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Study Notes: Respiration in Organisms
Key Concept: Cellular Respiration
Cellular respiration is the process of breaking down food (glucose) within the cells of an organism to release energy. Since this process occurs inside the cells of all living beings, it is the fundamental mechanism by which life is sustained.
When the breakdown of glucose occurs with the use of oxygen, it is
called aerobic respiration. This is the most common form of respiration
in higher organisms, resulting in the production of carbon dioxide,
water, and energy.
\( C_6H_{12}O_6 + O_2 \rightarrow CO_2 + H_2O \) + Energy
Glucose (in the absence of oxygen) --> Alcohol + Carbon dioxide + Energy
Glucose (in muscle, in the absence of oxygen) --> Lactic acid + Energy
Muscle Cramps: The partial breakdown of glucose produces lactic acid. The accumulation of lactic acid in the muscle tissues causes cramps.
Relief and Synthesis: Relief from cramps is achieved through a hot water bath or a massage.
These treatments improve blood circulation, which increases the supply of oxygen to the muscle cells. This increased oxygen results in the complete breakdown of lactic acid into carbon dioxide and water, thereby eliminating the cause of the cramp.
The Pathway of Air:
- Air is taken in through the nostrils.
- It enters the nasal cavity, where it is filtered.
- The air passes through the pharynx and travels down the trachea (commonly known as the windpipe).
- Finally, it reaches the lungs, which are located in the chest cavity. The lungs are surrounded by ribs on the sides, and a large muscular sheet called the diaphragm forms the floor of the chest cavity.
| Feature | Inhalation | Exhalation |
|---|---|---|
| Ribs | Move up and outwards | Move down and inwards |
| Diaphragm | Moves down (contracts) | Moves up to its former position |
| Chest Cavity Volume | Increases | Decreases |
| Air Pressure & Flow | Volume increase leads to a decrease in air pressure; air rushes into the lungs. | Volume decrease leads to an increase in air pressure; air is pushed out of the lungs. |
- Average Adult at Rest: 15–18 breaths per minute.
- During Heavy Exercise: The rate can increase up to 25 breaths per minute as the body works to supply more oxygen to speed up the breakdown of food for energy.
| Gas | Inhaled Air | Exhaled Air |
|---|---|---|
| Oxygen | 21% | 16.4% |
| Carbon Dioxide | 0.04% | 4.4% |
Cockroaches: Insects have small openings on the sides of their bodies called spiracles. These openings lead to a network of air tubes called tracheae. Oxygen enters through the spiracles, travels through the tracheae, and diffuses directly into the body tissues. Carbon dioxide follows the same path in reverse.
Earthworms: Earthworms breathe through their skin. The skin is moist and slimy to the touch, allowing gases to pass through it easily.
Frogs: Frogs are unique in their dual breathing capability. Like humans, they possess a pair of lungs for breathing on land, but they can also perform gas exchange through their skin , which is kept moist and slippery.
Fish: Fish utilize gills for respiration. Gills are projections of the skin that are richly supplied with blood vessels. They allow the fish to absorb oxygen that is dissolved in the water.
In the leaves, gas exchange occurs through tiny pores called stomata. Below the ground, root cells also require oxygen to generate energy. They absorb air from the small air spaces present between soil particles. A critical concern for plant health is overwatering; if a potted plant is overwatered, the air spaces in the soil are filled with water, preventing the roots from taking in the oxygen they need to respire.
Glossary of Key Terms
Tracheae: A network of air tubes in insects used for gas exchange.
Spiracles: Small openings on the sides of an insect's body through which air enters.
Gills: Respiratory organs in fish that facilitate the exchange of gases dissolved in water.
Stomata: Microscopic pores on the surface of plant leaves used for gas exchange.
Health Note:
Pranayama: Regular practice of traditional breathing exercises (Pranayama) can increase the capacity of the lungs to take in more air. This provides more oxygen to the body's cells, leading to increased energy release and better overall health.
Aerobic and anaerobic respiration differ primarily in their requirement for oxygen and the end products they produce during the breakdown of glucose.
Aerobic Respiration
- Oxygen Requirement: This process occurs with the use of oxygen.
- End Products: The breakdown of glucose results in carbon dioxide, water, and energy.
- Occurrence: It takes place in the cells of almost all organisms for their survival.
-
Equation:
\( \text{Glucose} \xrightarrow{\text{in the presence of oxygen}} \) \( \text{carbon dioxide} + \text{water} + \text{energy} \).
Anaerobic Respiration
- Oxygen Requirement: This process occurs without using oxygen.
-
End Products: The products vary depending on the organism:
In Yeast: These organisms (called anaerobes) break down glucose into alcohol, carbon dioxide, and energy.
