry. However, the possibility of human State what is involved in the cloning issue. This cloning has attracted the most attention. may be in the form of a question or a statement describing the dilemma, but it should summarize the issue briefly and clearly. Gather information on cloning from newspa- pers, magazines, Internet sites, or television or radio broadcasts. How will you collect and record this information? Present possible alternatives. Consider alternatives such as permitting the cloning of Could cloning be used to produce armies of some species but not humans. super-soldiers or to make copies of great scientists Identify different perspectives on the issue. or professional athletes? Will parents in the future Who would want to speak on this issue? be able to choose children from a catalogue? Laws Think of as many people or groups are being put in place in Canada and other countries as possible. that will restrict the cloning of human beings. Bioethics is the study of moral issues in the fields Identify potential benefits and concerns for of medical treatment and research. Although there each alternative. Which alternative is likely to are many ways of analyzing bioethical issues, there be most acceptable by the community? are certain steps that are common to all discussions. In this investigation, you will consider the bioethics of cloning human beings. What are the advantages Analyze and disadvantages of human cloning? Should there be any controls on the experimentation? Might 1. Choose one of the following ways to analyze there be health risks for human clones that scientists this bioethical issue. are not aware of? Who should be allowed to perform Write out your analysis of the issue in the human cloning and under what conditions? form of a magazine or journal article. Create a poem, play, or story that pre- How Can Science Help? sents your analysis of the issue. Scientists must first understand cell structures and Make a poster that shows your position processes in order to identify ways to clone organ- on the issue and your reasoning. isms. To test their hypotheses about cloning, they must conduct many investigations. They must then make long-term observations of cloned mammals in order to monitor their health and check that For tips on societal decision making, turn to Skill Focus 8. Passing It On MHR 29  Budding Some animals, such as sea sponges and hydra, reproduce asexually by budding. A cell, usually near the base of one of these organisms, pro- duces a new group of cells called a bud. When the bud has completely The Mexican whiptail developed, it detaches itself and becomes independent. Yeast cells also lizard reproduces reproduce by budding. The bud, which contains its own nucleus, even- asexually. The females tually becomes a single, indepedent cell. lay eggs, which develop into baby whiptails. The strange thing about these lizards is that the eggs are never fertilized by male whiptails. In other words, the offspring have only one parent! These offspring end up with the same Figure 1.25 Sponge buds may remain Figure 1.26 Hydras are very small organisms attached to the parent, which results in a that live in water. Based on what you have genetic information as colony. What advantage does the bud have learned about budding, describe what is the mother lizard. by being attached to its parent? happening in this picture. Sexual Reproduction In general, sexual reproduction occurs when two parents supply genetic material to the offspring. Since both parents supply the genetic material, the offspring will not be exactly like either one. Instead, the offspring will display a combination of characteristics from both parents. While new combinations of characteristics occur in organisms that reproduce sexually, new combinations do not occur with asexual repro- duction. Can you think of some reasons why involving two parents in reproduction might be a useful adaptation? Figure 1.27 Different The Best of organisms use various forms of sexual zygospores Both Worlds reproduction. In fact, many Many organisms are capable organisms are capable of of both asexual and sexual both sexual and asexual reproduction! Some of the reproduction. As you learned bacterial forms of sexual conjugation earlier, in order to reproduce reproduction we will asexually, some moulds, such examine are shown here. as Rhizopus, produce spores. sexual reproduction Spores may be black, blue, in plants yellow, red, or some other When each sporangium, characteristic colour. Rhizopus or spore case, splits open, it releases spores that float can also reproduce sexually by about on air currents. sexual reproduction forming zygospores. As Airborne spores have been in animals shown on page 31, unlike found in the atmosphere asexual spores, zygospores at altitudes of more than contain genetic material from 160 km. two different sources. 