topic 3 - exchange of substances Flashcards
why do single celled organisms diffuse easily
small surface area to volume ratio so distance of diffusion is smaller
adaptations of good exchange surfaces
-high surface area
-thin
-near blood supply
what do fish use for gas exchange
gills, which have an arch of gill filaments with lots of lamellae attached
what is the counter current exchange system in fish
blood and oxygen flow in opposite directions across the lamellae to maintain a steep diffusion gradient so the maximum amount of oxygen in the water can diffuse into the deoxygenated blood
how do fish ventilate
opens mouth to lower floor of buccal cavity so water flows in
shuts mouth so buccal cavity raises and increases pressure
water forced over gill filaments due to the pressure differences in the cavities
how do insects respire
muscle contraction forces oxygen through spiracles (small openings) in its tracheoles through diffusion
how do plants allow gas exchange
through stomata in leaves, no cell is far from stomata which reduces diffusion distance
structure of the cartilage in the lungs
supports the trachea and bronchi and prevents lungs from collapsing in the event of pressure drop from exhalation
structure of ciliated epithelium
present in bronchi, bronchioles and trachea, involved in moving mucus up to the throat where it can be swallowed to prevent lung infection
structure of goblet cells
secrete mucus in bronchi, bronchioles and trachea to trap bacteria with the help of lysozymes to break it down
structure of smooth muscle in lungs
ability to contract constricts the airway to control how much airflow goes to the alveoli
structure of elastic fibres
stretch when exhaling and recoil when inhaling controlling flow of air
process of inspiration
external intercostal muscles contract
internal intercostal muscles relax
ribs raise upwards
diaphragm contracts and flattens
volume inside thorax increases therefore pressure decreases compared to atmosphere
process of expiration
external intercostal muscles relax
internal intercostal muscles contract
ribs lower
diaphragm relaxes and raises upwards
volume inside thorax decreases therefore pressure increases compared to atmosphere
what is vital capacity
max volume of air that can be inhaled or exhaled in a single breath
what affects vital capacity
age, gender, height
what is tidal volume
the volume of air we breath in and out at each breath at rest
what is breathing rate
number of breaths per minute
how do you calculate breathing rate
use a spirometer graph and count peaks or troughs
what is the expiratory reserve volume
the volume of air that can be exhaled on top of the tidal volume eg during exercise
what is digestion
the hydrolysis of large biological molecules into smaller ones which can be absorbed across a membrane
how are carbohydrates digested
amylase in mouth breaks down polymers
maltase in ileum breaks down monosaccharides
sucrase and lactase break down disaccharides sucrose and lactose
how are lipids digested
lipases hydrolyse ester bond between fatty acids and monoglyceride
lipids are emulsified by bile salts from the liver
broken down in ileum
two advantages of bile salts
increase surface area of lipid
speed up reaction to break down lipids
how are proteins digested
endopeptidases- hydrolyse peptide bonds between specific amino acids in the middle of a polypeptide
exopeptidases- hydrolyse bonds at end of polypeptides
dipeptidases- break dipeptides into specific amino acids
how are lipids transported into epithelium cells
micelles contain bile salts and fatty acids
make fatty acids more soluble in water
fatty acids absorbed by diffusion
triglycerides reformed in epithelial cells
vesicles move to cell membrane
how much oxygen can one haemoglobin bind to
4 oxygen molecules
what is partial pressure of oxygen
greater the amount of dissolved oxygen in cells, greater the partial pressure
what happens when the partial pressure of oxygen increases
affinity of haemoglobin increases so more loading (occuring in the lungs)
why does partial pressure of oxygen decrease and what happens to haemoglobin
respiration uses up oxygen therefore affinity of haemoglobin decreases so oxygen is released in respiring tissues
how does the affinity of haemoglobin change depending on saturation
after haemoglobin binds to 1 oxygen, its affinity increases due to a change in shape so can bind to more oxygens easier
what is positive cooperativity in haemoglobin
2nd and 3rd oxygens bind easier
why is fetal haemoglobin more affinitive
by the time oxygen reaches the placenta, the oxygen saturation of the blood has decreased so the fetus needs to survive at a low partial pressure
what happens to haemoglobin if carbon dioxide is present (Bohr effect)
affinity of haemoglobin decreases causing it to be released as carbon dioxide creates acidic conditions causing the haemoglobin to change shape making it easier to release oxygen
4 common features of circulatory system
suitable medium- blood (mostly containing water so substances can easily dissolve in it)
means of moving the medium- often a pump eg heart to maintain pressure differences
mechanism to control flow around body- valves
close system of vessels-
function of the aorta
LEFT and carries blood to body
function of pulmonary artery
RIGHT and carries blood to lungs
function of pulmonary vein
LEFT and brings back blood from lungs
function of vena cava
RIGHT and brings back blood from body
why is the heart myogenic
in right atrium there is a region of fibres called the sinoatrial node which is the pacemaker. this creates a wave of electrical stimulation to make the atria contract at roughly the same time
how do the electrical signals get to the ventricles
reaches the atrioventricular node and passes down the bundle of His to the apex of the heart which branches into Purkyne fibres which carry the wave upwards causing the ventricles to contract at the apex
what is cardiac diastole
atria and ventricular muscles relaxed
blood enters atria via vena cava/ PV
increased pressure in atria
what is atrial systole
atria muscular walls contract increasing pressure further
atrioventricular valves open so blood flows in ventricles
ventricular muscular walls relaxed
what is ventricular systole
ventricle muscular walls contract increasing pressure
