Exchange and transport systems Flashcards
Fish gill structure + adaptations
- Each gill is made of gill filaments which give a big surface area for gas exchange
- Gill filaments are covered in lamellae which further increase surface area
- Lamellae have lots of blood capillaries + thin surface layer of cells to speed up diffusion
Fish counter-current system
Blood flows through lamellae in 1 direction, water flows in opposite direction -> maintains a large concentration gradient between water + blood -> concentration of oxygen in water is always higher than in blood, so as much oxygen as possible diffuses from water into blood
Gas exchange in insects (6 steps)
- Air moves into tracheae through spiracles on surface
- Oxygen travels down concentration gradient towards cells
- Tracheae branch off into smaller tracheoles which have thin, permeable walls + oxygen diffuses directly into individual cells
- CO2 from cells moves down concentration gradient towards spiracles
- Insects use rhythmic abdominal movements to move air in + out of spiracles
Insect adaptations to control water loss (3)
- Close spiracles using muscles
- Waterproof, waxy cuticle all over body + tiny hairs around spiracles -> both reduce evaporation
What is the main gas exchange surface of plants?
Surface of mesophyll cells in the leaf (large surface area, stomata in epidermis)
How do guard cells control water loss?
Water enters guard cells, making them turgid, which opens stomata.
If plant starts to get dehydrated, guard cells lose water + become flaccid, which closes stomata.
Adaptations of xerophytes (warm, dry, windy) (5)
- Stomata sunk in pits + layer of hairs on epidermis that trap moist air -> reduces concentration gradient of water between leaf + air
- Curled leaves with stomata inside to protect from wind
- Reduced number of stomata
- Waxy, waterproof cuticles on leaves + stems to reduce evaporation
Process of inspiration
- External intercostal + diaphragm muscles contract (active process)
- Ribcage moves upwards + outwards, diaphragm flattens -> increases volume of thoracic cavity -> decreases pressure
- Air flows down concentration gradient into lungs
Process of expiration
- External + diaphragm muscles relax
- Ribcage moves downwards + inwards, diaphragm becomes curved -> volume of thoracic cavity decreases so air pressure increases
- Air is forced down pressure gradient, out of lungs
Forced expiration
External intercostal muscles relax + internal intercostal muscles contract, pulling ribcage further down + in (antagonistic movement)
How does oxygen diffuse from alveoli to blood? (what layers of tissue)
Oxygen diffuses out of alveoli, across the alveolar epithelium + capillary endothelium, and into haemoglobin in the blood
What is tidal volume?
Volume of air in each breath - usually between 0.4dm3 and 0.5dm3
What could exposure to asbestos cause?
Fibrosis - formation of scar tissue in lungs which is thicker + less elastic than normal lung tissue -> reduces tidal volume so reduces rate of gas exchange
Describe digestion of carbohydrates
- Amylase catalyses hydrolysis or glycosidic bonds in starch to produce maltose (a disaccharide)
- Membrane-bound disaccharides break down disaccharides into monosaccharides by hydrolysing glycosidic bonds
Where are membrane-bound disaccharides found?
attached to cell membranes of epithelial cells lining the ileum (final part of the small intestine)
Where is amylase produced and released?
Salivary glands - released into mouth
Pancreas - released into small intestine
How are the 3 monosaccharides absorbed?
Glucose + galactose are absorbed by active transport with sodium ions via a co-transporter protein
Fructose is absorbed via facilitated diffusion through a different transporter protein
Describe digestion of lipids
- Bile salts emulsify lipids -> cause lipids to form small droplets which increases surface area of lipid that’s available for lipases to work on
- Lipases catalyse breakdown of lipids into monoglycerides + fatty acids via hydrolysis of ester bonds
- Monoglycerides + fatty acids stick with bile salts to form micelles
Where are lipases produced and released?
Made in pancreas, work in small intestine
Where are bile salts produced?
Liver
Flow diagram of lipid digestion
Big lipid droplet + bile salts -> emulsification -> small lipid droplets -> lipase digestion -> monoglycerides + fatty acids via hydrolysis-> micelles
Adsorption of monoglycerides + fatty acids
- Micelles constantly break up + reform so can release monoglycerides + fatty acids, allowing them to be absorbed
- Monoglycerides + fatty acids are lipid-soluble so can diffuse directly across the epithelial cell membrane
How are proteins broken down?