In Human Muscle Cells: During heavy exercise when oxygen is insufficient, glucose undergoes partial breakdown to produce lactic acid and energy.
-
Equations:
Yeast: \( \text{Glucose} \xrightarrow{\text{in the absence of oxygen}} \) \( \text{alcohol} + \text{carbon dioxide} + \text{energy} \).
Muscle Cells: \( \text{Glucose} \xrightarrow{\text{in the absence of oxygen}} \) \( \text{lactic acid} + \text{energy} \).
Key Differences at a Glance
| Feature | Aerobic Respiration | Anaerobic Respiration |
|---|---|---|
| Oxygen | Used. | Not used. |
| Breakdown of Glucose | Complete breakdown into \( CO_2 \) and water. | Partial breakdown (in muscles) or produces alcohol (in yeast). |
| By-products | Carbon dioxide and water. | Alcohol and \( CO_2 \) (yeast) OR Lactic acid (muscles). |
| Energy Release | Releases energy. | Releases energy, but often associated with muscle cramps in humans due to lactic acid accumulation. |
How does lactic acid accumulation cause muscle cramps during exercise?
Muscle cramps occur during heavy exercise—such as fast running, cycling, or heavy weight lifting—due to a temporary deficiency of oxygen in the muscle cells. While the demand for energy during these activities is high, the supply of oxygen required to produce that energy is limited.
To fulfill this high energy demand, muscle cells switch to anaerobic respiration, which breaks down glucose without using oxygen. This process involves a partial breakdown of glucose, resulting in the production of lactic acid and energy. The chemical process can be represented as:
\( \text{Glucose (in muscle)} \xrightarrow{\text{in the absence of oxygen}} \) \( \text{lactic acid} + \text{energy} \)
The accumulation of this lactic acid in the muscle tissues is what causes the painful sensation of a cramp.
You can get relief from these cramps through a hot water bath or a massage. These methods improve blood circulation, which increases the supply of oxygen to the muscle cells. This additional oxygen then allows the accumulated lactic acid to be completely broken down into carbon dioxide and water, resolving the cramp.
How do yeast cells differ from humans during anaerobic respiration?
Yeast cells and humans differ significantly in how they perform anaerobic respiration, both in terms of the duration of the process and the end products produced.
1. Nature and Duration of the Process
- Yeast: These are single-celled organisms known as anaerobes because they can survive in the absence of air. They regularly get their energy through anaerobic respiration.
- Humans: In humans, anaerobic respiration occurs only for a short time in muscle cells. This happens when there is a temporary deficiency of oxygen, such as during heavy exercise like fast running, cycling, or weight lifting, where the demand for energy is higher than the oxygen supply.
2. End Products
The chemical breakdown of glucose results in different by-products:
-
Yeast: The breakdown of glucose in the absence of oxygen produces alcohol and carbon dioxide, along with energy.
Equation: \( \text{Glucose} \xrightarrow{\text{in the absence of oxygen}} \) \( \text{alcohol} + \text{carbon dioxide} + \text{energy} \).
-
Humans (Muscle Cells): The partial breakdown of glucose in human muscles produces lactic acid and energy, but not carbon dioxide.>/p>
Equation: \( \text{Glucose} \xrightarrow{\text{in the absence of oxygen}} \) \( \text{lactic acid} + \text{energy} \).
3. Consequences and Uses
- Yeast: Because they produce alcohol, yeast cells are used commercially to make wine and beer.
- Humans: The production of lactic acid in humans is associated with muscle cramps. Relief from these cramps is typically found through a hot water bath or massage, which improves oxygen supply and helps break down the lactic acid into carbon dioxide and water.
MCQs on Respiration in Organisms
1. The process of breakdown of food in the cell with the release of
energy is called:
(a) External respiration
(b) Cellular respiration
(c)
Inhalation
(d) Exhalation
Answer: (b) Cellular respiration
2. Yeast is used in the wine and beer industry because it respires
anaerobically to produce:
(a) Lactic acid
(b) Water
(c) Alcohol
(d) Oxygen
Answer: (c) Alcohol
3. During heavy exercise, we get cramps in the legs due to the
accumulation of:
(a) Carbon dioxide
(b) Alcohol
(c) Water
(d) Lactic
acid
Answer: (d) Lactic acid
4. What is the normal range of the breathing rate per minute for an
average adult person at rest?
(a) 9–12
(b) 21–24
(c) 15–18
(d) 30–33
Answer: (c) 15–18
5. During inhalation, the movement of the ribs and diaphragm is as
follows:
(a) Ribs move down and inwards; diaphragm moves up.
(b) Ribs move up
and outwards; diaphragm moves down.
(c) Ribs move up and outwards;
diaphragm moves up.
(d) Ribs move down and inwards; diaphragm moves
down.
