2. Life Processes in living organisms Part -1

1. Fill in the blanks and explain the statements.

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a. After complete oxidation of a glucose molecules, 38 number of ATP molecules are formed.
b. At the end of glycolysis, pyruvic acid molecules are obtained.
c. Genetic recombination occurs in pachytene phase of prophase of meiosis-I.
d. All chromosomes are arranged parallel to equatorial plane of cell in metaphase phase of mitosis.
e. For formation of plasma membrane, phospholipid molecules are necessary.
f. Our muscle cells perform anaerobic type of respiration during exercise.

2. Write definitions.

(a) Nutrition
Ans. The process of intake of food and its utilization by an organism is called as 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 oxidised 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.
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b. Mitosis and meiosis.(Sep. ’21)

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c. Aerobic and anaerobic respiration. (Nov. ’20)

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4. Give scientific reasons.

a. Oxygen is necessary for complete oxidation of glucose.

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(1) In cellular respiration, three processes take place one after the other, these are glycolysis, Krebs cycle and electron transport chain reactions. (2) In absence of oxygen, only glycolysis can occur but further two reactions will not take place. (3) If glycolysis occurs in absence of oxygen, it produces alcohol. (4) By anaerobic glycolysis only two molecules of ATP are produced. (5) This results in less energy supply to the body. Therefore, oxygen is necessary for complete oxidation of glucose.

b. Fibers are one of the important nutrients.

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(1) Fibres are indigestible substance. (2) They are thrown out along with other useless and undigested matter. (3) This aids in egestion. Some fibres also help in digestion of other substances. (4) Thus, fibres are considered as one of the important nutrients.

c. Cell division is one of the important properties of cells and organisms. (Sept. ’21)

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(1) Cell division is very essential for all the living organisms. (2) The growth and development is possible only due to cell division. (3) The emaciated body can be restored only through the cell division which adds new cells. (4) Offspring is produced only through the cell division that take place in parents. (5) All such functions show that cell division is one of the important properties of cells and organisms.

d. Sometimes, higher plants and animals too perform anaerobic respiration.

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(1) When there is deficiency of oxygen in the surrounding, the aerobic respiration is not possible. (2) In such case, to survive, higher plants switch over to anaerobic respiration. (3) In some animal tissues in case of oxygen deficiency cells perform anaerobic respiration.

e. Kreb’s cycle is also known as citric acid cycle.

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(1) Sir Hans Kreb proposed this cycle and hence it is called Krebs cycle. (2) These are series of cyclic chain reactions which begins with acetyl coenzyme-A molecules which act with molecules of oxaloacetic acid. (3) The first molecule formed in this reaction is called citric acid. Therefore, Krebs cycle is also called citric acid cycle.

5. Answer in detail.

a. Explain the glycolysis in detail.

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(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.

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Somatic cells and stem cells divide by mitosis. Mitosis is completed through two main steps. Those two steps are karyokinesis (nuclear division) and cytokinesis (cytoplasmic division). Karyokinesis is completed through four steps.
A. Prophase : In prophase, condensation of basically thin thread-like chromosomes starts. Due to this, they become short and thick and they start to appear along with their pairs of sister chromatids. Centrioles duplicate and each centriole moves to opposite poles of the cells. Nuclear membrane and nucleolus start to disappear.
B. Metaphase : Nuclear membrane completely disappears in metaphase. Chromosomes complete their condensation and become clearly visible along with their sister chromatids. All chromosomes are arranged parallel to equatorial plane (central plane) of the cell. Special type of flexible protein fibers (spindle fibers) are formed between centromere of each chromosome and both centrioles.
C. Anaphase : In anaphase, centromeres split and thereby sister chromatids of each chromosome separate and they are pulled apart in opposite directions with the help of spindle fibers. Separated sister chromatids are called as daughter chromosomes. Chromosomes being pulled appear like bunch of bananas. In this way, each set of chromosomes reach at two opposite poles of the cell.
D. Telophase : 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. Nuclear
membrane is formed around each set of chromosomes reached at poles. Thus, two daughter nuclei are formed in a cell. Nucleolus also appears in each daughter nucleus. Spindle
fibers completely disappear.
In this way, karyokinesis completes and cytokinesis begins.

The cytoplasm divides by cytokinesis and two new cells are formed which are called as 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. However, in case of plant cells, instead of the notch, a cell plate is formed exactly along 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.

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Phase – I – Leptotene : In this stage already replicated chromatin network condenses and start converting into long thin thread like chromosomes.

Phase – II – Zygotene : It this stage homologous chromosomes come closer to each other. This pairing is called ‘Synapsis’.

Phase – III – Pachytene : Sister chromatids become visible in this stage. Crossing over occurs between nonsister chromatids of the homologous chromosomes. The crossing over is called as ‘Chiasma or Chiasmata’ and this leads to genetic recombination causing variations.

Phase – IV – Diplotene : In this stage, recombined sister chromatids start repelling. Nucleolus and nuclear membrane start disappearing.

Phase – V – Diakinesis : Chromosomes further condense and shorten. Nucleolus and nuclear membrane completely disappear, spindle fibres begin to appear.

d. How all the life processes contribute to the growth and development of the body?

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(i) Various organ systems are continuously performing their functions in human body. (ii) Along with the various systems like digestive, respiratory, circulatory, excretory and control system, different external and internal organs are performing their functions independently but through complete co-ordination. (iii) This overall system is in need of continuous source of energy. (iv) Besides, it is co-ordinated 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 Kreb’s cycle with reaction.

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(i) Both molecules of acetyl-CoA enter the mitochondria. (ii) Cyclic chain of reactions called as 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.

5. How energy is formed from oxidation of carbohydrates, fats and proteins? Correct the diagram given below.

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