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A-Level Biology - AQA > ✅6 - Exchange > Flashcards

✅6 - Exchange Flashcards

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1
Q

What are the features of specialised exchange surfaces?

A

A large surface area to volume ratio
Very thin so that diffusion distance is short
Selectively permeable to allow selected materials to cross
Movement of environmental medium to maintain a gradient
A transport system to ensure movement of internal medium

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2
Q

What is Fick’s law?

A

Diffusion ∝ Surface area x difference in concentration / length of diffusion pathway

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3
Q

How does gas exchange occur in single celled organisms?

A

Oxygen is absorbed by diffusion across body surface, Carbon Dioxide diffuses out

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4
Q

What are tracheae?

A

An internal network of tubes in insects, supported by strengthened rings

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5
Q

What are tracheoles?

A

Smaller, dead end tubes which the tracheae divide into

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6
Q

How do gases move in and out of the tracheal system?

A

Along a diffusion gradient
Mass transport
The water in the ends of the tracheoles

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7
Q

How do gases move in and out of the tracheal system by diffusion?

A

When cells respire, O2 at the ends of tracheoles used up, creates diffusion gradient and O2 diffuses in and along tracheae. CO2 creates gradient int he opposite direction

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8
Q

How do gases move in and out of the tracheal system by mass transport?

A

The contraction of muscles of insect squeeze tracheae enabling mass movement of air in and out

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9
Q

How does water in the ends of tracheoles enable movement of gases in and out?

A

In periods of activity, muscle cells respire and produce lactate, which lowers water potential of muscle cells. Water moves into the cells and the volume of tracheoles decreases, drawing air into them

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10
Q

What are the limitations of the tracheal system?

A

Relies mostly on diffusion

Diffusion pathway must be short

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11
Q

What are fish gills made up of?

A

A gill bar, gill filaments and lamellae

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12
Q

What is countercurrent flow?

A

The flow of water over the gill lamellae and the flow of blood within them are in opposite directions

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13
Q

What does countercurrent flow allow?

A

Maximum gas exchange

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14
Q

What does the arrangement of blood vessels in countercurrent flow allow?

A

Blood that is already well loaded with oxygen meets water which has its maximum concentration of oxygen, so diffusion takes place
Blood with little oxygen meets water which has most, but not all its oxygen removed. Again, diffusion takes place from blood to water

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15
Q

What is maintained across the lamellae?

A

A diffusion gradient for oxygen uptake

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16
Q

How much of the oxygen in the water is taken up by blood?

A

80%

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17
Q

How is gas exchange in plants similar to in insects?

A

No living cell is far from the external air

Diffusion takes place in the gas phase (air) which makes it more rapid than in water

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18
Q

How are leaves adapted for rapid diffusion?

A

Many stomata and so no cell is far from one, short diffusion pathway
Numerous interconnecting air spaces throughout the mesophyll so that gases can come into contact with them
Large surface area of mesophyll cells for rapid diffusion

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19
Q

What are stomata?

A

Minute pores that occur mainly on the underside of leaves and that can open and close to control the rate of gas exchange

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20
Q

What controls the opening and closing of the stomata?

A

Guard cells

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21
Q

Why is it important to open and close the stomata?

A

To prevent water loss

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22
Q

What adaptions do insects have to conserve water loss?

A

Small surface area to volume ratio
Waterproof coverings
Spiracles

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23
Q

Why can plants not have a small surface area to volume ratio?

A

Because photosynthesis requires a large surface area

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24
Q

What are xerophytes?

A

Plants which have evolved with adaptions against water loss through transpiration

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25
Q

What are adaptions of plants to prevent water loss?

A 
A thick cuticle
Rolling up of leaves
Hairy leaves
Stomata in pits or grooves
Reduced surface area to volume ratio of leaves
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26
Q

How does a thick cuticle prevent water loss?

A

The thicker the cuticle, the less water can escape through it, eg holly leaves

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27
Q

How does rolling up leaves prevent water loss?

A

Most leaves have stomata on lower epidermis, so rolling protects lower epidermis from outside, helping to trap a region of still, warm air within. This region becomes saturated with water vapour and so there is no water potential gradient

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28
Q

How does having hairy leaves prevent water loss?

A

A thick layer of hairs traps still, moist air next to the leaf surface and the water potential gradient is reduced, so less water is lost

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29
Q

How does having stomata in pits or grooves prevent water loss?

A

Traps still, moist air close to the leaf to reduce water potential gradient

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30
Q

How does reduced surface area to volume ratio of leaves prevent water loss?

A

By having leaves that are small and roughly circular in cross section, eg pine needles, water loss is reduced

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31
Q

Why does the volume of oxygen absorbed and carbon dioxide removed need to be large in mammals?

A

They are relatively large organisms with a large volume of living cells
They maintain a high body temperature which is related to them having high metabolic and respiratory rates

32
Q

Why are the lungs located inside the body?

A

Air is not dense enough to support or protect them

The body as a whole would otherwise lose a great deal of water and dry out

33
Q

What are the main parts of the human gas exchange system?

A 
Lungs
Trachea
Bronchi
Bronchioles
Alveoli
34
Q

How are is the trachea supported?

A

By rings of cartilage

35
Q

What dot he bronchi and trachea produce?

