3. exchange and transport systems P1 Flashcards
how does an organisms size relate to their surface area to volume ratio?
the larger the organism, the lower the surface area to volume ratio
explain the advantage of larger animals having a specialised system that facilitates oxygen uptake [2]
larger organisms have a smaller surface area to volume ratio, so it overcomes the long diffusion pathway
how does an organisms surface area to volume ratio relate to their metabolic rate?
the lower the surface area to volume ratio, the lower the metabolic rate
name three features of an efficient gas exchange surface
- large surface area, eg. folded membranes in mitochondria
- thin/ short diffusion distance (e.g. wall of capillaries is one cell thick)
- steep concentration gradient maintained by blood supply or ventilation, eg. alveoli
why can’t insects use their bodies as an exchange surface?
they have a waterproof chitin exoskeleton and a small surface area to volume ratio in order to conserve water
name and describe the three main features of an insect’s gas transport system
spiracles - holes on the body’s surface which may be opened or closed by a valve for gas or water exchange.
tracheae - large tubes extending through all body tissue, supported by rings to prevent collapse
tracheoles - smaller branches dividing off the tracheae
explain 3 ways in which an insect’s tracheal system is adapted for efficient gas exchange [3]
tracheoles have thin walls so short diffusion distance to cells
large number of tracheoles/ branched, so large surface area for gas exchange
fluid in end of tracheoles that moves out into tissue during exercise, so larger surface area
explain the process of gas exchange in insects
gasses move in and out of the tracheae through the spiracles
a diffusion gradient allows oxygen to diffuse into the body tissue while waste CO2 diffuses out.
contraction of muscles in the tracheae allows mass movement of air in and out
suggest and explain how a reduced tidal volume affects the exchange of CO2 between the blood and the alveoli [3]
less Co2 exhaled/ moves out of lung
so reduced concentration gradient between blood and alveoli
so less movement of CO2 out of blood.
why can’t fish use their bodies as an exchange surface?
they have a waterproof, impermeable outer membrane and a small surface area to volume ratio.
name and describe the two main features of a fish’s gas transport system
gills - located within the body, supported by arches, along which are multiple projections of gill filaments, which are stacked up in piles
lamellae - at right angles to the gill filaments, give an increased surface area. blood and water flow across them in opposite directions (counter-current exchange system)
explain the process of gas exchange in fish
the fish opens its mouth to enable water to flow in, then closes its mouth to increase pressure.
the water passes over the lamellae and the oxygen diffuses into the bloodstream
waste CO2 diffuses into the water and flows back out of the gills
explain how the counter-current mechanism allows efficient oxygen uptake in the fish gas exchange system [3]
blood and water flow in opposite directions.
blood always passes water with a higher oxygen concentration
this maintains a concentration gradient along the length of the filament
name and describe three adaptations of a leaf that allow efficient gas exchange
- thin and flat to provide short diffusion pathway and large SA:VOL
- many stomata to allow water to easily enter
- air spaces in the mesophyll which allow gases to move around the leaf, facilitating photosynthesis
how do plants limit their water loss while still allowing gases to be easily exchanged?
stomata regulated by guard cells which allows them to open and close as needed most stay closed to prevent water loss while some stay open to let oxygen in.
explain why plants that grow in soils with very little water grow only slowly [2]
stomata close, so less CO2 uptake for less photosyntheses
describe the pathway taken by air as it enters the mammalian gas exchange system
nasal cavity —> trachea —> bronchi—> bronchioles—> alveoli
describe the trachea and its function in the gas exchange system
wide tube supported by cartilage to keep the air passage open during pressure changes
lined by cilia which move mucus towards the throat to be swallowed, preventing lung infections
carries air to bronchi
describe the bronchi and their function in the gas exchange system
like the trachea, they are supported by rings of cartilage and are lined by cilia
allow passage of air into bronchioles
describe the bronchioles and their function in the gas exchange system
don’t need to be kept open by cartilage, therefore mostly have only muscle and elastic fibres so that they can contact and relax easily during ventilation
allow passage of air into the alveoli
describe the alveoli and their function in the gas exchange system
mini air sacs, lined with epithelial cells, site of gas exchange
walls only one cell thick, which creates a short diffusion path
describe and explain the mechanism that causes lungs to fill with air [3]
diaphram contracts and external intercostal muscles contract
this causes the volume to increase and the pressure to decrease
air moves down a pressure gradient
explain the process of expiration
diaphragm relaxes and internal intercostal muscles contract
volume of thorax decreases, and pressure increases.
what’s is tidal volume?
the volume of air we breathe in and out during each breath at rest
what is breathing rate?
the number of breaths we take per minute
how do you calculate pulmonary ventilation rate?
