UNIT 1 CHEMICALS OF LIFE

Transcription

1 Biology Form 4 Page 1 Ms. R. Buttigieg UNIT 1 CHEMICALS OF LIFE In this unit we shall be by looking at the chemicals that make an essential part of our life and without which we cannot survive. We shall also be investigating the biochemistry (chemicals of life) of these substances and how they work together. 1.1 water (see GSCE Biology pg. 11) One of the most common substances in the world. Each water molecule is made up of 2 hydrogen atoms and 1 oxygen H 2 O. H Organisms need water in order to survive. Water makes up approximately 65 % of our body weight and cells contain about 75% of water. O H Water is important to living organisms because: It is a good solvent (substances can dissolve in it) important as many reactions of the body take place in solution. Chemical reactions in our cells take place in water Water takes part in important chemical reactions e.g. photosynthesis. Our blood plasma is mainly water so water helps in transporting substances around the body Water is found in sweat that cools us down Helps in keeping a constant body temperature due to its high heat capacity can absorb a lot of heat without changing a lot in temperature. Has a high heat of vaporization it absorbs a lot of heat before it evaporates. So our body can cool with only a small quantity of water being lost. Waste products are removed from our bodies in water It helps plants to remain turgid. Water boils (becomes a gas) at 100 o C and freezes (becomes a solid commonly referred to as ice) at 0 o C. So the majority of organisms cannot survive at or above 100 o C and at or below 0 o C as the cells are damaged due to the water they contain which changes its form.

2 Biology Form 4 Page 2 Ms. R. Buttigieg Experiment - The Occurrence of Water in Living Things 1. All living organisms consist mostly of water. 2. The adult human body is about 60% water, by weight, and 75% by volume. 3. As much as 95% of the weight of some plants is due to the water they contain. Experimental Question: Which organic material has the greatest percentage of water: grass, grapes, or carrot? State Your Hypothesis: Collecting Data 1. Weigh a handful of grass clippings then set them on a newspaper to dry overnight. Record data for before and after weights 2. Measure the weight of a few grapes, then cut them in half and place on newspaper to dry. Record the weight both before and after drying. Materials Needed balance grass clippings grapes newspaper carrot 3. Measure the weight of a carrot then cut into strips and set out to dry. Record data. Data Table Fresh (g) Dried (g) Total water lost (g) Percent Water grass grapes carrot Analysis 1. Why was it necessary to cut the items into strips? 2. Which material contained the most water (percentage)? 3. Grass is a leaf, grapes are fruits, and a carrot is a root. Based on the data of this lab, do different parts of the plant contain more water than others? Suggest a reason for this.

3 Biology Form 4 Page 3 Ms. R. Buttigieg 1.2 Composition and properties of carbohydrates, lipids and proteins (GCSE Biology Chapter 2 pgs 11-13; Food test experiments pg. 95) In this section we will be looking at the importance of these food types as: Energy sources Food stores Structural materials. We shall also be investigating the materials making them up. A. Carbohydrates These are organic substances that contain 3 elements: Carbon, Hydrogen and Oxygen. Hydrogen and oxygen are usually in the ratio of 2:1. Food sources include bread, cereals, sugar. These can be divided into 3 main groups: 1. Monosaccharides - carbohydrates made from a single sugar molecule. a. e.g. glucose, fructose, galactose. b. These are often made of ring structures c. They are soluble in water d. They are important as an energy source e. They serve as building blocks for larger molecules (disaccharides and polysaccharides) 2. Disaccharides carbohydrates made when two monosaccharides combine together. a. e.g. glucose and glucose combine to form maltose fructose and glucose combine to form sucrose b. When the 2 monosaccharides combine a water molecule (2 hydrogen and 1 oxygen) is lost we call this a condensation reaction. c. The bond linking them together is called a glycosidic bond.

4 Biology Form 4 Page 4 Ms. R. Buttigieg 3. Polysaccharides - carbohydrates made from many monosaccharides linked together (even with 10, 000). Three important polysaccharides are: starch, cellulose, glycogen i. Starch is a major food store in plants. ii. Glycogen is a major food store in animals. iii. Cellulose is the main component of cell walls and is very strong. These are made from lots of glucose molecules joined together. B. Lipids Like carbohydrates, lipids are compounds that contain the elements carbon, hydrogen and oxygen. The only difference is that lipids contain much less oxygen in their molecules. The most common lipids are fats and oils. The difference between them is that fats are solid at room temperature, while oils are liquids. Both fats and oils are insoluble in water. Lipids are made from 3 molecules of fatty acids and 1 molecule of glycerol. These lipids are known as triglycerides as they consist of 3 fatty acids combined with glycerol. The fatty acids, combine with glycerol in a condensation reaction where water is lost. There are many different fats and oils depending on the fatty acid that combines with glycerol. Examples of fatty acids are: Palmitic acid, oleic acid, stearic acid. We need fat: 1. as a store of energy 2. to make cell membranes 3. for warmth (insulation) 4. as some body organs are surrounded by fat for protection Too much fat can be harmful. Cholesterol is a fatty deposit that can narrow arteries and contribute to heart disease.

