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    which of the following structures in insects functions in gas exchange?


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    20.1 Systems of Gas Exchange – Concepts of Biology – 1st Canadian Edition


    Learning Objectives

    By the end of this section, you will be able to:

    Describe the passage of air from the outside environment to the lungs

    Explain how the lungs are protected from particulate matter

    The primary function of the respiratory system is to deliver oxygen to the cells of the body’s tissues and remove carbon dioxide, a cell waste product. The main structures of the human respiratory system are the nasal cavity, the trachea, and lungs.

    All aerobic organisms require oxygen to carry out their metabolic functions. Along the evolutionary tree, different organisms have devised different means of obtaining oxygen from the surrounding atmosphere. The environment in which the animal lives greatly determines how an animal respires. The complexity of the respiratory system is correlated with the size of the organism. As animal size increases, diffusion distances increase and the ratio of surface area to volume drops. In unicellular organisms, diffusion across the cell membrane is sufficient for supplying oxygen to the cell (Figure 20.2). Diffusion is a slow, passive transport process. In order for diffusion to be a feasible means of providing oxygen to the cell, the rate of oxygen uptake must match the rate of diffusion across the membrane. In other words, if the cell were very large or thick, diffusion would not be able to provide oxygen quickly enough to the inside of the cell. Therefore, dependence on diffusion as a means of obtaining oxygen and removing carbon dioxide remains feasible only for small organisms or those with highly-flattened bodies, such as many flatworms (Platyhelminthes). Larger organisms had to evolve specialized respiratory tissues, such as gills, lungs, and respiratory passages accompanied by a complex circulatory systems, to transport oxygen throughout their entire body.

    Figure 20.2.  The cell of the unicellular algae Ventricaria ventricosa is one of the largest known, reaching one to five centimeters in diameter. Like all single-celled organisms, V. ventricosa exchanges gases across the cell membrane.


    For small multicellular organisms, diffusion across the outer membrane is sufficient to meet their oxygen needs. Gas exchange by direct diffusion across surface membranes is efficient for organisms less than 1 mm in diameter. In simple organisms, such as cnidarians and flatworms, every cell in the body is close to the external environment. Their cells are kept moist and gases diffuse quickly via direct diffusion. Flatworms are small, literally flat worms, which ‘breathe’ through diffusion across the outer membrane (Figure 20.3). The flat shape of these organisms increases the surface area for diffusion, ensuring that each cell within the body is close to the outer membrane surface and has access to oxygen. If the flatworm had a cylindrical body, then the cells in the center would not be able to get oxygen.

    Figure 20.3.  This flatworm’s process of respiration works by diffusion across the outer membrane. (credit: Stephen Childs)


    Earthworms and amphibians use their skin (integument) as a respiratory organ. A dense network of capillaries lies just below the skin and facilitates gas exchange between the external environment and the circulatory system. The respiratory surface must be kept moist in order for the gases to dissolve and diffuse across cell membranes.

    Organisms that live in water need to obtain oxygen from the water. Oxygen dissolves in water but at a lower concentration than in the atmosphere. The atmosphere has roughly 21 percent oxygen. In water, the oxygen concentration is much smaller than that. Fish and many other aquatic organisms have evolved gills to take up the dissolved oxygen from water (Figure 20.4). Gills are thin tissue filaments that are highly branched and folded. When water passes over the gills, the dissolved oxygen in water rapidly diffuses across the gills into the bloodstream. The circulatory system can then carry the oxygenated blood to the other parts of the body. In animals that contain coelomic fluid instead of blood, oxygen diffuses across the gill surfaces into the coelomic fluid. Gills are found in mollusks, annelids, and crustaceans.

    Figure 20.4.

    This common carp, like many other aquatic organisms, has gills that allow it to obtain oxygen from water. (credit: “Guitardude012″/Wikimedia Commons)

    The folded surfaces of the gills provide a large surface area to ensure that the fish gets sufficient oxygen. Diffusion is a process in which material travels from regions of high concentration to low concentration until equilibrium is reached. In this case, blood with a low concentration of oxygen molecules circulates through the gills. The concentration of oxygen molecules in water is higher than the concentration of oxygen molecules in gills. As a result, oxygen molecules diffuse from water (high concentration) to blood (low concentration), as shown in Figure 20.5. Similarly, carbon dioxide molecules in the blood diffuse from the blood (high concentration) to water (low concentration).

    Source : opentextbc.ca

    CH 34 QUIZ (Respiration) Flashcards & Practice Test

    Start studying CH 34 QUIZ (Respiration). Learn vocabulary, terms, and more with flashcards, games, and other study tools.

    CH 34 QUIZ (Respiration)

    5.0 1 Review

    Which of the following structures is the site of gas exchange in insects?

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    According to the new dietary guidelines, which of the following would be the healthiest choice for protein?

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    an egg

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    1/36 Created by madimelancon

    Terms in this set (36)

    Which of the following structures is the site of gas exchange in insects?


