chapter 7 bilogy form 4

7/27/2019 Chapter 7 Bilogy form 4

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Protozoa (unicellular organisms) paramecium


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Protozoa (unicellular organisms)amoeba


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Protozoa are unicellular microorganisms suchas the Amoeba and paramecium. They arevery small in size and have large total surfacearea to volume ratios. The gaseous exchangesare achieved by simple diffusion and theyoccur rapidly and efficiently across the thinplasma membrane.


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Protozoa (unicellular organisms)


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Oxygen from the atmosphere diffuses into thecells down the partial pressure gradient whilecarbon dioxide diffuses out of the cellsthrough their permeable membranes via thesame mechanism. The respiratory structure ofthe protozoa is thus a very simple one.


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fish


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A fish needs a specialised respiratory structure for gaseous exchanges inwater. Water has less oxygen and does not flow as freely as atmosphericair. The specialised respiratory organs for efficient gaseous exchanges inwater for fish are called gills. A bony fish has four pairs of gills which arecovered by the operculum.Each gill is supported by a small rod of bone called the gill arch. Thesurface of each gill filament has many plate-like projections calledlamellas. The plate-like structures increase the surface area. These gilllamellas contain a network of blood capillaries so that oxygenated anddeoxygenated blood can flow to and away from the gills.


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Structure of gills


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AdaptationThe gill filaments are highly specialised forgaseous exchanges. Their characteristicsinclude:


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Characteristics of the gills filaments


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The breathing mechanism

The breathing mechanism of the fish involves the opening and closingof the mouth and the operculum. During inspiration, the fish opensits mouth and the floor of the buccal cavity is lowered thus loweringthe pressure. The high water pressure on the outside presses theoperculum to close. In the way, water is drawn into the buccal cavity.Conversely, during expiration, the mouth of the fish closes and thefloor of the buccal cavity is raised and pressure increases. Water fromthe outside is then forced to flow into the opercular cavity and overthe gills. In this way, the gaseous exchanges occur.


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Breathing mechanism of a fish


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Diffusion of oxygen from water into blood capillaries over the gilllamella


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Insects


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Unlike fish which use gills for gaseous exchanges, insects usetracheae (singular: trachea). Tracheae are air-filled hollow tubesthat branch and re-branch throughout the whole body. Eachtrachea has a pair opening to the outside called spiracles. Thesespiracles are located on the thorax and abdomen of an insect.Usually, most insects have ten pairs of spiracles each. Eachspiracle is protected by hair to prevent foreign bodies fromentry. The opening and closing of the spiracles are achieved bymeans of valves which are controlled by tiny muscles.


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Traceal system


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Tracheal systemThe fine tubes of the tracheae that branch throughoutthe body are called tracheoles. They end in the fluid ofthe body cells. The gaseous exchanges takes placebetween the tracheoles and body cells by diffusion.Oxygen diffuses from the tracheoles into the body cellswhereas carbon dioxide diffuses out from the body cellsinto the tracheoles and are removed from the body.


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AdaptationThe tracheoles are highly adapted for efficient gaseousexchanges. There are numerous and very fine tracheolesthroughout the body that provide a large surface area. Inaddition, tracheoles have moist walls so that oxygen can bedissolved easily before diffusing into the body cells thusincreasing the rate of diffusion. The thin epithelial walls of thetracheoles also facilitate the diffusion processes and at thesame time, increase the rate of diffusion.


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The breathing mechanismThe breathing mechanism of insects involves rhythmic contractions andrelaxations of the abdominal muscles. The rhythmic movements change thevolume and pressure of the abdomen and they cause air to be drawn andforced in and out of the tracheae through the spiracles.During inhalation, the abdominal muscles relax and the valves of the spiraclesopen. The pressure in the tracheae decreases and accordingly, air is drawn intothe tracheae through the spiracles; the air subsequently moves to the end of thetracheoles for gaseous exchanges. During exhalation, the abdominal musclescontract. This causes the pressure in the tracheae to increase and hence forcesthe air to move out through the spiracles.


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Amphibians


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Amphibians, such as frogs, live partly on landand partly in water. As such, their respiratorystructure must be adapted so they can breatheboth in water and on land. They breathe throughthe skin, mouth and lungs. Therefore, themechanism of respiration for the amphibianinvolves three methods:


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Mechanism of amphibians


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Respiratory structure of a frog


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Adaptation for cutaneous respiration

The skin of amphibians adapts as it is thin so as to allowgaseous exchanges to occur easily and efficiently. When theamphibians are on land, the skin is also moist so that thegases from the atmosphere can be dissolved readily. There arealso many blood capillaries in the skin so that when they arein water, the large number of blood capillaries increases therate of exchanges of the oxygen and carbon dioxide betweenthe blood capillaries and the surrounding water.


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Adaptation for buccal respiration

The thin wall of the large mouth cavity containsmany blood capillaries. The large number of bloodcapillaries increases the rate of diffusion of oxygenand carbon dioxide in the mouth cavity. At thesame time, the thin epithelium lining is moist. Thisfacilitates the gaseous exchanges through theepithelium.


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Adaptation of lungs for pulmonary respiration

Amphibians use pulmonary respiration when they are on land.The inner walls of the lungs are heavily folded. This increasesthe surface area and thus increases the rate of gaseousexchanges. The walls of the lungs are also thin and this allowsthe gases to diffuse readily. The walls are also moist, enablingthe oxygen to dissolve first in them before diffusing across.There are also networks of blood capillaries on the walls of thelungs which help to increase the rate of gaseous exchanges.


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The breathing mechanism of pulmonary respirationDuring inhalation, the floor of the mouth is lowered. The volumeinside the mouth increases and the pressure decreases. Due to thepressure differences, air is drawn through the nostrils into the mouth.The nostrils then close and the floor of mouth rises. The pressure inthe cavity increases and air is forced into the lungs. The gaseousexchanges take place between the blood in the lung capillaries and theinhaled air.During exhalation, the nostrils open and the air is pushed outthrough the glottis, buccal cavity and the nostrils. This is achieved bythe contraction of the abdominal muscles which pressing against thelungs.


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Respiratory structures and the breathing mechanism inhumansThe human respiratory system consists of a complexrespiratory structure. It is made up of the nasal cavity,pharynx, tracheae, bronchi, bronchioles and lungs. Therespiratory process involved air entering through the nostrilsand subsequently into the pharynx, tracheae, bronchi,bronchioles, finally ending in air sacs called alveoli. There areas many as 700 million air sacs surrounded by a capillarynetwork for the purpose of gaseous exchanges.


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Human respiratory system


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Adaption

The adaptations in human lungs for efficientgaseous exchanges are as follows:


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The Breathing Mechanism in Humans during Inhalation andExhalation

The breathing mechanism involves air entering thelungs during inhalation and air moving out of the lungsduring exhalation. The lungs do not have muscles butbreathing is made possible by the action of a set ofantagonistic intercostals muscles and the action of thediaphragm muscles. The figure below show the locationof the intercostal muscles.


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The location of the intercostals muscles


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The breathing mechanism in humans during inhalation andexhalation


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The mechanism of breathing in humans


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THE END

chapter 7 bilogy form 4

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