By a combination of different proteases (endopeptidases + exopeptidases) which hydrolyse peptide bonds between amino acids
Endopeptidases + examples
Hydrolyse proteins within a protein
e.g. trypsin produced in pancreas + released into small intestine
e.g. pepsin released into stomach by cells in stomach lining (only work in acidic conditions -> hydrochloride acid)
Exopeptidases + dipeptidases
Hydrolyse peptide bond at the ends of proteins - remove single amino acids
Dipeptidases are exopeptidases that work on dipeptides - separate 2 amino acids
Dipeptidases located in cell-surface membrane of epithelial cells in the small intestine
How are amino acids absorbed?
Co-transport
1. Sodium ions are actively transported out of the ileum epithelial cells into the blood -> creates a sodium ion concentration gradient
2. Sodium ions diffuse from the lumen of the ileum into the epithelial cells through sodium-dependent transporter proteins, carrying the amino acids with them
What is the Bohr effect?
- When cells repite they produce CO2 which raises the partial pressure of CO2 (pCO2)
- Increases the rate of oxygen unloading (lower affinity) so the dissociation curve shifts right -> saturation of blood with oxygen is lower for a given pO2 so more oxygen is released
Do organisms that live in environments with a low concentration of oxygen have a lower or higher affinity for oxygen?
Higher affinity - dissociation curve is left (need to grab as much oxygen as possible in lungs from limited supply)
Do very active organisms have a lower or higher affinity for oxygen?
Lower affinity for oxygen - dissociation curve is right (need to release as much oxygen as possible in tissue quickly)
Adaptations of arteries
Thick, muscular walls with elastic tissue to stretch and recoil - maintains high blood pressure
Folded inner lining (endothelium) - allows artery to stretch to maintain high blood pressure
Adaptation of arteriales
Muscles inside the arterioles contract to restrict blood flow or relax to allow full blood flow -> direct blood to different areas of demand in the body
Adaptations of veins
Wider lumen + very little elastic/muscle tissue - low blood pressure
Valves - prevent blood flowing backwards
Contraction of body muscles around them - helps blood flow
What is tissue fluid?
Fluid that surrounds cells in tissues
Made from small molecules that leave the blood plasma e.g. oxygen, water, nutrients
Cells take in O2 + nutrients from the tissue fluid and release metabolic waste into it
Describe pressure filtration
- At the start of the capillary bed, the hydrostatic (liquid) pressure inside the capillaries is greater than the hydrostatic pressure in the tissue fluid.
- Difference in hydrostatic pressure means an overall outward pressure forces fluid out of the capillaries + into the spaces around the cells, forming tissue fluid
- As fluid leaves, the hydrostatic pressure reduces in the capillaries
-> much lower at the venule end of
the capillary bed (nearest to the veins) - Due to the fluid loss + an increasing concentration of plasma proteins (which don’t leave the capillaries), the water potential at the venule end of the capillary bed is lower than the water potential in the tissue fluid
- Some water re-enters the capillaries from the tissue fluid at the venule end by osmosis
- Excess tissue fluid is drained into the lymphatic system which transports it back into the circulatory system
Structure of ventricles in contrast to atria
Thicker walls than atria -> push blood out of heart rather than short distance into ventricles
Unique structure of left ventricle
Thicker, more muscular walls than the right ventricle -> needs to contract powerfully to pump blood all the way round the body
Location and function of semi-lunar (SL) valves
Link the ventricles to the pulmonary artery + aorta to stop blood flowing back into the heart after the ventricles contract
Location and function of atrioventricular (AV) valves
Link the atria to the ventricles to stop blood flowing back into the atria when the ventricles contract
How does high pressure affect valves? (2)
Higher pressure behind valve -> forced open
High pressure in front of valve -> forced shut
Blood only flows in 1 direction in the heart
Explain the first stage of the cardiac cycle
- Ventricles are relaxed
- Atria contract, decreasing the volume + increasing the pressure inside the chambers -> pushes the blood into the ventricles
- Slight increase in ventricular pressure + chamber volume as the ventricles receive the ejected blood from the contracting atria
Explain the second stage of the cardiac cycle
- Atria relax
- Ventricles contract, decreasing volume + increasing pressure
- Pressure becomes higher in the ventricles than atria -> forces AV valves shut to prevent back-flow
- Pressure in ventricles is higher than in aorta + pulmonary artery -> forces open SL valves so blood is forced out into arteries
Explain the third stage of the cardiac cycle
