EXCHANGE AND TRANSPORT:

SURFACE AREA TO VOLUME RATIO:

  • single-celled organisms do not have specialised transport systems

  • substances can enter the cell by passive transport as the diffusion distances are short

  • however, multicellular organisms require specialised transport systems and gas exchange surfaces

  • this is because:

    • the diffusion distance is greater

    • their metabolic rate is higher

    • their surface area : volume ratio is smaller

  • therefore large organisms have specialised gas exchange surfaces and a mass transport system

  • EG in mammals the alveoli and cardiovascular system .

  • characteristics of a mass transport system:

    • vessels

    • directional movement

    • transport medium

    • maintenance of speed

  • the features of an efficient exchange surface are::

    • large surface area

    • thin so short diffusion distance

    • steep concentration gradient

CELL MEMBRANES AND TRANSPORT OF SUBSTANCES:

  • all cells and organelles are surrounded by a partially permeable membrane composed of phospholipids with protein molecules between phospholipid molecules

  • membrane proteins consist of:

    • transport proteins

    • receptor proteins

    • enzymes

    • structural proteins

    • receptor proteins

  • the main function of the membrane is controlling the movement of substances in and out of the cell/organelle

  • it also contains receptors for other molecules such as hormones and enables adjacent cells to stick together

  • the fluidity of the membrane ( proteins and lipids are free to move) and the mosaic- like arrangement of the proteins give the structure of the membrane its name - the fluid mosaic model

  • the movement of molecules through cell membranes depends on the properties of the molecule as well as the requirements of the cell

  • there are several types of movement:

    • DIFFUSION - the passive net movement of molecules from an area of high concentration to an area of low concentration along a concentration gradient. the molecules move directly through the phospholipid bilayer and the rate of gas exchange by diffusion becomes more rapid as surface area increases, diffusion distance decreases and the diffusion gradient becomes steeper

    • FACILITATED DIFFUSION - requires a channel protein in the cell membrane to transport polar, charged and water soluble molecules across the membrane

    • OSMOSIS - the movement of water molecules from an area of low solute concentration to an area of high solute concentration through a partially permeable membrane

    • ENDOCYTOSIS / EXOCYTOSIS - the movement of large particles into and out of cells via the formation of vesicles. in endocytosis, particles are enclosed in vesicles made from the cell surface membrane and are transported into the cell. in exocytosis, vesicles containing large particles fuse with the cell surface membrane and are transported out of the cell

TURGOR AND OSMOTIC PRESSURE:

  • OSMOSIS = the movement of water molecules from an area of high water potential to an area of low water potential across a partially permeable membrane ( more dilute to less dilute )

  • WATER POTENTIAL= a measure of the potential energy of water in a system, indicating the direction in which water will move and it is influenced by solute concentration and pressure as water moves from an area of higher to lower water potential

  • OSMOTIC POTENTIAL= ( also known as solute potential) is the component of water potential that results from the presence of solutes in water, its always negative as solutes lower the water potential causing water to move towards the higher solute concentration

  • in animals WATER POTENTIAL = OSMOTIC POTENTIAL

  • TURGOR PRESSURE = is the inward pressure exerted by the plant cell wall on the protoplasm, as the protoplasm expands and pushes out

  • in plants turgor pressure is also a factor

  • turgor pressure is generated because water moves in by osmosis causing the protoplasm to swell and push against the cell wall generating hydrostatic pressure

  • this generates a reactive force that pushes inwards

  • a combination of these forces is turgor pressure and it prevents water moving into the cell

  • when turgor pressure is balanced with osmotic potential the cell is at turgor

GASEOUS EXCHANGE SYSTEMS:

  • IN MAMMALS

  • mammals conduct gas exchange via the lungs

  • BOYLES LAW = volume is inversely proportional to pressure

  • therefore inhalation happens by the contraction of the intercostal muscles and diaphragm

  • this causes the volume to increase which causes the pressure to decrease and air moves into the lungs by diffusion down the pressure gradient

