mod 2.2 - nutrient and gas requirements Flashcards
(105 cards)
1
Q
What are autotrophs?
A
Autotrophs, or producers make their own energy by converting inorganic compounds (eg: carbon dioxide and water) to organic compounds.
The process of converting inorganic carbon into organic compounds is called carbon fixation, because the autotroph ‘fixes’ the inorganic carbon into organic molecules such as glucose.
These organic compounds are then consumed by heterotrophs.
2
Q
What further groups are autotrophs divided into according to how they obtain the energy required for carbon fixation?
A
Photosynthetic autotrophs/photoautotrophs: which use light energy.
Chemosynthetic autotrophs/chemoautotrophs: which use chemical energy.
3
Q
What are photosynthetic autotrophs?
A
They obtain energy required for carbon fixation from light or solar energy.
They undergo photosynthesis, and produce the organic compound glucose (in plants).
Most autotrophs are photosynthetic; all green plants but also algae, Euglena and cyanobacteria.
4
Q
Explain the photosynthetic autotroph Venus flytrap.
A
Carnivorous plants, such as the Venus flytrap (Dionaea muscipula) obtain some nutrients such as nitrogen, potassium and phosphorus by capturing and consuming other organisms. However, because they obtain most of their organic compounds through photosynthesis, they are considered as photosynthetic autotrophs.
5
Q
What are chemosynthetic autotrophs?
A
Obtain energy required for carbon fixation from inorganic chemical reactions (chemosynthesis). All known chemosynthetic organisms are prokaryotes. Come chemoautotrophs obtain energy by the oxidation of inorganic molecules. eg: Ammonium ions (NH4+) to nitrite ions (NO2-) Nitrite ions (NO2-) to nitrate (NO3-) Sulfide ions (S2-) to sulfide ions (SO42-) Chemoautotrophs can live in the more extreme environments where these ions can be found → extremophiles.
6
Q
What are examples of chemoautotrophs?
A
Methanogens live in places with low oxygen (digestive tracts of animals and in wetlands) where they obtain energy from a carbon-fixing reaction in which carbon and hydrogen react to form a simple organic compound: methane.
Archaea that live off the carbon in coal.
Bacteria that convert sulfur to sulfate in deep sea thermal vents.
Various nitrifying bacteria that fix nitrogen gas from the air or convert ammonia to nitrate to nitrate ions underground, helping plant growth in the process.
Denitrifying bacteria that return nitrogen to the air.
Bacteria that decompose crude oil.
7
Q
What are heterotrophs?
A
They obtain organic compounds by consuming other organisms or their products.
Heterotrophs use the nutrients organic compounds contain they consume to obtain energy.
All heterotrophs depend directly or indirectly on autotrophs for nutrients and energy.
All animals and fungi are heterotrophs; and some bacteria and many protists.
8
Q
What are photoheterotrophs?
A
These are specialised prokaryotes that use solar energy, rather than organic compounds as a source of energy.
However, unlike photoautotrophs, photoheterotrophs cannot fix carbon from carbon dioxide into organic compounds; so they use organic compounds obtained from other organisms as their carbon source for growth and renewal, not as an energy source.
eg: green non-sulfur bacteria, purple non-sulfur bacteria and heliobacteria.
9
Q
What are chemoheterotrophs?
A
Most heterotrophs are chemoheterotrophs.
They obtain energy from organic compounds by cellular respiration.
Animals, protists, fungi and most heterotrophic bacteria are chemoheterotrophs.
These can further be divided into groups:
10
Q
What are herbivorous heterotrophs?
A
Animals that only eat plant material (herbivores).
eg: kangaroos, horses, parrots, caterpillars and snails.
11
Q
What are carnivorous heterotrophs?
A
Animals that only eat other animals (carnivores).
eg: dingoes, eagles, crocodiles, sharks and spiders.
12
Q
What are omnivorous heterotrophs?
A
Broad dieted animals that eat a mixture of both plants and animals.
Omnivores are opportunistic eaters, eating foods that are readily available to them.
eg: humans, bears and lizards.
13
Q
What are saprotrophic heterotrophs?
A
Include most fungi and some bacteria.
They eat by digesting organic material by extracellular means; meaning they secrete enzymes onto dead and decaying organic material, such as carcasses, leaf litter or fruit. Once the enzymes have broken down the large molecules, the saprotrophic organisms absorb the simple organic nutrients through endocytosis.
