Chapter 10

Question 1

Explain the functional roles of the extracellular matrix in animals

Answer 1

1. Support and Shape: maintains the integrity and strength of organs
2. Tissue Growth and Maintenance: ECM supports local tissue growth and the maintenance of an entire organ
3. Cell communication and signaling: ECM is involved in cell communication within tissues. When a molecule within the matrix binds a receptor, it induces chemical signals that ultimately change activities within the cell
4. Buffering effects of local stressors: ECM has a functional value in buffering the effects of local stressors in the area
5. roles of fibrous proteins: Collagen, elastin, fibronectin, and laminin are examples. Collagen provides stretch resistence and tensile strength, elastin provides stretch and resilience, and fibronectin aids in cell migration and positioning within the ECM, and laminin forms sheet-like structures
6. Homeostatic balance: ECM helps retain a level of water and homeostatic balance

Question 2

Outline the major structural components of the ECM of animals

Answer 2

1. Fibers: these are divided into two categories
   a. Structural fibers: these include collagen, the most abundant protein in the ECM, which provides tensile strength
   b. Adhesive Fibers: these include fibronectin and laminin, which aid in cell migration and positioning within the ECM and form sheet-like structures respectively
2. Ground Substance: This primarily consists of GAGs) and proteoglycans. Proteoglycans are composed of a protein core with several long chain super groups surrounding it. They interact with water and other ECM components to create a hydrated, gel-like environment

Question 3

Describe the structure and function of plant cell walls

Answer 3

1. Cellulose: main component of the cell wall is cellulose, a carbohydrate that forms long fibers and gives the cell wall its rigidity.
2. Hemicellulose and Pectin: Other important carbohydrates that have hydrogen bonds connecting them to the cellulose microfibrils, while pectins trap water molecules to create a gel
3. Proteins: the cell wall has proteins that serve as structural support or enzymes

Functions:
1. Structural support: The primary function of the cell wall is to provide strucrual support to the cell. It helps maintain the shape of the cell and protects it against mechanical stress
2. Regulation of transport: Regulates the transport of molecules in and out of the cell. It allows many small molecules to pass through it, but not larger molecules that could harm the cell
3. Turgor pressure: Turgor pressure is a force created by the inside of the cell pushing out. The cellulose microfibrils form a matrix with the proteins, hemicelluloses, and pectins to provide a strong framework that can resist turgor pressure
4. Protection: Provides protection against physical shocks and pathogens

Question 4

Compare and contrast the structures and functions of anchoring junctions, tight junctions, and gap junctions found in animal cells

Answer 4

Anchoring Junctions:
Structure: Anchoring junctions are composed of transmembrane cell-adhesion molecules (CAMs) and/or adhesion receptors that link the lateral surfaces of one cell to another or the basal surfaces of the cell to the extracellular matrix (ECM). Adaptor proteins connect the adhesion molecules to the cytoskeleton and signaling molecules.
Function: They stabilize the cell’s position, provide stability and rigidity, and support tissue integrity by holding cell sheets together.

Tight Junctions:
Structure: Tight junctions are areas where the membranes of two adjacent cells join together to form a barrier. The cell membranes are connected by strands of transmembrane proteins such as claudins and occludins.
Function: Tight junctions bind cells together, prevent molecules from passing in between the cells, and also help to maintain the polarity of cells. They are often found at epithelial cells, which are cells that line the surface of the body and line body cavities.

Gap Junctions:
Structure: Gap junctions are made up of connexin proteins. Groups of six connexins form a connexon, and two connexons are put together to form a channel that molecules can pass through.
Function: The main function of gap junctions is to connect cells together so that molecules may pass from one cell to the other. This allows for cell-to-cell communication, and makes it so that molecules can directly enter neighboring cells without having to go through the extracellular fluid surrounding the cells

Question 5

Outline the structures and functions of the four types of animal tissues: epithelial, connective, nervous, and muscle tissues