30 MHR Biological Diversity  S K I L L C H E C K Initiating and Planning Performing and Recording 1-E Analyzing and Interpreting Communication and Teamwork Making a Mould Sporangia ASEXUAL You know that mould will grow on bread, but does Spores REPRODUCTION any kind of bread provide the right food source? Is there a difference between homemade bread and store-bought bread? What other conditions must mating type be present for bread mould to grow? Hypha Hypha mating type Question SEXUAL REPRODUCTION Are certain conditions required for the growth CONJUGATION of bread mould? Zygospore Hypothesis With your group, agree on a hypothesis about Long strands of cells called hyphae grow out of the Rhizopus why bread becomes mouldy in certain situations. spores. Where the tips of two hyphae touch, a zygospore, which contains genetic material from both hyphae, is formed. Safety Precaution Apparatus Materials culture dishes disposable gloves microscope or dissecting scope different types of bread camera (optional) sealing tape Mould is a biological hazard. tweezers water Never inhale mould spores. blank paper pencils Wash your hands after removing your gloves. Procedure to conduct your research. You should include With your group, design a procedure that will the use of a low-magnification microscope or allow you to test your hypothesis. Based on your dissection scope to examine the bread for hypothesis, predict what you expect to observe. results. Be sure to include steps for proper dis- posal of materials at the end of the experiment. In your design proposal be sure to include When you have received approval from your your hypothesis, prediction, the materials teacher, conduct your experiment. you will need, how you will record your observations, and the steps you will follow Wash your hands after this investigation. Analyze 3. How well does mould grow in different 1. Describe your results. Use charts, diagrams, situations? Under what conditions did you or photographs. Write brief descriptions to observe the most mould growth? accompany your illustrations. Extend Your Skills Conclude and Apply 4. With your group, design 2. Did your results support your hypothesis? an experiment to answer Why or why not? Did other groups get additional questions you For tips on designing have about the growth your own experiment, similar results using their procedures? of mould. turn to Skill Focus 6. Passing It On MHR 31  Bacterial Conjugation Some harmful bacteria Bacteria are able to transfer genetic material directly from one cell to are able to resist medicines another in a process called bacterial conjugation. As with conjugation such as antibiotics. Antibiotic resistance is a in fungi, bacterial conjugation is a primitive form of sexual reproduction heritable trait. One bacterial since two parent cells are involved. The benefit is that new combinations cell can quickly pass this of inherited characteristics may be trait on to another through produced as a result. conjugation. As a result, It is interesting to note that bacterial the spread of antibiotic conjugation results in genetic recombi- resistance in bacteria is nation but not reproduction, because very hard to control. there is no increase in the number of cells. Following conjugation, new cells will be produced by binary fission. At this time, the newly recombined genetic material (and characteristics) Figure 1.28 In bacterial conjugation a is passed on to the new cells. connection forms between two cells. The There are about 35 000 species of spore-bearing one-way transfer of genetic material plants, 700 species of from one cell to another can then occur. gymnosperms, and Sexual Reproduction in Plants 200 000 species of Plants have developed diverse adaptations and structures for reproduction. angiosperms living on Ferns and mosses reproduce by forming spores. Angiosperms and Earth today. Why do you gymnosperms reproduce sexually by forming seeds. As you may recall think angiosperms are so from your earlier work, angiosperms are flowering plants. Over half of successful? Record your thoughts on this question all known plant species are angiosperms. Some have large and showy in your Science Log as flowers like dahlias, chrysanthemums, or dandelions. Others, such as you read through the rest the flowers of grasses, are hard to see. Why do you think there are so of Topic 3. many different kinds of flowers? You may remember that gymnosperms do not produce flowers. Instead, they produce seeds inside of cones, which is why the largest group are called conifers. You are probably familiar with conifers such Like angiosperms such as as spruce, fir, and pine. maples, ginkgo trees shed their distinctively shaped leaves in autumn. However, Figure 1.29 Some ginkgoes are actually angiosperms, such as gymnosperms, and the these sunflowers, have last of an ancient group large blossoms. whose other members are now extinct. 