3.3 Organisms exchange substances with their environments

Question 1

what is mass transport used for

Answer 1

maintains final diffusion gradients that bring substances to + from cell membranes of individual cells
maintains relatively stable environment that is tissue fluid

Question 2

small organism SA;V

Answer 2

higher SA;V

Question 3

describe the relationship between SA;V and metabolic rate

Answer 3

• rate of heat loss per unit body mass increases as SA increases
• so higher metabolic rate/ faster respiration
• to generate enough heat to maintain constant body temp

Question 4

why do larger organisms need a specialised surface for gaseous exchanged

Answer 4

• small SA;V ratio

- high demand for 02 + to remove co2

Question 5

state the adaptations of a gas exchange surface

Answer 5

thin flat shape
-large sf area
-short diffusion pathway
for rapid diffusion

Question 6

gas exchange in an insect

Answer 6

• air moves through spiracles on surface of insect
• air moves through tracheae
• gas exchange directly to/from cells via conc gradient

Question 7

adaptations of an insect for gas exchange

Answer 7

lots of thin, branching tracheoles–>short diffusion pathway + SA–>rapid diffusion
rhythmic abdominal movements–>creates pressure gradient–>greater exchange of gases

Question 8

gas exchange in fish

Answer 8

counter current flow

• blood flows through lamellae, water over lamellae in opp directions
• conc gradient of o2 between water + blood maintained along whole length of lamellae
• maximising diffusion of o2

Question 9

adaptations of a fish for gas exchange

Answer 9

• each gill made of lots of gill filaments-covered in many lamellae-large sf area
• vast network of capillaries on lamellae-remove o2 to maintain conc gradient
• thin/flattened epithelium - shorter diffusion pathway between water + blood

Question 10

gas exchange in plants

Answer 10

• co2/02 diffuse via stomata
• stomata opened by guard ells
• c02/02 diffuse into mesophyll layer into air spaces
• co2/o2 diffuse down conc gradient

Question 11

adaptations of plants for gas exchange

Answer 11

lots of stomata close together 
-large sf area for exchange 
interconnecting air spaces
-gases come into contact with mesophyll cells
thin
-short diffusion pathway

Question 12

adaptatopns of xerophytic plants to reduce water loss

Answer 12

Thick cuticle/ wax layer = waterproof/impermeable to water
Sunken stomata = trap humidity to reduce diffusion gradient
Hairy = trap humidity to reduce diffusion gradient
Small leaves/reduced to spines,needles = reduce S.A. for water loss
Leaves roll up in dry weather= less S.A. for water loss/stomata covered/traps humidity
Reduced no. of stomata = reduced S.A. for water loss

Question 13

gross structure of human gas exchange system

Answer 13

trachea
splits into two bronchi
into bronchioles
end in air sacs-> alveoli

Question 14

gas exhange in alveoli

Answer 14

• o2 diffuses from alveoli
• down conc gradient
• across alveolar epithelium
• across capillary endothelium
• into blood

Question 15

why is ventilation needed

Answer 15

maintains a conc gradient

• brings in air with higher o2 conc
• removes air with lower o2 conc

Question 16

adaptations of alveoli for gas exchange

Answer 16

epithelium one cell thick
-short diffusion distance -> faster diffusion
large SA;V
-fast diffusion
permeable
good blood supply from network of capillaries
-maintains conc gradient
elastic tissues allows to recoil after expansion
surfactant

Question 17

adaptations of the lung for efficient/rapid gas exchange

Answer 17

many alveoli/capillaries 
-large SA->fast diffusion
thin walls 
-short diffusion distance
ventilation/circulation
-maintains conc gradient

Question 18

describe inspiration

Answer 18

• external intercoastal muscles contract, internal relax
• ribcage moves up + outwards
• diaphragm contracts
• increase volume in thoracic cavity
• decreases pressure in thoracic cavity
• atmospheric pressure greater than in cavity
• air moves down pressure gradient into lungs

Question 19

describe expiration

Answer 19

• external intercoastal muscles relax, internalcontract
• ribcage moved down + inwards
• diaphragm relaxes
• decreases vol in thoracic cavity
• increases pressure
• pressure in cavity greater than in atmosphere
• air moves down pressure gradient out of lungs

Question 20

describe fibrosis

Answer 20

formation of scar tissue in lungs 
increases diffusion distance ->decreases rate of diffusion
faster ventilation rate 
lungs expand + recoil less 
reduced tidal volume 
reduced forced vital capacity

Question 21

describe asthma

Answer 21

inflamed bronchi
smooth muscle lining bronchi contracts
constriction of airway->reduced airflow->reduced FEV->less o2 enters blood -> reduced rate of respiration->less energy released->fatigue weakeness

Question 22

how to improve reliabilty

Answer 22

• large sample
• randomly chosen
• healthy
• equal no. of test subjects
• repeat

Question 23

what happens during digestion

Answer 23

large biological molecules are hydrolysed
to smaller molecules
that can be absorbed across cell membranes

Question 24

how is starch digested

Answer 24

by amylase 
starch-->maltose
membrane bound maltase
maltose-->glucose 
hydrolysis of glycosidic bond

Question 25

where is amylase produced + released

Answer 25

produced by salivary gland, released into mouth

produced by pancreas, released into small intestine

Question 26

where is maltase found

Answer 26

attached to epithelial cells

lining ileum of small intestine

Question 27

how are disaccharides digested

Answer 27

• by membrane bound disaccharides
• maltase
• sucrase
• lactase
• hydrolysis of glycosidic bond

Question 28

how are lipids digested

Answer 28

• by lipase
• bile salts produced in liver
• bile salts emulsify lipids into smaller lipid droplets
• lipase hydrolyses lipids–>monoglycerides+fatty acids
• breaking ester bond
• monoglycerides, fatty acids, bile salts join together to form micelles

Question 29

why are bile salts useful

Answer 29

increase sf area to speed up action of lipase

Question 30

where is lipase made + released

Answer 30

made in pancreas

released to small intestine

Question 31

how are micelles used to absorb lipids

Answer 31

• monoglycerides + fatty acids diffuse out of micelles in lumen into epithelial cell
• as lipid soluble
• monoglycerides + fatty acids recombine to form triglycerides
• which form into globules
• globules coated with proteins to form chylomicrons
• leave via exocytosis + enter lymphatic vessels
• return to blood circulation

Question 32

what 3 types of enzymes digest proteins

Answer 32

endopeptidases
exopeptidases
dipeptidases

Question 33

how do endopeptidases work

Answer 33

hydrolyse peptide bonds within a protein

break protein into two or more smaller peptides

Question 34

how do exopeptidases work

Answer 34

hydrolyse peptide bonds at end of protetin molecules

removing a single amino acid

Question 35

how do dipeptidases work

Answer 35

often membrane bound in ileum
hydrolyse peptide bond between a dipeptide
=2 amino acids

Question 36

how is co-transport used to absorb amino acids+monosaccharides

Answer 36

1. Na+ actively transported out of epithelial cells lining ileum into blood
   by Na+/k+ pump
   creating a conc gradient of Na+ higher in lumen than epithelial cell
2. Na+ and glucose move by facillitated diffusion into epithelial cell from lumen
   via co transporter protein
   3.creating a conc gradient of glucose, higher in epithelial cell than blood
   4.glucose moves out epithelial cell into blood by facillitated diffusion via protein channel