3. Chapter: Cell Processes Table of Contents Section 3: Energy for LifeEnergy for Life Section 1: Chemistry of LifeChemistry of Life Section 2: Moving Cellular MaterialsMoving Cellular Materials

4. Compounds are made up of two or more elements in exact proportions. For example, pure water is always made up of hydrogen atoms bonded to oxygen atoms in a ratio of two hydrogen atoms to one oxygen atom. Compounds and Molecules Chemistry in Life 1 There are two types of compounds— molecular compounds and ionic compounds.

5. The smallest part of a molecular compound is a molecule. A molecule is a group of atoms held together by the energy of chemical bonds. Molecular Compounds Chemistry in Life 1

6. Molecular Compounds Chemistry in Life 1 When chemical reactions occur, chemical bonds break, atoms are rearranged, and new bonds form. The molecules produced are different from those that began the chemical reaction.

7. Molecular Compounds Chemistry in Life 1 Water does not have the same properties as oxygen and hydrogen. Molecular compounds form when different atoms share their outermost electrons. Two atoms of hydrogen each can share one electron on one atom of oxygen to form one molecule of water.

8. Atoms also combine because they’ve become positively or negatively charged. Ions Chemistry in Life 1 Atoms are usually neutral—they have no overall electric charge. When an atom loses an electron, it has more protons than electrons, so it becomes positively charged.

9. When an atom gains an electron, it has more electrons than protons, so it becomes negatively charged. Ions Chemistry in Life 1 Electrically charged atoms—positive or negative—are called ions.

10. Ions of opposite charges attract one another to form electrically neutral compounds called ionic compounds. Ionic Compounds Chemistry in Life 1 Table salt is made of sodium (Na) and chlorine (Cl) ions. When they combine, a chlorine atom gains an electron from a sodium atom. The chlorine atom becomes a negatively charged ion, and the sodium atom becomes a positively charged ion.

11. These oppositely charged ions then are attracted to each other and form the ionic compound sodium chloride, NaCl. Ionic Compounds Chemistry in Life 1

12. Ionic Compounds Chemistry in Life 1 Messages are sent along your nerves as potassium and sodium ions move in and out of nerve cells. Calcium ions are important in causing your muscles to contract.

13. In a solution, two or more substances are mixed evenly. Mixtures Chemistry in Life 1 A suspension is formed when a liquid or a gas has another substance evenly spread throughout it. Unlike solutions, the substances in a suspension eventually sink to the bottom.

14. All living things are made up of compounds that are classified as organic or inorganic. Organic Compounds Chemistry in Life 1 Rocks and other nonliving things contain inorganic compounds. Organic Compounds always contain carbon and hydrogen and usually are associated with living things.

15. Organic molecules can contain hundreds or even thousands of atoms that can be arranged in many ways. Organic Compounds Chemistry in Life 1

16. Organic Compounds Chemistry in Life 1 Four groups of organic compounds make up all living things—carbohydrates, lipids, proteins, and nucleic acids.

17. Carbohydrates are organic molecules that supply energy for cell processes. Carbohydrates Chemistry in Life 1 Sugars and starches are carbohydrates that cells use for energy. Some carbohydrates also are important parts of cell structures.

18. Lipids do not mix with water. Lipids Chemistry in Life 1 Lipids such as fats and oils store and release even larger amounts of energy than carbohydrates do. One type of lipid, the phospholipid, is a major part of cell membranes.

19. Certain proteins called enzymes regulate nearly all chemical reactions in cells. Proteins are made up of smaller molecules called amino acids. Proteins Chemistry in Life 1 Proteins are the building blocks of many structures in organisms. Your muscles contain large amounts of protein. Proteins are scattered throughout cell membranes.

20. Another nucleic acid, ribonucleic acid, or RNA, is needed to make enzymes and other proteins. Large organic molecules that store important coded information in cells are called nucleic acids. Nucleic Acids Chemistry in Life 1 One nucleic acid, deoxyribonucleic acid, or DNA—genetic material—is found in all cells at some point in their life.

21. Inorganic compounds are the source for many elements needed by living things. Most inorganic compounds are made from elements other than carbon. Inorganic Compounds Chemistry in Life 1 Generally inorganic molecules contain fewer atoms than organic molecules.

22. Inorganic compounds can contain the elements nitrogen, phosphorus, and sulfur. Inorganic Compounds Chemistry in Life 1 One of the most important inorganic compounds for living things is water.

