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Markdown Content:
Why is energy required for the
metabolic process?
What is the main substrate in the
production of energy?
What are the types of respiration?
What are the processes that
occur in aerobic respiration
and fermentation?
## Do you KNOW...
# How is tempe
# processed ?
# Cellular
# Respiration
# 7
# CHAPTER
112 7.1 Production of energy through cellular
respiration
7.1.1 Justify the necessity of energy in
metabolic processes.
7.1.2 Identify the main substrate used in
energy production.
7.1.3 List the types of cellular respiration:
aerobic respiration
anaerobic respiration
fermentation
7.2 Aerobic respiration
7.2.1 Conceptualise energy production
from glucose during aerobic
respiration in cells.
7.2.2 Write a word equation for aerobic
respiration in cells.
7.2.3 Conduct an experiment to study
aerobic respiration.
7.3 Fermentation
7.3.1 State the factors that cause
fermentation to occur in cells.
7.3.2 Explain by using examples of energy
production from glucose during
fermentation in:
human muscle cells
Lactobacillus
yeast
plants such as paddy
7.3.3 Write and explain word equations for:
lactic acid fermentation
alcohol fermentation
7.3.4 Conduct an experiment to study
fermentation in yeast.
7.3.5 Compare and contrast aerobic
respiration and fermentation.
113 Production of energy
# through cellular respiration
In Chapter 5, you have learned about two types of metabolic reaction,
which are anabolism and catabolism . Both of these reactions involve
energy.
The catabolism process releases energy.
The anabolism process uses energy.
Without energy, the anabolic processes such as protein formation which
is the basic muscle substance will not occur.
## The main substrate in energy production
Cellular respiration is carried out to generate the energy needed by all
living cells. Cellular respiration is the oxidation process of organic
molecules through several stages to release energy. The main substrate
for cellular respiration is glucose . Chemical energy found in glucose is
released to produce energy required by cells. In humans and animals,
glucose is obtained through the digestion of carbohydrates from the
food eaten.
In green plants, light energy can be trapped by chlorophyll for the
photosynthesis process to produce glucose.
## Types of cellular respiration
There are two types of cellular respiration, which are aerobic and
anaerobic respiration. Aerobic respiration occurs in the presence
of oxygen. Anaerobic respiration occurs in the absence of oxygen.
Fermentation is an alternative pathway of obtaining energy besides
cellular respiration. In fermentation, the breakdown of glucose is
incomplete in conditions of limited oxygen or without oxygen. This
chapter focuses only on aerobic respiration and fermentation. 7.1
7.1.2 7.1.1 7.1.3
1 Give five examples of the necessity of
energy in a metabolic process.
2 State the main substrate in the production
of energy.
3 State the meaning of cellular respiration and
the types of cellular respiration.
4 Explain how humans, animals and plants
acquire glucose to produce energy.
Formative Practice 7.1
Conduct a group
discussion about
the energy
requirements in the
metabolic process.
Activity Zone
114 7.2.1 7.2.2
ICT 7.1
Video: Aerobic respiration
(Accessed on 21 August 2019)
The number of
mitochondrion
in the muscle
cells of an athlete
increases after
intensive training.
Explain how this
contributes to
the achievement
of the athlete as
compared with
those who do not
undergo intensive
training.
Brainstorm!
Aerobic respiration is the breakdown of glucose involving oxygen to
produce chemical energy. Oxygen is used to oxidise glucose to produce
carbon dioxide, water and energy.
The aerobic respiration process begins with the glycolysis process.
Glycolysis means the breakdown of glucose by enzymes. This process
occurs in the cytoplasm. One glucose molecule is broken down into two
pyruvate molecules.
The following process occurs in the mitochondrion. Pyruvate produced
from glycolysis is then oxidised through a series of reactions to produce
carbon dioxide , water and energy . A large amount of this energy is used
to produce adenosine triphosphate (ATP) molecules.
# Aerobic Respiration 7.2
The aerobic respiration is simplified as follows.
ATP molecules are produced when a group of non-organic phosphate is
added to adenosine diphosphate (ADP).
ADP + phosphate ATP energy
ATP molecules have weak phosphate links.
When the phosphate links on ATP molecules are broken, the energy
released is supplied to cells to help us carry out our daily activities.
ATP ADP + phosphate
energy
The complete process of glucose oxidation is simplified as follows:
Word equation:
Glucose + oxygen Carbon dioxide + water + energy
(2898 kJ)
Glucose Pyruvate
(Occurs in the cytoplasm)
Glycolysis
Carbon dioxide + water + energy
(Occurs in the mitochondrion)
Oxidation of Pyruvate
115 CHAPTER 7 7.2.3
> Activities 2.1
Experiment To study aerobic respiration Activity 7.1
Problem statement
Do living organisms carry out aerobic respiration?
