Class 9th Biology Unit 7 BIOENERGETICS Importants Question And Answer
Short And Simple Question And Answer
Q.1. Explain cell works as open system?
Ans: A cell works as open system. It means that substances are entering and leaving the cell all the times. Substances that are entered into cell are converted into products through metabolism. Cell uses these products and also transports them to other cells.
Q.2. Explain different forms of energy in living organisms?
Ans: Energy is used in breakdown of substances and also in formation of products inside the cell.
Forms of energy: In living organisms, energy exists in two forms:Kinetic energy (K.E): It is involved in doing work.Potential energy (P.E): It is stored for future use.P.E is stored in chemical bonds and is released as kinetic energy when these bonds brea
Q.3 Define bioenergetics? Explain energy transformation in organisms?
Ans: Bioenergetics: It is the study of energy relationships and energy transformations in living organisms.
Energy transformation in organisms: a. Organisms obtain energy by metabolizing the food.
b. Food contains potential energy in its bonds.
c. Large amount of kinetic energy is released after breakdown of these bonds.
d. Some K.E is stored in ATP molecules as potential energy. Remaining K.E is released as heat.
e. P.E of ATP is changed into K.E to carry out life activities.
Q.4. What is meant by oxidation-reduction reaction (redox reaction)? How it acts as energy source
Ans: In these reactions electrons are exchanged between atoms
Oxidation: Loss of electrons is called oxidation.
Reduction: Gain of electrons is called reduction.
Oxidation-reduction reaction (redox reaction): It is a reaction in which oxidation and reduction occur simultaneously. arrangement in atoms. For example:
Electrons as energy source: Electrons can be an energy source. It depends upon their location and
a) When electrons are present in oxygen, they are not good energy source due to stable connection with oxygen atom.
b) When electrons are removed from oxygen and attached to carbon or hydrogen atom, then they relçase energy aridiinove back to oxygen atom.
Role of hydrogen in living organisms redox reaction involves the loss and gain of hydrogen atom (contains one proton and one electron).
Oxidation: Loss of hydrogen atom is called oxidation. It actually involves loss of an electron.
Reduction. Gain of hydrogen atom is called reduction. It actually involves gain of an electron.
Significance of redox reactions: Redox reactions are the direct source of energy for all life processes like movement, growth and reproduction etc.
Q.5. Why ATP? Interpret that ATP is the major energy currency of all cells?
Ans ATP: Adenosine triphosphate (ATP) is the major energy currency of all cells. ATP was discovered by Karl Lohmann in 1929.
Fritz Lipmann in 1941 proposed that ATP is the main energy transfer molecule in the cell. Uses of ATP: It is the main energy source for many cellular functions like:
a) Synthesis of DNA, RNA, and proteins
d) Active transport
e) Exocytosis and endocytosis.
c) Transmission of nerve impulses
Structure of ATP: ATP molecule has three subunits:
. Adenine: It is a double-ringed nitrogenous base. a
b. Ribose: It is a five-carbon suge
c. Phosphate groups: Three phosphate groups in a linear chain.
ATP as energy currency/source: The covalent bond connecting two phosphate groups is indicated by
the “tilde” (~). It is a high energy bond. The energy in this bond is released when one phosphate (Pi) isBIOENERGETICS,
separated from ATP. When one phosphate bond breaks, then 7.3 kcal (7,300 calories) energy is released and ADP (adenosine diphosphate) is formed.
ADP+ Pl+ energy (7.3 kcal/mole)
In some cases, ADP is further broken down to AMP (adenosine monophosphate) and Pi as follows:
AMP+Pi+ energy (7.3 kcal/mole)
A cell can form ATP by recombining ADP with Pi by using 7.3 kcal of energy per mole. This energy is obtained from the oxidation of foodstuff.
➤ ATP is generated by energy-releasing processes.
➤ ATP is broken down by energy-consuming processes.
Q.6. Write a note on photosynthesis in plants?
Ans: Photosynthesis: It is sa process in which plants prepare glucose (food) from carbon dioxide the presence of sunlight and chlorophyll, with oxygen as a by-product.
and water in 1 SGD
6CO₂ + 12H₂O
chloropby!! light energy
Importance of photosynthesis:
a. Photosynthesis is an anabolic process.
b. It is an important component of bioenergetics.
c. All life depends on photosynthesis.