This process of decomposing and recycling organic matter is essential for ecosystems to function, as the process returns nutrients back into the environment, driving the cycle of energy.
14
Q
What are parasitic heterotrophs?
A
Also known as parasites, derive their energy and nutrients directly from other living organisms.
They feed on the cell contents, tissues or body fluids of their host.
Their host is harmed and sometimes killed in this process.
Parasites are highly diverse and can be found in all five kingdoms.
15
Q
What are endoparasites?
A
Parasites that live in the host. (eg: tapeworms, liver flukes)
16
Q
What are ectoparasites?
A
Parasites that live outside the host. (eg: ticks and lice)
17
Q
What is the carbon source of autotrophs?
A
Carbon dioxide.
18
Q
What is the carbon source of heterotrophs?
A
Organic compounds.
19
Q
What is the energy source of photoautotrophs?
A
Solar energy (sunlight).
20
Q
What is the energy source of chemoautotrophs?
A
Inorganic molecules.
21
Q
What is the energy source of photoheterotrophs?
A
Solar energy (sunlight).
22
Q
What is the energy source of chemoheterotrophs?
A
Organic compounds.
23
Q
Where does gas exchange in plants occur?
A
Occurs through the stoma (plural stomata). Plants conduct gas exchange through their stomatal pores in their leaves.
24
Q
Where is the stomata located?
A
It is the opening to an air space located in the lower epidermis on a leaf, and consists of two highly epidermal cells: guard cells. These guard cells surround a pore, creating an opening through the epidermis and cuticle.
25
What is the stomata's function?
Stomata are open during the day to increase the rate of photosynthesis when sunlight is available.
When the guard cells are turgid, or swollen, the stomatal opening is large, allowing water and gases to enter and exit the leaf. They become turgid when potassium ions (K+) accumulate and the water potential of the guard cells decreases.
The stomata close when light levels drop and the plants don’t need any more carbon dioxide gas for photosynthesis.
When guard cells lose water, the cells become flaccid and the stomatal opening closes, preventing water and gas from leaving the plant.
26
How do stomata regulate gas exchange?
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When plants open their stomata to allow carbon dioxide gas in for photosynthesis, oxygen gas is released, and water is lost as water vapour during the process of transpiration (the passive movement of water through a plant from the roots and its evaporation as water vapour through the stomatal pores in leaves).
Transpiration involves the upwards movement of water against the force of gravity (transpiration-cohesion-tension theory → see module 2.3).
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27
What happens when the stomata is open?
When the stoma is open (depending on temperature), water is lost which is important as it draws water in from the soil.
When water availability is decreased, photosynthesis is limited and carbon dioxide increases as cellular respiration occurs.
Only on really humid days do stomata stay open as water concentration is equal.
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What are the gas exchange structures in plants?
Stomata, lenticels and chloroplasts.
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What are lenticels?
Pores on the woody parts of plant and shrubs,
Diffusion of water, carbon dioxide and oxygen occur here, but this is slow as woody parts of plants don’t require oxygen.
30
What are chloroplasts?
Photosynthesis occurs here.
Each chloroplast has an outer and inner membrane which regulate the movement of materials into and out of the organelle.
Inside these membranes is a fluid matrix called stroma and a highly complex inner thylakoid membrane system, which fold to form flat hollow discs, which form stacks called grana (singular: granum). Between the grana are flat membrane sheets called thylakoid lamellae (singular: lamella).
31
How does carbon dioxide affect photosynthesis?
If the stomata are closed, photosynthesis will use up the carbon dioxide available, reducing the carbon dioxide concentration in the leaves.
With less carbon dioxide available, the rate of photosynthesis will be limited, even with the presence of light.
32
How does water affect photosynthesis?
The amount of water used in photosynthesis is small compared with the amount needed to keep the cells alive, therefore a living plant cell will normally have sufficient water for photosynthesis to occur.
When the water availability is low and a plant is suffering from water stress, the stomata in the leaf close to conserve water → which limits the amount of carbon dioxide that can enter the leaves for photosynthesis.
33
How does light energy affect photosynthesis?
The limit will be the point at which all the photosynthesis systems and enzymes in the chloroplasts are working at their optimum rate.
In the natural environment, the amount of light available for photosynthesis depends on the amount of sunlight.
