Exchange

Question 1

what are the five characteristics of exchange surfaces?

Answer 1

• large surface area increases rate of exchange
• very thin so short diffusion pathway
• selectively permeable
• movement of environmental medium to maintain a diffusion gradient
• a transport system to maintain a diffusion gradient

Question 2

how does gas exchange occur within insects?

Answer 2

spiracle > tracheae > tracheoles > to muscles and body tissue

Question 3

what are three ways in which respiratory gases move in and out of the tracheal system by?

Answer 3

• along a diffusion gradient
• mass transport
• the ends of the tracheoles are filled with water

Question 4

why are the ends of the tracheoles filled with water?

Answer 4

muscle cells carry out anaerobic respiration, produces lactate which LOWERS water potential.
water in tracheoles decrease in volume and draws air further into them. diffusion is more rapid.

Question 5

what are the conditions for effective diffusion in insects?

Answer 5

a short diffusion pathway - which is why insects are of such small size.

Question 6

how does gas exchange occur within fish?

Answer 6

gills > gill filaments > gill lamellae

Question 7

what is the counter-current exchange principle?

Answer 7

blood and water in opposite directions
diffusion takes place twice
diffusion gradient maintained across entire width of gill lamellae
roughly 80% of oxygen available absorbed
if in same direction, then only 50% of oxygen available would be absorbed (as diffusion gradient would only be maintained across part of the length of the gill lamellae)

Question 8

what is the structure of a plant leaf?

Answer 8

short, fast diffusion pathway

very large surface area in the air spaces within a leaf

Question 9

what are leaf adaptations for rapid diffusion?

Answer 9

many stomata
numerous interconnecting air-spaces so that ready contact with mesophyll
large surface area of mesophyll

Question 10

where can you find stomata?

Answer 10

on the bottom of the leaf, but also a few on the top

Question 11

what are the adaptations of stomata?

Answer 11

they can open and close to control rate of gaseous exchange as well as conserve water

Question 12

what are the three adaptations of insects the reduce water loss?

Answer 12

small SA:V ratio - to minimise area where water lost
waterproof coverings - rigid chitin skeleton covered with a waterproof cuticle
spiracles - can be closed to reduce water loss

Question 13

what are xerophytes?

Answer 13

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

Question 14

what are five plant adaptations to reduce water loss?

Answer 14

• a thick cuticle
• rolling up of leaves
• hairy leaves
• stomata in pits or grooves
• a reduced SA:V ratio of the leaves

Question 15

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

Answer 15

lungs > trachea > bronchi > bronchioles > alveoli

Question 16

what is ventilation?

Answer 16

breathing - when air is constantly moving in and out of the lungs

Question 17

what is inspiration?

Answer 17

inhalation - when air pressure of the atmosphere is greater than the air pressure inside the lungs, air is forced into the lungs

Question 18

what is expiration?

Answer 18

exhalation - when the air pressure in the lungs is greater than that of the atmosphere, air is forced out of the lungs

Question 19

what does the contraction of both sets of intercostal muscles lead to?

Answer 19

internal intercostal muscles - leads to expiration

external intercostal muscles - leads to inspiration

Question 20

what are the five things that happen during inspiration?

Answer 20

external intercostal muscles contract
ribs upwards and outwards
diaphragm contracts (downwards), increase in volume of thorax
reduction in pressure in lungs
atmospheric pressure now greater than pulmonary pressure, air forced into lungs

Question 21

what are the five things that happen during expiration?

Answer 21

internal intercostal muscles contract
ribs downwards and inwards
diaphragm relax (upwards), volume of thorax decreases
increase in pressure in lungs
pulmonary pressure now greater than that of the atmosphere, and so air is forced out of the lungs

Question 22

what are six reasons for diffusion between the alveoli and the blood being rapid?

Answer 22

• rbc slowed as they pass through pulmonary capillaries, allowing more time for diffusion
• distance between the two is reduced
• walls of both alveoli and capillaries are very thin, therefore diffusion distance is short
• alveoli and pulmonary capillaries have a very large total surface area
• steep concentration gradient of gases to be exchanged is maintained
• blood flow through the pulmonary capillaries maintains a concentration gradient

Question 23

what is the structure of the digestive system?

Answer 23

salivary glands > oesophagus > stomach > ileum (small intestine) > large intestine > rectum
pancreas secretes pancreatic juices

Question 24

how does physical breakdown occur?

Answer 24

through chewing using teeth

muscles in stomach wall churn the food up

Question 25

how does chemical breakdown occur?

Answer 25

carried out by enzymes, and they all function by hydrolysis.
carbohydrases hydrolyse carbohydrates
lipases hydrolyse lipids
proteases hydrolyse proteins

Question 26

what is the process of carbohydrate digestion?

Answer 26

saliva in salivary glands contain amylase
food swallowed, enters stomach, acid denatures amylase + prevents further hydrolysis of starch
small intestines - mixes w/ pancreatic juices which contain pancreatic amylase
continues hydrolysis of any remaining starch to maltose
muscles in the intestine wall push the food along the ileum, epithelial lining produces maltase, a membrane-bound disaccharidase. maltase hydrolyses the maltose from starch breakdown to a-glucose

Question 27

what do sucrase and lactase hydrolyse?

Answer 27

the single glyosidic bonds in sucrose and lactase molecules
sucrase - makes glucose and fructose
lactase - makes glucose and galactose

Question 28

how does lipid digestion occur?

Answer 28

hydrolysed by lipases.
found in pancreas
form fatty acids and monoglycerides
lipids split up into micelles by bile salts (produced in liver), called emulsification, increase SA of the lipids so that the action of lipases is speeded up.

Question 29

how does protein digestion occur?

Answer 29

hydrolysed by peptidases (proteases)
endopeptidases - hydrolyses peptide bonds in the middle
exopeptidases - on the ends
dipeptidases - between two amino acids

Question 30

what are the properties of villi that increase efficiency of absorption?

Answer 30

• increases SA
• very thin walled, reduces diffusion distance
• contain muscles so can move, maintain diffusion gradients
• well supplied with blood vessels , maintain a diffusion gradient
• epithelial cells lining villi have microvilli, further increases SA

Question 31

how are amino acids and monosaccharides absorbed?

Answer 31

through diffusion and co-transport

Question 32

how are triglycerides absorbed?

Answer 32

monoglycerides and fatty acids in combination with bile salts
form micelles
micelles break down, releasing monoglycerides and fatty acids
diffuse into epithelial cells
monoglycerides and fatty acids transported ro the endoplasmic reticulum
recombined to form triglycerides
triglycerides associate with cholesterol and lipoproteins to form chylomicrons
CHYLOMICRONS ADAPTED FOR LIPID TRANSPORT
move out of epithelial cells by exocytosis
enter lymphatic capillaries called lacteals
into blood system via lymphatic vessels
triglycerides in chylomicrons hydrolysed by enzyme in endothelial cells of blood capillaries