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

3. Chemistry of Life 1
The Nature of Matter
Matter is anything that has mass and takes up space.
Energy is anything that brings about change.
Everything in your environment, including you, is made of matter.
Energy can hold matter together or break it apart.

4. Chemistry in Life 1
Atoms
At the center of an atom is a nucleus that contains protons and neutrons.
Although they have nearly equal masses, a proton has a positive
charge and a neutron has no charge.
Outside the nucleus are electrons, each of which has a negative charge.
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5. Chemistry in Life 1
Atoms
Electrons are the part of the atom that is involved in chemical reactions.
An atom is mostly empty space. Energy holds the parts of an atom together.

6. Chemistry in Life 1
Elements
When something is made up of only one kind of atom, it is called an element.
An element can’t be broken down into a simpler form by chemical reactions.
Scientists have given each element its own one- or two-letter symbol.

7. Chemistry in Life 1
Elements
All elements are arranged in a chart known as the periodic table of elements.
The table provides information about each element including its mass, how many protons it has, and its symbol.

8. Chemistry in Life 1
Elements

9. Compounds and Molecules
Chemistry in Life 1
Compounds and Molecules
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.
There are two types of compounds— molecular compounds and ionic compounds.

10. Chemistry in Life 1
Molecular Compounds
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.

11. Chemistry in Life 1
Molecular Compounds
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.

12. Chemistry in Life 1
Molecular Compounds
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.
Water does not have the same properties as oxygen and hydrogen.

13. Chemistry in Life 1
Ions
Atoms also combine because they’ve become positively or negatively charged.
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.

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

15. Chemistry in Life 1
Ionic Compounds
Ions of opposite charges attract one another to form electrically neutral compounds called ionic compounds.
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.

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

17. Chemistry in Life 1
Ionic Compounds
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.

18. Chemistry in Life 1
Mixtures
A mixture is a combination of substances in which individual substances retain their own properties.

19. Chemistry in Life 1
Mixtures
Mixtures can be solids, liquids, gases, or any combination of them.
Most chemical reactions in living organisms take place in mixtures called solutions.

20. Mixtures 1 In a solution, two or more substances are mixed evenly.
Chemistry in Life 1
Mixtures
In a solution, two or more substances are mixed evenly.
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.

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

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

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

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

25. Lipids 1 Lipids do not mix with water.
Chemistry in Life 1
Lipids
Lipids do not mix with water.
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.

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

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

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

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

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

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

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

33. Characteristics of Water
Chemistry in Life 1
Characteristics of Water
The atoms of a water molecule are arranged in such a way that the molecule has areas with different charges.
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.

34. Characteristics of Water
Chemistry in Life 1
Characteristics of Water
This attraction, or force, between water molecules is why a film forms on the surface of water. “ Surface Tension”
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.

35. Characteristics of Water
Chemistry in Life 1
Characteristics of Water
Because water molecules are so strongly attracted to each other, the temperature of water changes slowly. “Specific Heat”
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.

36. Characteristics of Water
Chemistry in Life 1
Characteristics of Water
When water freezes, ice crystals form.
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.

37. Section Check 1
Question 1
_______ is anything that has mass and takes up space.
Answer
The answer is Matter. Everything in your environment is made of matter.

38. Question 2 Answer 1 A(n) _______ is made up of only one kind of atom.
Section Check 1
Question 2
A(n) _______ is made up of only one kind of atom.
Answer
The answer is element. An element can’t be broken down into a simpler form by chemical reactions.

39. Question 3 1 Which best describes the structure in this illustration?
Section Check 1
Question 3
Which best describes the structure in this illustration?
A. atom
B. element
C. molecular
compound
D. ionic compound

40. Section Check 1
Answer
The answer is C. Molecular compounds form when different atoms share their outermost electrons.

41. Moving Cellular Materials2
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.
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.

42. Moving Cellular Materials2
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.
The movement of substances through the cell membrane without the input of energy is called passive transport.
Three types of passive transport can occur.

43. Moving Cellular Materials2
Diffusion
Molecules in solids, liquids, and gases move constantly and randomly.
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.