Trees and taller plants shade plants on the forest floor, while the amount of light available to aquatic plants depends on how fair underwater they will grow.
Sunlight will also vary during the cycle of a day and will change with the seasons and the weather.
34
What are vascular plants?
They usually grow in terrestrial environments, and are characterised by the presence of vascular tissue, which is specialised for transporting fluids.
Vascular tissue includes:
Xylem: transports water and inorganic nutrients (mineral ions) absorbed from the soil up the plant.
Phloem: transports dissolved sugars produced by photosynthesis from the leaves throughout the plant, and organic substances such as amino acids.
35
What is the root system of plants?
The root tissue of plants is usually located in the soil and is not visible without extracting a plant from its soil bed.
Roots have a critical role in anchoring a plant to the soil, as well as absorbing water and dissolved minerals from the soil for growth and photosynthesis.
Roots also store glucose produced by the plant.
36
How is water transported into roots?
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Water travels into root hairs through osmosis.
Dissolved ions (minerals) from the soil come into root hairs by diffusion.
Roots require air; they go through aerobic respiration.
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37
What are the layers of roots?
Roots have structural adaptations that help them absorb water → the exterior of the root is the epidermis, composed of epidermal cells. Some of these epidermal cells have long, fine extensions called root hairs, which increase SA and maximise water and mineral uptake.
The next layer of a root is the cortex, which is composed of parenchyma cells, which can store nutrients and starch.
The innermost central region of the root contains the vascular tissue: xylem and phloem.
38
What is the shoot system?
This system is above the soil, and offers support and allows for the transport system inside the shoot system.
Dermal tissue (outside of the shoot system) offers support and is waterproof.
Guard tissue: tissue that fills out the stem.
39
What are the layers of leaves?
In vascular plants, a leaf is an organ composed of three distinct layers of specialised cells, or tissues: upper epidermis, mesophyll and lower epidermis.
40
What is the structure and function of the cuticle?
Thin, waxy waterproof layer. It protects the inner cells, prevents water loss and allows sunlight to penetrate for photosynthesis.
41
What is the structure and function of the epidermis (upper and lower)?
Transparent and usually thin. Protects the inner cells, prevents water loss and allows sunlight to penetrate for photosynthesis.
42
What is the structure and function of the epidermis and cuticle?
Contains guard cells surrounding guard cells surrounding stomata. Regulates gas exchange and water loss-- the waxy cuticle protects the lead from excess water loss and the opening and closing of the stomata controls the amount of gas and water vapour entering and exiting the leaf.
43
What is the palisade mesophyll?
Tightly packed column-shaped cells with many chloroplasts, close to the upper epidermis. It's function is photosynthesis.
44
What is the spongy mesophyll?
Loosely packed, rounded cells with fewer chloroplasts, with air spaces around the cells. It's function is gas exchange, including the diffusion of carbon dioxide throughout the leaf.
45
What is the xylem and phloem?
Has tubular vessels. Its function is to transport fluids.
46
What is 3-D imaging?
3-D imaging: taking pictures of plants from different angles which are then measured to annotate the external structure.
47
What is magnetic resonance imaging (MRI)?
Magnetic resonance imaging (MRI): using radio waves and magnetic fields to form 3D pictures of the anatomy and processes of the organisms.
PET scan: greater detailed picture.
48
What is an x-ray?
X-ray: examines internal structures of plants.
49
What is a micro-CT?
Micro-CT: uses x-ray images to create 3D internal images.
50
What methods are used to track the development and movement of the products of photosynthesis?
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Melvin Calvin (Nobel prize 1961) used radioactive isotope Carbon-14 (P-6, E-6, N-8) to show sunlight actually acts on the chlorophyll.
Nowadays to trace photosynthesis, we use computers and radioactive isotopes.
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51
What is digestion?
Digestion: The breaking down of large and complex food particles into smaller particles.
52
What are the nutritional requirements of heterotrophs?
Carbohydrates: important source of immediate energy.
Lipids: required for cell membranes, hormones and vitamins.
Amino acids: required for protein synthesis. Nine essential amino acids are those that cannot be made by the organism; must be included in the diet.
Vitamins: a diverse group of organic compounds made by plants and some animals and microorganisms and are required for cellular processes and needed to make certain enzymes. Many must be obtained from diet.
Minerals: essential for cellular processes. Eg: protein, calcium, iron.
53
What is mechanical/physical digestion?
