Mock Revision Topic 3

Question 1

What is the relationship between the size of an organism/structure and its SA:VOL?

Answer 1

As size increases, the surface area to volume ratio
decreases

Question 2

How could a single celled organism be adapted to increase its ability to exchange gases? (3)

Answer 2

1. Flat
2. Long
3. Cell membrane projections

Question 3

Name the structures in the tracheal system of an insect (3)

Answer 3

1. Spiracles
2. Trachea
3. Tracheoles

Question 4

Explain the counter current principle in fish gills (5)

Answer 4

1. Blood flows in the opposite direction to water
2. Water always has a higher concentration of oxygen than blood
3. Equilibrium never reached
4. Diffusion gradient maintained along the whole length of the gill lamella
5. Diffusion can happen all along the whole length of the
   gill lamella

Question 5

Describe the path of an oxygen molecule from a chloroplast to the air (6)

Answer 5

1. Thylakoid
2. Stroma
3. Cytoplasm
4. Cell wall
5. Air space
6. Stomata

Question 6

Terrestrial insects and xerophytic plants have to balance which 2 opposing needs and so make structural and functional compromises?

Answer 6

Gas exchange vs Water retention

Question 7

Name the structures of the human gas exchange system (9)

Answer 7

1. Trachea
2. Lung
3. Bronchus
4. Bronchiole
5. Alveolus
6. Diaphragm
7. Rib cage
8. External intercostal muscles
9. Internal intercostal muscles

Question 8

Describe the essential features of the alveolar epithelium as a surface for gas exchange (2)

Answer 8

1. A single layer of flattened epithelial cells – the alveolar wall
2. A single layer of endothelial cells – the capillary wall

Question 9

Describe the mechanism of breathing in and how this affects volume/pressure in the thoracic cavity (5)

Answer 9

Inspiration
1. External intercostal muscles contract pulling the ribs upwards and outwards
2. While the internal intercostal muscles relax
3. The diaphragm muscle contracts pulling the diaphragm down so it flattens
4. Both these actions increase the volume of the thoracic cavity.
5. The pressure inside the lungs decreases below atmospheric pressure and air enters the lungs along a pressure gradient.

Question 10

Describe the mechanism of breathing outand how this affects volume/pressure in the thoracic cavity (6)

Answer 10

Expiration
1. External intercostal muscles relax
2. Internal intercostal muscles contract pulling the ribcage downwards and inwards
3. Diaphragm muscles relax and the diaphragm moves upwards to its dome shape
4. These actions decrease the volume of the thorax
5. The pressure inside the thorax increases above atmospheric and air is forced out of the lungs
6. Elastic recoil of the lung tissue helps to force air out of the lungs during expiration

Question 11

What is the formula for calculating pulmonary
ventilation rate?

Answer 11

Pulmonary Ventilation = Tidal volume x Ventilation rate

Question 12

Define digestion (3)

Answer 12

1. The process in which large molecules are hydrolysed
2. By enzymes to produce smaller molecules
3. That can be absorbed and assimilated

Question 13

For amylase, name the substrate, product and where it is found (2)

Answer 13

Starch into maltose
Salivary glands and pancreas

Question 14

For maltase , name the substrate, product and where it is found (2)

Answer 14

Maltose into glucose
Ileum epithelium

Question 15

For membrane-bound dissacharidases, name the substrate, product and where it is found (2)

Answer 15

Dissacharides into glucose
Ileum epithelium

Question 16

For lipase, name the substrate, product and where it is found (2)

Answer 16

Triglycerides into glycerol, fatty acids and monoglycerides Pancreas

Question 17

For bile salts, name the process and where it is found (2)

Answer 17

Emulsification
Liver/gall bladder

Question 18

For endopeptidases, name the substrate, product and where it is found (2)

Answer 18

Large polypeptides into smaller polypeptides and peptides
Stomach

Question 19

For exopeptidases , name the substrate, product and where it is found (2)

Answer 19

Smaller polypeptides into dipeptides and amino acids Pancreas

Question 20

For membrane-bound dipeptidases, name the substrate, product and where it is found (2)

Answer 20

Dipeptides into amino acids
Ileum epithelium

Question 21

Describe the process of co-transport of amino acids or monosaccharides (8)

Answer 21

1. Sodium ions move into the epithelial cells down a concentration gradient
2. Therefore, when sodium ions enter the epithelial cells
   they are actively transported out of these cells and into the blood capillaries
3. This occurs via specific carrier proteins (sodium-potassium pump) with potassium ions moving in the opposite direction to sodium ions
4. Sodium ions will now continue to diffuse into the
   epithelial cells from the lumen of the intestines
5. Through a carrier protein in the cell- surface membrane
6. Glucose moves through with the sodium ions, hence the term ‘co-transport’ via a glucose-sodium co transporter
7. The glucose then passes into the blood capillary by
   facilitated diffusion
8. Through another specific channel or carrier protein