Hypothesis
Living organisms use oxygen and release carbon dioxide during aerobic
respiration.
Variable
Manipulated: Presence of living organisms
Responding: Increase in the level of coloured liquid
Fixed: Initial level of coloured liquid
Materials
Water, coloured liquid, soda lime, living organism (cockroach) and petroleum jelly
Apparatus
Boiling tubes, screw clip, wire gauze, 250 ml beaker, capillary tube, ruler, rubber tube and water bath
screw clip capillary tube capillary tube boiling tube A boiling tube B wire gauze level of coloured liquid level of coloured liquid soda lime water bath to maintain temperature cockroach rubber tube
Apparatus set-up to study aerobic respiration process
Procedure
1 Prepare the apparatus as shown in the figure above.
2 Prepare two boiling tubes labelled A and B.
3 Fill both boiling tubes with 10 g soda lime.
4 Put the wire gauze in the middle of boiling tube A.
5 Put a cockroach on the wire gauze in boiling tube A while the boiling tube B is left empty.
6 Wipe all connections of the apparatus with petroleum jelly.
7 Close the screw clip and mark the height of the initial level of the coloured liquid in the capillary
tube for both boiling tubes.
8 Leave the apparatus for an hour.
9 Measure and record the final height of the coloured liquid in both capillary tubes after an hour with
a ruler.
10 Record your observations in the following table.
Wipe all connectors
with petroleum jelly
to ensure that the
apparatus prepared
is airtight.
Take Note!
The apparatus
set-up is called a
respirometer. It is
used to measure the
rate of respiration
of an organism by
estimating the rate of
oxygen used.
Biological Lens
116 7.3.1
Fermentation is the incomplete breakdown of
glucose in conditions of limited oxygen or
without oxygen. Fermentation is different
from aerobic respiration in its metabolic
pathway after the glycolysis stage.
After glycolysis, the pyruvate
produced will undergo either
alcohol fermentation or lactic
acid fermentation .
# Fermentation 7.3
Results
Boiling tube Initial level (cm) Final level (cm) Difference in levels
(cm)
A
B
Discussion
1 What is the purpose of preparing boiling tube B?
2 What is the function of soda lime in the boiling tube?
3 Is there a change in the level of coloured liquid in capillary tube A? Explain your answer.
Conclusion
Is the hypothesis accepted? Suggest a suitable conclusion.
1 State the meaning of aerobic respiration.
2 Suggest another substrate apart from
glucose that can be used by cells for cellular
respiration.
3 State the word equation for aerobic
respiration.
4 Describe the processes involved in aerobic
respiration to produce energy.
Formative Practice 7.2
117 CHAPTER 7 Ethanol is used in the making of
beer and wine.
The released carbon dioxide makes
bread dough rise.
Paddy plants that grow in waterlogged areas with less
oxygen are able to carry out alcohol fermentation .
Ethanol produced in the tissues during the
fermentation process is toxic to most plants but
the cells of paddy plants have a higher
tolerance for ethanol compared to
other species.
Paddy plants produce plenty
of alcohol dehydrogenase
enzymes that can break down
ethanol molecules into non-toxic
carbon dioxide.
YEAST PLANTS
The incomplete breakdown of glucose to ethanol, carbon dioxide and energy.
Glucose Ethanol + carbon dioxide + energy (210 kJ)
ALCOHOL FERMENTATION
ICT 7.2
> Video: Anaerobic respiration
> (Accessed on 21 August 2019)
The incomplete breakdown of glucose in limited or no
oxygen conditions.
FERMENTATION
> Activities 2.1
Project
Produce and market food products
produced through fermentation
Activity 7.2
Procedure
1 Your teacher will divide your class into a few groups.
2 Each group will choose one food product that is produced through the fermentation process and
market that product in school. Examples of products are tapai, yoghurt or bread.
3 Each group needs to prepare a proposal before starting the project. The proposal must contain:
introduction of the project including the objectives
execution cost
production and marketing plan
expected outcome
4 If necessary, get advice from your teacher or parents to ensure the smooth delivery of the project.
5 Conduct the project as planned.
6 At the end of the project, each group must prepare a complete report.
> 7.3.2 7.3.3
118 This process is carried out by the muscle cells during vigorous training.
During vigorous training, the rate of oxygen used exceeds the oxygen supplied by the blood
circulatory system.
The muscle is in an oxygen-deficiency state and is said to undergo oxygen debt .
During this process, glucose cannot break down completely. For each glucose molecule that is
broken down, only two ATP molecules or 150 kJ energy will be produced.
The produced lactic acid accumulates until it reaches a level of concentration that can cause fatigue
and muscle cramps.