The process of having a mechanism for breaking down large food into pieces to increase its surface area to make sure the enzymes work with a larger SA to ensure full digestion.
To improve the efficiency of digestion, physical digestion should take place before chemical digestion.
Mechanical digestion does not chemically change the food molecules.
54
Where does mechanical digestion begin?
Mechanical digestion begins in the mouth → physical breaking down of food by teeth → then the stomach physically churns food to further break down anything too big (3 layers of stomach).
Bile, produced in the liver that is released into the small intestine emulsifies fats (breaks up large fatty masses into small droplets → increases SA for enzymes).
55
What is chemical digestion?
When digestive enzymes (eg: amylase, trypsin, pepsin, protease, lipase) break apart complex molecules into simple molecules.
Digestive enzymes greatly increase the rate of breakdown of food molecules.
Most digestive enzymes work by splitting food molecules via the process of hydrolysis.
Glucose comes from large carbohydrate molecules.
Amino acids come from proteins.
Glycerol and fatty acids come from lipids.
Nucleic acids come from nucleotides in DNA and RNA
56
What are the two types of chemical digestion?
Extracellular and intracellular digestion.
57
What is extracellular digestion?
Digestion that takes place outside of the cells; including on the surface. Eg: a sea star turns its stomach inside out and releases enzymes directly onto the animal it has trapped.
58
What is intracellular digestion?
Many invertebrate animals and protozoans use this, where their cells engulf small pieces of food into a membrane-bound food vacuole within the cell; and enzymes are released into the vacuole, food is digested and the resulting small molecules pass through the vacuole membrane and into the cell’s cytosol.
59
What do carnivorous digestive systems look like?
Included dingoes, cats and Tasmanian devils, have strong jaws for biting with long, sharp canine teeth designed to tear meat.
Digestive systems of carnivores are shorter and simpler than herbivores, as there is less extractable energy per gram, and their digestive systems produce all the enzymes needed,
They don’t have a large caecum (a pouch where small and large intestines join), because bacteria aren’t required to break down plant matter.
60
What do herbivorous digestive systems look like?
Including cows, rabbits, kangaroos and koalas, herbivores spend much more time eating because plant matter must be repeatedly ground by teeth before the enzyme cellulase breaks down the cell walls (cellulose).
They have flat teeth and a longer digestive system as plant matter is harder to digest.
The process of the breakdown of cellulose in the gut occurs without oxygen by fermentation (anaerobic respiration). Depending on where fermentation takes place, they are categorized into hindgut (takes place in the caecum and/or first part of the large intestine eg: koala and wombat) or foregut fermenters (takes place in the chamber just before the stomach eg: kangaroo).
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What do omnivorous digestive systems look like?
Their digestive tracts break down a variety of plant and animal material.
62
Function of mouth in digestion:
Teeth mechanically break food into small pieces.
Saliva lubricates food and enzyme amylase digests starch into maltose; amylase mixes with food and once food is broken down the bulbus of food is swallowed by the tongue.
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Function of epiglottis in digestion:
Prevents food from entering the trachea and respiratory system, directing it down the oesophagus.
Is also associated with the gag and cough reflex.
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What is the epiglottis?
A flap at the entrance to the larynx.
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Function of oesophagus in digestion:
Tube down which food travels to the stomach, aided by muscular contractions. (peristalsis)
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What is peristalsis?
Muscular contractions.
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Function of stomach in digestion:
Secretes protein-digesting enzymes (proteases) and gastric juices to aid in food digestion.
Peristalsis of stomach muscles further breaks the ood down and pushes it through the digestive system.
At the entrance of the stomach, there is a sphincter → a muscle that controls movement in and out of the stomach. One bulbis enters, it releases and contracts, continuing to break down food.
68
Function of liver in digestion:
Has important roles in regulating metabolism, toxin removal and processing nutrients.
Stores excess glucose as glycogen for later conversion back to glucose when needed for energy,
Is the site of bile production for the breakdown of fats.
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Function of gallbladder in digestion:
Stores and concentrated bile before releasing it to the small intestine.
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Function of pancreas in digestion:
Produces digestive enzymes that are activated when the food reaches the duodenum (first part of the small intestine).
Produces the hormones insulin and glucagon, which regulate sugar levels in the blood.
Produces sodium bicarbonate, which neutralises stomach acids in the food.
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Function of small intestine in digestion:
Absorbs nutrients and minerals from food.
