Bio HL2 Test 1 - Pineda

cell size as specialization

different cells are specialized in size to support their functions (average human cell is 10-30 um in diameter)

sperm

longer (50 um) but extremely narrow and small in volume

shape and volume reduces resistance, allowing it to swim

egg

largest volume (110 um) of any human cell (visible to the naked eye)

allows storage of large food reserves in cytoplasm

bird eggs have a larger storage (yolk)

red blood cells

smaller (6-8 um), indented in middle (~1 um)

size and shape allow passage through capillaries

large SA:V loads and unloads oxygen faster

white blood cells

smaller (10 um) when inactive, but enlarges (30 um) when activated

growth in volume allows increased amounts of rER and Golgi for protein synthesis (antibodies)

motor neurons

long axons (up to a meter or more)

carries signals from CNS (brain & spinal cord) to distant muscle

striated muscle fibres

larger than average (20-100 um)

allows for exertion of greater forces & contraction

SA:V

volume of the cytoplasm determines cell’s metabolism

sum of all reactions that occur

bigger the cell, higher the volume, greater the metabolism

more nutrients needed & waste produced

SA determines cell’s rate of diffusion (material exchange)

substances move in/out of cells via plasma membrane

bigger the cell, lower the membrane, greater the SA

faster solutes can enter/exit cell

when diffusion cannot keep up with metabolism, the cell dies

low SA:V means nutrients cannot enter quickly enough and waste will accumulate, thus cell divides to maintain a high SA:V

adaptations to increase SA:V

red blood cells: high SA:V allows oxygen to load & unload rapidly

its biconcave shape decreases volume, but creates shorter maximum distance to cytoplasm

proximal convoluted tubules (kidney)

inner membrane has many microvilli, which increases SA

outer membrane also has invaginations (infoldings), also increases SA

both create ample space for placement of channel and pump proteins that carry out selective reabsorption

cell division

organisms produce new cells via cell division

necessary for growth, maintenance, and reproduction

a mother cell divides into two daughter cells

every cell can be traced to zygote, the original cell

formed from fusion of sperm and egg

cell proliferation

rapid increase in number of cells when division exceeds death

growth

in animals, cell proliferation occurs during embryotic and juvenile growth, stopping once adult size is reached

growth plates in bones are during childhood and adolescence allowing increase in height

in plants, cell proliferation is limited to meristems

apical meristems are found at tips of stems and roots

some remain as meristeam and continue to divide, while others differentiate to take on specific function

cell replacement

new skin cells replace old ones that were lost due to friction

nasal layer of epidermis carries out cell division and newly produced cells are displaced towards skin surface

produces large amounts of keratin (hydrophobic) which dehydrates the cells

once surface is reached, cells are flattened and dead

tissue repair

undifferentiated stem cells can divide to heal wounds

basal layer of cells in epidermis carries out cell division and newly produced cells are displaced towards skin surface

produces large amounts of keratin (hydrophobic) which dehydrates the cells

once surface is reached, cells are flattened and dead

tissue repair

undifferentiated stem cells can divide to heal wounds

basal layer of cells can replace damaged outer layer

stem cells in dermis can repair deeper damage

if damage is severe, skin grafts may be necessary

role of mitosis and meioisis

nuclear division is necessary to avoid anucleate cells

such cells cannot grow or maintain itself, with limited lifespan (RBC)

mitosis and meiois