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Cells. Questions & Answers. 1. What is the basic organizational structure of the human body? The cell 2. How many cells are in the human body? 50-100 trillion 3. What is cell differentiation? When cells specialize 4. What is the result of differentiation?

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Questions & Answers


1. What is the basic organizational structure of the human body?

The cell

2. How many cells are in the human body?

50-100 trillion

3. What is cell differentiation?

When cells specialize

4. What is the result of differentiation?

Cells vary in size and shape due to their unique function.


5. What are the 3 main parts of a cell?

Cell membrane, nucleus and cytoplasm

6. The cytoplasm is composed of organelles suspended in a gel-like liquid called cytosol.

7. Cells vary considerably in size. In what units are they measured?

Micrometers (µm) = 1/1,000 mm


8. Describe the structure of the cell membrane.


b. Surfaces formed by the phosphate “heads”, which are hydrophilic.

c. Fatty acid “tails” make up the interior of the membrane, which is hydrophobic.


9. What are the 3 main functions of the cell membrane?

1. Forms the outermost limit of the cell

2. Selective permeability – controls what enters and leaves the cell.

3. Signal transduction – allows cell to receive and respond to incoming messages


10. There are 5 main types of proteins found in the cell membrane. List the function of each:

1. Receptor proteins – receive and transmit messages

2.Integral proteins – form pores, channels and carriers; transduce signals

3. Enzymes – catalyze chemical reactions

4. CAMs – cellular adhesion molecules

5. Cell surface proteins – identify cells as self


11. Which type of molecules pass easily through the cell membrane, water-soluble or lipid-soluble?


12. What are some examples of lipid-soluble molecules?

O₂, CO₂ and steroid hormones

13. What are some examples of water-soluble molecules to which the membrane is impermeable?

Amino acids, proteins, sugars, nucleic acids and ions.


14. Organelle

Ribosome – Free or bound to ER

15. Structure

Tiny spheres made of rRNA and protein.

16. Function

Protein synthesis


17. Organelle

Endoplasmic reticulum – rough and smooth

18. Structure :

Membrane-bound flattened sacs, canals and vesicles; RER studded with ribosomes; extension of the nuclear membrane

19. Function:

RER – protein synthesis

SER – makes lipids, breaks down drugs




21. Structure

membranous sacs that vary in size and contents

Formed by cell membrane in endocytosis, by Golgi apparatus and by ER

22. Function

transport of substances


23. Organelle

Golgi apparatus

24. Structure

Stack of flattened, membranous sacs called cisternae

25. Function

Modifies, packages and delivers proteins synthesized in the RER


26. Organelle


27. Structure

Membrane-enclosed sac containing a highly folded inner membrane, forming cristae.

28. Function

Converts energy in glucose and other nutrients into ATP.


29. Organelle


30. Structure

Vary greatly, often tiny sacs. Contain digestive enzymes.

31. Function

“Garbage disposal” – enzymes digest debris and foreign particles, such as bacteria


32. Organelle


33. Structure

Membranous sacs that resemble lysosomes

34. Functions

a. Enzyme peroxidase– catalyzes reactions that produce H₂O₂ (hydrogen peroxide) – toxic to cell

b. Enzyme catalase– breaks down H₂O₂

c. Over 40 other enzymes


35. Cell part


36. Structure

Hairlike motile extensions on surface of cells

37. Function

Propel fluids across the cell’s surface (ie. mucus)


38. Cell part


39. Structure

Long tail-like projection

40. Function

Motility (ie. sperm)


41. Cell part


42. Structure

Microfilaments and microtubules (thin rods and tubes)

43. Function

Support cytoplasm, help move organelles and substances within the cytoplasm


44. Cell part

Nuclear envelope

45. Structure

Porous double-membrane that separtates the nuclear contents form the cytoplasm

46. Function

Maintains integrity of nucleus, controls passage of materials between nucleus and cytoplasm


47. Organelle


48. Structure

Nonmembranous body of protein and RNA

49. Function

Makes ribosomes


50. Cell part


51. Structure

Loosely coiled double-stranded fibers of DNA and protein

52. Function

Codes for protein


53. There are 2 types of transport across the cell membrane – passive and active. Which type requires no energy?


54. Why?

It is a physical process in which particles move with (or down) the concentration gradient