C6H12O6 + 602 + 6H₂O
d. It occurs in plants, some protists (algae), and some bacteria.
Q.7 Ans: Water and carbon dioxide are the raw materials of photosynthesis.
. Write a note on intake of water and carbon dioxide in plants during photosynthesis?
Intake of water: (through osmosis)
Water in soil is absorbed by roots and root hairs through o
This water is transported to leaves through xylem tissues
Intake of CO2: (through diffusion)
Air enters into the leaf through stomata.
Then this air reaches into the air spaces present around mesophyll cells.
Here CO₂ present in the air is absorbed in water, (around mesophyll cells) and then it diffuses into
➤ Stomata cover 1-2% of the leaf surface but large amount of air is passed through them.
Q.8.Summarize two major phases of mechanism of photosynthesis?
Ans: Mechanism of photosynthesis: Photosynthesis occurs in two phases which are called light reactions
and dark reactions.
Light energy is needed in these reactions.
Lightenergy is used to make high-energy
molecules ATP and NADPH).
They occtir on thylakoid of chloroplast.
Q.9 Describe the mechanism of light reactions? Light Reactions: The summary of light reactions is as follows:
Ans: Dark Reactions Light reactions.
energy is not needed in these
Carbon dioxide is reduced into glucose by
using energy of ATP and NADPH.
They occur in stroma of chloroplast.
a) When chlorophyll molecules absorb light, their energy level increases and their electrons are
b) Electrons move through electron transport chain and form ATP.
c) Light breaks water molecule (photolysis) and oxygen is released.
d) The hydrogen atoms of water give electrons to chlorophyll and become ions (H’).
e) The electrons of chlorophyll and the hydrogen ions reduce NADP into NADPH.
Z-scheme: The whole series of light reactions is called Z- scheme due to its Z-shaped flow chart.
Photolysis: Breakdown of compounds (water) in presence of light.
Q.10. Describe the mechanism of dark reactions (Calvin cycle)?
Ans: Malvin Calvin and his colleagues at the University of California discovered the details of dark reactions (Calvin cycle). The summary of dark reactions is as follows:
a) CO₂ molecules combine with 3-carbon compounds and form 2 temporary 6-carbon compounds.
b) Each 6-C compound divides into two 3- carbon compounds. ) c
3-C compounds are reduced to 3-carbon carbohydrates in presence of ATP and NADPH.
d) 3-carbon carbohydrates are used to make glucose and also to regenerate Fig: Dark Reaction (Calvin cycle) the original 5-carbon compounds (by using AΤΡ).
Q.11. Describe the role of chlorophyll and light in photosynthesis?
Ans: Role of light:
Sunlight energy is absorbed by chlorophyll.
It is converted into chemical energy to carry out photosynthesis.
Only 1% of light is absorbed while the rest is reflected or transmitted.
Light of different wavelengths (colors) are absorbed by different pigments. Blue and red lights carry out more photosynthesis.
Role of chlorophyll:
Pigments: These are the substances that absorb visible light. Different pigments absorb light of different wavelengths (colours).
Photosystems: These are the clusters of photosynthetic pigments in thylakoid.
Chlorophyll-a is the main photosynthetic pigment.
Chlorophyll-b and carotenoids are called accessory pigments.
Chlorophylls absorb mainly blue and red lights.
Some wavelengths which are not absorbed by chlorophyll-a are absorbed by accessory pigments and
vice-versa. Accessory pigments: These pigments help chlorophyll-a for absorption of light of different wavelength.
Q.12. What is meant by limiting factor? Described limiting factors in photosynthesis?
Ans: Limiting factor: It is an environmental factor whose absence of deficiency can decrease the rate of a metabolic reaction.
Limiting factors in photosynthesis: Main limiting factors in photosynthesis are:
a) Light intensity
c) Concentration of CO2
a) Effect of light: Rate of photosynthesis decreases as the light intensity decreases and increases as
d) Availability of water
light intensity increases. But at very high light intensity rate of photosynthesis becomes constant. Effect of temperature: Rate of photosynthesis decreases as the temperature decreases and increases
b) as temperature increases but up to a limit. If light intensity is low then temperature has little effects on photosynthesis.
c) Effect of CO2: Rate of photosynthesis increases with increase of CO₂ concentration. Very high concentration of CO2 causes closing of stomata and the rate of photosynthesis decreases.
d) Effect of water: Free availability of water increases the rate of photosynthesis.
