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Grade 11F Science Related Reading/Biology Name:____________________ Class:____________________ Diversity of Life Biology Gr11F Date:____________________ Read the passage below. Then answer the questions that follow. Gut Instinct Vocabulary Development Bacteria, a type of germ, are tiny organisms, each made of a single cell. They’re far too small to see with the naked eye — but don’t let their tiny size make you think they’re not important. You should get to know bacteria. For every cell in your brain, bones, organs and blood, there are 10 bacteria. They’re not going anywhere, so you might as well get used to them. Copy the key vocabulary written in bold in the space provided below. Try to write their definitions in your notebook Bacteria, which outnumber all eukaryotes combined, differ from eukaryotes in at least seven ways. Bacteria are prokaryotes. Unlike eukaryotes, prokaryotes lack a cell nucleus and all other membrane-bound organelles. They do contain ribosomes, granules of stored nutrients, enzymes, and certain internal structures, however. Most bacterial cells are about 1 µm in diameter; most eukaryotic cells are more than 10 times that size. They are single cells. Bacterial chromosomes consist of a single circular piece of DNA. Prokaryotes also have plasmids, small extra loops of DNA. They reproduce by binary fission, a process in which one cell pinches into two identical cells. Bacterial flagella are simple structures that spin like a corkscrew to move the cell. Some also have short, thin, protein tubes called pili that attach to surfaces or to other cells. ______________ ______________ ______________ ______________ ______________ Reading Check How many chromosomes does a bacterium have? Scientists classify bacteria based on their structure using a technique called Gram staining. Gram staining involves coloured dyes. Gram-positive bacteria have a thick layer of peptidoglycan in their cell wall and no outer membrane. They stain darkly with Gram staining dyes because their peptidoglycan layer is very thick. Gram-negative bacteria have a thin layer 1 Grade 11F Science Related Reading/Biology of peptidoglycan in their cell walls covered by an outer membrane. The thin peptidoglycan layer does not trap the dark dye, but does absorb the pink dye. Their outer membrane makes them more resistant to medicines and the body’s defenses than Gram-positive bacteria. These tiny organisms have diverse metabolic abilities. For example, some get their energy from sunlight through photosynthesis “photoautotrophs”. Others get energy from inorganic molecules that contain sulfur or nitrogen “chemoautotrophs”. Most bacteria get nutrients and energy by feeding on other organisms “heterotrophs”. Bacteria can be helpful: Some live in the intestines and aid with digestion. They can also be harmful: Some bacteria cause serious disease. And, believe it or not, some bacteria can be both helpful and harmful. For example, the kinds of E. coli bacteria that live in your intestines are helpful. But the kinds of E. coli consumed through contaminated food are a major cause of food poisoning. In a recent and surprising study, scientists suggest that bacteria living in the intestines can affect brain development and behavior. That connection may seem strange, since the brain and bowels are far apart. On the other hand, maybe the finding begins to explain why we talk about having a “gut instinct.” In the study, scientists from Sweden and Germany studied “germfree” mice that had been raised in a sterile environment and kept away from bacteria their whole lives. During various tests of mouse behavior, the germfree mice were more adventurous than regular mice. The germfree mice were bolder and more likely to take risks, like exploring new tunnels in mazes. Those tests suggest that bacteria can influence mouse behavior. To further explore the question of how bacteria acts on the brain, the scientists tried restoring bacteria to the germfree mice — and found another interesting twist. 2 Looking closer What type of bacteria cannot make their own food? _______________ _______________ _______________ _______________ _______________ _______________ _______________ _______________ _______________ _______________ __________ Grade 11F Science Related Reading/Biology After they received bacteria, newborn, germfree mice took fewer risks and acted like the mice that had always been around bacteria. But when the scientists exposed adult, germfree mice to bacteria, those mice didn’t change their behaviors. They remained bold and adventurous. The researchers don’t know how bacteria affect the brain. But the experiments show that bacteria somehow affect behavior, and the influence happens very early in the mouse’s life. This is a microscopic closeup of E. coli, your single-cell frenemy. The kinds of E. coli that live in your intestines help everything run smoothly. But when E. coli is ingested through contaminated food, the bacteria can cause big problems for humans. Credit: Rocky Mountain Laboratories, NIAID, NIH The