55. Examples

Diffusion, osmosis, facilitated diffusion, and filtration


56. Why does active transport require energy?

Because it is a physiological process in which particles are moved against (or up) the concentration gradient by the cell membrane

57. Examples

Transport proteins, endocytosis, exocytosis and transcytosis


58. What is facilitated diffusion?

Diffusion across the membrane with the help of a channel or carrier protein

59. What is osmosis?

Diffusion of water through a selectively permeable membrane

60. Does water move toward a higher or lower concentration of solutes?



61. What is filtration?

When smaller molecules are forced through porous walls of capillaries, but larger molecules remain in the blood.

62. What is the driving force for filtration?

Blood pressure

63. Why is filtration considered a passive process?

Because it can occur due to the pressure caused by gravity alone.


64. Endocytosis is a form of active transport. What are the three types?

1. Pinocytosis – substance is liquid

2. Phagocytosis – substance is solid

3. Receptor-mediated endocytosis – requires the substance to bind to a membrane receptor


65. Exocytosis is also active transport. Describe how it works:

Vesicle formed in the cell, then fuses with cell membrane and releases contents outside the cell.

66. What are some examples of exocytosis?

Waste removal; release of neurotransmitters from nerve cells


67. What is transcytosis?

Endocytosis followed by exocytosis

68. Function?

Transport a substance rapidly through a cell

69. Example?

HIV virus crossing a cell


70. What is the cell cycle?

Series of changes a cell undergoes from the time it is formed until the time it divides.

71. What are the three stages of the cell cycle?

Interphase, mitosis and cytokinesis


72. What occurs during Interphase?

Cell is very active – grows and maintains routine functions

73. What are the 3 phases of Interphase?

G₁, S and G₂.

74. What occurs during each phase?

G₁ and G₂ - Cell grows and makes organelles

S phase – replicates DNA in preparation for mitosis.


75. What occurs during mitosis?

Karyokinesis = nucleus divides

Cytokinesis = cytoplasm divides

76. List the 4 phases of nuclear division in order:

Prophase , metaphase, anaphase and telophase

77. How does cytokinesis occur in animal cells?

Contractile ring pinches cytoplasm in half


78. One reason cells must divide is to maintain a (high or low) surface area to volume ratio?


79. Cell division rate varies greatly among cell types.Between skin, blood and neuron cells, which type(s) divide often?

Skin and blood

80. What stimulates cell division?

Growth factors and hormones

81. Cell division is suppressed by contact inhibition.

82. The consequence of a loss of cell cycle control are tumors.


83. What are the 2 types of tumors?

Benign = usually remains localized

Malignant = can metastasize (spread); cancerous

84. Two types of genes can cause cancer. What are they?

a. Oncogenes– activate other genes that increase cell division

b. Tumor suppressor genes – normally regulate mitosis, but become inactivated


85. What is a stem cell?

Undifferentiated cell that can make 2 new stem cells (self-renewal) or a new stem cell and a partially differentiated progenitorcell.

86. A cell that can give rise to any type of cell is called totipotent. A cell that can give rise to many, but not all, cell types is called pluripotent.

Which cell is totipotent, and which is pluripotent?

Stem cell =totipotent

Progenitor cell = pluripotent


87. All cells in the human body, with the exception of red blood cells, which expel their nucleus, have a complete set of chromosomes. How do cells specialize and develop their distinct characteristics?

By expressing different sets of genes.

88. The term blastis used to describe an immature differentiated cell, such as an osteoblast (immature bone cell) and myoblast, (immature muscle cell.)


89. What is apoptosis?

Programmed cell death

90. It is a fast, orderly multi-step process:

Cell surface “death receptor” receives a message to die. Enzymes called caspases are activated inside the cell, where they cut up various cell components that are then encapsulated by pieces of cell membrane. The cell is gone within a(n) hour.

91. Why must mitosis and apoptosis by synchronized?

So that tissues and organs neither overgrow nor shrink.

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