Living Things and Air

Complete each statement using the most appropriate scientific term. More than one word may be used in a blank.

1. Air is a __________ rather than a compound because its gases are not chemically combined.
2. Nitrogen makes up approximately __________% of air, while oxygen makes up approximately __________%.
3. The proportions of carbon dioxide and __________ in air may vary according to environmental conditions.
4. Nitrogen is suitable for food packaging because it is relatively __________ and reduces contact between food and oxygen.
5. A glowing splint __________ when it is inserted into a gas jar containing oxygen.
6. When carbon dioxide is passed through limewater, an insoluble white substance called __________ is formed.
7. Dry cobalt chloride paper changes from __________ to __________ in the presence of water.
8. Solid carbon dioxide changes directly into gaseous carbon dioxide by a process called __________.
9. Liquid nitrogen is useful for freezing food and preserving tissues because it has a very __________ boiling point.
10. Carbon dioxide can be used in some fire extinguishers because it is __________ than air and does not support __________.

State whether each statement is true or false. If it is false, rewrite the incorrect part to make the statement correct.

1. Air is a compound containing chemically combined nitrogen and oxygen.
2. The percentage of water vapour in air is the same in all places and at all times.
3. The large amount of nitrogen in air dilutes oxygen and reduces the speed at which substances burn.
4. Carbon dioxide makes up approximately 4% of normal atmospheric air.
5. Both limewater and hydrogencarbonate indicator can be used to test for carbon dioxide.
6. Oxygen burns brightly when a lighted splint is placed inside it.
7. A gas that does not relight a glowing splint must be nitrogen.
8. Dry cobalt chloride paper is pink before it is used to test for water.
9. Carbon dioxide can be used in some fire extinguishers because it does not support the burning of ordinary materials.
10. Pure oxygen can produce a hotter flame than air because air contains nitrogen that dilutes the oxygen.

1. A student states:
   “Air must be a compound because samples of air contain both nitrogen and oxygen.”
   1. State the approximate percentages of nitrogen and oxygen in air.
   2. Give two reasons why air is a mixture rather than a compound.
   3. Name one component of air whose proportion can vary considerably.
2. Three gas jars P, Q and R contain oxygen, carbon dioxide and nitrogen, but their labels have been removed. The student is given a glowing splint and red hydrogencarbonate indicator. Describe a logical sequence of tests that would positively identify all three gases. Include the expected result at each stage.
3. A glowing splint is inserted into an unknown gas and goes out. The student concludes that the gas must be carbon dioxide.
   1. Explain why the conclusion is not valid.
   2. Describe a further test that distinguishes carbon dioxide from nitrogen.
   3. State the expected result for each gas.

1. A gas is tested using limewater and red hydrogencarbonate indicator.
   1. State the positive result obtained using limewater.
   2. Name the insoluble substance responsible for the result.
   3. Write the word equation for the limewater test.
   4. State the colour change of hydrogencarbonate indicator.
   5. Explain why the indicator changes colour.
2. A student places a glass funnel over a burning candle and draws the gases through two testing stations.
   Station 1 contains dry cobalt chloride paper.
   Station 2 contains limewater.
   1. State the colour change at Station 1.
   2. Name the substance detected at Station 1.
   3. State the observation at Station 2.
   4. Name the substance detected at Station 2.
   5. State two conclusions about the products of candle combustion.
3. Equal volumes of fresh limewater are placed in two beakers.
   Beaker A: carbon dioxide from a soft drink is bubbled through it.
   Beaker B: the limewater is left exposed to classroom air.
   1. Explain why Beaker A becomes milky quickly.
   2. Explain why Beaker B does not become milky immediately.
   3. Predict what may form on its surface after several days.

1. A manufacturer is deciding whether to fill potato-chip bags with ordinary air, pure oxygen or pure nitrogen.
   1. Which gas should be selected?
   2. Explain why ordinary air is less suitable.
   3. Explain why pure oxygen is unsuitable.
   4. State the property of nitrogen that makes it suitable.
2. Carbon dioxide can extinguish an ordinary paper fire, but it should not be used for some highly reactive metal fires.
   1. State two properties that make carbon dioxide suitable for extinguishing ordinary fires.
   2. Explain how these properties help to stop combustion.
   3. Explain why carbon dioxide may not extinguish burning magnesium.
3. Solid carbon dioxide, or dry ice, is used to produce a low-lying stage fog.
   1. Name the change of state that occurs.
   2. State the approximate temperature at which dry ice changes into a gas.
   3. Explain why the carbon dioxide remains close to the floor.
   4. Explain why lying in a large amount of this fog could be dangerous.

A factory manager claims that the gas released from an exhaust pipe is pure nitrogen. A scientist collects a sample and obtains the following results.

1. Does the glowing-splint result prove that the gas is nitrogen? Explain.
2. What does the hydrogencarbonate-indicator result show?
3. What does the cobalt chloride paper result show?
4. Evaluate the manager’s claim using all three results.

Complete each statement using the most appropriate scientific term.