5 Biology Form 4 Page 5 Ms. R. Buttigieg C. Proteins These are complex organic substance made up of: carbon, hydrogen, oxygen, nitrogen and often sulphur and phosphorus. Our body cells are mostly made of protein. Proteins are made from many amino acids joined together. Amino acids are joined together by peptide bonds. Found in meat, eggs, fish, beans, and nuts. An amino acid contains an acidic group (COOH) and an amino group (NH 2 ) R* Amino group H H N C H C O OH Acid group R* is a different element or group for each amino acid. It is what makes amino acids different from each other. Amino acids join together by condensation reactions (water is removed) to form long polypeptide chains. Amino acid + Amino acid dipeptide Amino acid + Amino acid + Amino acid tripeptide Amino acid + Amino acid + Amino acid + Amino acid + Amino acid + polypeptide There are 20 different amino acids and these are combined together in different ways to form different proteins each having a different shape. If the shape is changed this can result in a different protein. When temperatures rise above 50 o C, proteins lose their shape and so their properties. We say that they have become denatured and their peptide bonds are broken. Even if the protein is cooled again the shape cannot be regained.

6 Biology Form 4 Page 6 Ms. R. Buttigieg We need proteins: 1. for growth and to build new cells which replace old ones. 2. as they form part of cell membranes and of some organelles of the cells (e.g. ribosomes) 3. for forming hormones and enzymes (these will be discussed later on) D. Fibre Fibre (also called roughage) comes from plants. Fibre is not actually digested; it just keeps food moving smoothly through your system. Fibre provides something for your gut muscles to push against, so prevents constipation. Cereals and vegetables contain a lot of fibre. Summary Food substance Elements present Use in body Deficiency disease Found in Carbohydrate Basic units are monosaccharides consisting of a 6 carbon ring, that join to form disaccharides or polysaccharides. Carbon (C), Hydrogen (H) Oxygen (O) There are always twice as many hydrogen atoms as oxygen e.g. C 6H 12O 6 Supply of energy (Glycogen is a store of energy, sugars are a ready supply) 1g yield 17 kj of energy Often linked to lack of enough food of any type i.e. starvation Cane sugar, sucrose, fruit and honey (glucose) Potatoes, rice, cereals (starch) Liver (glycogen) Protein Basic units amino acids joined together by peptide bonds Carbon (C), Hydrogen (H) Oxygen (O) Nitrogen (N) Often also Sulphur (S) Phosphorus (P) Growth and repair of cells and tissues, Making enzymes 1g yield 17 kj of energy Kwashiorkor: swollen abdomen, loss of hair Meat, fish, soya, milk, cheese, peas and beans, eggs Lipids (Fats & Oils) basic units are fatty acids joined to glycerol Carbon (C), Hydrogen (H) Oxygen (O) Store of energy, For insulation 1g yield 39 kj of energy Lack of certain fatty acids causes various diseases Dairy products, milk, fish, nuts, oils, fatty meat

7 Biology Form 4 Page 7 Ms. R. Buttigieg Food Tests Food Substances used for test Details of test Sign of a positive result Iodine solution Starch Drop iodine solution into the solution to be tested Solution turns blue black Glucose Benedict s solution Add Benedicts solution too the solution and boil in water bath for 2 minutes Solution turns orange red Fat Protein Ethanol Sodium hydroxide, copper sulphate (Biuret test) Ethanol is shaken with the substance to be tested and then a few drops of the ethanol are dropped in the water Add several drops of dilute sodium hydroxide solution followed by several drops of copper sulphate solution A milky white emulsion forms in the water Solution turns purple.

8 Biology Form 4 Page 8 Ms. R. Buttigieg Junior Lyceum Annual Complete the following table about food tests: What are the testing reagent/s? Reducing Sugar Starch Protein Lipid/Fat What is the colour of a positive result? Junior Lyceum Annual 2003 (8 marks) 2. A student claims that nuts are rich in oil and protein. Describe two separate simple tests by which the student can show that nuts are rich in these two nutrients. (3, 4) 3. Answer the following on a separate paper (or on the back of this page): 1. Why are carbohydrates important? 2. Name the two main carbohydrates. 3. What is the chemical test for starch? 4. What is the chemical test for glucose? 5. Why is fat needed in our bodies? 6. How would you test for fat? 7. Why is protein important to our cells? 8. What is the chemical test for protein? 9. Why is fibre important in our diet? 10. Name a food that contains fibre.

