Exchange surfaces

Question 1

What is the relationship between surface area to volume ratio and metabolic rate for a smaller organism.

Answer 1

1. (Smaller so) larger surface area to volume ratio;
2. More heat loss (per gram)
3. Faster rate of respiration releases heat;

Question 2

Exchange Surface adaptations

Answer 2

1. Thin/small so short diffusion pathway;
2. Flat/long/small/thin so large surface area to volume ratio

Question 3

Fish – Ventilation Mechanism (6)

Answer 3

1. mouth opens, operculum / opercular valve shuts; 2. floor of mouth lowered;
2. water enters due to decreased pressure / increased volume;
3. mouth closes, operculum / opercular valve opens; 5. floor raised results in increased pressure / decreased volume;
4. high / increased pressure forces / pushes water over gills;

Question 4

Fish Gill – Adaptations (2)

Answer 4

1. Many lamellae/filaments so large surface area;
2. Thin (surface) so short diffusion pathway;

Question 5

Fish Gill – adaptations for efficient gas exchange (8)

Answer 5

1. Large surface area provided by lamellae/filaments;
2. Increases diffusion/makes diffusion efficient;
3. Thin epithelium/distance between water and blood;
4. Water and blood flow in opposite directions/counter current;
5. maintains concentration gradient (along gill) /equilibrium not reached;
6. As water always next to blood with lower concentration of oxygen;
7. Circulation replaces blood saturated with oxygen; 8. Ventilation replaces water (as oxygen removed)

Question 6

Fish Gill – counter-current mechanism (3)

Answer 6

1. Water and blood flow in opposite directions;
2. Blood always passing water with a higher oxygen concentration;
3. Diffusion gradient maintained throughout length (of gill)

Question 7

Insect Tracheole System – adaptations for faster rate of diffusion (6)

Answer 7

1. Tracheoles have thin walls so short diffusion distance to cells;
2. Highly branched/large number of tracheoles so short diffusion distance to cells;
3. Highly branched/large number of tracheoles so large surface area (for gas exchange);
4. Tracheae provide tubes full of air so fast diffusion (into insect tissues);
5. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas exchange surface;
6. Body can be moved (by muscles) to move air so maintains diffusion/concentration gradient for oxygen/carbon dioxide;

Question 8

Insect Tracheole System – structure and function (4)

Answer 8

1. Spiracle;
2. Tracheole/trachea;
3. Oxygen used in (aerobic) respiration;
4. Oxygen moves down a diffusion gradient

Question 9

Insect Tracheole System – Abdominal Pumping (3)

Answer 9

1. Abdominal pumping/pressure in tubes linked to carbon dioxide release;
2. (Abdominal) pumping raises pressure in body;
3. Air/carbon dioxide pushed out of body /air/carbon dioxide moves down pressure gradient (to atmosphere);

Question 10

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf (4)

Answer 10

1. (Carbon dioxide enters) via stomata;
2. (Stomata opened by) guard cells;
3. Diffuses through air spaces;
4. Down diffusion gradient;

Question 11

Lungs – Adaptations for gas exchange (9)

Answer 11

1. alveoli provide a large surface area;
2. walls of alveoli thin to provide a short diffusion pathway;
3. walls of capillary thin / close to alveoli provides a short diffusion pathway;
4. walls (of capillaries / alveoli) have flattened cells;
5. cell membrane permeable to gases;
6. many blood capillaries provide a large surface area;
7. intercostal / chest muscles / diaphragm muscles / to ventilate lungs / maintain a diffusion / concentration gradient;
8. wide trachea / branching of bronchi / bronchioles for efficient flow of air;
9. cartilage rings keep airways open; (reject moist and thin membranes)

Question 12

Lungs – Pathway for oxygen (5)

Answer 12

1. Trachea and bronchi and bronchioles and alveoli;
2. Down pressure gradient;
3. Down diffusion gradient;
4. Across alveolar epithelium;
5. Across capillary endothelium/epithelium;

Question 13

Lungs – Explain how ventilation maintains a concentration gradient (2)

Answer 13

1. Air high in oxygen is continuously entering the alveoli during inspiration
2. Air low in oxygen is continuously being removed from the alveoli during expiration

Question 14

Lungs – Inspiration (7)

Answer 14

1. external intercostal muscles contract
2. internal intercostal muscles relax
3. ribs move up and out
4. diaphragm muscle contracts and the diaphragm flattens / moves down
5. volume of thoracic cavity increases
6. pressure in thoracic cavity decreases below atmospheric pressure
7. so air moves in down a pressure gradient

Question 15

Lungs – Expiration (7)

