biology topic 3

• The need for specialised exchange surfaces arises as the size of the organism, and its surface area to volume ratio, increases.
• In single-celled organisms, the substances can easily enter the cell as the distance that needs to be crossed over is short.
• In multicellular organisms, that distance is much larger due to a higher surface area to volume ratio.
• The movement of these sugars can now be traced through the plant using autoradiography.
• Those areas that have been exposed to the radiation produced by the 14 C in the sugars will appear black.
• The regions that appear black in the autoradiograph correspond to the area where the phloem is and therefore suggest that this is where the sugars are transported.
• Multicellular organisms require specialised exchange surfaces for efficient gas exchange of carbon dioxide and oxygen.
• Features of an efficient exchange surface include large surface area, for instance the root hair cells or folded membranes, such as those of the mitochondria.
• An efficient exchange surface should also be thin to ensure that the distance that needs to be crossed by the substance is short.
• The exchange surface also requires a good blood supply/ventilation to maintain a steep gradient, for example that of the alveoli.
• Fish have a small surface area to volume ratio for gas exchange, apart from this they also have an impermeable membrane so gases can’t diffuse through their skin.
• Bony fish have four pairs of gills, each gill supported by an arch.
• Along each arch there are multiple projections called gill filaments, with lamellae on them which participate in gas exchange.
• Blood and water flow across the lamellae in a counter current direction, meaning they flow in the opposite direction to one another.
• This ensures that a steep diffusion gradient is maintained so that the maximum amount of oxygen is diffusing into the deoxygenated blood from the water.
• The projections are held apart by water flow, therefore, in the absence of water they stick together, thus meaning fish cannot survive very long out of water.
• Ventilation is required to maintain a continuous unidirectional flow.
• Ventilation begins with the fish opening its mouth followed by lowering the floor of buccal cavity.
• Afterwards, fish closes its mouth, causing the buccal cavity floor to raise, thus increasing the pressure.
• The water is forced over the gill filaments by the difference in pressure between the mouth cavity and opercular cavity.
• The operculum acts as a valve and pump and lets water out and pumps it in.
• Insects do not possess a transport system therefore oxygen needs to be transported directly to tissues undergoing respiration.
• This is achieved with the help of spiracles, small openings of tubes, either bigger trachea or smaller tracheoles, which run into the body of an insect and supply it with the required gases.
• Gases move in and out through diffusion, mass transport as a result of muscle contraction and as a result of volume changes in the tracheoles.
• Plants are adapted to efficient gas exchange through many adaptations in their leaves.
• Leaves have many small holes called stomata which allow gases to enter and exit the leaves.
• The large number of these means no cell is far from the stomata, reducing the diffusion distance.
• Leaves also possess air spaces to allow gases to move around the leaf and easily come into contact with photosynthesising mesophyll cells.
• The lungs are a pair of lobed structures with a large surface area located in the chest cavity that are able to inflate.
• The lungs are surrounded by the rib cage which serves to protect them.
• Breathing rate is the number of breaths per minute, which can be calculated from the spirometer trace by counting the number of peaks or troughs in a minute.
• Haemoglobin is a water soluble globular protein which consists of two beta polypeptide chains and two alpha helices, each molecule forming a complex containing a haem group.
• The tidal volume can be exceeded, in cases such as during exercise where the inspiratory reserve volume is reached in an attempt to increase the amount of air breathed in.
• After the unloading process, the haemoglobin returns to the lungs where it binds to oxygen again.
• Vital capacity is the maximum volume of air that can be inhaled or exhaled in a single breath, which varies depending on gender, age, size as well as height.
• Haemoglobin carries oxygen in the blood as oxygen can bind to the haem (Fe2+) group, each molecule carrying four oxygen molecules.
• Dissociation curves illustrate the change in haemoglobin saturation as partial pressure changes.
• The volume of air which is always present in the lungs is known as the residual volume.
• Tidal volume is the volume of air we breathe in and out at each breath at rest.
• The expiratory reserve volume is the additional volume of air that can be exhaled on top of the tidal volume.