Topic 3B: More Exchange and Transport Systems Flashcards
What enzymes break down carbohydrates?
- Amylase
- Membrane-bound disaccharidases
Where are each made and where do they act?
- Amylase - salivary glands, pancreas - mouth, ileum
- Membrane-bound disaccharidases - cell membranes of epithelial cells in ileum
How would starch be digested?
- amylase - starch –> maltose
- maltase (MBD) - maltose –> glucose
What bonds are hydrolysed in carbohydrates?
- glycosidic
What enzymes break down lipids?
- lipases
Where are they made and where do they act?
- made in pancreas
- act in ileum
What other substance helps in digesting lipids?
- bile salts
Where are they made and what do they do?
- liver
- emulsify fats to smaller drops to have a larger SA:V for a larger area for lipases to work on
What are lipids hydrolysed into?
- monoglycerides and fatty acids
What bonds are hydrolysed in lipids?
- ester
What can the products of lipids then form?
- monoglycerides and fatty acids can stick with bile salts to form micelles
What enzymes break down proteins?
- endopeptidases
- exopeptidases
- dipeptidases
What do endopeptidases do?
- hydrolyse peptide bonds within the protein
What are examples of endopeptidases?
Where are they made and where do they act?
- Trypsin, chymotrypsin
- Made in pancreas and secreted into ileum
- Pepsin
- Released into stomach by cells in the stomach lining
- Only works in acidic conditions - HCL in stomach
What so exopeptidases do?
- Hydrolyse peptide bonds at the end of proteins
- Remove single amino acids
What do dipeptidases do?
- Exopeptidases that break up dipeptides
- Hydrolyse the bond on the middle
Where are dipeptidases usually found?
- Cell surface membrane of epithelial cells of ileum
What bonds are hydrolysed in proteins?
- Peptide
How are monosaccharides absorbed?
- Glucose absorbed by active transport with Na+ via cotransporter
- Galactose absorbed the same with same cotransporter
- Fructose uses facilitated diffusion with a different transport protein
How are monoglycerides and fatty acids absorbed?
- Micelles help move them to the epithelium
- Constantly break up and reform - release them to be absorbed
- Easily move across membrane as they are lipid soluble
How are amino acids absorbed?
- Na+ actively transported out of epithelial cells into blood
- Makes conc gradient to ileum
- Na+ diffuse from ileum into epithelial cells through sodium dependent transporter protein
- Bring amino acids with them
What is the structure of haemoglobin?
- Quaternary structure
- 4 polypeptide chains
- Each has a haem group (Fe2+)
How does O2 load to haemoglobin?
- Each haemoglobin molecule can carry 4 O2 molecules
- Loads in lungs to form oxyhaemoglobin
What is partial pressure?
- Measure of concentration of a gas
How does pO2 affect O2 affinity of haemoglobin?
- Higher pO2 = higher affinity = O2 loads on
- Lower pO2 = lower affinity = O2 unloads
Where does O2 load and unload and why?
- Loads in lungs - high pO2
- Unloads at tissues - low pO2
What does a dissociation curve show?
- How saturated the haemoglobin is with O2 at different partial pressures
What does the curve show at low pO2?
- Low affinity
- O2 released rather than loaded
- Low O2 saturation
What does the curve show at high pO2?
- High affinity
- More readily combines than unloads
- High O2 saturation
What is the shape of the dissociation curve and why?
- S shaped
- When first O2 molecule joins - shape changes to make it easier for others to load
- As it gets more saturated - harder again to join
- Steep bit in the middle - was easy to load
- Shallow at each end - harder to load
How does CO2 affect O2 unloading?
- Higher pCO2 at cells - lowers O2 affinity for Hb
- O2 unloads more readily
- Dissociation curve moves right - lower saturation for that pO2 so more O2 released
What is this affect of CO2 called?
- Bohr effect
How is haemoglobin different for organisms in low O2 environments?
- Higher affinity
- Curve moves left
- Need to load as much O2 as possible - lower pO2
How is haemoglobin different in very active organisms?