Answer 5

Epithelial:
a. Structure: composed of cells and an extracellular matrix. The cells can be different shapes and can be arranged in a single layer or multiple layers
b. Function: It forms the covering on all internal and external surfaces of your body, lines body cavities and hollow organs, and is the major tissue in glands. Has a variety of functions including protection, secretion, and absorption

Connective:
a. Structure: composed of cells and the extracellular matrix. Extracellular matrix consists of protein fibers and ground substances
b. Function: provide internal support, adhesion, and cohesion between tissues to form organs and systems. Provides a matrix that gives metabolic support to cells and is the medium for the transport of nutrients and waste products between organs

Nervous:
a. Structure: nerve cells/neurons and glial cells. Neurons transmit electrical impulses, while neuroglia do not. Neuroglia support and protect neurons
b. Function: main tissue of nervous system; monitors and regulates the functions of the body

Muscle:
a. Structure: made of muscle fibers. Cytoplasm in the muscle fibers is sarcoplasm and contains a network of membrane called sarcoplasmic reticulum
b. Muscle tissue applies forces to different parts of the body by contraction. It controls the movement of an organism

Question 6

Summarize the structures and functions of the three types of plant tissues: dermal, ground, and vascular tissues

Answer 6

Dermal:
a. Structure: Covers the outside of the plant and is composed of epidermal cells. In non-woody plants, a thin, waxy layer called a cuticle covers these cells
b. Function: protects plant from injury and water loss

Ground:
a. Structure: found throughout plant and is composed of parenchyma cells, which have thin walls, many chloroplasts, and large central vacuoles
b. Function: serves as a site for photosynthesis, provides a supporting matrix for the vascular tissue, helps to store water and sugars, and allows plants to grow and heal

Vascular:
a. Structure: Arrangement of multiple cell types in vascular plants. It includes xylem, which is created from hollow, dead cells, and phloem, which is made up of living cells
b. Function: allows for the transport of water, minerals, and products of photosynthesis throughout the plant

Question 7

Tissue

Answer 7

Groups of cells that have similar structure and functions

Question 8

Organ

Answer 8

Collection of two or more tissues that perform a specific function or set of functions
Gap junctions are abundant in these where the cells need to communicate

Question 9

Cytoskeleton

Answer 9

Cytoskeleton maintains the cell shape by providing mechanical resistance to deformation and supporting the plasma membrane
Cell movement: it can contract, allowing cells to migrate and change their environment. It also plays a role in cell motility, such as the movement of a white blood cell in your immune system
Organelle positioning: aids in the correct positioning of organelles within the cell
Transport of vesicles: Cytoskeleton provides tracks for the transport of vesicles within the cell
Tissue Stability: through association with extracellular connective tissue and other cells, the cytoskeleton stabilizes entire tissues

Question 10

Cells junctions

Answer 10

Specialized structures that adhere cells to each other or to the ECM
Animal:
Anchoring, Tight, Gap

Plant:
Middle lamella and Plasmodesmata

Question 11

Extracellular matrix

Answer 11

Network of material that is secreted from ANIMAL cells and forms a complex meshwork outside of cells. The ECM provides strength, support, and organization

Question 12

Collagen

Answer 12

A protein secreted from animal cells that forms large fibers in the ECM
Imparts tensile strength, which is a measure of how much stretching force a material can bear without tearing apart

Question 13

Elastin

Answer 13

Forms elastic fibers in the ECM that can stretch and recoil

Question 14

Laminin

Answer 14

Adhesive type: connects cells to the ECM and helps to organize components in the ECM

Question 15

Fibronectin

Answer 15

Adhesive type: connects cells to the ECM and helps to organize components in the ECM

Question 16

Occludin and Claudin

Answer 16

Make up transmembrane proteins in tight junctions and form interlaced strands in the plasma membrane. These strands of proteins are found in adjacent cells and bind to each other, forming a tight seal between cells

Question 17

Epidermis

Answer 17

Epidermis:
- refers to the newly made dermal tissue (complex tissue that forms a covering on various parts of the plant) on the surfaces of leaves, stems, and roots. Plant epidermal cells have a thick primary cell well and are tightly interlocked by their middle lamellae

