S2 Science. Cells, DNA and Microbes. Summary Booklet. Class. Name

Transcription

1 S2 Science Cells, DNA and Microbes Summary Booklet Name Class

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3 Cells All living things are made of cells. Cells are too small to see with the naked eye. A microscope is needed to magnify cells, so they can be seen. Parts of a microscope Eyepiece lens High power objective lens Limb Focus knob Nosepiece Low power objective lens Stage clips Stage Light source Foot Part Eyepiece lens Limb Focus knob Nosepiece Stage Stage clips Light source Foot Objective lens Function (the job it does) Look through this to see the slide The arm used for carrying the microscope Is turned to bring the slide into focus, so you can see it clearly Turns around to select the correct objective lens Where the slide is placed Holds the slide in place A mirror or light bulb that shines light up through the slide The base on which the microscope stands The lens next to the slide that can be changed to alter the magnification

4 Calculating Total Magnification of a Microscope The magnification of an eyepiece lens is usually x 10, so it makes everything below it appear 10 times bigger. The magnification of the objective lens changes depending on which (low, medium or high power) you choose to use. The objective lens is below the eyepiece lens, so the TOTAL magnification is calculated by: Total = Eyepiece x Objective magnification magnification magnification e.g. = x10 x x4 = x40 Making a microscope slide Living material must be very thin to allow light to pass through it. A stain (e.g. iodine) is often used to make the cell structures easier to see. 1. Carefully spread the sample of cells thinly in the centre of the slide. Make sure the tissue is not folded. 2. Add a drop of stain (e.g. iodine) to the sample so you can see the structures more clearly. 3. Carefully lower a cover slip over the sample, taking care not to trap any air bubbles. If there are air bubbles covering the sample, lift the cover slip and lower it again. 4. Using the paper towel, dry the underside of the slide and remove any excess stain from the sides of the cover slip.

5 Animal Cells Animal cells contain a nucleus, cytoplasm and a cell membrane. Structure Function (the job it does) Nucleus Contains DNA and controls all the cell s activities Cell membrane Controls the entry and exit of substances Cytoplasm Where all the chemical reactions occur

6 Plant Cells Plant cells also contain a nucleus, cytoplasm and a cell membrane. However, green plant cells also contain a vacuole, chloroplasts and a cell wall made of cellulose. Structure Function Chloroplast Contains green chlorophyll to trap light energy. Cell wall Made of cellulose. Gives the cells shape and support. Vacuole Contains cell sap, a mixture of water, salts and sugar.

7 Variety of Cells There are many different types of plant and animal cells, each specially adapted to carry out a specific job. Cell Type Name of cell Diagram Function Animal Red blood cell Carries oxygen around the body Animal White blood cell Helps to fight infection Animal Nerve cell Carries messages to and from the brain Animal Muscle cell Contracts to allow movement Animal Sperm cell Carries DNA and fertilizes an egg cell Plant Leaf cell Contains chloroplasts to make food by photosynthesis Plant Guard cell Controls the opening of the leaf pore to allow gas exchange

8 DNA The nucleus of the cell contains chromosomes. Chromosomes are made of genes. Genes are made of DNA. Your DNA is unique to you (unless you have an identical twin) and is inherited from your parents. The genes we inherit from our parents make proteins and these proteins make us look the way we do e.g. hair colour, eye colour, etc. Mother 2 copies of DNA in each cell Where do our genes come from? From our parents egg from mother nucleus containing 1 copy of mother s DNA sperm from father nucleus containing 1 copy of father s DNA Father 2 copies of DNA in each cell Child Cell divides DNA from both parents Each cell has a complete set of DNA Fertilised egg nucleus containing complete set of DNA (set=2 copies, 1 copy from each parent)

9 However, the environment can also affect the way we look: Hair styles Injuries Tattoos Piercings Diet and Exercise can all affect our appearance too! DNA Profiling and DNA Databases Many people and organisations (scientists, doctors, the Police) are interested in analysing people s DNA and keeping information about their DNA in a database. A DNA database is a computer programme containing information about people s DNA. A DNA profile shows information about the DNA of an individual person. There are many advantages and disadvantages of DNA profiling and databases. You should be prepared to share your opinion of these issues.

10 Advantages of DNA Profiling and Databases: Police can use it as evidence from crime scenes Criminals can be identified more easily Victims can be identified more quickly Can be used to identify the parents or other relatives of a person Scientists can use it to find genes responsible for genetic diseases. Parents could have their DNA analysed to find out the risk of having a child that may be affected by certain genetic diseases such as cystic fibrosis Can be used to trace pedigree lines in animals e.g. dogs, horses, sheep, etc. Disadvantages of DNA Profiling and Databases: X People s DNA could be accessed without their permission (invasion of privacy). Details about their health and relatives could be seen X Insurance companies/ mortgage lenders might use the information to increase their prices for certain customers X Person might find out about a condition they didn t know they) or a relative) might have and be upset or anxious about it X DNA collected at a crime scene must be carefully collected and stored to ensure it doesn t become contaminated

