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Biology > Chapter 6 - Exchange > Flashcards

Chapter 6 - Exchange Flashcards

1
Q

What does the surface area to volume ratio refer to?
Explain what happens between different sized organisms

A
  • Substances enter/leave through the SURFACE of the cells
  • metabolic processes take place within the VOLUME of the cell

-As the size of an object INCREASES, the SA:V ratio DECREASES

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2
Q

Bigger organisms have (with reference to diffusion pathways and SA:V ratio)

A
  • smaller SA:V ratios
  • longer diffusion pathways
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3
Q

Why is increasing body mass associated with a reduction in metabolic rate per kg of body mass?

A
  • many metabolic reactions release heat energy (via respiration)
  • large organisms have a low SA:V ratio so find it difficult to lose heat
  • overheating will denature proteins by breaking hydrogen and ionic bonds
  • so to avoid overheating, larger organisms reduce their metabolic rate.
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4
Q

What do small animals do about heat loss?

A
  • small animals have high SA:V ratios
  • this means they have high rates of heat loss
  • therefore they have higher metabolic rates to release enough heat to provide KE to sustain enzyme-catalysed reactions
  • this means they also have higher feeding rates to get enough substrates (e.g. glucose) to respire
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5
Q

What is gas exchange?

A

The process by which gases such as oxygen and carbon dioxide move passively by diffusion across a surface down a concentration gradient

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6
Q

How do single celled organisms carry out gas exchange?
- refer to their SA:V ratio, diffusion distances and what occurs.

A

Organisms like bacteria (prokaryote) and amoebas (eukaryotes) are unicellular
They have:
- High SA:V ratio
- Short diffusion distances

Therefore they rely on gas exchange with their external environment via SIMPLE DIFFUSION across the cell surface membrane

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7
Q

What is the system called that insects use for gas exchange?

A

Tracheal system

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8
Q

Describe the process of the tracheal system in insects

A
  1. Oxygen diffuses into the insects through pores called SPIRACLES
  2. The gas then enters wide tubes called tracheae
  3. The tracheae each branch into narrower tubes called tracheoles
  4. Tracheoles allow oxygen to directly diffuse to the cells
  5. Carbon dioxide diffuses out in the opposite direction.
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9
Q

How is the tracheal system adapted for efficient gas exchange? [4]

A
  1. tracheoles have thin walls SO short diffusion distance to cells
  2. highly branched tracheoles SO short diffusion distance to cells
  3. Highly branched tracheoles SO large SA for gas exchange
  4. Trachea provide tubes full of air SO fast diffusion into insects tissues
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10
Q

Where do fish carry out gas exchange?

A
  • at the gills
    Gills are made up of: gill filaments attached to a single gill arch
  • gas exchange occurs at the gill lamellae
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11
Q

Where do fish get their oxygen from?

A
  • from the water: oxygen dissolves from air into the water
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12
Q

Describe the countercurrent flow of the fish gas exchange system.

A
  1. Water and blood flows in opposite directions
  2. Blood is ALWAYS passing water with a HIGHER oxygen concentration
  3. This ensures that the concentration gradient of oxygen is maintained across the entire length of the gill
  4. This means that oxygen is DIFFUSING into the blood across the WHOLE LENGTH of the gill
  5. This means more oxygen enters blood and there can be more AEROBIC RESPIRATION to release energy for swimming
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13
Q

What are some adaptations of the fish gill for gas exchange? [3]

A
  1. Each gill has many GILL FILAMENTS, each with many LAMELLAE - this creates a large SA
  2. Each lamellae is lined by a THIN EPITHELIUM = a short diffusion pathway
  3. Each lamella has a large number of CAPILLARIES so blood can rapidly leave the lamella once oxygenated which maintains the concentration gradient
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14
Q

What is the importance of oxygen and carbon dioxide for plants?

A

OXYGEN is needed for aerobic respiration

CARBON DIOXIDE is needed for photosynthesis

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15
Q

How does gas exchange occur in plants?

A
  1. Gas exchange between leaf and air occurs through pores called stomata.
  2. Stomata are mainly on the underside of leaves, which minimises water loss since they are less exposed to sunlight.
  3. During the day, as plants photosynthesise, there is a concentration gradient for carbon dioxide to enter the leaf and oxygen to leave.
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16
Q

What are the adaptations of a plant leaf?
Refer to stomata and mesophyll

A
  1. They have many stomata so diffusion pathways are short
  2. Many air spaces in mesophyll: to increase SA of contact between air and cells
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17
Q

What is transpiration?

A
  • the loss of water from stomata via evaporation
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18
Q

What are the similarities between plants and insects gas exchange?

A
  1. Both occur through pores (stomata in leaves/spiracles in insects);
  2. These pores can close to reduce water loss;
  3. Gas diffuses directly to cells from the atmosphere e.g. oxygen via tracheae/tracheoles in insects; carbon dioxide via air spaces in leaf mesophyll.
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19
Q

How do terrestrial insects reduce water loss?

