165 Chapter 2 Answers: Biology: The Study of Life

2.2 Shared Traits of All Living Things: Review Questions and Answers

  1. Identify the seven traits that most scientists agree are shared by all living things.  Seven traits that most scientists agree are shared by all living things include homeostasis, organization, metabolism, growth, adaptation, response to environmental stimuli, and reproduction.
  2. What is homeostasis? What is one way humans fulfill this criterion of living things?  Homeostasis is the maintenance of a more-or-less constant internal environment. A human example is maintaining a constant internal body temperature regardless of the surrounding temperature.
  3. Define reproduction and describe two different examples.  Reproduction is the process by which living things give rise to offspring. An example of reproduction is a single cell dividing to form two daughter cells, which is how bacteria reproduce.
  4. Assume that you found an object that looks like a dead twig. You wonder if it might be a stick insect. How could you ethically determine if it is a living thing?  Answers may vary. Sample answer: To determine if the object is a living thing, I would poke it or blow on it and see if it responded to the stimulus. If it did — for example, by moving away from the stimulus — then it is probably a living thing and not just a dead twig.
  5. Describe viruses and which traits they do and do not share with living things. Do you think viruses should be considered living things? Why or why not?  A single virus, called a virion, consists of a set of genes (DNA or RNA) inside a protective protein coat called a capsid. Viruses have organization, but they are not cells and do not possess the cellular “machinery” that living things use to carry out life processes. As a result, viruses cannot undertake metabolism, maintain homeostasis, or grow. They do not seem to respond to their environment and they can reproduce only by invading and using “tools” inside host cells. The only traits viruses seem to share with living things is the ability to evolve adaptations to their environment. Students may or may not think viruses should be considered living things, but they should discuss recent evidence suggesting that viruses may once have existed as cells and shared an evolutionary history with cellular life.
  6. People who are biologically unable to reproduce are certainly still considered alive. Discuss why this situation does not invalidate the criteria that living things must be capable of reproduction.  Certain individual people may not be capable of reproduction, but they are still part of a larger group of organisms (the human species) that can.
  7. What are the two types of metabolism described here. What are their differences?  Catabolism and anabolism. Catabolism is the breaking down of matter, while anabolism is the building up of matter.
  8. What are some similarities between the cells of different organisms? If you are not familiar with the specifics of cells, simply describe the similarities you see in the pictures above.  Sample answer: Some similarities are having a nucleus, a cell membrane, and being the basic structural and functional unit of the organism.
  9. What are two processes in a living thing that use energy?  Sample answer: Maintenance of homeostasis and growth.
  10. Give an example of a response to stimuli in humans.  Answers may include responses to stimuli detected via any of the senses. Sample answer: When someone calls your name in a crowd, you probably turn to look for them.
  11. Do unicellular organisms (such as bacteria) have an internal environment that they maintain through homeostasis? Why or why not?  Bacteria are alive so they must maintain homeostasis of their internal environment, by definition. Their internal environment is the inside of their cell.
  12. Evolution occurs through natural  selection.
  13. If alien life is found on other planets, do you think the aliens will have cells? Discuss your answer.  Answers will vary. Sample answer: Not necessarily. By our definition, living things must have some kind of organization, but for potential alien life forms, this organization may take a different form than that of a cell.
  14. Movement in response to an external chemical is called chemotaxis, while movement towards light is called phototropism.

