Gas exchange

Question 1

describe gas exchange in single-celled organisms( protists and prokaryotes)

Answer 1

1- oxygen is required to produce ATP during aerobic respiration and CO2 is produced as a waste product
2- this produces concentration gradient of these gases in opposite directions
3- single celled organisms have large SA to VR to meet their gas exchange needs by diffusion across their cell membranes
4- however large organisms , have relatively small SA to VR so they cant rely on diffusion(alone)

Question 2

what makes a good exchange surface?

Answer 2

• large surface area
• large concentration gradients
• thin exchange surface (few membrane or thin walls)

Question 3

FICK’S LAW
rate of diffusion=

Answer 3

SA x conc gradient
= —————————-
diffusion distance

Question 4

EXPLAIN how insects balance water loss and gas exchange

Answer 4

1- waterproofing covering - over their body surfaces, usually a rigid outer skeleton (exoskeleton) covered with a waterproof cuticle
2- relatively small SA to VR - to minimise the area over which water is lost

Question 5

How does oxygen move through the insect? [4]

Answer 5

1- Oxygen diffuses in through the open spiracles;
2- Spiracle closes;
3- Oxygen moves through the trachea into the tracheoles;
4- Oxygen delivered directly to the respiring tissues;

Question 6

why does OXYGEN diffusion happen in the gas exchange(tracheal) systems of insects

Answer 6

1- tissue respire using oxygen which reduces the conc of oxygen at the tissue
2- oxygen moves from the tracheae (area of high conc) to the tissue ( area of low conc )
3- this lowers the oxygen concentration in the tracheae so oxygen moves into the tracheae from outside the insect via the spiracles

Question 7

why does CARBON DIOXIDE diffusion happen in the gas exchange(tracheal) systems of insects

Answer 7

1- respiration produces CO2 increasing the conc at the tissue
2- CO2 moves from the tissue (area of high conc) to the tracheae ( area of low conc )
3- this lowers the CO2 concentration in the tissues so CO2 moves from the tracheae into outside the insect via the spiracles

Question 8

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

Answer 8

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;
OR
Fluid in the end of the tracheoles that moves out (into tissues) during exercise so larger surface area (for gas exchange);
Body can be moved (by muscles) to move air so maintains diffusion / concentration gradient for oxygen / carbon dioxide;

Question 9

Describe how the structure of the insect gas exchange system:
* provides cells with sufficient oxygen
* limits water loss.

Explain your answers. [6]

Answer 9

1- Spiracles, tracheae, tracheoles;
2- Spiracles allow diffusion (of oxygen)
OR (Oxygen) diffusion through tracheae/tracheoles;
3-Tracheoles are highly branched so large surface area (for exchange);
4- Tracheole (walls) thin so short diffusion distance (to cells) OR Highly branched tracheoles so short diffusion distance (to cells) OR Tracheoles enter cells so short diffusion distance;
5- Tracheole permeable to oxygen/air;
6- Cuticle/chitin/exoskeleton (impermeable) so reduce water loss;
7- Spiracles (can) close so no/less water loss OR Spiracles have valves so no/less water loss;
8- Hairs around spiracles reduce water loss;

Question 10

explain two ways in which the structure of fish gills is adapted for efficient gas exchange

Answer 10

1- many filaments/ lamellae so there’s a large SA
2- lamellae are thin for a short diffusion pathway

Question 11

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange. [6]

Answer 11

1 Large surface area provided by many lamellae over many gill filaments;
2 Increases diffusion/makes diffusion efficient;
3 Thin epithelium/distance between water and blood;
4 Water and blood flow in opposite directions/countercurrent;
5 (Point 4) 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 12

Describe and explain the advantage of the counter-current principle in gas exchange across a fish gill. [3]

Answer 12

1- Water and blood flow in opposite directions;
2- Maintains diffusion/concentration gradient of oxygen OR Oxygen concentration always higher (in water);
3- (Diffusion) along length of lamellae/filament/gill/capillary;

Question 13

What are the 3 adaptations of a leaf for gaseous exchange

Answer 13

1- flat: gives LSA to volume ratio
2- many stomata: pores to allow air to move in and out of leaf
3- air spaces in leaf : so short diffusion distance between mesophyll cells and air

Question 14

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

Answer 14

1- carbon dioxide enters via stomata
2- stomata are opened by guard cells
3- diffuses through air spaces
4- down the diffusion gradient

Question 15

Describe the process of starch digestion [5]

Answer 15

(salivary/pancreatic) Amylase;
Starch to Maltose;
Maltase;
Maltose to glucose;
Hydrolysis;
Glycosidic bonds

Question 15

Explain why plants grown in soil with very little water grow only slowly [2]

Answer 15

1- Stomata close;
2- Less carbon dioxide (uptake) for less photosynthesis/glucose production;

Question 16

State and explain the leaf adaptations in xerophytic plants to reduce water loss

Answer 16

1- reduced number of stomata so less surface area for water loss
2- stomata in pits so reduced concentration gradient
3- hairs to trap water vapour so reduced conc gradient
4- rolled leaves so reduced conc gradient
5- leaves reduced to spines so less SA for water loss
6- thick waxy cuticles so increased diffusion distance

Question 17

Explain the 5 properties of any respiratory surface for efficient gas exchange

Answer 17

1- large surface area
2- permeable
3- thin walls/ fewer membranes
4- moist..gases diffuse more readily in solution
5- efficient transport system.. maintains a conc gradient

Question 18

Explain the role of trachea , bronchi and bronchioles in the lung structure

Answer 18

1- trachea is a tube-like structure that carries air from mouth to the lungs
2- bronchi : the trachea splits into two bronchi which allows air to travel to the right and left lung
3- bronchioles: bronchi is further divided into these smaller branches , these then supply the alveoli with air

Question 19

State and explain the alveoli structure

Answer 19

small sacs at the end of the bronchioles that act as the interface (barrier) between the air in the lungs and the blood
- have a LSA and a dense capillary network to maintain efficient diffusion rates
- have a rich blood supply which circulates blood to maintain a large conc gradient between the gases in the blood and in the alveoli
-

Question 20

how is the deoxygenated blood brought to the lungs and how does it return when its oxygenated

Answer 20

deoxygenated blood is brought to the lungs by the pulmonary artery from the heart
it returns to the heart when oxygenated via the pulmonary vein

Question 21

how are the gases in the alveolar air separated from the blood

Answer 21

by alveolar squamous epithelium and the endothelial wall of the capillary

Question 22

explain how one feature of an alveolus allows efficient gas exchange to occur

Answer 22

the alveolar squamous epithelium is a one cell thick layer with a very thin diffusion distance to optimise diffusion

Question 23

Describe the gross structure of the human gas exchange system and how we breathe in and out
( 6 marks)

Answer 23

1- trachea — bronchi— bronchioles– alveoli
2- (right order)
3- Diaphragm (muscles) contract and diaphragm flattens;
4-External intercostal muscles contract and ribcage pulled up/out;
5- (Causes) volume increase and pressure decrease in thoracic cavity (to below atmospheric pressure);
Breathing out
6. Diaphragm (muscles) relaxes and diaphragm moves up;
7. External intercostal muscles relax and ribcage moves down/in;
8. (Causes) volume decrease and pressure increase in thoracic cavity (to above atmospheric pressure);