Question 18

Basal Lamina

Answer 18

A thin, dense layer of the ECM that lines most human tissues

Question 19

Microtubules

Answer 19

Microscopic hollow tubes made of the proteins alpha and beta tubulin that are part of a cell’s cytoskeleton
- they provide structure and shape to eukaryotic cells
- are involved in cell movement, cell division, and transporting materials within cells
- They form the internal structure of cilia and flagella
- provide platforms for intracellular transport
- constantly assembling and disassembling via the addition and removal of dimers
- involved in maintaining the structure of the cell and, together with microfilaments and intermediate filaments, they form the cytoskeleton

Question 20

Microfilaments

Answer 20

also known as actin filaments are the smallest filaments of the cytoskeleton in eukaryotic cells
- composed of two strands of subunits of protein actin wound in a spiral
- play crucial roles in cell movement, muscle contraction, and cell division
- Muscle contraction
- Cell movement - one end of a microfilament must elongate while the other end must shorten, and myosin acts as a motor to make this happen
- has a role in cytoplasmic streaming, which is the flow of cytoplasm throughout the cell

Question 21

Intermediate filaments

Answer 21

primary component of the cytoskeleton
involved in essential cellular processes, such as integrity, division, and migration
The primary function is to create cell cohesion and prevent the acute fracture of epithelial cell sheets under tension.

Question 22

Tubulin and Microtubules

Answer 22

The tubulin proteins alpha and beta polymerize into long chains or filaments that form microtubules
Microtubules are rigid, hollow, fibrous shafts of tubulin, which provide structural support, intracellular transport, and DNA segregation to eukaryotic cells

Question 23

Actin

Answer 23

Family of proteins that form microfilaments in the cytoskeleton and the thin filaments in muscle fibrils.
Exists in two forms: G-actin and F-actin.
is the monomeric subunit of microfilaments and thin filaments
-participates in many important process like muscle contraction, cell motility, cell division, cell signaling, and the establishment and maintenance of cell junctions and cell shape

Question 24

Cell adhesion molecules (CAMs)

Answer 24

A subset of cell surface proteins that are involved in the binding of cells with other cells or with the ECM, in a process called cell adhesion. They help cells stick to each other and to their surroundings

Question 25

Cadherins vs Integrins

Answer 25

Cadherin is a cell adhesion molecule that mediates cell-to-cell adhesion, whereas integrin is a cell adhesion molecule that mediates cell-to-ECM adhesion
Cadherins:
- Adherens Junctions and Desmosomes

Integrins:
- Hemidesmosomes and Focal Adhesions

Question 26

Adherens junction

Answer 26

connect cells to each other via cadherins
- In many cases, these junctions are organized into bands around cells. In the cytosol, adherens junctions bind to cytoskeletal filaments called actin filaments

Question 27

Desmosomes

Answer 27

Connects cells to each other via cadherins
These junctions are spotlike points of intercellular contact that rivet cells together
Connected to cytoskeletal filaments called intermediate filaments

Question 28

Hemidesmosome

Answer 28

Connects cells to the ECM via integrins
Interacts with intermediate filaments

Question 29

Focal Adhesions

Answer 29

Connects cells to ECM via integrins
In the cytosol, focal adhesions bind to actin filaments

Question 30

Tight junctions vs Gap junctions

Answer 30

Tight:
- creates watertight seal between two adjacent animal cells
- blocks the passage of solutes and water molecules between epithelial layers in verebrates
- connected areas of the plasma membrane that stich cells together
- prevents water from passing through the tissue

Gap:
- Channels between neighboring cells that allow for the transport of ions, water and other substances
- Use connexin proteins to form pores
- Act like tunnels for water and ions
- Allows the direct cytoplasmic exchange between two cells

Question 31

Connexon

Answer 31

-A channel that forms gap junctions in vertebrates, consisting of six connexin proteins in one cell aligned with six connexin proteins in an adjacent cell

