Selina Concise Solutions for ICSE Class 7 Biology Chapter 4 Photosynthesis and Respiration

Synopsis -

• The process of preparing or synthesising food using water from the soil and carbon dioxide from the air, together chlorophyll and sunlight is called photosynthesis.
• Photosynthesis occurs in the mesophyll cells of the leaf. These cells contain numerous plastids called chloroplasts.
• With in the plastids is present the green pigment called chlorophyll.
• On the lower surface of the leaf are numerous pores called stomata, which open into small air cavities inside the leaf.
• Stomata are tiny openings found mainly on the lower surface of leaves. These openings are surrounded by a pair of bean-shaped cells called guard cells.
• All plants have a transport system called vascular system. It is composed of two types of tissues called xylem and phloem.
• There are two end-products of photosynthesis :
  Glucose (C₆H₁₂O₆)
  Oxygen
• The energy released during respiration is stored as chemical energy in the form of ATP - adenosine tri-phosphate.
• Aerobic respiration -
  C₆H₁₂O₆ + 6O₂
  6CO₂ + 6H₂O + 38ATP
• Anaerobic respiration -
  C₆H₁₂O₆
  2C₂H₅OH + 2CO₂ + 2ATP
• During vigorous exercise, the cells respire anaerobically and form lactic acid which accumulate in the muscle cells causing fatigue and pain.
• Cellular respiration is called internal respiration which takes place in the cells of living organisms.
• Component | inspired air | expired air
  O₂ | 21% | 16%
  CO₂ | 0.03% | 4%
  N₂ | 79% | 79%
  Water vapours | low | high
• The frog respires through
  1. skinmouth
  2. lining
  3. lungs.
• The respiratory organs of the fish are gills.
• Transpiration is the loss of water in the form of water vapour from the aerial parts of the plant.
• Transpiration occurs through stomata.
• The factors which affect the rate of transpiration are
  1. Sunlight
  2. Temperature
  3. Wind
  4. Humidity
• The significance of transpiration
• Maintain the concentration of the sap inside the plant body.
• Causes cooling effect

Review Questions

Multiple Choice Questions

1. Put a tick (✓ ) against the most appropriate alternative in the following statements.

(i) Carbohydrates are stored by plants in the form of:
(a) Vitamins
(b) Proteins
(c) Fats
(d) Glucose .
Answer: (d) Glucose .
Glucose is the simplest carbohydrate produced by plants to provide energy for growth. While it can be converted to starch for long-term storage, it is the primary form of energy currency within the plant.
Teacher's Tip: Remember "G" for Glucose is the "Goal" of photosynthesis.
Exam Tip: If "Starch" was an option, it would be the more common storage form, but among these, glucose is the correct choice.

(ii) Stomata are present on the surface of:
(a) Leaves
(b) Roots
(c) Stem
(d) Flower petals
Answer: (a) Leaves
Leaves have tiny pores called stomata that allow gases like oxygen and carbon dioxide to enter and exit. These pores are mostly located on the underside to prevent excessive water loss.
Teacher's Tip: Think of stomata as the tiny "windows" of the leaf.
Exam Tip: Mention that stomata are guarded by bean-shaped cells called guard cells for extra detail.

(iii) Which one of the following is an end-product of photosynthesis ?
(a) Fructose
(b) Glucose
(c) Cellulose
(d) Lactose
Answer: (b) Glucose
During photosynthesis, light energy is used to convert raw materials into sugar. This sugar, known as glucose, serves as food for the plant and other living beings.
Teacher's Tip: The equation for photosynthesis always ends with C₆H₁₂O₆, which is glucose.
Exam Tip: Always list both glucose and oxygen if a question asks for "products" in plural.

Short Answer Questions

1: Why do leaves generally look green ?
Answer: The green colour of a leaf is due to the presence of chlorophyll.
Chlorophyll is a pigment found inside chloroplasts that reflects green light while absorbing other colors. This specific pigment is essential for capturing energy from sunlight.
Teacher's Tip: Think "Chlo-RO-phyll" makes the leaf "Grow" (green).
Exam Tip: Underline the keyword 'chlorophyll' to make your answer stand out to the examiner.

2: Which four of the following are needed for photosyn-thesis in a leaf:
(i) Carbon dioxide:
(ii) Oxygen:
(iii) Nitrates :
(iv) Water:
(v) Chlorophyll:
(vi) Soil:
(vii) Light:
Answer: (i) Carbon dioxide: from air
(iv) Water: from soil
(v) Chlorophyll: contained in leaf
(vii) Light: from sunlight
These four components work together in the leaf to synthesize glucose from inorganic matter. Without any one of these, the plant cannot produce its own food.
Teacher's Tip: Remember the phrase "WC LC" - Water, Carbon dioxide, Light, Chlorophyll.
Exam Tip: When listing these, always try to mention their sources as shown in the textbook answer.

