Chapter 5: Cell Structure and Function

1. Chapter 5: Cell Structure and Function 5-1 The Cell Theory

2. The Cell Theory • All living things are made of cells • Cells are the basic units of structure and function in living things • Anton van Leeuwenhoek, a Dutch biologist, was the inventor of the microscope • Enabled him to see things that no one had ever seen before

3. The Cell Theory • Van Leeuwenhoek’s work interested other people • Robert Hooke examined slices of cork • Saw that it was composed of thousands of tiny chambers • Called these chambers cells • Over the next 200 years, other scientists began to discover that cells were not only found in plants but in other living things too • Robert Brown—1833—discovered the nucleus • Matthias Schleiden—1838—stated that all plants are made of cells • Theodore Schwann—1839—all animals are made of cells • Rudolf Virchow—1855—all cells arise from preexisting cells

4. The Cell Theory • The observations of these scientists are summarized into the cell theory • All living things are composed of cells. • Cells are the basic units of structure and function in living things. • All cells come from preexisting cells.

5. Chapter 5: Cell Structure and Function 5-2: Cell Structure

6. Cell Structure • Enormous variety in the size and shape of cells • Despite differences in size and shape, there are certain structures that are common to most cells • The cells of animals, plants, and related organisms have three basic structures: the cell membrane, or boundary of the cell; the nucleus, or control center; and the cytoplasm, or material between the cell membrane and the nucleus

7. Cell Membrane • All cells are separated from their surroundings by a cell membrane • Regulates what enters and leaves the cell • Aids in protection and support of the cell • It must communicate with other cells, take in food and water, and eliminate wastes • Composed of several kinds of molecules • Lipids (bilayer) • Proteins • Carbohydrates

9. Cell Wall • In organisms such as plants, algae, and some bacteria, the cell membrane is surrounded by a cell wall • Helps protect and support the cell • Very porous—allows water, oxygen, carbon dioxide, and other substances to pass through • Made of cellulose

11. Nucleus • In many cells we can see a large, dark structure, called the nucleus • Contains DNA • Prokaryotes are organisms whose cells lack nuclei • Bacteria • Small and unicellular • Eukaryotes are organisms whose cells contain nuclei • Mostly multicellular

13. Nuclear Envelope • Surrounding the nucleus are two membranes that form the nuclear envelope • Form the boundary around the nucleus • Contains dozens of nuclear pores allowing substances to flow in and out of the nucleus

14. Nucleolus • Most nuclei contain a small region called the nucleolus that is made up of RNA and proteins • The structure in which ribosomes are made • Aid in the production of proteins within the cell

15. Chromosomes • The DNA in the nucleus of eukaryotic cells is attached to special proteins and forms large structures called chromosomes • Contain the genetic information that must be passed to each new generation of cells

17. Cytoplasm • The cytoplasm is the area between the nucleus and the cell membrane • Contains many important structures

18. Chapter 5:Cell Structure and Function 5-3: Cytoplasmic Organelles

19. Cytoplasmic Organelles • The structures inside the cytoplasm are generally called organelles • An organelle is a tiny structure that performs a specialized function in the cell. • Each organelle has a special job

20. Mitochondria and Chloroplasts: Power Stations • All living things require energy • The mitochondrion and the chloroplast are key organelles that change energy from one form to another • Mitochondria change chemical energy in food into compounds that the cell can use • Chloroplasts trap solar energy and convert it into chemical energy

22. Mitochondria and Chloroplasts: Power Stations • Mitochondrion • Contains two special membranes • Outer membrane surrounds the organelle • Inner membrane has many folds that increase the surface area of the mitochondrion • Chloroplast • Found only in plant cells and algae • Three membranes • Two envelope-like membranes • Third membrane where the sun’s energy is changed into chemical energy

23. Ribosomes: Protein Factories • Ribosomes are the structures in which proteins are made • Made of RNA and protein • Some are attached to membranes; some are found free in the cytoplasm • Among the smallest organelles

25. Endoplasmic Reticulum and Golgi Apparatus: Manufacturers and Shippers • Many cells are filled with a complex network of sacs known as the endoplasmic reticulum, or ER • Transports materials through the inside of the cell • Two types: • Smooth—no ribosomes attached • Rough—ribosomes attached—involved in the synthesis of proteins

