surface area to volume and size relationship
as size increases, surface area to volume ratio decreases
surface area to volume and metabolic rate relationship
higher the surface area to volume ratio, higher the rate of heat loss so a higher metabolic rate to maintain body temperature
Fick’s law
rate of diffusion = concentration gradient x surface area / diffusion pathway length
gas exchange in plants: maintain concentration gradient
CO2 into the plant, O2 out the plant and CO2 is used in photosynthesis
gas exchange in plants: surface area
millions of stomata where the gas can enter and leave
gas exchange in plants: diffusion pathway length
leaves are thin and flat
xerophytic plants limit water loss
hairy leaves
rolled leaves
sunken stomata
= traps humid air and reduces water potential gradient
pine needle leaves
= lower surface area to volume ratio so less evaporation
gas exchange in insects
spiracles (openings of small tubes)
trachea into tracheoles
gas exchange in insects: ventilation movements
abdomen pumping increases pressure
forcing stale air out
= maintaining (increasing) concentration gradient
terrestrial insects limit water loss
waxy layer
spiracles can close
hairs around spiracles
= reduce water potential gradient
gill structures
gill arch, gill filament, gill lamellae
gas exchange in fish: maintain concentration gradient
counter-current flow (blood flows in opposite direction to oxygen/water)
maintaining diffusion gradient across whole gill surface
gas exchange in fish: surface area
gill filament’s folds increase surface area and on top of that there are gill lamellae folds to increase surface area further
structures of lungs
lung, trachea, bronchi, bronchioles, alveoli
diaphragm, internal/external intercostal muscles, ribcage
inspiration
external intercostal muscles contract pushing ribcage up and out
diaphragm contracts down
increases the volume (in the thoracic cavity)
decreasing the pressure
fresh air moves down the pressure gradient into the lungs
expiration
external intercostal muscles and diaphragm relax (domed shape)
internal intercostal muscles contract
decrease in volume (in thoracic cavity)
increasing the pressure
air moves down the pressure gradient our of the lungs
gas exchange in alveoli: maintain concentration gradient
low O2 concentration air is continually replaced by breathing
gas exchange in alveoli: surface area
lots of small balls/spheres
extensive capillary network
gas exchange in alveoli: diffusion pathway length
one cell thick alveolar epithelium and capillary epithelium
production of amylase
in salivary glands and pancreas
function of amylase
to break down starch into maltose (polysaccharide into disaccharides)
hydrolyses glycosidic bonds
function of membrane-bound disaccharidase
hydrolyse disaccharides into monosaccharides
attached to cell-surface membrane of epithelial cells in ileum
production of lipase
made in pancreas
secreted in small intestines
function of lipase
breaks down lipids into monoglycerides and fatty acids
hydrolysis of ester bonds
bile salts
produced by the liver to emulsify lipids into smaller droplets
forming micelles
digestion and transportation of lipids (mark scheme)
micelles contain bile salts and fatty acids/monoglycerides
makes fatty acids/monoglycerides more soluble in water
fatty acids/monoglycerides absorbed by diffusion
triglycerides reformed in cells
vesicles move to cell-surface membrane
function of endopeptidase
hydrolyse internal peptide bonds
producing more ends
function of exopeptidase
hydrolyse external peptide bonds
function of membrane-bound dipeptidase
hydrolyses dipeptides into amino acids
absorption of amino acids
via co-transport with sodium ions (same as glucose)
structure of haemoglobin
quaternary globular proteins containing 4 haem groups, alpha and beta chains, and Fe2+ ions
function of haemoglobin
ability to bind and unbind with oxygen to form oxyhaemoglobin
transport molecule
shape of oxyhaemoglobin dissociation curve
S-shaped
axes of oxyhaemoglobin dissociation curve
y-axis = percentage saturation of haemoglobin
x-axis = partial pressure of oxygen
explaining shape of oxyhaemoglobin dissociation curve
initially it takes a large increase in partial pressure of oxygen to bind the first oxygen
once the first oxygen is bound the shape of the haemoglobin protein changes, allowing for the second and third oxygen molecules to bind easily (with little increase in partial pressure of oxygen)
then, the shape changes again so it is difficult to bind the fourth and final oxygen molecule, requiring a greater increase in partial pressure of oxygen
Bohr shift: adaptation to exercise
due to the increase in temperature from respiration and decrease in pH due to CO2 and lactic acid, the oxyhaemoglobin dissociation curve shifts to the right
this makes the haemoglobin proteins worse at binding to oxygen so more is released into the tissue to respire with
affinity to oxygen definition
the ability of haemoglobin to bind to oxygen
affinity to oxygen: higher altitudes/foetal haemoglobin
greater affinity to oxygen (steeper curve)
because there is a lower partial pressure of oxygen at higher altitude/lower concentration of oxygen at the placenta
which is advantageous as enough O2 will be supplied to all cells/tissue
function of arteries
carry oxygenated blood away from the heart under high pressure
