State the three main factors that affect the need for an exchange system	Size, SA:Vol ratio and level of activity
Explain why smaller organisms have a lower demand for oxygen than larger organisms	Smaller organisms have a larger SA:V ratio than larger organisms; simple diffusion can be sufficient for unicellular organisms but due to many-layered multicellular organisms, it would be too slow. Multicellular organisms therefore need transport systems
Describe and explain three features of a good exchange surface	Large SA (folded walls; provides more space for relevant molecules to pass through); thin, permeable barriers (reduces diffusion distance); good blood supply (keeps high concentration gradients for rapid diffusion)
Describe how human alveoli are adapted to reduce diffusion distances	Alveolus wall one cell thick; capillary wall one cell thick; walls of alveoli/capillaries contain squamous (flattened) cells; caoillaries are in close contact with alveoli walls; capillaries are narrow to restrict RBC movement
Describe the role of surfactant in alveoli	Coats the internal surface of the alveoli to reduce cohesive forces between water molecules, preventing collapse
Describe the mechanism of inspiration	Diaphragm contracts (moves down and flattens); external intercostal muscles contract to push ribcage up and out; volume of thorax increased and so pressure decreases below atmospheric pressure; air rushes into lungs down a pressure gradient
Why do alveolar walls contain elastic fibres?	To stretch during inspiration and recoil , pushing air out, during expiration
Which tissue type comprises alveolar walls?	Squamous epithelium
The trachea is lined with ciliated epithelial tissue and goblet cells. Describe the functions of these.	Goblet cells produce mucus onto the tracheal lining, trapping dust and microorganisms. The cilia then beat and move the mucus away from the lungs and towards the throat
The trachea and bronchi are lined with cartilage. Describe why.	C-shaped rings of cartilage line these tubes, preventing collapse during inspiration. The C-shape allows food to pass down the oesophagus behind the trachea
Describe how the nasal cavity is adapted for exchange	Large SA with a good blood supply, warming air to body temperature; lined with hair (which secretes mucus) to trap dust and MOs, protecting from infection; moist surfaces to increase the humidity of the incoming air, reducing evaporation from exchange surfaces
Describe the roles of smooth muscle and elastic tissue in the airways	Smooth muscle can contract to constrict airways (not under conscious control, i.e. involuntary); elastic fibres elongate smooth muscle again, recoiling the airway to its original shape and size (dilates airway)
Describe precautions that must be taken when using a spirometer	Subject should be free of asthma; there should be no air leaks in the apparatus; mouthpiece should be sterilised; soda lime should be fresh and functioning
Describe what is meant by 'vital capacity' and state the factors that it depends upon	The maximum volume of air that can be moved by the lungs in one breath; measured by taking one deep breath and expiring all the possible air from the lungs. Depends on: size (height) of person; age/gender; exercise levels.
State the usual range for vital capacity	2.5 - 5.0 dm3
Describe what is meant by 'inspiratory reserve volume'.	The maximum volume of extra air you can breathe in forcibly (vital capactiy - tidal volume - ERV)
Describe what is meant by 'expiratory reserve volume'.	The maximum volume of extra air you can breathe out forcibly (vital capacity - tidal volume - IRV)
Describe what is meant by 'residual volume' and state the standard volume	The volume of air that remains in the lungs even after forced expiration, i.e. the air that remains in the airways and alveoli (usually 1.5 dm3)
Describe what is meant by 'tidal volume' and state a typical figure	Volume of air moved in and out with each breath at rest. A normal value would be 0.5 dm3 (500cm3)
What is the difference between 'ventilation rate' and 'breathing rate'?	BR = no. of breaths taken per min; VR = total volume of air inhaled per min
State the equation for ventilation rate	Ventilation rate = tidal volume x breathing rate (breaths per minute)
The normal breathing rate of a healthy 50 year old woman is 18 breaths per minute and her tidal volume is 500 cm3. During strenuous exercise, her ventilation rate increases to 45 000 cm3min-1 and she is breathing 30 times a minute. Calculate her tidal volume during this exercise and state how much higher than normal this figure is.	TV = 1500 cm3 ...1 dm3 higher than normal
Most bony fish have 5 pairs of gills which are covered by a bony flap, known as the …? What is the function of this bony flap?	Operculum; protects the gills and ensures a constant flow of water
