2. Unit 3 Chemistry and Life

3. Menu To work through a topic click on the title. Photosynthesis and Respiration The Effect of Chemicals on the Growth of PlantsThe Effect of Chemicals on the Growth of Plants Food & Diet Drugs End

4. Photosynthesis and Respiration

5. Photosynthesis Plants make their own food by taking in substances from their surroundings (the environment). Plants use light energy to produce glucose from carbon dioxide and water. Oxygen is also produced.

6. This process is photosynthesis. The equation for the photosynthesis is: carbon dioxide + water  glucose + oxygen

8. During photosynthesis carbon dioxide is absorbed through the leaves of plants. Water is drawn up through the roots and oxygen gas is released into the air through the leaves. The light energy required for photosynthesis is absorbed by the chlorophyll in the leaves.

9. Respiration Animals need sources of energy. They use this energy for a lot of things, including warmth and movement. Animals can obtain energy from the reaction of glucose with oxygen to produce water and carbon dioxide. This process is called respiration.

10. Respiration is the reverse of photosynthesis. glucose + oxygen  carbon dioxide + water + energy Since photosynthesis and respiration are going on at the same time the amounts of oxygen and carbon dioxide in the air stay the same.

11. The Greenhouse Effect Carbon dioxide in the atmosphere causes the greenhouse effect. The clearing of forests means that less carbon dioxide is removed from the atmosphere by photosynthesis.

12. Increased levels of carbon dioxide in the air may also be due to greater use of fuels. More carbon dioxide in the atmosphere could cause it to keep more of the Sun's energy as heat, a process known as global warming.

13. Photosynthesis and Respiration Click here to repeat Photosynthesis and Respiration. Click here to return to the Menu Click here to End.

14. The Effects of Chemicals on the Growth of Plants

15. Using chemicals to save plants The amounts of healthy crops can be reduced in the following ways: crops are eaten by pests, e.g. insects and slugs bacteria and fungi can cause plants to become diseased weeds use up essential substances in the soil, so there is less food for the plants.

16. Pesticides are used to control pests Fungicides prevent diseases Herbicides kill weeds. Pesticides are toxic and so must be used with care. Natural predators can also be used to safely control pests.

17. Fertilisers For healthy plant growth the following elements are needed: Nitrogen Phosphorous Potassium. These elements are taken in through the roots of plants as compounds dissolved in water.

18. In areas of natural vegetation, decay of vegetable and animal remains returns all essential elements to the soil. Harvesting of crops prevents the natural return of these essential elements to the soil.

19. Fertilisers are added to the soil to restore essential elements. Examples of natural fertilisers include compost and manure.

20. Increased demand for food has resulted in the use of artificial fertilisers. Artificial fertilisers are made by the chemical industry The major artificial fertilisers are compounds containing ammonium, nitrate, phosphate or potassium. To be effective, fertilisers must be soluble in water.

21. The extensive use of nitrate fertilisers may have increased the amount of nitrates in rivers, lochs and the public water supply. The presence of large quantities of nitrates can leave the water lifeless.

22. Some plants, such as clover, beans and peas have root nodules which change nitrogen from the air into nitrates.

23. The Effects of Chemicals on the Growth of Plants Click here to repeat The Effects of Chemicals on the Growth of Plants Click here to return to the Menu Click here to End.

24. Food and Diet

25. Elements in the Body A balanced diet provides the body with all the elements and compounds you need. The main elements in your body are Oxygen Carbon Hydrogen Nitrogen.

26. Elements are present in the diet and in the body as chemical compounds and not as the free elements. Essential compounds include carbohydrates, fats and proteins. More than 60% of body weight is made up of water.

27. Minerals supply the body with small quantities of calcium for bones and teeth iron for the blood trace elements Some trace elements are toxic, if you take too much of them.

28. Carbohydrates Carbohydrates form an important class of food made by plants. Carbohydrates are used by the body to produce energy.

29. Carbohydrates are compounds which contain carbon, hydrogen and oxygen. Carbohydrates can be divided into sugars and starches.

30. Sugars Glucose, fructose, maltose and sucrose (table sugar) are sugars. Sugars are sweet and very soluble in water.

31. Most sugars can be detected by Benedict's test. Sucrose cannot be detected by Benedict’s test. Sugars are carbohydrates with small molecules.

32. Starch Starch can be distinguished from other carbohydrates by the iodine test. Starch is not sweet and does not dissolve in water.

33. Reactions of carbohydrates Starch is a polymer made of many glucose molecules linked together. Plants convert the glucose into starch for storing energy.

