topic 3 Flashcards
small organisms
-large SA:V
-large SA means big surface for exchange of substances
-small diffusion pathway for substance exchange
-therefore, very small organisms can simply exchange substances across their surface.
large organisms
-smaller SA:V and higher metabolic rate so demand for efficient exchange of substances is higher
adaptations to increase SA:V
-villi and microvilli for efficient absorption of digested food
-alveoli and bronchioles for gas exchange in animals
-spiracles and tracheoles for gas exchange in insects
-gill filaments and lamellae for gas exchange in fish
-thin wide leaves for gas exchange of plants
-many capillaries for substance exchange in blood
fish adaptations
-large SA:V created by many gill filaments covered by many gill lamellae for efficient gas exchange.
- short diffusion distance due to very thin gill lamellae
-concentration gradient Is maintained due to counter-current flow mechanism.
-counter-current flow is when water flows over the gills in the opposite direction to the flow of blood in the capillaries.
-this ensures that equilibrium is not reached so a diffusion gradient is maintained across the entire length of the gill lamellae.
insect adaptations
to reduce water loss:
-small SA:V for water to evaporate
-waterproof exoskeleton
-spiracles where water can evaporate from, can open and close to reduce water loss.
for gas exchange:
-developed a system of breathing tubes that deliver oxygen directly to all tissue and organs.
-air enters body via external opening called spiracles
-these lead to tubes called tracheae and tracheoles.
-tubes have rigid rings to keep them open
-spiracles are sunken which traps moisture to prevent further evaporation.
-lots of tracheoles so large SA for diffusion of gases
-walls of tracheoles are thin and there is a short distance between spiracles and tracheoles so short diffusion pathway.
-the absorption of O2 and production of CO2 sets up a steep conc gradient
proteases
-produced in stomach, pancreas and ileum of small intestine.
-used in stomach and duodenum & ileum of small intestine
-endopeptidases hydrolyse peptide bonds between specific amino acids in the middle of a polypeptide to form dipeptides and tripeptides.
-exopeptidases hydrolyse peptide bonds between specific amino acids at the ends of a polypeptide to produce dipeptides or individual amino acids.
-membrane-bound dipeptidases hydrolyse the peptide bond in a dipeptide.
carbohydrases
-produced in salivary glands, pancreas and small intestine
-used in mouth and duodenum & ileum of small intestine
-salivary glands secretes saliva containing amylase into the buccal cavity. this catalyses the hydrolysis of starch into maltose.
-in the duodenum, pancreatic amylase is secreted which catalyses the hydrolysis of any undigested starch into maltose.
-in the ileum, membrane-bound maltase breaks down maltose into glucose
lipases
-produced in the pancreas
-used in the duodenum of the small intestine
-lipases break down triglycerides and phospholipids to produce a glycerol molecule + 3 fatty acids or a glycerol molecule + 2 fatty acids + phosphate group
-large lipid droplets entering the small intestine are broken down by agitation
bile salt molecules
-hydrophobic tail and negatively charged hydrophilic head
-lipid droplets are emulsified by bile salts in bile to form a lipid emulsion
-bile is made in the liver and stored in the gall bladder
-the gall bladder contracts to release bile into the duodenum
-emulsification stops lipid droplets from forming larger droplets so increases SA for lipase to efficiently digest the triglycerides
-the emulsion droplets are soluble in water
-pancreatic lipase catalyses the hydrolysis of triglycerides at the surface of the emulsion droplets forming monoglycerides, glycerol and fatty acids.
-these products are insoluble in water
-the products combine with bile salts to form small water-soluble molecules called micelles.
-the molecules that make up micelles are clustered together with their polar ends facing the surface of the micelles making it soluble
-they transport the fatty acids, monoglycerides and glycerol to the epithelial cells of the intestine wall and release them for absorption.
-micelles fit between the microvilli
-the individual monoglycerides and fatty acids diffuse through the cell membrane
-they are turned into triglycerides in the SER
-the Golgi apparatus processes triglycerides and combines them with proteins forming lipoproteins.
-these are then packaged for release and transported through lymphatic vessels
how do sodium ions normally enter the blood
active transport using ATP or carrier proteins:
the Na+ - glucose symporter - the pump which moves glucose and Na+ across the epithelial cell membrane together (co-transport)
the sodium - potassium pump - uses ATP to move sodium ions out of the cell and potassium ions into the cell
structures and functions of the human gaseous exchange system
cartilage- prevents collapse of airways under low pressure when breathing in
ciliated epithelium - involved in moving
mucus along to prevent lung infection by moving it towards the throat where it can be swallowed.
Goblet cells – involved in mucus secretion to trap bacteria and dust to reduce the risk of infection with the help of lysozymes which digest bacteria
squamous epithelium- smooth and thin for shorter diffusion path
smooth muscle- constrict airways to protect alveoli
elastic fibres - allow alveoli to stretch and spring back during exhalation
gaseous exchange definition
the diffusion of oxygen from the air in the lungs into the blood and CO2 from the blood into the air in the lungs
why we need so much O2
humans are relatively large organisms with a large number of living cells
to maintain a constant body temp, metabolic and respiratory rates
overall structure of the human gaseous exchange system
alveoli, bronchioles, bronchi, trachea, lungs
features of alveolar epithelium which allow efficient gas exchange
-many small alveoli give large surface area to volume ratio
-walls only one layer of squamous epithelial cells giving a short diffusion distance
-cell surface membranes of alveolar epithelium are partially permeable
-The constant blood supply by capillaries means that a steep concentration gradient is constantly maintained.
-elasticity of walls means they strech and recoil to expel air during exhalation
ventilation definition
The flow of air in and out of the alveoli is referred to as ventilation and is composed of two stages; inspiration and expiration
inspiration
During inspiration, the external intercostal muscles contract whereas the internal muscles relax, as a result this causes the ribs to raise upwards. The diaphragm contracts and flattens. In combination, the intercostal muscles and diaphragm cause the volume inside the thorax to increase, thus lowering the pressure. The difference between the pressure inside the lungs and atmospheric pressure creates a gradient, thus causing the air to be forced into the lungs.
expiration
During expiration, the internal intercostal muscles contract whereas the external muscles relax therefore lowering the rib cage. The diaphragm relaxes and raises upwards. This action in combination decrease the volume inside the thorax, therefore increasing the pressure, forcing the air out of the lungs.
spirometer
a device used to measure lung volume. A person using a spirometer breathes in and out of the airtight chamber, thus causing it to move up and down, leaving a trace on a graph which can then be interpreted.
vital capacity
the maximum volume of air that can be inhaled or exhaled in a single breath.
Tidal volume
the volume of air we breathe in and out at each breath at rest
Breathing rate
the number of breaths per minute. It can be calculated from the spirometer trace by counting the number of peaks or troughs in a minute