3: What is the source of energy for photosynthesis ?
Answer: Light is the ultimate source of energy in photosynthesis because plants take in the sunlight CO₂ and H₂O and converts it into glucose.
Sunlight provides the thermal and light energy required to trigger the chemical reaction in the chloroplasts. This energy is then trapped and stored in the chemical bonds of glucose.
Teacher's Tip: The sun is like the "battery" that powers the plant factory.
Exam Tip: Use the term 'Solar Energy' interchangeably with sunlight for scientific accuracy.

4: Which gas is taken in and which one is given out by the leaf in bright sunlight ?
(i) Taken in :
(ii) Given out:
Answer: (i) Carbon dioxide
(ii) Oxygen
During the day, plants prioritize photosynthesis, which requires CO₂ as a raw material. Oxygen is then released as a gaseous byproduct into the atmosphere.
Teacher's Tip: Plants "inhale" what we "exhale" during the day.
Exam Tip: Be careful! In the dark, this process reverses slightly because only respiration happens.

5: Suppose we compare the leaf with a factory, match the items in Column A with those in Column B.
Column A (LEAF) | Column B (FACTORY)
(i) Cells in the leaf | (a) Raw materials
(ii) Chloroplast | (b) Power
(iii) Sunlight | (c) Machinery
(iv) Oxygen and water | (d) End product
(v) Carbon dioxide and water | (e) By product
(vi) Glucose | (f) Work room
Answer:
Column A (Leaf) | Column B (Factory)
(i) Cells in the leaf | (c) Machinery
(ii) Chloroplast | (f) Work room
(iii) Sunlight | (b) Power
(iv) Oxygen and water | (e) By product
(v) Carbon dioxide and water | (a) Raw materials
(vi) Glucose | (d) End product
This comparison helps us understand how each part of the plant plays a specific role in food production. Just like a factory, every "worker" and "room" must be functional for the final product to be made.
Teacher's Tip: Think of Chloroplasts as the "kitchen" or "work room" where the cooking happens.
Exam Tip: Draw a small table for matching questions to keep your answer sheet organized.

6: State whether the following statements are True or False:

(i) Green plants prepare their food by using two raw materials, oxygen and water.
Answer: False. Green plants prepare their food by using raw materials, CO₂, chlorophyll and water.

(ii) The chlorophyll enables the plants to use light energy.
Answer: True

(iii) The free oxygen in the atmospheric air is the result of photosynthesis.
Answer: True

(iv) Photosynthesis occurs only in chlorophyll-containing parts of the plant.
Answer: True
(As provided above in the text)
These statements cover the basic requirements and outcomes of the photosynthetic process. It is important to remember that CO₂, not oxygen, is the starting gas.
Teacher's Tip: For False statements, always write the correct version to show you understand why it is wrong.
Exam Tip: Read every word carefully; "oxygen" instead of "carbon dioxide" is a common trick in True/False questions.

7: Differentiate between aerobic and anaerobic respiration. Write the overall chemical equations of the two kinds of respiration in plants.
(i) Aerobic:
(ii) Anaerobic:
Answer:
Aerobic respiration
1. It occurs in the presence of oxygen.
2. Here there is complete breakdown of glucose releasing carbon-di-oxide, energy, water and energy.
3. More energy is released (38 ATP).
Anaerobic respiration
1. It occurs in the absence of oxygen.
2. There is partial breakdown of glucose into ethyl alohol, carbon-di-oxide and
3. Lesser energy is released (2 ATP).
(i) Aerobic respiration:
C₆H₁₂O₆ + 6O_2 → 6CO₂ + 6H₂O + 38ATP
(ii) Anaerobic respiration:
C₆H₁₂O_{6   →}{enzymes} 2C₂H₅OH + 2CO₂ + 2ATP
Aerobic respiration is the most efficient way to get energy and is used by most organisms. Anaerobic respiration happens in places like yeast or in our muscles during heavy exercise.
Teacher's Tip: "Aero" means air/oxygen; "An-aero" means without air/oxygen.
Exam Tip: Use a T-chart format when asked to differentiate between two concepts.

Question 8: Explain how photosynthesis is different from respiration.
Answer:
Photosynthesis
1. Anabolic process
2. Food is produced here.
3. Oxygen is by-product.
4. Chlorophyll and sunlight are required.
5. Occur only during daytime.
6. Occurs in green plants only.
Respiration
1. Catabolic process
2. Food is broken down form here to release energy
3. Carbon-di-oxide is the by-product.
4. Chlorophyll and sunlight are notrequired.
5. Occurs all the time
6. Occurs in all living beings including plants.
Equations:
Photosynthesis: 6CO₂ + 12H₂O _→{sunlight}  C6H₁₂O₆ + 6O₂ + 6H₂O
Respiration: C₆H₁₂O₆ + 6O_{2 →} 6CO₂ + 6H₂O + energy
Photosynthesis builds up energy-rich molecules, while respiration breaks them down to release that energy. They are essentially opposite processes that keep life in balance.
Teacher's Tip: Remember "Photosynthesis stores energy, Respiration releases energy."
Exam Tip: Mentioning that respiration occurs "all the time" is a key point often missed by students.