23. Living things are composed of more than 50 percent water and depend on water to survive. Importance of Water Chemistry in Life 1 You can live for weeks without food but only a few days without water.

24. Importance of Water Chemistry in Life 1 Although seeds and spores of plants, fungi, and bacteria can exist without water, they must have water if they are to grow and reproduce.

25. All the chemical reactions in living things take place in water solutions, and most organisms use water to transport materials through their bodies. Importance of Water Chemistry in Life 1 Plants use water to move minerals and sugars between roots and leaves.

26. The atoms of a water molecule are arranged in such a way that the molecule has areas with different charges. Characteristics of Water Chemistry in Life 1 Water molecules are like magnets. The negative part of a water molecule is attracted to the positive part of another water molecule just like the north pole of a magnet is attracted to the south pole of another magnet.

27. This attraction, or force, between water molecules is why a film forms on the surface of water. Characteristics of Water Chemistry in Life 1 The film is strong enough to support small insects because the forces between the water molecules are stronger than the force of gravity on the insect.

28. Because water molecules are so strongly attracted to each other, the temperature of water changes slowly. Characteristics of Water Chemistry in Life 1 The large percentage of water in living things acts like an insulator. The water in a cell helps keep its temperature constant, which allows life- sustaining chemical reactions to take place.

29. When water freezes, ice crystals form. Characteristics of Water Chemistry in Life 1 In the crystals, each water molecule is spaced at a certain distance from all the others. Because this distance is greater in frozen water than in liquid water, ice floats on water. Bodies of water freeze from the top down. The floating ice provides insulation and allows living things to survive.

30. Passive Transport Cells take in food, oxygen, and other substances from their environment. They also release waste material. A cell has a membrane around it that works like a window screen. Moving Cellular Materials 2 A cell’s membrane is selectively permeable (PUR mee uh bul). It allows some things to enter or leave the cell while keeping other things outside or inside the cell.

31. Passive Transport Which way things move through a cell membrane depends on the size of the particles, the path taken through the membrane, and whether or not energy is used. Moving Cellular Materials 2 The movement of substances through the cell membrane without the input of energy is called passive transport. Three types of passive transport can occur.

32. Diffusion Molecules in solids, liquids, and gases move constantly and randomly. Moving Cellular Materials 2 This random movement of molecules from one area where there is relatively more of them into an area where there is relatively fewer of them is called diffusion, which is one type of cellular passive transport.

33. Diffusion Molecules of a substance will continue to move from area into another until the relative number of these molecules is equal in the two areas. When this occurs, equilibrium is reached and diffusion stops. Moving Cellular Materials 2

34. Osmosis—The Diffusion of Water Water molecules move by diffusion into and out of cells. The diffusion of water through a cell membrane is called osmosis. Moving Cellular Materials 2 If cells weren’t surrounded by water that contains few dissolved substances, water inside of cells would diffuse out of them.

35. Osmosis—The Diffusion of Water Losing water from a plant cell causes its cell membrane to come away from its cell wall. Moving Cellular Materials 2 This reduces pressure against its cell wall, and a plant cell becomes limp.

36. Osmosis—The Diffusion of Water If water around the cells would move into them, the cells would fill with water. Moving Cellular Materials 2 Their cell membranes would press against their cell walls. Pressure would increase, and the cells would become firm.

37. Facilitated Diffusion Some substances pass easily through the cell membrane by diffusion. Moving Cellular Materials 2 Other substances, such as glucose molecules, are so large that they can enter the cell only with the help of molecules in the cell membrane called transport proteins. This process, a type of passive transport, is known as facilitated diffusion.

38. Active Transport Sometimes a substance is needed inside a cell even though the amount of that substance inside the cell is already greater than the amount outside the cell. Moving Cellular Materials 2 For example, the roots of a plant already might contain more of those mineral molecules than the surrounding soil does.

39. Active Transport The tendency is for mineral molecules to move out of the root by diffusion or facilitated diffusion. Moving Cellular Materials 2 When an input of energy is required to move materials through a cell membrane, active transport takes place.

40. Endocytosis and Exocytosis Large protein molecules and bacteria, for example, can enter a cell when they are surrounded by the cell membrane. Moving Cellular Materials 2 The cell membrane folds in on itself, enclosing the item in a sphere called a vesicle. Vesicles are transport and storage structures in a cell’s cytoplasm.

