Explore Chapter 8: Bioenergetics from the Class 9th Biology New Syllabus for Punjab Boards. This post provides detailed insights into photosynthesis, cellular respiration, ATP production, and factors affecting energy metabolism. It includes solved MCQs, short questions, and key points for exam preparation. Ideal for students studying under Punjab boards who want a comprehensive understanding of bioenergetics for better exam performance.
A. Select the correct answers for the following questions:
1. When we get energy from ATP, which bonds are broken?
- Options:
a) P-P bonds
b) C-H bonds
c) C-N bonds
d) C=O bonds - Answer: a) P-P bonds
- Explanation: Energy is released from ATP when the high-energy phosphate bonds (P-P bonds) are hydrolyzed. Typically, the terminal phosphate group is removed, converting ATP to ADP.
- Tip: Remember “ATP = Adenosine Tri-Phosphate,” where the energy is stored in the phosphate bonds.
2. Light reactions of photosynthesis occur in:
- Options:
a) Plasma membrane of cell
b) Cytoplasm of cell
c) Stroma of chloroplasts
d) Thylakoids of chloroplasts - Answer: d) Thylakoids of chloroplasts
- Explanation: The light-dependent reactions of photosynthesis occur in the thylakoid membranes, where chlorophyll absorbs light and converts it into chemical energy (ATP and NADPH).
- Tip: Think of “thylakoid” as the “power plant” of the chloroplast for light reactions.
3. Which type of chlorophyll is most common in plants?
- Options:
a) Chlorophyll a
b) Chlorophyll b
c) Chlorophyll c
d) Chlorophyll d - Answer: a) Chlorophyll a
- Explanation: Chlorophyll a is the primary pigment responsible for photosynthesis in plants. It absorbs light most efficiently in the blue-violet and red regions of the spectrum.
- Tip: Chlorophyll a is “essential,” while others are “accessory pigments.”
4. Where does the reaction of photosynthesis take place?
- Options:
a) Chloroplast
b) Mitochondria
c) Cytoplasm
d) Ribosomes - Answer: a) Chloroplast
- Explanation: Photosynthesis occurs in chloroplasts, with light reactions in the thylakoids and the Calvin cycle in the stroma.
- Tip: Remember that chloroplasts are exclusive to plants and are the “photosynthesis factory.”
5. When yeast ferments glucose, the products are:
- Options:
a) Alcohol and CO₂
b) Alcohol and water
c) Lactic acid and H₂O
d) Alcohol and H₂O - Answer: a) Alcohol and CO₂
- Explanation: In anaerobic conditions, yeast ferments glucose to produce ethanol (alcohol) and carbon dioxide as by-products.
- Tip: Associate “yeast” with “alcoholic fermentation.”
6. In which part of the chloroplast does the light-dependent reaction occur?
- Options:
a) Stroma
b) Thylakoid membrane
c) Outer membrane
d) Matrix - Answer: b) Thylakoid membrane
- Explanation: The light-dependent reactions take place in the thylakoid membrane, where light is absorbed to produce ATP and NADPH.
- Tip: Light = “Thylakoid”; Calvin cycle = “Stroma.”
7. Which molecule donates electrons in the light-dependent reactions of photosynthesis?
- Options:
a) NADPH
b) Water
c) Oxygen
d) Carbon dioxide - Answer: b) Water
- Explanation: Water (H₂O) is split during photolysis in the light-dependent reactions, releasing electrons, protons, and oxygen as a by-product.
- Tip: Remember that “water splitting” produces the electrons needed for photosynthesis.
8. Which process in aerobic respiration produces the most ATP?
- Options:
a) Glycolysis
b) Electron transport chain
c) Fermentation
d) Krebs cycle - Answer: b) Electron transport chain
- Explanation: The electron transport chain (ETC) produces the most ATP (approximately 34 molecules per glucose molecule) during aerobic respiration, using the energy from NADH and FADH₂.
- Tip: The ETC is the “energy powerhouse” of respiration.
9. In yeast cells, anaerobic respiration leads to the production of:
- Options:
a) Lactic acid
b) Ethanol
c) Acetic acid
d) Glucose - Answer: b) Ethanol
- Explanation: Under anaerobic conditions, yeast converts glucose into ethanol and CO₂ via fermentation.