Answer: (b) Ribs move up and outwards; diaphragm moves down
6. In cockroaches, air enters the body through small openings on the
sides of the body called:
(a) Gills
(b) Spiracles
(c) Lungs
(d) Tracheae
Answer: (b) Spiracles
7. Earthworms breathe through their:
(a) Lungs
(b) Gills
(c) Moist skin
(d) Spiracles
Answer: (c) Moist skin
8. Fish utilize oxygen dissolved in water for respiration through
special structures called:
(a) Tracheae
(b) Stomata
(c) Gills
(d) Spiracles
Answer: (c) Gills
9. Plants exchange gases (oxygen and carbon dioxide) through tiny pores
in their leaves called:
(a) Spiracles
(b) Stomata
(c) Tracheae
(d) Root hairs
Answer: (b) Stomata
10. What is the approximate percentage of carbon dioxide in the air we
exhale?
(a) 0.04%
(b) 21%
(c) 16.4%
(d) 4.4%
Answer: (d) 4.4%
NCERT Exercise Questions:
1. Why does an athlete breathe faster and deeper than usual after finishing the race?
During a race, the demand for energy is high, but the supply of oxygen to produce that energy is limited. To meet this demand, muscle cells perform anaerobic respiration, which results in the partial breakdown of glucose and the accumulation of lactic acid. After the race, the athlete breathes faster and deeper to take in extra oxygen, which helps completely break down the accumulated lactic acid into carbon dioxide and water.
2. List the similarities and differences between aerobic and anaerobic respiration.
- Similarities: Both are forms of cellular respiration where food (glucose) is broken down within the cells to release energy.
- Differences: Aerobic respiration occurs in the presence of oxygen and completely breaks down glucose into carbon dioxide and water. Anaerobic respiration occurs in the absence of oxygen; in yeast, it produces alcohol and carbon dioxide, while in human muscles, it produces lactic acid.
3. Why do we often sneeze when we inhale a lot of dust-laden air?
The air contains unwanted particles like dust and pollen. While many are trapped by hair in the nasal cavity, some pass through and irritate the lining of the cavity. Sneezing is a reflex that expels these foreign particles, ensuring that only clean air enters the lungs.
4. Take three test-tubes. Fill ¾th of each with water. Label them A, B and C. Keep a snail in test-tube A, a water plant in test-tube B and in C, keep snail and plant both. Which test-tube would have the highest concentration of \( CO_2 \)?
Test-tube A would have the highest concentration of \( CO_2 \). The snail in Tube A only performs respiration, releasing \( CO_2 \). In Tube B, the plant releases \( CO_2 \) during respiration but consumes it during photosynthesis. In Tube C, the plant utilizes some of the \( CO_2 \) released by the snail for photosynthesis, keeping the overall concentration lower than in Tube A.
Objective Questions
5. Tick the correct answer:
- (a) In cockroaches, air enters the body through: (iii) spiracles.
- (b) During heavy exercise, we get cramps in the legs due to the accumulation of: (ii) lactic acid.
- (c) Normal range of breathing rate per minute in an average adult person at rest is: (ii) 15–18.
- (d) During exhalation, the ribs: (ii) move downwards (and inwards).
6. Match the items in Column I with those in Column II:
| Column I | Column II |
|---|---|
| (a) Yeast | (iii) Alcohol |
| (b) Diaphragm | (iv) Chest cavity |
| (c) Skin | (i) Earthworm |
| (d) Leaves | (v) Stomata |
| (e) Fish | (ii) Gills |
| (f) Frog | (vi) Lungs and skin |
7. True (T) or False (F):
- (i) During heavy exercise the breathing rate of a person slows down. (F) — It increases up to 25 times per minute.
- (ii) Plants carry out photosynthesis only during the day and respiration only at night. (F) — Respiration is a continuous process vital for survival.
- (iii) Frogs breathe through their skins as well as their lungs. (T).
- (iv) The fishes have lungs for respiration. (F) — They use gills.
- (v) The size of the chest cavity increases during inhalation. (T).
Word Clues (from the puzzle grid)
8. Identify the terms based on the clues:
- (i) The air tubes of insects: Tracheae.
- (ii) Skeletal structures surrounding chest cavity: Ribs.
- (iii) Muscular floor of chest cavity: Diaphragm.
- (iv) Tiny pores on the surface of leaf: Stomata.
- (v) Small openings on the sides of the body of an insect: Spiracles.
- (vi) The respiratory organs of human beings: Lungs.
- (vii) The openings through which we inhale: Nostrils.
- (viii) An anaerobic organism: Yeast.
- (ix) An organism with tracheal system: Cockroach.
9. The mountaineers carry oxygen with them because: (b) The amount of air available to a person is less than that available on the ground.
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