organisms exchange substances with their environment TOPIC 3

Question 1

Describe the relationship between the size and structure of an organism and its SA:V ratio.

Answer 1

-As size increases, SA:V decreases
-More thin/elongated structures have a higher SA:V.

Question 2

Suggest an advantage of calculating SA:mass for organisms instead of SA:V

Answer 2

SA:mass is easier to find because it is hard to find volume of irregular shapes.

Question 3

What is metabolic rate?

Answer 3

Amount of energy used by an organism within a given period of time.

Question 4

How is metabolic rate measured?

Answer 4

By measuring oxygen uptake.

Question 5

Explain the relationship between SA:V and metabolic rate.

Answer 5

As SA:V increases, metabolic rate increases because:
-rate of heat loss per unit body mass increases
-so organisms need a higher rate of respiration to release energy in the form of heat
-to maintain a constant body temperature.

Question 6

Describe the 3 main components that make up the tracheal system of an insect.

Answer 6

1. 𝗦𝗽𝗶𝗿𝗮𝗰𝗹𝗲𝘀: pores on surface that can open/close to allow diffusion.
   2.𝗧𝗿𝗮𝗰𝗵𝗲𝗮𝗲: large tubes full of air that allow diffusion
   3.𝗧𝗿𝗮𝗰𝗵𝗲𝗼𝗹𝗲𝘀: smaller branches from trachea, permeable to allow gas exchange with cells.

Question 7

Explain how an insect’s tracheal system is adapted for gas exchange.

Answer 7

𝗧𝗿𝗮𝗰𝗵𝗲𝗼𝗹𝗲𝘀:
-Thin walls so short diffusion distance to cells
-Highly branched tracheoles so large surface area.
𝗧𝗿𝗮𝗰𝗵𝗲𝗮𝗲:
-provide tubes full of air so fast diffusion
𝗖𝗼𝗻𝘁𝗿𝗮𝗰𝘁𝗶𝗼𝗻 𝗼𝗳 𝗮𝗯𝗱𝗼𝗺𝗶𝗻𝗮𝗹 𝗺𝘂𝘀𝗰𝗹𝗲𝘀:
-changes pressure in body causing air to move in/out
-maintains concentration gradient for diffusion.

Question 8

Describe both structural and functional adaptations in terrestrial insects which allow efficient gas exchange while limiting water loss.

Answer 8

𝘁𝗵𝗶𝗰𝗸 𝘄𝗮𝘅𝘆 𝗰𝘂𝘁𝗶𝗰𝗹𝗲: increases diffusion distance so less evaporation.
𝘀𝗽𝗶𝗿𝗮𝗰𝗹𝗲𝘀: can open to allow gas exchange AND close to reduce water loss. 𝗵𝗮𝗶𝗿𝘀 around spiracles: trap moist air, reducing water potential gradient so less water loss (evaporation).

Question 9

Explain how gills of fish are adapted for gas exchange.

Answer 9

-Gills are made of many filaments covered with 𝗺𝗮𝗻𝘆 𝗹𝗮𝗺𝗲𝗹𝗹𝗮𝗲 increasing surface area for diffusion.
-𝘁𝗵𝗶𝗻 𝗹𝗮𝗺𝗲𝗹𝗹𝗮𝗲 𝘄𝗮𝗹𝗹: short diffusion distance between water/blood.
-Lamallae have 𝗹𝗮𝗿𝗴𝗲 𝗻𝘂𝗺𝗯𝗲𝗿 𝗼𝗳 𝗰𝗮𝗽𝗶𝗹𝗹𝗮𝗿𝗶𝗲𝘀- maintains a conc. gradient as O2 is removed quickly and CO2 is taken in.

Question 10

Explain the counter current flow system in fish.

Answer 10

1.Blood and water flow in opposite directions through lamellae.
2.So oxygen conc. is always higher in water, to ensure that oxygen constantly diffuses into blood (high conc. to low)
3. This maintains a conc. gradient of O2 between water and blood.
4.For diffusion along the whole length of lamallae.

