2.4 Exchanging Gases Further Questions and Answers

2.4 – Exchanging gases – Further questions and answers

Q1.

Bk Ch2 S2.4 FQ1

When we inflate a balloon we push air into it; when the balloon deflates, air is squeezed out. Explain how the activity of breathing can be compared with this.

A1.

Bk Ch2 S2.4 FA1

When the muscular walls of the chest cavity contract the volume of the lungs increases and the air pressure decreases in relation to the external air. This causes air to be forced into the lungs: inhalation. When the muscles of the chest cavity relax the volume of the chest decreases and the air pressure within the lungs increases. This forces air to be pushed out of the lungs: exhalation.

Q2.

Bk Ch2 S2.4 FQ2

The mechanism of gas exchange that occurs at the respiratory surface in all organisms is diffusion.

aUse the diagram of a human alveolus with blood supply to explain why

ioxygen diffuses from the alveolar air into the blood, and

iicarbon dioxide diffuses from the blood into the alveolar air.

bWhat would you expect to happen to the diffusion rates of oxygen and carbon dioxide for someone breathing into a paper bag? Explain.

A2.

Bk Ch2 S2.4 FA2

aiBlood entering the capillary of the alveolus has a low concentration of oxygen and the alveolar air is higher in oxygen concentration. Oxygen moves down the concentration gradient from the alveolar space into the bloodstream by diffusion.

iiCarbon dioxide is in high concentration in the incoming blood and in lower concentration in the alveolar air. Carbon dioxide moves from the region of high concentration (blood) to the region of low concentration (alveolus) by diffusion.

bRates of diffusion would decrease. Someone breathing into a paper bag is increasing the concentration of carbon dioxide they are breathing in and decreasing the concentration of oxygen they are breathing in. This means that the concentration gradients for oxygen and carbon dioxide are both becoming smaller. A decreased concentration gradient will cause a decrease in the rate of diffusion.

Q3.

Bk Ch2 S2.4 FQ3

Carbon monoxide is a poisonous gas present in cigarette smoke and the exhaust fumes of cars. Explain why carbon monoxide is dangerous.

A3.

Bk Ch2 S2.4 FA3

Carbon monoxide is dangerous because it will more easily bind with the haemoglobin of red blood cells than oxygen, preventing cells from receiving the oxygen they need for cellular respiration.

Q4.

Bk Ch2 S2.4 FQ4

Study the Table 2.7, which illustrates the distribution of stomates on the leaves of different species.

aSuggest an explanation for the distribution of stomates on the lower epidermis of leaves of different species compared with the upper epidermis.

bConsider eucalypt species. Do you think that the distribution of stomates on upper and lower epidermis would follow a similar pattern? Explain your answer.

A4.

Bk Ch2 S2.4 FA4

aThe lower epidermis is facing away from direct sunlight and therefore the rate of water loss by evaporation would be less compared with the upper epidermis. Having more stomates distributed on the lower epidermis of leaves than the upper epidermis reduces the water loss through the stomates.

bEucalypt leaves hang vertically, giving both surfaces equal exposure to sunlight. The distribution of stomates on each leaf surface is likely to be the same.

Q5.

Bk Ch2 S2.4 FQ5

Water conservation is critical for plants living in arid environments. Research a selected plant species adapted to desert conditions.

aDiscuss the distribution and density of stomates.

bWhat are the consequences of water conservation on gas exchange, the rates of respiration and photosynthesis, and on growth for desert-adapted plants? Explain.

A5.

Bk Ch2 S2.4 FA5

aDesert-adapted plants such as cacti typically have a reduced number of stomates and these may be found sunken into the leaf or stem tissue, thereby reducing water loss by evaporation.

bWater conservation is critical for desert-adapted plants. In their hot, arid environment stomates will be closed for much of the day to avoid water loss. The closure of stomates reduces the rate of exchange of oxygen and carbon dioxide and this in turn means a decrease in the rates of cellular respiration and photosynthesis. A low rate of photosynthesis decreases the capacity of a plant to grow.

Q6.