Question 9: Do the plants respire all day and night or only during the night ?
Answer: The plants respire only during the night. Plants take in oxygen and give out carbon dioxide. Hence, there is some truth in the belief that one should not sleep under the trees at night.
Respiration is the process of breaking down food for energy, which actually occurs continuously in all living cells. However, during the day, the CO₂ produced by respiration is used up by photosynthesis, so we only "notice" the CO₂ output at night.
Teacher's Tip: Think of it this way: Living things must breathe (respire) as long as they are alive, day or night!
Exam Tip: Use the term 'net gas exchange' to explain why we notice oxygen release during the day and CO₂ at night.

Question 10: What happens to the energy liberated during respiration?
Answer: The energy liberated during respiration is utilised for carrying out various life processes. Some of the energy liberated during the breakdown of 03 the glucose molecule, is in the form of heat, but a large part of it is converted into chemical energy called Adenosine Triphosphate (ATP). Any activity inside the cell is carried out by the energy released by these ATP molecules.
Energy released from food is like charging a battery called ATP. When the cell needs to move, grow, or repair itself, it "uses up" these ATP batteries.
Teacher's Tip: ATP is the "Currency" of the cell.
Exam Tip: Always provide the full form of ATP: Adenosine Triphosphate.

Long Answer Questions

Question 1: In order to carry out photosynthesis, what are the substances that a plant must take in ? Also mention their sources.
Answer: For preparing food, the plants require the following :
1. Water (from soil)
2. Carbon dioxide (from air)
3. Chlorophyll (contained in the leaf)
4. Energy (from sunlight)
The process of preparing or synthesising food using water from the soil and carbon dioxide from the air, together chlorophyll and sunlight is called photosynthesis. This entire process is a series of complex chemical reactions Photosynthesis is represented as follows:
carbon dioxide + water   _→  [sunlight]{chlorophyll}   glucose + oxygen
Plants act as the primary producers of the food chain by absorbing inorganic materials from their surroundings. This conversion of non-living matter into energy-rich food is what supports almost all life on Earth.
Teacher's Tip: Imagine the leaf is a solar-powered kitchen.
Exam Tip: Drawing the chemical equation alongside the list of substances will gain you extra marks.

Question 2: What is the role of chlorophyll in photosynthesis ?
Answer: This pigment is of utmost importance as it absorbs the sunlight which provides energy for the process of photosynthesis occurs inside the chloroplast of the leaf.
Chlorophyll acts as a catalyst that traps solar energy and converts it into a form that can drive chemical reactions. Without this pigment, the plant would not be able to "capture" the light it needs to make food.
Teacher's Tip: Chlorophyll is like the "solar panel" on a house.
Exam Tip: Be sure to mention that chlorophyll is found specifically within organelles called 'chloroplasts'.

Question 3: Do plants need oxygen ? If so, what is its source ?
Answer: Yes plants need oxygen, all the free oxygen in the atmospheric air is the result of photosynthesis. No animal can survive without oxygen as it is needed for respiration. Even the plants use the same oxygen in dark for their own respiration.
Plants require oxygen for the process of cellular respiration to break down the glucose they have made. While they produce plenty of oxygen during the day, they still need to absorb it from the air to stay alive, especially at night.
Teacher's Tip: Plants are both oxygen makers and oxygen users!
Exam Tip: Clarify that during the day, plants produce more oxygen than they use, making them "oxygen suppliers" for us.

Additional Questions - CHECK YOUR PROGRESS

Question 1: What is external respiration ?
Answer: External respiration or breathing is a mechanical or physical process that involves inhaling (breathing in) air rich in oxygen and exhaling (breathing out) air rich in carbon dioxide.
This process is essentially the gas exchange between the body's respiratory system and the outside environment. It does not involve chemical reactions or energy release; it is just the physical movement of air.
Teacher's Tip: Breathing is just "Air In, Air Out."
Exam Tip: Use the term 'Ventilation' as a synonym for external respiration to impress the examiner.

Question 2: Write the equation showing the process of respiration.
Answer: C₆H₁₂O₆ + 6O₂
 6CO₂ + 6H₂O + energy (38 ATP)
glucose + oxygen → carbon dioxide + water
This equation represents the complete chemical breakdown of sugar in the presence of oxygen. The main purpose of this reaction is to generate ATP, which the cell uses for all its work.
Teacher's Tip: Notice how this is almost the exact opposite of the photosynthesis equation.
Exam Tip: Make sure the numbers in your chemical formula are correctly written as subscripts.

Question 3: In what form is the energy released during respiration stored ?
Answer: The energy released is stored in the form of an energy-rich chemical substance called ATP (Adenosine triphosphate).
ATP is often described as the "molecular unit of currency" for intracellular energy transfer. When a cell needs energy, it breaks a phosphate bond in ATP to release the stored power.
Teacher's Tip: Think of ATP as a fully charged battery.
Exam Tip: Always spell out the full name of ATP at least once in your answer.

