6.Exchange between organisms and their environment Flashcards

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1
Q

For an effective exchange…

A

the exchange surface of the organism must be large compared with their volume.

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2
Q

Name features of specialised exchange surfaces

A
  • large SA:V ratio
  • short diffusion pathway
  • selectively permeable (to allow selected materials across)
  • a transport system to maintain a diffusion gradient
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3
Q

What is Fick’s Law

A

Rate of diffusion α (surface area x concentration) / distance

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4
Q

Describe gas exchange in single-celled organisms

A

They have large SA:V meaning oxygen can just diffuses across their body surface

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5
Q

What are tracheae (i)

A

Internal network of tubes inside an insect

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6
Q

What are tracheoles

A

Smaller dead end tubes that are sub branches of tracheae

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7
Q

Name three ways gases move in and out the tracheal system

A
  • along a diffusion gradient
  • mass transport (abdominal pumping)
  • through water or gas phase at end of tracheoles
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8
Q

Describe how gases move in and out the tracheal system along a diffusion gradient

A
  • when cells are respiring oxygen is used up so concentration gradient is created
  • causes oxygen to diffuse from atmosphere into and along the tracheal system
  • when cells are respiring carbon dioxide is produces so concentration gradient is created
  • carbon dioxide diffuses along and out the tracheal system
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9
Q

Describe how gases move in and out the tracheal system via mass transport

A
  • abdominal pumping is the contraction of muscles in insects
  • squeezes the trachea enabling mass movements of air in and out
  • speeds up gas exchange
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10
Q

Describe how gases move in and out the tracheal system at the end of the tracheoles

A
  • during periods of high activity muscles cells around the tracheoles respire anaerobically
  • this produces lactate which is soluble and lowers the water potential of the muscle cells
  • the water therefore moves via osmosis into the cells
  • this causes air to be drawn in as it decreases the pressure
  • also means the final diffusion pathway is gas rather than liquid phase and therefore more rapid
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11
Q

What are spiracles

A

Tiny pores that gases enter and leave the tracheal system. Mainly stay closed to reduce water loss

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12
Q

What is a limit of the tracheal system

A

Relies on diffusion meaning for it to be effective the diffusion pathway needs to be short. This limits the size the insects can attain.

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13
Q

Describe the structure of gills

A
  • made up of gill filaments, stacked

- gill lamellae are at right angles to the gill filaments

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14
Q

What is a countercurrent system

A

a mechanism by which the efficiency of exchange between two substances is increased by having them flow in opposite directions

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15
Q

Countercurrent flow means that…

A
  • blood already well loaded with oxygen meets water with max concentration so diffusion still takes place
  • blood with little oxygen meets water with little oxygen but diffusion can still take place
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16
Q

Name 2 ways gas exchange in plants is similar to that of insects

A
  • no living cell is far from external air and therefore a source of Co2 and oxygen
  • diffusion takes place in a gas phase which makes it more rapid (compared to a liquid phase)
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17
Q

What adaptations for gas exchange do leaves show

A
  • many stomata, no cell is far from stomata and therefore diffusion pathway is short
  • numerous interconnecting air spaces that occur throughout the mesophyll so that gases can readily come in contact with mesophyll cells
  • large SA:V ratio means rapid diffusion
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18
Q

What are stomata

A
  • minute pores that occur mainly on leaves
  • each stoma is surrounded by a pair of guard cells
  • they control rate of gas exchange as they can open and close the stomatal pore
  • they are important in controlling water loss
  • close at times when water loss would be excessive
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19
Q

What problem do plants and insects have

A

The opposing needs of an efficient gas-exchange system and the requirement to conserve water

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20
Q

Describe the ways insects are adapted to reduce water loss

A
  • small SA:V ratio to minimise the area over which water can be lost
  • waterproof coverings over their body surfaces, insects have outer skeleton of waterproof chitin
  • spiracles are the opening of the tracheae at the body surface which can be closed to reduce water loss
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21
Q

Describe the ways plants are adapted to reduce water loss

A
  • waterproof covering

- ability to close stomata

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22
Q

What are xerophytes

A

Plants that are adapted to living in areas where water is in short supply

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23
Q

Name the ways xerophytes have evolved to reduce water loss

A
  • a thick cuticle
  • rolling up of leaves
  • hairy leaves
  • stomata in grooves or pits
  • reduced SA:V of leaves
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24
Q

