6: Exchange

Question 1

Features of specialised exchange surfaces

Answer 1

• large sa to volume ratio (increases rate of exhange)
• very thin (short diffusion pathway)
• selectively permeable
• transport system
• good blood supply

Question 2

do single celled organisms have a large sa to volume ratio or small

Answer 2

large

Question 3

Gas exchange in insects

Answer 3

• conserve water
• exoskeleton for protection and a lipid later to prevent water loss
• internal network of tubes called tracheae, supported by strengthened rings to prevent collapsing
• these divide into smaller dead end tubes called tracheoles
• spiracles (run along abdomen)

Question 4

3 ways respiratory gases move in and out of insects tracheal system

Answer 4

• along diffusion gradient
• mass transport (contract and relax abdominal muscles to move gas)
• ends of tracheoles are filled with water (flying= anaerobic = lactate = lowers water potential= water to move from trachiole to cells = drop in pressure so air from atmosphere is drawn in

Question 5

3 ways insects limit water loss

Answer 5

• small sa to volume ratio that water can evaporate from
• waterproof exoskeleton
• spiracles (controls water entering and leaving)

Question 6

adaptions for efficient diffusion in insects

Answer 6

• large number of trachioles = large sa
• short diffusion pathway between spiracles and tracheoles
• steep diffusion gradient between co2 and o

Question 7

Fish gas exchange

Answer 7

• waterproof
• small surface area to volume ratio so require a gas exchange surface which is gills
• water contains 30x less oxygen than in air

Question 8

gas exchange surface features

Answer 8

• short diffusion pathway
• large sa to volume ratio
• maintain a concentration gradient

Question 9

fish gills

Answer 9

• 4 layers
• gills are made up of stacks of gill filaments (large sa)
• each filament is covered in thin gill lamellae at right angles
• open mouth out through side of head
• countercurrent flow = maintain diffusion grad

Question 10

countercurrent exchange principle

Answer 10

• never reach equilibrium
• water flows over the gills in opposite direction to the blood in the capillaries
• maintains diffusion grad along ENTIRE length of lamellae

Question 11

Gas exchange in plants occurs at stomata

Answer 11

• large number holes called stomata, no cell is ever far from stomata reducing diffusion distance
• stomata close at night to prevent water loss, when photosynthesis wont be occuring

Question 12

structue of leaf

Answer 12

• palisade mesophyll (where most photosynthesis occurs)
• spongy mesophyll
• stomata (gap formed by two guard cells, site of gas exchange)

Question 13

Xerophytes adaptations

Answer 13

• adapted to survive environments with limited water
• in marram grass - sand dunes
• CURLED LEAVES to trap moisture increase humidity
• THICK CUTICLE to trap water
• TINY HAIRS to trap moisture increase humidity
• SUNKEN STOMATA IN PITS to trap moist air and reduce water potential gradient
• longer roots

Question 14

Human gas exchange system

Answer 14

• lungs (made up of highly branched tubules called bronchioles.
• trachea (supported by rings of cartilage, produce muchus)
• bronchi (divisions of trachea to each lung, produce mucus)
• bronchioles (walls made of muscles lined by epithelial cells
• alveoli (air sacs lined with epithelium, elastic fibres to stretch)

Question 15

Ventilation caused by

Answer 15

• diaphragm
• antagonistic muscles (external intercostal muscles contracts it causes inspiration)

Question 16

Inspiration

Answer 16

• external contract leads to inspiration, internal contract relax
• ribs pull upwards and outwards which increases volume in thorax
• diaphragm contracts and flattens
• increased thorax volume causes reduction in pressure in lungs
• atmospheric pressure is now greater so air moves into lungs

Question 17

gas exchange in alveoli

Answer 17

• short diffusion pathway as alveoli are made up of single layer of cells and so is capillary
• oxygen diffuses across thin epithelial cells into the blood
• 300 million in lungs so large sa
• each surrounded by network of capillaries to exchange gases and thereofre maintains conc grad

Question 18

Parts of digestive system

Answer 18

• oesophagus: carries food from mouth to stomach
• stomach; glands that produce enzymes which digest protein
• iluem (small intestine) villi and microvilli
• large intenstine absorbs water
• rectum where faeces is stored
• salivary glands; contain enzyme amylase which hydrolyses starch into maltose
• pancreas; secretes pancreatic juice. proteases to hydrolyse proteins, lipase to hydrolyse lipids and amylase to hydrolyse starch

Question 19

Two stages of digestion

Answer 19

• Physical digestion (teeth and churned)
• Chemical digestion (hydrolyses large insoluble molecules by enzymes)

Question 20

Types of digestive enzymes

Answer 20

• Carbohydrases (hydrolyses carbohydrates into monosaccharides)
• Lipases (hydrolyses lipids into fatty acids and glycerol)
• Proteases (hydrolyses proteins into amino acids)

Question 21

Carbohydrate digestion

Answer 21

• takes more than one enzyme to hydrolyse a large molecule into monosaccharides
• the enzyme AMYLASE is produced in the mouth and pancreas
• it hydolyses polysaccharides into disaccharides MALTOSE by hydrolysing the glycosidic bonds
• starts in mouth, duodenum, ileum

Question 22

Protein digestion

Answer 22

1) Endopepitdases (hydrolyse peptide bonds in the middle of polymer chain between amino acids
2) Exopeptidases (hydrolyse at the end of a polymer chain between the amino acids)
3) Membrane-bound dipeptidases (hydrolyse peptide bonds between the two amino acids)
- protein digestion starts in stomach, to duodenum, to ileum.

Question 23

Lipid digestion

Answer 23

• Digested by lipase and the action of bile salts
  CHEMICAL: Lipase produced in the pancreas hydrolyses ester bonds in triglycerides to form monoglycerides and fatty acids
  PHYSICAL: lipids are split up into droplets called micelles by bile salts (produced in liver) - emulsification to increase sa for faster hydrolysis of lipase

Question 24

Micelles function

Answer 24

delivers fatty acids, monoglycerides and glycerol to epithelial cells of the ileum for absorption

Question 25

Ileum function

Answer 25

absorbing the products of digestion which are fatty acids, amino acids, monoglycerides and monosaccharides

Question 26

Ileum adaptions

Answer 26

projections called villi have:
- increased sa for diffusion
- very thin walled
- contain muscles so can mix the contents of ileum to maintain diffusion grad
- well supplied with blood vessels so blood can carry away absorbed molecules which maintains diffusion grad
- microvilli further increase sa for absoprtion

Question 27

How does ileum absorb the products of digestion

Answer 27

• monosaccharides and amino acids absorbed by facilitated diffusion and co-transport
• monoglycerides and fatty acids remain with bile salts, structures called micelles. micelles come into contact with epithelial cells lining villi where they break down and release products, these then diffuse in as non polar
• once in cell the endoplasmic reticulum and golgi appartus turn these back into triglycerides
• this is a formation of a chylomicron, and then released by exocytosis
• absorbed into lymphatic vessel into bloodstream