Question 4: Name the two types of respiration.
Answer: Aerobic respiration and anaerobic respiration.
Aerobic respiration requires oxygen to release a lot of energy, while anaerobic respiration happens without oxygen and releases very little energy. Most complex organisms rely primarily on the aerobic type.
Teacher's Tip: "Aerobic" sounds like "Air," which contains oxygen.
Exam Tip: If the question is worth more than 1 mark, briefly define each type.

Question 5: Name the organ of respiration in fishes.
Answer: Gills
Gills are specialized organs that extract dissolved oxygen from water as it passes over them. They have a large surface area and many blood vessels to make gas exchange efficient underwater.
Teacher's Tip: Gills are the "underwater lungs" of a fish.
Exam Tip: Mention that gills have 'filaments' to increase the surface area for better oxygen absorption.

Question 6: What are the holes on the sides of the body of insects called ?
Answer: Spiracles
These tiny openings lead to a network of tubes called tracheae that carry oxygen directly to every cell in the insect's body. Spiracles can often be opened or closed to regulate air flow and water loss.
Teacher's Tip: Insects "breathe through their sides."
Exam Tip: Don't confuse spiracles (the holes) with tracheae (the tubes).

CHECK YOUR PROGRESS - Answer the following in one word.

1: What is the muscular sheet below the lungs called ?
Answer: Diaphragm
The diaphragm is a dome-shaped muscle that contracts and flattens to help create the pressure changes needed for breathing. It separates the chest cavity from the abdominal cavity.
Teacher's Tip: Think of it as the "floor" of your chest.
Exam Tip: Spelling counts! Remember the silent 'g' in diaphragm.

2: Which organ is called the voice box ?
Answer: Larynx
The larynx contains vocal cords that vibrate when air passes over them, allowing us to speak and make sounds. It is located at the top of the trachea.
Teacher's Tip: Larynx = Lyrics (singing).
Exam Tip: Don't confuse Larynx (voice box) with Pharynx (throat).

3: Which membrane covers the lungs ?
Answer: Pleural membrane
This thin, double-layered membrane protects the lungs and secretes a fluid that reduces friction during the movement of breathing. It ensures the lungs can expand and contract smoothly.
Teacher's Tip: It's like a protective "shrink-wrap" for your lungs.
Exam Tip: Be ready to define 'pleural fluid' as well, which is found between these layers.

4: Where does exchange of gases takes place ?
Answer: Lungs (alveoli)
Alveoli are tiny, grape-like air sacs at the end of the respiratory tract where oxygen enters the blood and carbon dioxide leaves it. Their extremely thin walls allow for rapid diffusion of gases.
Teacher's Tip: Alveoli are the "business end" of the respiratory system.
Exam Tip: Mention 'alveoli' specifically, as that is the exact site of exchange.

5: What is formed when oxygen combines with haemoglobin ?
Answer: Oxyhaemoglobin
Haemoglobin is the red pigment in blood that has a high affinity for oxygen, forming this temporary compound for transport. Once the blood reaches a cell that needs oxygen, the compound breaks apart.
Teacher's Tip: Oxygen + Haemoglobin = Oxyhaemoglobin (it’s in the name!).
Exam Tip: Oxygen is transported mostly as oxyhaemoglobin, whereas CO₂ is often dissolved in plasma.

6: What is carbamino hemoglobin ?
Answer: Carbon-dioxide combines with haemoglobin to form carbomino haemoglobin.
This is one of the ways carbon dioxide is transported from the body's tissues back to the lungs for exhalation. About 20% of the body's CO₂ is carried this way.
Teacher's Tip: Think of haemoglobin as a "bus" that carries oxygen one way and some CO₂ the other way.
Exam Tip: Distinguish this clearly from Carboxyhaemoglobin, which is formed with carbon monoxide (toxic).

EXERCISES - A. Tick the most appropriate answer.

1: The products of respiration are :
a. carbon dioxide and oxygen
b. oxygen and energy
c. carbon dioxide, water and energy
d. carbon dioxide, oxygen and energy.
Answer: c. carbon dioxide, water and energy
When food is "burned" in the cell using oxygen, it produces these three things. The energy is the goal, while CO₂ and water are the waste products we get rid of.
Teacher's Tip: Just look at the right side of the respiration equation!
Exam Tip: Read every option carefully; option 'd' is a common trick including oxygen as a product.

2: Glucose is oxidized to produce ethyl alcohol during
a. excretion
b. aerobic respiration
c. anaerobic respiration
d. photosynthesis
Answer: c. anaerobic respiration
In organisms like yeast, glucose is broken down without oxygen, resulting in alcohol and CO₂. This process is also known as fermentation.
Teacher's Tip: Alcohol is only produced when there is NO oxygen.
Exam Tip: Remember that in humans, anaerobic respiration produces lactic acid, not alcohol.

