B3.1 Gaseous exchange Flashcards
Which of the following apply to gaseous exchange in a leaf and in the lung?
I. Oxygen moves down its concentration gradient.
II. Gases move by active transport.
III. Gases dissolve before entering the cells.
IV. Oxygen and carbon dioxide diffuse in opposite directions.
A. All of the above
B. I, II, and IV only
C. I only
D. II only
D
Which of the rows in table B3.1.1 correctly match the main functions of the tissues found in a transverse section of a leaf?
C
Which of the following are adaptations of the spongy mesophyll for the intake of carbon dioxide to photosynthetic leaf cells?
I. A water layer on the cell surface.
II. Air spaces between the mesophyll cells.
III. The presence of stomata.
IV. A large surface area
A. All of the above
B. I, II, and IV only
C. I only
D. II only
D
A potometer is used to measure water uptake by a cut shoot of a plant. The data shows the
mean rate of water uptake by cut shoots of the same plant for 10 minutes. Four
environmental conditions were tested, with 6 repeats at each. The first measurement was
discarded and the mean of the following 5 measurements was recorded in the table. The
temperature, light intensity and humidity were monitored 10 times during each
measurement of water uptake and their mean values recorded in the table B3.1.2
List the independent and dependent variables in this investigation. (2 marks)
Dependent variable Water uptake
Independent variables Temperature and humidity
A potometer is used to measure water uptake by a cut shoot of a plant. The data shows the
mean rate of water uptake by cut shoots of the same plant for 10 minutes. Four
environmental conditions were tested, with 6 repeats at each. The first measurement was
discarded and the mean of the following 5 measurements was recorded in the table. The
temperature, light intensity and humidity were monitored 10 times during each
measurement of water uptake and their mean values recorded in the table B3.1.2
Light intensity was a controlled variable in this investigation. Explain why the light intensity
should be controlled. (2 marks)
Light intensity affects stomatal opening.
Stomatal opening affects the rate of water loss.
A potometer is used to measure water uptake by a cut shoot of a plant. The data shows the
mean rate of water uptake by cut shoots of the same plant for 10 minutes. Four
environmental conditions were tested, with 6 repeats at each. The first measurement was
discarded and the mean of the following 5 measurements was recorded in the table. The
temperature, light intensity and humidity were monitored 10 times during each
measurement of water uptake and their mean values recorded in the table B3.1.2
Suggest why the first measurement in each condition was discarded from the calculation of
the mean rate of water uptake for each condition. (1 mark)
To give time for the temperature and humidity to change inside the leaves.
So that the plant has time to adjust to the temperature/humidity.
A potometer is used to measure water uptake by a cut shoot of a plant. The data shows the
mean rate of water uptake by cut shoots of the same plant for 10 minutes. Four
environmental conditions were tested, with 6 repeats at each. The first measurement was
discarded and the mean of the following 5 measurements was recorded in the table. The
temperature, light intensity and humidity were monitored 10 times during each
measurement of water uptake and their mean values recorded in the table B3.1.2
Calculate the percentage increase in water uptake between experiment 1 and 3. (1 mark)
The water uptake increased from 120 to 165 = 165-120
As a percentage of condition 1 = 45/120 x 100% = 37.5% (accept 38%)
A potometer is used to measure water uptake by a cut shoot of a plant. The data shows the
mean rate of water uptake by cut shoots of the same plant for 10 minutes. Four
environmental conditions were tested, with 6 repeats at each. The first measurement was
discarded and the mean of the following 5 measurements was recorded in the table. The
temperature, light intensity and humidity were monitored 10 times during each
measurement of water uptake and their mean values recorded in the table B3.1.2
Explain the increase in water uptake between trials 2 and 3. (2 marks)
The rate of water uptake depends upon the rate of transpiration.
Transpiration (rates) depend upon evaporation of water inside the leaf.and diffusion of
water vapour out of the leaf.
Evaporation diffusion, and therefore transpiration rates increase with a rise in temperature
because there is more heat energy at higher temperatures.
The image B3.1.3 shows the stomata in the lower epidermis of one leaf of the stem used in the
investigation and a micrometer. Both images are taken at a magnification of x200 in a light
microscope.
Explain how you could use the photographs of the micrometer and of the stomata (one is
labelled A in the photograph) to estimate the mean stomatal density of the leaf. (3 marks)
Count the number of stomata in the photograph.
Include partial stomata in two sides of the photograph but not the other 2 sides.
Calculate the area of the photograph using the micrometer (and a ruler)
Divide the stomatal count by the area.
Repeat the experiment, by taking more photos, to obtain a mean and increase reliability.
Use the image B3.1.4 of a transverse section of a dicotyledonous leaf to explain why transpiration is
an inevitable consequence of gaseous exchange in a leaf. (2 marks)
Gas exchange and transpiration occur (mostly) through the stomata.
The stomata open for gaseous exchange.
This increases water loss by transpiration through the stomata.
The lung is involved in the exchange of gases with the environment Explain three
adaptations of the lung that make the process of gaseous exchange efficient. (6 marks)
The lungs have a Large surface area
This occurs because the lung is divided into numerous alveoli/air sacs.
The air in the lungs is replaced by Ventilation
Ventilation maintains concentration gradients of gases between the alveoli and the blood.
Capillary beds carry blood to the alveoli.
This closeness of blood to air enables Oxygen to enter the blood by diffusion, the capillaries
carry the oxygenated blood away from the alveoli maintaining the diffusion gradient with
the alveoli.
Surfactant is produced by type II pneumocytes
The surgactant reduces surface tension in the alveoli, preventing the collapse of alveoli.
The lungs have a Branched network of bronchioles.
To carry air to all of the alveoli in all parts of the lungs.
(Award a mark for each point, allowing for different wordings)
Discuss the changes in affinity of haemoglobin for oxygen when it moves into rapidly
respiring tissues.
Rapidly respiring tissues produce carbon dioxide.
Rapidly respiring tissues need a greater amount of oxygen.
Carbon dioxide diffuses into the blood.
Carbon dioxide attaches to an allosteric site on haemoglobin.
Lowering haemoglobin affinity for oxygen.
Causing greater release of oxygen to rapidly respiring tissues.
This ensures that (areas of the body with) rapidly respiring tissues are supplied with more
oxygen.
The phenomenon is known as the Bohr shift.
Note – a graph showing any of the above points should be given credit.
Award one mark for each point, six of the points are required for six mark