- High O2 demand
- Lower affinity
- Curve shifts left
- Need to unload more readily to cells to respire
Describe arteries
- Thick and muscular walls
- Elastic tissue - stretch and recoil as heart beats - maintain pressure
- Folded endothelium - so artery can stretch - maintain pressure
Describe arterioles
- Divide off from arteries - direct blood to where it’s needed
- Muscular walls - can contract - constrict flow or relax to maintain pressure
Describe veins
- Low pressure - carry blood back to heart
- Wide lumen, little muscle or elastic
- Valves - prevent backflow
- Flow helped by contraction in body muscles around them
Describe capillaries
- Structured for exchange of substances
- Close to cells - short diffusion pathway
- One cell thick - short pathway
- Large number & capillary beds - high SA
- Narrow lumen - forces blood to slow - inc diffusion time
How is tissue fluid formed?
- Arteriole end - high hydrostatic pressure - fluid pushed out
- Plasma proteins remain - too large to leave
- Forms high solute conc = low water potential
- Water does move back in but pressure is so high net movement is out of the capillary
What happens to tissue fluid at the venule end?
- Lower hydrostatic pressure and higher osmotic pressure
- Water reabsorbed by osmosis
- Useful materials have been taken in by cells and replaced with waste products
- 90% reabsorbed - rest goes to lymphatic system and drains back into the blood near the heart
Describe the atria
- Thinner elastic walls
- Stretch to collect blood and pump to ventricles
Describe the ventricles
- Thicker muscular walls to contract to pump blood
- Left - thicker and more muscular - has to pump blood to body
- Same internal volumes
What valves are present in the heart?
- Atrioventricular - between atria and ventricles - tricuspid (right) and bicuspid (left)
- Semi lunar valves - between ventricles and aorta / pulmonary artery
How do valves work?
- Open one way
- When there is a higher pressure behind - forced open
- When a higher pressure is in front - forced closed - prevent backflow of blood
What is the septum?
- Separates left and right sides of the heart
- Stops oxygenated and deoxygenated blood from mixing
Describe diastole
- All relaxed - Semi lunars close - higher pressure in aorta and pulmonary artery
- Blood fills atria - pressure increases slightly
- Pressure is greater in atria so AV open
- Blood flows passively into ventricles
Describe atrial systole
- Ventricles are relaxed
- Atria contract - blood pumped into ventricles as atrial volume dec so pressure inc
- Ventricular pressure inc slightly as they gain blood
Describe ventricular systole
- Atria relax
- Ventricles contract - dec volume, inc pressure
- Pressure is higher in ventricles so AV close and SL open
- Blood pumped out into arteries
What makes the heart sounds?
- Lubb - ventricles contract - AV close
- Dubb - atria contract - SL shut
What is the equation for cardiac output?
cardiac output = stroke volume x heart rate
How does an atheroma form?
- Endothelium of artery is damaged (e.g. by high blood pressure)
- White blood cells, lipids from the blood clump under lining to make fatty streaks
- Over time a fibrous plaque forms - WBC, lipids, connective tissue –> this is an atheroma
What does an atheroma cause?
- Partially blocks the lumen of the artery
- Restricts blood flow
- Blood pressure increases
What is an aneurysm?
- After an atheroma - blood at the now high pressures can push through the inner artery layers
- Pushes through the outer artery to make a balloon-like swelling –> aneurysm
- Can burst –> haemorrhage
What is thrombosis?
- Atheroma ruptures endothelium of the artery - damages the wall - leaves a rough surface
- Platelets and fibrin collect at the damage - clots –> thrombosis
- Can block artery
- Can dislodge and block somewhere else
- Can break a bit of and form a clot elsewhere
What is a myocardial infarction?
- Heart attack
- Coronary artery blocks - heart O2 supply is stopped
- Can damage and kills heart tissue
- Pain in chest & upper body, shortness of breath, sweating
How does a high cholesterol diet increase risk of heart disease?
- High cholesterol = higher chance of fatty deposits –> inc blood pressure and risk of clots –> CHD
- High sat fat diet = high cholesterol = fatty deposits
- High salt = high blood pressure = high risk
How is smoking a risk factor for heart disease?
