Chapter 3 Cell Structures

Question 1

Which scientist came up with the germ theory of disease?

Answer 1

Fracastoro (Louis Pasteur contributed)

Question 2

Who was the first scientist to use the term ‘cells’?

Answer 2

Robert Hooke in 1665

Question 3

What inspired Hooke to call them ‘cells’?

Answer 3

The structure of cork, which resembled a honeycomb, reminded him of small rooms (‘cellulae’ in Latin).

Question 4

What are the three main tenets of Modern Cell Theory?

Answer 4

1. The cell is the fundamental unit of structure and function in living things.
2. All organisms are made of one or more cells.
3. Cells arise from other cells through cell division.

Question 5

What additional aspects are included in Modern Cell Theory?

Answer 5

1. Cells carry genetic material passed to daughter cells during cell division.
2. All cells are similar in chemical composition.
3. Energy flow (metabolism) occurs within cells.

Question 6

What are the four processes shared by all living things?

Answer 6

Growth, reproduction, responsiveness, and metabolism.

Question 7

What are the key differences between prokaryotic and eukaryotic cells?

Answer 7

• Prokaryotic Cells: Lack a nucleus and membrane-bound organelles, smaller (1.0 µm or smaller). Examples: Bacteria and archaea.
• Eukaryotic Cells: Have a nucleus, membrane-bound organelles, larger (10–100 µm). Examples: Animals, plants, fungi, algae, protozoa.

Question 8

What is the function of the cell envelope?

Answer 8

It provides structure and shape, protects from osmotic forces, aids in attachment, helps resist antimicrobial drugs, and allows material exchange.

Question 9

What is the composition of the bacterial cytoplasmic membrane?

Answer 9

A phospholipid bilayer with integral and peripheral proteins.

Question 10

What model describes the cytoplasmic membrane structure?

Answer 10

The fluid mosaic model.

Question 11

How do passive and active transport differ?

Answer 11

• Passive Transport: Does not use energy; moves molecules down the concentration gradient.
• Active Transport: Requires energy (e.g., ATP); moves molecules against the concentration gradient.

Question 12

What are the steps of Gram staining?

Answer 12

1. Primary stain with crystal violet.
2. Add iodine (mordant).
3. Decolorize with alcohol.
4. Counterstain with safranin.

Question 13

Why do Gram-positive bacteria stain purple and Gram-negative red?

Answer 13

The thick peptidoglycan layer in Gram-positive bacteria retains the crystal violet-iodine complex. Gram-negative bacteria’s thinner layer and outer membrane lose it during decolorization.

Question 14

What is peptidoglycan made of?

Answer 14

A sugar backbone of alternating N-acetylglucosamine (NAG) and N-acetylmuramic acid (NAM) with peptide cross-links.

Question 15

How do Gram-positive and Gram-negative cell walls differ?

Answer 15

• Gram-Positive: 30-40 thick peptidoglycan, teichoic acids (lipoteichoic acids)
• Gram-Negative: 1-3 thin PG layers, outer & inner membrane with lipopolysaccharides (LPS), periplasmic space

Question 16

What makes acid-fast bacteria unique? Give an example.

Answer 16

They have a waxy mycolic acid layer in their cell walls, making them resistant to Gram staining. Examples: Mycobacterium species.

Question 17

What are obligate intracellular pathogens? Give an example.

Answer 17

Bacteria that must invade a host cell to replicate, as they cannot produce ATP independently. Example: Chlamydia trachomatis.

Question 18

Why can’t all bacteria be Gram stained?

Answer 18

Some lack peptidoglycan, have incompatible wall components, or cannot be cultured independently.

Question 19

What is the purpose of the cell wall in bacteria?

Answer 19

To maintain shape, prevent lysis from osmotic pressure, and provide rigidity.