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Section 3 - Organisms exchange substances with their environment - Coggle…
Section 3 - Organisms exchange substances with their environment
6 Exchange
Surface area to volume ratio
Relationship between surface area and volume
Small organisms have a small volume and a relatively large surface area
Simple diffusion is adequate for exchange
High SA : Vol ratio
More heat loss
As the size of he organism increases, volume increases faster than surface area
Simple diffusion would take too long
Low SA : Vol ratio
Metabolic rate
Activity levels
High metabolic rate = more materials exchanged
Smaller organisms have a higher basal metabolic rate per unit of body mass
Specialised exchange surfaces
What is exchanged?
Oxygen, carbon dioxide
Glucose, amino acids, nutrients
Urea
Thin for a short diffusion distance
Alveolar membrane
Large surface area : volume ratio
Example - microvilli
Selectively permeable
Maintenance of concentration gradient
Example - bloodstream removing substance
Example - countercurrent mechanism in fish
Larger organisms have different body shapes and specialised exchange systems to increase SA : Vol ratio
Gas exchange
Human gas exchange system
Structures
Lungs supported by ribcage
Trachea
Bronchi
Bronchioles
Alveoli
Gas exchange membrane
4 more items...
Ventilation
Inspiration and expiration
Movement of ribs
Contraction or relaxation of diaphragm
Changes in thoracic volume and pressure, movement of air out or in
Antagonistic intercostal muscles - internal and external
Single-celled organisms
Large SA : Vol ratio
Small
Diffusion adequate for gas exchange
Insects
Size of organism limited by diffusion
Waterproof covering
Contraction of muscles
Mass transport of air
Network of tubes - tracheae and tracheoles
Spiracles
Can be opened and closed
Compromise between gas exchange and water loss
Short diffusion distance to cells
Fluid-filled ends of tracheoles
Diffusion is faster
Fish
Gill filaments
Gill lamellae at right angles to filaments
Countercurrent mechanism
Blood and water flow in opposite directions
Oxygen diffusion gradient maintained over whole length of lamellae
More oxygen diffusion
Plants
Compromise between gas exchange and water loss
Waterproof coverings to reduce water loss
Stomata and guard cells
Short diffusion pathway
Xerophytes
Thick waxy cuticle
Stomata in pits / grooves
Hairy or rolled up leaves
Air spaces increase surface area for exchange
Digestion and absorption
Absorption
Ileum
Microvilli on epithelial cells
Monoglycerides and fatty acids
Micelles break down at ileum lining
Diffuse across membrane
Chylomicrons
Exocytosis into lacteals
Enter blood from lymph system
Monosaccharides
Co-transport with sodium ions
ATP needed to generate sodium gradient
Sodium ions move down their concentration gradient, bringing glucose and amino acids too
Carrier proteins
Facilitated diffusion
Carrier proteins
Amino acids
Facilitated diffusion
Digestion
Hydrolysis of larger molecules into smaller ones
Physical breakdown
Teeth, chewing
Chemical breakdown
The physical breakdown increases surface area for enzymes to act on
Enzyme hydrolysis
Hydrolysis reactions require water
Lipases
Ester bond
Triglycerides into monoglycerides and fatty acids
Lipids are in micelles due to bile salts
Surface area increased
Proteases
Peptidases
Endopeptidases - hydrolyse peptide bonds in central regions of protein
Exopeptidases - hydrolyse peptide bonds of terminal amino acids
Membrane-bound dipeptidases - hydrolyse peptide bonds in dipeptides
Carbohydrases
Amylase - hydrolyses glycosidic bonds in starch, produces maltose
Salivary and pancreatic
Maltase - hydrolyses glycosidic bonds in maltose, produces glucose
Membrane-bound disaccharidase (maltase, sucrase, lactase)
7 Mass transport
Animals
Haemoglobin
Different types for different species and environments
Transports oxygen
Unloading = at the tissues
Changes in affinity for oxygen
Loading = in the lungs
Changes in affinity for oxygen
Oxyhaemoglobin dissociation curve
Positive cooperativity
S-shaped curve
Bohr effect and carbon dioxide
pH
Quaternary protein with 4 haem (Fe2+) groups
Each Fe2+ ion can carry one oxygen molecule
Circulatory system
Closed, double
Coronary arteries for the heart
Pulmonary artery and vein to and from lungs
Renal artery and vein to and from kidney~
Vena cava and aorta to and from heart
Heart and blood vessels
Capillaries
Tissue fluid
One-cell-thick wall
Valves
Veins
Valves
Deoxygenated blood
Arteries
Muscle and elastic layers
High pressure
Thick walls
Atria and ventricles
Cardiac cycle
Cardiac output
Pressure and volume changes
Diastole and systole
Plants
Xylem
Transports water in stem and leaves
Transpiration pull
Stomata - evaporation of water
Cohesion-tension theory
Continuous column of water
H-bonds
Changes in diameter / trunk
Phloem
Transports organic substances and ions
Ringing and tracer experiments
Mass flow theory for translocation
Active transport of sugars
Sieve tube elements