Enzymes produced in the pancreas and the small intestine and bile from the liver and gallbladder further breakdown food products to facilitate nutrient and water absorption.
Has many blood vessels to absorb nutrients and waste products of digestion and deliver them to the circulatory system.
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Function of large intestine in digestion:
Absorbs water with soluble compounds, such as vitamins and minerals.
Undigested food leaves the body as faeces.
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What is the structure of the small intestine?
Principal organ of absorption.
‘Small’ refers to its diameter and is long and has a large SA, making it good for absorption.
The internal surface area is further increased by millions of tiny folds called villi (singular villus) and by the presence of microvilli on the exposed surface of the epithelial cells lining the lumen.
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Where does absorption happen in the small intestine?
The epithelial lining in the small intestine is one cell thick; allows rapid transfer of nutrients to the blood and lymphatic vessels beneath the surface.
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How do nutrients pass through the small intestine?
Via facilitated diffusion/active transport.
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How do lipid-soluble molecules pass through the small intestine?
Lipid-soluble molecules (and vitamins) (products of fat digestion - fatty acids and glycerol) diffuse easily through membranes of epithelial cells through diffusion.
They then reassemble into fats before passing into lacteals (capillaries of the lymphatic system near the small intestine; have a milky appearance from high fat content).
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How do water-soluble molecules pass through the small intestine?
Water-soluble molecules (aa’s, simple sugars - glucose) and vitamins and minerals pass through the membranes of epithelial cells by active transport and facilitated diffusion.
Most of the water that enters the small intestine is absorbed passively, through osmosis as the products of digestion are absorbed.
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How does blood pass through the intestine?
Blood leaving the intestine first passes into the liver through the hepatic portal vein. Here, absorbed nutrients are removed and stored in the liver before the blood passes into the general venous circulation.
79
What are energy reserves in animals?
The storage carbohydrate in animals is glycogen, similar to starch.
It is a large molecule made of glucose subunits, and when it is needed, carbohydrate stores are used first and most easily.
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Are amino acids stored in tissues?
Amino acids cannot be stored in animal tissues, unlike carbohydrates and fats.
Amino acids are needed to build proteins and therefore must be provided in an animal’s diet. Vegetarians can substitute meats with other things like beans which are a good source of amino acids.
81
What is energy balance?
For energy balance, energy input (eating) must equal energy output (usage). If there is more input, this extra energy is stored as chemical energy (in fat or glycogen), and if there is less input, fat or glycogen is broken down to release energy.
82
What is the basal metabolic rate?
Basal metabolic rate: the amount of energy required to maintain basic functions in a resting, unstressed animal per unit of time.
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What affects the metabolic rate in humans?
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Body composition (the proportion of fat to bone or muscle): muscle tissue uses energy at a faster rate than fat tissue, so more muscle means a greater energy requirement.
Level of activity: individuals vary in the amount of energy they use to carry out physical activity; resulting in large differences in metabolic rate.
Biological sex: males generally use energy at a higher rate because on average they have a lower fat-to-muscle ratio.
Age: metabolic rate increases in periods of growth (childhood and adolescence and pregnancy). Metabolic rate declines with later ages, because of decreased physical activity and changes in body composition.
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84
What is coeliac disease?
Where the villi of the small intestine is damaged by the body’s immune system in response to gluten.
The villi will repair itself once the individual has transitioned to a gluten free diet.
85
What is liver disease?
Alcohol is toxic, and the enzymes that break it down are found in the liver.
A heavy drinker’s liver cells cannot carry out normal cellular respiration; and substances meant to be broken down for energy are converted into fats instead, and accumulate in the liver.
It is reversible for a while, but cells filled with fat start to die (alcoholic hepatitis) and this is followed by cirrhosis which is the formation of scar tissue in the liver. Death may occur when the liver is unable to carry out normal functions.
86
How does gas exchange occur?
Gas exchange always takes place by diffusion (passive movement of a substance along its concentration gradient) across a mo1st cell membrane.
The immediate environment of cells is the layer of fluid that surrounds them. Oxygen must first dissolve in the layer of extracellular fluid covering the gas exchange surface before it can cross cell membranes and enter the body.
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What are the properties of efficient gas exchange structures?
Large SA, the barrier to be crossed (cell membrane/fluid layers) should be as thin as possible and should consist of a material that allows the gas to pass easily through, moist surface to encourage diffusion.