Answer 15

1. internal intercostal muscles contract
2. external intercostal muscles relax
3. ribs move down and in
4. diaphragm muscles relax and diaphragm returns to dome-shape
5. volume of thoracic cavity decreases
6. pressure in thoracic cavity increases above atmospheric pressure
7. air moves out down a pressure gradient

Question 16

Lungs – Asthma and bronchi

Answer 16

1. Muscle walls of bronchi/bronchioles contract;
2. Walls of bronchi/bronchioles secrete more mucus;
3. Diameter of airways reduced;
4. (Therefore) flow of air reduced;

Question 17

Lungs – Asthma and bronchi

Answer 17

1. Muscle walls of bronchi/bronchioles contract;
2. Walls of bronchi/bronchioles secrete more mucus;
3. Diameter of airways reduced;
4. (Therefore) flow of air reduced;

Question 18

Lungs – Calculate pulmonary ventilation

Answer 18

Pulmonary Ventilation = Tidal Volume x Breathing Rate

Question 19

Xerophytes – Adaptations to desert plants (6)

Answer 19

1. Hairs so ‘trap’ water vapour and water potential gradient decreased;
2. Stomata in pits/grooves so ‘trap’ water vapour and water potential gradient decreased;
3. Thick (cuticle/waxy) layer so increases diffusion distance;
4. Waxy layer/cuticle so reduces evaporation/transpiration;
5. Rolled/folded/curled leaves so ‘trap’ water vapour and water potential gradient decreased;
6. Spines/needles so reduces surface area to volume ratio;

Question 20

Name and describe 5 adaptations of a leaf that allow efficient gas exchange

Answer 20

1. Thin and flat to provide short diffusion pathway and large surface area to volume ratio
   2.air spaces in the mesophyll allow diffusion of carbon dioxide and oxygen , facilitating photosynthesis
   3.arrangement of leaves minimises shadowing to allow maximum light absorption.
   4.transparent cuticle and epidermis that let light through to the photosynthetic mesophyll cells.
2. guard cells: control opening of stomata in response to changes in light intensity.
3. waxy cuticle which reduces evaporation and water loss.

Question 21

Why can’t fish use their bodies as an exchange surface

Answer 21

1. they have a waterproof, impermeable outer membrane
2. a small surface area to volume ratio.

Question 22

Explain three ways in which an insect’s tracheal system is adapted for efficient gas exchange. (3)

Answer 22

1. Tracheoles have thin walls so short diffusion distance to cells;
2. Highly branched so large number of tracheoles so short diffusion
   distance to cells;
3. Highly branched / large number of tracheoles so large surface area (for gas exchange);
4. Fluid in the end of the tracheoles that moves out (into tissues) during exercise so faster diffusion through the air to the gas
   exchange surface;
5. Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;

Question 23

Describe how the structure of the insect gas exchange system:
* provides cells with sufficient oxygen
* limits water loss.
Explain your answers.
(4)

Answer 23

1. Spiracles (lead) to tracheae (that lead) to tracheoles;
2. Open spiracles allow diffusion of oxygen from air
3. Tracheoles are highly branched so large surface area (for exchange);
4. Tracheole (walls) thin so short diffusion distance (to cells)
5. Tracheole walls are permeable to oxygen;
6. Cuticle/chitin in tracheae impermeable so reduce water loss;
7. Spiracles close (eg.during inactivity) preventing water loss;

Question 24

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 24

1. smaller SA:V ratio means the diffusion distance is greater
2. Thus substances cannot as easily enter the cells

Question 25

Explain why oxygen uptake is a measure of metabolic rate in organisms. (1)

Answer 25

1. (Oxygen used in) respiration 2. which provides energy / ATP; OR which is a metabolic process /chemical reaction;

Question 26

Why do multicellular organisms require specialised gas exchange surfaces?

Answer 26

1. smaller SA:V ratio means the diffusion distance is greater 2. Thus substances cannot as easily enter the cells

Question 27

Describe xerophytic plants.

Answer 27

a plant which is adapted for survival in extreme environments

Question 28

Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and the alveoli (3)

Answer 28

1. Less carbon dioxide exhaled/moves out of the lungs 2. (So) reduced diffusion/concentration gradient (between blood and alveoli); 3. More carbon dioxide stays in blood

Question 29

Explain why death of alveolar epithelium cells reduces gas exchange in human lungs. (3)

Answer 29

1. Reduced surface area; 2. Increased distance for diffusion; 3. Reduced rate of gas exchange;

Question 30

Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. Do not refer to surface area or moisture in your answer. (2)

Answer 30

1. Flattened cells OR Single layer of cells; 2. Reduces diffusion distance / pathway; 3. Permeable; 4. Allows diffusion of oxygen/carbon dioxide;