- Tip: Recall the industrial use of yeast in brewing and alcohol production.
Answers to MCQs:
- How many ATP molecules are produced from one glucose molecule during anaerobic respiration?
Answer: a) 2 - What is a common byproduct of anaerobic respiration in animal cells?
Answer: c) Lactic acid
Short Answers:
- Importance of oxidation-reduction reactions:
Oxidation-reduction reactions are essential in cellular respiration and photosynthesis. They help transfer energy by moving electrons between molecules. - Meaning and roles of ATP and ADP:
- ATP (Adenosine Triphosphate): The main energy carrier in cells. It stores and provides energy for cellular activities.
- ADP (Adenosine Diphosphate): A lower-energy molecule that is converted back to ATP during cellular respiration.
- Word equation for photosynthesis:
Carbon dioxide + Water → Glucose + Oxygen
(In the presence of sunlight and chlorophyll) - Why is chlorophyll important for photosynthesis?
Chlorophyll absorbs light energy from the sun, which is needed to drive the process of photosynthesis. - How is oxygen produced during photosynthesis?
Oxygen is produced as a byproduct when water molecules are split during the light-dependent reactions of photosynthesis. - Organisms that carry out photosynthesis and responsible organelle:
Plants, algae, and some bacteria carry out photosynthesis. The chloroplast is the organelle responsible for absorbing light. - Main purpose of cellular respiration:
To produce energy in the form of ATP, which is used for various cellular activities. - Equation for aerobic respiration:
Glucose + Oxygen → Carbon dioxide + Water + Energy (ATP) - Role of oxygen in aerobic respiration:
Oxygen is essential for breaking down glucose completely to release energy efficiently. - Definition of anaerobic and aerobic respiration:
- Anaerobic respiration: Respiration that occurs without oxygen, producing less ATP.
- Aerobic respiration: Respiration that requires oxygen, producing more ATP.
- End products of anaerobic respiration in animals and yeast:
- Animals: Lactic acid and ATP.
- Yeast: Ethanol, carbon dioxide, and ATP.
- How muscles respond to oxygen deficiency during exercise:
Muscles switch to anaerobic respiration, producing lactic acid and causing fatigue. - Ways respiratory energy is used in the body:
- Muscle contraction
- Cell division
- Active transport of molecules
- Maintaining body temperature
Detailed Answers:
- Explain ATP as the chief energy currency of all cells:
ATP is the primary molecule that stores and transfers energy in cells. It powers cellular processes like muscle contraction, nerve impulses, and biosynthesis. ATP releases energy when its phosphate bonds are broken, turning into ADP. - Outline the processes involved in photosynthesis:
Photosynthesis occurs in two stages:
- Light-dependent reactions: Light energy splits water into oxygen, hydrogen ions, and electrons.
- Light-independent reactions (Calvin cycle): Carbon dioxide combines with hydrogen ions to form glucose using energy from ATP and NADPH.
- Write a note on the intake of carbon dioxide and water by plants:
Plants absorb carbon dioxide through tiny pores called stomata in their leaves. Water is absorbed by roots from the soil and transported to leaves via xylem vessels. - Explain the types and importance of anaerobic respiration:
- Types:
- Lactic acid fermentation in animals.
- Alcoholic fermentation in yeast.
- Importance:
- Provides energy in low-oxygen conditions.
- Used in industries like brewing and baking.
- Outline the mechanism of aerobic respiration:
Aerobic respiration occurs in three stages:
- Glycolysis: Glucose is broken down into pyruvate, producing 2 ATP.
- Krebs cycle: Pyruvate is broken down further, releasing carbon dioxide and energy-rich molecules.
- Electron transport chain: Oxygen accepts electrons, forming water and generating a large amount of ATP (about 36 molecules).
- Compare the processes of respiration and photosynthesis:
- Photosynthesis:
- Occurs in chloroplasts.
- Converts light energy into chemical energy.
- Reactants: Carbon dioxide and water.
- Products: Glucose and oxygen.
- Respiration:
- Occurs in mitochondria.
- Converts chemical energy (glucose) into usable energy (ATP).
- Reactants: Glucose and oxygen.
- Products: Carbon dioxide and water.
