Respiration

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Respiration in Cells

Respiration is a chemical process that breaks down glucose to release energy; it is enzyme-controlled.
Respiration can be aerobic (with oxygen) or anaerobic (without oxygen).
Aerobic respiration releases much more energy per glucose molecule than anaerobic respiration.
Most aerobic respiration reactions occur in the mitochondria.
Energy released is used for: muscle contraction, protein synthesis, cell division, growth, active transport, nerve impulses, and maintaining body temperature.

Uses of Energy in the Body of Humans

Aerobic Respiration

Aerobic respiration requires oxygen and is the complete breakdown of glucose.
Word equation: glucose + oxygen → carbon dioxide + water (+ energy).
Balanced symbol equation: C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O.
This equation is the reverse of photosynthesis.

Word equation for aerobic respiration

Anaerobic Respiration in Animals

Anaerobic respiration does not use oxygen and is an incomplete breakdown of glucose.
In animals (e.g., during vigorous exercise), glucose is converted to lactic acid.
Word equation: glucose → lactic acid (+ a small amount of energy).
Lactic acid build-up lowers pH in muscle cells, which can denature enzymes.
Lactic acid is transported to the liver where it is oxidised (using oxygen) back to carbon dioxide and water – this is repaying the oxygen debt.

Word equation for anaerobic respiration in animals

Anaerobic Respiration in Yeast

In yeast, anaerobic respiration produces ethanol and carbon dioxide.
Word equation: glucose → ethanol + carbon dioxide (+ a small amount of energy).
Used in bread making (CO₂ makes dough rise) and brewing (ethanol in beer, CO₂ gives fizz).

Word equation for anaerobic respiration in yeast

Comparing Aerobic and Anaerobic Respiration

Aerobic: uses oxygen, complete breakdown, large energy release, products CO₂ and H₂O.
Anaerobic (animals): no oxygen, incomplete, small energy release, product lactic acid only.
Anaerobic (yeast): no oxygen, incomplete, small energy release, products ethanol and CO₂.
Anaerobic respiration in animals does not produce carbon dioxide.

Comparing aerobic and anaerobic respiration

Effect of Temperature on Respiration Rate

Respiration rate can be measured using methylene blue dye – it turns from blue to colourless as oxygen is used up.
Independent variable: temperature; dependent variable: time for colour change (rate of respiration).
Rate increases up to ~40 °C due to more kinetic energy and enzyme–substrate collisions.
Above 40 °C, rate decreases because enzymes denature (active site changes shape).
Control other variables: volume/concentration of dye, yeast suspension, glucose, and pH.

Methylene blue apparatus

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1.Glucose is broken down in the chemical processes of aerobic respiration. Which row correctly shows the products of this breakdown? | Row | Products | |---|---| | A | carbon dioxide and water | | B | lactic acid only | | C | ethanol and carbon dioxide | | D | oxygen and glucose |
Easy
- ARow A
- BRow B
- CRow C
- DRow D
2.Which of the following processes require, and are dependent on, the activity of enzymes? 1. aerobic respiration 2. glucose → lactic acid 3. osmosis 4. anaerobic respiration in yeast
Medium
- A1 and 2
- B1 and 3
- C1, 2 and 4
- DAll of them
3.A student investigated respiration in yeast. Every 30 minutes they replaced the water with the same volume but it was 10°C warmer and counted the bubbles given off in 2 minutes. What are the independent and dependent variables in this experiment?
Medium
- Aindependent: number of bubbles, dependent: time
- Bindependent: time, dependent: number of bubbles
- Cindependent: water temperature, dependent: number of bubbles
- Dindependent: water temperature, dependent: volume of water
4.Which of the following do humans require energy for? 1. Producing proteins 2. Cell division 3. Generation of nerve impulses 4. Maintaining body temperature
Easy
- A1 & 3
- B2, 3 & 4
- C4 only
- DAll of the above
5.Which of the following options correctly shows the products produced by anaerobic respiration in yeast and in animals?
Medium
- Aanimals: lactic acid (no), carbon dioxide (yes); yeast: lactic acid (no), carbon dioxide (no)
- Banimals: lactic acid (yes), carbon dioxide (no); yeast: lactic acid (no), carbon dioxide (yes)
- Canimals: lactic acid (no), carbon dioxide (yes); yeast: lactic acid (yes), carbon dioxide (no)
- Danimals: lactic acid (yes), carbon dioxide (yes); yeast: lactic acid (no), carbon dioxide (no)
6.Why does anaerobic respiration of glucose release less energy in muscle cells than aerobic respiration? 1. Energy is lost in oxygen. 2. Energy remains trapped in the chemical bonds in the molecule lactic acid. 3. Energy remains trapped in the chemical bonds in the molecule ethanol. 4. Energy is lost in carbon dioxide.
Medium
- A1, 2 and 4
- B2 only
- C2 and 3
- D4 only
7.The diagram below shows an experimental set-up which can be used to investigate gas exchange in a plant leaf. In which direction would the ink drop move and for what reason?
Hard
- Adirection: to the right, reason: photosynthesis
- Bdirection: to the left, reason: photosynthesis
- Cdirection: to the right, reason: respiration
- Ddirection: to the left, reason: respiration
8.The diagram below shows an experiment set up by a group of students to investigate respiration in yeast. Which row of the table below correctly describes the contents of the flask after 20 hours?
Medium
- Anew compound: ethanol (alcohol), gas produced: oxygen
- Bnew compound: ethanol (alcohol), gas produced: carbon dioxide
- Cnew compound: lactic acid, gas produced: oxygen
- Dnew compound: lactic acid, gas produced: carbon dioxide

