exchange surfaces + breathing

Question 1

Need for exchange systems

Answer 1

• all living cells require a nutrient and oxygen supply
• they also need to be able to remove waste products
  in unicellular organisms, this can take place over the surface of the body by diffusion
  in multicellular organisms, an exchange system is needed because of…
  - size
  - surface area : volume ratio ( SA/V)
  - metabolic activity

Question 2

Multicellular organisms

Answer 2

• longer diffusion path
  diffusion alone is too slow, innermost cells would not be reached
• small SA : V
  not all cells would be reached by diffusion alone
• high metabolic activity
  demand for oxygen for more aerobic respiration is very high, oxygen needs to be transported efficiently and quickly

Question 3

Unicellular organisms

Answer 3

• short diffusion path
  diffusion supplies sufficient oxygen and nutrients
• large SA : V
  surface area is large enough to supply al cells with sufficient oxygen
• low metabolic activity
  lower demand for oxygen

Question 4

Features of GOOD exchange surface

Answer 4

• large surface area
  provides space for molecules to pass through
  e.g. root hair cells
• thin barrier/layer
  shorter diffusion path/ distance
  e.g. alveoli have a cell membrane which is 1 cell thick and permeable
• rich blood supply
  maintains a concentration gradient so diffusion can occur quickly
  e.g. gills of fish, alveoli

Question 5

Mammalian gas exchange

Cartilage

Answer 5

• strong flexible cartilage rings support the trachea and bronchi, preventing the collapse of these structures
• rings are C shaped, increasing flexibility for food to pass down the oesophagus

Question 6

Mammalian gas exchange

Ciliated epithelium

Answer 6

• line airways

- waft mucous and dust away from the lungs

Question 7

Mammalian gas exchange

Goblet cells

Answer 7

• line airways

- produce and secrete mucous which traps pathogens and particles

Question 8

Mammalian gas exchange

Smooth muscle

Answer 8

• makeup walls of bronchioles, bronchi, trachea
• control airflow to the alveoli by constricting/ relaxing passageways
• constricts the lumen also to prevent harmful substances from reaching the alveoli

Question 9

Mammalian gas exchange

Elastic fibres

Answer 9

• makeup walls of bronchioles, bronchi, trachea
• elongate the smooth muscle
• elastic recoil (fibres) = squeeze air out in expiration
• elastic stretch = draw in air in inspiration

Question 10

Mammalian gas exchange

Bronchi, bronchioles, trachea

Answer 10

• passageway for air

Question 11

Mammalian gas exchange

Alveoli

Answer 11

• tiny folds of lung epithelium which increase SA
• tiny air sacs
• MAIN gas exchange surface in mammals
  oxygen into blood out of alveoli, carbon dioxide out of blood into alveoli

Question 12

Adaptations of alveoli

Answer 12

1. large SA
   large SA: V ratio, efficient diffusion
2. thin layers (1 cell thick)
   short diffusion path
3. rich blood supply
   maintains steep concentration gradient for efficient diffusion
4. good ventilation
   maintains concentration gradient, keeps gases diffusing

Question 13

Ventilation

Answer 13

ensures the concentration of oxygen is higher in the alveoli than in the blood

Question 14

Rib cage

Answer 14

provides semi-rigid case

Question 15

Diaphragm

Answer 15

a domed sheet of muscle that forms the floor of the thorax

Question 16

Internal intercostal muscles

External intercostal muscles

Answer 16

found between ribs and facilitate - internal - exhalation, external - inhalation

Question 17

Inspiration

Answer 17

• energy-using process

1. diaphragm contracts, flattens and lowers
2. external muscles contract
3. ribs move up and out
4. volume in thorax increases
5. pressure in thorax decreases

= air drawn into the lungs

Question 18

Expiration

Answer 18

• passive process

1. diaphragm relaxes, move up and rests
2. internal muscles relax
3. ribs move down and in
4. volume in thorax decreases
5. pressure in thorax increases

= air pushed out of lungs

Question 19

Spirometer; vital capacity

Answer 19

• max air volume that can be exchanged between max inspiration and max expiration
• affected by size, age and gender

Question 20

Spirometer; tidal volume

Answer 20

• volume of air inhaled or exhaled at each breath at rest

- affected by activity, pregnancy and smoking

Question 21

Spirometer; oxygen uptake

Answer 21

• volume of oxygen absorbed by lungs in 1 min

- affected by the depth of breath and breathing rate

Question 22

Spirometer; breathing rate

Answer 22

• no. of breaths per min

Question 23

Insect gas exchange

Answer 23

insects perform gas exchange with an air filled tracheal system
effective, the organism is small

1. air enters via spiracles
2. air is transported into the body through tracheae
3. air passed to tracheoles, filled with tracheal fluid, gas exchange occurs between air and tracheal fluid

Question 24

Chitin

Answer 24

• mechanical support

- impermeable layer

Question 25

Increasing gas exchange in insects

Answer 25

• mechanical ventilation
  air actively pumped into system
• air sacs
  increase volume of air moved through system

Question 26

Fish gas exchange process

Answer 26

1. mouth of fish opens (operculum is closed)
2. buccal cavity floor is lowered
3. increase in volume in the mouth, decrease in pressure
4. water enters the mouth of the fish - down a concentration gradient
5. opercular cavity expands
6. buccal cavity floor is raised
7. pressure increases, is higher than opercular cavity
8. water moves into the buccal cavity
9. mouth closed
10. operculum opens
11. sides of opercular cavity move inwards, increasing pressure
12. water forced out over gills

Question 27

Gills

Answer 27

gill filament - absorbs oxygen and rids of carbon dioxide

• lamellae - increase SA
• rich blood supply - maintains a concentration gradient

Question 28

Countercurrent system

Answer 28

blood flows in opposite direction to the water
more oxygen is absorbed into the blood as it moves along
always a concentration gradient as the volume of oxygen in water is always higher than the volume of oxygen in the blood