Chapter 2 – Life Processes in Living Organisms Part - 1
1. Fill in the blanks and explain the statements.
a. After complete oxidation of a glucose molecules, ______ number of ATP molecules are formed.
Ans: 38.
Explanation: The 34 ATP molecules generated through the electron transfer chain, along with 2 molecules each of ATP, are generated through glycolysis and Kreb’s cycle form a net total of 38 ATP molecules.
b. At the end of glycolysis, ______ molecules are obtained.
Ans: Pyruvic acid.
Explanation: A molecule of glucose is oxidized step by step in the process of glycolysis where two molecules of each, i.e. pyruvic acid, ATP, NADH₂ and water are formed.
c. Genetic recombination occurs in ______ phase of prophase of meiosis-I.
Ans: Pachytene
Explanation: During Meiosis-I, in pachytene stage, recombination/crossing over, i.e. exchange of genetic material takes place between non-sister chromatids of homologous chromosomes.
d. All chromosomes are arranged parallel to equatorial plane of cell in ______ phase of mitosis.
Ans: Metaphase.
Explanation: Nuclear membrane completely disappears in the metaphase. Chromosomes completely condense and become clearly visible along with sister chromatids. The chromosomes get parallely arranged to the equatorial plane of the cell.
e. For formation of plasma membrane, ______ molecules are necessary.
Ans: Phospholipids.
Explanation: They form the basic structure of cell membranes which are essential for the semipermeability of the plasma membrane.
f. Our muscle cells perform ______ type of respiration during exercise.
Ans: Anaerobic.
Explanation: During exercise, the oxygen supply may not be enough for the needs of muscles. Hence, anaerobic respiration occurs in the muscle cells and lactic acid accumulates, which is a result of fermentation during which glucose is broken down by anaerobic respiration.
2. Write definitions.
a. Nutrition.
Ans: The process of intake of food and its utilization by an organism is called nutrition.
b. Nutrients
Ans: Nutrients are components of food which provide energy and help in growth and maintenance of the body.
c. Proteins.
Ans: Proteins are the macromolecules formed by bonding together many amino acids.
d. Cellular respiration
Ans: Cellular respiration is a process where foodstuffs are oxidized either with or without the help of oxygen to produce energy.
e. Aerobic respiration.
Ans: Aerobic respiration is the process of producing energy from foodstuffs with the help of oxygen.
f. Glycolysis.
Ans: Glycolysis is the process in which a molecule of glucose is oxidized in a step by step process and two molecules of each, i.e. pyruvic acid, ATP, NADH₂ and water are formed.
3. Distinguish between
a. Glycolysis and TCA cycle.
Ans:
| Glycolysis | TCA cycle |
|---|---|
(i) Glycolysis occurs in the cytoplasm | (i) TCA cycle occurs in the mitochondria |
(ii) Two molecules each of pyruvic acid, ATP, NADH₂ and water are formed | (ii) Molecules of CO₂, H₂O, NADH₂ and FADH₂ are formed. |
(iii) It is also called the EMP pathway. | (iii) It is also called as Kreb’s cycle. |
(iv) No carbon dioxide is released. | (iv) Carbon dioxide is released. |
b. Mitosis and meiosis.
Ans:
| Mitosis | Meiosis |
|---|---|
(i) Mitosis takes place in the somatic cells. | (i) Meiosis takes place in the germ cells. |
(ii) Occurs in both sexually as well as asexually reproducing organisms. | (ii) Occurs only in sexually reproducing organisms. |
(iii) The cell divides only once. | (iii) There are two cell divisions, Meiosis I and Meiosis II. |
(iv) Chromosome number remains constant at the end of mitosis. | (iv) Chromosomal number is reduced from diploid to haploid, at the end of meiosis. |
c. Aerobic and anaerobic respiration.
Ans:
| Aerobic respiration | Anaerobic respiration |
|---|---|
(i) Process occurs in the presence of oxygen. | (i) Process occurs in the absence of oxygen. |
(ii) Common in all higher plants and animals. | (ii) Common in certain microorganisms but very rare in all higher plants and animals. |
(iii) Energy is released in greater amounts in the form of ATP. | (iii) Energy is released in lesser amounts in the form of ATP. |
(iv) Glucose is completely oxidised. | (iv) Glucose is incompletely oxidised. |
(v) The end products are CO₂ and water. | (v) The end products are CO₂ and organic acids or alcohol. |
4. Give scientific reasons.
a. Oxygen is necessary for complete oxidation of glucose.