3: In insects like grasshopper, there is a well-developed system of air tubes called
a. tracheae
b. gills
c. lungs
d. alveoli
Answer: a. tracheae
The tracheal system consists of tubes that branch throughout the insect's body to deliver air directly to cells. This bypasses the need for a blood-based oxygen transport system.
Teacher's Tip: Tracheae are like tiny "air pipes."
Exam Tip: Associate "spiracles" with the entry holes and "tracheae" with the internal tubes.

4: Frogs breathe through the
a.moist skin
b. lungs
c.mouth cavity
d. all of these
Answer: d. all of these
Frogs are versatile breathers; they use their lungs on land, their skin in water, and the lining of their mouth for extra gas exchange. This allows them to survive in both aquatic and terrestrial environments.
Teacher's Tip: Frogs are "multi-taskers" when it comes to breathing.
Exam Tip: If "all of these" is an option and two answers seem right, it's usually the correct choice.

5: Inside the chest, the trachea divides into two branches called
a.bronchi
b. bronchioles
c.bronchus
d. alveolus
Answer: a.bronchi
The main windpipe (trachea) splits into a left and right bronchus to enter each lung. These then continue to branch into smaller and smaller tubes.
Teacher's Tip: The trachea is like a tree trunk, and the bronchi are the first two big branches.
Exam Tip: Note that 'bronchus' is singular, while 'bronchi' is plural.

6: In humans beings, during inhalation the diaphragm.
a.moves up
b. moves down
c. remains at its position
d.moves down moves up
Answer: b. moves down
When you breathe in, the diaphragm contracts and flattens out, moving downward. This increases the space in your chest, pulling air into the lungs.
Teacher's Tip: Inhale = Down (to make room).
Exam Tip: Connect 'moving down' with 'increasing volume' for a better understanding of pressure.

7: Exhaled air contains
a. more carbon dioxide
b.more oxygen
c.more nitrogen
d.more hydrogen
Answer: a. more carbon dioxide
Since our cells produce CO₂ as a waste product during respiration, the air we breathe out has a much higher percentage of it than the air we breathe in. We also exhale some unused oxygen.
Teacher's Tip: We "dump" the waste gas when we exhale.
Exam Tip: Remember that exhaled air actually still has about 16% oxygen, just less than what we inhaled.

8: Plants have these for exchange of gases.
a.spiracles and stomata
b.lenticels and spiracles
c.lenticels and stomata
d.buds and flowers
Answer: c.lenticels and stomata
Stomata are found on leaves and green stems, while lenticels are small openings on the woody stems and roots of older plants. Together, they ensure the whole plant can respire and photosynthesize.
Teacher's Tip: Stomata are for soft parts; lenticels are for woody parts.
Exam Tip: Insects have spiracles, so any option with "spiracles" is wrong for plants.

B. Fill in the blanks.

1. The two respiration of respiration are aerobic and anaerobic.
Answer: aerobic and anaerobic.
These represent respiration with oxygen and without oxygen. Understanding both is key to knowing how different organisms generate energy.
Teacher's Tip: Use "With O₂" and "Without O₂" as a shortcut.
Exam Tip: Ensure you spell "anaerobic" correctly with the 'a-n-a-e' sequence.

2. Muscles of human beings switch to anaerobic respiration in the absence of oxygen.
Answer: respiration
When we exercise very hard, our blood can't deliver oxygen fast enough, so our muscles produce energy without it temporarily. This leads to the buildup of lactic acid.
Teacher's Tip: This is why your muscles "burn" after a fast sprint.
Exam Tip: Mention 'lactic acid' if asked about the product of this muscle respiration.

3. In aerobic respiration, food is completely oxidized into carbon dioxide, water and energy.
Answer: aerobic
Aerobic respiration is efficient because it breaks down glucose entirely. This complete breakdown maximizes the amount of ATP energy produced per molecule of sugar.
Teacher's Tip: Complete oxidation = Complete energy release.
Exam Tip: Use the word 'completely' to distinguish aerobic from anaerobic respiration.

4. Below the lungs is a muscular sheet called diaphragm.
Answer: diaphragm.
This muscle is the primary driver of the breathing mechanism in mammals. Its rhythmic contraction and relaxation change the air pressure inside the lungs.
Teacher's Tip: Without the diaphragm, your lungs couldn't pull in air on their own.
Exam Tip: Be prepared to describe how its movement causes inhalation.

5. Bronchi divide into smaller tubes called bronchioles.
Answer: bronchioles.
The branching system of the lungs ensures that air reaches every part of the lung tissue. These tiny bronchioles eventually lead to the alveolar sacs.
Teacher's Tip: "Bronchi-oles" are "Little Bronchi."
Exam Tip: Use the term 'Respiratory Tree' to describe this branching structure.

6. In human beings, exchange of gases takes place in alveoli (lungs).
Answer: alveoli
The alveoli provide a massive surface area for gas exchange, roughly the size of a tennis court in an adult human. Their proximity to capillaries makes the process very fast.
Teacher's Tip: Alveoli are where the "action" happens.
Exam Tip: Always mention that gas exchange happens by the process of 'diffusion'.

