Chapter 6- Exchange

Question 1

Features of specialised exchange surfaces

Answer 1

-Large SA- increase SA:V -> increases exchange rate
-Thin- short diffusion pathway
-Selectively permeable- selected materials can cross- controls rate of movement
-Movement of external + internal mediums- maintains diffusion gradients

Question 2

Surface area to volume ratio

Answer 2

Smaller organism- higher SA:V
As size increases - volume increases faster than SA- smaller SA:V - need specialised exchange organs/processes

Question 3

Gas exchange in single-celled organisms

Answer 3

Small- large SA:V
Oxygen absorbed by diffusion across surface + CO2 from respiration diffuses out

Question 4

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

Answer 4

1. Along diffusion gradient (insect at rest)
   -Oxygen used in respiration -> concentration falls -> diffusion gradient -> oxygen diffuses in -> CO2 produced - opposite direction gradient -> CO2 diffuses out
2. Mass transport (high activity)
   -Contract abdominal muscles -> large volumes of air forced out (abdominal pumping) -> new air enters on relaxation -> speeds up exchange
3. Ends of tracheoles filled with water (high activity)
   -Muscle cells in tracheoles respire anaerobically -> produces lactic acid which is soluble -> dissolves in cells + lowers their water potential -> water moves into cells by osmosis -> volume of air in tracheoles decrease -> draws air in

Question 5

How are insects adapted for gas exchange?

Answer 5

Main structures: spiracles, tracheae, tracheoles, muscle cells
Spiracles = tiny pores, opened/closed by valves, prevents water loss
Limitation of insect gas exchange -> relies solely on diffusion, must have short diffusion pathway + insects must be small

Question 6

Gas exchange in fish

Answer 6

Small SA:V
Have gills + each has a gill arch which has gill filaments which has lamellae
Blood + water flow in a counter current mechanism- maintains diffusion gradient across entire lamellae length -> max amount of diffusion

Question 7

Adaptations for gas exchange in a leaf

Answer 7

Many stomata- no cell is far away- short diffusion pathway
Interconnecting air spaces- gases in contact with mesophyll cells
Large SA of mesophyll cells

Question 8

How do stomata help with gas exchange?

Answer 8

Pores- mainly on underside of leaves
Each stoma surrounded by guard cells- open+close -> control rate of exchange + reduces water loss

Question 9

How do insects limit water loss?

Answer 9

Small SA:V - minimises area
Waterproof coverings
Spiracles- close to reduce water lost- mostly when insects are at rest

Question 10

How do plants limit water loss?

Answer 10

Waterproof covering over leaves
Thick cuticle- water can’t escape
Rolling up of leaves protects lower epidermis + traps air that has a high water potential so there’s no gradient for water to be lost
Hairy leaves + stomata in pits/grooves = traps still, moist air next to leaves -> reduces water potential gradient - less water loss
Reduced SA:V of leaves e.g. pine needles- reduces rate of water loss

Question 11

Structure of the human gas exchange system

Answer 11

Lungs supported/protected by rib cage
Lungs = lobed structures
Trachea = flexible airway protected by cartilage rings, made of muscle
Bronchi = 2 divisions of trachea, produces mucus + has cilia, can by supported by cartilage
Alveoli = air-sacs at end of bronchioles, collagen + elastic fibres, lined with epithelium
Alveolar membrane = site of gas exchange

Question 12

What are the two sets of intercostal muscles (muscles which lie between the ribs)?

Answer 12

Internal intercostal muscles (contraction -> expiration)
External intercostal muscles (contraction -> inspiration)

Question 13

Process of inspiration (breathing in + active process)

Answer 13

External intercostal muscles contract + internal intercostal muscles relax
Ribs pulled up + out + diaphragm contracts -> increases thorax volume
Decreased pressure in lungs
Creates pressure gradient -> air drawn in

Question 14

Process of expiration (breathing out + largely passive process)

Answer 14

External intercostal muscles relax + internal intercostal muscles contract
Ribs move down + in + diaphragm relaxes = decreases thorax volume
Increases pressure in lungs
Creates pressure gradient (pulmonary pressure is >) - air forced out

Question 15

How are the lungs adapted for gas exchange?

