Biology Teach Yourself Series Topic 2: Cells

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1 Biology Teach Yourself Series Topic 2: Cells A: Level 14, 474 Flinders Street Melbourne VIC 3000 T: W: tssm.com.au E: TSSM 2013 Page 1 of 14

2 Contents Cells... 3 Prokaryotic and Eukaryotic Cells... 3 As it appears in Unit Review Questions... 5 Cells... 7 As it appears in Unit Review Questions... 8 Organelles... 9 As it appears in Unit Review Questions Organelles As it appears in Unit Review Questions Solutions to Review Questions TSSM 2013 Page 2 of 14

3 Cells Every living thing is composed of cells. A cell has an outer plasma membrane, which separates its contents from the external environment. Cytosol, the fluid component of cells, consists predominantly of water but also contains other dissolved substances. DNA contains the genetic material that controls the metabolism of the cell. Prokaryotic and Eukaryotic Cells As it appears in Unit 1 Cells are classified into two key groups, prokaryotes and eukaryotes. Prokaryotes lack membrane-bound organelles and contain a single, circular chromosome which floats free within the cytosol. Whilst they lack membrane-bound organelles prokaryotes do possess ribosomes that are involved in the synthesis of proteins. Eukaryotic cells do contain membrane-bound organelles, including a nucleus which holds numerous linear chromosomes. Prokaryotic organisms belong to the kingdoms Archaea and Bacteria. All are single celled organisms. The plasma membrane of these organisms is surrounded by a cell wall which is primarily composed of the complex carbohydrate murein. This differs from the cell wall of plant cells which is composed of the carbohydrate cellulose and that of fungi, which is composed of the carbohydrate chitin. Prokaryotic cells often possess flagella (as shown in the diagram below) or cilia to assist them in moving through their aquatic environment. Flagella Cell Wall DNA Ribosome Plasma Membrane Eukaryotic cells can belong to any of the four remaining kingdoms: Fungi, Plantae, Animalia or Protista. Whilst some Fungi are unicellular, most are multicellular and all are heterotrophic, meaning that they must obtain organic material by digesting other organisms. Unlike the prokaryotic organisms, fungal cells never have flagella or cilia and thus fungi are not able to move. TSSM 2013 Page 3 of 14

4 Members of kingdom Plantae are multicellular and, like fungi, are unable to move. Plants, however, differ from fungi as they are autotrophic. This means that they are able to produce organic compounds from inorganic materials using light energy. Plant cells possess a large central vacuole, which is used to store water and helps to provide the cell with rigidity. Animals are multicellular organisms, which are heterotrophs and need to consume and digest organic material. Animal cells possess membrane-bound organelles but they lack a cell wall. Kingdom Protista is the most varied of the five kingdoms. Protists can be both unicellular such as Amoeba or Paramecium and multicellular such as Sea Weed. They can be plant-like, animal-like or fungus-like but they lack the dedicated characteristics of fungal, plant and animal cells. TSSM 2013 Page 4 of 14

5 Review Questions 1. Use the diagram below to answer the following questions. a. To which kingdom would this cell belong? Why? b. Name one organelle that is visible in the above cell. c. Would this cell be able to manufacture enzymes? Explain. 2. Outline the difference between a heterotroph and an autotroph 3. A prokaryotic cell A. Has a circular chromosome B. Contains chloroplasts C. Lacks ribosomes D. Possesses a cell wall composed of chitin TSSM 2013 Page 5 of 14

6 Questions 4 and 5 refer to the following information. W X Y 4. The cell above is likely to be from a: A. plant B. bacteria C. fungus D. animal 5. Which structure is labeled with an X? A. nucleus B. vacuole C. ribosome D. chloroplast TSSM 2013 Page 6 of 14

7 Cells As it appears in Unit 3 Unit 3 Biology examines the functions of the cell. This includes cell death through either necrosis or programmed cell death (apoptosis). Within healthy tissues, there is a balance between cell replication and cell death. If this balance is disturbed and there is an unrestrained increase in cells a tumour results. A tumour that continues to grow and impacts on healthy tissue is considered malignant or cancerous. The main cause of tumours is a lack of apoptosis. In apoptosis cells respond to signals. There are two main signal pathways that instigate apoptosis: the death receptor pathway and the mitochondrial pathway. The death receptor pathway is activated when cells are no longer required even though they are still able to function normally. For example, in the embryo fingers and toes develop within groups of cells. The cells between the fingers and toes are not necessary and as a result receive an external message to undergo apoptosis. Specific receptors are found on the surface of cells receive the message to initiate apoptosis. When this message is received a chain reaction occurs: Caspases (enzymes that slice proteins) are activated and phagocytes are stimulated. The cells involved begin to shrink and caspases enter through the nuclear pores where they slice the DNA. Phagocytes consume the remaining organelles and release cytokines to inhibit the inflammation of nearby cells. The release of cytokines does not occur in necrosis. The mitochondrial pathway involves signals from inside a cell. These signals are initiated when major damage occurs to a cell, for example, the breakdown of internal membranes. This triggers a chain reaction within the cell, including the activation of caspases, which pass through the nuclear pores and dismantle the DNA. The remainder of the mitochondrial pathway is similar to the death receptor pathway outlined above. The mitochondrial pathway can also be activated by the cell itself when it becomes infected by a virus. This action prevents the virus from spreading to other cells and causing further harm to the host. Necrosis takes place when a cell becomes seriously damaged so that it is no longer able to control the movement of substances through the plasma membrane. This causes the cell to swell and burst, spreading its contents throughout nearby cells, causing the inflammation of surrounding tissue. TSSM 2013 Page 7 of 14