  • exhalation the intercostals and diaphragm relax so the volume decreases which increases the pressure which mean air moves out down the pressure gradient

  • oxygen moves into the capillaries from the alveoli via diffusion

  • the alveoli provide a large surface area for diffusion and both the capillaries and the alveoli are made up of one layer of flattened epithelial cells to provide a short diffusion distance

  • blood in the capillaries is deoxygenated as the oxygenated blood is continuously carried away so the concentration gradient is steep

  • IN INSECTS

  • insects have a specialised gaseous exchange system despite being small because they have an exoskeleton which prevents them from taking gas in via diffusion through their skin

  • insects have openings in their body surface called spiracles

  • these can be opened and closed by sphincters which close to prevent water loss

  • oxygen diffuses in through the spiracles and down tubes called trachea, gas exchange doesn’t happen here due to rings of chitin being present which prevents the trachea from collapsing

  • oxygen then diffuses into smaller tunes called tracheoles which are permeable and so gas exchange occurs here

  • sometimes water builds up here which slows down diffusion as the gas has to diffuse through the water before reaching the cells

  • the water is removed in active insects because lactic acid builds up in the cells which decreases their water potential meaning the water moves out of the tracheoles into the cells by osmosis which allows gaseous exchange to occur

  • some very active insects have to ventilate their respiratory systems via mechanical ventilation which involves pumping/ wiggling their abdomens to help move air into their spiracles

  • IN FISH

  • gas exchange in water is more difficult for fish because water is denser and more viscous than air and only contains 5% oxygen

  • fish use Boyles law to continually pump water over their gills

  • this allows gas exchange to occur

  • the gills are made up of filaments covered by folds called lamellae

  • continuous movement of water over the gills keeps them spread out to increase the surface area of the gills and to stop them sticking together

  • the floor of the mouth opens and the operculum ( gill flap ) closes and the floor of the mouth is then raised to increase the pressure but a valve stops the water leaving

  • the increased pressure forces the operculum open which forces water over the gills

  • to maintain the maximum concentration gradient between the water and the rich blood supply within the network of capillaries in the lamellae, a countercurrent exchange system operates

  • this is where the water flowing over the gills and blood in the gill filaments flow in opposite directions maintaining a steep concentration gradient over the entire gill filament

  • IN PLANTS

  • there are multiple layers of a plant leaf:

    • waxy cuticle- prevents water loss

    • upper epidermis- is transparent to allow maximum light through to the cells containing chloroplasts

    • palisade mesophyll layer- cells are stacked vertically to fit in as many cells as possible as they contain chloroplasts so maximum photosynthesis

    • spongy mesophyll layer- air spaces provide an increased surface area for gas exchange

    • lower epidermis, guard cells and stomata- guard cells open and close the stomata to prevent excessive water loss and walls of guard cells adjacent to stomata are thicker to enable opening and closing

  • during the day when conditions are favourable for photosynthesis, the stomata open which allows water loss to be balanced

  • this allows carbon dioxide to diffuse in and and oxygen made by photosynthesis to diffuse out

  • the stomata opens by ions ( mainly positive potassium K+) moving into the guard cells by active transport which causes water to move in by osmosis because the water potential is decreased which makes the guard cell turgid

  • this causes the guard cell to swell meaning the stomata opens allowing gases to diffuse in and out

  • lenticles are areas of loosely arranged cells which act as a pore to allow gas exchange in lignified (woody) plants

CIRCULATION AND THE HEART::

  • HEART STRUCTURE-

  • FOUR CHAMEBRS- right and left atria and the right and left ventricles

  • FOUR MAIN BLOOD VESSELS- the pulmonary artery which takes deoxygenated blood from the heart to the lungs, the aorta which takes oxygenated blood to the rest of the body, the vena cava which takes deoxygenated blood from the body to the heart and the pulmonary vein which takes oxygenated blood from the lungs to the heart

  • ATRIOVENTRICULAR VALVES- prevent back flow of blood from the atriums to the ventricles