A
  • periodically closing their spiracles;
  • covering their body in a waterproof cuticle;

The waterproof cuticle is impermeable to gas and water, so gas exchange can only occur through open spiracles. Whenever spiracles close to reduce water loss, this further reduces the amount of gas exchange that can occur.

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20
Q

What are xerophytic plants?

A

Plants that are adapted to living in environments with little LIQUID water e.g. deserts, ice

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21
Q

How are xerophytic plants adapted to reduce water loss?[6]

A
  1. Lower number of stomata per unit area to reduce evaporation;
  2. Hairs so ‘trap’ water vapour and water potential gradient decreased;
  3. Stomata in pits/grooves so ‘trap’ water vapour and water potential gradient decreased;
  4. Thick waxy cuticle layer so increases diffusion distance;
  5. Rolled leaves so ‘trap’ water vapour and water potential gradient decreased;
  6. Spine/needle-shaped leaves so reduces surface area to volume ratio;
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22
Q

What does the endothelial cell of capillary do in humans gas exchange?

A

Shortens the diffusion distance between alveoli and capillary

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23
Q

How is the alveolar epithelium adapted for efficient gas exchange? [2]

A
  1. One cell thick so short diffusion pathway.
  2. Large surface area in total throughout the lungs for rapid diffusion.
24
Q

What are some other adaptations of the human gas exchange system? [3]

A
  1. Red blood cells slow down as they pass through the narrow capillaries, giving more time for gas exchange;
  2. The capillary endothelium is also one cell thick so short diffusion pathway
  3. Red blood cells are pushed up against the capillary endothelium, shortening diffusion pathways further.
25
Q

Describe the process of inspiration. [3]

A
  1. Diaphragm contracts + external intercostal muscles contract;
  2. This causes volume increase and pressure decrease in the thoracic cavity.
  3. Air moves in because the pressure in the thoracic cavity moves below the atmospheric pressure.
26
Q

Describe the process of expiration.

A
  1. Diaphragm relaxes + internal intercostal muscles contract;
  2. This causes volume decrease and pressure increase in the thoracic cavity.
  3. Air moves out because the pressure in the thoracic cavity moves above the atmospheric pressure.
27
Q

What does digestion involve?

A

large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes.

28
Q

What is a triglyceride?

A

a glycerol molecule bonded to three fatty acid molecules by ester bonds.

29
Q

How are triglycerides digested?
Where does it occur, what digests it and where does this enzyme come from?

A
  • Triglycerides are digested in the small intestine by lipase, which is secreted from the pancreas.
  • Lipase in the small intestine hydrolyses a triglyceride molecule to a monoglyceride and 2 fatty acids.
30
Q

What do bile salts do?

A

They help lipid digestion by emulsifying large lipid globules into an emulsion of small droplets

31
Q

Why does emulsification occur?

A
  • smaller droplets provide a larger SA for lipase to act on
  • this therefore results in a faster digestion than if the lipid molecules were large
32
Q

What are micelles?

A
  • even smaller droplets as a result of digestion
  • they consist of monoglycerides and fatty acids with associated bile salts
  • they carry the monoglycerides and fatty acids to the cell surface membrane of the ileum epithelial cells for ABSORPTION
33
Q

Describe the role of micelles.

A
  1. The micelles travel to and contact with the surface membrane of the ileum epithelial cells and break apart.
  2. This releases the non-polar monoglycerides and fatty acids, which diffuse straight through the phospholipid bilayer into the cell.
  3. When in the cell, monoglycerides and fatty acids recombine in the smooth ER to make triglycerides
  4. Then sent to Golgi apparatus via vesicles which process them into CHYLOMICRONS
  5. Vesicles move to and fuse with cell membrane at BASE OF THE CELL and chylomicrons leave by exocytosis
  6. CHYLOMICRONS are taken up nearby the lymph capillaries
34
Q

What are starch and maltose?
What are they made of, bonds?

A
  • Starch is a polysaccharide: a polymer of many repeating alpha glucose monomers bonded to each other by glycosidic bonds.
  • Maltose is a disaccharide. It consists of two glucose molecules bonded together by a glycosidic bond.
35
Q

How is starch and maltose digested?

A

Starch:
1. Amylase is an enzyme found in saliva in the mouth and is also secreted into the small intestine.
2. Starch is hydrolysed to maltose by amylase.

Maltose:
Maltose is hydrolysed to glucose molecules by a membrane-bound disaccharidase called maltase.

36
Q

Why are some digestive enzymes membrane bound?[2]

A
  1. Prevents them be carried away from the ileum with any remaining food.
  2. Creates a high local concentration of the product for immediate absorption by ileum epithelial cell.
37
Q

What do lactase and sucrase hydrolyse?

A

Lactase hydrolyses:
Lactose to glucose and galactose

Sucrase hydrolyses:
Sucrose to glucose and fructose

38
Q

What are the 3 enzymes involved in protein digestion and what do they do?

A
  1. Endopeptidases: hydrolyse peptide bonds between specific amino acids in the middle of a polypeptide
  2. Exopeptidases: hydrolyse peptide bonds between specific amino acids at the ends of a polypeptide
  3. Dipeptidases: hydrolyse the peptide bond in a dipeptide
39
Q

How is polypeptide digestion sped up?