11 Microbes A microbe is another name for a micro-organism. The main types of micro-organism are: Viruses Yeasts Bacteria Fungi A substance decays when it is broken down by micro-organisms. Microorganisms that cause decay are called decomposers. Substances that can be broken down by micro-organisms are biodegradable. Substances that cannot be broken down by micro-organisms are non-biodegradable. To grow, micro-organisms need: A suitable temperature Air (oxygen) Moisture A suitable food source Food can be preserved by: Method Condition removed Refrigeration Freezing Canning Vacuum packing Drying Warmth Warmth Air (oxygen) Air (oxygen) Water

12 Sterile nutrient agar has no microbes on it. A control plate is set up to prove that there were no microbes growing in the agar before the samples were added. A colony is made up of a group of the same type of microbes growing together. Some micro-organisms are useful for making products such as: Yeast for making wine, bread and beer Bacteria for making yogurt We have useful bacteria in our gut which help us with digestion. Some micro-organisms are harmful and cause diseases. Viruses can cause illnesses like: Chicken pox Measles Common cold Influenza (flu) Cold sores AIDS Bacteria can cause illnesses like: Tuberculosis Tetanus Impetigo Fungi can cause: Athlete s foot Ringworm Many bacterial infections can be controlled by using antibiotics. The effects of some viral infections can be reduced by using antiviral drugs.

13 Test yourself questions Cells 1. What 3 structures are found in both animal and plant cells? 2. In plant cells, what structure is found around the outside of the cells and what is it made of? 3. Name as many structures as you can that are found in the cells of green plants. 4. What is the function of each the parts you have named? 5. What is the function of (a) a red blood cell (b) a white blood cell (c) a nerve cell (d) a guard cell DNA 1. Where in a cell can you find chromosomes? 2. What are genes made of? 3. Where do we get our genes from? 4. What information is contained in your genes? 5. Does anyone else have the exact same DNA as you? 6. What environmental factors might affect your appearance? 7. What is a a. DNA database? b. What is a DNA profile 8. Who would you trust with your DNA? Explain why would you trust them? 9. Explain why DNA databases/ DNA profiling might be useful? 10. Explain the disadvantages of DNA databases/ DNA profiling? Microbes 1. What conditions do microbes need to grow and multiply? 2. Name some methods of preserving foods. 3. Explain the meaning of the term biodegradable 4. Explain why a scientist would set up a control plate when growing microbes in a lab. 5. What is a colony? 6. Explain why petri dishes used for growing microbes should be sealed and never reopened. 7. Name some useful micro-organisms. 8. Name as many illnesses/ conditions as you can that are caused by micro-organisms. 9. How can bacterial infections be treated? 10. What type of microbe causes athlete s foot?

14 Answers Cells 1. Nucleus, cytoplasm, cell membrane 2. Cell wall made of cellulose 3. Nucleus, cytoplasm, cell membrane AND cell wall, vacuole, chloroplasts 4. Nucleus controls all the cell s activities Cytoplasm where all the chemical reactions occur Cell membrane controls the entry and exit of materials 5. (a) transports oxygen to the body cells (b) helps fight infection (c) (d) carries messages to and from the brain controls the opening of the pore to allow carbon dioxide into the leaf and allow oxygen to get out DNA 1. In the nucleus 2. DNA 3. Our parents 4. The information to make proteins, to make us look the way we do e.g. eye colour, hair colour, etc. 5. No. Your DNA is unique to you, unless you have an identical twin!! 6. Hairstyle, diet, exercise, injuries, tattoos, piercings, hair dye, suntan, etc. 7. a. A DNA database is a computer that stores information about people s DNA b. A DNA profile contains detailed information about one person s DNA 8. This will be your personal opinion based on the discussions you had in class. 9. Might be useful for: Identifying and prosecuting criminals Identifying parents or other relatives Finding out if a person carries a gene for a genetic condition e.g. cystic fibrosis Giving parents information about genetic problems in their families to allow them to plan whether or not to have children/ get help quickly if they are going to have a child with a genetic condition 10. Possible disadvantages: invasion of privacy other people accessing the information without permission/ finding out about you health and family Suffering the anxiety of knowing you (or a relative) has a condition Possible to make mistakes with DNA profiling although giving inaccurate results is very rare Information being used to discriminate against certain individuals Microbes 1. a suitable temperature, moisture, air (oxygen) and a suitable food source 2. freezing, refrigeration, drying, canning (tinning), vacuum packing, wax coverings for cheese 3. means a substance that can be broken down or decayed by micro-organisms 4. to prove that there were no microbes growing in the agar before the samples were added i.e. the agar was sterile 5. a group of microbes of the same type growing together 6. to prevent the microbes from escaping so they can be disposed of safely 7. gut bacteria, yeast( for making wine, bread, etc.), bacteria (for making yoghurt, treating sewage, etc.) 8. e.g. athlete s foot, ringworm, impetigo, tuberculosis, tetanus, common cold, influenza, measles, chicken pox, AIDS and many more 9. SOME bacterial infections can be treated using antibiotics 10. fungus