  • SEMI LUNAR VALVES- stops a backflow of blood from the pulmonary artery and aorta to the ventricles

  • TENDINOUS CORDS- stop the atrioventricular valves from turning inside out when pressure increases due to contractions

  • SEPTUM- prevents the mixing of oxygenated and deoxygenated blood

  • CORONARY ARTERIES- wrap around the heart to supply blood to the cardiac muscle of the heart

  • CARDIAC MUSCLE-thicker on the left side of the heart because a higher pressure is needed to pump blood further to all tissues in the body

CIRCULATORY SYSTEMS:

  • circulatory systems can be:

    • OPEN- a type of circulatory system where blood isnt confined to blood vessels and flows freely through body cavities directly bathing cells and organs

    • CLOSED- where blood is confined to blood vessels only and gases diffuse in and out of the vessels

    • SINGLE- where the blood is pumped only once around the whole system

    • DOUBLE- where the blood is pumped twice

  • the advantages of a double circulatory system are:

    • the concentration gradient is maintained as the oxygenated and deoxygenated blood do not mix

    • blood pressure to the body tissues is higher

    • blood pressure to the lungs is lower which avoids damaging the capillaries in the lungs and increases the time for gas exchange

    • organisms can develop larger bodies

    THE CARDIAC ELECTRICAL CONDUCTION CYCLE:

  • the heart has the ability to initiate its own contraction so its referred to as myogenic

  • 1- depolarisation ( part of an impulse ) innates in the sinoatrial node ( SA node )

  • 2-depolarisation spreads across the atria, causing atrial systole. the impulse cannot spread directly to the ventricles due to a region of nonconductive tissue

  • 3-the atrioventricular node is stimulated

  • 4-there is a slight delay before atrial diastole

  • 5- the atrioventricular node passes depolarisation into the conducting fibres called the bundle of His which takes the impulse down the septum

  • 6-the bundle of His splits into two branches called the Purkinje fibres which take the impulse through the lower ventricular myocardium and causes ventricular systole

  • the three stages of the cardiac cycle are:

  • ATRIAL SYSTOLE- during atrial systole the atria contract which increases pressure causing the atrioventricular valves to open so blood flows into the ventricles

  • VENTRICULAR SYSTOLE- contraction of the ventricles causes the atrioventricular valves to close and the semilunar valves to open which allows blood to leave the ventricles through the aorta and the pulmonary artery

  • CARDIAC DIASTOLE-the atria and ventricles relax and the pressure inside the heart chambers decreases which causes the semilunar valves in the aorta and the pulmonary arteries to close to prevent backflow of blood

  • THE FUNCTIONS AND COMPONENTS OF BLOOD:-

  • the functions of blood are-

    • transport

    • defence against pathogens

    • formation of lymph and tissue fluid

    • a medium for gaseous exchange

  • the components of blood are:

    • PLASMA-

      • transports digested food products ( EG glucose and amino acids ), nutrient molecules, hormones and excretory products ( EG carbon dioxide and urea )

      • transfers heat around the body

    • ERETHROCYTES ( RED BLOOD CELLS )-

      • transports oxygen and carbon dioxide

      • adapted via their biconcave shape, lack of nucleus and haemoglobin

    • LEUKOCYTES ( WHITE BLOOD CELLS )-

    • granulocytes:

      • neutrophils ( phagocytosis )

      • basophils ( histamine- inflammation/allergic response )

      • eosinophils ( response to parasites, allerigic reactions, inflammation, immunity )

    • agranulocytes:

      • monocytes

      • lymphocytes

    • PLATLETS-

      • fragments of megakaryocytes

      • involved in blood clotting

  • BLOOD CLOTTING:

  • thrombosis also known as blood clotting, prevents blood loss when a blood vessel is damaged, prevents the entry of disease causing microorganisms and provides a framework for repair

  • it happens from a cascade of reactions which lead to a clot formation:

  • 1- when a blood vessel is damaged, platelets attach to exposed collagen fibres

  • 2- a protein called thromboplastin is released from platelets and this protein triggers the conversion of an inactive protein called prothrombin into an active enzyme called thrombin

  • 3- thrombin catalyses the conversion of soluble fibrinogen into insoluble fibrin

  • 4- fibrin forms a network of fibres in which platelets, red blood cells and debris are trapped to form a blood clot

  • ATHEROSCLEROSIS:

  • ATHEROSCLEROSIS- the hardening of arteries caused by the build up of fibrous plaque called an atheroma

  • atheroma formation is the cause of many cardiovascular diseases and occurs as following:

    • 1- the endothelium which lines the arteries is damaged EG from high cholesterol levels, smoking or high blood pressure

    • 2- this increases the risk of blood clotting in the artery and leads to an inflammatory response meaning white blood cells move to site of damage

    • 3-overtime white blood cells, cholesterol, calcium salts and fibres build up and harden which leads to plaque( atheroma) formation

    • 4- the build up of fibrous plaque leads to the narrowing of the artery and it restricts blood flow which increases the blood pressure, which in turn damages the endothelial lining and the process repeats

  • atherosclerosis is a multi-factorial and has modifiable and non-modifiable risk factors

  • factors include things like age, genetics, diet, gender, high blood pressure and cholesterol levels, smoking, physical inactivity and obesity all increase the risk of developing atherosclerosis

  • so the risk of developing cardiovascular disease can be reduced by stopping smoking, regular exercise, reducing alcohol consumption, dietary changes and maintaining a healthy body weight

  • atherosclerosis can cause angina, strokes, myocardial infarction and aneurysms

TRANSPORT OF GASES IN THE BLOOD:

  • STRUCTURE OF HAEMOGLOBIN-

    • a water soluble globular protein

    • it consists of four polypeptide chains ( 2 alpha and 2 beta ) so has a tertiary structure

    • it also includes a haem group (Fe2+)

  • it can carry oxygen in the blood as oxygen can bind tot he haem group and then be released when its required

  • each haem (Hb) group can carry four o2 molecules ( so 8 oxygen atoms all together )

  • the affinity of oxygen for haemoglobin varies depending on the partial pressure of oxygen, the greater the concentration of dissolved oxygen in cells, the greater the partial pressure of oxygen

  • therefore as the partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases

  • during respiration, oxygen is used and the partial pressure decreases which as a result decreases the affinity of haemoglobin for oxygen

  • as a result oxygen dissociates from haemoglobin in respiring tissues where its needed

  • after the unloading process, the haemoglobin returns to the lungs where it binds to oxygen again

  • dissociation curves illustrate the change in haemoglobin saturation as partial pressure changes

  • the saturation of haemoglobin is affected by its affinity for oxygen, therefore in the case where partial pressure is high, haemoglobin has a high affinity for oxygen and is therefore highly saturated and vice versa

  • oxygen dissociation curves have a sigmoidal shape because saturation affects affinity as oxygen binds cooperatively to haemoglobin

CO2 Transport in the Blood | Physiology | Geeky Medics

  • foetal haemoglobin has a higher affinity for oxygen in comparison to adult haemoglobin

  • this is important because maternal and foetal haemoglobin run in a countercurrent exchange system through the placenta

  • the difference in affinity is needed so that when oxygen dissociates from maternal haemoglobin it can bind to foetal haemoglobin ensuring the foetus gets enough oxygen

  • myoglobin is another respiratory pigment that’s used for storage

  • it has a higher affinity for oxygen than haemoglobin and it acts as a storage molecule for oxygen

  • its only made up of one polypeptide subunit

  • BOHR EFFECT-

  • the affinity of haemoglobin for oxygen is also affected by the partial pressure of carbon dioxide

  • in the presence of carbon dioxide the affinity of haemoglobin for oxygen decreases which causes it to be released

  • this means that oxygen dissociates from haemoglobin and can be used in respiring tissues

  • this means the oxygen dissociation graph shifts to the right and is known as the Bohr effect