Ans:
(i) Aerobic cellular respiration is the process by which cells use oxygen to help them convert glucose into energy.
(ii) Without oxygen, glucose will be incompletely oxidized and very less energy (2ATP) is produced.
(iii) In the presence of oxygen glucose is completely oxidised to produce more energy (38 ATP).
(iv) Therefore, oxygen is necessary for complete oxidation of glucose.
b. Fibers are one of the important nutrients.
Ans:
(i) Fibers are indigestible substances.
(ii) They are thrown out along with other useless and undigested matter.
(iii) This aids in egestion. Some fibres also help in digestion of other substances.
(iv) Green leafy vegetables, fruits, cereals, etc. are considered as important in diet as they supply nutritious fibers.
(v) Thus, fibers are considered as one of the important nutrients.
c. Cell division is one of the important properties of cells and organisms.
Ans:
(i) Due to the property of cell division only, a new organism is formed from the existing one, a multicellular organism grows up and an emaciated body can be restored.
(ii) It is required for wound healing and formation of blood cells.
(iii) Hence, cell division is one of the important properties of cells and organisms.
d. Sometimes, higher plants and animals too perform anaerobic respiration.
Ans:
(i) The process of respiration yields energy which occurs by the oxidation of foodstuffs.
(ii) To perform aerobic respiration, higher plants and animals perform aerobic respiration.
(iii) Cases when oxygen gets depleted these organisms respire anaerobically to obtain energy.
(iv) Therefore, sometimes higher plants and animals too perform anaerobic respiration.
e. Krebs cycle is also known as citric acid cycle.
Ans:
(i) Sir Hans Kreb proposed this cycle and hence it is called the Krebs cycle.
(ii) These are a series of cyclic chain reactions which begin with acetyl-coenzyme-A molecules which act with molecules of oxaloacetic acid.
(iii) The reactions are catalyzed with the help of specific enzymes.
(iv) The first molecule formed in this reaction is called citric acid.
(v) Therefore, the Krebs cycle is also called the citric acid cycle.
5. Answer in detail.
a. Explain the glycolysis in detail.
Ans:
Glucose → Pyruvic acid → Acetyl ‒ CoA → CO₂ + H₂O + Energy
(Glycolysis) (Kreb’s cycle)
(i) Process of glycolysis occurs in cytoplasm.
(ii) A molecule of glucose is oxidized step by step in the process and two molecules of each i.e. pyruvic acid, ATP, NADH₂ and water are formed.
(iii) Molecules of pyruvic acid formed in this process are converted into molecules of Acetyl – Coenzyme A.
(iv) Two molecules of NADH₂ and two molecules of CO₂ are released during this process.
b. With the help of suitable diagrams, explain the mitosis in detail.
Ans:
(1) Somatic cells and stem cells divide by mitosis.
(2) Mitosis is completed through two main steps,
(a) Karyokinesis (nuclear division)
(b) Cytokinesis (cytoplasmic division)
(3) Karyokinesis is completed through 4 steps.
(a) Prophase :
(i) Condensation of basically thin thread – like chromosomes starts.
(ii) Due to this, they become short and thick and they start to appear along with the pairs of sister chromatids.
(iii) Centrides duplicate and each centride moves to opposite poles of the cell.
(iv) Nuclear membrane and nucleus start to disappear.
(b) Metaphase :
(i) Nuclear membrane completely disappears. Chromosomes complete their condensation and become clearly visible.
(ii) All chromosomes are arranged parallel to the equatorial plane (central plane) of the cell.
(iii) Special types of flexible protein fibers (spindle fibers) are formed between centrioles and centromeres of each chromosome.
(c) Anaphase :
(i) Centromeres split and thereby sister chromatids of each chromosome separate and they are pulled apart in opposite directions with the help of spindle fibers.
(ii) Separated sister chromatids are called daughter chromosomes.
(iii) In this way, each set of chromosomes reach at two opposite poles of the cell.
