B2.3 Cell Specialisation

Question 1

Fertilisation

Answer 1

fusion of gametes to produce single egg cell.

Question 2

how is an embryo formed

Answer 2

through repeated divisions cell undergoes to generate embryo of many cells. Mitosis in cells ensures embryo are genetically identical.

Question 3

How do cells specialise

Answer 3

early stage embryo, cells unspecialised, as it grows cells develop along pathways and specialise to different functions.
develop an ideal structure with enzymes necessary

Question 4

what is differentiation

Answer 4

the development of cells in different ways to carry out specific functions.
different sequence of genes is expressed in different cell types

Question 5

what is gene expression?

Answer 5

when a gene is used in a cell, ‘switched on’ and info in is used to make a protein/other gene product.
development of cell involves expressing particular genes but not others.

Question 6

why does position of a cell in embryo determine how it differentiates

Answer 6

must be enough cells of each type and must be in positions where they are needed.

Question 7

how is the position of a cell indicated and how is the pathway of differentiation determined?

Answer 7

gradients of signalling chemicals indicate cells position, acting as regulators, determining differentiation pathway.

Question 8

what is a stem cell?

Answer 8

cell that is able to divide repeatedly.
e.g skin stem cells repeatedly divide, replacing lost skin cells.

Question 9

what happens when a cell is produced by division of a stem cell?

Answer 9

can remain as a stem cell or differnetiate into specific cell type, once differentiated, no longer stem cells.

Question 10

what are stem cells categorized as

Answer 10

undifferentiated/partially differentiated, capable of differentiating along diff pathways.

Question 11

where is the location of stem cells in adult humans

Answer 11

some remain in adult body, e,g bone marrow skin liver, these give tissues regeneration and repair.
precise location is the ‘stem cell niche’

Question 12

what does the stem cell niche provide

Answer 12

an microenvironment with conditions needed for stem cells to remain inactive/undiffernetiated over long periods.
and also to proliferate rapidly/differentiate when required.
e.g striated muscle, during injury changes in niche cause proliferation and differentiation to replace damages.

Question 13

why are niches of research interest?

Answer 13

can be simulated outside of body for particular stem type.
can produce human tissue in vitro(glass) and use it for restorative surgery.

also non-therapeutic uses, e.g producing large quantities of muscle fibres/meat.

Question 14

what are totipotent stem cells?

Answer 14

can differentiate into any cell type and are found in early stage embryos.

Question 15

how do embryonic stem cells change?

Answer 15

cells commit to particularly pathway of differentiation during development, may commit along one path/another.
can change to pluripotent. being able to differentiate into a range but not every type.

Question 16

what are multipotent stem cells

Answer 16

can differentiate into several types of mature cells.

Question 17

how does the size of mature differentiated cell such as sperm adapted to perform its function

Answer 17

50micrometer long, extremely narrow, reduces resistance and allows swimming to egg more easily.

Question 18

how does the size of mature differentiated cell such as sperm adapted to perform its function

Question 19

how does the size of mature differentiated cell such as red blood cells adapted to perform its function

Answer 19

6-8 micrometres in diameter but indented on both sides, 1micrometre think middle.
small size+shape allows passage along narrow capillaries give large SA-VOL ratio, loading+unloading of oxygen faster.
biconcave shape gives lower vol, and smaller max distance from cytoplasm to plasma membrane.

Question 20

how does the size of mature differentiated cell such as white blood cells adapted to perform its function

Answer 20

B-lymphocytes are only about 10 micrometres in diameter when inactive, enlarge to 30 micrometres if activated become antibody secreting plasma cells.

Question 21

how does the size of mature differentiated cell such as cerebellar granule cells adapted to perform its function

Answer 21

cell body only 4 micrometres in diameter.
twin axons extend for about 3mm (3000micro) in cerebellar cortex.
very small volume allows cerebellum to accommodate 50 billion of them-75% of brains neurons.

Question 22

how does the size of mature differentiated cell such as motor neurons adapted to perform its function

Answer 22

cell body is about 20 micrometres in diameter, large size allows enough proteins to be synthesised to maintain immensely long axon.
can extend for a metre (million micrometre), so can carry signals from CNS to distant muscle.

Question 23

how does the size of mature differentiated cell such as striated muscle fibres adapted to perform its function

Answer 23

larger than normal, diameter 20-100 micrometre, lengths can exceed 100mm (100k micro).

Dimensions allow fibre to exert > force, and contract by a greater length than smaller muscle cells.

Question 24

Metabolism

Answer 24

chemical reactions taking place in cyto, metabolic rate is proportional to vol of cell.
for meta to continue, substances used in reactions must be absorbed by cell and waste products must be expelled.
rate at which substances move in/out of cells depends on surface area.

Question 25

what is formula of surface area to vol ratio

Answer 25

surface area (mm^2)/volume (mm^3)

Question 26

why is SA to vol ratio important to cell

Answer 26

if too small, substances will not enter cell as quickly as required.
waste products will accumulate as produced more rapidly than excreted.
if ratio too small, cells may overheat as heat is produced faster than it is lost.

