Respiration In Plants And Animals
Energy is the basic
requirement of all living organisms. It is required for the ongoing life
processes inside the body and for the activities performed by an organism.
Energy is obtained from the food consumed. Respiration is the process through
which energy from food is released for use by the body.
Respiration can be
defined as Inhalation of oxygen and exhalation of carbon dioxide coupled with
the chemical reactions that release energy from digested food.
BREATHING AND RESPIRATION
Respiration is a process
which releases usable energy. It occurs in all living cells. Respiration is a
form of combustion in which food is burned in the presence of oxygen to release
energy. But there is a difference between combustion and respiration. During
combustion, energy is released rapidly, whereas during respiration, energy is
released in a gradual step-wise manner. This ensures that at each step, energy
can be stored in different forms to be used by the body. Respiration involves
two basic processes:
Breathing: The process of exchange
of gases i.e., inhalation or intake of oxygen and exhalation or release of
carbon dioxide is called breathing. Such type of respiration is called external
respiration.
Different plants and
animals have different organs for exchange of gases. Humans and some other
animals breathe through special organs of respiration called the lungs. Cellular
respiration takes place inside the cell
The amount of inhaled air
contains 21% of oxygen and 0.04% of carbon dioxide, while the air we breathe
out contains 16.4% of oxygen and 4.4% of carbon dioxide.
Cellular respiration: This
involves a series of chemical reactions which take place in the body cells.
Inhaled oxygen helps in the oxidation of digested food to release energy and
heat. This type of respiration occurs in all living organisms ranging from very
simple organisms like bacteria to very complex organisms like humans. Such type
of respiration is also called internal respiration.
Differences
between breathing and respiration
Breathing
1. It is a physical
process in which oxygen is taken in and carbon dioxide is given out.
2. It occurs outside the
cells.
3. There is no release of
energy.
Respiration
1. It is a biochemical
process in which glucose from the food is oxidised to carbon dioxide and water
2. It occurs inside the
cells.
3. There is a gradual and
step-wise release of energ
RESPIRATION
IN PLANTS
During the day, plants
use carbon dioxide to prepare food and release oxygen. However, respiration in
plants takes place during the day as well as at night. They use oxygen to
oxidize food to produce energy and release carbon dioxide during respiration.
Plants do not have any
special respiratory organs but different plants have different parts
participating in the process of respiration.
Exchange of carbon
dioxide and oxygen in plants occurs through the process of diffusion through
small openings in leaves and stems.
Carbon dioxide-rich air
from various parts of the plant diffuses out and oxygen-rich air from outside
diffuses into the plant. Rate of gaseous exchange in plants is much slower than
in animals.
Diffusion is the movement
of gases from a region of higher concentration to a region of lower
concentration.
Stomatal
apparatus
There are a number of
small openings in the soft aerial parts (stems and leaves) of a plant for
gaseous exchange. These pores are called stomata (singular: stoma) in leaves
and lenticles in stems. The stoma, guard cells and other nearby cells together
form the stomatal apparatus.
1. Stomata are small
openings for the gaseous exchange through which oxygen is absorbed and carbon
dioxide is given out during respiration.
2. Two guard cells
control the opening and closing of stomata. They expand and shrink depending on
the flow of water from the surrounding cells.
3. Several subsidiary
cells support the structure and function of the stomatal apparatus.
Oxygen is supplied to
cells in the roots of plants through the process of root respiration. Root
cells get oxygen from the air trapped between the soil particles. This is why
if a plant is over watered, root cells cannot get air and are not able to breathe.
In air, oxygen content is
21% whereas in water, it is 0.5% at 37°C.
RESPIRATION
IN ANIMALS
Animals take oxygen
either from water or air depending on their habitat.
Unicellular and small multicellular animals
Unicellular organisms
include all protozoa and bacteria. Each cell respires independently and carries
out exchange of gases individually. Simple multicellular organisms, like
sponges and hydra, also show respiration at the level of each cell. Water flows
through the body of sponges and hydra, allowing gaseous exchange by each cell
of the cell membrane.
Higher multicellular animals
Higher and complex
multicellular organisms have specialized and advanced organs of respiration.
Skin: Animals like earthworms, leeches and
some amphibians breathe through their skin. The skin of these animals is smooth
and remains moist.