Question 32

Secondary cell wall vs Primary cell wall

Answer 32

Primary:
- formed in a growing cell and is present in all plant cells
- elastic and capable of expansion in a growing cell and grows in thickness by intussusception (growth by the deposition of cellulose)
- It is 1-3µm thick and consists of a single layer of wall material
- its cellulose micro-fibrils are short, wavey and loosely arranged ***
- lacks pits and additional materials
- water content = 60%
- low cellulose content but high hemicellulose, protein and lipid contents

Secondary
- Formed in mature cell and is present in certain cells only. E.g. cells involved in mechanical support and water transportation
- rigid and incapable of expansion
- Grows in thickness by accretion (growth or increase by the gradual accumulation of additional layers or matter)
- Has 3 or more layers of wall material and is 5-10µm thick
- its cellulose micro-fibrils are long, straight and compactly arranged **
- has pits and additional materials like lignin, suberin, etc.
- Its water content is about 30-40%
- high cellulose content and low hemicellulose, protein and lipid contents

Question 33

Plasmodesmata

Answer 33

A membrane-lined, ER-containing channel that connects the cytoplasm of adjacent plant cells
- functionally similar to gap junctions in animal cells; they open pores that allow the passage of ions and molecules between the cytosols of adjacent plant cells
- The plasma membrane of one cell is continuous with the plasma membrane of the adjacent cell, which forms a pore that permits the diffusion of molecules from the cytosol of one cell to the cytosol of the other
- has a central tubule, called a desmotubule, connecting the smooth ER membranes of adjacent cells

Question 34

What are three types of cytoskeletal elements? For each, indicate the subunits they are composed of, their relative size, and major functions

Answer 34

Microfilaments:
-Subunits: Composed of actin proteins
-Relative Size: They are the narrowest with a diameter of about 7 nm
-Major Functions: They play a crucial role in cell motility, muscle contraction, and cell division. They also serve as tracks for the movement of a motor protein called myosin

Intermediate Filaments:
- Subunits: Composed of various proteins, depending on the type of cell in which they are found
- Relative Size: They have a diameter of 8-12 nm
- Major Functions: They provide support for microfilaments and microtubules by holding them in place. They form keratins found in epithelial cells and neurofilaments in neurons

Microtubules:
- Subunits: Composed of tubulin proteins arranged to form a hollow, straw-like tube
- Relative Size: They are the largest with a diameter of about 25 nm
- Major Functions: They help support and shape the cell and act as “routes” along which organelles can move. They also play a role in cell division

Question 35

What are the major types and functions of cell junctions

Answer 35

Tight Junctions:
- They create a watertight seal between two adjacent animal cells
- They block the passage of solutes and water molecules between epithelial layers in vertebrates
- They are connected areas of the plasma membrane that stitch cells together

Desmosomes:
- They allow for some flow between cells
- They are found mostly in tissue needing strong support, such as cardiac, gastrointestinal, and bladder tissue

Gap Junctions:
- They are channels between neighboring cells that allow for the transport of ions, water, and other substances
- They are found in tissue types that need smooth communication, such as cardiac muscle, smooth muscle, and nerves

Plasmodesmata:
- They are narrow openings between plant cells that are lined with cell membranes
- They allow for the transportation of water, nutrients, signaling molecules, and even genetic material
- These living bridges allow for direct communication between cells of the same multicellular organism

Question 36

Adherins junctions and desmosomes both attach cells to other cells and are made up of cadherins.
How, then, are they different?