tidal volume x breathing rate (can be measured using a spirometer)
describe the pathway taken by an oxygen molecule from an alveoli to the blood [2]
across alveoli epithelium, epithelium of capillary
explain how one feature of an alveoli allows efficient gas exchange to occur [2]
alveolar epithelium is one cell thick, creating a short diffusion pathway
explain why death of alveolar epithelium cells reduces gas exchange in human lungs [3]
reduced surface area
so increased distance for diffusion
so reduced rate of gas exchange
describe the gross structure of the human gas exchange system and how we breathe in and out. (6)
Trachea, bronchi, bronchioles, alveoli
breathing in - diaphragm contracts and external intercostal muscles contract. this causes the volume to increase and the pressure to decrease in the thorax.
breathing out - diaphragm relaxes and internal intercostal muscles contract. this causes the volume to decrease and the pressure to increase in the thorax.
explain 2 ways in which the structure of fish gills is adpapted for efficient gas exchange [2]
many lamellae/ filaments, so large surface area
thin surface so short diffusion pathway
MASS TRANSPORT IN PLANTS
describe the cohesion-tension theory of water transport in the xylem [5]
transpiration/ evaporation of water molecules from leaf
lowers WP of mesophyll/ leaf cells
water pulled up xylem, creating tension
water molecules cohere together by hydrogen bonds, forming continuous water column
adhesion of water molecules to walls of xylem
phloem pressure is reduced during the hottest part of the day. use your understanding of transpiration and mass flow to explain why [3]
high rate of transpiration/ evaporation
tension in xylem causes less water movement from xylem to phloem
or
tension in xylem causes an insufficient WP in phloem to draw water from xylem.
explain why coloured water moved up the stalks of celery [3]
water evaporates from leaves, which lowers the water potential and creates tension.
cohesion/ adhesion/ hydrogen bonds maintains column
describe the mass flow hypothesis for the mechanism of translocation in plants [4]
in source/ leaf sugars are actively transported into the phloem, by companion cells.
this lowers the WP of sieve cell and water enters by osmosis from xylem
increase in hydrostatic pressure causes mass transport towards sink/root
sugars used/converted in root for respiration/ storage
use your understanding of mass flow to explain how pressure is generated inside a phloem tube [3]
sucrose is actively transported into phloem lowering water potential
water moves into phloem from xylem via osmosis
the student used a sharp scalpel to cut the celery. describe how she should ensure she handled the scalpel safely [2]
cut away from body
against hard/ flat surface
describe the structure of haemoglobin
globular, water soluble. consists of 4 polypeptide chains, each carrying a haem group (quaternary structure)
describe the role of haemoglobin
oxygen molecules bind to the haem groups and are carried around the body to where they are needed in respiring tissues
name three factors affecting oxygen-haemoglobin binding
partial pressure/concentration of oxygen
partial pressure/concentration of carbon dioxide
saturation of haemoglobin with oxygen
how does partial pressure of oxygen affect oxygen-haemoglobin binding?
as partial pressure of oxygen increases, the affinity of haemoglobin for oxygen also increases, so oxygen binds tightly to haemoglobin. when partial pressure is low, oxygen is released from haemoglobin
how does partial pressure of carbon dioxide affect oxygen-haemoglobin binding?
as partial pressure of CO2 increases, the conditions become acidic causing haemoglobin to change shape. The affinity for oxygen therefore decreases, as oxygen is released from haemoglobin. this is known as the bohr effect
binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind. explain why [2]
the binding of the first oxygen changes the tertiary structure of haemoglobin, which creates a second binding site.
explain why oxygen is released from haemoglobin in respiring tissues
partial pressure of oxygen is low and high concentration of carbon dioxide in respiring tissues, so affinity decreases
describe the advantage of the Bohr effect during intense exercise[2]
reduces the affinity for oxygen for dissociation, for more aerobic respiration in the tissues/muscles/cells
describe and explain the effect of increasing CO2 concentration on the dissociation of oxyhaemoglobin [2]
increases oxygen dissociation by decreasing blood PH
how does carbon dioxide effect the position of an oxyhaemoglobin dissociation curve?
curve shifts to the right because haemoglobin’s affinity for oxygen has decreased.
give the pathway a red blood cell takes when travelling in the human circulatory system from kidneys to lungs [3]
renal vein —> vena cava to right atrium —> right ventricle to pulmonary artery
relate the structure of the chambers to their function
atria - thin-walled and elastic so they can stretch when filled with blood
ventricles - thick muscles pump blood under high-pressure. The left ventricle is thicker than the right because it has to pump blood all the way around the body (higher pressure)
relate the structure of arteries to their function
- thick walls to handle high-pressure without tearing
- muscular an elastic to stretch and recoil, helping to maintain the high pressure.
oxygenated blood, except pulmonary artery.
relate the structure of arterioles to their function
- muscle layer is thicker so that the movement of blood into the capillaries can be controlled
- elastic layer is thinner than in arteries because blood pressure is lower in the arterioles.
relate the structure of veins to their function
- thin walls due to lower pressure therefore requiring valves to ensure blood doesn’t flow backwards.
