Topic 6 - Exchange

Question 1

Adaptations of gas exchange surfaces: across the body of a single-celled organism

Answer 1

• Thin, flat shape and large surface area to volume ratio
• Short diffusion distance to all parts of cell for rapid diffusion

Question 2

tracheal system of an insect

Answer 2

1. Air moves through spiracles (pores) on insect surface
2. Air moves through trachea
3. Which divide into tracheoles where gas exchange occurs directly to/from cells
   - O2 used by cells during respiration –> establishes a conc. gradient for O2 to diffuse down
   - CO2 produced by respiration –> diffuses down conc. gradient from respiring cells

Question 3

Adaptations for gas exchange

Answer 3

Question 4

Structural and functional compromises between opposing the needs for efficient gas exchange and the limitation of water loss as shown by terrestrial insects

Answer 4

Question 5

Adaptation for gas exchange in fish

Answer 5

Question 6

Adaptation for gas exchange - counter current flow:

Answer 6

1. Blood and water flow in opposite directions through/over lamellae
2. So oxygen concentration always higher in water (than blood near)
3. So maintains a concentration gradient of O2 between water and blood
4. For diffusion along whole length of lamellae

If water and blood flowed in the same direction (parallel flow) equilibrium would be reached, so oxygen wouldn’t diffuse into blood along the whole gill plate

Question 7

Leaf cross section

Answer 7

Question 8

Closed and open stomata diagram

Answer 8

Question 9

Adaptation for gas exchange in leaf

Answer 9

Question 10

Structural and functional compromises between opposing the needs for efficient gas exchange and the limitation of water loss as shown by xerophytic plants

Answer 10

Xerophyte = a plant adapted to live in very dry conditions e.g. cacti

Question 11

Diagram of human gas exchange system

Answer 11

Question 12

Adaptations of human gas exchange system

Answer 12

Question 13

The essential features of the alveolar epithelium as a surface over which gas exchange takes place

Answer 13

• Thin / flattened cells / one cell think –> short diffusion distance
• Folded –> large surface area
• Permeable –> allows diffusion of oxygen and carbon dioxide
• Moist –> gases can dissolve
• Good blood supply from network of capillaries –> maintains concentration gradient

Question 14

Gas exchange in the lungs

Answer 14

• Oxygen diffuses from alveolar air space into blood down its concentration gradient
• Across the alveolar epithelium then across the capillary endothelium

The opposite for carbon dioxide

Question 15

What is ventilation (mechanism of breathing)

Answer 15

The mechanism of breathing to include the role of the diaphragm and the antagonistic interaction between the external and internal intercostal muscles in bringing about pressure changes in the thoracic cavity

Question 16

Stages of inspiration

Answer 16

1. External intercostal muscles contract, internal intercostal muscles relax (antagonistic) –> ribcage moves up/out
2. Diaphragm muscles contact –> flattens
3. Increasing volume in thoracic cavity (chest)
4. Decreasing pressure in thoracic cavity
5. Atmospheric pressure high than pressure in lungs –> air moves down pressure gradient into lungs

Question 17

Stages of expiration

Answer 17

1. Internal intercostal muscles can contract, external intercostal muscles relax –> ribcage moves down/in
2. Diaphragm relaxes –> moves upwards
3. Decreasing volume in thoracic cavity
4. Increasing pressure in thoracic cavity
5. Atmospheric pressure lower than pressure in lungs –> air moves down pressure gradient out of lungs

Question 18

Two types of expiration

Answer 18

• Normal expiration is passive (no muscle contraction required), aided by elastic recoil in alveoli
• Forced expiration is active because internal intercostal muscles contract

Question 19

Why is ventilation needed

Answer 19

• Maintains an oxygen concentration gradient
• Brings in air containing higher concentration of oxygen
• Removes air with lower concentration of oxygen

Question 20

Tidal volume

Answer 20

Volume of air in each breath

Question 21

Ventilation rate

Answer 21

Number of breaths per minute

Question 22

Forced expiratory volume (FEV)

Answer 22

Maximum volume of air a person can breathe out in 1 second

Question 23

Forced vital capacity (FVC)