The breakdown of glucose into lactic acid and energy.
Glucose Lactic acid + energy
LACTIC ACID FERMENTATION
> Some bacteria
> can only survive
> in anaerobic
> conditions. Predict
> what can happen to
> this type of bacteria
> when oxygen is
> supplied.
Brainstorm!
HUMAN MUSCLE CELLS
> oxygen debt repaid oxygen intake during exercise exercise lack of oxygen (oxygen debt) recovery oxygen intake at the beginning of exercise at the end of exercise Time (minutes) at the end of recovery
> FIGURE 7.1 Lack of oxygen in muscles and oxygen debt repaid
> 7.3.2 7.3.3
The bacteria Lactobacillus carries out milk fermentation to
produce yoghurt .
Lactobacillus acts on the lactose (milk sugar) and turns it into
lactic acid.
The lactic acid will then coagulate casein (milk protein) to
produce yoghurt.
Lactic acid is the source of a sour taste in yoghurt.
LACTOBACILLUS
Once the vigorous activity stops,
the intake of excess oxygen
will oxidise the lactic acid into
carbon dioxide, water and energy.
When all the lactic acid has been
expelled, the oxygen debt is
repaid .
Figure 7.1 shows a lack
of oxygen in muscles
and oxygen debt is
repaid.
> Lactobacillus bacteria
119 CHAPTER 7 7.3.4
> Activities 2.1
Experiment To study the process of yeast fermentation Activity 7.3
Problem statement
What are the products of yeast fermentation?
Hypothesis
Yeast fermentation produces energy, carbon dioxide and ethanol.
Variables
Manipulated: Presence of yeast
Responding: Changes in temperature, lime water and ethanol smell
Fixed: The volume of boiled glucose solution and the anaerobic condition
Materials
5% yeast suspension, 5% boiled glucose solution, lime water and paraffin oil
Apparatus
Boiling tube, test tube, thermometer, measuring cylinder, delivery
tube and cork
Procedure
1 Fill 2 boiling tubes with 15 ml of 5% glucose solution that has
been boiled and left to cool.
2 Label the boiling tubes as A and B.
3 Put 5 ml 5% yeast suspension into boiling tube A.
4 Add paraffin oil into both of the boiling tubes.
5 Close both boiling tubes with the cork that has a hole and
a delivery tube. Prepare 2 test tubes with 2 ml of lime water
respectively. Dip the end of each delivery tube into each test
tube that contains lime water.
6 Leave the apparatus for 1 hour.
7 Measure and record the initial and final temperature using a
thermometer.
8 Record your observations in the table below.
Results
Boiling
tube
Temperature (C)
Change in lime water Smell of
solution Beginning of
experiment
End of
experiment
A
B
Discussion
1 How is the anaerobic condition maintained to ensure that the fermentation process is complete?
2 What is the function of preparing boiling tube B?
Ensure that the end
of the delivery tube is
soaked in lime water.
Take Note!
thermometer boiling tube A boiling tube B delivery tube
> -10 0 10 20 30 40 50 60 70 80 90 100 110 -10 10 10
5% boiled glucose solution + yeast suspension paraffin oil lime water thermom delivery tube
5% gluc solu
thermometer boiling tube A boiling tube B delivery tube
> -10 0 10 20 30 40 50 60 70 80 90 100 110 -10 10 10
5% boiled glucose solution + yeast suspension paraffin oil lime water
thermometer delivery tube
> -10 0 10 20 30 40 50 60 70 80 90 100 110 -10 10 10 0
5% boiled glucose solution lime water paraffin oil
Apparatus set-up to study the
yeast fermentation process
120 Comparison between aerobic respiration and
## fermentation
There are a few similarities and differences between fermentation and
aerobic respiration (Figure 7.2 and Table 7.1).
FIGURE 7.2 Similarities between aerobic respiration and fermentation
> 7.3.5
Why is aerobic
respiration more
suitable for yeast
compared with
fermentation?
Brainstorm!
3 What is the purpose of boiling the glucose solution earlier?
4 How do the results show that fermentation has taken place in boiling tube A?
Conclusion
Is the hypothesis accepted? Suggest a suitable conclusion.
The breakdown
process of glucose
and its conversion
to chemical energy
Produces chemical energy
in the form of ATP
The process begins with glycolysis when
glucose is converted to pyruvate
Occurs in yeast,
bacteria, animals
and plants
The process
begins in the
cytoplasm
DIFFERENCES
Aerobic Respiration Fermentation
The breakdown process of glucose is completed
in the presence of oxygen.
The breakdown process of glucose is incomplete
without oxygen or in limited oxygen conditions.
Occurs in cytoplasm and mitochondrion. Occurs in cytoplasm.
Produces water. Does not produce water.