Describe the structure of gills in bony fish	Two rows of gill filaments; these are slender branches of tissue known as primary lamellae and are attached to a bony arch. Each gill filament is folded into secondary lamellae providing a very large surface area
Describe ventilation in bony fish	Buccal cavity (mouth) can change volume; floor of mouth moves downwards, drawing water into the buccal cavity; mouth closes and water is pushed through the gills. As water is pushed from the buccal cavity through the gills, the operculum moves outwards
How is air supplied to respiring tisses in an insect?	Tracheal system
How does air enter the tracheal system in an insect?	Spiracle
The ends of tracheoles in insects are filled with tracheal fluid. What is the function of this fluid?	Gaseous exchange occurs between air in tracheole and the tracheal fluid
When an insect is active, what changes occur in the insect to increase their oxygen supply?	Tracheal fluid can be withdrawn into the body fluid to increase the surface area of the tracheole wall exposed to air
Describe three features of an effective transport system	A fluid to carry nutrients/oxygen/wastes around the body (blood); a pump to create pressure that will push the fluid around the body (heart); exchange surfaces (capillaries)
Describe three disadvantages of single circulatory systems, as seen in fish	Blood pressure drops as blood passes through the gill capillaries; blood flows slowly through as it is under low pressure; the rate of delivery of oxygen/nutrients to respiring tissues is limited (and removal of CO2 and urea)
Explain why fish do not need as much energy as mammals	They are not as metabolically active as mammals as they do not maintain their body temperature
Describe what is meant by the term open circulation	Blood is not always held in vessels, but it circulates throughout the body cavity and the tissues and cells bathe directly in blood
State two disadvantages of open circulatory systems	Blood pressure is low and blood flow is therefore slow; circulation can be affected by body movements (or lack of)
State four advantages of closed circulation over open circulation	Blood travels at higher pressure and therefore flow is faster; oxygen/nutrients supplied and CO2/urea removed more quickly; transport is independent of body movements.
What is the inner tissue lining of a blood vessel called? What is its role?	Endothelium; reduced friction with the flowing blood
Describe the three structural layers of an artery	Tunica intima - thin layer of elastic tissue which allow walls to stretch and recoil (opposes muscle); tunica media - thick layer of smooth muscle; tunica adventitia - thick layer of collagen and elastic tissue providing strength to withstand the high pressure and recoiling against the muscle
What is the role of arterioles?	Take blood from artery to capillary; they have a layer of smooth muscle which contracts restricting and slowing blood flow
Describe how capillaries are adapted for exchange	Narrow lumen (squeezes red blood cells against walls so transfer of oxygen is better to the tissues); walls consist of single layer of endothelial cells (reduces diffusion distance); walls are permeable (allows blood plasma and dissolved substances to leave the blood)
Describe the function of a venule	Takes blood from the capillaries to the veins
Describe how veins are adapted to carry blood back to the heart	Wide lumen to ease blood flow; thin layers of elastic/muscle/collagen in walls as no need to stretch and recoil; valves to prevent backflow of blood
Where is hydrostatic pressure created of the blood created?	In the ventricles of the heart
What is oncotic pressure?	The pressure created by the osmotic effects of the solutes
What substances might affect the oncotic pressure of the blood?	Dissolved solutes such as mineral ions, sugars and proteins
State the cell types that are most likely to be found in blood plasma, tissue fluid and lymph	Blood plasma - red blood cells, neutrophils, lymphocytes; tissue fluid - neutrophils (especially during infection); lymph - lymphocytes
Why can proteins known as plasma proteins not leave the blood plasma?	They are too large to pass between the squamous cells of the capillary wall
Why can neutrophils enter the tissue fluid but erythrocytes cannot?	Neutrophils can change shape very easily (multilobed nucleus) and squeeze themselves between cells. Erythrocytes cannot change shape as much
Describe the role of the lymph fluid	A system of tubes that returns excess tissue fluid to the blood system
How does tissue fluid facilitate exchange of substances to body cells?	Tissue fluid surrounds body cells so exchange occurs across plasma membranes