34. During digestion starch is broken down to glucose. Digestion takes place so that the carbohydrate can dissolve in blood. The glucose is carried by the blood stream to body cells where respiration occurs.

35. In digestion the starch is broken down by acid and by enzymes. Body enzymes function best at body temperature. Enzymes are destroyed at high temperatures.

36. Fats and Oils Fats and oils are important types of food obtained from both plants and animals.

37. Fats and oils are much more concentrated sources of energy than carbohydrates.

38. Fats and oils can be detected by a filter paper test. Put some oil or fat on a piece of filter paper and a transparent spot appears.

39. Animal fats are called saturates. Saturates are believed to increase the level of a substance called cholesterol in the bloodstream. A high cholesterol level may cause heart disease.

40. Vegetable oils are called polyunsaturates. Polyunsaturates are less likely cause heart disease.

41. Medical opinion suggests that it is better for your heart if you eat less fat. Where possible foods containing polyunsaturates should be eaten.

42. Proteins Proteins form an important class of food obtained from both plants and animals.

43. Proteins provide material for body growth and repair.

44. Testing for proteins If proteins are heated with soda lime an alkaline gas is released (turns pH paper blue).

45. Proteins Proteins are chemicals made from carbon, hydrogen, oxygen and nitrogen. Proteins are polymers made up of many amino acid molecules linked together.

46. The amino acids required to make animal proteins are obtained from animal and vegetable foods. In the body, animals make up particular proteins from those amino acids, as they are required for certain jobs.

47. During digestion proteins in foods are broken down to amino acids. A vegetarian diet must include a wide variety of vegetables to supply all the necessary amino acids.

48. Fibre Fibre keeps the gut working well, preventing constipation. Fibre absorbs water and swells

49. This swollen fibre is bulky so the gut muscles work on as food is squeezed along.

50. Vitamins Vitamins are complicated carbon compounds. They are needed to keep the body healthy.

51. If our diet lacks important vitamins we will suffer from poor health.

52. Food additives Food additives are substances which are added to the food we eat. Food additives can be used only if they have been tested and approved.

53. Food additives can be used to increase the nutritional value of food. Sometimes extra materials are added. Sometimes missing materials are supplied, for example vitamins and minerals

54. Food additives can be used to improve the keeping qualities of food. Adding food preservatives means that the food will not go off as quickly.

55. Food additives can also be used to: alter the appearance of food by adding colour. alter the taste of food by adding flavour.

56. Food and Diet Click here to repeat Food and Diet. Click here to return to the Menu Click here to End.

57. Drugs

58. A drug is a substance, which alters the way the body works. Drugs can damage health because of the way they can affect the body and lifestyle.

59. Alcohol Alcohol is a drug. If we take too much alcohol it can have many harmful effects on our bodies, particularly the liver and the brain.

60. Alcohol is measured in units. A bottle of alcopop or a pint of beer contains about 2 units. A pub measure of spirit or a glass of wine contains about 1 unit. Alcohol is broken down by the body at about 1 unit per hour.

61. Alcoholic drinks can be made by the fermentation of starch and sugars present in fruit and vegetables.

62. The type of alcoholic drink varies with the plant from which the starch or sugar comes.

63. Fermentation During fermentation glucose is broken down to form alcohol; carbon dioxide is also produced. Fermentation is brought about by enzymes present in yeast. The chemical name for the alcohol produced by fermentation is called ethanol.

64. Distillation Distillation is used to increase the concentration of alcohol in the liquid produced by fermentation. Water and alcohols are separated by distillation because they boil at different temperatures. This separation is not complete.

65. Other drugs Some drugs, including medicines, alcohol, nicotine and caffeine are legal. Other drugs, including cannabis, LSD and ecstasy are illegal. Being unable to manage without a drug is called addiction.

66. Methanol, another alcohol, is very poisonous, causing blindness and death. Methylated spirits (meths) contains methanol. It has both a colour and a bad tasting substance added to it to prevent people from drinking it.

67. Medicines Chemical reactions are going on all the time to keep the body working properly. Medicines contain drugs which help the body when it is not working correctly.

68. Some drugs, including antibiotics, can fight micro-organisms which interfere with the chemical reactions. Medicines are usually made up of many chemicals. Only some of these chemicals (the active ingredients) work on the body.

69. Drugs Click here to repeat Drugs. Click here to return to the Menu Click here to End.

70. The End Hope you found the revision useful. Come back soon!!