AS OCR biology - exchange surfaces
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| What is gas exchange? | The process of acquiring gases like oxygen from the environment and returning waste gases like carbon dioxide
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| What are the properties of single-celled organisms? | They have large surface area to volume ratios, the outer membrane is permeable to oxygen, carbon dioxide and water, there is a short diffusion pathway, moist surfaces increase permeability of gases,often live in water so substances they need surround them
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| Why do large mutlicellular organisms need transport systems? | Multiple layers of cells, nutrients and oxygen would be used up by otuer cells before reaching centre. Not all cells in contact with external medium. Low surface area to volume ratio. High level of metabolic activity - respiration, homeostasis, movement
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| How can multicellular organisms avoid having transport systems? | By flattening out (tapeworms), external gills, increased folding
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| What is an exchange surface + good properties? | Surface specialised to allow fast diffusion from one side of the surface to the other. Large surface area e.g. invaginations, thin membrane so short diffusion pathway, steep concentration gradient high supply of moelcules on one side, fast removal
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| How does gas exchange take place in insects? | they have a waterproof, impermeable skeleton so oxygen diffuses through spiracles and tracheoles to reach every cell, no trasnport system so they have remained small through evolution
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| How does gas exchange take place in fish? | Mass flow ventilation mechanism - constant stream of water over gills, low conc of o2 in water. bulk movement of water due to changes in pressure, achieved by opening and closing the mouth
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| What is the structure of gills? | 2 piles of filaments attached to bony grill arches, filaments are made up of lamellae which have a large surface area, good blood supply, walls are only 1 cell thick, tips overlap to slow down water for maximum oxygen absoprtion
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| What is gas exchange in mammals? | Oxygen diffuses from the air in the alveoli into the capillaries, carbon dioxide diffuses from the capillaries into the air int he alveoli
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| How are the lungs adapted to gas exchange? | Alveoli provide a large surface area. Cell membranes are permeable to oxygen and carbon dioxide. Walls of alveoli and capillaries are 1 cell thick, squamous epithelia, short diffusion pathway <1 micrometer. Capillaries are close to alveolus walls. cont..
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| Continued | Alveoli are well vacularised. thin layer of moisture on alveoli. surfactant is a mix of protein and lipid which reduces surface tenion and cohesive forces between water in alveoli, helps them to inflate and deflate, prevents collapse. steep conc gradient
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| How dos air reach the alveoli in the lungs? | Air enters through the mouth and nose, the epiglottis prevents food entering the trachea, air moves through the trachea, bronchi and bronchioles
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| What are alveoli? | Small air-filled sacs where gas exchange takes place
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| What are the components of the trachea and bronchi? | Cartilage, smooth muscle, elastic fibres in loose tissue, ciliated epithelial cells, goblet cells and glandular tissue
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| What are the components of the bronchioles? | Larger bronchioles have cartilage but smaller ones don't, mainly consist of smooth muscle and elastic fibres, with clusters of alveoli at the ends
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| What is the function / structure of the cartilage? | Incomplete rings of cartilage allow flexibility, moving neck doesn't constrict airways, oesophagus can expand to swallow. C-shaped rings in trachea, less regular in the bronchi. Structural role. Prevents trachea collapsing with low air pressure inhalation
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| What is the components of the loose tissue? | Glandular tissue, connective tissue, smooth muscle, elastic fibres, blood vessels
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| What is the function of smooth muscle? | Contracts to constrict the airway to restrict air flow to and from alveoli, occurs during an asthma attack, allergic reaction or when there are harmful substances in the air, involuntary control
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| What is the function of elastic fibres? | Elastic fibres are deformed when smooth muscle contracts, when smooth muscle relaxes elastic fibres recoil to their original shape to dilate the airway
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| What is the function of goblet cells and glandular tissue? | Found under epithelium, secrete mucus to trap microorganisms from the air to prevent infection in the lungs
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| What is the function of ciliated epithelial cells? | Cilia move to waft mucus containing trapped microorganisms up the trachea to the back of the throat, mucus is swallowed, acid in stomach kills bacteria
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| What happens in the lungs during inspiration? | Diaphragm contracts, flatter, pushes digestive organs down. External intercostal muscles contract raise ribs. Volume of thoracic cavity increases. Elastic fibres stretched. Air pressure drops below atmospheric, air moves into lungs down pressure gradient
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| What happens in the lungs during expiration? | Diaphragm relaxes into dome shape, raised by contract abdominal wall. External intercostal muscles relax ribs lower. Volume of thoracic cavity decreases. Elastic fibres recoil. Air pressure rises above atmospheric, air moves out lungs down pressure grad
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| What is breathing? | Breathing is the movements that allow air to move in and out of the lungs
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| 1 breath = ? | inspiration + expiration
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| What is tidal volume? | The volume of air moved in or out of the lungs in 1 breath at rest, approx 0.5 dm3. Provides body with enough oxygen for its needs, removes enough carbon dioxide to maintian a safe level
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| What is the ventilation rate? | Breathing rate per min x volume of air moved in and out in 1 breath. At rest: 12 x tidal volume, measured in dm3/minute
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| What is the inspiratory reserve volume? | The volume of air that is inspired above the normal tidal volume during a deep breath in, occurs during exercise, approx 3dm3
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| What is the expiratory reserve volume? | The volume of air that is expired above the normal tidal volume, approx 1 dm3
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| What is the residual volume? | The volume of air that alwasy remains in the lungs even after maximum exhalation, prevents lungs collapsing, approx 1.5 dm3
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| What is dead space? | The volume of air in the trachea, bronchi and bronchioles that is not involved in gas exchange
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| What is vital capacity? | the largest volume of air moved in and out of the lungs in 1 breath, inspiratory reserve volume + expiratory reserve volume + tidal volume
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| What affects vital capacity? | age, gender heigh, health and fitness, body mass, smoking, asthma
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| What is total lung capacity? | The total of teh inspiraotry reserve volume, expiratory reserve volume, tidal volume and residual volume
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| How does a spirometer work? | Patient must be healthy, no heart/respiratory problems. Patient wears a nose clip. Sterilised disposable mouthpiece. Patient breaths in medicinal-grade oxygen (no impurities) from a chamber floating on water (chamber sinks when inhale, rises when exhale)
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| continued | A datalogger or a revolving drum records the movement of a pen to produce a spirometer trace. Function of soda lime - absorbs CO2 that is exhaled as a safety measure, allows calculation of O2 uptake. patient breaths normally, deeply and during exercise
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| What is the medulla? | The respiratory centre in the brain that controls the rate of breahting
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| How does the body stop inhaling and exhaling? | To end inhalation: stretched lungs stimulates stretch receptors in bronchi, impulse to medulla to inhibit inhalation. To end exhalation: lung are deflated, stretch receptors aren't stimulated, inhalation is no longer inhibited
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| How does the body return the breathing rate during high activity (e.g. exercise) back to normal? | High blood CO2 conc.Chemoreceptors sensitive to CO2 in carotid artery & aorta send impulse to medulla.Brain sends impulses more often to diaphragm & intercostal muscles, rate &depth of breathing increase.CO2 removed, level drop, receptors not stimulated
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| What mechanism is this an example of and why? | Negative feedback mechanism - a change in condition causes a response that reverses the change.
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