(except pulmonary artery)
structures of arteries
lumen
elastic tissue
folded epithelium
thick muscle wall
function of arteriole
narrower arteries connecting to capillaries
higher proportion of smooth muscle cells so they can contract and partially cut off blood flow (narrowing the lumen)
function of veins
carry deoxygenated blood back to the heart under low pressure
(except pulmonary vein)
structure of veins
wide lumen
endothelium
thin muscle wall
pocket valves
function of elastic tissue
to stretch and recoil smoothing out spikes in blood pressure so less stress of blood vessels
function of folded endothelium
smooths lining of lumen, prevents plaque building up
folds allow lumen to open up
function of muscle wall
narrows or widens lumen to regulate blood pressure
(in veins) contract to push blood up vein
function of pocket valve
prevents back flow of deoxygenated blood
function of capillaries
exchange products with tissue
features of capillaries
one cell thick endothelium
one red blood cell thick diameter/lumen
capillary beds between tissue/cells
pulmonary prefix
related to the lungs
renal prefix
related to kidney
coronary prefix
related to heart
structures of the heart
vena cava
pulmonary artery
pulmonary vein
aorta
atrioventricular valve
semi-lunar valve
cardiac cycle
contraction of atria
blood forced into ventricles
contraction of ventricles
atrioventricular valves shut
blood forced out the heart
semi-lunar valves shut
relaxation of ventricles and atria
heart rate equation
cardiac output = stroke volume x heart rate
circulation of blood (valves)
ie. when the pressure before the valve is greater than after, the valve opens (vice versa)
tissue fluid
plasma forced out the arteriole end due to high hydrostatic pressure, forms tissue fluid
tissue fluid bathes the cells, exchanging products with them
fluid moves back via osmosis, down the water potential gradient
excess water returns by lymphatic system
lymph vessel
returns water to blood
drains excess water
transports fats and plasma proteins
dissection practical: skills
lab coats, gloves, and goggles to avoid contamination with biological material
scalpel must be sharp for fine and precise cutting; always cut away from the body and keep fingers away from blade
scissors to cut large sections of tissue
dissection practical: limitations
difficult to see smaller, finer structures
specimens do not reflect how the tissue would look in a living organism
dissecting one specimen so anomalies may be ignored/glossed over
must be same age and same species as others
dissection practical: ethical concerns
questions on whether the dissected animals were ‘raised to be killed’
against some religious beliefs
must be from a reputable source and disposed in the correct manner
dissection practical: scientific drawing
make sure drawings are large with detail and labels
no shading
use single and continuous lines
no colouring
label lines should be drawn with ruler
label lines should not cross
label lines should not be arrows
label all structures
include magnification/scale
xylem tissue
transports water up the plant
made of dead cells forming completely unbroken tube through plant (no end wall or air bubbles)
transpiration
water evaporation
tension
cohesion
water enters
water evaporation
water evaporates through stomata
kinetic energy causes water to evaporate
cohesion-tension theory
cohesion means that water leaving through the stomata pulls the molecule behind it with it, creating a whole unbroken column of water to move upward
cohesion-tension theory
tension means there is adhesion between the water molecule and cellulose of xylem, pulling the walls inward
factors affecting rate of transpiration
light intensity
temperature
wind
humidity
translocation
movement of solutes around the plant by generating pressure gradient between source and sink
energy-requiring process that occurs in the phloem
features of phloem
companion cells
sieve plate
sieve tube elements
thin layer of cytoplasm
function of companion cells
carry out the living functions for sieve cells
a companion cell for each sieve cells
function of sieve tube elements
living cells that form a tube for transporting solutes
no nucleus and few organelles
mass flow hypothesis
in source sugars actively transported into phloem
by companion cells
lowers water potential of sieve cells and water enters by osmosis from xylem tissue
increase in hydrostatic pressure causes mass movement towards sink, down pressure gradient
sugars removed into sink cells via diffusion and active transport, raising water potential in phloem
sugars used for respiration/converted to starch for storage in sink
water moves back to xylem, reducing pressure
ringing experiment
evidence for mass flow hypothesis
remove strip of bark containing all phloem and creates a sugary bulge above ring
shows sugar moves downward
radioactive tracers
evidence for mass flow hypothesis
can track substances down the plants ie carbon dioxide-14 autoradiography
aphid experiment
evidence for mass flow hypothesis
shows pressure gradient as sap travels further higher up the plant
potometer
measure rate of water uptake
make sure no air gap under bung and cut the plant in water
open the tap to move the air bubble to 0
potometer doesn’t measure rate of transpiration, why?
turgidity of cell uses water too
photosynthesis uses up water too
probably not 100% sealed