9 Biology Form 4 Page 9 Ms. R. Buttigieg 1.3 Vitamins (see GSCE Biology pg. 13, 88,89) We only need these in small amounts, but they are important for good health. These can be found in fruit, vegetables and cereals. Deficiency diseases occur if vitamins are lacking. Sources and functions of vitamins A, C and D in a human diet. Vitamin Source (Found in) Function Deficiency symptoms A Retinol Butter, milk, cheese, liver, margarine, eggs Important for the formation of a substance important in night vision. Helps resist disease. Poor night vision that may lead to complete night blindness. C Oranges, lemons, Keeps the skin strong and Without it the skin cracks and the Ascorbic acid grapefruit, carrots, potatoes, fresh green vegetables, tomatoes supple. Helps resistance to infections. gums bleed a condition called scurvy. Wounds fail to heal. D Butter, milk, cheese, Important in bone and tooth Calciferol egg-yolk, liver, fish formation. Also helps the liver oil. bones harden in children Natural fats in the skin change to a form of calciferol in sunlight. Without it the bones stay soft ( a disease called rickets). In adults causes osteomalacia which may result in fractures. Experiment to estimate the amount of vitamin C DCPIP is a liquid that loses its colour when it comes into contact with vitamin C. Pour 1cm 3 of DCPIP solution into a test tube. Take a 1cm 3 syringe of vitamin C and see how many drops it takes to decolorize the DCPIP. Compare the amounts of vitamin C in different fruit juices. DID YOU K OW THAT: Vegetarians do not eat meat but there are different kinds of vegetarians. Some don t eat meat but eat fish; others eat no meat or fish but eat dairy products. Vegans eat no animal products at all, but it is important they replace the protein, vitamins and minerals (like iron and calcium) with other forms like cereals, seeds, beans and nuts.

10 Biology Form 4 Page 10 Ms. R. Buttigieg 1.4 Mineral salt requirements (see GSCE Biology pg , 87,88) Also referred to as: mineral, salts or mineral salts. Functions of nitrogen and magnesium in plants. Plants obtain their minerals by absorbing them with the help of their roots from the soil. They pass into the xylem, which then transports them through the plant cells. Mineral Use in plant Deficiency symptoms Nitrogen For growth as it is important to build amino acids and proteins. Poor growth and yellow leaves Magnesium Used to make chlorophyll. Yellow leaves Note: Nitrogen is obtained in the form of nitrates from the roots. Sources and functions of calcium, phosphorus and iron in a human diet. Mineral Source (Found in) Function Deficiency symptoms Iron Red meat (liver & kidney), eggs, groundnuts, bread, spinach and gree n vegetables. Needed for the hemoglobin that is found in blood and is important in carrying oxygen round the body. Anemia not enough red blood cells. Insufficient hemoglobin is made and the oxygen carrying capacity of blood is reduced. Phosphorus Present in nearly all food. Mostly found in: cheese, meat and fish Needed in bones and in DNA Calcium Milk, cheese, hard tap water 1. Deposited in bones and teeth to make them hard. 2. Helps in blood clotting. 3. Helps in transmission of nerve impulses. Usually present so deficiencies don t occur Weak bones, rickets and excess bleeding.

11 Biology Form 4 Page 11 Ms. R. Buttigieg Work to do: 1. Choose 2 vitamins and 2 minerals and state a) the food in which they can be found, b) their uses in the body and c) their deficiency diseases. (12 marks) 2. Junior Lyceum Explain why each of the following is needed in the human diet. Name one good source for each. a. Calcium: (1) Source: (1) b. Iron: (1) Source: (1) c. Vitamin C: (1) Source: (1) 3. Junior Lyceum (total 6 marks) The table below shows four different snacks and four statements relevant to different food groups. MEAL STATEMENT A ) scrambled eggs on toast a) stops scurvy B) glass of milk b) helps towards healthy bones and teeth C) spaghetti c) body builders and iron providers D) glass of orange juice d) good energy food a) Pair up each of the meals above with the most appropriate statement. A B C D (4) b) People who do a lot of physical exercise often believe that they need a large amount of protein. (i) Explain why this belief may be wrong. (2) (ii ) Suggest a more appropriate nutrient and give a good source of the nutrient suggested. Nutrient Source (2)

