The Ultimate Guide to Long/Comprehensive Answers on Bioenergetics for Grade IX level students

Maximizing Your Exam Success: A Comprehensive Guide to Long Bioenergetics Answers for School Students 

    As a grade IX student preparing for your board exams or entry/competitive tests, bioenergetics is a crucial subject that can make or break your score. Understanding the complex concepts of ATP production, photosynthesis, and respiration can be challenging, but with the right guidance and practice, you can achieve success. In this comprehensive guide, we will provide you with long and easy-to-understand answers to some of the most important questions in bioenergetics. From the structure of ATP and chloroplasts to the mechanisms of photosynthesis and respiration, this article will provide you with a clear understanding of these fundamental concepts. Our goal is to help you maximize your exam success and achieve a high score in tests such as ETEA, NMDCAT, NTS, NEET, CST, and more.

Long/Comprehensive answers on Bioenergetics
From Notes Libray of H.E.S (Health, Education, and Skills) 

What is ATP? Discuss its structure. 

ATP (Adenosine tri-phosphate)

    ATP is the main source of energy present in all living cells. Therefore, it is also called the “energy currency of living cells.” Cell hydrolysis (water splitting) ATP to ADP and inorganic phosphate (P_i) and almost 7.3 Kcal of energy is released. This energy is then used by living cells.

Structure of ATP

    Each ATP molecule has the following three components

(a) Adenine: It is an organic molecule having carbon-nitrogen rings.
(b) Ribose sugar (5 carbon): A five-carbon sugar is called ribose.    

• When adenine is covalently bonded to a ribose sugar, it makes a molecule called adenosine.

(c) Phosphate group: Three phosphate groups are arranged in the form of a linear chain.

Energy bond

 There are two types of phosphate bonds in ATP, i.e.

• High-energy phosphate bond: They yield more energy on hydrolysis and are represented by the curved symbol (~). When energy is required for any cellular activity these bonds are broken down to release energy.
• Low-energy phosphate bonds: They yield less energy upon hydrolysis and are represented by a straight line (-).

Why is ATP regarded as the currency of living cells?

ATP is the energy currency of living cells

    ATP is an energy-rich molecule and is called "the energy currency of living cells".

Synthesis of ATP (Endergonic reaction)

    Synthesis of ATP occurs through the following steps.

• In a reaction, first adenine combines with a 5-carbon ribose sugar to make a molecule called adenosine i.e. 

        Adenine + Ribose → Adenosine

• When phosphate is bonded to adenosine, it makes a nucleotide called Adenosine Monophosphate (AMP) i.e.

        Adenosine + Phosphate + Energy → Adenosine monophosphate

• Then another phosphate group is added to AMP and forms Adenosine diphosphate (ADP) i.e.

        AMP + Pi + Energy → Adenosine diphosphate        

• Another phosphate is added to ADP and forms ATP i.e.

        ADP + Pi + Energy → Adenosine triphosphate (ATP)      

Breaking of ATP (Exergonic reaction)

    ATP is constantly hydrolyzed by the cell into ADP and Phosphate and energy is released for cellular activities i.e.

        ATP + H2O  →  ADP + Pi + Energy (7.3 Kcal)

    At the same time, ATP molecules are constantly regenerated from ADP and phosphate using energy. This energy comes from the breakdown of glucose molecules during respiration. So in this way, a constant cycle of ATP breaking and reforming goes on in the living cells.

Describe the structure of chloroplast in detail.   

Structure of Chloroplast

    Chloroplast consists of the following three components

I. Outer membrane

    Each chloroplast is surrounded by a double membrane covering or envelope that encloses the grana or stroma.

II. Grana

    A granum consists of many flattened fluid-filled membranous sacs or discs called thylakoids (from the Greek word “thylakos” which means sac or pouch). It forms stacks that resemble a pile of coins. Many granum are inter-connected by intergrana. The grana are visible under a light microscope as grain. Chlorophyll and Carotenoids are present within the membrane of thylakoids.

Function: It is the sight of light trapping reaction (light reaction) of photosynthesis.

III. Stroma

    The double membrane of the chloroplast surrounds a large central space called the stroma. The stroma contains a gel-like enzymatic-rich solution called matrix.

Function: It is the light-independent reaction (dark reaction) of photosynthesis.

Discuss the mechanism of photosynthesis.  (OR)                          Explain light and dark reactions of photosynthesis. 

Mechanism of photosynthesis

    Photosynthesis is a complex process that is completed by a series of steps or reactions. There are two main steps of photosynthesis i.e.

1. Light reaction or Light-dependent reaction

The reaction step of photosynthesis which take place in the presence of light is called light reaction or light-dependent reaction. 

Mechanism of light reaction

• The light reaction takes place in grana.
• It is started when photosynthetic pigments (chlorophyll and carotenoid) capture the light energy.
• Photosynthetic pigments consist of two types of photosystems i.e.
• Photosystem-I: It absorbs light of 700 nm and is called P-700.
• Photosystem-II: It absorbs light of 680 nm and is called P-680.      
• Water and the energy of sunlight is used in light reaction. The products of the light reactions are ATP and NADPH2. Both these are transported from grana for use in dark reactions.                       

2. Dark reaction or Light independent reaction or Calvin cycle

The reaction of photosynthesis which doesn’t need direct energy from sunlight is called the dark reaction or Calvin cycle.