C. State if the following statements are true or false. Correct the statement if it is false.

1. The oxidation pf food to release energy and water is called breathing.
Answer: False. The oxidation of food to release energy and water is called Respiration.
Breathing is just a physical act, while respiration is a chemical process that happens inside every cell. Respiration is what actually keeps the "fire" of life burning.
Teacher's Tip: Breathing is physical; Respiration is chemical.
Exam Tip: When correcting a False statement, write out the full correct sentence for better marks.

2. Anaerobic respiration takes place in our bones.
Answer: False. Anaerobic respiration takes place in our muscles.
While most of our body uses oxygen, our muscles have the special ability to function without it for short bursts. This allows for quick, intense physical movements.
Teacher's Tip: Bones are for support; muscles are for movement (and anaerobic bursts).
Exam Tip: Specifically mention 'during vigorous exercise' to explain when this happens.

3. The microscopic air sacs present in the lungs are called bronchi.
Answer: False. The microscopic air sacs present in the lungs are called alveolar sacs.
Bronchi are the tubes that carry air into the lungs, not the sacs where exchange happens. The alveolar sacs are at the very ends of the smallest tubes.
Teacher's Tip: Bronchi = Tubes; Alveoli = Bags.
Exam Tip: Don't get confused by similar-sounding words like Bronchi and Bronchioles.

4. Respiration that takes place through skin is called pulmonary respiration.
Answer: False. Respiration that takes place through skin is called cutaneous respiration.
"Pulmonary" refers to the lungs, while "cutaneous" refers to the skin. Many amphibians use cutaneous respiration to supplement their lung-based breathing.
Teacher's Tip: 'Cuticle' is related to skin; 'Pulmo' is Latin for lung.
Exam Tip: Frogs are the classic example used for cutaneous respiration.

5. Stomata are present on mature roots and woody stems.
Answer: False. Lenticels are present on mature roots and woody stems.
Stomata are usually limited to green, soft tissues like leaves. As stems become woody and bark forms, they develop lenticels to allow gas exchange.
Teacher's Tip: Stomata are for soft leaves; Lenticels are for hard bark.
Exam Tip: Note that lenticels stay open all the time, unlike stomata.

6. In photosynthesis oxygen is released as a by-product
Answer: True
Oxygen is "waste" to a plant during photosynthesis, which is lucky for us! This byproduct is what built up the breathable atmosphere of Earth.
Teacher's Tip: One man's trash is another man's treasure; a plant's waste is our life-blood!
Exam Tip: Mention that this oxygen comes from the splitting of water molecules.

D. Match the following.

Column A (Organism) | Column B (Organ of Respiration)
1. fish | a. lungs
2. human beings | b. tracheae
3. frog | c. gills
4. cockroach | d. moist skin, mouth cavity and lungs
5. bird | e. lungs
Answer:
1. fish | c. gills
2. human beings | a. lungs
3. frog | d. moist skin, mouth cavity and lungs
4. cockroach | b. tracheae
5. bird | e. lungs
Different animals have evolved different ways to breathe based on where they live and how active they are. From simple tubes in insects to complex lungs in humans, each system is adapted for efficiency.
Teacher's Tip: Match the environment to the organ: Water = Gills, Land = Lungs.
Exam Tip: Remember that insects (like cockroaches) don't have blood that carries oxygen, so they use tracheae.

E. Differentiate between

(i) aerobic respiration and anaerobic respiration.
Answer:
Aerobic Respiration
1. It takes place in the presence of oxygen.
2. Complete oxidation of food takes place.
3. 38 molecules of ATP are produced by oxidation of one gram mole of glucose.
4. CO₂ and H₂O are the end products.
Anaerobic Respiration
1. It takes place in the absence of oxygen.
2. Incomplete oxidation of food takes place.
3. 2 molecules of ATP are produced by oxidation of gram mole of glucose.
4. Ethyl alcohol (C₂H₅OH) and CO₂ are the end products.
Aerobic respiration is like a high-efficiency engine that burns fuel completely for maximum power. Anaerobic respiration is like a backup generator; it works when oxygen is gone but is much less efficient.
Teacher's Tip: Remember "Aerobic = 38 ATP, Anaerobic = 2 ATP."
Exam Tip: Mentioning the chemical products (like ethyl alcohol) is essential for full marks.

(ii) External respiration and Internal respiration
Answer:
External respiration
1. It is the mechanical process of inhaling and exhaling air It does not involve any enzymes.
2. It involves taking in oxygen and giving out carbon dioxide.
3. No energy is released.
4. It takes place outside the cell.
Internal respiration
1. It is a complex biochemical process in which enzymes are involved.
2. It involves the oxidation of glucose into carbon dioxide, water and energy.
3. Energy is released and stored in the form of ATP.
4. It takes place inside the cell.
External respiration is just the transport of gases to and from the lungs. Internal respiration is the actual "work" of turning food into energy that happens in our mitochondria.
Teacher's Tip: Think "In the lungs" vs "In the cells."
Exam Tip: Don't forget to mention 'enzymes' when discussing internal respiration.