32 MHR Biological Diversity  A Blueberry C Embryo flower development sepal leaf ovary seed coat pistil filament stem style stamen root anther stigma cotyledon petals B Pollen tube D Fruit formation development ovules develop egg into seeds ovule ovary blueberry fruit style ovary wall pollen grain stigma becomes juicy Figure 1.30 A The stigma, style, and ovary make up the pistil, the female part of the flower. The anthers, which are supported by the filaments, produce and store pollen grains containing sperm nuclei. Each stamen is composed of an anther and a filament. B When a pollen grain lands on the stigma, a pollen tube is formed. A sperm nucleus then travels down the tube to fertilize one egg. C Prior to fertilization, other cells in the ovule have been developing into a cotyledon, a structure that nourishes the embryo. Blueberry plants are dicotyledons, which means two cotyledons In self-pollination, both surround the embryo in each seed. D In angiosperms, a fruit, such as a pod, nut, or the sperm and egg cells come fleshy fruit of a berry, surrounds the developing seeds. The fruit usually develops from the wall from the same plant. of the ovary. However, wind, water, insects, birds, and other In sexual reproduction in plants and animals, fertilization occurs when animals often carry pollen an egg and sperm cell, the female and male gametes, join to form a new over from one plant to another. In this case, cell. The first cell of the growing organism, which contains genetic cross-pollination occurs. information from both parents, is called a zygote. In cross-pollination, You may recall that flowers are the reproductive organs of gametes from two differ- angiosperms. The female reproductive organ is called the pistil and ent parent plants are the male reproductive organ is the stamen. Figure 1.30 shows the involved. Gardeners who egg contained in the ovule at the base of the pistil. Pollen grains, each of grow orchids and other which contains a sperm nucleus, are produced on the plant’s stamens. expensive show-flowers, often keep the flowers in Try to locate some of these reproductive structures on a real flower. enclosed greenhouses. Pollination occurs after pollen reaches the pistil of a flower. As you Why? Why do you think can see in Figure 1.30, the pollen grain grows an extension called a cross-pollination would pollen tube. The pollen tube grows into the pistil until it reaches the be a useful adaptation ovule. Once the pollen tube has reached the ovule, the sperm nucleus for plants in the wild? travels down the tube to fertilize the egg. The zygote then undergoes Why would self-pollination be an advantage in some many cell divisions to form a multicellular embryo containing a minia- cases? In your Science ture leaf, root, and stem. The embryo is supplied with food by one or Log, list the advantages two cotyledons, and together these structures make up the developing of cross-pollination seed. When growing conditions are good in terms of warmth, mois- and self-pollination. ture, and oxygen in the soil, the seed will germinate. Passing It On MHR 33  Plants Reproduce Sexually and Asexually Many plants have adaptations for both sexual and asexual reproduction. As you have seen, some plants reproduce asexually from meristem cells. The Western wood lily grows wild in Alberta For instance, the bulbs of some flowers are really modified leaves that and Saskatchewan. store food for the plant. A new plant may emerge when the bulb is Unfortunately, over- planted in the soil. Why do you think angiosperms, which can repro- picking has made the duce sexually, have adaptations for reproducing asexually? flower rare in some areas. Picking the flowers damages the leaves that Figure 1.31A The potatoes we eat are actually part of an nourish the bulb. What underground stem called a tuber. The eyes of the new advantage does the potato are the buds of a new plant. These plants Western wood lily reproduce asexually by growing new shoots from have by being able to underground stems. reproduce asexually from bulbs? Does reproduction from bulbs add to variation in this species? How is variation increased in this wild flower? Write you answers in your Science Log. Figure 1.31B The spider plant reproduces asexually from special stems, called runners, shown here hanging from the main plant. Strawberries reproduce by forming runners that lie on the ground. Lilacs spread by producing suckers, which are outgrowths of the root or the lower part of the stem. Figure 1.31C Asparagus is a flowering plant and part of the lily family. Asparagus plants die back to the ground in the winter. In the At one time, large spore- spring, new plants regrow from their roots. Since it is very easy to grow plants such as bearing plants were the asparagus from the roots, growers may sell most numerous of all plant only the roots instead of the whole plant. species. In your Science Can you think of some advantages and Log, write a hypothesis to disadvantages of developing and selling suggest the type of climate plants this way? Earth must have had to support such populations of spore-bearing plants. Infer how climate change can affect plant survival. Figure 1.31D The life cycle of mosses is referred to as the Hint: mosses and ferns alternation of generations. This is because during one require moisture to part of the cycle, asexual spores are produced; in a later part of the cycle, egg and sperm cells are produced. complete the sexual stage The spores, which are produced in large numbers, are of reproduction. able to withstand unfavourable temperatures and dry conditions. They are also very light and can be carried great distances to locations with better growing conditions. On damp ground, a spore can develop into new moss. Sperm cells produced by the moss then swim to egg cells to complete the sexual stage of the life cycle. 