B2.3 Cell Specialization

Question 1

What is cell differentiation?

Answer 1

process that leads to the formation of specialized cells and tissues. genes are “switched on” while others are not.

Question 2

How does cell differentiation occur in an embryo?

Answer 2

gradients of signaling chemicals indicate cell’s position in embryo and determine pathway of differentiation it follows.

Question 3

What are stem cells?

Answer 3

the building block of human body, cells that give rise to every cell, tissue, and organ in fetus body.

Question 4

What are the 2 main capacities of stem cells?

Answer 4

1. ability of endless self-renewal - a stem cell is unspecialized but can go through numerous cycles of cell division while maintaining the undifferentiated state.
2. potency (capacity to differentiate pathways to become specialized)

Question 5

What are embryonic stem cells?

Answer 5

found in early embryo tissues up until 3-5 days after fertilization.

Question 6

What are adult stem cells?

Answer 6

found in juvenile and adult tissues in the brain, heart, bone marrow, lungs, and other organs for repair.

Question 7

What is a totipotent stem cell?

Answer 7

stem cells which can form ALL types of cells (5 days)

Question 8

What is a pluripotent stem cell?

Answer 8

form most cells (7 days)

Question 9

What is a multipotent stem cell?

Answer 9

form specialized lineage of cells -> tissue -> organ (after 7 days)

Question 10

What are niches in the context of cells?

Answer 10

area of a tissue that provides a specific environment where stem cells exist in an undifferentiated self-renewable state; where they receive stimuli to determine their behavior.

Question 11

What is a stimuli?

Answer 11

signals such as chemicals which bind to cell surface receptors of the stem cell and trigger to stay undifferentiated OR commit to a more differentiated state by causing the expression of genes.

Question 12

What are some locations of stem cell niches?

Answer 12

• bone marrow (multipotent, give rise to a large # of different blood cells)
• hair follicle (hair growth, skin and hair follicle generation)

Question 13

How is cell size determined?

Answer 13

it is an aspect of cell specialization

Question 14

Size of sperm cell

Answer 14

50µm

Question 15

Size of egg cell

Answer 15

110µm

Question 16

Size of red blood cells

Answer 16

6-8µm

Question 17

Size of white blood cells

Answer 17

10µm

Question 18

Size of motor neurons

Answer 18

20µm in diameter

Question 19

Size of striated muscle cell

Answer 19

20-100µm in diameter, 100mm in length

Question 20

What is the shape of a sperm cell, and how is it adapted to its function?

Answer 20

shape: long/slender w/ long tail
- narrowness and small volume reduce resistance, allow swim to egg easy
- the middle piece contains many mitochondria for energy production

Question 21

What is the shape of an egg cell, and how is it adapted to its function?

Answer 21

shape: largest volume of any human cell.
- large volume allow large quantities of food reserves used when haploid cell is fertilized

Question 22

What is the shape of a red blood cell, and how is it adapted to its function?

Answer 22

shape: bi-concave and flat
- shape increases SA allow for passage along narrow blood vessels + fast loading/unloading of O2.
- no nucleus

Question 23

What is the shape of a white blood cell, and how is it adapted to its function?

Answer 23

shape: many different types of WBC exist
- some produce antibodies against viruses
- some take in pathogens by phagocystosis
- large volume allow space for many rough endoplasmic reticulum + golgi apparatuses for protein synthesis.

Question 24

What is the shape of a motor neuron, and how is it adapted to its function?

Answer 24

shape: long and thin
- carries electrical signals from one place to another along the axon
- causes contraction of muscle fibers/release of molecules from glands

Question 25

What is the shape of a striated muscle cell, and how is it adapted to its function?

Answer 25

shape: larger than normal cells - size allow exertion of greater forces and contract by a greater length - multiple nuclei - composed of many contractile elements called myofibrils

Question 26

What does the surface area to volume ratio of a cell mean?

Answer 26

it dictates the rate at which substances enter and leave the cell. - a single cell is limited in its growth: the bigger it grows the smaller the SA:V ratio

Question 27

qhange of materials across a cell surface depend on?

Answer 27

the surface area

Question 28

What do the need for exchange (metabolism rate) depend on?

Answer 28

the volume

Question 29

What happens if the SA is big/small?