Describe the simple structure of haemoglobin	Four subunits (each with a polypeptide chain and a haem group); haem groups each contain an Fe2+ ion at the centre; iron ions can attract and hold an oxygen molecule
What is the process known as by which oxyhaemoglobin releases its oxygen to respiring cells?	Dissociation
What is the main difference between foetal haemoglobin and adult haemoglobin?	It has a higher affinity for oxygen than adult haemoglobin
Describe three ways in which carbon dioxide is transported	5% dissolved directly in the plasma; 10% directly with haemoglobin in the form of carbaminohaemoglobin; 85% in the form of hydrogencarbonate ions
Describe the formation of hydrogencarbonate ions	Carbon dioxide from the blood plasma diffuses into RBCs anf combines with water to form carbonic acid (catalysed by carbonic anhydrase); carbonic acid then dissociates into hydrogencarbonate ions and protons
Describe how the charge inside a RBC is maintained when hydreogencarbonate ions diffuse into the plasma	Chloride ions move into the RBCs from the plasma (chloride shift)
Describe how the pH inside a RBC is buffered as hydrogen ions build up inside, making the RBC very acidic	Hydrogen ions are taken out of solution and combined with haemoglobin to form haemoglobinic acid (HHb)
What is the net result of the Bohr effect?	More oxygen is released where more carbon dioxide is produced in respiration
With reference to protein structure, explain how increasing hydrogen ion levels affects haemoglobin.	More hydrogen ions --> lower pH (more acidic cytoplasm); tertiary structure of Hb altered which reduces its affinity for oxygen
What is the purpose of semilunar valves?	To prevent backflow of blood from arteries to the ventricles
Why is the left ventricular wall so much thicker than the right ventricular walls?	Blood is pumped throught the aorta and needs sufficient pressure to overcome the resistance of the systemic circulation
Why are there so many mitochondria in cardiac muscle?	Supply energy for contraction
What is the purpose of intercalated discs between adjacent muscle cells?	Ensures an even, synchronised contraction
Briefly outline the events of atrial systole	Left and right atria contract together; blood is squeezed from the atria through the atrioventricular valves into the ventricles, down a pressure gradient.
Briefly outline the events of ventricular systole	Ventricular blood pressure rises very quickly to a level above the arteries; semilunar valves open and blood rushes out of ventricles into the arteries
Briefly outline the events of diastole	Once ventricular contraction is complete, heart muscle starts to relax, heart starts to fill with blood again and semilunar valves close
What is meant by the term myogenic?	Cardiac muscle can initiate its own contractions
What tissue is responsible for initiating the heartbeat?	Sinoatrial node (SAN)
What tissue propagates the electrical signal from the atria to the ventricles, resulting in ventricular systole?	Atrioventricular node (AVN)
Why is there a delay before the AVN depolarises the ventricular walls?	To allow the atria to finish contracting
Describe the role of the Purkyne tissue	Specially adapted muscle fibres that conduct the wave of excitation from the AVN down the septum to the ventricles
What do the letters PQRST indicate in an ECG?	P = atrial excitation; QRS = ventricular excitation; T = diastole
What terms describe a slow and a fast heart rate?	Bradycardia; tachycardia
What happens in atrial fibrillation?	Atria beat more frequently than ventricles, meaning no clear P wave can be seen on ECG
What is an ectopic heart beat?	An early ventricular beat
Plant transport systems consist of 2 major specialised vascular tissues. Name these, state their transport material and the direction of transport	Xylem - water, soluble mineral ions (upwards); phloem - assimilates (up or down)
What tissue is found in between the xylem and phloem? What is its function?	Meristematic tissue (source of stem cells)
What is the purpose of parenchyma cells in xylem tissue?	To separate and support the vessels (act as packing tissue)
What is the purpose of lignin in xylem vessels?	Strengthens vessel wall and prevents collapse
How do bordered pits form and what is their purpose?	Where lignification is incomplete, leaving gaps in the cell wall; the bordered pits in 2 adjacent vessels are aligned to allow water to leave one vessel and pass into the next, as well as leave the xylem
Describe three adaptations of xylem vessels that relate structure to function	1) Dead cells aligned end to end to form a continuous column; (2) Tubes are narrow so water column doesn't break easily and capillary action can be effective; (3) Bordered pits allow sideways movement of water between vessels; (4) Lignin allows stretching of xylem (spiral, annular or reticulate patterns) as plant grows