Soal lainnya

9.The diagram below shows an experiment set up by a teacher to demonstrate how an investigation into anaerobic respiration in yeast cells can be carried out. Predict what would happen to the coloured liquid in the glass tube.
Medium
- ADoesn't move
- BMoves to the left
- CMoves rapidly to the right
- DMoves slowly to the right
10.Respiration is the same as breathing.
Easy
True or false?
11.Which of the following is the correct word equation for aerobic respiration?
Easy
- Aglucose + oxygen → carbon dioxide + water
- Bcarbon dioxide + water → glucose + oxygen
- Cglucose + water → carbon dioxide + oxygen
- Dglucose + carbon dioxide → water + oxygen
12.Anaerobic respiration releases more energy per glucose molecule than aerobic respiration.
Easy
True or false?
13.Which of the following is a use of energy released from respiration in humans?
Easy
- AMuscle contraction
- BPhotosynthesis
- CExcretion
- DDigestion
14.Anaerobic respiration in yeast produces which two products?
Easy
- Aethanol and carbon dioxide
- Blactic acid and carbon dioxide
- Cethanol and oxygen
- Dlactic acid and oxygen
15.During anaerobic respiration in human muscle cells, carbon dioxide is produced.
Easy
True or false?
16.Match each organism to the correct product of anaerobic respiration.
Easy
- Human muscle cells
- Yeast
- Lactic acid
- Ethanol and carbon dioxide
17.During recovery after vigorous exercise, lactic acid is removed by being transported to the liver and oxidised. This process requires extra oxygen. What is this extra oxygen called?
Easy
- AOxygen debt
- BOxygen deficit
- COxygen reserve
- DOxygen excess
18.Place the following steps in the correct order to describe how lactic acid is removed from the body after exercise.
Medium
- Lactic acid is transported to the liver via the blood.
- Lactic acid is oxidised in liver cells using oxygen.
- Carbon dioxide and water are produced as waste products.
- Lactic acid builds up in muscle cells during vigorous exercise.
19.Which of the following is the correct balanced symbol equation for aerobic respiration?
Easy
- AC6H12O6 + 6O2 → 6CO2 + 6H2O
- BC6H12O6 → 2C3H6O3
- C6CO2 + 6H2O → C6H12O6 + 6O2
- DC6H12O6 → 2C2H5OH + 2CO2
20.Which of the following are products of anaerobic respiration in yeast? (Select all that apply)
Easy
- AEthanol
- BLactic acid
- CCarbon dioxide
- DWater
- EOxygen
21.Match each organism or cell type to the correct product(s) of anaerobic respiration.
Medium
- Human muscle cells
- Yeast cells
- Plant root cells (anaerobic conditions)
- Lactic acid
- Ethanol and carbon dioxide
- Ethanol and carbon dioxide
22.Place the following steps in the correct order to describe how lactic acid is removed from the body after vigorous exercise.
Medium
- Lactic acid is transported in the blood to the liver.
- Lactic acid is oxidised in liver cells to carbon dioxide and water.
- Oxygen is taken up by the blood in the lungs and delivered to the liver.
- Lactic acid diffuses from muscle cells into the blood.
23.Which of the following are uses of the energy released from respiration in humans? (Select all that apply)
Medium
- AMuscle contraction
- BProtein synthesis
- CDiffusion of oxygen into cells
- DActive transport across cell membranes
- EGeneration of nerve impulses
24.Which of the following processes would release the most energy in a cell from one molecule of glucose?
Easy
- AAerobic respiration in yeast
- BAerobic respiration in animals
- CAerobic respiration in plants
- DAll of the above release the same amount of energy
25.Four metabolic reactions are shown: 1. C6H12O6 + 6O2 → 6CO2 + 6H2O, 2. glucose → lactic acid, 3. 6CO2 + 6H2O → C6H12O6 + 6O2, 4. glucose → ethanol + carbon dioxide. Which reactions take place in yeast cells to release energy?
Medium
- A1 and 2
- B1 and 3
- C3 and 4
- D1 and 4
26.The graph below shows the effect of temperature on the rate of respiration in yeast. Which statement best explains the decrease in rate above 40°C?
Medium
- AThe yeast cells die at high temperatures
- BThe enzymes involved in respiration denature
