Chapter 6: Organisms Exchange Substances with their Environment

Question 1

Describe and explain how fish maintain a flow of water over their gills [4 marks]

Answer 1

1. mouth open, operculum shuts
2. floor of mouth lowered
3. water enters due to decreased pressure
4. mouth closes, operculum opens
5. floor raised results in increased pressure
6. increased pressure then pushes water over gills

Question 2

Describe and explain how the structure of the mammalian breathing system enable efficient uptake of oxygen into the blood [6 marks]

Answer 2

1. alveoli provide a large surface area
2. walls of alveoli thin to provide a short diffusion pathway
3. walls of capillary thin to provide a short diffusion pathway
4. walls have flattened cells
5. cell membrane is permeable to gases
6. many blood capillaries provide a large surface area
7. intercostal muscles maintain a concentration gradient
8. wide trachea for efficient flow of air
9. cartilage rings keep airways open

Question 3

Describe how the structure of the insect gas exchange system
- provides cells with sufficient oxygen
- limits water loss [5 marks]

Answer 3

1. spiracles, tracheae, tracheoles
2. spiracles allow diffusion of oxygen
3. tracheoles are highly branched so large surface area for gas exchange
4. tracheole walls thin so short diffusion distance
5. tracheole walls are permeable to oxygen
6. exoskeleton is impermeable so reduce water loss
7. spiracles can close so no water loss
8. hairs around spiracles reduce water loss

Question 4

Describe how humans breathe in and out [5 marks]

Answer 4

Breathing in
1. diaphragm contracts and is pulled down
2. external intercostal muscles contract and ribcage is pulled out
3. volume increases and pressure decreases in lungs
Breathing out
4. diaphragm relaxes and moves up
5. external intercostal muscles relax and ribcage moves in
6. volume decrease and pressure increase in lungs

Question 5

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them [5 marks]

Answer 5

1. many alveoli / alveoli walls provide a large surface area
2. many capillaries provide a large surface area
3. fast diffusion
4. alveoli or capillary walls are thin so a short distance between alveoli and blood
5. flattened epithelium
6. short diffusion distance
7. fast diffusion
8. ventilation
9. maintains a concentration/diffusion gradient
10. so fast diffusion

Question 6

Describe the gross structure if the human gas exchange system and how we breathe in and out [6 marks]

Answer 6

1. trachea, bronchi, bronchioles, alveoli
2. in the correct order
3. breathing in - diaphragm contracts and external intercostal muscles contract
4. volume increases and and pressure decreases in lungs allowing air to move in
5. Breathing out - diaphragm relaxes and internal intercostal muscles contract
6. volume decrease and pressure increase in thoratic cavity

Question 7

Describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels [5 marks]

Answer 7

1. micelles contain bile salts and fatty acids
2. makes fatty acids more soluble
3. fatty acids absorbed by diffusion
4. triglycerides reformed in cells
5. vesicles move to cell membrane

Question 8

The epithelial cells that line the small intestine are adapted for the absorption of glucose. Explain how. [6 marks]

Answer 8

1. microvilli provide a large surface area
2. many mitochondria produce ATP for active transport
3. carrier proteins for active transport
4. channel/carrier proteins for facilitated diffusion
5. co-transport of sodium ions and glucose
6. membrane bound enzymes digest disaccharides to produce glucose

Question 9

Describe the processes involved in the absorption of the products of starch digestion [5 marks]

Answer 9

1. glucose moves in with sodium
2. via a carrier/channel protein
3. sodium removed by active transport
4. into blood
5. maintaining low concentration of sodium
6. glucose moves into the blood
7. by facilitated diffusion

Question 10

Describe the role of the enzymes of the digestive system in the complete breakdown of starch [5 marks]

Answer 10

1. amylase;
2. starch to maltose
3. maltase
4. maltose to glucose
5. hydrolysis
6. of glycosidic bond

Question 11

Describe how proteins are digested in the human gut [4 marks]

Answer 11

1. hydrolysis of peptide bonds
2. Endopeptidases break polypeptides into smaller peptide chains
3. exopeptidases remove terminal amino acids
4. dipeptidases hydrolyze dipeptides into amino acids

Question 12

Glucose is absorbed from the lumen of the small intestine into epithelial cells. Explain how the transport of sodium ions is involved in the absorption of glucose by epithelial cells [5 marks]

Answer 12

1. Na+ ions leave the epithelial cell and enter blood
2. by active transport
3. so Na+ conc in cell is lower then in the lumen
4. Na+ ions enter by facilitated diffusion
5. glucose absorbed with Na+ against their concentration gradient