3.3 Organisms exchange substances with their environment: Flashcards
The figure below represents a capillary surrounded by tissue fluid.
The values of the hydrostatic pressure are shown.
Arteriole end:
Hydrostatic pressure = 4.3 kPa
Venule end:
Hydrostatic pressure = 1.6 kPa
Tissue fluid:
Hydrostatic pressure = 1.1 kPa
Use the information in the figure above to explain how tissue fluid is formed.
Tissue fluid is formed when small molecules are forced out of the capillary and into the tissue fluid.
The tissue fluid has an overall outward force of 3.2 KPa.
The hydrostatic pressure falls from the arteriole end of the capillary to the venule
end of the capillary. Explain why.
As there is a constant loss of water against the capillary lining.
High blood pressure leads to an accumulation of tissue fluid. Explain how.
High blood pressure results in high hydrostatic pressure.
Increase outward pressure from the arterial end of the capillary so more tissue fluid is formed.
The water potential of the blood plasma is more negative at the venule end of the
capillary than at the arteriole end of the capillary. Explain why.
Water has left the capillary.
But the proteins are too large to leave the capillary.
This increases the concentration of the blood proteins and the water potential.
Breathing out as hard as you can is called forced expiration.
Describe and explain the mechanism that causes forced expiration.
The internal intercostal muscles are contracting and the external intercostal muslces are relaxing.
The diaphragm muscles are also relaxed.
This causes the decrease in volume of chest/ thoracic cavity.
Air is pushed down a pressure gradient.
Forced expiration volume (FEV) is the volume of air a person can breathe out in 1
second. Using data from the first second of forced expiration, calculate the percentage
decrease in the FEV for group B compared with group A.
Group A: 4.2 dm3
Group B: 0.8 dm3
0.8/4.2 x 100 = 19%
The people in group B were recovering from an asthma attack.
Explain how an asthma attack caused the drop in the mean FEV shown in the figure
below.
Muscle walls of bronchi / bronchioles contract;
Walls of bronchi / bronchioles secrete more mucus;
Diameter of airways reduced;
(Therefore) flow of air reduced
Explain the advantage for larger animals of having a specialised system that facilitates oxygen uptake.
Larger animals have a smaller surface area to volume ratio.
With the specialised system, O2 will be able to diffuse more faster.
Mammals such as a mouse and a horse are able to maintain a constant body temperature.
Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse.
A mouse has a larger surface area to volume ratio.
A larger SA:V increases the rate of exchange i.e. heat } more heat is lost.
Faster rate of respiration/ metabolism releases heat.
A scientist calculated the surface area of a large number of frog eggs. He found that the mean surface area was 9.73 mm2. Frog eggs are spherical. The surface area of a sphere is calculated using this equation
Surface area = 4πr2
where r is the radius of a sphere π = 3.14
Use this equation to calculate the mean diameter of a frog egg.
Show your working.
4πr2 = SA
SA = 9.73mm2
4πr2 = 9.73
4(3.14)r2 = 9.73
12.56r2 = 9.73
√12.56r2 = √9.73
r = √9.73 / √12.56
r = 0.8801599449
X2
d = 1.76031989
d = 1.76
Explain why oxygen uptake is a measure of metabolic rate in organisms.
Oxygen is used in respiration which provides energy/ATP.
Name the process by which oxygen reaches the cells inside the body of a tubifex worm.
Simple diffusion.
Using the information provided, explain how two features of the body of the tubifex worm allow efficient gas exchange.
The worm is small therefore it has a larger SA:V.
The worm is also think allowing a short diffusion pathway.
Describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. Do not refer to
surface area or moisture in your answer. (2)
The epithelium cell is only one cell thick which allows a shorter diffusion pathway.
Suggest and explain how a reduced tidal volume affects the exchange of
carbon dioxide between the blood and the alveoli. (3)
Less CO2 will be exhaled so there is a reduced diffusion gradient between the blood and the alveoli.
More CO2 stays in the blood.
