B2.3 cell specialization

Question 1

Why is the ability of cells to reproduce themselves important in multicellular organisms?

Answer 1

Cell reproduction allows for growth and the replacement of damaged or dead cells in multicellular organisms.

Question 2

What is the initial single cell in the development of most multicellular organisms, and how does it progress?

Answer 2

Multicellular organisms start as a single cell called a zygote formed from the fusion of gametes. The progression is: gametes → zygote → embryo → fetus → infant.

Question 3

How do cells in a zygote initially behave, and what is differentiation in cell development?

Answer 3

Initially, cells produced by the zygote are unspecialized. However, they quickly start differentiating, a process that leads to the formation of specialized cells. Differentiation involves the expression of certain genes but not others, leading to various cell types.

Question 4

What determines the specific development of cells and their functions in an organism?

Answer 4

Each body cell contains the entire genetic information needed for the complete organism. However, cell development in specific ways is determined by which genes become active. The activation of genes depends on the signals received by the cell.

Question 5

How is the staggering number of different cell types produced from a single original cell explained?

Answer 5

The differentiation process, which leads to the formation of numerous cell types, occurs due to the selective expression of certain genes triggered by specific signals received by the cell.

Question 6

What is cell signaling, and why is it essential in controlling cell differentiation?

Answer 6

Cell signaling is the transfer of information from the cell surface to the nucleus, crucial in controlling gene expression and, consequently, cell differentiation.

Question 7

What are morphogens, and how do they influence cell differentiation?

Answer 7

Morphogens are signal molecules that control cell differentiation by forming concentration gradients in different regions of the early embryo. These gradients determine regional development and the expression of different genes.

Question 8

How does the gradient of signal molecules impact the development of different parts of an embryo?

Answer 8

Signal molecule gradients in the embryo lead to the expression of different genes in various regions, resulting in the development of distinct features in different parts of the embryo.

Question 9

Why do some specialized cells, like nerve and muscle cells, have a diminished ability or lose the ability to reproduce, while others, like epithelial cells, retain rapid reproduction ability?

Answer 9

Some specialized cells lose their ability to reproduce or have a limited capacity to do so. Nerve and muscle cells fall into this category. In contrast, epithelial cells such as skin cells retain the ability to reproduce rapidly throughout their lifespan, with the cells produced being of the same type as the original cell.

Question 10

How do signaling molecules influence the differentiation of cells as the embryo develops?

Answer 10

As the embryo develops, various signaling molecules beyond morphogens become influential factors in cell differentiation, contributing to the development of different cell types and structures.

Question 11

What are stem cells, and what unique abilities do they possess?

Answer 11

Stem cells are cells within organisms capable of dividing and differentiating into various cell types. They retain the ability to divide indefinitely and can differentiate into all cell types found in an organism.

Question 12

Where are stem cells commonly found in plants, and what are meristematic tissues?

Answer 12

In plants, stem cells reside in regions of meristematic tissue, which are located near root and stem tips. Meristematic tissues consist of rapidly reproducing cells capable of becoming various types of tissue within the root or stem.

Question 13

How do gardeners utilize stem cells in plants?

Answer 13

Gardeners utilize the stem cells present in meristematic tissues by taking stem or root cuttings. These cuttings, containing meristematic cells, are used to grow new plants through the regeneration and differentiation of these cells into various tissue types.

Question 14

What are the two unique properties of stem cells?

Answer 14

Stem cells possess the ability to self-renew and recreate functional tissues.

Question 15

How does the process of self-renewal occur in stem cells?

Answer 15

When stem cells divide, they can produce daughter cells that either remain as stem cells or differentiate into specialized cells, allowing for the continuation of stem cells.

Question 16

What happens during cell differentiation in stem cells?

Answer 16

Cell signaling ensures the expression of specific genes as the cell develops, leading to differentiation into specialized cell types.

Question 17

Where do scientists focus their examination in stem cell research in humans, and what are stem cell niches?

Answer 17

Scientists study specific locations or stem cell niches in humans. Stem cell niches are areas where stem cells proliferate regularly and demonstrate differentiation. Examples in humans include the bone marrow and hair follicles.

Question 18

What are the roles of stem cells in the bone marrow and hair follicles?

Answer 18

In the bone marrow, stem cells coexist with self-renewing stem cells, producing blood cells and ensuring a constant supply of stem cells for differentiation. Hair follicles in the skin contain epithelial stem cells involved in hair growth, skin regeneration, and the production of oil-producing glands associated with hair follicles.