12 Biology Form 4 Page 12 Ms. R. Buttigieg 1.5 Enzymes (see GSCE Biology pg ) Enzymes are PROTEI S that are capable of making reactions happen at a faster rate so are also CATALYSTS. Enzymes work on substances called the substrates. The place on the enzyme where the reaction takes place is called the active site. Each enzyme is specific for one substrate. Enzymes have 5 important properties: 1. They are all proteins 2. Each enzyme controls one particular reaction 3. They can be re-used 4. They are affected by temperature 5. They are affected by ph There are 2 main types of enzymes Breaker enzymes (catabolic) & Builder enzymes (anabolic) Breaker enzymes called catabolic enzymes help break large molecules into smaller ones. An example where these enzymes are important is in digestion where large food molecules are broken down into small ones that can be used. In the digestive system 3 of the main substances that need digesting are starch, proteins and fats. They are each broken down with the help of a different enzyme Food Broken into Enzyme Produced in Starch Maltose (a sugar) Amylase Mouth, pancreas Protein Amino acids Protease Stomach, pancreas Fat Fatty acids and glycerol Lipase Pancreas Answer these: 1. Name the enzyme that digests proteins 2. Explain why lipase does not digest starch. 3. List the 5 properties of enzymes

13 Biology Form 4 Page 13 Ms. R. Buttigieg Builder enzymes called anabolic enzymes help small molecules to join together and form bigger ones. These are important in helping to build important molecules in our cells. An example where builder enzymes are used is in the formation of new proteins from amino acids that are joined together by peptide bonds. Enzymes and temperature In many reactions, increasing the temperature results in an increase in the reaction rate, while decreasing them results in a slower rate. The same can be said for enzyme-controlled reactions. However, this is only true up to 50 o C for above this temperature, enzymes get denatured (lose their shape so cannot combine with the substrates) and cannot continue to carry out their function. Enzymes and ph What is the optimum temperature indicated by the graph? Most enzymes have a particular ph at which they work best. For example protease enzymes in the stomach work best at ph 2. Amylase (the enzyme in saliva) cannot work at this ph. The ph at which an enzyme works best is called the optimum ph. If an enzyme is placed in an extreme ph it can also get denatured.

14 Biology Form 4 Page 14 Ms. R. Buttigieg Intracellular and extracellular enzymes Intra means inside; extra means outside Intracellular enzymes are those that work inside cells in reactions that take place there; like respiration. Extracellular enzymes are those that are secreted from cells to work outside them, like what happens with fungi that digest food extracellularly by secreting enzymes e.g. on bread. Another example are the enzymes secreted into the digestive system by organs like the pancreas to break down food particles. Economic uses of enzymes (see GSCE Biology pg. 18, 330) Enzymes are cheap to use in industry as: They don t need high temperatures to work so less fuel needed Can be re-used so are only needed in small amounts. They are specific for particular substances so can be controlled more. Examples of enzyme uses are in: Brewing (making beer) Baking Cheese making Biological washing powders In brewing and baking enzymes present in living yeast change sugar to alcohol and carbon dioxide. In cheese making an enzyme called rennin is extracted from calves stomachs (now produced artificially by genetic engineering called chymosin). It helps in clotting milk in the first stages of cheese making. Complete the following: (9 marks) a) Enzymes up the rate of chemical. b) Enzymes are because they only work on one substrate. c) The substrate fits into the site on the surface of the. d) With an increase in, the rate of reaction but eventually a temperature is reached which the enzyme. e) Enzymes can be re-used, so only amounts are needed.

15 Biology Form 4 Page 15 Ms. R. Buttigieg 1.6 A balanced diet in humans (see GSCE Biology pg ) This is a diet containing the right balance of the different foods that meet the needs of individuals. These needs are dependent on the lifestyle, activity and developmental stage of an individual. Basically it must contain: Carbohydrates Lipids Proteins Minerals Vitamins Fibre Water In the right quantities. Foods like bread, cereal and potatoes they would be very important providing energy, and that would give us the energy for growth, the energy to run round to do normal activities, or the energy to go out and play. Fruit and vegetables would give us lots of important vitamins and minerals which we need and some of these can help protect us against heart disease and cancer. As for milk and diary foods go they would be very important from the point of view of providing enough calcium. Calcium is needed for bone development and growth. Meat and foods like chicken and fish and eggs, they are important for protein and also for some minerals and especially iron. Protein would be very important again for growth and the development of muscles and tissue which makes our body grow and iron is also important for healthy blood.