34 MHR Biological Diversity Sexual Reproduction in Animals Animals have many different reproductive strategies. In all cases for sexual reproduction to be successful in animals (or plants), certain requirements must be met. Both male and female gametes must arrive While mating, a female frog may try to dislodge in the same place at the same time for fertilization to occur. The zygote the male who embraces requires specific conditions in order to develop. It needs enough nutri- her. Only males that ents and moisture, and in some cases, warmth and protection. can remain attached Gametes are delicate and dry out quickly. Their life spans are short, long enough will fertilize so the release of eggs and sperm must be carefully timed. A liquid envi- the eggs. How might ronment is important because it prevents drying and gives the sperm a this behaviour affect fluid to swim through to reach the egg. In animals such as sponges, the characteristics of the offspring? most worms, and many fish and amphibians, fertilization occurs outside the female. However, in insects, reptiles, birds, mammals, and some fish and amphibians, fertilization occurs within the body of the female. Why might internal fertilization be a useful adaptation for life on land? Figure 1.32 When frogs mate, the male and female release gametes into the water at the same time. With external fertilization, the risk to the sperm is extreme. Water must be present in order to keep the eggs and sperm alive. Fish or other animals may eat the gametes or water currents may sweep the sperm and eggs away from each other. Extreme temperatures, pollutants, or lack of oxygen may destroy the gametes. Since the majority of gametes are wasted, large numbers must be produced so that at least some will survive. Those that do may form zygotes, which will develop in the water. Mammals carry out internal fertilization, which is one of the reasons for their high rate of successful fertilizations, or reproductive success. With internal fertilization, egg cells are protected inside the body of the When sponges female parent where conditions are warm and moist. Sperm deposited by reproduce sexually, the male in the female’s body moves almost directly toward the egg, so they use internal risks to the survival of the gametes are greatly reduced. fertilization. Because If a mature egg cell is present, fertilization may occur. As with flower- sponges cannot travel ing plants, the egg and sperm join to form a zygote. In the for mating, sperm early stages of development, after the zygote grows must be released and divides many times, it is called an embryo. externally into the water. Once the sperm In most mammals the embryo develops close find their way to to or within the female’s body. another sponge, they are captured by special cells, taken Figure 1.33 Internal fertilization removes the dangers of harsh climates and possible predators. The moist into the sponge’s environment also helps the flagellated sperm to swim to the body, and transferred location of the egg within the female reproductive tract. As to the eggs internally. shown here, many sperm will reach the egg. However, only one sperm will fertilize the egg to form the zygote. Passing It On MHR 35  Figure 1.34 The female opossum gives birth to offspring that are smaller than a honeybee. To complete their development, they must remain in the mother’s pouch The duck-billed platypus for another three months. and the echidna are the only mammals that lay eggs. However, like other Figure 1.35 The reproductive mammals, the young are cycle of mammals and birds fed their mother’s milk and requires a great deal of one or protected until they can both parents’ energy. look after themselves. Many gastropods such as snails and slugs are hermaphrodites: each individual has both male and female reproductive organs. This is called simultaneous hermaphro- ditism. Others, however, are sequential hermaphrodites. They are male when younger and female when older and large enough to produce and carry eggs. TOPIC 3 Review 1. Explain the difference between budding and binary fission. There is great diversity in the strategies different 2. Apply Name one type of organism that reproduces both sexually and organisms use to asexually. Explain how this can occur. reproduce. Do you think that reproductive success 3. In what way is conjugation a primitive form of sexual reproduction? contributes to variation within a species? How is 4. Describe the exact location of the egg cell and sperm nucleus of a biological diversity related flowering plant. to reproductive success? 6. Thinking Critically Salmon lay eggs, while whales give birth to live Answer these questions in your Science Log. young. Which animal do you think probably produces more young at one time: the salmon or the whale? Explain your choice. 5. Thinking Critically Fireweed flowers are shaped so that they cannot pollinate themselves. Near the end of the growing season, however, a change occurs in any flower that has not been pollinated. The stamens curve around so that the anthers touch the stigma within the same flower. (a) Explain the reproductive advantage of preventing self-pollination in fireweed. (b) Explain the reproductive advantage of permitting self-pollination in fireweed. 36 MHR Biological Diversity