Answer 29

big: cell may lose heat too rapidly, therefore high metabolism needed to compensate for loss small: require substances/heat cannot enter/exit the cell member quickly enough

Question 30

What happens if the volume is big/small?

Answer 30

big: more energy required for all metabolic processes small: substances are used and processed quickly

Question 31

How does SA:V ratio affect heat exchange?

Answer 31

large masses with a low SA:V ratio have difficulties exchanging heat between the body core and the surrounding environment. - large body size tends to isolate an animal's core from its environment (longer travel distance for heat) small masses have higher heart rate at rest to compensate for rapid heat loss instead.

Question 32

How does SA:V ratio affect the basal metabolic rate (min. # of calories needed)?

Answer 32

big=decreased metabolic rate because the small SA would fail to keep up with the metabolic demands of the organism.

Question 33

How do yeast cells optimize their SA:V ratio?

Answer 33

they grow up to a certain point but then the SA:V ratio becomes too small, then it will divide to form 2 new cells -> increases SA:V

Question 34

How do root with root hair cells optimize their SA:V ratio?

Answer 34

root absorbs water/nutrients from soil, the root hair allows root SA to increase while V stays same -> increases SA:V ratio making nutrient uptake more efficient

Question 35

How do cactuses optimize their SA:V ratio?

Answer 35

they need to reduce loss of water from its surface. it reduces its SA to avoid water loss, needles further provide protection and reflect sunlight.

Question 36

How do small intestine with villi/microvilli optimize their SA:V ratio?

Answer 36

small intestines absorb nutrients from the food we eat. to increase the speed nutrients are absorbed, the inner membrane of small intestine is folded and overed in villi/microvilli that increase the SA for absorption.

Question 37

What are some adaptations to increase the SA:V ratio of cells?

Answer 37

- flattening of cells (red blood cells) - microvilli (small intestine) -invagination (proximal convoluted tubules)

Question 38

How is the bi-concave shape of red blood cells an adaptation to its function?

Answer 38

- the lack of nucleus in RBC allow space for more haemoglobin which O2 binds to - shape gives large SA:V ratio

Question 39

How is proximal convoluted tubules in kidneys adapted to its function?

Answer 39

small tubes responsible for selectively filtering out substances from the blood which pass through the glomerolus. the base and sides of these cells have deep, complex invaginations that contain a high density of sodium-potassium pumps that drive the active transport of substances out/in the blood.

Question 40

What are the adaptations of type I pneumocytes in alveoli?

Answer 40

very thin and wide w/o many organelles. volume of cytoplasm is small, separated only by cell membranes to the capillary. gas exchange takes place here.

Question 41

What are the adaptations of type II pneumocytes in alveoli?

Answer 41

cubic shape w/ cytoplasm rich in organelles. they produce surfactant which are stored in lamellar bodies

Question 42

What is surfactant?

Answer 42

film of moisture secreted by exocytosis from the lamellar bodies of type II pneumocytes. allow gases to dissolve and increase diffusion/reduce surface tension

Question 43

What are lamellar bodies?

Answer 43

in type II pneumocytes, specialized secretory vesicles which store the large amounts of phospholipids and proteins produced by the rER

Question 44

What are alveoli?

Answer 44

air sacs within lungs that provide a very large SA for diffusion. the respiratory surface of the alveolus is only one cell layer thick and surrounded by a dense capillary network for an efficient gas exchange.

Question 45

What are type I and type II pneumocytes?

Answer 45

the two different types of specialized cells which aid the diffusion of gases in alveoli.

Question 46

What is the effect of reducing surface tension of alveoli by surfactant?

Answer 46

without surfactant, the alveoli would collapse under surface tension during expiration -> pneumonia/lung diseases

Question 47

What are striated muscle cells?

Answer 47

muscles used to move the body

Question 48

What are cardiac muscle cells?

Answer 48

muscle tissue of the heart and smooth muscle cells that cause the movement of inner organs

Question 49

Describe the structure/function of striated muscle cells

Answer 49

move and stabilize skeletal positions, protect inner organs, and generate heat. striations seen are caused by the light and dark bands of the sarcromeres in myofibrils; they are cylindrical structures arranged in parallel.

Question 50

Describe the structure/function of cardiac muscle cells

Answer 50

myofibrils with light and dark bands aligned and appear striated. much shorter cells with only one nucleus. at junctions, cells attach to each other. branched -> electrical signals to be propagated