Bk Ch2 S2.4 FQ6

It is important not to pile soil or compost around the base of a tree, because it might kill the tree. Explain why this is so.

A6.

Bk Ch2 S2.4 FA6

The woody stems of trees rely on lenticels to allow the exchange of oxygen and carbon dioxide. When soil or compost is piled around the base of a tree the lenticels become blocked, stopping gaseous exchange. Without oxygen for cellular respiration the cells at the base of the tree will die, organic materials will no longer be able to be transported across this point and this will eventually lead to the death of the entire tree.

Q7.

Bk Ch2 S2.4 FQ7

Marine kelps are large multicellular organisms, yet they do not have specialised transport systems. Explain why this is so.

A7.

Bk Ch2 S2.4 FA7

Large marine kelps are composed of flat, ribbon-like thalluses that are only a few cells thick; every cell is in close proximity to the watery, external environment. Nutrients and wastes are exchanged directly with the environment; no specialised transport system is necessary.

Q8.

Bk Ch2 S2.4 FQ8

aOutline a simple experiment you could set up, using a carnation flower and food dye to test the hypothesis that ‘water travels through xylem in an upward direction’.

bDescribe the experimental results that would support the hypothesis. (You will need a microscope for part of this answer.)

A8.

Bk Ch2 S2.4 FA8

aPlace a freshly cut white carnation flower with its stem in a glass of brightly coloured food dye. Leave for a couple of hours. Later observation should reveal food dye clearly visible in the vascular tissue of the flower, indicating that the food dye, dissolved in the water, has moved upwards through the stem into the flower.

bCut a thin cross-section of the stem tissue and mount onto a microscope slide. Add a drop of water and cover with a coverslip. Microscopic observation should reveal evidence of the food dye in the xylem tissue of the vascular bundles, and not in the phloem.

Q9.

Bk Ch2 S2.4 FQ9

Research the use of radioactive isotopes in medicine.

 Make a list of elements that are used.

 For what medical conditions are radioactive isotopes useful?

 How are the isotopes used in the body?

 What can they tell us?

 What, if any, side effects may result from the use of radioactive isotopes?

 Evaluate the advantages and disadvantages of using radioactive isotopes as a diagnostic tool.

A9.

Bk Ch2 S2.4 FA9

•Suggested elements include thallium-201, phosphorus-32, iodine-131, technetium-99m.

•Radioactive isotopes are used in the diagnosis and treatment of many conditions, for example detection of bone fractures; tumours such as breast, brain; diseases of the gall bladder, prostate gland, liver, ovaries.

•Isotopes act like markers that illuminate and therefore identify any abnormal tissue during imaging. Usually a patient will be given a drink containing a particular kind of isotope; sometimes an injection is used depending on the target tissue. The kind of isotope that is used depends on the body tissue in question.

•Isotopes are useful because they can be used to target particular body tissues. Different types of body cells take up chemicals in differing concentrations. For example, iodine is concentrated in the thyroid gland where it is needed so iodine-131 is used to diagnose abnormalities of the thyroid gland because that is where the radioactive isotope will accumulate. Abnormal cell growth will be identifiable by a ‘hot spot’ that appears during imaging. Phosphorus is needed in large quantities by dividing cells so phosphorus isotopes would be useful in diagnosing cancers. Isotopes are used to show the location of unusually growing (cancerous) cells and whether cancerous tissue is malignant (spreading).

•There are few side effects associated with the use of radioactive isotopes as a diagnostic tool because they are used in such minute amounts and for a single application. However nausea, weight and hair loss may occur as a result of radioactive isotopes used in cancer treatments where exposure to an isotope is over a longer period of time. There is a potential risk to the radiographer undertaking the gamma-ray imaging, which provides the image of the isotope after it has been taken up by the body tissues. Exposure to gamma radiation can lead to some kinds of cancers. To reduce exposure laboratory personnel must take precautions, such as protective clothing.

•Radioactive isotopes are used extensively as diagnostic tools because they are safe and precise in terms of targeting particular body tissues and there are few long-term side effects. However, radioactive isotopes are expensive to use.

2.4 Exchanging gases FQApage 1 of 3