- wider lumen with little muscular and elastic tissue which maximises the volume of blood that is carried to the heart.
deoxygenated blood, except pulmonary vein (oxygenated to hesrt from lungs)
explain how an arteriole can reduce the blood flow into capillaries [2]
Muscle contracts which constricts/narrows lumen
Explain how the left atrioventricular valve maintains a uni directional flow of blood
pressure and left atrium is higher than ventricle causing valve to open.
Pressure in left ventricle is higher than an atrium causing valve to close
describe what happens during atrial
systole
ventricles are relaxed. the atria contract, decreasing the volume and increasing the pressure. this pushes blood into the ventricles.
describe what happens in ventricular systole
The atria relax. The ventricles contract, decreasing their volume. the pressure becomes higher in the ventricles than the atria, which forces the AV valves to shut to prevent backflow.
The pressure in the ventricles is also higher than in the aorta and pulmonary artery, which forces open the semilunar valves and blood is forced out into these arteries
describe what happens during atrial and ventricular diastole
The ventricles atria both relax
the higher pressure in the pulmonary artery and aorta closes the semilunar valves to prevent backflow.
blood returns to the heart and the atria fill again due to the higher pressure in the vena cava and pulmonary vein. increase pressure in atria.
relate the structure of a capillary to its function
- walls are only one cell thick so short diffusion pathway
- always found very near cells and exchange tissues so there’s a short diffusion pathway
- large number of capillaries providing a large surface area for exchange.
What is tissue fluid?
A substance containing glucose amino acids, oxygen and other nutrients. it supples these to the cells while also removing any waste materials.
How is tissue fluid formed?
at the arteriole end of the capillaries, the hydrostatic pressure inside the capillaries is great enough to push molecules/ fluid out of the capillary,
explain the role of the heart in the formation of tissue fluid [2]
- Contraction of ventricles produces high hydrostatic pressure
- this forces water (and some dissolved substances) out of blood capillaries
Explain how water from tissue fluid is returned to the circulatory system [4]
plasma proteins remain
This reduces the water potential of blood
water moves to blood by osmosis
and returns to blood by lymphatic system
Define digestion
The hydrolysis of large insoluble molecules in the smaller molecules that can be absorbed across cell membranes
Which enzymes are involved in carbohydrate digestion? Where are they found?
amylase in mouth
maltase, sucrase, lactase in membrane of small intestine
what are the substrates and products of the carbohydrate digestive enzymes?
amylase —> starch into maltose
maltase —> maltose into 2x glucose
sucrase —> sucrose into glucose and fructose
lactase —> lactose into glucose and galactose
describe how carbohydrates are digested
broken down by Amylase and membrane bound disaccharidases.
amylase catalyses the conversion of starch (polysaccharide) into maltose (disaccharide), by hydrolysing the glycolic bonds in starch.
Membrane bound disaccharidases breakdown disaccharides (e.g. maltose) into monosaccharides (e.g. glucose) which again involves the hydrolysis of glycosidic bonds.
cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. explain how. [3]
sodium ions actively transported from ilium cell to blood.
This maintains a diffusion gradient for sodium ions to the cells from gut.
Glucose enters by facilitated diffusion with sodium ions.
how are lipids digested
bile salts are produced by the liver and emulsify the lipids, causing them to form small droplets, increasing the surface area for lipases to work on.
lipase catalyses the breakdown of lipids into monoglycerides and fatty acids by hydrolysing the ester bond between the monoglycerides and fatty acids.
the monoglycerides and fatty acids stick with the bile salts to form micelles.
explain the advantages of lipid droplet and micelle formation [3]
droplets increase surface area for lipase action so faster hydrolysis of lipids.
micelles carry fatty acids and glycerol to ilium epithelial cell.
Describe the processes involved in the absorption and transport of digested lipid molecules from the ilium to the lymph vessels [5]
- micelles contain bile salts, fatty acids/ monoglycerides
- micelles make fatty acids more soluble in water
- they carry fatty acids to the lining of the ileum
- fatty acids are absorbed by diffusion
- triglycerides reformed in cells
- vesicles move to the cell membrane (exocytosis)
suggest how the golgi apparatus is involved in the absorption of lipids [3]
Modifies and processes triglycerides, combines them with proteins and packaged for release
describe the role of enzymes in the digestion of proteins in a mammal [4]
endopeptidases hydrolyse the peptide bonds in the middle of protein/ polypeptide.
exopeptidates hydrolyse the peptide bonds at the end of protein/ polypeptide.
dipeptidases hydrolyse the peptide bond beteeen dipeptide, producing single amino acids.
describe how the products of protein digestion are absorbed across cell membranes.
amino acids are absorbed via co-transport. sodium ions are actively transported out of the ileum epithelial cells into the blood.
This creates a sodium ion concentration gradient
this causes sodium ions to move in by co-transport, bringing amino acids with it.