2.3 Basic Principles of Biology: Review Questions and Answers

  1. Self-marking
  2. How does sweating help the human body maintain homeostasis?  Sweating helps the human body maintain homeostasis by cooling the body when it starts to overheat so the internal temperature is kept more or less the same. When sweat evaporates from the skin, it uses up some of the excess heat energy on the skin, thus helping to keep the body cool.
  3. Explain cell theory and gene theory.  According to cell theory, all living things are made of cells, and living cells come only from other living cells. Gene theory states that the characteristics of living things are controlled by genes, which are passed from parents to their offspring.
  4. Describe an example of homeostasis in the atmosphere.  Sample answer: The concentration of oxygen in the atmosphere is maintained at 21 per cent by a balance between two opposing processes: removal of oxygen from the atmosphere by most living things and addition of oxygen to the atmosphere by living things such as plants.
  5. Describe how you can apply the concepts of evolution, natural selection, adaptation, and homeostasis to the human ability to sweat.  Sample answer: The human ability to sweat is an adaptation that helps maintain homeostasis in a hot environment by removing heat from the body when it evaporates. Like other adaptations, the ability to maintain homeostasis by sweating evolved by natural selection sometime in our evolutionary past.
  6. Which of the four unifying principles of biology is primarily concerned with:
    • How DNA is passed down to offspring? Gene theory
    • How internal balance is maintained?  Homeostasis
  7. Genes are located on chromosomes.
  8. Define an adaptation and give one example.  An adaptation is a trait that helps a living thing survive and reproduce in a given environment. Sample answer: The chameleon’s ability to change colour to match their background is an adaptation.
  9. Explain how gene theory and evolutionary theory relate to each other.  Gene theory states that genes are passed down from parents to their offspring. Genes determine the characteristics or traits of an organism. If these traits are particularly beneficial or adaptive, natural selection will cause the organisms with beneficial traits to produce more offspring compared to those without the beneficial traits. This results in a change in traits over time, which is called evolution.
  10. Does evolution by natural selection occur within one generation? Why or why not?  No. Evolution is defined as a change in the characteristics of living things over time. Evolution through natural selection causes differences in the amount of offspring produced. Having offspring (or not) is, by definition, more than one generation.
  11. Explain why you think chameleons evolved the ability to change their colour to match their background, as well as how natural selection may have acted on the ancestors of chameleons to produce this adaptation.  Sample answer: I think that when ancestors of chameleons could change their colour to match their background, they were less likely to be detected and killed by predators than those that couldn’t change their colour. Therefore, the individuals that had the colour matching ability were more likely to survive and reproduce than those that didn’t. This is an example of natural selection. Over time, this led to the population evolving the colour changing ability, as those that didn’t have the ability died out.

2.4 Diversity of Life: Review Questions and Answers

  1. What is biodiversity? Identify three ways that biodiversity may be measured.  Biodiversity refers to all the variety of life that exists on Earth. Three ways biodiversity may be measured are species diversity, genetic diversity, and ecosystem diversity. Species diversity, which is the commonest way of measuring biodiversity, refers to the number of different species in an ecosystem or on Earth as a whole. Genetic diversity refers to the variation in genes within all these species. Ecosystem diversity refers to the variety of ecosystems on Earth, where an ecosystem is a system formed by populations of many different species interacting with each other and their environment.
  2. Define biological species. Why is this definition often difficult to apply?  A biological species is a group of actually or potentially interbreeding organisms that are similar enough to each other to produce fertile offspring together. This definition is often difficult to apply because it isn’t always possible to make the observations needed to determine whether different organisms can interbreed. For one thing, many species reproduce asexually so individuals never interbreed. Also, it is usually impossible to know whether extinct organisms just represented by fossils could interbreed.
  3. Explain why it is important to classify living things, and outline the Linnaean system of classification.  It is important to classify living things in order to make sense of the overwhelming diversity of life on Earth. Classification is an important step in understanding the present diversity and past evolutionary history of life on Earth. The Linnaean system of classification consists of a hierarchy of groups called taxa that include the kingdom (most inclusive), phylum, class, order, family, genus, and species (least inclusive). Similar species are classified in the same genus, similar genera are classified in the same family, and so on all the way up to the kingdom.
  4. What is binomial nomenclature? Give an example.  Binomial nomenclature is the two-word method of naming species that was invented by Linnaeus. An example is the name of our own species, Homo sapiens.
  5. Self-marking
  6. Contrast the Linnaean and phylogenetic systems of classification.  The Linnaean system of classification is based on morphological similarities and differences among living things. It presents a static, or unchanging, view of the classification of living things that may or may not reflect their evolutionary history. A phylogenetic system of classification, in contrast, is a way of classifying living things that takes into account their phylogeny. Phylogeny is the evolutionary history of a group of related organisms. A phylogenetic classification is typically represented by a phylogenetic tree or other tree-like diagram, in which branching points represent common ancestors.
  7. Describe the taxon called the domain, and compare the three widely recognized domains of living things.  The domain is a new taxon that is a larger and more inclusive taxon than the kingdom. The three widely recognized domains of living things are the Bacteria, Archaea, and Eukarya. The Bacteria and Archaea domains consist only of single-celled organisms whose cells lack a nucleus. The Eukarya domain consists of both single-celled and multicellular organisms whose cells have a nucleus.
  8. Based on the phylogenetic tree for the three domains of life above, explain whether you think Bacteria are more closely related to Archaea or Eukarya.  Based on the phylogenetic tree, Bacteria appear to be more closely related to Archaea, because the Eukarya branched off from the Archaea lineage later.
  9. A scientist discovers a new single-celled organism. Answer the following questions about this discovery.
    • If this is all you know, can you place the organism into a particular domain? If so, what is the domain? If not, why not?  No, because all three domains of life contain single-celled organisms, so you cannot immediately identify it as being a member of any one domain.
    • What is one type of information that could help the scientist classify the organism?  Answers will vary. Sample answer: If the scientist knew whether or not the new organism had a nucleus, that would help them classify it because Eukarya have a nucleus and Archaea and Bacteria don’t.
  10. Define morphology. Give an example of a morphological trait in humans.  Morphology refers to the form and structure of organisms. Examples will vary. Sample example. Having four limbs is a morphological trait of humans.
  11. Which type of biodiversity is represented in the differences between humans?  Genetic diversity, since the differences are within the species.
  12. Why do you think it is important to the definition of a species that members of a species can produce fertile offspring?  Answers will vary. Sample answer: If individuals can interbreed but their offspring can’t reproduce, no further generations will be produced and the line will stop there. Therefore this line does not have the ability to be self-sustaining, and so the parents are not considered to be members of the same species.
  13. Go to the A-Z Animals Animal Classification Page. In the search box, put in your favorite animal and write out it’s classification.   Answers will vary.

