Gaseous exchange

Question 1

Abdominal pumping increases the efficiency of gas exchange between the tracheoles and muscle tissue of the insect. Explain why.

Answer 1

1. More air/oxygen enters / air/oxygen enters quickly/quicker2. (So) maintains/greater diffusion or concentration gradient

Question 2

Abdominal pumping is an adaptation not found in many small insects. These small insects obtain sufficient oxygen by diffusion.Explain how their small size enables gas exchange to be efficient without the need for abdominal pumping.

Answer 2

Large(r) SA:VOL / short(er) diffusion distance (to tissues)

Question 3

The ends of tracheoles connect directly with the insect’s muscle tissue and are filled with water. When flying, water is absorbed into the muscle tissue. Removal of water from the tracheoles increases the rate of diffusion of oxygen between the tracheoles and muscle tissue. Suggest one reason why.

Answer 3

1. Greater surface area exposed to air2. Gases move/diffuse faster in air than through water3. Increases volume/amount of air

Question 4

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf.

Answer 4

1. (Carbon dioxide enters) via stomata2. (Stomata opened by) guard cells3. Diffuses through air spaces4. Down diffusion gradient;

Question 5

Explain how oxygen is loaded, transported and unloaded in the blood.

Answer 5

1. Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin2. In red blood cells3. Loading/uptake/association in lungs4. at high p.O25. Unloads/ dissociates / releases to respiring cells/tissues6. at low p.O27. Unloading linked to higher carbon dioxide (concentration)

Question 6

The haemoglobin in one organism may have a different chemical structure from the haemoglobin in another organism. Describe how.

Answer 6

Different primary structure/amino acids/different number of polypeptide chains

Question 7

Explain how fish are adapted for gas exchange.

Answer 7

1) Each gill is made of lots of thin plates called gill filaments, which give a big surface area for exchange of gases2) The gill filaments are covered in lots of tiny structures called lamellae, which increases the surface area even more.3) The lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion4) Blood flows through the lamellae in one direction and water flows over in the opposite direction. This is called a counter-current system. It maintains a large concentration gradient between the water and the blood

Question 8

Explain how insects are adapted for gas exchange.

Answer 8

1) insects have microscopic air-filled pipes called tracheae which they use for gas exchange.2) Air moves into the tracheae through pores on the surface called spiracles3) Oxygen travels down the concentration gradient towards the cells. Carbon dioxide from the cells moves down its own concentration gradient towards the spiracles to be released into the atmosphere.4) The tranchae branch off into smaller tracheoles which have thin, permable walls and go to individual cells. This means that oxygen diffuses directly into the respiring cells - the insects circulatory system doesn’t transport o25) insects use rhythmic abdominal movements to move air in and out of spiracles

Question 9

Explain how single-celled organisms are adapted for gas exchange

Answer 9

1) They absorb and release gases by diffusion through their outer surface2) They have a relativley large surface area, a thin surface and a short diffusion pathway.

Question 10

How is oxygen carried round the body by haemoglobin?

Answer 10

1) Haemoglobin has a high affinity for oxygen - each molecule can carry four oxygen molecules2) In the lungs, oxygen joins to haemoglobin in red blood cells to form oxyhaemoglobin3) This is a reversible reaction - when oxygen leaves oxyhaemoglobin near the body cells, it turns back to haemoglobin.

Question 11

How is haemoglobin different in different organisms?

Answer 11

1) organisms that live in environments with a low concentration of oxygen have haemoglobin with a higher affinity for oxygen than human haemoglobin - the dissociation curve is to the left of ours2) Organisms that are very active and have a high oxygen demand have haemoglobin with a lower affinity for oxygen than human haemoglobin - the curve is to the rightof the human one.

Question 12

How does the carbon dioxide concentration affect oxygen unloading?

Answer 12

1) when cells respire they produce carbon dioxide, which raises the pCO22) This increases the rate of oxygen unloading - the dissociation curve shifts down. The saturation of blood with oxygen is lower for a given pO2 meaning that more oxygen is being released3) This is caused the Bohr effect

Question 13

describe how haemoglobin loads and unloads oxygen in the body.

Answer 13

1. Loading/uptake/association of oxygen at high p.O22. In lungs (haemoglobin) is (almost) fully saturated / in lungs haemoglobin has a high affinity for oxygen3. Unloads/releases/dissociates oxygen at low p.O24. Unloading linked to higher carbon dioxide concentration

Question 14

There is less oxygen at high altitudes than at sea level. People living at high altitudes have more red blood cells than people living at sea level. Explain the advantage of this to people living at high altitude.

Answer 14

More haemoglobinSo can load/pick up more oxygen (in the lungs)

Question 15

An increase in respiration in the tissues of a mammal affects the oxygen dissociation curve of haemoglobin. Describe and explain how.

Answer 15

Increase in/more carbon dioxideO2 dissociation curve moves to the right/depressed

Question 16

Gas exchange in fish takes place in gills. Explain how two features of gills allow efficient gas exchange.

Answer 16

Filaments/lamellae provide large surface areaThin/flattened epithelium/ one/two cell layers so short diffusion pathway (between water and blood)Countercurrent/blood flow maintains concentration/diffusiongradient

Question 17

Haemoglobin molecules:Describe the 1’, 2’, tertiary and quaternary structure

Answer 17

Primary structure: Four polypeptide chains.- Secondary structure: Each of the polypeptide chains are coiled into a helix.- Tertiary structure: Each polypeptide chain is folded into a precise shape.- Quaternary structure: All four polypeptides are linked to form a spherical molecule. Each polypeptide is associated with a haem group which contains an iron ion- combines with a single O2 molecule making four O2 molecules carried by a single haemoglobin molecule.

Question 18

What is the role of Hb?

Answer 18

The role of haemoglobin is to transport oxygen. To be efficient at transporting oxygen it must:- Readily associated with oxygen at the surface where gas exchange takes place.- Readily dissociate from oxygen at tissues requiring it.In the presence of carbon dioxide, the new shape of haemoglobin binds more loosely to oxygen which makes haemoglobin release its oxygen.

Question 19

Why have different haemoglobins?

Answer 19

Haemoglobins with a high affinity for oxygen- Take up oxygen more easily but release it less readily.Haemoglobin with a low affinity for oxygen- Take up oxygen less easily but release it more readily.

Question 20

Loading and unloading oxygenThe process when haemoglobin combines with oxygen is called __________or____________The process where haemoglobin released its oxygen is called __________or____________

Answer 20

loading or associatingunloading or dissociating

Question 21

describe and explain how the countercurrent system leads to efficient gas exchange across the gills of the fish

Answer 21

blood and water reflow in opposite directions
high diffusion gradient kept
along the whole length of the lamellae