- Ventricles + atria relax
- Higher pressure in arteries closes SL valves to prevent back-flow into ventricles
- Blood returns to heart + atria fill again due to higher pressure in vena cava + pulmonary vein-> starts to increase pressure of atria
- As ventricles continue to relax, pressure falls below that of atria -> AV valves open so blood flows passively into ventricles
Atheroma formation
- If damage occurs to the endothelium (e.g. high blood pressure), white blood cells, lipids + connective tissue build up under the lining and harden to form an atheroma (fibrous plaque)
- Partially blocks lumen + restricts blood flow, which causes blood pressure to increase
e.g. coronary heart disease occurs when lots of atheromas in coronary arteries -> restrict blood flow to heart + can lead to a myocardial infarction
Aneurysm formation
- Atheroma plaques damage + weaken arteries, and narrow them which increases blood pressure
- Blood travelling through a weakened artery at high blood pressure may push the inner layers through the outer elastic layer to form an aneurysm (balloon-like swelling)
- Aneurysm may burst, causing a haemorrhage
Thrombosis formation
- Atheroma plaque can rupture the endothelium of artery - > damages artery wall + leaves a rough surface
- Platelets + fibrin accumulate at the site of damage + form a blood clot (thrombus)
- Blood clot can cause a complete blockage of artery or become dislodged + block a blood vessel elsewhere
- Debris from rupture can cause another blood clot to form further down artery
Explain the cohesion-tension theory of water transport
- Water evaporates from leaves at the top of the xylem (transpiration) -> creates tension which pulls more water into leaf
- Water molecules are cohesive so column of water in xylem moves upwards
- Water enters stem through the roots
Process of transpiration (2 steps)
- Water evaporates from moist cell walls + accumulates in spaces between cells in the leaf
- When stomata open, water vapour diffuses out of leaf down concentration gradient
4 factors that affect transpiration rate
Light – stomata open when it is light to let in CO2 for photosyntheses
Temperature – warmer water molecules have more energy so evaporate from cells in leaf faster -> increases concentration gradient between inside + outside
Humidity – lower humidity = faster transpiration (need dry air for high concentration gradient)
Wind – blows away water molecules from around stomata so maintains high concentration gradient
General method to estimate transpiration rate
Use a potometer (measures water uptake which is directly related to water loss) + record distance moved by bubble/time
When preparing, ensure everything is airtight so no air enters xylem of plant shoot
Method to dissect plants
- Use a scalpel to cut a thin cross-section of stem
- Transfer each section to dish containing a stain + leave for 1 minute -> allows you to see position of xylem vessels + examine structure
- Rinse off sections in water + mount into slides
How is phloem tissue adapted for transporting solutes?
Sieve tube elements are living cells that for tube – they have no nucleus + few organelles so there is a companion cell for each sieve tube element -> carry out living functions for sieve cells e.g. provide energy for active transport of solutes
Translocation
Movement of solutes (sucrose + amino acids) in phloem
Moves solutes from sources (where it’s made e.g. leaves) to sinks (where it’s used)
Enzymes maintain a concentration gradient from source to sink by changing solutes at the sink -> always a lower concentration at sink
1st step of mass flow hypothesis (at source end)
- Active transport is used to load solutes from companion cells into the sieve tubes of phloem at the source
- This lowers water potential inside sieve tubes so water enters tubes by osmosis from xylem + companion cells
- This creates high pressure inside sieve tubes at source end
2nd step of mass flow hypothesis (at sink end)
- Sink end - solutes are removed from phloem to be used up
- Increases water potential inside sieve tubes, so water leaves tubes by osmosis
- This lowers pressure inside sieve tubes
3rd step of mass flow hypothesis
- Pressure gradient from source end to sink end -> pushes solutes along sieve tubes towards sink
- When they reach sink, solutes are used or stored
2 arguments that support the mass flow hypothesis
- a radioactive tracer can be used to track the movement of organic substances in a plant
- if a ring of bark is removed from a woody stem, a bulge forms above the ring -> fluid in bulge has a high concentration of sugars than fluid from below ring -> evidence of downward flow of sugars
2 arguments against the mass flow hypothesis
- sugar travels to many different sinks, not just to one with highest water potential
- sieve plates would create a barrier to mass flow -> a lot of pressure would be needed for solutes to get through at a reasonable rate