A

Mucus, to trap dirt particles and they have cilia to move the dirt laden mucus towards the throat

36
Q

Why do alveoli have elastic fibres?

A

To allow them to stretch

37
Q

What does contraction of the internal intercostals lead to?

A

Expiration

38
Q

What does contraction of the external intercostals lead to?

A

Inspiration

39
Q

What is the process of inspiration?

A

External intercostals contract, internals relax
Ribs pulled upwards and outwards, volume increases
Diaphragm contracts and flattens, increases volume
Pressure reduced, air drawn in

40
Q

What is the process of expiration?

A

Internal intercostals contract, externals relax
Ribs move downwards and outwards, volume decreases
Diaphragm relaxes, pushed up, volume decreased
Pressure increased, air forced out

41
Q

Where is the site of gas exchange in mammals?

A

The epithelium of the alveoli

42
Q

How many alveoli are in each lung?

A

300 million

43
Q

Why is diffusion of gases between alveoli and blood very rapid?

A

Red blood cells slowed as they pass through pulmonary capillaries
Distance between alveolar air and RBCs decreased as RBCs flattened against capillary walls
Walls of capillary and alveoli very thin
Large total surface area
Breathing constantly ventilates lungs, heart constantly pumps blood, steep concentration gradient

44
Q

What are the main parts of the digestive system?

A 
Oesophagus
Stomach
Ileum
Large intestine
Rectum
45
Q

What role does the stomach play in digestion?

A

Muscular sac with inner later that produces enzymes. Stores and digests food, especially proteins. Has glands that produce enzymes to digest protein

46
Q

What role does the ileum play in digestion?

A

Long muscular tube, food further digested by enzymes produced in the walls and glands. Inner walls folded into villi then microvilli, large surface area

47
Q

What role does the large intestine play in digestion?

A

Absorbs water, most of water is from the secretions of digestive glands

48
Q

What do the salivary glands produce?

A

Amylase, which hydrolyses starch to maltose

49
Q

What does the pancreas produce?

A

Pancreatic juice, contains proteases, lipases and amylase

50
Q

What are the two stages of digestion?

A

Physical breakdown

Chemical digestion

51
Q

What is physical breakdown?

A

When food is large and broken down into smaller pieces by structures such as the teeth, increasing surface area

52
Q

What is chemical digestions

A

Hydrolyses large, insoluble molecules into smaller, soluble ones, carried out by enzymes

53
Q

What does amylase do?

A

Hydrolyses alternate glycosidic bonds in starch to produce disaccharides of maltose

54
Q

What breaks down maltose?

A

Maltase

55
Q

What is maltase produced by?

A

The lining of the ileum

56
Q

What does salivary amylase do?

A

Hydrolyses starch into maltose and contains salts that help to maintain pH around neutral

57
Q

When is amylase denatured?

A

When it enters the stomach and conditions are acidic

58
Q

What is produced by the pancreas and intestinal wall?

A

Alkaline salts to maintain the pH at around neutral so that amylase can fucntion

59
Q

What are membrane-bound disaccharidases?

A

Maltase that is not released into the lumen of the ileum but instead part of the cell surface membrane of epithelial cells

60
Q

What is sucrase?

A

Hydrolyses single glycosidic bonds in the sucrose molecule

61
Q

What is lactase?

A

Hydrolyses single glycosidic bonds in lactose

62
Q

Where are lipases produced?

A

The pancreas

63
Q

What do lipases do?

A

Hydrolyse the ester bonds found in triglycerides to form fatty acids and monoglycerides

64
Q

What are lipids first broken own into?

A

Micelles

65
Q

What are lipids broken down into micelles by?

A

Bile salts produced by the liver

66
Q

What is the process of breaking lipids down into micelles called?

A

Emulsification

67
Q

What are endopeptidases?

A

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

68
Q

What are exopeptidases?

A

Hydrolyse peptide bonds on the terminal amino acids of the peptide molecules formed by endopeptidases, release dipeptides and single amino acids

69
Q

What are dipeptidases?

A

Hydrolyse the bond between two amino acids of a dipeptide

70
Q

How do villi increase efficiency of absorption?

A

Increase surface area for diffusion
Very thin walls, reduced distance
Contain muscle so can move, helps maintain diffusion gradient as movement mixes contents of ileum
Well supplied with blood vessels so can carry away absorbed molecules and maintain diffusion gradient
Microvilli

71
Q

What are the processes of absorbing amino acids and monosaccharides?

A

Co-transport and diffusion

72
Q

How are micelles absorbed?

A

They come into contact with the epithelial cells lining the villi and break down, releasing monoglycerides and fatty acids, which diffuse across the cell membrane

73
Q

What happens when monoglycerides and fatty acids have been absorbed?

A

They are transported to the endoplasmic reticulum where they are recombined to form triglycerides, then associating with cholesterol and lipoproteins in the golgi to form chylomicrons

74
Q

What are chylomicrons?

A

Special particles adapted for the transport of lipids

75
Q

What happens to the cylomicrons?

A

They move out of the epithelial cell by exocytosis and enter lymphatic capillaries called lacteals at the centre of each villus

76
Q

How are triglycerides transported into cells by chylomicrons?

A

They pass into the blood stream and the triglycerides are hydroysed by an enzyme in the endothelial cells of blood capillaries where they diffuse into cells

A-Level Biology - AQA (22 decks)

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