44. Moving Cellular Materials2
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.

45. Osmosis—The Diffusion of Water
Moving Cellular Materials 2
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.
If cells weren’t surrounded by water that contains few dissolved substances, water inside of cells would diffuse out of them.

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

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

48. Facilitated Diffusion
Moving Cellular Materials 2
Facilitated Diffusion
Some substances pass easily through the cell membrane by diffusion.
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.

49. Moving Cellular Materials2
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.
For example, the roots of a plant already might contain more of those mineral molecules than the surrounding soil does.

50. Moving Cellular Materials2
Active Transport
The tendency is for mineral molecules to move out of the root by diffusion.
When an input of energy is required to move materials through a cell membrane, active transport takes place.

51. Endocytosis and Exocytosis
Moving Cellular Materials 2
Endocytosis and Exocytosis
Large protein molecules and bacteria, for example, can enter a cell when they are surrounded by the cell membrane.
When 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.

52. Endocytosis and Exocytosis
Moving Cellular Materials 2
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.

53. Endocytosis and Exocytosis
Moving Cellular Materials 2
Endocytosis and Exocytosis
The contents of a vesicle can be released by a cell using the process called exocytosis (ek soh si TOH sis).
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.

54. Question 1 Answer 2 What is diffusion?
Section Check 2
Question 1
What is diffusion?
Answer
Diffusion is the type of passive transport in which molecules in a more dense area randomly move to an area that is less dense until equilibrium is reached.
NC: 6.02

55. Section Check 2
Question 2
_______ is the diffusion of water through a cell membrane.
Answer
The answer is osmosis. Cells contain water and are surrounded by water. These water molecules move by diffusion into and out of cells.
NC: 6.02

56. Question 3 2 Which carries oxygen throughout your body?
Section Check 2
Question 3
Which carries oxygen throughout your body?
A. red blood cells
B. white blood cells
C. sex cells
D. none of the above
NC: 6.04

57. Section Check 2
Answer
The answer is A. Oxygen molecules from the lungs diffuse into red blood cells which carry oxygen throughout your body.
NC: 6.04

58. Trapping and Using Energy
Energy for Life 3
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.
The chemical reactions of metabolism need enzymes.

59. Trapping and Using Energy
Energy for Life 3
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.
Without the right enzyme, a chemical reaction in a cell cannot take place.
Each chemical reaction in a cell requires a specific enzyme.
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60. Energy for Life 3
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.
Organisms that cannot make their own food are called consumers.

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

62. Producing Carbohydrates
Energy for Life 3
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.
In plant cells, these pigments are found in chloroplasts.

63. Producing Carbohydrates
Energy for Life 3
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.

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

65. Storing Carbohydrates
Energy for Life 3
Storing Carbohydrates
Plants make more sugar during photosynthesis than they need for survival.
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.

66. Energy for Life 3
Respiration
Some of the energy from the food you eat is used to make you move.
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.

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

68. Breaking Down Carbohydrates
Energy for Life 3
Breaking Down Carbohydrates
The type of food molecules most easily broken down by cells is carbohydrates.
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.

69. Breaking Down Carbohydrates
Energy for Life 3
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.
This process uses oxygen, releases much more energy, and produces carbon dioxide and water as wastes.

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

71. Energy for Life 3
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.
Like respiration, fermentation begins in the cytoplasm.

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

73. Fermentation 3 These reactions release some energy and produce wastes.
Energy for Life 3
Fermentation
These reactions release some energy and produce wastes.
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.

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

75. Section Check 3
Question 1
_______ is the total of all chemical reactions in an organism.
Answer
The answer is metabolism. All of the activities of an organism involve chemical reactions in some way.
NC: 6.04

76. Question 2 3 Which does this equation represent? A. respiration
Section Check 3
Question 2
Which does this equation represent?
A. respiration
B. fermentation
C. photosynthesis
D. chemosynthesis
NC: 6.02, 6.04

77. Section Check 3
Answer
The answer is C. During photosynthesis, plants take in carbon dioxide and water and combine it with light energy to make sugars, which they use for food.
NC: 6.02, 6.04

78. Section Check 3
Question 3
_______ is the type of food molecules most easily broken down by cells.
Answer
The answer is carbohydrates. As carbohydrates are broken down, energy is released.
NC: 6.02, 6.04

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