Question 22

Describe the role of micelles in the absorption
of lipids (2)

Answer 22

1. Micelles transport the poorly soluble monoglycerides
   and fatty acids to the surface of the epithelial cell
2. Where they can be absorbed by diffusing through the
   phospholipid bilayer of the epithelial cell surface
   membrane

Question 23

Describe haemoglobin (3)

Answer 23

1. Haemoglobin is an iron containing pigment
2. Which loosely and reversibly combines with
   oxygen to form oxyhaemoglobin
3. Each haemoglobin molecule consists of four haem units and four polypeptide chains

Question 24

Name 3 different types of haemoglobin and where they are found

Answer 24

1. Adult haemoglobin: red blood cells
2. Fetal haemoglobin: red blood cells of fetus
3. Myoglobin: muscle

Question 25

Describe the oxyhaemoglobin dissociation curve when it shifts to the left (2)

Answer 25

1. Haemoglobin has a higher affinity for oxygen at a given partial pressure oxygen 2. It quickly loads (associates with) oxygen in the lungs where the partial pressure of oxygen is high.

Question 26

Describe the oxyhaemoglobin dissociation curve when it shifts to the right (4)

Answer 26

1. Haemoglobin has a lower affinity for oxygen at a given partial pressure of oxygen 2. Bohr shift 3. Haemoglobin unloads (dissociates) some of its O2 to the rapidly respiring cells. 4. The release of oxygen is increased due to the higher concentration of carbon dioxide in the tissues.

Question 27

Explain what is meant by the ‘cooperative nature of oxygen binding’ (2)

Answer 27

1. The binding of the first oxygen molecule changes the tertiary/quaternary structures of haemoglobin 2. This uncovers the binding site of the next haem unit allowing the next oxygen molecule to bind

Question 28

What is the Bohr effect? (5)

Answer 28

1. The Bohr effect is due to the decrease in pH produced as carbon dioxide dissolves in the blood plasma 2. To form an acid which increases the concentration of hydrogen ions 3. It depresses the O2 dissociation curve (i.e. it moves to the right) 4. And haemoglobin has a lower affinity for oxygen and dissociates more readily at the same partial pressure of oxygen 5. More oxygen released to respiring tissues.

Question 29

Describe the location of the coronary arteries

Answer 29

Flows into the heart muscle

Question 30

Name and describe the location of the blood vessels entering the heart (6)

Answer 30

1. Vena carva 2. Deoxygenated blood from the body (except lungs) 3. Flows into the right atrium 4. Pulmonary vein 5. Oxygenated blood from the lungs 6. Flows into the left atrium

Question 31

Name and describe the location of the blood vessels leaving the heart (6)

Answer 31

1. Pulmonary artery 2. Blood flows into the right ventricle 3. Which contracts to move deoxygenated blood into the pulmonary artery leading to the lungs 4. Aorta 5. Blood flows into the left ventricle 6. Which contracts to move oxygenated blood into the aorta leading to the rest of the body / organ systems

Question 32

Name and describe the location of the blood vessels related to the kidneys (4)

Answer 32

1. Renal artery 2. Into kidneys 3. Renal vein 4. From kidneys

Question 33

Name and describe the location of the blood vessels related to the liver (4)

Answer 33

1. Hepatic artery 2. Into liver 3. Hepatic vein 4. From liver

Question 34

Describe the pressure, volume and associated valve movements during a cardiac cycle to maintain unidirectional flow of blood (13)

Answer 34

1. Contraction of the atria 2. Pressure becomes higher in the atria then the ventricles 3. Atrioventricular valves open 4. Blood moves from atria to ventricles 5. Contraction of ventricles and atria relax 6. Pressure higher in the ventricles than the atria. 7. Atrioventricular valves close 8. Pressure higher than the pulmonary artery and aorta 9. Semilunar valves open and blood leaves the heart 10. Ventricles relax 11. Pressure in aorta / pulmonary artery higher than ventricles 12. Semi lunar valves close 13. Blood stops leaving the heart

Question 35

How does the structure of arteries relate to its function? (5)

Answer 35

1. Have a thicker wall and a smaller lumen than veins 2. And contain more elastic fibres and smooth muscle fibres 3. Do not possess valves except for the aorta and pulmonary artery 4. Transport blood at a higher pressure than veins 5. Carry oxygenated blood (except for the pulmonary artery)

Question 36

How does the structure of veins relate to its function? (6)

Answer 36

1. Carry blood under low pressure towards the heart 2. The walls of veins are thinner than arteries 3. And contain less elastic fibres and smooth muscle 4. The lumen is larger than in arteries so that even at low pressure, blood flows back to the heart at the same rate that it leaves along the arteries 5. Contracting muscles in the legs and body press on the veins and squeeze the blood along. 6. Veins have semi-lunar valves at intervals, preventing back-flow ensuring blood travels in one direction towards the heart