8 Review Questions 6. When a cell s DNA becomes damaged why does the cell undergo apoptosis rather than waiting for necrosis to set in? 7. What role does apoptosis play in the formation of a tumour? 8. Outline the role played by phagocytes in apoptosis. 9. Apoptosis A. Results in the production of new cells B. Can results in the death of healthy cells C. Is only triggered by external signals D. Recycles each part of the dead cell. TSSM 2013 Page 8 of 14

9 Organelles As it appears in Unit 1 Cells contain numerous organelles which are able to carry out a range of specific activities. A number of organelles are found in most cells, however, a small range of organelles are unique to some kingdoms or cell types. The following table details the function of a range of organelles. Cytoplasm The entire contents of a cell aside from the nucleus. It is composed of more than 90% water and also includes salts, enzymes and organelles (other than the nucleus). Cytosol: Chloroplast: The liquid transport medium of a cell. A green organelle found in some plant cells that is the site of photosynthesis. It is made up of numerous folded layers of membrane. Endoplasmic reticulum: An interconnected network of membranes that connects the plasma membrane and other organelles. It can be rough (with associated ribosomes) or smooth (lacking ribosomes). It is involved with the production, transport and storage of materials throughout the cell. Golgi apparatus: The site of the final synthesis and packaging of proteins into membrane-bound vesicles in preparation for being secreted from the cell. Mitochondria: Organelle made up of folded membranes that are the site of cellular respiration. Nucleus: Surrounded by a double-layered nuclear membrane (nuclear envelope), which contains pores that permit communication with the cytoplasm. The nucleus contains linear chromosomes composed of DNA and proteins. It controls cellular activities. Plasma membrane: Composed of a phospholipid bilayer, which encloses the cytoplasm in all cells. It controls the movement of substances into and out of the cell. It is also responsible for cell recognition and chemical communication between cells. Ribosomes: Small organelles that are not membrane-bound. They are either located in the cytosol or associated with endoplasmic reticulum. They are sites of protein production. Vacuole: Plant cells generally contain large central vacuoles containing cell sap that provides turgidity to the cell and acts as a depository for water and waste. Vacuoles are used by other kingdoms for digestion (food vacuoles) or water balance (contractile vacuoles). TSSM 2013 Page 9 of 14

10 Review Questions A B 10. a. To which kingdom does the cell above, most likely belong? How can you tell? Name and describe the function of organelles A and B. b. Organelle A Function c. Organelle B Function TSSM 2013 Page 10 of 14

11 11. The following questions relate to the cell shown below. A B a. Organelle A is a green coloured organelle, what is the function of this organelle? b. Organelle B contains cellulose, what is the function of this organelle? 12. Which one of the following supplies a cell with energy? A. A chloroplast B. A mitochondria C. A nucleus D. A vacuole 13. Which of the following organelles would be the most difficult to view under a microscope? A. Nucleus B. Chloroplast C. Mitochondria D. Ribosome TSSM 2013 Page 11 of 14

12 Organelles As it appears in Unit 3 Unit 3 explores a wider range of organelles, which are summarised in the table below and looks at the use of organelles to determine the function and kingdom of the cell in question. Plastids: A group of organelles found only in plant cells. They include chloroplasts, amyloplasts and tonoplasts. Tonoplast: The membrane of a plant cell vacuole that regulates the movement of substances into and out of the vacuole. Amyloplast: Centrioles: Starch granules that allow the plant to determine up and down. Composed of microtubules. Involved in the separation of chromosomes during cell division in protists and animal cells. Lysosomes: Membrane-bound vesicles that contain enzymes involved in the breakdown of foreign material and are present in most animal cells. Review Questions 14. Aside from a cell wall and a chloroplast, how could you differentiate between a plant and an animal cell? 15. A plant cell can be distinguished from an animal cell by the presence of a A. Nucleus B. Chloroplast C. Mitochondria D. Cell wall 16. The role played by lysosomes within a cell is A. Digestion of foreign material by enzymes B. Site of cellular respiration C. Site of water storage D. Repair of cell structures such as the cell membrane TSSM 2013 Page 12 of 14

7 Characteristics of Life

7 Characteristics of Life 1. Interdependence 2. Metabolism 3. Homeostasis 4. Cellular Structure and Function 5. Reproduction 6. Heredity 7. Evolution The Cell Theory All living things are composed of one