3. Exchange of Substances Flashcards
Surface area to volume ratio
surface area of organism divided by volume, the larger the organism the smaller its surface area to volume ratio
Fish gills
many stacks of gill filaments covered in many gill lamellae at right angles providing a large surface area, surrounded by many capillaries with thin endothelium providing a short diffusion distance
Countercurrent flow system
blood and water flow in opposite directions, blood always next to water with a higher concentration of oxygen, steep diffusion gradient maintained across entire length of gill
Insect tracheal system
spiracles for oxygen to diffuse in, air filled trachea for rapid diffusion, many highly branched tracheoles with thin permeable walls providing a large surface area and short diffusion distance, abdominal movements to maintain steep diffusion gradient
Insect water loss
can close spiracles to reduce water loss, waterproof exoskeleton and thick waxy cuticle to reduce evaporation
Dicotyledonous plants
stomata for oxygen to diffuse in, spongey mesophyll layer providing a large surface area, palisade mesophyll layer where photosynthesis occurs
Guard cells
control the opening and closing of stomata, when turgid stomata open, when flaccid stomata close reducing water loss by evaporation
Xerophytic plants
plants adapted to survive in dry environments with limited water, sunken stomata, hairs on epidermis and curled leaves to trap water vapour reducing water potential gradient so less water loss by osmosis, thick waxy cuticle to reduce evaporation
Respiratory system
oxygen diffuses down trachea, bronchi, bronchioles, alveoli, across alveolar epithelium, capillary endothelium into blood
Alveoli
tiny air sacs, surrounded by many capillaries, one cell thin endothelium providing a short diffusion distance
Inspiration
diaphragm contracts and flattens, external intercostal muscles contract, ribs move up and out, volume of thorax increases, pressure of thorax decreases, air moves down pressure gradient into lungs
Expiration
diaphragm relaxes and domes, internal intercostal muscles contract, ribs down and in, volume of thorax decreases, pressure of thorax increases, air moves down pressure gradient out lungs
Pulmonary ventilation
volume of air that enters lungs each minute, calculated by multiplying tidal volume by breathing rate
Digestion
hydrolysis of large insoluble molecules into smaller soluble molecules that can be absorbed across cell membranes
Carbohydrate digestion
amylase hydrolyses starch into maltose, maltase hydrolyses maltose into glucose, membrane-bound disaccharides attached to the ileum help hydrolyse maltose into glucose, glucose absorbed by facilitated diffusion
Lipid digestion
bile salts emulsify lipids increasing their surface area to volume ratio, lipases hydrolyse lipids into monoglycerides and fatty acids, micelles which contain bile salts and fatty acids, make fatty acids more soluble in water and bring fatty acids to epithelial cells lining the ileum, fatty acids are absorbed by simple diffusion
Protein digestion
endopeptidases hydrolyse peptide bonds within the polypeptide chain, exopeptidases hydrolyse peptide bonds at the ends of the polypeptide chain, membrane-bound dipeptidases hydrolyse peptide bonds between dipeptides, amino acids absorbed by facilitated diffusion
Haemoglobin
quaternary structure protein found in red blood cells, haem group in each chain containing Fe2+ which binds to oxygen forming oxyhaemoglobin
Oxyhaemoglobin dissociation curve
S shape curve, oxygen loads onto haemoglobin in regions with high partial pressure of oxygen (alveoli), oxygen unloads in regions of low partial pressure of oxygen (respiring cells)