88
Why should there bean efficient removal of the substance after transfer?
Inadequate blood flow past the respiratory surface will allow oxygen to accumulate, slowing further transfer.
In most large animals, energy is required to ventilate the respiratory surface and circulate blood past its inner surface. The efficient supply and removal of oxygen maintains a high concentration gradient across the exchange surface, and therefore a high rate of diffusion.
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When is energy expenditure is most economical?
When the rates of ventilation and blood flow to the respiratory tissue are matched.
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Breathing air:
When you breathe air, oxygen is absorbed by the respiratory system and transferred to your cells via the circulatory system.
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What is the structure and function of the nasal cavity?
Air is drawn through the nose and passes into the nasal cavity and pharynx (back of the throat).
Breathing through the nose is preferable as the air is filtered, moistened and warmed in the nasal passages.
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What is the structure and function of the airways?
From the pharynx, air passes into the airways: the trachea, paired bronchi (singular bronchus) and branching bronchioles.
The trachea and bronchi are lined with cells covered in cilia (singular cilium) and secrete mucus.
Particles of dust or bacteria are trapped by this mucus and swept by the cilia back up to the pharynx and swallowed.
93
What is the structure and function of the alveoli?
Air enters the terminal air sacs, called alveoli, where gas exchange takes place.
A constant supply of oxygen to cells is the most critical input for endotherms, such as mammals and birds, because they use energy to warm their bodies, and therefore need oxygen at a great rate for cellular respiration.
The alveoli has a large SA for gas exchange; total in adults being 30-70m2.
Each alveolus is lined with a very thin layer of flattened cells, called the alveolar epithelium; which is richly supplied with blood capillaries, facilitating diffusion of gases between the alveoli and the capillaries.
Once oxygen enters the capillaries, it has entered the circulatory system.
94
What is the advantage of breathing air?
Advantage of breathing air: requires less energy than breathing water and provides more oxygen, however animals that breathe air must have a large, moist gas exchange surface. Because water evaporates continuously from this surface, it is a major site of water loss for all terrestrial organisms.
95
Where are the lungs located in mammals?
Mammalian lungs are found in the chest cavity/thorax, which is enclosed under a small negative pressure that keeps the lungs expanded. The floor of the chest cavity is the muscular diaphragm.
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What mechanism in the lungs ventilates it?
Mammals use a ‘suction pump’ mechanism to ventilate their lungs.
97
How is the chest cavity expanded?
The chest cavity is expanded (letting air in) by the contraction of the diaphragm downwards and the raising of the ribs. This inhalation is an active process.
98
How is the chest cavity flattened?
Exhalation is normally the result of the elastic recoil of the thorax as it returns to its relaxed state. Only forceful exhalation involves an active compression of the lungs.
99
What is tidal volume?
Tidal volume is the volume of air moved in and out at each breath.
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What is the vital capacity?
Vital capacity is the maximum volume of air that we can move into and out of our lungs, which is much more than normal resting levels. Tidal volume varies according to the need for oxygen.
101
Why is it called tidal volume?
Air moves tidally in and out of mammalian lungs through the same airways. This is not as efficient as one-way flow as there is still some stale air left in the airways and in the alveoli. The next inhalation draws the stale air back into the lungs; making it impossible to fill our lungs completely with fresh air.
102
What is the residual volume?
The volume of air left in the respiratory system at the end of the exhalation is referred to as the residual volume.
103
What is asthma?
Where cells lining the airways (bronchi and bronchioles) are sensitive to foreign particles in the air, like pollen.
Airways swell, fill with mucus and become constricted; which reduces the space through which air can flow.
This increases the resistance to the flow of air into and out of the lungs, making it difficult to breathe out. An increase of the pressure on the lungs to force air out, airways are compressed.
104
What is emphysema?
Caused by the breakdown of air sacs in the lungs, reducing the lung SA availability for gas exchange.
It occurs in older people most likely due to smoking.
Involves an increased resistance to airflow in the small airways, making breathing more difficult.
105
What is pneumonia?
Caused by an infection that causes the lungs to become inflamed and the air sacs (alveoli) to fill with white blood cells and fluid.
This interferes with respiration, because the fluid in the alveoli reduces the area of the lung surface in contact with air. The inflamed lung tissue is also swollen, so that oxygen must diffuse further before it can enter the blood.