Question 11

What would happen if both blood and water flowed in the same direction?

Answer 11

equillibrium would be reached so oxygen wouldn’t diffuse into the blood along lamellae.

Question 12

Explain how the leaves of a dicotyledonous plant is adapted for gas exchange.

Answer 12

-𝗺𝗮𝗻𝘆 𝘀𝘁𝗼𝗺𝗮𝘁𝗮: large surface area for gas exchange.
-𝘀𝗽𝗼𝗻𝗴𝘆 𝗺𝗲𝘀𝗼𝗽𝗵𝘆𝗹𝗹: contains air spaces- large surface area for gases to diffuse through
-𝘁𝗵𝗶𝗻: short diffusion distance.

Question 13

Describe adaptations in xerophytic plants for gas exchange while limiting water loss.

Answer 13

-𝗧𝗵𝗶𝗰𝗸𝗲𝗿 𝘄𝗮𝘅𝘆 𝗰𝘂𝘁𝗶𝗰𝗹𝗲: increases diffusion distance for water so less evaporation
-𝗦𝘂𝗻𝗸𝗲𝗻 𝘀𝘁𝗼𝗺𝗮𝘁𝗮 𝗶𝗻 𝗽𝗶𝘁𝘀/ 𝗿𝗼𝗹𝗹𝗲𝗱 𝗹𝗲𝗮𝘃𝗲𝘀/ 𝗵𝗮𝗶𝗿𝘀: traps water vapour, so reduced water potential gradient between leaf/air, so less evaporation.
-𝘀𝗽𝗶𝗻𝗲𝘀/𝗻𝗲𝗲𝗱𝗹𝗲𝘀: reduces surface area to volume ratio.

Question 14

What makes up the human gas exchange system?

Answer 14

-Trachea
-Bronchi
-Bronchioles
-Capillary network
-Alveoli
ALL found in lungs

Question 15

What is the alveolar epithelium?

Answer 15

A single layer of cells that line the walls of the alveoli.

Question 16

Describe how the alveolar epithelium is adapted for gas exchange.

Answer 16

-consists of flattened cells: short diffusion distance
-folded: large surface area
-permeable: allows diffusion of O2/CO2
-large network of capillaries: good blood supply which maintains conc. gradient.

Question 17

Describe how gas exchange occurs in the lungs.

Answer 17

-Oxygen diffuses from alveolar air space into blood down its conc. gradient
-first across alveolar epithelium then across capillary endothelium.
(OPPOSITE FOR CARBON DIOXIDE: first capillary endothelium, then alveolar epithelium)

Question 18

Explain the importance of ventilation.

Answer 18

-Brings in air containing a high conc. of O2 and removes air with lower conc. of O2.
-maintains conc. gradient

Question 19

Describe the process of Inspiration (breathing in).

Answer 19

1. External intercostal muscles contract
2. Ribcage is pulled up / out
3. Volume 𝗶𝗻𝗰𝗿𝗲𝗮𝘀𝗲𝘀 and pressure 𝗱𝗲𝗰𝗿𝗲𝗮𝘀𝗲𝘀 in thoracic cavity
4. Air moves into lungs down pressure gradient.

Question 20

Describe the process of expiration (breathing out).

Answer 20

1. External intercostal muscles relax
2. Ribcage moves down / in
3. Volume 𝗱𝗲𝗰𝗿𝗲𝗮𝘀𝗲𝘀 and pressure 𝗶𝗻𝗰𝗿𝗲𝗮𝘀𝗲𝘀 in thoracic cavity
4. Air moves out of lungs down pressure gradient.

Question 21

Suggest why expiration (breathing out) is normally passive at rest.

Answer 21

-Internal intercostal muscles do not normally need to contract
-during expiration lungs naturally spring back to their original size (elastic recoil).