Describe how rolling of leaves reduces water loss

A
  • causes air to be trapped in a region around the lower epidermis (where most stoma are found)
  • this region becomes saturated with water vapour causing a high water potential
  • there is no water potential gradient
  • no water is lost from the leaf.
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25
Q

Describe how hairy leaves reduces water loss

A
  • traps moist air near leaf surface
  • water potential gradient between inside and outside is reduced
  • less water is lost by evaporation
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26
Q

What is inspiration

A
  • inhaling

- when air pressure is greater than the air pressure inside the lungs

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27
Q

What is expiration

A
  • exhaling

- when air pressure in the lungs is greater than that of the atmosphere

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28
Q

What are the three muscles that cause pressure changes within the lungs

A
  • diaphragm
  • internal intercostal muscles
  • external intercostal muscles
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29
Q

Which intercostal muscle is responsible for expiration

A

Internal intercostal muscles

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30
Q

Which intercostal muscle is responsible for inspiration

A

External intercostal muscles

31
Q

What happens during inspiration

A
  • external intercostal muscles contract
  • internal intercostal muscles relax
  • ribs move outwards, increasing the volume of the thorax
  • diaphragm muscles contract causing it to flatten, increasing the volume of the thorax
  • reduces pressure
  • atmospheric pressure is now greater than pulmonary
  • air is forced into the lungs
32
Q

What happens during expiration

A
  • internal intercostal muscles contract
  • external intercostal muscles relax
  • ribs move inwards, decreasing the volume of the thorax
  • diaphragm relax contract causing it to be pushed up by the abdomen, decreasing the volume of the thorax
  • increases pressure
  • atmospheric pressure is now lower than pulmonary
  • air is forced out the lungs
33
Q

Name the main parts of the human gas exchange system

A
  • lungs
  • trachea
  • bronchi
  • bronchioles
  • alveoli
34
Q

What is the trachea

A
  • flexible airway
  • supported by rings of cartilage
  • prevents the trachea from collapsing when pressure falls when breathing in
  • walls are made of muscle
35
Q

What are the bronchi

A
  • two divisions of the trachea, each leading to one lung
  • similar structure to trachea
  • like trachea, also produce mucus
36
Q

What are bronchioles

A
  • branching subdivisions of the bronchi

- muscle lined which allows them to constrict so they can control air flow in and out of the alveoli

37
Q

What are alveoli

A
  • small air sacs at the end of bronchioles
  • between the alveoli there are some collagen and elastic fibres
  • elastic fibres allow the alveoli to stretch as they fill with air when breathing out
  • lined with epithelium cells
38
Q

What is the site of gas exchange in mammals

A

Alveoli

39
Q

Describe reasons why the diffusion of gases between the alveoli and the blood will be very rapid

A
  • red blood cells are slowed as the pass through pulmonary capillaries, allowing more time for diffusion
  • short diffusion distance, both alveoli and capillaries wall are 1 cell thick
  • alveoli and pulmonary capillaries have a very large total surface area
  • ventilation of lungs and blood due to constant breathing and blood circulation, maintains concentration gradient
40
Q

Name the major parts of the digestive system

A
  • oesophagus
  • stomach
  • ileum
  • large intestine
  • rectum
  • salivary glands
  • pancreas
41
Q

What is the ileum

A
  • a long muscular wall
  • inner walls are folded into villi (large SA)
  • micro villi on epithelial cells of each villus
  • function is too absorb the products of digestion into the bloodstream
42
Q

What is the pancreas

A

Large gland that secrets pancreatic juice. The secretion contains proteases, lipase and amylase

43
Q

What are the two stages of digestion

A
  • physical breakdown

- chemical digestion

44
Q

What is physical breakdown

A

Food is broken down into smaller pieces by structures such as the teeth. Provides a larger surface area for chemical digestion

45
Q

Name three important digestive enzymes

A
  • carbohydrase
  • lipases
  • proteases
46
Q

Where is amylase produced

A

Mouth and pancreas

47
Q

What does amylase do

A

Hydrolyses the alternate glyosidic bonds of the starch molecule to produce disaccharide maltose

48
Q

Where is maltase produced

A

Lining of the ileum

49
Q

What does maltase do

A

Hydrolyses glyosidic bonds in maltose, producing the monosaccharide alpha glucose