The skin is supplied
richly with blood vessels so that it can carry oxygen to the rest of the body
and bring carbon dioxide from the body parts and release it.
Gills: Gills are special respiratory organs
which facilitate breathing in aquatic animals, like fish, prawns and mussels
The gills have a large number of filaments that are richly supplied with blood
capillaries. They help gills release carbon dioxide into the water. They also
help fish take in oxygen dissolved in water.
Spiracles and trachea:
Insects like grasshoppers, mosquitoes, etc. respire through very fine air holes
on their bodies called spiracles. Air enters through the spiracles and is
distributed all over the body by tracheal tubes. Trachea are branched
respiratory tubes which open on the surface of the body. Oxygen-rich air enters
the trachea through these openings and reaches internal body parts. Here,
oxygen is used up and carbon dioxide-rich air is released from the spiracles.
This tubular air passage system helps in the gaseous exchange in small animals.
Lungs: Lungs are specialised organs of
respiration in higher animals like birds and mammals.
Gills present in tadpoles
are replaced by a pair of lungs as they grow into frogs. Frogs also respire
through their skin and buccal cavity.
RESPIRATION
IN HUMANS
The various organs that
function together in the human body for the exchange of gases constitute the
human respiratory system. The organs of the human respiratory system include:
1. Nasal cavity: Air enters the body
through nostrils in the nose. The hair follicles present inside the nostrils
trap dust and help filter the inhaled air. The mucus in the nasal cavity
moistens the air and fine blood vessels in the nasal cavity warm up the air.
2. Pharynx: It is the common passage
that opens both into the oesophagus (food pipe) and the trachea (wind pipe).
3. Glottis and epiglottis:
The opening of the pharynx into the trachea is called glottis. The glottis is
guarded by a flap-like structure called epiglottis which prevents the entry of
food into trachea. The epiglottis closes when food is swallowed.
4. Larynx: The uppermost part of
trachea is the larynx. It is a sound producing organ and is also known as the
voice box. In males, it tends to protrude and is known as Adam's apple.
5. Trachea: It is the wind pipe
which allows air to pass into lungs. The trachea is supported by a number of
C-shaped cartilaginous rings which prevent it from collapsing when there is no
air inside. The inner lining of the trachea has mucus which traps very fine
dust particles present in the air. The inner lining also has fine hair-like
structures called cilia which help to push the dust trapped by the mucus back
into the pharynx.
6. Bronchi and bronchioles: Trachea
in the chest region divides into two tubes called bronchi (singular: bronchus),
which enter into the lungs. Each bronchus after entering its respective lung
further divides into finer branches called bronchioles, which end in air sacs.
The air sacs are made up of very small, thin-walled structures called alveoli.
The alveoli, which look like bunches of grapes, are surrounded by a network of
very fine blood capillaries. They help in the exchange of oxygen and carbon
dioxide.
7. Lungs: In humans, there are two
elastic balloon-like structures located in the thoracic cavity inside the chest
called lungs. Each lung has millions of alveoli.
The supporting bones and
muscles of the respiratory system that help in the efficient working of the
respiratory system are:
8. Rib cage: This is a bony chamber in
our chest which protects the soft lungs.
9. Muscles of the rib cage:
These muscles help in the upward and downward movement of rib cage, and
contraction and relaxation of lungs, thereby facilitating movement of air in
and out of the lungs.
10. Diaphragm: In mammals, the lungs
rest on a strong dome-shaped muscle called the diaphragm. This also facilitates
the movement of air by expansion and contraction.
BREATHING
Observe the rhythmic up
and down movement of the set of bones in your chest when you take deep breaths.
These are the bones of the rib cage which help in the movement of air in ar out
of the lungs. Rib cage muscles and the diaphragm work together to bring about
the following effects:
Inhalation (inspiration)
During inhalation the rib
cage moves upward and outward and the diaphragm contracts and moves downwards,
more space is created inside the chest cavity. Lungs exparc and we inhale
oxygen-rich air.
Exhalation (expiration)
During exhalation the rib
cage moves downward and inward and the diaphragm relaxes and moves upwards,
space in the chest cavity reduces. This pushes out the carbor dioxide rich air
from our lungs.
Extra Knowledge- Breathing
is controlled by the brain's respiratory centre. The respiratory centre
regulates the rhythmic, alternating cycles of inspiration and expiration.
