BackNext Home 1 BackNext Home 2 Do you know how the holes are formed? What is the gas involved in the formation of the holes?

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Do you know how the holes are formed?

What is the gas involved in the formation of the holes?

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What kind of organisms in the bread produces this gas?

How does this kind of organism produce this gas?

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In bread-making, yeast is added to the dough (生麵團 ). It produces carbon dioxide gas in anaerobic respiration (缺氧呼吸 ).

The gas makes the dough rise and become spongy.

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8.1 How is the energy stored in food released?

2 ways:

1) By burning

2) By respiration

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Releasing energy by burning

When a piece of food is burnt, it reacts with oxygen. Oxidation (氧化作

用 )

food + O2

chemical energy

one single step

water + CO2

heat & light energy

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Releasing energy by burning

If glucose is burnt completely, all the energy in it will be released.

food + O2

chemical energy

one single step

water + CO2

heat & light energy

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Releasing energy by

Organisms do not release energy from food by burning because ……

burning releases a large amount of heat at one time kill the cell

Cell releases energy in food by

respiration (呼吸作用 )

respiration

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Releasing energy by respiration

Respiration is a process which organisms release energy

from food through the controlled oxidative breakdown of food.

a series of gradual and controlled chemical reactions.

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Releasing energy by respiration

The word equation for respiration is

glucose + oxygen energy + CO2 + waterenzymes

can be tested by red hydrogencarbonate indicator (碳酸氫鹽指示劑 ) and lime water (石灰水 )

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comparison between burning and respiration

burning respiration

glucoseglucose

(in the cell)

O2

O2

H2O H2O

CO2 CO2

heat heatlight ATP

• fast• gradual

• one-step reaction • many-step reaction & controlled by enzymes

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8.1Investigation of carbon dioxide production in a living mouse

Colour of red hydrogencarbonate indicator changes with the concentration of carbon dioxide in air.

concentration of carbon dioxidecolour of hydrogencarbonate

indicator

> 0.03% Yellow

- 0.03% (atmospheric concentration) Red / orange

< 0.03% Purple

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Procedure:1 Set up the apparatus as shown. Note the colours of the

solutions in flasks A, B and C.

potassium hydroxide solution

Investigation of carbon dioxide production in a living mouse

air in

red hydrogencarbonate indicator

bell jar

living mouse


to suction pump

8.1

Production of CO2 in respiration

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Procedure:2 Turn on the suction pump to draw a stream of air through the

apparatus for 30 minutes.



air in


bell jar

living mouse


to suction pump

8.1

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Procedure:3 Record any colour changes in the flask.



air in


bell jar

living mouse


to suction pump

8.1

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Questions

1 Why is potassium hydroxide solution used in flask A?

To absorb carbon dioxide from the incoming air. One can deduce 推論 that any carbon dioxide detected in flask C is due to the mouse.

ANS:

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2 What are the functions of the redred hydrogencarbonate indicator in flasks B and C?

Flask B: To test whether there is any carbon dioxide in the air entering the bell jar.Flask C: To test whether there is any carbon dioxide in the air leaving the bell jar.

ANS:

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3 What can you tell from the result of flask B?Carbon dioxide is absentabsent in the air entering the bell jar.

ANS:

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4 What can you tell from the result of flask C?

ANS: Carbon dioxide is releasedreleased (= given out) by the mouse.

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5 How would you set up a control for this practical?

Set up a similar apparatus (i.e. that

is the same in all ways except one

aspect / factor) without putting a

mouse in the bell jar.

ANS:

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Control experiment- To show that the result of an

experiment is due to the factor under investigation and NOT any other factors

- The three Cs : comparechangeconstant

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-To show that the result of an experiment (the dependent variable) is due

to the factor under investigation (the independent variable) and

NOT any other factors (the controlled variables)

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-To show that the result of an experiment (the dependent variable) is due

to the factor under investigation (the independent variable) and

NOT any other factors (the controlled variables)

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To compare

To changeTo keep constant

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6 What precautions should be taken if the mouse is replaced by a potted plant? Explain.

Wrap the pot with a plastic bag. Otherwise, carbon dioxide released by the m___________ in the soil will affect the results.(To be continued.)

ANS:

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Cover the bell jar with Cover the bell jar with a black clotha black cloth. Otherwise, the plant will absorb carbon dioxide for p__________ and this will affect the results of the respiration experiment.

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…… continued from previous page

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ConclusionWhat conclusion can you draw from this practical?

The mouse is living. ANS:


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X

The mouse carried out respiration.X

The mouse produced carbon dioxide.