50
Q

Describe the steps of starch hydrolysis (mouth)

A
  • food enters mouth and is mixed with saliva

- saliva contains salivary amylase and salts to keep pH around 7 (optimal pH for salivary amylase)

51
Q

Describe the steps of starch hydrolysis (stomach)

A
  • food enters stomach

- acid denatures the amylase stopping hydrolysis of starch

52
Q

Describe the steps of starch hydrolysis (small intestine)

A
  • food passes into small intestine where it mixes with pancreatic juice
  • pancreatic juice contains pancreatic amylase which hydrolyses the remaining starch to maltose
  • alkaline salts maintain the pH so amylase can function (~pH 7)
53
Q

What are alkaline salts produced by

A
  • the pancreas

- intestinal wall

54
Q

Describe the steps of starch hydrolysis (ileum)

A
  • muscle in intestine wall push food along the ileum
  • epithelial wall produces disaccharidase maltase
  • maltase is not released into the lumen of the ileum but is part of the cell surface membrane (membrane bound disaccharidase
  • maltase hydrolyses the maltose into alpha glucose
55
Q

What is different about the disaccharidase in the ileum compared to amylase

A
  • not released into the ileum
  • is part of the cell-surface membrane
  • therefore known as membrane-bound disaccharidase
56
Q

Describe how sucrose and lactose are hydrolysed

A
  • sucrase or lactase hydrolyses the single glyosidic bond in the sucrose or lactose
  • produces the monosaccharides glucose + fructose and glucose + galactose
57
Q

Where are lipases produced and found

A
  • produced in the pancreas

- act in the stomach

58
Q

What do lipases do

A

Hydrolyse the ester bond in triglycerides to form fatty acids and monoglycerides

59
Q

What are micelles

A

Tiny droplets of bile salts associated with monoglycerides and fatty acids

60
Q

Describe emulsification

A

Where lipids are split into micelles by bile salts which increases the SA of lipids so the action of lipases speed up

61
Q

Name 3 types of peptidases

A
  • endopeptidases
  • exopeptidases
  • dipeptidases
62
Q

What do endopeptidases do

A

Hydrolyse the peptide bonds between amino acids in the central region of a protein molecule forming a series of peptide molecules

63
Q

What do exopeptidases do

A

Hydrolyse the peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases. This releases dipeptides and single amino acids

64
Q

What do dipeptidases do

A

Hydrolyse the peptide bond between the two amino acids of a dipeptide. These are membrane-bound, part of the epithelial cells lining the ileum

65
Q

Name enzymes produced by the epithelium

A
  • maltase
  • lactase
  • sucrase
  • dipeptidases
66
Q

Where do endopeptidases work

A

Stomach

67
Q

Where do exopeptidases work

A

Small intestine (duodenum)

68
Q

What is the function of the ileum

A

Absorb the products of digestion

69
Q

Describe how villi increase the rate of absorption

A
  • increase the surface area for diffusion
  • they contain muscle so are able to move. The movement mixes the contents of the ileum which maintains concentration gradient
  • thin wall, reduces diffusion distance
  • well supplied with blood to maintain concentration gradient
  • posses microvilli to further increase SA for diffusion
70
Q

By what mechanisms are amino acids and monosaccharides absorbed

A

Co-transport

71
Q

Describe the role of micelles in the absorption of triglycerides

A
  • monoglycerides and fatty acids remain associated with bile salts, these are known as micelles
  • they come in contact with epithelial cells lining the villi of the ileum
  • this causes them to break down releasing the monoglycerides and fatty acids
  • here they passively diffuse across the cell surface membrane of the epithelial cells
72
Q

By what mechanism are triglycerides absorbed

A

Passive diffusion as they are non-polar molecules (so lipid soluble

73
Q

What happens when monoglycerides and fatty acids are absorbed by the epithelial cells of the ileum

A
  • they are transported to the endoplasmic reticulum
  • recombined to form triglycerides
  • they then are transported to the Golgi apparatus where they associate with cholesterol and lipoproteins to form chylomicrons
  • chylomicrons move out the epithelial cells by exocytosis where they enter lymphatic capillaries (lacteals) found at the centre of each villus
  • here they pass into the blood system
  • triglyceride in the chylomicrons are hydrolysed by an enzyme in the endothelial cells of blood capillaries from where they diffuse into cells