Breathing rate: The
number of breaths per minute is called breathing rate. One breath includes one
inhalation and one exhalation. Breathing rate for an adult in resting position
is 15 to 18 times.
The amount of air
breathed in or out in one breath during normal respiration is known as tidal
volume. It is around 500 ml for an adult human being. Tidal volume is lower
during rest and sleep and high during exercise.
CELLULAR
RESPIRATION
Site of cellular
respiration
Cellular respiration
occurs in all living cells in their mitochondria (singular: mitochondrion). A
mitochondrion is a sac-like structure in a cell. It is called the powerhouse of
the cell because it is the site of respiration and release of energy.
Types of respiration
During cellular
respiration, glucose is broken down chemically to release energy contained in
it. Depending on the presence and absence of oxygen, cellular respiration may
be:
1. Aerobic respiration: When
cellular respiration takes place in the presence of oxygen, it is called
aerobic respiration. The end products formed during aerobic respiration are
water, carbon dioxide and energy. It can be summarised in the following
chemical equation: Glucose + Oxygen →
Carbon dioxide + Water + Energy
2.Anaerobic respiration: When
respiration takes place in the absence of oxygen, it is called anaerobic
respiration. During anaerobic respiration, lesser energy is released as
compared to aerobic respiration, and different end products are formed:
(a) In lower organisms
like yeast, in the absence of oxygen, glucose breaks down into ethyl alcohol,
carbon dioxide, and a little energy. This process is called fermentation.
Glucose in absence of Oxygen
alcohol + Carbon dioxide + Energy
(b) During strenuous
exercise like long distance running, our body is not able to get enough oxygen.
Hence, anaerobic respiration takes place in our muscle cells, resulting in the
production of lactic acid. This is due to the partial breakdown of glucose in
the body. The accumulation of lactic acid causes muscular cramps. We get relief
from these cramps by taking hot water bath or massage. This improves the blood
circulation in the body leading to increased supply of oxygen. On getting
sufficient oxygen, the complete breakdown of lactic acid into carbon dioxide
and water occurs and you get relief from cramps.
Anaerobes are those
organisms that can survive in the absence of oxygen.
Circulation
of gases in the human body
Oxygen reaches the lungs
through inhaled air and is carried by the blood to all other parts of the body.
Carbon dioxide, the waste product of respiration, is taken back to the lungs
through blood. When blood carrying carbon dioxide reaches the lungs, exchange of
gases takes place. The carbon dioxide in the lungs gets expelled out, via the
bronchi and trachea, through the nose or mouth.
NEW TERMS
- Cellular respiration: Series of chemical reactions involved in the release of energy from digested food.
- Diffusion: Movement of gas molecules from the area of higher concentration to the area of lower concentration.
- Diaphragm: A muscular sheet forming the floor of chest cavity.
- Aerobic respiration: Cellular respiration which takes place in the presence of oxygen.
- Anaerobic respiration: Cellular respiration which takes place in the absence of oxygen.
- Spiracles: Air holes through which exchange of gas takes place in some insects.
- Trachea: Wind pipe that allows air to pass into lungs/system of tubes in the body of insects for exchange of gases.
- Pharynx: Common passage that opens both into the food pipe and the wind pipe.
- Glottis: Opening of the pharynx into the trachea.
- Epiglottis: Flap-like structure in the glottis that prevents the entry of food into the trachea.
- Alveoli: Very small, thin-walled structures found in the lungs that help in the exchange of oxygen and
- Stomata: Pores in the leaves of plants for gaseous exchange.
- Inspiration: Process of inhalation of oxygen-rich air.
- Expiration: Process by which air is exhaled.
Respiration in Plants and Animals – MCQs
1. Why is energy essential for living
organisms?
A. For growth only
B. For reproduction only
C. For life processes and activities
D. For movement only
Answer: C
Explanation: Energy is needed for all life processes and daily
activities.
2. Energy is obtained by organisms from:
A. Air
B. Water
C. Sunlight
D. Food
Answer: D
Explanation: Food provides energy during respiration.
3. Respiration is the process of:
A. Making food
B. Releasing energy from food
C. Absorbing nutrients
D. Excreting waste
Answer: B
Explanation: Respiration releases energy stored in food.