Glucose is oxidised completely into carbon
dioxide and water.
Glucose is not oxidised completely into ethanol
and carbon dioxide or lactic acid.
One molecule of glucose generates 2898 kJ of
energy
One molecule of glucose generates 210 kJ
(alcoholic fermentation) or 150 kJ (lactic acid
fermentation) of energy
TABLE 7.1 Differences between aerobic respiration and fermentation
SIMILARITIES BETWEEN AEROBIC RESPIRATION AND
FERMENTATION
1 State where the process of fermentation
usually occurs.
2 Give three examples of microorganisms and
food produced by the fermentation process.
3 While helping your father to cut the grass at
the farm, you come across a snake. Terrified,
you run away from the snake. Explain the
cellular respiration that takes place in the
muscle cells of your legs.
4 State the differences between aerobic
respiration and fermentation.
Formative Practice 7.3
121 CHAPTER 7 The main substrate
in energy production
is glucose
Fermentation
Production of energy
through cellular respiration
CELLULAR RESPIRATION
Have you mastered the following important concepts?
The necessity of energy in metabolic processes
The main substrate in the production of energy
Types of cellular respiration
Energy production from glucose during aerobic respiration in cells
Word equation for aerobic respiration in cells
Factors that cause fermentation to occur in cells
Example of energy production from glucose during fermentation
Lactic acid fermentation and alcohol fermentation
Yeast fermentation process
Differences bet ween aerobic respiration and fermentation
# Summary
# Self Reflection
The incomplete breakdown of
glucose in limited oxygen or no
oxygen
Alcohol fermentation
Lactic acid fermentation
The breakdown of glucose in the
presence of oxygen to produce
chemical energy
Occurs in cytoplasm
Glucose Pyruvate
Occurs in mitochondrion (pyruvate oxidation)
Carbon dioxide + water + energy
Aerobic Respiration Anaerobic Respiration
122 1 What are the uses of alcohol fermentation products?
2 Why do muscles carry out cellular respiration that produces lactic acid during vigorous
training?
3 Why does cellular respiration in muscles that produce lactic acid supply less energy
compared to aerobic respiration?
4 Explain why an individual usually feels tired faster compared with an athlete, when both of
them are running together.
5 A 100-metre sprinter usually holds his breath while running compared with a long-distance
runner. After running, the sprinter needs seven litres of oxygen to remove the lactic acid in
his muscle cells. Explain this difference between the sprinter and the long-distance runner.
6 Photograph 1 shows the activities by two individuals, P and Q.
Q
P
(a) (i) Based on Photograph 1, identify the respiration that occurs in the muscles of
individuals P and Q.
(ii) State the products of respiration in P and Q.
(b) During the 100-metre sprint on Sports Day, a pupil experienced muscle cramps and
had to stop running. Explain why muscle cramps happen.
(c) Paddy plants grown in waterlogged areas have tolerance to ethanol compared
with other plants.
(i) State the type of fermentation that occurs in paddy plant cells.
(ii) Write the word equation for the fermentation process that occurs in the paddy
plant cells.
(iii) Suggest another cell that can carry out the fermentation process as in
question c(ii).
# Summative Practice 7
PHOTOGRAPH 1
123 CHAPTER 7 Essay Questions
7 (a) Explain why energy is required in metabolic processes.
(b) Compare aerobic respiration with fermentation.
(c) Mic roorganisms such as yeast and bacteria usually play an important role in the
fermentation process to produce food. Explain why yoghurt can spoil if it is not kept in
the refri gerator.
Enrichment
8 A person who is not used to exercising will experience muscle cramps when doing
vigorous exercise because of the accumulation of lactic acid in the cells. However, for
high-performance athletes, such problems do not occur because their bodies have a high
tolerance for lactic acid. In your opinion, how do high performance athletes overcome the
problem of lactic acid accumulation? Give your reasoning.
9 Studies have shown that intake of sodium bicarbonate or baking powder ( baking soda ) can
increase muscle efficiency during intense activities that involve muscle fermentation. Give
your justification.
10 While conducting an experiment using yeast, Mei Ling found that if grape juice is kept with
yeast in a covered container, the yeast will slowly break down the glucose in the grapes.
However if the container does not contain any oxygen, the yeast will break down the
glucose at a faster rate, and the alcohol content in the container will rise very fast. At the
end of the experiment, Mei Ling found that the breakdown rate of glucose becomes slow
again even though there are some grapes that have not been oxidised. Explain Mei Lings
observation.
11 Susan tried to make bread using dry yeast bought from a shop. When she mixed the yeast
with plain flour, she found that her bread did not rise after half an hour. Explain how you can
help Susan solve her problem.
> Complete answers are
> available by scanning the
> QR code provided
124