1. Photosynthesis mainly takes place in the __________ of a plant.
2. Green leaf cells contain structures called __________, in which the green pigment __________ is found.
3. During photosynthesis, carbon dioxide and __________ are converted into glucose and oxygen.
4. Photosynthesis converts __________ energy into chemical energy stored in __________.
5. The gas released as a by-product of photosynthesis is __________.
6. Plants can convert glucose into __________ for storage and __________ for making cell walls.
7. Before investigating the factors necessary for photosynthesis, a plant should be kept in darkness for at least __________ hours.
8. During the starch test, hot alcohol removes __________ from the leaf.
9. After the alcohol treatment, the leaf is washed in hot water to remove the alcohol and __________ the leaf.
10. Iodine solution changes from __________ to __________ when starch is present.

State whether each statement is true or false. If it is false, rewrite the incorrect part to make the statement correct.

1. Photosynthesis mainly occurs in roots because roots absorb water.
2. Chlorophyll absorbs the light energy needed for photosynthesis.
3. Oxygen is the main food made by a plant during photosynthesis.
4. Light energy is converted into chemical energy stored in glucose.
5. Plants use all the glucose they make immediately in respiration.
6. A plant is destarched by keeping it in darkness for at least 24 hours.
7. Boiling a leaf in water removes its chlorophyll.
8. Hot alcohol should be heated directly over a Bunsen flame so that chlorophyll can be removed quickly.
9. The white parts of a variegated leaf normally do not contain chlorophyll.
10. Finding starch in a leaf after an investigation provides evidence that photosynthesis has taken place.

1. Write the word equation for photosynthesis.
2. Identify:
   1. the two reactants;
   2. the main product;
   3. the by-product.
3. State the energy conversion that occurs during photosynthesis.
4. Explain the role of chlorophyll in photosynthesis.
5. Explain how a plant can use glucose for each of the following:
   1. releasing energy;
   2. storing food;
   3. building cell walls;
   4. making proteins and chlorophyll.

The four main stages of a starch test are shown below.

1. State the purpose of each of the four stages.
2. State:
   1. the positive result for starch;
   2. the negative result for starch.
3. A student places a test tube of alcohol directly over a Bunsen flame.
   1. Explain why this is dangerous.
   2. Describe how the alcohol should be heated safely.
4. Predict how forgetting to wash the leaf after the alcohol treatment may affect the leaf and the final observation.

A student destarches a plant and covers part of one leaf on both sides with opaque black paper. The plant is then placed in bright light for eight hours.

1. Explain why the black paper must cover both sides of the leaf.
2. Identify:
   1. the independent variable;
   2. the dependent variable.
3. Predict the iodine-test result for:
   1. the covered part of the leaf;
   2. the uncovered part of the leaf.
4. State the conclusion of the investigation.
5. Another student takes a plant directly from a sunny garden and carries out the same experiment without destarching it. Both the covered and uncovered regions turn blue-black.
   1. Explain why this result is unreliable.
   2. Explain why the covered region may still contain starch.
   3. Describe how the plant should have been prepared.
   4. Explain why keeping a plant in darkness removes its stored starch.

1. A properly destarched variegated plant is placed in bright light. One of its leaves has green and white regions.
   1. Identify the independent variable.
   2. Predict the iodine-test result for the green regions.
   3. Predict the iodine-test result for the white regions.
   4. Explain the difference between the results.
   5. State the conclusion.
2. Two similar, destarched plants are placed in sealed transparent bell jars.
   Jar A contains a chemical that absorbs carbon dioxide.
   Jar B contains an equal volume of water, which does not absorb carbon dioxide.
   Both jars receive the same light for the same length of time.
   1. Why are the plants destarched first?
   2. Identify the independent variable.
   3. State the purpose of Jar B.
   4. Name three control variables.
   5. Predict the starch-test result for a leaf from each plant.
   6. State the conclusion.

A student places an aquatic plant in water and positions a lamp at distances of 10 cm, 20 cm, 30 cm and 40 cm. The student counts the number of gas bubbles produced in five minutes at each distance.

1. Identify:
   1. the independent variable;
   2. the dependent variable.
2. Name the gas in the bubbles.
3. Explain why each measurement should be repeated.
4. State two variables that should be controlled.
5. Explain why the lamp warming the water would make the investigation unfair.
6. Give one limitation of counting bubbles as a method of measuring the volume of gas produced.
7. The production of bubbles eventually stops increasing even when the lamp is moved closer. Suggest why adding more light may no longer increase the rate of photosynthesis.

Four sealed boiling tubes contain red hydrogencarbonate indicator.

1. Predict the final colour in Tube P.
2. Predict the final colour in Tube Q and explain your answer.
3. Predict the final colour in Tube R and explain your answer.
4. Predict the final colour in Tube S and explain your answer.
5. Explain why Tube P is necessary.
6. A leaf from the plant in Tube Q turns blue-black after iodine solution is added. Explain how this result is connected to the indicator colour in Tube Q.