mass transport systems

Mass transport systems Move substances to & from excahnge surfaces Substances are dissolved or suspended in fluid Fluid travels in vessels Prevents accumulation of waste

Mass flow transport occurs within larger organisms and more active organisms because their SA:VOL can never be large enough to provide all the cells with the necessary metabolites. Pressure differences within the organism move the materials from and area of high concentration, called the source, to an area of lower concentration, called the sink.

Gas exchange in flowering plants & mammals It is necessary to supply all cells with oxygen for respiration and to excrete carbon dioxide. Gas exchange surfaces are specialised to maximise the rate of gas exchange: Large surface area Moist surface for respiratory gases to dissolve Diffusion gradients for both O2 & CO2 Permeable to both O2 & CO2 Short diffusion path

Surface area x difference in concentration Fick’s Law expresses the relationship between the rate of diffusion, surface area, concentration gradient & membrane thickness. RATE OF DIFFUSION Surface area x difference in concentration = Membrane thickness

A good exchange surface needs to be adapted to allow a high rate of diffusion. It needs to have: large SA method to maintain a high conc. gradient short diffusion distance e.g alveoli in the lungs to pick up oxygen and remove carbon dioxide, root hair cells to take up minerals such as nitrates by AT, leaf for gas exchange for photosynthesis.

A poor exchange surface needs to be adapted to reduce the rate of diffusion. It needs to have: small SA method to reduce a high conc. gradient large diffusion distance e.g leaf to reduce transpiration

the rate of gas exchange Factors affecting the rate of gas exchange in a mammal

Mammals have highly specialised exchange surfaces because they have a small surface area to volume ratio and an impermeable body covering. The alveolar wall forms the gas exchange surface.

Adaptations of the lung surface Thin respiratory surface creates a short diffusion distance Single layer of squamous epithelium of the alveoli Single layer of squamous endothelium of blood capillary wall The capillaries sit tight against the alveoli and the capillaries are so narrow that the red blood cells )erythrocytes) must squeeze through, ensuring contact with the endothelial wall and reducing the diffusion pathway

Squamous epithelium lining the alveoli lumen of alveolus

squamous endothelium lining blood capillary wall.

Adaptations of the lung surface Large surface area provided by alveoli Approximately 700 million alveoli with a surface area of 75m2, 30 times larger than the surface of the body. Moist outer surface of alveoli

Adaptations of the lung surface Steep concentration gradients are created by Mass flow of air to the respiratory surface i.e. ventilation Brings oxygen into the lungs and removes carbon dioxide Rich vascular supply through the capillaries Brings carbon dioxide rich blood to the alveoli and removes oxygen rich blood Together these maintain a steep diffusion gradient of oxygen from the alveoli into the blood and carbon dioxide from the blood into the alveoli.

Diffusion gradient for O2 Breathing movements ensure that there is always a high concentration of O2 in the alveoli Good blood supply constantly removes O2 (which combines with haemoglobin in RBC) ensuring the concentration is low Large difference between O2 concentration creates steep concentration gradient for efficient gas exchange

Adaptations of the lung surface Moist outer surface of alveoli, deep inside the body to reduce water loss by evaporation gases dissolve for diffusion across the surfaces Surfactant in the moisture layer of alveoli reduces surface tension This prevents the alveoli collapsing which would reduce the SA for gas exchange Macrophages Protect against infection by digesting microorganisms by phagocytosis

Diffusion gradient for CO2 Breathing movements ensure that there is always a low concentration of CO2 in the alveoli Good blood supply constantly brings CO2 (released in cell respiration) from the body ensuring the concentration is high Large difference between CO2 concentration creates steep concentration gradient for efficient gas exchange

Concentration gradient circulation diffusion diffusion Lungs Respiring cell Blood transports gases and metabolites Large SA for gas exchange Large SA for gas exchange circulation Deoxygenated Oxygenated

Lung surfactant The watery film lining the lungs creates a surface tension which would cause the alveoli to collapse and stick together when air is exhaled. Surfactant is a mixture of phospholipid molecules found between the watery film on the inner surface of the alveoli and the air inside them It reduces the surface tension so that the alveolar surfaces do not stick together, they remain open for gas exchange IMPORTANT AT BIRTH. First breath very difficult, but causes surfactant to line alveoli; subsequent breaths easier. Premature babies do not have sufficient to keep alveoli open.

Air exhaled Hydrophobic head immersed in water next to alveolar wall Walls of the alveolus drawn inwards Surfactant prevents alveolar membranes sticking together Hydrophobic head immersed in water next to alveolar wall Hydrophobic tail in air space Water lining the inner surface of alveolus

Past paper essay question Give an account of the features of the gas exchange surface in a mammal and explain how these result in efficient gas exchange. (13 marks)

https://pbs.twimg.com/tweet_video/B-30NonUAAER7Yf.mp4 breathing The term used to describe the processes involved in ventilating the lungs and the alveoli. https://pbs.twimg.com/tweet_video/B-30NonUAAER7Yf.mp4

The respiratory system

The breathing mechanism Breathing involves the alternate increase and decrease of air pressure in the lungs relative to that outside. A fall in air pressure in the thorax causes inspiration A rise in air pressure in the thorax causes expiration

Inspiration/inhalation (breathing in) ACTIVE PROCESS external intercostal muscles contract & internal intercoastal muscles relax ribs and sternum move up and out width of thorax increases front to back and side to side diaphragm contracts diaphragm moves down, flattening depth of thorax increases top to bottom   volume of thorax increases. pressure between the pleural surfaces decreases.  air pressure in alveoli is less than atmospheric pressure.  air is forced in by the higher external atmospheric pressure lungs expand to fill thoracic cavity. 

expiration (breathing out) PASSIVE PROCESS External intercostal muscles relax internal intercostal muscles contract ribs and sternum move down and in width of thorax decreases front to back and side to side diaphragm relaxes diaphragm moves up & returns to a dome shape depth of thorax decreases top to bottom. So the …  volume of thorax decreases.  pressure between the pleural surfaces increases.  lung tissue recoils from sides of thoracic cavity  air pressure in alveoli is more than atmospheric pressure.  air is forced out.

inspiration

expiration

Use class text books to BRIEFLY outline the following conditions The effects of smoking Use class text books to BRIEFLY outline the following conditions Lung cancer Emphysema Cilia damage Bronchitis

PRACTICALS: The respirometer The J tube