- CThe glucose is used up more quickly
- DOxygen becomes less soluble in water
27.In an experiment to investigate the effect of temperature on respiration rate in yeast, which of the following should be kept constant?
Medium
- ATime taken for colour change
- BTemperature of water bath
- CConcentration of yeast suspension
- DNumber of bubbles produced
28.Anaerobic respiration in yeast produces carbon dioxide and ethanol.
Easy
True or false?
29.Respiration is a chemical process that involves the breakdown of nutrient molecules to release energy.
Easy
True or false?
30.During vigorous exercise, lactic acid builds up in muscles. How is this lactic acid removed during recovery?
Medium
- AIt is excreted by the kidneys
- BIt is converted back to glucose in the muscles
- CIt is transported to the liver and oxidised
- DIt is broken down by anaerobic respiration
31.In an experiment to investigate the effect of temperature on respiration in yeast, methylene blue indicator is used. What does a faster colour change from blue to colourless indicate?
Medium
- AA slower rate of respiration
- BA faster rate of respiration
- CNo respiration occurring
- DAnaerobic respiration only
32.Match each organism to the correct product(s) of anaerobic respiration.
Medium
- Humans (muscle cells)
- Yeast
- Ethanol and carbon dioxide
- Lactic acid
33.Complete the sentence.
Easy
Respiration is a ____ process that involves the breakdown of nutrient molecules to release energy.
34.In the balanced equation for aerobic respiration, how many molecules of oxygen are required to react with one molecule of glucose?
Easy
35.State one reason why anaerobic respiration releases less energy than aerobic respiration.
Medium
36.Complete the sentence about anaerobic respiration in humans.
Easy
During vigorous exercise, glucose is broken down without oxygen to produce ____ and a small amount of energy.
37.Complete the sentence about the effect of temperature on respiration.
Medium
As temperature increases up to the optimum, the rate of respiration ____ because molecules have more kinetic energy and collide more frequently.
38.In an experiment to investigate the effect of temperature on respiration in yeast, methylene blue indicator is used. At 20°C, the dye took 120 seconds to turn colourless. At 35°C, it took 40 seconds. How many times faster is the rate of respiration at 35°C compared to 20°C?
Medium
39.Complete the sentence about aerobic respiration.
Easy
Aerobic respiration uses ____ to break down ____ completely, releasing energy, carbon dioxide and ____.
40.State the word equation for anaerobic respiration in yeast.
Easy
41.In the balanced equation for aerobic respiration, C6H12O6 + 6O2 → 6CO2 + 6H2O, how many molecules of carbon dioxide are produced from one molecule of glucose?
Easy
42.State one reason why the rate of respiration in yeast decreases when the temperature rises above 40°C.
Easy
43.Complete the sentence about the effect of temperature on respiration rate.
Easy
As temperature increases up to about ____ °C, the rate of respiration ____ because molecules have more ____ energy and collide more frequently.
44.Explain how the rate of aerobic respiration in yeast can be measured using methylene blue indicator.
Medium
45.Explain why anaerobic respiration releases less energy per glucose molecule than aerobic respiration.
Medium
46.In the balanced equation for aerobic respiration, how many molecules of oxygen are required to react with one molecule of glucose?
Easy
- A8
- B5
- C6
- D7
47.In an experiment to investigate the effect of temperature on respiration in yeast, methylene blue indicator is used. At 20°C, the dye took 120 seconds to turn colourless. At 35°C, it took 40 seconds. How many times faster is the rate of respiration at 35°C compared to 20°C?
Medium
- A2
- B4
- C5
- D3
48.In the balanced equation for aerobic respiration, C6H12O6 + 6O2 → 6CO2 + 6H2O, how many molecules of carbon dioxide are produced from one molecule of glucose?
Easy
- A6
- B8
- C7
- D5

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