4. Which gas is inhaled during breathing?
A. Nitrogen
B. Oxygen
C. Carbon dioxide
D. Hydrogen
Answer: B
Explanation: Oxygen is required for respiration.
5. Respiration occurs in:
A. Only animals
B. Only plants
C. Only humans
D. All living cells
Answer: D
Explanation: Respiration is universal to all living cells.
6. Breathing is a process of:
A. Digestion
B. Energy release
C. Gas exchange
D. Circulation
Answer: C
Explanation: Breathing involves inhalation and exhalation of gases.
7. Breathing is also known as:
A. Internal respiration
B. Cellular respiration
C. External respiration
D. Anaerobic respiration
Answer: C
Explanation: Breathing involves exchange of gases with environment.
8. Oxygen percentage in inhaled air is:
A. 4.4%
B. 16.4%
C. 21%
D. 0.04%
Answer: C
Explanation: Atmospheric air contains 21% oxygen.
9. Which gas is released during
respiration?
A. Oxygen
B. Hydrogen
C. Carbon dioxide
D. Nitrogen
Answer: C
Explanation: Carbon dioxide is the waste gas of respiration.
10. Cellular respiration takes place:
A. Outside the body
B. In lungs
C. Inside cells
D. In blood
Answer: C
Explanation: Cellular respiration occurs inside body cells.
11. Cellular respiration is also called:
A. External respiration
B. Internal respiration
C. Breathing
D. Diffusion
Answer: B
Explanation: It occurs inside cells.
12. Which process releases energy?
A. Breathing
B. Diffusion
C. Respiration
D. Photosynthesis
Answer: C
Explanation: Respiration releases usable energy.
13. Which is a physical process?
A. Respiration
B. Breathing
C. Oxidation
D. Fermentation
Answer: B
Explanation: Breathing is a physical process.
14. Plants respire:
A. Only during day
B. Only at night
C. Both day and night
D. Only during photosynthesis
Answer: C
Explanation: Respiration occurs continuously.
15. Plants exchange gases mainly through:
A. Roots
B. Flowers
C. Stomata and lenticles
D. Fruits
Answer: C
Explanation: Stomata and lenticles help in gaseous exchange.
16. Diffusion means movement from:
A. Low to high concentration
B. High to low concentration
C. Roots to leaves
D. Leaves to roots
Answer: B
Explanation: Diffusion follows concentration gradient.
17. Guard cells regulate:
A. Photosynthesis
B. Transpiration only
C. Opening of stomata
D. Root pressure
Answer: C
Explanation: Guard cells control stomatal opening.
18. Overwatering plants affects
respiration because:
A. Roots get more oxygen
B. Roots cannot get air
C. Leaves dry
D. Stomata close
Answer: B
Explanation: Air spaces in soil get filled with water.
19. Unicellular organisms respire through:
A. Lungs
B. Gills
C. Skin
D. Cell membrane
Answer: D
Explanation: Each cell exchanges gases directly.
20. Earthworms breathe through:
A. Lungs
B. Gills
C. Skin
D. Spiracles
Answer: C
Explanation: Moist skin allows gas exchange.
21. Oxygen for root respiration comes
from:
A. Water
B. Leaves
C. Air in soil
D. Stem
Answer: C
Explanation: Roots use air trapped between soil particles.
22. Gills are found in:
A. Birds
B. Fish
C. Earthworms
D. Humans
Answer: B
Explanation: Fish respire through gills.
23. Spiracles are respiratory openings in:
A. Fish
B. Amphibians
C. Insects
D. Mammals
Answer: C
Explanation: Insects respire through spiracles.
24. Tracheal system is found in:
A. Frogs
B. Fish
C. Insects
D. Birds
Answer: C
Explanation: Tracheae distribute air in insects.
25. Tadpoles respire using:
A. Lungs
B. Skin
C. Gills
D. Trachea
Answer: C
Explanation: Tadpoles are aquatic.
26. Epiglottis prevents food from
entering:
A. Pharynx
B. Larynx
C. Trachea
D. Oesophagus
Answer: C
Explanation: It closes trachea during swallowing.
27. Adam’s apple is formed by:
A. Trachea
B. Larynx
C. Pharynx
D. Bronchus
Answer: B
Explanation: Larynx protrudes in males.