Q.13. Define respiration and cellular respiration? How does respiration resemble with burning process
Ans: Respiration: It is a process in which energy is produced in form of ATP by breakdown of C-H bonds of food in presence of oxygen.
Cellular respiration: It is the cellular energy yielding process.
Resemblance with burning process: The process of respiration is same to the burning process. When we burn a fuel, it uses oxygen and yields energy in the form of light and heat. In burning process oxygen is used to break the C-H bonds present in fuel molecules.
Q.14. Explain different types of cellular respiration?
Ans: Cellular respiration has two types:
1) Aerobic respiration:
a) Aerobic respiration occurs in presence of oxygen.
2) Anaerobic respiration
b) In it glucose is complete oxidized and large amount of energy is released.
c) In the first phase glucose molecule (6C) is broken down into two molecules of pyruvic acid (3C).
d) In the second phase, pyruvic acid molecules are completely oxidized into CO₂ and water and energy is released. The overall reaction is as follows.
C6H12O6 + 602
2) Anaerobic respiration (Fermentation):
600₂ + 12120 + Energy
a) Anaerobic respiration occurs in absence of oxygen.
b) In it glucose is incomplete oxidized and less amount of energy is released.
c) In the first phase glucose molecule (6C) is broken down into two molecules of pyruvi d) In the second phase, pyruvic acid molecule (C3H4O3) iş incompletely oxidized into ethyl alcohol
ic acid (3C). or lactic acid.
Q.15. Explain different types of anaerobic respiration (Fermentation)?
Ans: Anaerobic respiration is classified as alcoholic fermentation and lactic acid fermentation.
a) It occurs in bacteria, yeast etc.
b) In this pyruvic acid is broken down into alcohol (C2H5OH)) and CO2.
Pyruvic Acid Lactic acid fermentation:
Ethyl Alcohol + Carbon Dioxide
a) It occurs in skeletal muscles of humans and other animals during hard physical exercises.
b) It also occurs in bacteria present in milk.
c) In this pyruvic acid molecule is converted into lactic acid (C3H6O3).
Q.16. Give the importance of fermentation?
Ans: Importance of Fermentation:
Lactic Acid There was no supply of O₂, at the time of evolution of life on Earth. So early organisms respired anaerobically and got energy for their life activities. 2. Free oxygen is available today. But still some bacteria and some fungi get energy from anaerobic respiration and are called anaerobes. Humans provide energy to their skeletal muscle cells during hard work through anaerobic respiration
(Oxygen availability is not so much).
Q.17. Explain the mechanism of respiration?
Ans: Mechanism of respiration: Aerobic respiration is a continuous process. It is divided into three main
1 . Glycolysis:
2- Krebs cycle
3- Electron transport chain (ETC)
a) In glycolysis, glucose (6C) molecule is broken into two molecules of pyruvic acid (3C).
b) It occurs in cytoplasm.
c) It does not require oxygen. So it occurs in both respirations i.e. aerobic and anaerobic.
a) In Krebs cycle, pyruvic acid molecules are completely oxidized and ATP, NADH and FADH2 are also formed.
b) Before entering in Krebs cycle, pyruvic acid is changed into a 2-carbon compound called acetyl- CoA.
c) This cycle was discovered by Sir Hans Krebs so it is called Krebs cycle.BIOENERGETICS, Class 9th
Electron transport chain (ETC).
a) It is the final step of cellular respiration.
b) It is the transfer of electron on an electron transport chain.
c) In this NADH and FADH₂ release electrons and hydrogen ions.
d) These electrons are taken up by electron carriers. When electrons move through the series of electron carriers they lose energy, which is used to form ATP.
e) At the end, electrons and hydrogen ions combine with molecular oxygen and form water.
ADP FAD NAD
COATP + NADH + FADH
H₂O ATP NAD+ [FAD
Q.18. Write a note on energy budget of respiration?
Ans: Energy budget of respiration: (Difference in ATP production b/w aerobic and anaerobic respiration)
During aerobic respiration oxidation of one glucose molecule produces 36 ATP molecules.
During anaerobic respiration oxidation of one glucose molecule produces only 2 ATP molecules. Because Krebs cycle and ETC are not present in it.