Question 27

how are proximal convoluted tubule cells adapted to increase SA to vol Ratio?

Answer 27

tubules in outer surface of kidney receive large vol of fluid filtered out of blood.
reabsorbs filtrate and its useful substances. Molecule/ion passes through both basal and apical membrane to get to blood
wall is only 1 cell thick, inner apical membrane in contact with filtrate, outer basal membrane close to capillaries.
waste remains as filtrate in blood.

Question 28

why does apical membrane and basal membrane have large SA

Answer 28

apical, large no. of microvilli, larger SA.
Basal, infoldings/invaginations, increase SA
both have space for pump and channel proteins to carry out selective reabsorption

Question 29

how is type 1 pneumocytes (cell in alveolar epithelium, outer layer) in alveoli adapted for diffusion of oxygen?

Answer 29

volume of cytoplasm is small.
cell is wide but thin, 0,15 micro thin.
wall of adjacent capillaries consists of single layer of very thin cells.
air in alveolus and blood in alveolar capillaries are less than 0.15 micro apart.
distance is very small ,increasing rate of gas exchange.

Question 30

what are type 2 pneumoctyes how do they differ from type 1

Answer 30

more numerous than type 1 (90% of alveolar cells).
occupy only 5% of surface area (alveolar)
about 10 micrometres across, cytoplasm is dense, contains mito, rER, lysosomes.
large amts phospho synthesised and stored by lamellar bodies

Question 31

how is type 2 pneumocytes (cell in alveolar epithelium, outer layer) in alveoli adapted for diffusion of oxygen?

Answer 31

alveolus is lined by film of moisture
allows o2 to dissolve and diffuse to blood
provides area where co2 can pass into air and be exhaled
phospholipids secreted spread to form single layer on surface of moisture film,
proteins secreted by lamellar bodies are dispersed between phospholipids
proteins act as surfactant, reducing surface tension
without,alveolus may collapse on itself,

Question 32

what are properties of muscle tissue

Answer 32

• muscle tissue is contractile, can shorten in length
• exerts pulling force that can be used to cause movement
• to return to original length, pulling force must be exerted once more
• usually provided by another muscle, they work in antagonistic pairs, contraction of 1 causes the other to lengthen.
• fibres have myofibrils, parallel cylindrical structures, light+dark bands aligned

Question 33

how are striated muscle fibres adapted?

Answer 33

attached to bones. striated muscles, composed of long, unbranched cylindrical structures, muscle fibres
single plasma membrane surrounds each fibre, multinuclei present
fibres longer than typical cells, as embryonic muscles fuse together

Question 34

how are cardiac muscle cells adapted

Answer 34

cardiac muscles, forms wall of heart, also have myofibrils, light+dark bands aligned.
straited appearance, however has shorter cells, most with one nucleus
cardiac muscle cells branched by intercalated discs, connections between p membrane and cytoplasm of adjacent cardiac cell, electrical signals can be propagated rapidly cell to cell.

Question 35

what happens if one cardiac muscle cell in wall of heart is stimulated to contract?

Answer 35

if one is stimulated to contract, stimulus passed onto all other cells, synchronization of muscle contraction and blood pumped quickly out of heart

Question 36

should muscle fibres be classed as a cell?

Answer 36

enclosed in p membrane, multinucleated, much larger than moist cells, average length is about 30mm

Question 37

what structures do egg cells have that enable them to receive one sperm only in fertilization?

Answer 37

• zona pellucida-layer of glycoproteins, containing ZP3, allowing sperm to bind and penetrate, later is chemically altered preventing more penetrations
• binding proteins help fuse with membrane of sperm
• vesicles of enzymes near p membrane of egg which are released into zona pellucida, make it impenetrable after nucleus of sperm enters.

Question 38

what structures do egg cells have to provide resources needed for zygote and for embryo to develop?

Answer 38

• Yolk, large vol of cyto inside egg, contains stores of lipids + other foods
• mito, produce ATP and divide repeatedly to generate all mito in adults body
• centrioles, needed for mitosis.

Question 39

how are sperm cells adapted to transfer haploid nucleus to cytoplasm of an egg in oviduct of female?

Answer 39

• very long flagellum, contains 9+2 microtubules, generating force for forward motion
• midpiece with mitochondria, multiple mitos wound round microtubules at base of tail, supply large quantities of ATP
• head, streamlined in shape to insert nucleus into cell.

Question 40

what are some structures sperms have to insert their nucleus into egg cells?

Answer 40

• receptors in zp3 glycoproteins in zona pellucida, where sperm binds
• acrosome, sac of enzymes, digests proteins+polysaccharaides in zona pellucida, so sperm can reach membrane of egg
• binding proteins in inner acrosomal membrane, binds to proteins in p membrane of egg, leading to fusion of membranes and entry of sperm nucleus