(iii) Photosynthesis and Respiration
Answer:
Photosynthesis
1. It is an anabolic process.
2. It takes place in the presence of sunlight
3. Oxygen is released as the by product.
4. It takes place in the green parts of the plant that is green leaves, young green stems.
5. Food is synthesised by plants using CO₂ and H₂O
Respiration
1. It is a catabolic process Sunlight is not necessary for the respiration.
2. Carbondioxide is released as the by product.
3. It takes place in all the parts of a plant.
4. Food is oxidized using oxygen to release energy
Photosynthesis builds food, while respiration uses that food for energy. This cycle is what keeps nutrients and energy flowing through the entire ecosystem.
Teacher's Tip: "Anabolic" means Building Up, "Catabolic" means Breaking Down.
Exam Tip: Highlighting that photosynthesis only happens in green parts is a very important distinction.

F. Answer the following in short.

1: Define respiration.
Answer: The process of conversion of glucose molecules in food into energy rich molecules, carbondioxide and water with the help of oxygen is known as respiration.
This is a chemical reaction that provides the energy necessary for all biological functions. It essentially "unlocks" the energy that plants have stored in food.
Teacher's Tip: Respiration = Food + Oxygen → Energy.
Exam Tip: Use the term 'cellular level' to show you know where it occurs.

2: What is the full form of ATP ?
Answer: ATP is the energy currency of cell. Its full form is Adenosine Triphosphate.
ATP molecules act like rechargeable batteries for our cells, providing the power needed for movement and chemical synthesis. Every time a cell does work, it "spends" some ATP.
Teacher's Tip: Remember "A-T-P" sounds like "A-T-M" where you get currency (money).
Exam Tip: Be precise with the spelling of 'Triphosphate'.

3: What is respiratory tract ?
Answer: The path through which the air travels to the lungs and back to the atmosphere in humans is called the respiratory tract
[nose] → [pharynx] → [larynx] → [trachea] → [bronchi] → [bronchioles] → [alveolar sacs] → [alveolus]
This tract acts as a series of connected "pipes" and filters that warm, moisten, and clean the air before it reaches the delicate gas-exchange tissues. The movement of air follows this exact sequence in both directions.
Teacher's Tip: Memorize the order: Nose, Throat (Pharynx), Voice Box (Larynx), Windpipe (Trachea).
Exam Tip: Drawing a quick flow-chart as shown in the answer is a great way to save time and be clear.

4: Define cutaneous respiration ?
Answer: The exchange of gases through moist skin and blood capillaries underneath is called cutaneous respiration.e.g. in frogs.
For this to work, the skin must remain wet so that gases can dissolve and pass into the bloodstream. This is why many amphibians live in damp places or have slimy skin.
Teacher's Tip: "Cutis" is Latin for "Skin."
Exam Tip: Always provide the example of 'frogs' or 'earthworms' when defining this.

5: What is the function of pleural fluid ?
Answer: Pleural fluid keeps the surface of the lungs moist for easy diffusion of gases (oxygen and carbon dioxide).
Beyond moisture, it also acts as a lubricant that allows the lungs to glide smoothly against the chest wall as you breathe. It prevents the friction that would otherwise damage the delicate lung tissue.
Teacher's Tip: It's like "oil" for your lung machinery.
Exam Tip: Mention 'reduction of friction' as a secondary function for extra credit.

6: What is the role of the diaphragm in breathing mechanism ?
Answer: Diaphragm moves up and down and helps in the exchange of air between the atmosphere and lungs.
When it moves down, it creates a vacuum that sucks air in; when it relaxes and moves up, it pushes air out. This pressure change is the fundamental physical cause of breathing.
Teacher's Tip: Think of a syringe - pulling the plunger down (diaphragm) draws in fluid (air).
Exam Tip: Specify that it 'contracts' to move down and 'relaxes' to move up.

G Answer the following in detail.

Question 1: How is the process of cellular respiration different from breathing ?
Answer:
Respiration
1. It is a complex bio- chemical process which involves enzymes.
2. It involves oxidation of glucose in to CO₂, water and energy.
3. Energy is released and stored in the form of ATP.
4. It takes place inside the cell
Breathing
1. It is a mechanical process without the involvement of enzymes.
2. It involves only the exchange of oxygen and CO₂.
3. No energy is released.
4. It takes place outside the cell.
Breathing is the physical delivery service that brings air to the "factory door," while respiration is the actual "production line" that uses that air. You can breathe without respiring (temporarily), but you cannot respire without a gas source.
Teacher's Tip: Breathing is the "Transport," Respiration is the "Reaction."
Exam Tip: Use a table to clearly separate the points and make it easy to grade.