• This was investigated by Melvin Calvin and is also called the Calvin cycle.
• This reaction takes place in the stroma of the chloroplast.
• It depends on the product of the light reaction.

Mechanism

• In this process, ATP and NADPH2 prepared in the light reaction are used to reduce CO2 for the synthesis of carbohydrates (sugar i.e. Glucose). For the reduction of CO2, ATP provides energy while NADPH2 provides hydrogen.

            CO₂ + NADPH₂ → C₆H₁₂O₆ + 6H₂O

Discuss the factors affecting the rate of photosynthesis.

Factors affecting the rate of photosynthesis

      The following factors affect the rate of photosynthesis.

I. Effect of light intensity

    Light is a form of radiant energy that is absorbed by chlorophyll and converted into chemical energy by the process of photosynthesis. The intensity of light affects the process of photosynthesis. Very intense light is harmful and damages the chlorophyll, while the light of moderate intensity accelerates the process. Weak light slows down the process of photosynthesis. Hence, at an optimum light intensity, the rate of photosynthesis will be maximum.

II. Effect of CO2 concentration

    It is one of the raw materials of photosynthesis and is the only source of Carbon in the production of Glucose. CO₂ is almost 0.03% in the air. This concentration of CO₂ almost remains constant in the air because it is produced in respiration by the entire living organism. When the stomata are closed the concentration of CO₂ falls down in the mesophyll tissue. This lower the rate of photosynthesis. Therefore, without CO₂ photosynthesis does not occur.

III. Effect of temperature

    Besides other factors, the optimum temperature is also necessary to carry out the process of photosynthesis. An increase or decrease in temperature affects the rate of photosynthesis. Generally, a temperature ranging between 20℃ and 30℃ is most suitable for photosynthesis. At higher temperatures i.e. above 30℃ the rate of photosynthesis lowers down. At 45℃ the process of photosynthesis stops completely. 

    Similarly, at low temperatures, the rate of photosynthesis decreases, and at freezing temperatures, it stops altogether. However, plants growing in dry and hot localities and in cold regions have developed adaptations for high and low temperatures.

Discuss types of anaerobic respiration in detail.

 Types of anaerobic respiration

    Following are the two types of anaerobic respiration.

1. Lactic acid fermentation

The type of anaerobic respiration in which the end product is lactic acid is called lactic acid fermentation.

    It occurs in many microorganisms and also in muscle cells of human beings when there is more energy demand.

Steps involved in lactic acid fermentation 

    Lactic acid fermentation is completed in two steps

• In the first step, glucose is broken down into pyruvic acid by the process known as glycolysis i.e.

        C₆H₁₂O₆ + 2 ATP → 2(C₃H₄O₃) + 4ATP

• In the second step, pyruvic acid is reduced by NADH+H into lactic acid. Only 2 ATP molecules are produced in this process i.e.              

        2 (C₃H₄O₃) → 2 (C₃H₆O₃)

2.  Alcoholic fermentation

The type of anaerobic respiration in which the end product is alcohol is called alcoholic fermentation.

    It is brought about by microorganisms such as yeast. Alcohol is the end product of anaerobic respiration in plants.

Steps involved in alcoholic fermentation 

    Alcoholic fermentation is completed in two steps

• In the first step, glucose is broken down into pyruvic acid by the process known as glycolysis i.e. 

        C₆H₁₂O₆ + 2 ATP → 2(C₃H₄O₃) + 4ATP                                   

• In the second step, pyruvic acid is reduced by NADH+H into ethyl alcohol. Only 2 ATP molecules are produced in this process i.e.     

        2 (C₂H₄O₃) → 2 (C₂H₅OH) + ATP + 2 CO₂

In detail describe the steps involved in aerobic respiration. 

Steps involve in aerobic respiration

    Aerobic respiration completes in three steps. These are

1. Glycolysis

    Meaning: “Glyco” mean glucose and “lysis” mean splitting

The stepwise enzymatic breakdown of glucose up to the formation of pyruvic acid is called glycolysis.

Location:   It takes place in the cytosol (cytoplasm) and is common in both aerobic and anaerobic respiration.

    In glycolysis, the glucose molecule splits into two molecules of pyruvic acid. Glucose is a six-carbon (6-C) compound while pyruvic acid is three carbon (3-C) compound. In this process two ATP molecules are used while four ATP molecules are produced, so the net gain is two ATP i.e.

        C₆H₁₂O₆ + 2 ATP → Pyruvic acid + 4 ATP

2. Krebs cycle

    Discovery: It was discovered by Sir Hans Krebs; therefore, it is called Krebs’s cycle.

The cyclic process in which high-energy pyruvic acids are broken down completely into CO₂ and water is called Krebs’s cycle.

Location:   It takes place in the mitochondria of the cell where all the necessary enzymes are present.

        2 Pyruvic acid → 6 CO₂ + 6 H₂O + 36 ATP

3. Electron transport chain (ETC)

The transport of electrons through a series of cytochromes is known as the electron transport chain.

Explanation

    In ETC, the oxidation of reduced coenzyme (NADH + H), which is produced in glycolysis and Krebs’s cycle by molecular oxygen, takes place. During this step, two electrons are released from NADH + H. These electrons are then passed along a series of electron carriers called cytochrome.

    The cytochromes are alternately reduced and oxidized. Electrons are passed along a series of carriers. They lose energy at each transfer, some of this energy is used to form ATP from ADP and inorganic phosphate. In the end, Oxygen accepts electrons to form water.