2.5 The Human Animal: Review Questions and Answers

  1. Outline how humans are classified. Name their taxa, starting with the kingdom and ending with the species. Humans are classified in the animal kingdom, chordate phylum, mammal class, primate order, hominid family, genus Homo, and species Homo sapiens.
  2. List several primate traits. Explain how they are related to a life in the trees.  Answers may vary. Sample answer: Primate traits include five digits on each extremity with flat nails and sensitive pads, an opposable thumb, three-dimensional vision, and very mobile upper limbs. All of these primate traits are adaptations for life in the trees. For example, the features of the hands along with three-dimensional vision are important for being able to grasp the next limb while moving through the branches without falling to the ground.
  3. Self-marking
  4. What are hominids? Describe how living hominids are classified.  Hominids are the primate family in which humans are placed. This family includes four living genera: chimpanzees, gorillas, orangutans, and humans. Among these four genera are just seven living species: two in each genera except humans, with our sole living species.
  5. Discuss species in the genus Homo.  The only living species in the genus Homo is Homo sapiens, the species into which all modern living humans are placed. Several earlier Homo species existed but are now all extinct. An example of an earlier species of Homo that is now extinct is Homo erectus.
  6. Relate climatic changes to the evolution of the genus Homo over the last million years.  During the period from about 800,000 to 100,000 years ago, the size of the brain increased dramatically in species within the genus Homo and modern Homo sapiens emerged. This was also a period of rapid climate change, and many researchers think that climate change was a major impetus for the evolution of a larger brain. As the environment became more unpredictable, a bigger, smarter brain helped our ancestors survive. We were able to use culture and technology as behavioral adaptations because of our increasing brain size.
  7. Why is it significant that we share 93% to 99% of our DNA sequence with other primates? i The fact that we share 93 to 99 per cent of our DNA sequence with other primates indicates that we are closely related to these animals and shared recent common ancestors.
  8. Which species do you think we are more likely to share a greater amount of DNA sequence with — non-primate mammals (i.e., horses) or non-mammalian chordates (i.e., frogs)? Explain your answer.  We probably share more DNA sequence with non-primate mammals than non-mammalian chordates, because we are mammals ourselves and therefore are more closely related to other mammals than other types of chordates. The chordate phylum is a broader group than the mammalian class.
  9. What is the relationship between shared DNA and shared traits?  DNA encodes for certain traits. Therefore, animals with a high degree of similarity in their DNA will also likely have a high degree of similarity in their traits.
  10. Compared to other mammals, primates have a relatively small area of their brain dedicated to olfactory processing. What does this tell you about the sense of smell in primates compared to other mammals? Why?  This indicates that primates rely less on their sense of smell compared to other mammals because they have less brain area dedicated to the processing of smells. If their brains are not able to process as much information about odors, they cannot use that information as well, and will have a “worse” sense of smell than animals that have more brain area dedicated to olfactory processing.
  11. Why do you think it is interesting that nonhuman primates can use tools?  Answers will vary. Sample answer: Tool use indicates advanced planning and manipulation of the environment to create and use useful tools. Humans are obviously quite adept at creating tools and technology, thanks to our intelligence, so it is interesting that other species also have the intelligence to create and use tools.
  12. Explain why the discovery of Homo naledi was exciting.  Answers will vary. Sample answer: The discovery of Homo naledi was exciting because it was the discovery of a previously unknown early species of the same genus as modern humans. It is one of the largest samples of fossils for any extinct early Homo species, and the site suggests cultural practices similar to later humans. This discovery may give insight into our origins and our place in evolutionary history.