Question 2: Explain the process of Cellular Respiration.
Answer: Cellular Respiration is a biochemical process which involves the oxidation of glucose to release energy, carbondioxide and water are released as by - products.
C₆H₁₂O₆ + 6O₂ \xrightarrow{enzymes} 6CO₂ + 6H₂O + energy
It involves a series of chemical reactions controlled by different enzymes. The energy released in the process is stored in the form of energy rich substance called ATP (Adenosine triphosphate). The ATP molecules are stored in the cells and later on can be broken down to release energy for various metabolic activities. The entire process takes place partially in the cytoplasm and partially in the mitochondria of our body cells. The process of conversion of glucose molecules in food in to energy rich molecules, CO₂ and water with the help of oxygen is known as respiration.
This process is the primary way that living things sustain their life functions, from moving a finger to thinking a thought. It is a highly controlled "burning" of fuel that captures as much energy as possible in ATP.
Teacher's Tip: The mitochondria is the "Powerhouse" where this all happens.
Exam Tip: Mentioning 'Mitochondria' and 'Enzymes' is vital for a high-quality detail answer.

Question 3: In human beings, what happens to oxygen after it is inhaled through the nose ?
Answer: Air rich in oxygen, enters the body through the nostrils (nose). From the nose, air enters the pharynx which leads to larynx and then trachea (windpipe). From trachea, it enters the bronchi and enters the lungs. From bronchi, it enters bronchioles and finally the alveoli. The oxygen diffuses through the thin walls of blood capillaries (surrounding) into the blood and combines with hemoglobin to form oxy haemoglobin. The oxygen in blood is carried to all body cells where internal respiration takes place in a series of chemical reactions and food (in the form of glucose) is converted into carbon-dioxide water and energy in the form of ATP, using the oxygen.
The journey of an oxygen molecule is a long one, from the atmosphere all the way into your microscopic cells. Once it reaches the blood, it hitchhikes on red blood cells to reach the parts of your body that need it most.
Teacher's Tip: Follow the map: Nose → Pipes → Air Sacs → Blood → Cells.
Exam Tip: Be sure to mention the role of 'hemoglobin' and the formation of 'oxyhaemoglobin' in your explanation.

Question 4: Show the mechanism of breathing in human beings.
Answer: The process of taking in oxygen and giving out carbondioxide is called breathing. It is a physical process and carried out by the movement of the various body parts.
1. Inhalation : When we inhale air our ribs move upwards and outwards and the diaphragm moves downwards. The volume of chest cavity increases and the air pressure is reduced, as a result of which air flows in to the lungs.
2. Exhalation : When we exhale air, that is breathe out air, the diaphragm moves upwards and the ribs move downwards and inwards. The space inside the chest cavity decreases and the air pressure is increased as, a result the air rushes out.
Breathing relies on changing the volume of your chest to change the pressure. It’s exactly like a set of bellows used to blow air into a fire; expand to suck in, squeeze to push out.
Teacher's Tip: Remember the "I-U-O" rule for inhalation: Inhale - Up and Out (ribs).
Exam Tip: Using arrows to show the direction of movement (e.g., diaphragm ↓) can make your answer clearer.

Question 5: Explain the process of exchange of gases in plants.
Answer: In plants, exchange of gases takes place through stomata and lenticels.
1. Stomata - They are tiny pores present on the lower surface of leaves and young green stems. The gaseous exchange takes place in plants mostly through stomata. They remain open during the day and close at night.
2. Lenticels - In certain trees, the mature roots and woody stems have tiny openings called lenticels which enable the oxygen to reach the intercellular spaces of interior tissues and carbon dioxide to be released into the atmosphere. The exchange of gases (oxygen and carbon dioxide) in plants takes place by two processes - photosynthesis and respiration
. Photosynthesis occurs during the day. It takes in carbon dioxide and gives out oxygen. A part of oxygen formed is used by plants for respiration and rest is given out through stomata
. Respiration occurs throughout day and night. Oxygen is used and carbon dioxide is given out. This carbon dioxide is used by the plant for photosynthesis during the day. At night, in the absence of photosynthesis, carbon dioxide is released into the air through stomata.
Plants don't have lungs, so they rely on these thousands of tiny "mouths" on their surface to let air diffuse in and out. This passive system works because their leaves have a high surface area and their metabolic needs are lower than animals.
Teacher's Tip: Leaves "breathe" through stomata, trunks "breathe" through lenticels.
Exam Tip: Emphasize that respiration happens 24/7, even though photosynthesis only happens in light.

H. Number the following organs in the correct order to show the path taken by fresh air at the time of inhalation.
trachea, nose, bronchioles, bronchi, larynx, alveoli, pharynx, lungs
Answer: nose → pharynx → larynx → trachea → bronchi → lungs → bronchioles → alveoli.
This sequence follows the air from the outside world down to the smallest units of the lung. Each step involves a narrowing of the tubes until the air reaches the microscopic exchange sacs.
Teacher's Tip: Use the first letter of each to make a mnemonic: N-P-L-T-B-L-B-A.
Exam Tip: Always use arrows (→) instead of just commas to show the direction of movement.