Class 9 Biology Simplified: Short Question and Answer Notes on Bioenergetics for BISE, Federal Board, and entry tests

Short, Conceptual Biology Notes for Grade IX level Students: An Essential Guide on Chapter 7 "Bioenergetics"

    Welcome to our guide on Chapter 7 of Biology, "Bioenergetics". This essential resource is designed specifically for Grade IX level students to help them understand and grasp the key concepts of bioenergetics, photosynthesis, and respiration. This article aims to provide clear, concise, and self-explanatory answers to the important short questions related to these topics, making it an ideal study tool for students preparing for competitive exams, entry tests, and BISE/Federal Boards exams. Here, we will delve into the definition of bioenergetics, its importance, and the basics of oxidation-reduction reactions. We will also cover the fundamental aspects of photosynthesis, including its definition, reactions, and the role of chlorophyll and carbon dioxide. Additionally, we will touch upon the concept of limiting factors, explore the different types of respiration and guide you through the calculation of ATP in aerobic glycolysis. Get ready to dive into the fascinating world of Bioenergetics with this comprehensive guide.

Biology Notes on Bioenergetics, Photosynthesis, and Respiration
From Notes Library of H.E.S (Health, Education, and Skills)

Define and explain the term bioenergetics. 

Bioenergetics

The study of processes by means of which living organisms store, use and release energy is called bioenergetics.                                               (OR)                                                      

The study of capturing and conversion of energy from one form to another form in the living system and its utilization in metabolic activities is called bioenergetics.   

    As we know that metabolism is the sum of constructive and destructive processes in which either energy is gained or released, therefore following are the two types of reactions

1. Endergonic reactions

The reactions that require energy is called endergonic reactions e.g. Photosynthesis.

2. Exergonic reaction

The reactions that release energy is called exergonic reactions e.g. respiration.

Shortly discuss the importance of Bioenergetics.

Importance of bioenergetics

    Bioenergetics is the study of energy transformations in living organisms, specifically the conversion of energy from food into a form that can be utilized by cells for various processes. It is important because 

• All cellular activities, such as growth, reproduction, movement, and response to stimuli, require energy, and understanding how this energy is acquired and used is crucial for understanding biological processes at the cellular and organismal levels. 
• Bioenergetics has important applications in fields such as agriculture, medicine, and biotechnology.
• Green plants capture solar energy and convert it into stored chemical energy in the process of photosynthesis. This energy is then transformed to mechanical and heat energy during respiration.

Define Oxidation-reduction reaction.

Oxidation-Reduction reaction (Redox reaction)

The reaction in which both oxidation and reduction take place simultaneously is called an oxidation-reduction reaction or simple redox reaction.  

      While

The loss of electrons or hydrogen during metabolic reactions is called oxidation.       

      And

The gain of electrons or hydrogen during metabolic reactions is called reduction.

Explanation

    Photosynthesis and respiration are basically oxidation-reduction processes. During photosynthesis, the energy of sunlight is absorbed by plants and used CO₂ and H₂O to make food molecules, which involve oxidation-reduction reactions. Similarly, in respiration food molecules are broken down into CO₂ and H₂O, and energy is released in the form of ATP which is then used by cells for life activities.

Why Oxidation-Reduction reaction is needed?

Importance of Oxidation-reduction reaction

    Biological energy is frequently stored and released by means of oxidation-reduction reactions.

• Photosynthesis involves the reduction of CO2 into sugar and the oxidation of water into molecular oxygen (O2).
• In respiration, the sugar is oxidized to produce water and CO2.
• Due to the redox reaction the transformation of energy takes place.
• Energy obtained as a result of the redox reaction is used to synthesize ATP.
• Life processes would be impossible without oxidation-reduction reactions.

Define photosynthesis, and write down its chemical reaction?

Photosynthesis

The process by which green plants can prepare their own food (organic) from inorganic substances (CO₂  and H₂O₎ with the help of sunlight and chlorophyll is called photosynthesis. 

    The word photosynthesis is the combination of two Greek words, photo means light and synthesis means to manufacture.

The overall reaction of photosynthesis

                      6CO₂ + 6H₂O  →   C₆H₁₂O₆ + 6 H₂O + 6 O₂                        

Reactants and products of Photosynthesis

    H₂O and CO₂ are the reactants in photosynthesis while glucose and Oxygen are the products of photosynthesis. Water is used and produced in the process.

Shortly discuss the importance of photosynthesis.

Importance of photosynthesis

• Green plants that carry out photosynthesis and prepare their own food are called autotrophs. Heterotrophs can’t carry out photosynthesis and are unable to use the direct energy of sunlight. 
• So all heterotrophs depend on green plants for their energy requirements. Thus photosynthesis makes available the energy of sunlight and carbon for the use of all living organisms. No life would be possible if the process of photosynthesis stops.
• Photosynthesis removes carbon dioxide from the atmosphere and helps regulate its concentration, reducing the impact of greenhouse gases.
• Photosynthesis is the foundation of nearly all food chains and ecosystems, supporting the survival of countless species.
• The products of photosynthesis can be used to produce biofuels, offering a renewable source of energy.