    According to the new dietary guidelines, which of the following would be the healthiest choice for protein?

    an egg

    You decide to follow the new dietary guidelines. Which of the following would be best for you to avoid?

    white rice

    Which of the following will you soon find on food labels?

    added sugar

    You are a physician. Why do you encourage your patients to decrease their sodium intake?

    To decrease blood pressure.

    You are interested in decreasing the amount of saturated fat you eat. Which of the following would be your best choice to use in your cooking?

    olive oil

    Cells lining the alveoli are coated with a thin layer of fluid called "surfactant." What is the function of this fluid?

    to prevent the alveoli from collapsing when air is exhaled

    In the lungs, carbon dioxide leaves red blood cells and enters the __________.

    alveoli 1

    Air enters through the nose or mouth.


    Air travels down the trachea and then enters the bronchi.

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    Respiratory system of insects

    Respiratory system of insects

    From Wikipedia, the free encyclopedia

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    Development of the tracheal system in .

    An insect's respiratory system is the system with which it introduces respiratory gases to its interior and performs gas exchange.

    Air enters the respiratory systems of insects through a series of external openings called spiracles. These external openings, which act as muscular valves in some insects, lead to the internal respiratory system, a densely networked array of tubes called tracheae. This network of transverse and longitudinal tracheae equalizes pressure throughout the system.

    It is responsible for delivering sufficient oxygen (O2) to all cells of the body and for removing carbon dioxide (CO2) that is produced as a waste product of cellular respiration. The respiratory system of insects (and many other arthropods) is separate from the circulatory system.


    1 Structure of the spiracle

    2 Structure of the tracheae

    3 Theoretical models

    4 References

    Structure of the spiracle[edit]

    Further information: Spiracle (arthropods)

    Indian moon moth () with some of the spiracles identified

    Scanning electron micrograph of a cricket spiracle valve

    Insects have spiracles on their exoskeletons to allow air to enter the trachea.[1] In insects, the tracheal tubes primarily deliver oxygen directly into the insects' tissues. The spiracles can be opened and closed in an efficient manner to reduce water loss. This is done by contracting closer muscles surrounding the spiracle. In order to open, the muscle relaxes. The closer muscle is controlled by the central nervous system but can also react to localized chemical stimuli. Several aquatic insects have similar or alternative closing methods to prevent water from entering the trachea. Spiracles may also be surrounded by hairs to minimize bulk air movement around the opening, and thus minimize water loss.

    The spiracles are located laterally along the thorax and abdomen of most insects—usually one pair of spiracles per body segment. Air flow is regulated by small muscles that operate one or two flap-like valves within each spiracle—contracting to close the spiracle, or relaxing to open it.

    Structure of the tracheae[edit]

    After passing through a spiracle, air enters a longitudinal tracheal trunk, eventually diffusing throughout a complex, branching network of tracheal tubes that subdivides into smaller and smaller diameters and reaches every part of the body. At the end of each tracheal branch, a special cell provides a thin, moist interface for the exchange of gases between atmospheric air and a living cell. Oxygen in the tracheal tube first dissolves in the liquid of the tracheole and then diffuses across the cell membrane into the cytoplasm of an adjacent cell. At the same time, carbon dioxide, produced as a waste product of cellular respiration, diffuses out of the cell and, eventually, out of the body through the tracheal system.

    Each tracheal tube develops as an invagination of the ectoderm during embryonic development. To prevent its collapse under pressure, a thin, reinforcing "wire" of cuticle (the taenidia) winds spirally through the membranous wall. This design (similar in structure to a heater hose on an automobile or an exhaust duct on a clothes dryer) gives tracheal tubes the ability to flex and stretch without developing kinks that might restrict air flow.

    The absence of taenidia in certain parts of the tracheal system allows the formation of collapsible air sacs, balloon-like structures that may store a reserve of air. In dry terrestrial environments, this temporary air supply allows an insect to conserve water by closing its spiracles during periods of high evaporative stress. Aquatic insects consume the stored air while under water or use it to regulate buoyancy. During a molt, air sacs fill and enlarge as the insect breaks free of the old exoskeleton and expands a new one. Between molts, the air sacs provide room for new growth—shrinking in volume as they are compressed by expansion of internal organs.

    Small insects rely almost exclusively on passive diffusion and physical activity for the movement of gases within the tracheal system. However, larger insects may require active ventilation of the tracheal system (especially when active or under heat stress). They accomplish this by opening some spiracles and closing others while using abdominal muscles to alternately expand and contract body volume. Although these pulsating movements flush air from one end of the body to the other through the longitudinal tracheal trunks, diffusion is still important for distributing oxygen to individual cells through the network of smaller tracheal tubes. In fact, the rate of gas diffusion is regarded as one of the main limiting factors (along with weight of the exoskeleton) that limits the size of insects.[2] Periods in Earth's ancient history, however, such as the Carboniferous, featured much higher oxygen levels (up to 35%) that allowed larger insects, such as meganeura, along with arachnids, to evolve.

    Source : en.wikipedia.org

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