28. C-shaped rings prevent collapse of:
A. Bronchi
B. Alveoli
C. Trachea
D. Lungs
Answer: C
Explanation: Cartilage supports trachea.
29. Exchange of gases occurs in lungs at:
A. Bronchi
B. Bronchioles
C. Alveoli
D. Trachea
Answer: C
Explanation: Alveoli have thin walls and capillaries.
30. Alveoli are surrounded by:
A. Nerves
B. Cartilage
C. Blood capillaries
D. Muscles
Answer: C
Explanation: Capillaries help exchange gases.
31. Lungs are protected by:
A. Skull
B. Vertebral column
C. Rib cage
D. Pelvis
Answer: C
Explanation: Rib cage protects lungs.
32. Diaphragm is a:
A. Bone
B. Cartilage
C. Muscle
D. Gland
Answer: C
Explanation: It helps in breathing movements.
33. During inhalation, diaphragm:
A. Relaxes and moves up
B. Contracts and moves down
C. Remains still
D. Moves sideways
Answer: B
Explanation: This increases chest cavity volume.
34. During exhalation, rib cage moves:
A. Upward
B. Outward
C. Downward and inward
D. Sideways
Answer: C
Explanation: Chest cavity size decreases.
35. Normal breathing rate of an adult is:
A. 5–10
B. 10–12
C. 15–18
D. 25–30
Answer: C
Explanation: Normal resting rate.
36. Tidal volume refers to:
A. Total lung capacity
B. Air exchanged per breath
C. Oxygen absorbed per day
D. CO₂ released
Answer: B
Explanation: About 500 ml per breath.
37. Site of cellular respiration is:
A. Nucleus
B. Ribosome
C. Mitochondria
D. Cytoplasm
Answer: C
Explanation: Mitochondria release energy.
38. Mitochondria are called powerhouse
because they:
A. Store DNA
B. Produce proteins
C. Release energy
D. Control cell
Answer: C
Explanation: Energy production occurs here.
39. Aerobic respiration requires:
A. Nitrogen
B. Carbon dioxide
C. Oxygen
D. Hydrogen
Answer: C
Explanation: Oxygen is essential.
40. End products of aerobic respiration
are:
A. Alcohol and CO₂
B. Lactic acid
C. CO₂, water and energy
D. Energy only
Answer: C
Explanation: Complete oxidation of glucose.
41. Anaerobic respiration releases:
A. More energy
B. Equal energy
C. Less energy
D. No energy
Answer: C
Explanation: Incomplete breakdown releases less energy.
42. Fermentation is anaerobic respiration
in:
A. Plants
B. Animals
C. Yeast
D. Humans
Answer: C
Explanation: Yeast produces alcohol.
43. Lactic acid is formed during:
A. Normal breathing
B. Sleeping
C. Strenuous exercise
D. Rest
Answer: C
Explanation: Due to lack of oxygen in muscles.
44. Muscle cramps occur due to
accumulation of:
A. Glucose
B. Oxygen
C. Lactic acid
D. CO₂
Answer: C
Explanation: Lactic acid causes cramps.
45. Hot water bath relieves cramps because
it:
A. Reduces glucose
B. Improves blood flow
C. Stops respiration
D. Removes sweat
Answer: B
Explanation: Improves oxygen supply.
46. Anaerobes are organisms that:
A. Need oxygen
B. Die without oxygen
C. Survive without oxygen
D. Live only in water
Answer: C
Explanation: They respire anaerobically.
47. Oxygen is transported in blood mainly
by:
A. Plasma
B. RBCs
C. WBCs
D. Platelets
Answer: B
Explanation: Haemoglobin carries oxygen.
48. Carbon dioxide is transported to lungs
by:
A. Nerves
B. Muscles
C. Blood
D. Lymph
Answer: C
Explanation: Blood carries CO₂
back to lungs.
49. Respiratory centre is located in:
A. Heart
B. Lungs
C. Brain
D. Spinal cord
Answer: C
Explanation: Brain controls breathing rhythm.
50. Increase in breathing rate during
exercise is due to:
A. Less oxygen demand
B. More CO₂
production
C. Less energy need
D. Reduced respiration
Answer: B
Explanation: Body needs more oxygen and removes more CO₂.
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