Explain the role of chlorophyll and sunlight in photosynthesis.

Role of chlorophyll in photosynthesis

    Chlorophyll is a complex organic compound that absorbs mainly blue and red portion of sunlight and converts it into chemical energy for the formation of carbohydrates (Glucose). The green portion is mainly reflected, so chlorophyll appears green. When chlorophyll absorbs light, its electrons are excited. The energy of excited electrons is used to make ATP.

    In plants and algae, chlorophyll is present in chloroplast while in photosynthetic prokaryotes it is present in the cell membrane.

Types of chlorophyll

    There are many types of chlorophyll, such as chlorophyll a, b, c, d, e, and bacteriochlorophyll.  The photosynthetic pigments are organized in the form of clusters called photosystems, in the thylakoid membrane of chloroplasts. Chlorophyll “a” is the main photosynthetic pigment while chlorophyll “b” and carotenoids are called accessory pigments.

Role of sunlight in photosynthesis

    Sunlight is the source of energy for all living things. Light is a form of energy called radiant energy. A small amount of sunlight is used for the photosynthetic process. Two photosynthetic pigments i.e. chlorophyll and carotenoids absorb energy from sunlight. 

How do plants take carbon-di-oxide and water for photosynthesis?

Intake of Carbon-di-Oxide (CO₂)

    CO₂ is present in the air (0.03 %) and it is one of the essential requirements of photosynthesis. CO₂ enters the plants through small openings called stomata. Stomata are present in the lower epidermis of the leaf. Each stoma is guarded by two bean-shaped guard cells.

Diffusion of CO₂

    CO₂ diffused from outside into intercellular spaces and attaches to the wet surface of mesophyll cells. Then it diffuses into the green cells and enters the stroma. In dark reaction carbon of CO₂ is fixed and becomes a part of the glucose molecule.

Intake of water (H₂O)

    Water is also an essential component of photosynthesis. Water is absorbed by the root hairs of the plants from the soil. Which is then transported upward to the stem and leaves through xylem vessels. A small amount of water is used in photosynthesis and other metabolic activities while most of the water is transpired.

What is the limiting factor? How concentration of CO₂ can act as a limiting factor in photosynthesis?

Concept of limiting factor

The concept of limiting factors was stated by “Lebig’s law of limiting factors”. It states that

When a chemical process is controlled by more than one factor, then the rate of that chemical process will be limited by the factor which is present in minimum quantity in relation to others.        (OR)

Any environmental factor, absence, or deficiency of which can decrease the rate of a metabolic reaction.

Limiting factor for photosynthesis

    The process of photosynthesis is affected by many factors such as light, chlorophyll, CO₂, water, and optimum temperature. But the rate of photosynthesis is limited by the factor which is at its minimum value. 

CO₂ as a limiting factor

    CO₂ is one of the main requirements of photosynthesis. When all other requirements are optimum then the low CO₂ will lower the rate of photosynthesis and then act as a limiting factor.  

Define respiration. What are its types? Also, describe its importance.

Respiration

The oxidation-reduction process which occurs inside the living cells during which organic food is broken down and energy is released is called respiration.

Reaction: C₆H₁₂O₆ + 6 O₂ → 6CO₂ + 6 H₂O + Energy            

Types of respiration

    Following are the two types of respiration i.e.

1. Anaerobic respiration or Fermentation

The respiration which takes place in the absence of free oxygen is called anaerobic respiration or fermentation.

    There are two types of anaerobic respiration i.e.

1. Lactic acid fermentation
2. Alcoholic fermentation

2. Aerobic respiration

The respiration which takes place in the presence of free oxygen is called aerobic respiration.

    Unlike anaerobic respiration, aerobic respiration involves in complete oxidation of food into CO₂ and water and more energy is released.

Reaction: C₆H₁₂O₆ → 6CO₂ + 6 H₂O + 38 ATP             

    Aerobic respiration is completed in three steps, are

1. Glycolysis
2. Krebs’s cycle
3. Electron transport chain (ETC)

Importance of respiration

    All living organisms perform various functions, such as growth, reproduction, movement, etc. which need energy. this energy is provided by the process of respiration. It is common to all living organisms because all of them need energy for life activities.

Calculate the amount of ATP produced in respiration. 

    One molecule of glucose when broken down into CO₂ and water in aerobic respiration, generates 36 ATP molecules. These ATP molecules are generated stepwise.

• In glycolysis, there is the production of 2 NADPH2 and 2ATP. 
• So 2 NADPH2 x 3 = 6 ATP + 2ATP = 8 ATP
• In Krebs’s cycle complete oxidation of pyruvic acid produces 15 ATP. So there are two pyruvic acid molecules oxidized in Krebs’s cycle i.e. 
• 15 ATP x 2 = 30 ATP Total ATP 38 ATP (8 ATP from glycolysis and 30 ATP from Krebs’s cycle). 
• But NADPH2 of glycolysis consumes two ATP when they are transported to mitochondria. So the Net gain is “36 ATP”.