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A valid conclusion must be supported with a control and with reference to the experiment only

ANS:


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8.2Investigation of carbon dioxide production in living germinating seeds

Procedure:1 Set up the apparatus as shown. Leave the tubes for a few

hours.soaked germinating seeds (surface sterilized)

moist cotton

wire gauze

lime water

boiled seeds (surface

sterilized)

A B

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Procedure:2 Record any colour changes in the lime water of tubes A and B.

soaked germinating seeds (surface sterilized)

moist cotton

wire gauze

lime water

boiled seeds (surface

sterilized)

A B

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Questions

1 What is the function of the moist cotton wool?

To provide the necessary amount of water for germination ( 種子發芽 )

ANS:

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2 Why should the surface of the seeds be sterilized?

To kill the micro-organisms on the To kill the micro-organisms on the surface of the seeds.surface of the seeds. Otherwise, carbon dioxide released by them during respiration will affect the results.

ANS:

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3 What is the reason for having a tube with boiled seeds?

As a controlcontrol ** (or control experiment) to show that only living seeds release carbon dioxide.

ANS:

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The living seeds give out carbon dioxide.

ANS:


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Brief RevisionBrief Revision1 ____ hydrogencarbonate indicator can

be used to test for the presence of carbon dioxide.

Red

2 When the concentration of carbon dioxide is high (> 0.03%), its colour will change to ______ .yellow

3 Besides hydrogencarbonate indicator, ____ _____ can also be used to test for the presence of carbon dioxide.lime water

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Places where respiration occurs in living cells

takes place in cytoplasm and mitochondria all the time

known as “cellular respiration”

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Places where respiration occurs in living cells

A_____ cells, e.g. muscle cells, liver cells and sperm (精子 ), contain a lot of mitochondria.

A sperm

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Energy transferred to ATP and lost as heat

• ATP (adenosine triphosphate 腺苷三磷酸 ) an energy carrier

• Some energy released from respiration will lost as heat.

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ATPATP carries a readily usable form of energy which is used for:

• muscle contraction

• active transport

• transmitting nerve impulses (神經脈衝 )

• producing new materials

• supporting many other biological processes

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ATPIn some organisms, energy can be used for

producing light (e.g. fireflies (螢火蟲 ))

generating electricity (e.g. electric eels ( 鰻 ))

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HeatSome of the energy in food is lost as heat.

Homoitherms (恆溫動物 ) like birds and mammals

make use of heat to maintain a constant body temperature.

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8.3Investigation of heat production in a living mouse

Procedure:

1 Set up the differential air thermometer as shown.

clip

thin-walled test tube

cotton wool

arm A

coloured liquid in U-shaped

capillary tube

arm B

graph paper

living mouse

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Procedure:

2 Open the clips on both sides of the thermometer. Wait until the coloured liquid levels in arms A and B become the same.

clip


cotton wool

arm A


capillary tube

arm B

graph paper

living mouse

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Procedure:

3 Close the clips. Record any changes in the liquid levels as time passes.

clip


cotton wool

arm A


capillary tube

arm B

graph paper

living mouse

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Questions1 What is the function of the cotton wool?

To prevent heat loss from the chambers.

或 to trap heat inside the chambers.

ANS:

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2 Why are the two clips opened at the startstart of the practical?

To equalize the air pressure on both sides of the U-shaped capillary tube. This ensures that both liquid levels are the SAME (= atmospheric pressure) at the start of the practical.

ANS:

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3 Explain the results.

● Heat is produced by the mouse and it warms up the air in the thin-walled test tube. ● The air in the test tube expands and results in an increase in air pressure. ● This pushes the air out of the test tube and hence forces the liquid level in arm B downwards. (To be continued.)

ANS:

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Since there is no temperature change in

the control (the side without the mouse),

the falling of the liquid level in arm B leads

to a rise of the liquid level in arm A.

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…… continued from previous page

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4 Can the practical be carried out for a long time? Why?

No. It is because the mouse will use up all the oxygen inside the chamber and die.

ANS:

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5 Which capillary tube, one with a wide bore (闊口徑 ) or a narrow bore, is more suitable for this practical? Why?

A capillary tube with a narrow borenarrow bore is more suitable for this practical because small change can be small change can be obviously recordedobviously recorded.

ANS:

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6 How will the results differ if the mouse is replaced by a frog of the same size?

The change in liquid level is smaller. The frog, being a poikilotherm, has a lower metabolic rate and less heat is released from its body.

ANS:

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Heat is produced by the living mouse.

ANS:


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8.4Design an investigation of heat production in living germinating seeds

From Practical 8.3, we know that a living mouse produces heat when it carries out respiration. Is there any heat production in geminating seeds as well?

Try to design an experiment to test your hypothesis.

Experiment

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8.2 What are the types of respiration?