Question 37

How does the structure of arterioles relate to its function? (2)

Answer 37

1. Have a higher proportion of muscle tissue compared to elastic tissue 2. Muscles can contract to control blood flow by reducing the size of the lumen

Question 38

How does the structure of capillaries relate to its function? (11)

Answer 38

1. The walls are one endothelial cell thick 2. Giving a very short diffusion pathway for the exchange of substances with the tissues 3. Gaps between the endothelial cells increase the permeability of the capillary 4. Very large numbers of capillaries and they are highly branched 5. Giving a large surface area for exchange with the tissues 6. The total cross-sectional area of capillaries is very high 7. Producing a large frictional resistance, reducing the rate of blood flow 8. Allowing more time for the exchange of substances 9. No cells are very far from a capillary, giving short diffusion pathways 10. Have a very small diameter and red blood cells are squeezed flat against the capillary wall 11. Reducing the distance for diffusion of oxygen

Question 39

What is the function of xylem vessels? How does their structure enable this function? (6)

Answer 39

1. Transport of water and ions 2. The xylem tissue is dead, there are no cell contents 3. This leaves hollow tubes so that there is minimal resistance to the flow of water and ions 4. The cell wall has been strengthened by lignin providing support and is impermeable to water 5. The cross-walls have broken down completely to allow free flow 6. They have pits that allow water and solutes to move out laterally

Question 40

Describe the cohesion-tension theory of water transport (9)

Answer 40

1. Solar heat energy causes the evaporation or transpiration of water from leaves 2. Water evaporates from the mesophyll cells and diffuses out through the stomata 3. The water potential of these mesophyll cells is reduced compared to inner mesophyll cells 4. Water moves from inner to outer mesophyll cells by osmosis down a water potential gradient 5. This water potential gradient extends across the leaf mesophyll cells to the xylem vessels 6. Water is drawn from the xylem creating a tension in the xylem vessels 7. The water column is maintained in the xylem by cohesive forces and adhesive forces 8. Cohesion refers to the attraction of the water molecules to each other by hydrogen bonding 9. Adhesion refers to the attraction of the water molecules to the xylem walls

Question 41

What is the function of phloem vessels? How does their structure enable this function? (6)

Answer 41

1. Transport of photosynthetic products is known as translocation 2. Sieve elements are joined end to end to form sieve tubes 3. The end walls of sieve elements are known as sieve plates as they possess pores 4. Mature sieve elements do not possess a nucleus 5. And the cytoplasm which is around the edge of the cell contains few organelles 6. Next to each sieve element is a companion cell with dense cytoplasm and many mitochondria.

Question 42

Describe the mass flow hypothesis for the mechanism of translocation in plants (9)

Answer 42

1. Photosynthetic products are produced in the mesophyll cells in the leaves, known as the source 2. These sugars are converted into sucrose 3. Sucrose is actively transported into the sieve tubes by companion cells 4. This lowers the water potential of the sieve tubes causing water to enter from xylem by osmosis 5. This creates a high hydrostatic or turgor pressure in the sieve tubes in the leaf 6. Sucrose and other photosythetic products (e.g. amino acids) are moved from the source to the sink down a pressure gradient by mass flow 7. At the sink sucrose is actively transported from the sieve tube into the sink, for growth or storage as insoluble starch. 8. This will increase the water potential 9. Water moves out of the sieve cells into the xylem which decreases the hydrostatic pressure

Question 43

Explain how ringing experiments provided evidence for mass flow (6)

Answer 43

1. Ringing involves removing a complete ring of phloem around part of a plant (usually the stem) 2. Preventing transport through the phloem at this point 3. The first experiments using ringing involved the removal of a complete ring of phloem from the trunk of a tree during the summer 4. A few months after ringing a tree trunk, a slight swelling develops above the ring 5. This swelling was linked to the build-up of photosynthetic products from the leaves 6. Which were prevented from being transported past the ring due to the removal of the phloem

Question 44

Explain ringing experiments and tracers provided evidence for mass flow (8)

Answer 44

1. Using radioactive isotope 14C as a tracer has enabled more sophisticated experiments using ringing 2. Obtain two plants of the same species at similar stages of growth 3. The stem of plant A is ringed, whereas the other plant B (the control) is left intact 4. A leaf below the ring in plant A, and at a similar position in plant B, is supplied with radioactive 14CO2 5. The plants are left for a few hours in sunlight 6. The transport of the radioactively labelled photosynthetic products can be detected using autoradiography 7. Autoradiography involves placing each plant between X-ray (or photographic) film 8. The film is then exposed by the radioactively labelled compounds showing their location