atrioventricular valves close and semilunar valves open
blood pushed into arteries
structure and function of arteries
carries blood away from heart
thick walled - withstand high BP
elastic tissue - stretch and recoil for smooth blood flow
smooth muscle- vary blood flow
smooth endothelium- reduce friction and ease flow
structure and function of arterioles
branch off arteries to feed blood into capillaries
thinner less muscular walls
structure and function of capillaries
site of metabolic exchange
one cell thick-fast exchange of substance
structure and function of venules
larger than capillaries but smaller than veins
structure and function of veins
carry blood from the body to the heart
wide lumen- maximise blood to heart
thin walled- low pressure of blood
valves- prevent blood backflow
little elastic tissue or smooth muscle- less blood
how is tissue fluid formed
as blood enters capillaries at the arteriole end by arterioles the small diameter results in a high hydrostatic pressure so water and small molecules are forced out, ultrafiltration
large proteins, platelets and RBC left behind as too large
what do lymph nodes in the lymph fluid do
filter out bacteria with the help of lymphocytes which destroy pathogens as part of the immune system defences
features of xylem tissue
-transport water and minerals
-long cylinders made of dead tissue with open ends
-xylem vessels contain pits which enable water to move sideways between the vessels
-thickened with lignin in spiral patterns to enable plant to remain flexible
what is transpiration
the loss of water vapour from the stomata by evaporation
how does light affect transpiration
more light- more stomata open for evaporation
how does temperature affect transpiration
more heat- more kinetic energy, faster moving molecules so more evaporation
how does humidity affect transpiration
more water vapour- water potential positive outside leaf so reduces water potential gradient
how does wind affect transpiration
wind blows away humid air to maintain water potential gradient
how does water move up a plant against gravity
cohesion tension theory
-cohesion
-adhesion
-root pressure
how does cohesion help water molecules to travel up a plant
water is a dipolar molecule so can form hydrogen bonds with other water molecules
this makes the water molecules stick together and travel up the xylem as a CONTINUOUS column
how does adhesion help water molecules to travel up a plant
water molecules stick to the xylem walls
narrower- more adhesion
how does root pressure help water molecules to travel up a plant
as water moves into roots by osmosis it increases the volume of liquid inside root so the pressure increases, forcing water upwards
describe steps of transpiration
1) water vapour evaporates out of stomata creating a lower pressure
2) more water is pulled up xylem to replace it due to negative pressure
3) cohesion of water molecules
4) adhesion
5) creating tension so column narrows
what 2 key cells are in the phloem
sieve tube elements
companion cells
features of sieve tube elements
living cells
dont contain nuclei
few organelles - makes it hollow so solution can be transported through
what do companion cells do
provide ATP required for active transport of organic substances
what are examples of the source and sink cells used in the phloem
source- photosynthesising cell
sink- respiring cell
how does the source sink model work
1) source cells producing sucrose lowers water potential so water enters by osmosis
2) sink cells using up sucrose increases water potential so water leaves by osmosis
3) increases hydrostatic pressure in source cell
4) solution is forced to the sink cell via the phloem
how does sucrose get from source to sieve tube element
1) sucrose diffuses down its conc gradient into the companion cell via facilitated diffusion
2) active transport of H+ occurs from the companion cell into the spaces within the cell walls using energy
3) this creates a conc gradient and therefore the H+ move down their conc gradient via carrier proteins into the sieve tubes
4) co transport of the sucrose with H+ occurs to transport sucrose into sieve tube element
how does sucrose move through sieve tube element
1) increase of sucrose in sieve tube element lowers water potential
2) water enters sieve tube element from the surrounding xylem vessels via osmosis
3) increases hydrostatic pressure causing liquid to be forced to sink cell
how does sucrose enter the sink cell
1) sucrose is used in respiration at sink
2) sucrose is actively transported into sink cell decreasing water potential
3) osmosis of water from the sieve tube element into sink cell
4) removal of water decreases the volume in sieve tube element so hydrostatic pressure decreases
5) movement of organic substances due to difference in hydrostatic pressure
how do tracers work in providing evidence for translocation
plants are provided with radioactively labelled carbon dioxide which is used in photosynthesis to make sugars with the carbon in
thin slices of stem are cut and put on xray film which turns black when radioactive
this highlights where the phloem are and shows sugars are transported in the phloem
how is the ringing experiment used to provide evidence for translocation
a ring of bark and phloem is removed from a tree trunk, the trunk will swell above the removed section
analysis of the liquid in this swelling shows it contains sugar, showing that when the phloem is removed sugar cannot be transported
role of micelles in absorption of fats in ileum
micelles include bile salts and fatty acids
make fatty acids more soluble in water
carry fatty acids to lining of ileum
higher conc of fatty acids maintained at lining of ileum
fatty acids absorbed by diffusion
advantages of lipid droplet and micelle formation
droplets increase surface area for lipase action
so faster hydrolysis of triglycerides
micelles carry fatty acids and glycerol to cell membrane
how is tissue fluid reabsorbed
large molecules remain in capillaries, lowering water potential
towards venule end of capillaries, the hydrostatic pressure is low due to loss of liquid, water re-enters the capillaries by osmosis with dissolved waste products
when equilibrium is reached where is the rest of the tissue fluid absorbed
lymphatic system, eventually drains back into the blood by the heart