ATP production during respiration:
1) In glycolysis, NADH gives 02 ATP molecules. While 01 ATP molecule is spent during
the transportation of NADH across mitochondria.
2) In ETC, each NADH gives 03 ATP molecules.
3) Each FADH₂ gives 02 ATP molecules.
During glycolysis ATP formation = 2 ATP (during both aerobic and anaerobic respiration) During glycolysis 2 NADH-4 ATP (during aerobic respiration)
During pyruvic acid oxidation 2 NADH = 6 ATP (during aerobic respiration)
During Krebs cycle= 6 NADH 18 ATP (during aerobic respiration) During Krebs cycle 2 FADH24ATP (during aerobic respiration) During ETC, ATP formation 2 ATP (during aerobic respiration)
Q.19. Differentiate between aerobic and anaerobic respiration?
Ans: Aerobic Respiration
It occurs in presence of oxygen.
36 ATP molecules are formed in it.
Its final products are CO2 and H2O.
It occurs in absence of oxygen.
2 ATP molecules are formed in it.
Its final products are lactic acid or CO2 and ethanol.
In this glycolysis occurs in cytoplasm while
It occurs in cytoplasm.
Krebs cycle and ETC occur in mitochondria.
It is main energy source for most organisms.
It is source of energy for anaerobic
organisms, some aerobic organisms and also
source of many products e.g. cheese etc.
Q.20. Differentiate between respiration and photosynthesis?
It is an anabolic process.
It is a catabolic process.
It uses light energy and stores it in the form of
It converts bond energy into chemical energy of ATP.
It occurs in all organisms.
It occurs in some bacteria, all algae and plants.
It occurs in cytoplasm and mitochondria.
It occurs in chloroplast.
It occurs all the time.
It occurs in day time only.
Q.21. Why is it said that all life forms are dependent on photosynthesis?
Ans: Autotrophs prepare their food by photosynthesis. All other organisms need this food for energy source. So we can say that all life forms depend on photosynthesis.
Q.22 What structures and phenomena are involved in the intake of carbon dioxide and water by plants?
Ans: Intake of water takes place by roots, root hairs through osmosis. Intake of CO2 takes place by stomata through diffusion.
Q.23. In what ways the respiratory energy is used in the body of organisms?
Ans: It is used for growth, movement and reproduction etc.
Q.24. What is NAD?
Ans: Nicotinamide adenine dinucleotide (NAD) is a coenzyme.
Its oxidized form is called NAD. Its reduced form is called NADH. It is formed by combining one electron and hydrogen to NAD. One form of NAD contains phosphate and called NADP
Q.25. What is FAD?
Ans: Flavin adenine dinucleotide (FAD) is a coenzyme. It gets 2 hydrogen atoms and reduces to FADH2.
Q.26. Which common fuel is used by a cell?
Ans: The most common fuel used by cell to get energy by cellular respiration is glucose.
Q.27. Differentiate between palisade mesophyll and spongy mesophyll?
Ans: Palisade mesophyll: It is the upper layer of mesophyll where photosynthesis occurs.
Spongy mesophyll: It is the lower layer of mesophyll which contains many air spaces.
Q.28. There is more chloroplasts in palisade mesophyll than in spongy mesophyll. Why?
Ans: Because palisade cells are on upper surface so they get and absorb more light.
Q.29 . Give difference of numbers of stomata of terrestrial and aquatic plants?
Ans: Terrestrifil plantsthave more stomata in lower epidermis and aquatic plants have more stomata in upper epidermis,
Q.30. Define mesophyll, variegated leaf, Acetyl CoA, Coenzyme A and starch?
Ans: Mesophyll: It is the inner tissue of leaf whose cells are green because they contain chloroplasts. Variegated leaf: It is a leaf with alternating green and white patches. For example, leaf of Geranium.
Acetyl CoA: It is used in oxidation of pyruvic acid. It is formed by combination of acetate with coenzyme-A.Coenzyme-A: It is an organic co-factor which is loosely attach with enzyme. Starch: It is a type of carbohydrate. Plants convert glucose into starch for storage.
Q.31. What is the ultimate source of hydrogen for this reduction?
Ans: Water In dark reaction, 3-carbon compounds are reduced to form carbohydrates.
Q.32. How does transport of water and salts take place in non-vascular plants?
Ans: In these plants water and salts reach the mesophyll cells of leaves by diffusion and osmosis.