Question 22

Suggest how different lung diseases reduce the rate of gas exchange. (3)

Answer 22

1.𝗧𝗵𝗶𝗰𝗸𝗲𝗻𝗲𝗱 alveolar tissue (e.g. fibrosis)- increases diffusion distance
2. Alveolar wall 𝗯𝗿𝗲𝗮𝗸𝗱𝗼𝘄𝗻- reduces surface area.
3. 𝗥𝗲𝗱𝘂𝗰𝗲𝗱 𝗹𝘂𝗻𝗴 𝗲𝗹𝗮𝘀𝘁𝗶𝗰𝗶𝘁𝘆- lungs expand / recoil less reducing conc. gradients of O2 / CO2.

Question 23

Suggest how different lung diseases affect ventilation. (3)

Answer 23

1. 𝗥𝗲𝗱𝘂𝗰𝗲𝗱 𝗹𝘂𝗻𝗴 𝗲𝗹𝗮𝘀𝘁𝗶𝗰𝗶𝘁𝘆- lungs expand / recoil less:
   -reducing volume of air in each breath (tidal volume)
   -reducing maximum volume of air breathed out in one breath.
2. 𝗡𝗮𝗿𝗿𝗼𝘄 𝗮𝗶𝗿𝘄𝗮𝘆𝘀 / 𝗿𝗲𝗱𝘂𝗰𝗲 𝗮𝗶𝗿𝗳𝗹𝗼𝘄 in and out of lungs (e.g. asthma)
   -reducing maximum volume of air breathed out in 𝟭 𝘀𝗲𝗰𝗼𝗻𝗱 (forced expiratory volume)
   3.𝗿𝗲𝗱𝘂𝗰𝗲𝗱 𝗿𝗮𝘁𝗲 𝗼𝗳 𝗴𝗮𝘀 𝗲𝘅𝗰𝗵𝗮𝗻𝗴𝗲- increased ventilation rate to compensate for reduced oxygen in blood.

Question 24

What is tidal volume?

Answer 24

Volume of air in each breath.

Question 25

How do you work out the Pulmonary Ventilation Rate (PVR)?

Answer 25

tidal volume x breathing rate

Question 26

Suggest why people with lung disease experience fatigue.

Answer 26

Cells receive less oxygen (𝟭), so rate of aerobic respiration is reduced (𝟭) so less ATP is made (𝟭).

Question 27

How is a concentration gradient maintained in both insects and humans?

Answer 27

𝗜𝗻𝘀𝗲𝗰𝘁𝘀:
-contraction of abdominal muscles changes pressure in body, causing air to move in / out.
-This maintains a concentration gradient for diffusion
𝗛𝘂𝗺𝗮𝗻𝘀:
-Blood in the capillaries flows in the opposite direction to the water, ensuring that the concentration gradient is maintained along the whole length of the capillary.
-A good blood supply from large network of capillaries maintains concentration gradient.

Question 28

Explain what happens in digestion.

Answer 28

-Large (insoluble) biological molecules are hydrolysed to smaller (soluble) molecules.
-that are small enough to be absorbed across cell membranes into blood.

Question 29

Describe the digestion of starch in mammals.

Answer 29

-Amylase hydrolyses starch to maltose by hydrolysing the glycosidic bonds in starch.
-Membrane-bound maltase hydrolyses maltose to glucose by hydrolysing glycosidic bonds.

Question 30

Where is amylase produced?

Answer 30

Produced in the salivary glands and pancreas.

Question 31

Where is membrane-bound maltase produced?

Answer 31

Produced in the cells of the mucous membrane lining the small intestine.

Question 32

Maltose hydrolyses into…

Answer 32

Glucose + Glucose

Question 33

Sucrose hydrolyses into…

Answer 33

Fructose + Glucose

Question 34

Lactose hydrolyses into…

Answer 34

Galactose + Glucose

Question 35

Describe the digestion of lipids in mammals.

Answer 35

-Bile salts emulsify lipids causing them to form smaller lipid droplets
-this increases the surface area of lipids for increased / faster lipase activity
-Lipase then hydrolyses lipids to form monoglycerides + fatty acids
-Hydrolysis of ester bond

Question 36

Where are lipase enzymes produced and secreted?