Aerobic respirationAerobic respiration (需氧呼吸 )

requires oxygen

glucose is completely broken down into carbon dioxide and water

a large amount of energy can be transferred to ATP molecules

takes place in cytoplasm and mitochondria

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Anaerobic respirationAnaerobic respiration (缺氧呼吸 )

can happen without oxygen

it takes place only in cytoplasm but not in mitochondria

glucose is only partly broken down

much less energy is released

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Demonstration of anaerobic respiration in germinating seeds

8.5

Procedure:

1 Put the seeds into a boiling tube and then a piece wire gauze. Fill the tube with paraffin oil.

wire gauze

boiling tube

soaked germinating seeds (surface sterilized)

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8.5

Procedure:

2 Invert the tube and insert it into a container of paraffin oil. Do not trap any air between the seeds and the oil.

paraffin oil

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8.5

Procedure:

3 Leave the tube for a few hours and record the change in oil level. Collect the gas as shown.

plastic tube

gas collected

syringe

push the plunger to collect the gas

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8.5

Procedure:

4 Bubble the gas through red hydrogencarbonate indicator as shown.

gas collected

push the plunger to collect the gas


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Anaerobic respirationAlcoholic fermentation in yeast Glucose is broken down anaerobically into ethanol (乙醇 ) and carbon dioxide.

alcoholic fermentation (酒精發酵 )

glucose energy (in ATP) + ethanol + CO2enzymes

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Design an investigation of alcoholic fermentation in yeastA king stored grapes in a jar. One day, he opened the jar and a strange smell came out. He labelled the jar ‘poison’ and put it aside. A servant drank the ‘poison’ by mistake. She found it tasty.

The ‘poison’ was actually made by alcoholic fermentation carried out by yeast growing naturally on grape skins.

Try to design and perform an experiment to recreate the same process.

8.6

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Anaerobic respiration1) Beer production

Yeast is added to malt (麥芽 ). yeast respires

without oxygen

turns the sugar in malt into alcohol

add hops (蛇麻草 ) to give beer a pleasant bitter taste

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Anaerobic respiration2) Wine production

Wine is made from grape juice.

1) Grapes contain a lot of sugars.

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2) The grapes are crushed.

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3) Crushed grapes are processed and filtered.

grape juice

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4) Grape juice is fermented by yeast to produce alcohol and carbon dioxide.

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5) Fermented grape juice is put into barrels and kept to develop a good flavour.

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6) The wine is put into bottles and tightly corked to prevent further oxidation.

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Anaerobic respiration3) Bread-making

Bread-making makes use of carbon dioxide.

1) The ingredients above are mixed to form a dough.

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2) The dough is pressed and stretched to the shape of a loaf.

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3) The dough is covered and put in a warm place.

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4) The carbon dioxide produced by the alcoholic fermentation of yeast makes the dough spongy.

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5) The spongy dough is baked in an oven. The dough rises more when the carbon dioxide expands at higher temperature. The alcohol evaporates.

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6) The bread is ready to serve.

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Anaerobic respirationLactic acid production in musclesIn humans, some skeletal muscles can respire anaerobically and contract even when oxygen is insufficient.

to provide additional energy in a very short time

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Anaerobic respirationLactic acid production in muscles

lactic acid is produced

glucose energy (in ATP) + lactic acidenzymes

results in muscle fatigue (肌肉疲勞 ) and cause pain

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After doing strenuous exercise, one has to breathe deeply for a period of time to take in extra oxygen.

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to break down the lactic acid into carbon dioxide and water or convert it to glucose

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This extra amount is called the oxygen debt (氧債 ).

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8.3 What is the importance of anaerobic respiration during exercise?

Extension

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8.28.2

Degree of dependence on anaerobic respiration of different sports

Try to find out which system is the major energy source for different sports.

Go to Activity Book 1, p.144

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Brief RevisionBrief Revision1 Yeast undergoes anaerobic respiration

to produce energy, ______ ______ and _______ .

carbon dioxide

2 In muscles, anaerobic respiration will produce energy and _____ ____ .lactic acid

3 Accumulation of lactic acid in the muscles will result in ______ ______ and cause pain.

muscle fatigue

ethanol

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Brief RevisionBrief Revision4 In order to break down the lactic acid in the

muscles, one has to take in extra oxygen. This extra amount is called ______ _____. oxygen debt

5 In cytoplasm, only anaerobic respiration can take place. True or false?False. Both anaerobic and some reactions in aerobic respirations can take place in cytoplasm.

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Brief RevisionBrief Revision6 Aerobic and anaerobic respirations can

take place at the same time in the muscles.True or false?

True. Anaerobic respiration can give extra energy at the same time when needed.

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Summary concept diagramSummary concept diagram

releases

can be

transferredto

is

lost as

Respiration

a series of reactions

chemicals energy in food anaerobic

respiration aerobic

respiration

oxygenATP heat

cytoplasm mitochondria

take place in does not

requirerequires

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leads toused in

examples are

anaerobic respiration

alcoholic fermentation

in yeast

lactic acid production in muscles

beer production

wine production

bread-making

oxygen debt and fatigue

Back to summary concept diagram

Summary concept diagramSummary concept diagram

BackNext Home 1 BackNext Home 2 Do you know how the holes are formed? What is the gas involved in the formation of the holes?

Documents

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respiration respiration

chemical energy

heat light energy slide

glucose oxygen energy

organisms release energy

respiration production

purple slide