Answer 23

Maximum volume of air a person can breathe out in a single breath

Question 24

Effect of lung diseases on ventilation

Answer 24

• Reduced elasticity –> lungs may expand / recoil less –> reduced tidal volume / FVC
  e.g. due to fibrosis - scar tissue builds up which is less elastic
• Narrower airways / reduced airflow in/out of lungs –> reduced FEV
  e.g. due to asthma - bronchi are inflamed

Question 25

Effect of lung diseases on gas exchange

Answer 25

- Thicker tissue in alveoli --> increased diffusion distance --> reduced rate of gas exchange e.g. due to fibrosis - scar tissue builds up which is thicker - Walls of alveoli break down --> reduced surface area --> reduced rate of gas exchange

Question 26

Link between gas exchange and ventilation

Answer 26

If gas exchange reduces, ventilation rate often increases to compensate for reduced oxygen in blood Impact: cells receive less oxygen --> rate of aerobic respiration reduced --> less ATP made --> fatigue

Question 27

During digestion, large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes

Answer 27

- Large biological molecules in food e.g. starch/protiens too big to be absorbed across cell membranes - Digestion breaks them into smaller molecules e.g. glucose/aminoacids --> absorbed from the gut to the blood

Question 28

Digestion in mammals of carbohydrates by amylases

Answer 28

Digestion of starch (polysaccharide) - Amylase hydrolyses starch to maltose (poly to disaccharide) - Membrane bound maltase (attaché to epithelial cells lining the ileum of the small intestine) --> hydrolyse maltose to glucose (di to monosaccharide) - Hydrolysis of glycosidic bond

Question 29

Digestion in mammals of membrane bound disaccharides

Answer 29

- Membrane bound disaccharides e.g. maltase, sucrose, lactase (attached to epithelial cells lining the ileum of the small intestine) --> hydrolyse disaccharide to 2x names monosaccharides - e.g. maltase - maltose --> glucose + glucose - e.g. sucrase - sucrose --> fructose + glucose - e.g. lactase - lactose --> galactose + glucose - Hydrolysis of glycosidic bond

Question 30

Digestion in mammals of lipids by lipase, including the action of bile salts

Answer 30

- Bile salts produced by the liver - Bile salts emulsify lipid to smaller lipid droplets: Increasing surface area (to volume ratio) of lipids speeds up action of lipase - Lipase made in the pancreas, released to small intestine - Lipase hydrolyses lipids --> monoglycerides + fatty acids - Breaking ester bond - Monoglycerides, fatty acids and bile salts stick together to form micelles

Question 31

Digestion in mammals of proteins by endopeptidases, exopeptidase and membrane-bound dipeptides

Answer 31

Endopeptidases: - Hydrolyse peptide bonds within a protein/between amino acids in the central region - Breaking protein into two or more smaller peptides Exopeptidase: - Hydrolyse peptide bonds at the ends of protein molecules - Removing a single amino acid Dipeptidases (type of exopeptidase): - Often bound in ileum - Hydrolyse peptide bonds between a dipeptide - =2 amino acids

Question 32

Mechanisms for the absorption of the products of digestion by cell lining the ileum of mammals, to include co-transport mechanisms for the absorption of amino acids and of monosaccharides

Answer 32

1. Sodium ions actively transported out of epithelial cells lining the ileum, into the blood, by the sodium potassium pump. Creating a concentration gradient of sodium 2. Sodium ions and glucose move by facilitated diffusion into the epithelial cells from the lumen, via a co-transporter protein 3. Creating a concentration gradient of glucose - higher conc. of glucose in epithelial cell than in blood 4. Glucose moves out of cell into blood by facilitated diffusion through a protein channel

Question 33

Mechanisms for the absorption of the products of digestion by cells lining the ileum of mammals, to included the role of micelles in the absorption of lipids

Answer 33

- Monoglycerides and fatty acids diffuse out of micelles (in lumen) into epithelial cell - Monoglycerides and triglycerides recombine to triglycerides which aggregate into globules - Globules coated with proteins to form chylomicrons - Leave via exocytosis and enter lymphatic vessels - Return to blood circulation