Module 3

• as the surface area to volume ratio decreases, the need for specialised exchange surfaces increases
• in single celled organisms, they do not require specialised cells as the distance that needs to be crossed over is short
• multicellular organism require specialised exchange surfaces as the distance to cross over is larger due to the decrease in surface area to volume ratio
• Features of efficient gas exchange include: high surface area to volume ratio, short distance and steep concentration gradient.
• Surface area to volume ratio could increase if there are folded membranes or root hair cells
• In the chest cavity, the lungs are a pair of structures with a large surface area that have the ability to inflate. The lungs are protected by the rib cage
• The external and intercostal between the rib cage are raised or lowered when contracted. The diaphragm separates the lungs from the abdomen area.
• The air enters through the nose into the trachea and passed through the bronchi to the bronchioles where it enters the tiny sacs known as the alveoli. This is where gas exchange takes place.
• The trachea, bronchi and bronchioles enable the flow of air into and out of the lungs
• In the trachea, there are rings of cartilage that hold the airways open to allow the passage of food down the oesophagus behind the trachea
• Bronchi are more narrow than tracheas
• Trachea are composed of several layers that forms a thick wall; the wall is mainly composed of cartilage in the form of incomplete C rings.
• The cartilage consists of a layer of glandular and connective tissue, elastic fibres and smooth muscle and blood vessels also known as loose tissue.
• The inner lining in lungs are squamous epithelial layer that is composed of goblet cells and ciliated epithelium cells
• The walls of bronchioles are made of smooth muscle and elastic fibres
• Cartilage acts as a support for trachea and bronchioles as it prevents the lungs from collapsing in the event of a pressure drop
• Ciliated epithelium cells are involved in moving mucus along to prevent lung infection
• Goblet cells involved in the secretion of mucus in order to trap the bacteria and dust. This reduces the risk of infection
• Smooth muscle has the ability to contract allowing them to play a role in constricting the flow of air to and from alveoli
• Elastic fibres stretch when inhaling and recoil when exhaling which helps to control the flow of air
• ventilation is the flow of air in and out of the alveoli which is composed from two stages: inspiration and expiration
• During inspiration, the external intercostal muscles contract and the internal intercostal muscles relax which causes the ribs to raise upwards.
• During inspiration, the diaphragm contracts and flattens causing the volume of the thorax to increase which lowers the pressure. The difference between the pressure inside and outside creates a gradient which allows the air to enter the lungs.
• During expiration, the internal intercostal muscles relax causing the rib cage to lower. The diaphragm relaxes and rises upwards; this causes a decrease in volume in the thorax which causes an increase in pressure. The increase in pressure results to air being forced to leave the lungs.
• Spirometer is a device used to measure lung volume
• A person using a spirometer breathes in and out of the airtight chamber; this causes it to move up and down which then leaves a graph which can be used to interpret.
• Vital capacity: the maximum volume of air that can be inhaled or exhaled in a single breath
• Tidal volume: the volume of air breathed in or out at each breath at rest
• Breathing rate is the number of breaths per minute
• The residual volume is the volume of air that is always present in the lungs; this prevents the lungs from collapsing
• The expiratory reserve volume is the additional volume of air that can be exhaled on top of the tidal volume
• Fish have a small surface area to volume ratio and have a impermeable membrane; this inhibits gas to diffuse through the skin. Therefore they require specialised gas exchange surfaces.
• Bony fish have four pairs of gills that are supported by an arch; each arch consists of gill filaments that have lamellae on them. They are involved in gas exchange.
• Blood and water flow across the lamellae in a counter current direction
• When the fish opens its mouth, the floor of the buccal cavity is lowered to enable the flow of water. Once the mouth closes, the buccal cavity raises to increase the pressure. The water is forced over the gill filaments due to the difference in pressure between the mouth cavity and the opercular cavity.
• The operculum acts as a valve and pump to let water out and pumps water in
• Insects does not have a transport system therefore requires oxygen to be transported directly to tissues undergoing respiration. The spiracles are opening of tubes that supplies the insects with the required gas. At the end of each tracheole, they contain tracheal fluid which dissolved the gases in order for them to enter the cells.
• Spiracles can be opened or closed to avoid excessive water loss
• Closed circulator systems come in two forms: double or single
• Single closed circulatory systems consists of 2 heart chambers meaning the blood passes the body once for every circuit of the body