Answer 36

• Adherens junctions connect to the actin filaments of neighboring cells, while desmosomes connect to the intermediate filaments of neighboring cells
• The extracellular region of adherens junctions lack a highly organized structure, whereas the extracellular region of desmosomes exhibits a highly organized structure
• Adherens junctions’ adhesion is always calcium-dependent, while desmosomes exhibit calcium-independent hyper adhesion
• Adherens junctions are found in epithelial cells, while desmosomes are found in all types of cells

Question 37

What do you think would happen if you interfered with the function of cadherins and integrins

Answer 37

• Because cadherins and integrins are essential for cell-cell and cell-ECM adhesion, interfering would disrupt these adhesions, potentially leading to loss of tissue integrity
• C and I are involved in signaling pathways that regulate cell growth, differentiation, and migration, so cell signaling would be impaired, leading to a slow or complete halt in the other processes

Question 38

Discuss the difference between gap junctions and tight junctions

Answer 38

Gap Junctions:
- Function: allows direct chemical communication between adjacent cells by forming channels that permit the transport of ions, water, and other substances
- Structure: Formed when a set of six connexins form an elongated, donut-like structure called a connexon. When the pores of connexons in adjacent animal cells align, a channel forms between the cells
- Distribution: widespread

Tight Junctions
- Function: regulate the movement of water and solutes between epithelial layers. They form a barrier that blocks the passage of molecules and ions through the space between cells
- Structure: formed by claudins and other proteins. They create a seal between the plasma membranes of adjacent cells, preventing leakage of extracellular fluid
- Distribution: specific areas of epithelial cells

Question 39

How are connexons and plasmodesmata similar?

Answer 39

They both form channels between adjacent cells, allowing for the transport of ions, nutrients, and other substances that enable cells to communicate
Gap junctions in animal cells (involve connexons) and plasmodesmata in plant cells

Question 40

Describe how ground tissue is similar to connective tissue

Answer 40

• both provide support and bind other tissues or organs together
• both contain a variety of cell types
• both have an ECM. In connective tissue, this is referred to as “ground substance.” In plants, the ECM includes the cell wall and space outside the cell membrane
• Both play a role in nutrient transport. In animals, blood, a type of connective tissue, is involved in nutrient transport. In plants, ground tissues is involved in the transport of water, minerals, and sugars
• Both involve storage. Adipose tissue (connective tissue) stores fat. In plants, certain types of ground tissue store starch
• both off protection. Connective tissue protects and cushions organs, while some types of ground tissue in plants offer protection against herbivores or aid in wound healing

Question 41

Describe the structural and functional differences between collagen and elastin

Answer 41

Collagen:
- made of the triple helix formed with three polypeptide chains
- key component found in tissues like cartilage, tendons, ligaments, bone, and skin. Made of amino acids
- not that flexible in nature, production continues throughout your life but reduces with age

Elastin:
- A protein created by fibroblasts which form a change of elastic fibre (the elastin fibres maintains your skin’s elasticity and firmness
- made with three random components but no helix is formed due to the combination
- Major protein component of tissues like lungs, arteries, bladder, skin, elastic ligaments, and cartilage. Made of soluble tropoelastin, glycine, valine, proline residues and modified alanine
- Allows many tissues of your body to continue being in their shape even after stretching. It helps skin return to its original statis after being poked or pinched
- known for its flexibility. nearly 100 times more flexible than collagen
- production stops when you hit puberty

Question 42

Describe how homophilic binding of different forms of cadherin proteins helps organize cells

Answer 42

Cadherins engage in homophilic binding, which means they bind to the same type of cadherin on another cell

Different forms of cadherin proteins enable cells to recognize and bind to each other, influencing cell arrangement, tissue formation, and organ development

Question 43

Plants do not possess any extracellular matrix, how do they protect their cells from damage?
a. Chloroplasts
b. Large vacuoles
c. Thickened plasma membrane
d. Cell wall
e. Dense cytoskeletal filaments

Answer 43

d. Cell wall
- cell wall is a rigid layer that’s located outside the cell membrane. It provides structural support, protection against mechanical stress, and a barrier against pathogenic organisms. It also helps maintain cell shape and turgor pressure

Question 44

Collagen can be found in —
a. Bone
b. Cartilage
c. Ligaments
d. Skin
e. All the above

Answer 44

e. All of the above
- Collagen is the most abundant protein in the body
- bones (providing structure
- cartilage (providing flexibility)
- ligaments (connecting bones to each other)
- skin (providing elasticity and strength)