Answer 15

-Total SA of alveoli = 70m^2
-Each alveolus lined with epithelial cells - vey thin
-Each alveoli has network of pulmonary capillaries - RBCs flattened against capillary walls which are a single cell thick

Question 16

How is gas diffusion between alveoli + blood quick?

Answer 16

-RBCs slowed through pulmonary capillaries - more diffusion time
-RBCs flattened against capillary walls - distance reduced
-Alveoli + capillary walls = very thin -> short diffusion pathway
-Alveoli + pulmonary capillaries = v.large SA
-Breathing ventilates lungs, heart constantly circulates blood + blood flows -> maintains steep conc. gradient

Question 17

What are the major parts of the digestive system?

Answer 17

-Oesophagus = carries food from mouth to stomach
-Stomach = produces enzymes + shortens/digests food
-Ileum = food further digested here, large SA, digestion products absorbed
-Large intestine = absorbs water
-Rectum = final section of intestine
-Salivary glands = near mouth, release secretions
-Pancreas = produces pancreatic juice containing enzymes

Question 18

Purpose + process of physical breakdown of food

Answer 18

-Large food broken down mechanically
-Provides large SA for chemical digestion

Question 19

Purpose of chemical digestion of food

Answer 19

Hydrolyses large, insoluble molecules -> small, soluble ones

Question 20

Carbohydrate digestion

Answer 20

1. Salivary amylase produces + hydrolyses starch to maltose
2. Pancreas produces pancreatic juice -> contains pancreatic amylase which hydrolyses starch -> maltose
3. Membrane-bound maltase hydrolyses maltose -> glucose (glycosidic bonds broken)

Question 21

Lipid digestion

Answer 21

-Emulsification aids digestion
-Bile salts produced by liver + stored in gall bladder
-Large lipid droplets split into micelles by bile salts
-Increases lipids SA - increases lipase activity - increases rate of lipid digestion
-Lipases (in pancreatic juice) hydrolyses triglycerides into monoglycerides + fatty acids (breaks ester bonds)
-Micelles carry monoglycerides/fatty acids to epithelial cell membrane (maintains high conc. at lining helps for diffusion)

Question 22

What are micelles?

Answer 22

Associations of bile salts, monoglycerides + fatty acids

Question 23

Protein digestion

Answer 23

1. Endopeptidases = hydrolyse central region of protein to form a series of peptide molecules
2. Exopeptidases = progressively release dipeptides + single amino acids by hydrolysing peptide bonds on terminal amino acids
3. Dipeptidases (membrane-bound) = break bonds between 2 amino acids of dipeptides

Question 24

Structure of the ileum

Answer 24

Highly folded
Has villi - increase SA
Thin walls - lined with epithelial cells + other side has blood capillaries

Question 25

Adaptations of the ileum

Answer 25

-Increase SA for diffusion
-Walls = very thin - short diffusion distance
-Contains muscle - maintains diffusion gradient (material rich food replaces old food)
-Blood vessels - carry away absorbed molecules - maintains gradient
-Epithelial cells on villi contain microvilli to increase SA

Question 26

How are amino acids + monosaccharides absorbed in the ileum?

Answer 26

By diffusion + co-transport

Question 27

How are triglycerides absorbed in the ileum?

Answer 27

1. Micelles come into contact with epithelial cell membranes -> break down -> release monoglycerides + fatty acids
2. MGs + FAs diffuse across phospholipid bilayer into epithelial cells
3. MGs + FAs move to endoplasmic reticulum where they are recombined to form triglycerides
4. Triglycerides move to Golgi apparatus -> associate with cholesterol + phospholipids to form chlyomicrons
5. Chylomicrons move out of epithelial cells by exocytosis
6. Chylomicrons enter lacteals + are transported away from intestines

Question 28

What are chylomicrons?

Answer 28

Lipoproteins that are adapted for transporting dietary lipids from intestines to other parts of the body, made from triglycerides, phospholipids + cholesterol