Answer 36

Produced in the pancreas and secreted into the small intestine.

Question 37

Function of endopeptidases.

Answer 37

Hydrolyse peptide bonds in the middle of polypeptides producing shorter polypeptides.
It is produced in the stomach and pancreas.

Question 38

Function of exopeptidases.

Answer 38

Hydrolyse peptide bonds at the ends of polypeptide chains to produce dipeptides.

Question 39

Why is the combined action of endopeptidases and exopeptidases more efficient than exopeptidases on their own?

Answer 39

because endopeptidases hydrolyse bonds in the middle of the polypeptides, which creates more ends and more SA for hydrolysis by exopeptidases.

Question 40

What are dipeptidases and where are they found?

Answer 40

They hydrolyse dipeptides into amino acids which are released into the cytoplasm of the cell.
Found within the cell-surface membrane of the epithelial cells in the small intestine.

Question 41

How are proteins digested?

Answer 41

Proteins are hydrolysed into amino acids in following steps:
-In the lumen of the stomach, 𝗲𝗻𝗱𝗼𝗽𝗲𝗽𝘁𝗶𝗱𝗮𝘀𝗲 hydrolyse peptide bonds in the middle of polypeptides.
-𝗲𝘅𝗼𝗽𝗲𝗽𝘁𝗶𝗱𝗮𝘀𝗲 hydrolyse the peptide bonds at the end of polypeptide chains to produce dipeptides.
-𝗱𝗶𝗽𝗲𝗽𝘁𝗶𝗱𝗮𝘀𝗲 𝗲𝗻𝘇𝘆𝗺𝗲𝘀 (which are found within the cell-surface membrane of the epithelial cells in the small intestine) hydrolyse dipeptides into amino acids which are released into the cytoplasm of the cell.

Question 42

Suggest why membrane-bound enzymes are important in digestion.

Answer 42

-They are located on cell membranes of epithelial cells lining the ileum
-By hydrolysing molecules at the site of absorption, they maintain concentration gradients for absorption.

Question 43

Describe the absorption of amino acids and monosaccharides in mammals.

Answer 43

1) Na+ is actively transported from epithelial cells lining ileum to blood (by sodium-potassium pump).
2)A concentration gradient is established of Na+ (higher in lumen than epithelial cell)
3) Na+ enters epithelial cell down its concentration gradient with monosaccharide / amino acid against its conc. gradient via a co-transporter protein.
4) Monosaccharide / amino acid moves down a concentration gradient into blood via facilitated diffusion.

Question 44

Describe the absorption of lipids by a mammal, including the role of micelles.

Answer 44

-Bile salts combine with monoglycerides and fatty acids to form micelles
-micelles make monoglycerides and fatty acids soluble in water
-micelles carry fatty acids and monoglycerides to cells lining the ileum, where they break down to release them
-this maintains a high conc. of fatty acids and monoglycerides near cells lining the ileum
-monoglycerides / fatty acids are absorbed into epithelial cell by diffusion (as now they’re soluble)
-triglycerides reformed in cells and aggregate into globules.
- globules coated with proteins forming chylomicrons which are then packaged into vesicles
-Vesicles move to cell membrane and fuse with it, releasing chylomicrons via exocytosis. –> chylomicrons enter lymphatic vessels and eventually return to blood circulation.

Question 45

Describe the role of red blood cells and haemaglobin (Hb) in oxygen transport.

Answer 45

Red blood cells contain lots of Hb:
-have no nucleus + biconcave- more space for Hb, high SA:V & short diffusion distance.
-Hb associates with oxygen at gas exchange surfaces where partial pressure of oxygen is high.
-This forms oxyhaemaglobin which transports oxygen
-Hb unloads oxygen near cells where pressure of oxygen is low.

Question 46

Describe the structure of haemaglobin.

Answer 46

-protein with a quaternary structure
-made of 4 polypeptide chains
-each chain contains a Haem group containing an iron ion.