A

By breaking up a polypeptide chain, endopeptidases create more “ends” for exopeptidases to act on. This speeds up polypeptide digestion.

40
Q

Why are there many different exo/endopetidases?

A
  • There are many different amino acids.
  • Different amino acids have different shapes.
  • The peptidases need to have active sites with shapes complementary to the specific amino acids to which they bind.
  • This allows them to form enzyme-substrate complexes.
41
Q

What do dipeptidases do?

A
  • attach to surface membranes of cells lining the small intestine and hydrolase dipeptide into amino acids
  • as a result the amino acids are absorbed by cells lining the ileum of the small intestine
42
Q

What is mass transport?

A

When all substances move in the same direction at the same speed

  • it provides efficient movement of substances to and from surfaces over large distances
43
Q

What do red blood cells contain and where are they found?

A
  • suspended in the blood plasma
  • they contain a protein called HAEMOGLOBIN which is used to transport oxygen
44
Q

How are red blood cells adapted for their function?[3]

A
  1. Large surface area to volume ratio to speed up diffusion;
  2. Flat (biconcave disc) so short diffusion pathways;
  3. No nucleus so more space for haemoglobin.
45
Q

Why do red blood cells also have no mitochondria?

A
  • aerobic respiration by mitochondria would use up the oxygen
  • also creates more space for haemoglobin
    -instead they respire anaerobically
46
Q

What is the structure of haemoglobin like?

A
  • has 4 POLYPEPTIDE CHAINS = 2 alpha and 2 beta giving it a QUATERNARY structure
  • each subunit has 1 non protein haem group
  • Each haem group contains an iron ion, Fe2+.
  • Each haem group can bind one oxygen molecule, O2.
  • Therefore, haemoglobin can bind four oxygen molecules in total.
47
Q

What is meant by the cooperative nature of haemoglobin?

A

-Binding of the first oxygen molecule changes the tertiary structure of haemoglobin;
-This creates another binding site for oxygen and a second oxygen molecule binds;
-This changes the tertiary structure of haemoglobin again and a third binding site is created;
- so the change in shape of haemoglobin caused by binding of the first oxygens makes the binding of further oxygens easier.

48
Q

What is meant by partial pressure, what is its symbol and what increases it?

A
  • The pressure exerted by an individual gas in a mixture of gases
  • pO2 is the symbol for “partial pressure of oxygen”.
  • Higher concentrations of a particular gas will increase the partial pressure for that gas.
49
Q

What is meant by the terms;
1. Oxygen loading
2. Oxygen unloading
3. Oxyhaemoglobin
4. Deoxyhaemoglobin

A
  1. Oxygen loading: haemoglobin associating with/picking up oxygen;
  2. Oxygen unloading: haemoglobin dissociating from/releasing oxygen;
  3. Oxyhaemoglobin: haemoglobin that has oxygen bound to it;
  4. Deoxyhaemoglobin: haemoglobin that does not have oxygen bound to it.
50
Q

Describe the process of loading, transport and unloading of oxygen by haemoglobin. [4]

A
  1. Haemoglobin is loaded with oxygen at the lungs, where there is a high pO2;
  2. In lungs, haemoglobin is almost fully saturated with oxygen;
  3. The heart pumps red blood cells around the body, each of which contains many haemoglobin molecules;
  4. At the respiring tissues of the body, where there is a low pO2, haemoglobin unloads oxygen to the tissues.
51
Q

With reference to the oxygen dissociation curve, why is the s shape important?

A
  • In the lungs, haemoglobin can become fully saturated at a lower pO2 than if the relationship was linear

The steep part means that:
1. for a small decrease in the pO2 there will be a large decrease in the % saturation of haemoglobin with O2.
2. So more O2 will be unloaded to the tissues for aerobic respiration.

  • the more the curve shifts to the RIGHT, the lower the AFFINITY of oxygen by haemoglobin
52
Q

What is the general meaning of the Bohr effect?

A

A higher carbon dioxide concentration will help oxygen to unload

53
Q

Describe the Bohr effect [4]

A
  1. Respiring tissues release CO2 as waste;
  2. CO2 accumulates in the blood and lowers its pH;
  3. This is due to CO2 dissolving in blood to form acid, which increases the hydrogen ion concentration of the blood;
  4. The drop in pH changes the tertiary structure of haemoglobin so oxygen is more easily released;
54
Q

What occurs in the lungs during mass transport in humans?

A
  1. CO2 diffuses down its concentration gradient from blood to the alveoli to be exhaled;
  2. This lowers the concentration of CO2 in the blood and raises blood pH;
  3. This changes the tertiary structure of haemoglobin back to a shape that can more readily bind oxygen;
  4. The high pO2 in the lungs means that haemoglobin is rapidly saturated with oxygen
55
Q

How do plants prevent transpiration?

A

They close the stomata at night as photosynthesis can’t occur anyway

  • if plants don’t have enough water, they will even force close their stomata during the day which reduces growth.

Biology (22 decks)

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