27. Endoplasmic Reticulum and Golgi Apparatus: Manufacturers and Shippers • Proteins are often modified by special enzymes that attach carbs and lipids to them • In most cases, the proteins are first moved into special compartments known as the Golgi apparatus • Flattened stack of membranes • After modification, the proteins may then be released from the cell **The Golgi apparatus modifies, collects, packages, and distributes molecules made at one location of the cell and used at another**

29. Lysosomes: Cleanup Crews • When a cell encircles a particle, the cell membrane forms a pocket around the foreign material • The foreign material must now be digested,or broken down • Lysosome • Contain chemicals and enzymes necessary for digestion • Formed by the Golgi apparatus • Plants cells do not have lysosomes

31. Vacuoles and Plastids: Storage Tanks • Vacuoles store materials such as water, salts, proteins, and carbohydrates • Plastids are plant organelles that may take many forms, one of which is the chloroplast • Involved in the storage of food and pigments • Examples: • Leukoplasts—store starch • Chromoplasts—store pigments

33. Cytoskeleton: Framework • Most cells are capable of some type of movement • Cytoskeleton – framework of filaments and fibers that support cell structure and drive cell movement • Microfilaments-long, thin fibers that function in the movement and support of the cell • Microtubules-hollow tubes made out of proteins • Cilia and flagella

35. Chapter 5:Cell Structure and Function 5 – 4 Movement of Materials Through the Cell Membrane

36. Diffusion • The driving force behind the movement of many substances across the cell membrane is called diffusion • Diffusion is the process by which molecules of a substance move from areas of higher concentration of that substance to areas of lower concentration • Several factors determine whether diffusion occurs across a membrane • Equilibrium point is reached • Permeability • Most membranes are known as selectively permeable

37. Osmosis • Water molecules pass through most cell membranes very rapidly • The diffusion of water molecules through a selectively permeable membrane is called osmosis • The force exerted by osmosis, or osmotic pressure, tends to move water across membranes from a more dilute solution into a more concentrated solution • If water moves in too freely, the volume of a cell will increase until the cell becomes swollen and bursts like an over inflated balloon

38. Osmosis • Cells deal with the problem of osmotic pressure in a variety of ways • Cells of many organisms do not come into contact with fresh water • Plant cells and bacteria have cell walls that prevent the cells from expanding • Some cells pump out the water with a contractile vacuole

39. Facilitated Diffusion • Osmosis and diffusion are forms of passive transport across the cell membrane because energy is not needed • But, many molecules are transported across a membrane in the direction of lowest concentration by a carrier protein • Facilitated diffusion • Is fast, specific, and does not require energy…it is still driven by diffusion • Can only occur if a concentration distance exists cross that membrane

40. Active Transport • Active transport is an energy-requiring process that enables material to move across a cell membrane against a concentration difference • Two types • Individual molecules are carried through membrane-associated pumps • Large amounts of materials are transported through movements of the cell membrane • Endocytosis • Process of taking material into the cell by means of infoldings, or pockets, of the cell membrane • Phagocytosis • Process that occurs when large particles are taken in by endocytosis • Pinocytosis • Process in which cells take in liquid and pinch off to form vacuoles within the cell • Exocytosis • Process that occurs when large materials are removed from the cell

41. Chapter 5:Cell Structure and Function 5 – 5 Cell Specialization

42. Cell Specialization • Cell specialization is one of the key characteristics of cells in a multicellular organisms • By cell specialization, we mean that cells are often uniquely suited to perform a particular function within the organism • Movement • Make products

43. Chapter 5:Cell Structure and Function 5 – 6 Levels of Organization

44. Levels of Organization • The levels of organization in a multicellular organism include cells, tissues, organs, and organ systems that make up the organism

45. Tissues • In multicellular organisms, cells – the first level of organization – are organized in specialized groups called tissues • A group of similar cells that perform similar functions • Most animals, which are multicellular organisms, have four main types of tissues • Muscle, epithelial, nerve, and connective tissue

46. Organs • An organ is a group of tissues that work together to perform a specific function • Many types of tissue may be used to form a particular organ • Each tissue performs an essential task to help the organ function successfully

47. Organ Systems • An organ system, or a group of organs, works together to perform a certain function • There are 10 organ systems in the body including the muscular system, circulatory system, and digestive system