What two components of phloem tissue are concerned with transport?	Sieve-tube elements and companion cells
Why do sieve tube elements contain no nucleus and very little cytoplasm?	Allows space for mass flow of sap to occur
How are companion cells adapted for active loading?	Many mitochondria to produce ATP
Describe 2 major pathways taken by water to move between cells	Apoplast - through spaces in cell walls and between cells (mass flow…not osmosis); symplast - moves through cytoplasm and between cells via plasmodesmata
What allows water to move through cells via the symplast pathway, and by which mechanism of movement?	Different water potential of cytoplasm of adjacent cells; Water moves by osmosis
What allows water to move continuously via the apoplast pathway?	Cohesion, by diffusion
Why does the presence of starch in the endodermis suggest that an active process is involved?	Starch acts as a store of sugars, which can be released and respired to release energy for active processes
What is the Casparian strip?	A band of waterproof, waxy suberin around each endodermis cell (on cell wall)
Explain the significance of the Casparian strip	Waterproof hence locks the apoplast pathway between the cortex and the medulla, forcing water and dissolved mineral ions to pass through the selectively permeable membrane into the cytoplasm, filtering out toxic chemicals
Describe how water is lost via stomata (refer to gradients)	Water vapour in higher concentration in air spaces than in space outside leaf; water diffuses down water vapour potential gradient
Describe the effects of light intensity, humidity and wind speed on the rate of transpiration	Light intensity (increased LI…increased rate as stomata more open); humidity (incr. humidity in air…decr. Rate as lower water vapour potential gradient); wind speed (incr. wind…incr. rate as maintaining high water vapour potential gradient)
State two precautions that should be taken to ensure no air bubbles are in the potometer setup	Set up u/w; cut stem u/w to prevent air entering xylem
The distance moved by the meniscus in a potometer is 45mm in 5 minutes. The radius of the capillary tube is 0.5 mm. Calculate the rate of transpiration.	7.1mm3/min
Describe how water moves up the stem via the transpiration pull	Loss of water by evaporation at the top of the plant must be replaced by water from the xylem. This puts water at the top of xylem under tension. Tension pulls the column of water up the xylem as water molecules are cohesive.
What property of water causes cohesion?	The polarity of the water molecule, which produces hydrogen bonds between the molecules
Define the term translocation	Transport of assimilates from source to sink (tissue that needs them)
State two sinks (for translocation) in a plant	Roots growing or active uptaking mineral ions; actively dividing meristematic tissue; part plants that are laying down food stores (e.g. developing seeds, fruits etc)
What is the difference between active loading and active transport?	Active transport is the movement of particles against their concentration gradient using metabolic energy (ATP). Active loading is a more extensive process which involves active transport at some stage. In this case, active loading uses active transport to pump hydrogen ions out of the companion cells. This results in movement of sucrose molecules by facilitated diffusion and diffusion.
Describe the role of hydrogen ions in active loading	The hydrogen ions are pumped out of the companion cells, creating a hydrogen ion concentration gradient across the cell membrane. The hydrogen ions can diffuse back into the companion cells through special transport proteins – but they only move if sucrose is carried in with them (cotransport). 8
Why is sucrose transported in phloem and not glucose?	More stable hence less likely to be metabolised in the transport process
How does sucrose move from the companion cells into the sieve tube elements?	Increasing sucrose conc causes water to also move into companion cells, which builds up turgor pressure (and water potential). The water carrying assimilates (sucrose) then enters sieve tubes down the pressure/WP gradient through plasmodesmata
Based on what principle does mass flow work in sieve tubes?	Turgor pressure difference - sieve tubes at source has higher turgor pressure due to "intake" of sucrose and water, whereas sieve tubes at sinks has lower turgor pressure due to the cells removing the sucrose from the sieve tubes
Based on what principles does phloem unloading work?	Diffusion of sucrose - by rapidly moving into surrounding cells or by converting into glucose, decreasing sucrose conc within cells hence maintaining sucrose conc difference between cells in sink and sieve tube

3 - Exchange and Transport