Matric Notes Biology Class 9th Ch 7 Bioenergetics Extra Short & Long Questions

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Short Questions

Q.1) Why is it ATP regarded as the currency of the living cell?

Answer: ATP as an energy currency:

    Cells use energy for performing activities like the synthesis of proteins, cell division, and growth etc. Energy is provided to all living cells by Adenosine Tri-Phosphate (ATP). It is an energy-rich molecule and is called as the”energy currency” of cells. Cells make ATPs to store energy while they break ATPs to get energy.

The covalent bonds between phosphates groups are high-energy bonds.

When a cell needs energy, one bond between phosphate groups is broken, it releases 7.3 kcal (7,300 calories) energy.

Q.2) What is the role of pigments during photosynthesis?

Answer: The photosynthetic pigments are organized in the form of clusters, called photosystems, in thylakoid membranes of chloroplasts. Chlorophyll-a is the main photosynthetic pigment. Others are called accessory pigments and include chlorophyll-b and carotenoids. Chlorophylls absorb mainly blue and red lights. Some wavelengths are not absorbed by chlorophyll -a and are very effectively absorbed by accessory pigments and vice versa.

Q.3) Compare lactic acid fermentation with alcoholic fermentation.

Answer:

Lactic acid fermentation	Alcoholic fermentation
Lactic acid fermentation refers to a metabolic process by which glucose is converted into lactic acid and cellular energy.	Alcoholic fermentation refers to a metabolic process by which glucose is converted into ethanol and carbon dioxide.
Occurs in bacteria, yeast and muscle cell.	Occurs in yeast and other microorganisms.
Used in the production of yogurt and cheese.	Used in the production of bread, beer, wine, and vinegar.

Q.4) Why are oxidation and reduction important for plants?

Answer: In photosynthesis, a chain of oxidation-reduction reactions occurs during which carbon dioxide and water are combined to make food molecules. In these oxidation-reduction reactions, energy is stored in food molecules. At night, photosynthesis stops and plant utilize the glucose formed at daytime by respiration. Respiration is also oxidation-reduction process during which food molecules are broken down into carbon dioxide and water. In these oxidation-reduction reactions, energy is liberated from food molecules.

Long Questions

Q.1) Explain the mechanism of photosynthesis.

Answer: Mechanism of photosynthesis:

   The mechanism of photosynthesis involves two steps:

1. Light Reaction
2. Dark Reaction

1. Light reaction:

  Light reactions take place in the granum of the chloroplast. Chlorophyll molecules absorb light. Their energy level increases and their excited electrons are released. These high energy electrons are used to produce ATP from ADP and Pi. Light also breaks the water molecule into hydrogen and oxygen (O2). Oxygen is released while hydrogen atoms are used to reduce NADP+ into NADPH.

2. Dark reaction:

  The details of dark reactions were discovered by Melvin Calvin. Dark reactions occur in the stroma of the chloroplast. These reactions do not require the energy of sunlight. During dark reactions, CO2 molecules are reduced to make carbohydrates. For the reduction of CO2, ATP provides energy while NADPH provides hydrogen.

Q.2) What is the concept of the limiting factor?what are the different limiting factors for photosynthesis?

Answer: Limiting factor:

“Any environmental factors absence or deficiency of which can decrease the rate of a metabolic reaction is called a limiting factor for that reaction”.

Different limiting factors for photosynthesis:

Many factors act as the limiting factors for photosynthesis. Important limiting factors of photosynthesis are:

i) Light intensity

ii) Temperature

iii) Concentration of carbon dioxide

i) Effect of Light Intensity:

Light is a form of radiant energy which the chlorophyll absorbs and converts into chemical energy. This chemical energy is stored in organic compounds. Light intensity and quality vary from place to place and time to time. At dawn and sunset and in winter the intensity of light is low. The intensity of light is maximum at midday. The quality and intensity of light affect the rate of photosynthesis. Very intense light damages chlorophyll and therefore has an indirect effect on the rate of photosynthesis. Very weak light has low energy and therefore energy absorption by the chlorophyll is low. This results in lower rate of photosynthesis.

ii) Effect of CO2 Concentration:

Carbon dioxide is one of the raw materials for photosynthesis. It provides carbon for the synthesis of glucose. As carbon dioxide concentrations rise, the rate of dark reaction increases. Various factors affect the closing and opening of stomata. When stomata are closed, the concentration of CO2 falls down in the mesophyll tissue. This lowers down the rate of photosynthesis.

iii) Effect of Temperature:

 Optimum temperature is necessary for a normal process of photosynthesis. An increase and decrease in temperature negatively affect the rate of photosynthesis. Generally, a temperature, ranging between 20°C and 30°C is most suitable for photosynthesis. When the temperature exceeds 30°C, the rate of photosynthesis lowers down. Similarly, at low temperatures, the rate declines, and at freezing temperature, it stops completely. However, plants growing in dry and hot localities and in cold regions have developed adaptations for high and low temperatures.

Q.3) Why is aerobic respiration considered to be more efficient than anaerobic respiration? 

Answer: Aerobic respiration is more efficient than anaerobic because it completely breaks down the food molecules and results in the release of all the energy stored in the bonds of a glucose molecule, while anaerobic respiration involves the incomplete breakdown of glucose molecule resulting in the release of less energy. Net gain of energy in the aerobic process is 36 ATP, while only 2 ATP molecules are produced from one glucose molecule in the anaerobic process. Thus, aerobic respiration is far more efficient than anaerobic.

Q.4) Aerobic respiration generates more ATP molecules than anaerobic process. Which process of aerobic respiration are responsible for this higher generation of ATP and how?

Answer: Aerobic respiration generates more ATP molecules than anaerobic because it completely breaks down the food (glucose) molecules and results in the release of all the energy stored in the bonds of a glucose molecule, while anaerobic respiration involves the incomplete oxidation of glucose molecule resulting in the release of less energy. Glycolysis occurs in both aerobic and anaerobic respiration. Both processes generate two ATP molecules and oxygen is not required for these processes. In the Krebs cycle and Electron transport chain 34 ATP molecules are generated (Aerobic respiration). Net gain of energy in the aerobic process is 36 ATP, while only 2 ATP molecules are produced from one glucose molecule in the anaerobic process. So, aerobic respiration generates more ATP molecules as compared to anaerobic respiration.