Question 19

What are the major types of stem cells

Answer 19

Totipotent
Pluripotent
Multipotent
Unipotent

Question 20

Totipotent

Answer 20

Capable of producing any tissue in an organism and found only in the very early stages of embryo development. They can potentially form a complete organism.

Question 21

Pluripotent

Answer 21

Arise from totipotent cells, exist in the early embryonic stage, and can mature into almost all different cell types but cannot produce a complete organism.

Question 22

Multipotent

Answer 22

Form a limited number of cell types, found later in embryonic development, and persist throughout an organism’s life.

Question 23

Unipotent

Answer 23

Forms only a single cell type, typically found late in the embryonic stage and exist in the functioning organism.

Question 24

How has recent research aimed to utilize stem cells in medical treatment, and what conditions might benefit from this approach?

Answer 24

Therapeutic cloning has been directed towards growing large numbers of embryonic stem cells in culture to replace lost or defective differentiated cells due to injury or disease. Diseases like Parkinson’s, Alzheimer’s, and certain forms of diabetes—caused by the loss of specific cells—could potentially benefit from implanted stem cells to alleviate symptoms or replenish depleted cells.

Question 25

What are some diseases where stem cell research shows promise in treating their symptoms?

Answer 25

Diseases like Parkinson’s and Alzheimer’s, resulting from the loss of functional brain cells, and certain types of diabetes where essential cells in the pancreas are depleted, are among those where stem cell implantation holds potential for treatment.

Question 26

What are the sizes of various human cell types?

Answer 26

• Sperm cell: 3 μm in diameter, 50 μm in length
• Egg cell: 120 μm
• Fat cell: 50-150 μm
• Red blood cell: 7.5 μm
• White blood cell: 12-15 μm
• Skeletal muscle cell: 10-50 μm in width, 40 mm in length; neuron (nerve cell): 350 μm in length

Question 27

What are the main functions of sperm and egg cells, and how do their sizes reflect these functions?

Answer 27

Sperm cells, relatively small, mainly transport genetic material for the formation of a viable zygote. Egg cells are larger and participate in fertilization to form a zygote during development.

Question 28

What are some adaptations of red blood cells, and how do these adaptations relate to their size and function?

Answer 28

Red blood cells, responsible for oxygen transport, have adaptations like containing hemoglobin, a biconcave disc shape for increased surface area, and the absence of mitochondria and a nucleus, which contributes to their small size and efficient oxygen transport.

Question 29

What distinguishes white blood cells from red blood cells, and why are white blood cells larger?

Answer 29

White blood cells, larger than red blood cells, play a role in defending against infections and retain their nucleus throughout their lifespan. Their increased size accommodates the necessary presence of the nucleus, granules, and various organelles, aiding in their defensive functions.

Question 30

What is the function of motor neurons, and what adaptations do they possess?

Answer 30

Motor neurons transmit impulses from the brain or spinal cord to muscles, enabling appropriate responses to stimuli. They feature long axons capable of conducting impulses over extensive distances within the body.

Question 31

What are striated muscle fibres, and what distinguishes them from smooth or cardiac muscle fibres?

Answer 31

Striated muscle fibres are specialized cells found in skeletal muscles, functioning as individual muscle cells. They are cylindrical, surrounded by membranes capable of conducting impulses, and can reach lengths of up to 12 cm, longer than fibres in smooth or cardiac muscles. The visible bands within these fibres represent contraction units.

Question 32

How do striated muscle fibres produce movement, and what role does their length play in this process?

Answer 32

Striated muscle fibres generate movement solely through contraction or shortening. Due to their relatively lengthy structure, coordinated contractions of all units within the fibre produce substantial movement.

Question 33

What factors influence cell size, and how are they significant in cell physiology?

Answer 33

Surface area-to-volume ratio, crucial for material exchange across cell membranes, impacting cell physiology.

Mitotic spindle function during cell division, where improper cell sizes can disrupt the process.

Question 34

How is cell size determined during differentiation, and what purpose do the unique adaptations in shape, structure, and size serve in cells?

Answer 34

Cell size is established during differentiation, resulting in cells tailored for specific functions within an organism. Adaptations in shape, structure, and size collectively optimize cells for maximum efficiency in performing their designated roles.

Question 35

What limits the size a cell can reach, and how does the surface area-to-volume ratio influence a cell’s functionality?

Answer 35

The surface area-to-volume ratio determines a cell’s size limit. Heat and waste production, as well as resource consumption rates, depend on the cell’s volume. Cell reactions occur inside, influenced by cell size. The cell membrane’s surface area controls material exchange. A larger cell has a lower surface area-to-volume ratio, hindering efficient material exchange.

Question 36

How does the relationship between cell width, surface area, and volume impact cell functionality?

Answer 36

As cell width increases, surface area and volume also increase. However, surface area grows slower (squared) than volume (cubed). This results in larger cells having relatively less surface area compared to volume, limiting material exchange crucial for cell functions.

Question 37

Why don’t large animals have larger cells?

Answer 37

Large animals do not possess larger cells but instead have a greater number of cells. Due to limitations imposed by the surface area-to-volume ratio, larger cells would have reduced surface area for material exchange, impacting their ability to perform vital life functions effectively.

Question 38

What modifications contribute to an efficient surface area-to-volume ratio in larger cells?

Answer 38

Modifications ensuring an advantageous surface area-to-volume ratio in larger cells involve alterations in cell shape, cellular projections inward and outward, strategic location concerning nutrient sources and waste disposal, and specific cell arrangements at a given site.

Question 39

How do red blood cells utilize their structure for efficient function?

Answer 39

Red blood cells possess a biconcave disc shape, maximizing their surface area-to-volume ratio. This structure, along with their flexibility, enables them to navigate through narrow capillaries, facilitating the delivery of oxygen to all body cells.

Question 40

What adaptations in kidney cells (proximal convoluted tubule cells) enhance their functionality?

Answer 40

The cube-shaped cells in the kidney’s proximal convoluted tubule are tightly packed, optimizing space efficiency. They feature microvilli projecting into the tubule lumen, expanding the cell’s surface area. Abundant mitochondria facilitate active transport, while channels on the cell’s opposite side aid in efficient transportation.

Question 41

Type I Pneumocytes

Answer 41

Cells covering 95% of the alveolar surface, facilitating gas exchange, with adaptations like thin, flat shape to minimize diffusion distance.

Question 42

Type II Pneumocytes

Answer 42

Cells producing pulmonary surfactant, reducing surface tension, preventing alveolar collapse, with cube-shaped structure and microvilli for increased surface area.

Question 43

Red Blood Cells (Erythrocytes)

Answer 43

Biconcave disc-shaped cells for greater surface area, facilitating oxygen transport and flexibility for movement through capillaries.

Question 44

Kidney Proximal Convoluted Tubule Cells

Answer 44

Cube-shaped cells with microvilli, closely packed, and numerous mitochondria facilitating fluid reabsorption and ion secretion.

Question 45

Motor Neurons

Answer 45

Neurons with long axons transmitting signals from the brain or spinal cord to muscles for movement.

Question 46

Striated Skeletal Muscle Cells

Answer 46

Long, cylindrical shape
Membrane capable of impulse propagation
Multinucleated with visible bands for voluntary movement

Question 47

Cardiac Muscle Fibers

Answer 47

Branching, striated cells
Single nucleus per cell
Connected by intercalated discs for coordinated heart contractions

Question 48

Skeletal Muscle Growth

Answer 48

Growth occurs by fusion of satellite cells with existing fibers
Unlike typical cell division, mature muscle fibers don’t proliferate

Question 49

Cell Characteristics in Skeletal Muscle Fibers

Answer 49

Despite unique growth patterns, they possess many organelles typical of cells
Lack the typical apoptosis and replacement process found in most cells

Question 50

Sperm Cell Adaptations

Answer 50

-Size: One of the smallest human cells; 3 um in width, 50 um in length
-Flagellum: Present in the mid-piece, allowing motility; mitochondria located nearby for energy supply
-Production: Continually produced in vast numbers throughout a male’s life
-Specialized Features: Head has an acrosomal vesicle aiding egg penetration; contains a haploid nucleus

Question 51

Egg Cell Adaptations

Answer 51

• Size: One of the largest human cells; 120 μm
• Motility: Non-motile; lacks a flagellum
• Structure: Non-streamlined, spherical shape; contains few cytoplasmic organelles
• Production: All early gamete-forming cells present before birth; no new egg-forming cells produced after birth
• Specialized Features: Special secretory vesicles to prevent entry of additional sperm after penetration; contains a haploid nucleus and organelles for embryo development