41. Endocytosis and Exocytosis This process of taking substances into a cell by surrounding it with the cell membrane is called endocytosis (en duh si TOH sus). Some one-celled organisms take in food this way. Moving Cellular Materials 2

42. Endocytosis and Exocytosis The contents of a vesicle can be released by a cell using the process called exocytosis (ek soh si TOH sis). Moving Cellular Materials 2 Exocytosis occurs in the opposite way that endocytosis does. A vesicle’s membrane fuses with a cell’s membrane, and the vesicle’s contents are released.

43. Trapping and Using Energy All of the activities of an organism involve chemical reactions in some way. The total of all chemical reactions in an organism is called metabolism. Energy for Life 3 The chemical reactions of metabolism need enzymes.

44. Trapping and Using Energy Enzymes in cells cause a change, but the enzyme is not changed and can be used again. Enzymes also can cause molecules to join. Energy for Life 3 Without the right enzyme, a chemical reaction in a cell cannot take place. Each chemical reaction in a cell requires a specific enzyme. Click image to view movie.

45. Photosynthesis Living things are divided into two groups— producers and consumers—based on how they obtain their food. Organisms that make their own food, such as plants, are called producers. Energy for Life 3 Organisms that cannot make their own food are called consumers.

46. Photosynthesis Plants and many other producers can convert light energy into another kind of energy—chemical energy. The process they use is called photosynthesis. Energy for Life 3 During photosynthesis, producers use light energy to make sugars, which can be used as food.

47. Producing Carbohydrates Producers that use photosynthesis are usually green because they contain a green pigment called chlorophyll (KLOR uh fihl). Chlorophyll and other pigments are used in photosynthesis to capture to capture light energy. Energy for Life 3 In plant cells, these pigments are found in chloroplasts.

48. Producing Carbohydrates The captured light energy is used to drive chemical reactions during which the raw materials, carbon dioxide and water, are used to produce sugar and oxygen. For plants, the raw materials come from air and soil. Energy for Life 3

49. Producing Carbohydrates Some of the captured light energy is stored in the chemical bonds that hold sugar molecules together. Energy for Life 3

50. Storing Carbohydrates Plants make more sugar during photosynthesis than they need for survival. Energy for Life 3 Excess sugar is changed and stored as starches or used to make other carbohydrates. Plants use carbohydrates as food for growth, maintenance, and reproduction. Consumers take in food by eating producers or other consumers.

51. Respiration Some of the energy from the food you eat is used to make you move. Energy for Life 3 Some of it becomes thermal energy, which is why you feel warm or hot when you exercise. Most cells also need oxygen to break down food.

52. Respiration During respiration, chemical reactions occur that break down food molecules into simpler substances and release their stored energy. Energy for Life 3 Just as in photosynthesis, enzymes are needed for the chemical reactions of respiration.

53. Breaking Down Carbohydrates The type of food molecules most easily broken down by cells is carbohydrates. Energy for Life 3 Respiration of carbohydrates begins in the cytoplasm of the cell. The carbohydrates are broken down into glucose molecules. Each glucose molecule is broken down further into two simpler molecules. As the glucose molecules are broken down, energy is released.

54. Breaking Down Carbohydrates The two simpler molecules are broken down again. This breakdown occurs in the mitochondria of the cells of plants, animals, fungi, and many other organisms. Energy for Life 3 This process uses oxygen, releases much more energy, and produces carbon dioxide and water as wastes.

55. Breaking Down Carbohydrates When you exhale you breathe out carbon dioxide and some of the water. Energy for Life 3 Respiration occurs in the cells of all living things.

56. Fermentation When cells do not have enough oxygen for respiration, they use a process called fermentation to release some of the energy stored in glucose molecules. Energy for Life 3 Like respiration, fermentation begins in the cytoplasm.

57. Fermentation Again, as the glucose molecules are broken down, energy is released. Energy for Life 3 But the simple molecules from the breakdown of glucose do not move into the mitochondria. Instead, more chemical reactions occur in the cytoplasm.

58. Fermentation These reactions release some energy and produce wastes. Energy for Life 3 Depending on the type of cell, the wastes may be lactic acid, alcohol, and carbon dioxide. The presence of lactic acid is why your muscle cells might feel stiff and sore after you exercise.

59. Related Processes During photosynthesis and respiration, what is produced in one is used in the other. Energy for Life 3 Photosynthesis produces sugars and oxygen, and respiration uses these products, The carbon dioxide and water produces during respiration are used during photosynthesis

60. End of Chapter Summary File