- Nicotine - increases risk of high blood pressure
- Carbon monoxide - reduces O2 transport by binding to haemoglobin instead of O2 - reduced O2 = increased heart attack risk
How does high blood pressure contribute to risk of heart disease?
- Increased risk of damage to artery walls - increased atheroma risk - even higher blood pressure
- Can cause clots and even CHD
- Blood pressure can be increased by being overweight, lack of exercise, alcohol consumption
How would you dissect a heart?
- Lab coat, clean, sharp, rust free tools
- Try to identify chambers of the heart and blood vessels and coronary arteries
- Cut down right and left ventricles –> compare thicknesses of walls
- Locate AV and SL valves
- Wash hands and disinfect surfaces etc
What do the xylem transport?
- water and mineral ions
What is the structure of the xylem?
- Dead cells
- End to end with no end walls –> uninterrupted flow
- Lignin lining - waterproof polymer - provides structure
What is transpiration?
- Water evaporation from leaves via stomata - moves down water potential gradient
What is cohesion - tension?
- Water evaporates via transpiration
- Tension is formed to pull water up and into leaves
- Cohesion and adhesion means water moves up as a column
- Water then enters the stem via the roots
How does light affect transpiration?
- More light = faster transpiration
- Stomata open in light for gas exchange for photosynthesis
- In dark - closed so little transpiration
How does temperature affect transpiration?
- Higher temperature = faster transpiration
- Water molecules have more energy so evaporate faster
- Increased concentration gradient inside and outside the leaf so diffuses out faster
How does humidity affect transpiration?
- Lower humidity = faster transpiration
- Drier so steeper concentration gradient
- Faster water loss
How does wind affect transpiration?
- Higher wind = faster transpiration
- Air blows away water from around stomata
- Increased concentration gradient so faster rate of loss
How would you do the potometer investigation?
- Cut shoot underwater so no air enters the xylem - cut at a slant for increased SA
- Assemble the shoot and potometer underwater
- Remove from the water leaving the end of the capillary tube under
- Check water and air tight, dry the leaves and let the plant acclimatise then shut the tap
- Remove the tube end and let a bubble form then put back in and record the starting position of the bubble
- Start the stopwatch and record the bubble movement in a given time to find rate
How would you dissect and observe a plant?
- Use a scalpel to cut a cross section of the stem - thin for a microscope
- Put in water with tweezers to stop them drying out
- Stain with TBO to stain lignin
- Rinse off the stain and put on a slide and observe
What does phloem transport?
- Solutes - mostly sugars
What is the structure of phloem?
- Sieve tube elements - living - no nucleus and few organelles
- Companion cells - carry out living processes for them
What is translocation?
- Moves solutes source to sink - requires energy
- Moves high to low conc
- Source e.g. leaves
- Sink e.g. meristems, roots, stem
- Enzymes maintain conc gradient by changing solutes at the sink to something else e.g. sucrose –> starch
Describe the mass flow hypothesis
- Active transport solutes from companion cells into sieve tube - lowers water potential - water moves in - increases pressure
- At sink solutes are removed - higher water potential - water moves out - decreases pressure
- Solutes move down pressure gradient
What evidence is there for mass flow?
- Ringing - bulge forms above ring and has higher sugar conc - shows downward flow of sugars
- Aphids - leave mouthparts - sap flows out quicker from near leaves - shows pressure gradient
- Metabolic inhibitor (stops ATP production) - stops translocation - shows active transport is used
What evidence is there against mass flow?
- Sugar moves to many sinks not just the one with the highest water potential
- Sieve plates would be a barrier to flow - would need lots of pressure to move at a reasonable rate
What is the investigation using radioactive tracers?
- Can use radioactive CO2 in a leaf - used in photosynthesis - sugars move in phloem
- Track this using autoradiography - kill plant (freeze in liquid nitrogen) and put on photo film
- Goes black where the radioactive substance is present
- Can kill plants at different times to show movement leaves to roots