Chapter 2 Case Study Conclusion: Review Questions and Answers

  1. What are the four basic unifying principles of biology?  Cell theory, gene theory, homeostasis, and evolutionary theory
  2. A scientist is exploring in a remote area with many unidentified species. He finds an unknown object that does not appear to be living. What is one way he could tell whether it is a dead organism that was once alive or an inanimate object that was never living?  Answers will vary. Sample answer: He could look at the object under a microscope to observe whether it has cells. If it has cells, it was once alive.
  3. Cows are dependent on bacteria living in their digestive systems to help break down cellulose in the plant material that they eat. Explain what characteristics these bacteria must have to be considered living organisms themselves (and not just part of the cow).  The bacteria must have all the characteristics of living things, including homeostasis, organization, metabolism, growth, adaptation, response to stimuli, and reproduction.
  4. What is the basic unit of structure and function in living things?  Cells.
  5. Give one example of homeostasis that occurs in humans. Answers will vary. Sample answer: Temperature regulation.
  6. Can a living thing exist without using energy? Why or why not?  No, because all living things use energy through the process of metabolism.
  7. Self-marking
  8. Self-marking
  9. Give an example of a response to stimuli that occurs in a unicellular organism.  Some unicellular organisms can move in response to external chemicals. This is called chemotaxis and is an example of a response to stimuli.
  10. A scientist discovers two types of similar looking insects that have not been previously identified. Answer the following questions about this discovery.
    • What is one way she can try to determine whether the two types are the same species?  Answers will vary. Sample answer: One way to determine whether they are the same species is to try to breed them with each other to see if they can produce fertile offspring. If they can produce fertile offspring, they are the same species.
    • If they are not the same species, what are some ways she can try to determine how closely related they are to each other?  Answers will vary. Sample answer: She could use their morphology as well as their biochemical and genetic similarities and differences to help determine how closely related the two species are to each other.
    • What is the name for a type of diagram she can create to demonstrate their evolutionary relationship to each other and to other insects?  A phylogenetic tree.
    • If she determines that the two types are different species but the same genus, create your own names for them using binomial nomenclature. You can be creative and make up the genus and species names, but be sure to put them in the format of binomial nomenclature.  Answers will vary. Sample answer: I will call the genus Flighty and the two species-specific names will be redheadus and greenheadus. Therefore, the two species names in binomial nomenclature would be Flighty redheadus and Flighty greenheadus.
    • If they are the same species but have different colours, what kind of biodiversity does this most likely reflect?  Genetic diversity, because it is diversity within a species. The colouration is probably controlled by genes.
    • If they are the same species, but one type of insect has a better sense of smell for their limited food source than the other type, what do you think will happen over time? Assume the insects will experience natural selection.  Answers will vary. Sample answer: The insects with the better sense of smell for their limited food source will probably be more likely to find food than the other insects, and therefore will likely have a higher rate of survival and reproduction. Over time, this would lead to an increase in the number of individuals in the population with a good sense of smell, and this trait may evolve further to become even better adapted to the environment.
  1. Amphibians, such as frogs, have a backbone, but no hair. What is the most specific taxon that they share with humans?  Because frogs have a backbone, we know they are in the same phylum, the chordates, as humans. This is the most specific taxon that we share with frogs because they are clearly not mammals (they do not have hair), so they are not in the same class as humans.
  2. What is one characteristic of extinct Homo species that was larger than that of modern humans?   Answers may vary but can include: bigger jaws and teeth.
  3. What is one characteristic of modern humans that is larger than that of extinct Homo species?  Answers may vary but can include: bigger cranium and brain.
  4. How does the long period of dependency (of infants on adults) in primates relate to learning?  The long period of dependency of infants on adults in primates provides more time and opportunity for adults to teach the young animals.
  5. Name one type of primate in the hominid family, other than humans.  Answers will vary but can include: chimpanzees, gorillas, and orangutans.
  6. Why do you think that scientists compare the bone structures (such as the feet) of extinct Homo species to ours?  Answers will vary. Sample answer: Scientists compare structures between extinct Homo species and modern humans to see how similar or different they were to us. It can also give us information about how those structures functioned (such as how these species walked or used their hands) that can give us insight into their behaviors and lifestyle.
  7. Some mammals other than primates — such as cats — also have their eyes placed in the front of their face. How do you think the vision of a cat compares to that of a mouse, where the eyes are placed more at the sides? The cat more likely has better three-dimensional vision than the mouse because the forward placement of the eyes causes increased overlap in the visual fields between the two eyes.
  8. Living sponges are animals. Are we in the same kingdom as sponges? Explain your answer.  Yes, we are in the same kingdom as sponges because we are both animals. You probably do not use these sponges at your sink — those are usually man-made!

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Human Biology by Christine Miller is licensed under a Creative Commons Attribution-NonCommercial 4.0 International License, except where otherwise noted.

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