researchers hope they can build on the study to eventually learn something about human behavior. But scientists know that the connection between bacteria and behavior in mice isn’t a direct one. People with fewer germs don’t necessarily put themselves in danger. And an unfortunate run-in with E. coli food poisoning isn’t going to make a person less likely to take risks — except, perhaps, in their choice of food. Sven Pettersson worked on the study connecting bacteria and brain development in mice. He is a microbiologist at the Karolinska Institute in Stockholm and the Genome Institute of Singapore. Microbiologists study life on the tiniest scales — like the single-cell existence of bacteria. Pettersson says that the study hints at interesting relationships that may exist between bacteria and other parts of the body. “It doesn’t take Einstein to realize that if you can do that for the brain, then [these kinds of] relationships could affect other organs in the body,” Pettersson told Science News. “It’s tickling to think about.” 3 Critical Thinking Are the ribosomes of E.coli surrounded by a membrane? Explain your answer. ______________ ______________ ______________ ______________ ______________ ______________ _______________ ___________________ Grade 11F Science Related Reading/Biology READING EFFECTIVELY In the space provided, write the letter of the phrase that best completes the statement. _____ 1. Most bacterial cells are a. more than 10 times larger than an average eukaryotic cell. b. as large as an average eukaryotic cell. c. one-tenth the size of an average eukaryotic cell. d. double the size of an average eukaryotic cell. _____ 2. Escherichia coli has long, thin, hairlike appendages called ___________, which are used for locomotion. a. flagella b. cilia c. pili d. ribosomes _____ 3. One difference between bacteria and eukaryotes is that a. bacteria have flagella whereas eukaryotes do not. b. bacterial chromosomes are circular, whereas eukaryotic chromosomes are linear. c. bacterial cells are much larger than eukaryotic cells. d. many bacteria are multicellular, whereas all eukaryotes are unicellular. _____ 4. Which of the following does not characterize the structure of Escherichia coli? a. a rigid cell wall b. flagella c. organelles d. pili _____ 5. Which of the following is an asexual form of reproduction in bacteria? a. transformation b. conjugation c. transduction d. binary fission _____ 6. Gram-positive bacteria stain purple because they have a. a thin layer of peptidoglycan in their cell wall. b. a thick layer of peptidoglycan in their cell wall. c. no peptidoglycan in their cell wall. d. no cell wall 4 Grade 11F Science Related Reading/Biology SKILL: READING EFFECTIVELY Read each question, and write your answer in the space provided. 1.Describe two ways in which prokaryotes differ from eukaryotes. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 2. What are chemoautotrophs? ______________________________________________________________ ______________________________________________________________ 3. If eight bacterial cells each undergo binary fission, how many bacterial cells will result? ______________________________________________________________ ______________________________________________________________ 4. In the study conducted by scientists in Sweden and Germany, what was the difference in behavior between “germfree” mice and regular mice? What does that indicate? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 5. Why do scientists believe that bacteria affect brain development and behavior in mice only if introduced early in life? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 6.How could scientists in the study obtain “germfree” mice? ______________________________________________________________ ______________________________________________________________ 5 Grade 11F Science Related Reading/Biology 7. Compare the structure of Gram-positive and Gram-negative bacteria. ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ 8. Why can infection by Gram-negative bacteria be more dangerous than in infection by Gram-positive bacteria? ______________________________________________________________ ______________________________________________________________ ______________________________________________________________ Complete each statement by writing the correct term or phrase in the space provided. 1. Bacteria often have small extra loops of DNA called ____________________. 2. The cell wall of bacteria contains a protein-carbohydrate compound called _______________________. 3. Gram-negative bacteria are more resistant to medicines because they have a(n) ______________________ ______________________. In the space provided, write the letter of the description that best matches the term or phrase. _____ 1. plasmid _____ 2. binary fission _____ 3. pili _____ 4. E. coli a. short outgrowths that enable bacteria to attach to surfaces or to other cells b. small extra loop of DNA c. asexual reproduction in bacteria d. helpful in intestines e. gets energy from other organisms _____ 5. heterotroph 6