(d) Telophase :
(i) The chromosomes which have reached at opposite poles of the cell now start to decondense due to which they again become thread like thin and invisible.
(ii) Nuclear membrane is formed around each set of chromosomes reached at poles.
(iii) Thus two daughter nuclei are formed in a cell.
(iv) Nucleolus also appears in each daughter nucleus. Spindle fibers completely disappear.
(4) In this way, karyokinesis completes and cytokinesis begins.
(5) Cytokinesis: The cytoplasm divides by cytokinesis and two new cells are formed which are called daughter cells. In this process, a notch is formed at the equatorial plane of the cell which deepens gradually and thereby two new cells are formed.
(6) However, in case of plant cells, instead of the notch, a cell plate is formed exactly along the midline of the cell and thus cytokinesis is completed.
c. With the help of suitable diagrams, explain the five stages of prophase-I of meiosis.
Ans:
(i) Prophase I is the most important stage of meiosis and differs considerably from the prophase of mitosis.
(ii) It is divided into 5 stages: leptotene, zygotene, pachytene, diplotene and diakinesis.
(iii) It involves essentially the crossing over and recombination of genetic material between non sister chromatids.
(iv) Phase – I – Leptotene :
In this stage the already replicated chromatin network condenses and starts converting into long thin thread-like chromosomes.
(v) Phase – II – Zygotene :
At this stage homologous chromosomes come closer to each other. This pairing is called ‘Synapsis’.
(vi) Phase – III – Pachytene :
Sister chromatids become visible in this stage. Crossing over occurs between non-sister chromatids of the homologous chromosomes. The crossing over is called ‘Chiasma or Chiasmata’ and this leads to genetic recombination causing variations.
(vii) Phase – IV – Diplotene :
In this stage, recombined sister chromatids start repelling. Nucleolus and nuclear membrane start disappearing.
(viii) Phase – V – Diakinesis :
Chromosomes further condense and shorten. Nucleolus and nuclear membrane completely disappear, spindle fibers begin to appear.
d. How all the life processes contribute to the growth and development of the body?
Ans:
(i) Various organ systems are continuously performing their functions in the human body.
(ii) Along with the various systems like digestive, respiratory, circulatory, excretory and control systems, different external and internal organs are performing their functions independently but through complete coordination.
(iii) This overall system is in need of a continuous source of energy.
(iv) Besides, it is coordinated by the control system of the body i.e. each life process contributes in its own way in the process of energy production.
(v) Thus, all life processes contribute to the growth and development of the body.
e. Explain the Krebs cycle with reaction.
Ans:
(i) Both molecules of Acetyl-CoA produced from pyruvic acid (from glycolysis) enter the mitochondria.
(ii) Cyclic chain of reactions called tricarboxylic acid cycle is operated on it in the mitochondria.
(iii) Acetyl part of Acetyl-CoA is completely oxidized through this cyclical process and molecules of CO₂, H₂O, NADH₂, FADH₂ are formed.
(iv) Net reaction of Kreb’s cycle:
Acetyl-CoA + 3NAD⁺ + FAD + GDP + Pi + 3H₂O → 2CO₂ + CoA + 3NADH + H⁺ + FADH₂ + GTP
6. How energy is formed from oxidation of carbohydrates, fats and proteins? Correct the diagram given below.
Ans: Process of obtaining the energy;
(i) Carbohydrates:
Carbohydrates like glucose are oxidized to pyruvic acid. Pyruvic acid is converted to acetyl-co-enzyme-A which is oxidized through Kreb’s cycle. The molecules of NADH₂, produced during this are oxidized through electron transfer chain reaction and finally energy is obtained.
(ii) Proteins:
Proteins are digested to amino acids and amino acids are converted into acetyl-co-enzyme-A. Acetyl-co-enzyme-A is oxidized through Kreb’s cycle. The molecules of NADH₂ produced during this are oxidized through electron transfer chain reaction and finally energy is obtained.
(iii) Lipids:
Lipids are converted to fatty acids and fatty acids to acetyl-co-enzyme-A. Acetyl-co-enzyme-A is oxidized through Kreb’s cycle. The molecules of NADH₂ produced during this are oxidized through electron transfer chain reaction and finally energy is obtained.
Corrected diagram:
