Topic 6 - Exchange Flashcards
Adaptations of gas exchange surfaces: across the body of a single-celled organism
- Thin, flat shape and large surface area to volume ratio
- Short diffusion distance to all parts of cell for rapid diffusion
tracheal system of an insect
- Air moves through spiracles (pores) on insect surface
- Air moves through trachea
- Which divide into tracheoles where gas exchange occurs directly to/from cells
- O2 used by cells during respiration –> establishes a conc. gradient for O2 to diffuse down
- CO2 produced by respiration –> diffuses down conc. gradient from respiring cells
Adaptations for gas exchange
Structural and functional compromises between opposing the needs for efficient gas exchange and the limitation of water loss as shown by terrestrial insects
Adaptation for gas exchange in fish
Adaptation for gas exchange - counter current flow:
- Blood and water flow in opposite directions through/over lamellae
- So oxygen concentration always higher in water (than blood near)
- So maintains a concentration gradient of O2 between water and blood
- For diffusion along whole length of lamellae
If water and blood flowed in the same direction (parallel flow) equilibrium would be reached, so oxygen wouldn’t diffuse into blood along the whole gill plate
Leaf cross section
Closed and open stomata diagram
Adaptation for gas exchange in leaf
Structural and functional compromises between opposing the needs for efficient gas exchange and the limitation of water loss as shown by xerophytic plants
Xerophyte = a plant adapted to live in very dry conditions e.g. cacti
Diagram of human gas exchange system
Adaptations of human gas exchange system
The essential features of the alveolar epithelium as a surface over which gas exchange takes place
- Thin / flattened cells / one cell think –> short diffusion distance
- Folded –> large surface area
- Permeable –> allows diffusion of oxygen and carbon dioxide
- Moist –> gases can dissolve
- Good blood supply from network of capillaries –> maintains concentration gradient
Gas exchange in the lungs
- Oxygen diffuses from alveolar air space into blood down its concentration gradient
- Across the alveolar epithelium then across the capillary endothelium
The opposite for carbon dioxide
What is ventilation (mechanism of breathing)
The mechanism of breathing to include the role of the diaphragm and the antagonistic interaction between the external and internal intercostal muscles in bringing about pressure changes in the thoracic cavity
Stages of inspiration
- External intercostal muscles contract, internal intercostal muscles relax (antagonistic) –> ribcage moves up/out
- Diaphragm muscles contact –> flattens
- Increasing volume in thoracic cavity (chest)
- Decreasing pressure in thoracic cavity
- Atmospheric pressure high than pressure in lungs –> air moves down pressure gradient into lungs
Stages of expiration
- Internal intercostal muscles can contract, external intercostal muscles relax –> ribcage moves down/in
- Diaphragm relaxes –> moves upwards
- Decreasing volume in thoracic cavity
- Increasing pressure in thoracic cavity
- Atmospheric pressure lower than pressure in lungs –> air moves down pressure gradient out of lungs
Two types of expiration
- Normal expiration is passive (no muscle contraction required), aided by elastic recoil in alveoli
- Forced expiration is active because internal intercostal muscles contract
Why is ventilation needed
- Maintains an oxygen concentration gradient
- Brings in air containing higher concentration of oxygen
- Removes air with lower concentration of oxygen
Tidal volume
Volume of air in each breath
Ventilation rate
Number of breaths per minute
Forced expiratory volume (FEV)
Maximum volume of air a person can breathe out in 1 second
Forced vital capacity (FVC)
Maximum volume of air a person can breathe out in a single breath
Effect of lung diseases on ventilation
- Reduced elasticity –> lungs may expand / recoil less –> reduced tidal volume / FVC
e.g. due to fibrosis - scar tissue builds up which is less elastic - Narrower airways / reduced airflow in/out of lungs –> reduced FEV
e.g. due to asthma - bronchi are inflamed
Effect of lung diseases on gas exchange
- Thicker tissue in alveoli –> increased diffusion distance –> reduced rate of gas exchange
e.g. due to fibrosis - scar tissue builds up which is thicker - Walls of alveoli break down –> reduced surface area –> reduced rate of gas exchange
Link between gas exchange and ventilation
If gas exchange reduces, ventilation rate often increases to compensate for reduced oxygen in blood
Impact: cells receive less oxygen –> rate of aerobic respiration reduced –> less ATP made –> fatigue
During digestion, large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes
- Large biological molecules in food e.g. starch/protiens too big to be absorbed across cell membranes
- Digestion breaks them into smaller molecules e.g. glucose/aminoacids –> absorbed from the gut to the blood
Digestion in mammals of carbohydrates by amylases
Digestion of starch (polysaccharide)
- Amylase hydrolyses starch to maltose (poly to disaccharide)
- Membrane bound maltase (attaché to epithelial cells lining the ileum of the small intestine) –> hydrolyse maltose to glucose (di to monosaccharide)
- Hydrolysis of glycosidic bond
Digestion in mammals of membrane bound disaccharides
- Membrane bound disaccharides e.g. maltase, sucrose, lactase (attached to epithelial cells lining the ileum of the small intestine) –> hydrolyse disaccharide to 2x names monosaccharides
- e.g. maltase - maltose –> glucose + glucose
- e.g. sucrase - sucrose –> fructose + glucose
- e.g. lactase - lactose –> galactose + glucose
- Hydrolysis of glycosidic bond
Digestion in mammals of lipids by lipase, including the action of bile salts
- Bile salts produced by the liver
- Bile salts emulsify lipid to smaller lipid droplets: Increasing surface area (to volume ratio) of lipids speeds up action of lipase
- Lipase made in the pancreas, released to small intestine
- Lipase hydrolyses lipids –> monoglycerides + fatty acids
- Breaking ester bond
- Monoglycerides, fatty acids and bile salts stick together to form micelles
Digestion in mammals of proteins by endopeptidases, exopeptidase and membrane-bound dipeptides
Endopeptidases:
- Hydrolyse peptide bonds within a protein/between amino acids in the central region
- Breaking protein into two or more smaller peptides
Exopeptidase:
- Hydrolyse peptide bonds at the ends of protein molecules
- Removing a single amino acid
Dipeptidases (type of exopeptidase):
- Often bound in ileum
- Hydrolyse peptide bonds between a dipeptide
- =2 amino acids
Mechanisms for the absorption of the products of digestion by cell lining the ileum of mammals, to include co-transport mechanisms for the absorption of amino acids and of monosaccharides
- Sodium ions actively transported out of epithelial cells lining the ileum, into the blood, by the sodium potassium pump. Creating a concentration gradient of sodium
- Sodium ions and glucose move by facilitated diffusion into the epithelial cells from the lumen, via a co-transporter protein
- Creating a concentration gradient of glucose - higher conc. of glucose in epithelial cell than in blood
- Glucose moves out of cell into blood by facilitated diffusion through a protein channel
Mechanisms for the absorption of the products of digestion by cells lining the ileum of mammals, to included the role of micelles in the absorption of lipids
- Monoglycerides and fatty acids diffuse out of micelles (in lumen) into epithelial cell
- Monoglycerides and triglycerides recombine to triglycerides which aggregate into globules
- Globules coated with proteins to form chylomicrons
- Leave via exocytosis and enter lymphatic vessels
- Return to blood circulation