Question 45

The passageways across the cell walls of animals are called plasmodesmata. These structures allow
for the direct diffusion of molecules from cell to cell.
a. This is true
b. This is false

Answer 45

b. This is false
Plasmodesmata are indeed passageways that allow for the direct diffusion of molecules from cell to cell, but they are found in plant cells, not animal cells. Animal cells use different structures, such as gap junctions, for direct communication between cells. So, the statement is false

Question 46

Which type of junction uses cadherins and acts as rivets between cells?
a. Adherence junctions
b. Desmosomes
c. Focal adhesions
d. Pili adhesions
e. Plasmodesmata

Answer 46

b. Desmosomes
Desmosomes are strong cell junctions that anchor cells to each other and provide mechanical stability to tissues. They are often compared to rivets or spot welds. They use cadherins (specifically desmogleins and desmocollins, which are types of cadherins) for their adhesive properties

Question 47

Which of the following is not an animal tissue?
a. Epithelial
b. Connective
c. Muscle
d. Vascular
e. Nervous

Answer 47

d. Vascular
Vascular tissue is not an animal tissue. It is a type of tissue found in plants, involved in transporting water, nutrients, and sugars between different parts of the plant. The other options - epithelial, connective, muscle, and nervous tissues - are all types of animal tissues

Question 48

Plants use tight junctions to adhere cells together.
a. This is true
b. This is false

Answer 48

b. This is false
Plants do not use tight junctions to adhere cells together. Tight junctions are a feature of animal cells, particularly epithelial cells, where they help to create a barrier between different body compartments. In plants, cells are adhered together by the middle lamella, a layer rich in pectins situated between the cell walls of adjacent plant cells. Additionally, plasmodesmata serve as communication channels between plant cells

Question 49

The high tensile strength of a tendon is due to the—
a. Fibronectin
b. Collagen
c. Laminin
d. Elastin

Answer 49

b. Collagen
The high tensile strength of a tendon is primarily due to collagen. Tendons are composed largely of collagen fibers, which provide them with the strength and flexibility to transmit forces from muscle to bone. Collagen fibers are arranged in parallel arrays, which maximizes their ability to withstand tensile (pulling) forces. This is why tendons are so strong and resistant to stretching

Question 50

Lungs need to be able to repeatedly stretch and retain their original shape, which protein is responsible
for this flexibility
a. Fibronectin
b. Collagen
c. Laminin
d. Elastin

Answer 50

d. Elastin
Elastin is the protein responsible for the flexibility of lungs. It allows tissues in the body to resume their shape after stretching or contracting, which is crucial for the normal functioning of lungs as they constantly expand and contract during breathing

Question 51

An experimental enzyme specifically digests claudin and occludin proteins in the intestinal epithelium.
What would happen to an animal that was given this enzyme?
a. Intestinal epithelial cells would die
b. Intestinal epithelial cells would begin to pump ions into the intestinal lumen
c. Intestinal epithelium would begin to leak fluid
d. Intestinal epithelium would lose elasticity
e. Intestinal epithelial cell would stop collagen production

Answer 51

c. Intestinal epithelium would begin to leak fluid
Claudin and occludin are integral components of tight junctions in the intestinal epithelium. Tight junctions seal the paracellular spaces between enterocytes, regulating the movement of substances between the intestinal lumen and the rest of the body. If an enzyme specifically digests claudin and occludin proteins, it would disrupt these tight junctions, potentially leading to increased intestinal permeability or “leaky gut.” This could result in the leakage of fluid, as well as other substances, from the intestinal lumen into the rest of the body

Question 52

The dermal tissue in plants is analogous to the _________ tissue in animals
a. Connective
b. Epithelial
c. Muscle
d. Nervous

Answer 52

b. Epithelial
The dermal tissue in plants is most analogous to the epithelial tissue in animals. Both serve as protective layers. The dermal tissue, also known as the epidermis, covers the outer surface of plants, while epithelial tissue covers the body surfaces of animals, lines body cavities and organ cavities, and forms glands