Life Processes in Living Organisms Part -1
Question 1.
Fill in the blanks and explain the statements.
a. After complete oxidation of a glucose molecules, ……….. number of ATP molecules are formed.
Answer: 38 number
b. At the end of glycolysis, ……………… molecules are obtained.
Answer: pyruvate
c. Genetic recombination occurs in ………… phase of prophuse of meiosis-I.
Answer: pachytene
d. All chromosomes are arranged parallel to equatorial plane of cell in …………. phase of mitosis.
Answer: metaphase
e. For formation of plasma membrane, _______ molecules are necessary.
Answer: phospholipid
f. Our muscle cells perform ……………… type of respiration during exercise.
Answer: anaerobic
Question 2.
Write definitions.
a. Nutrition.
Answer:
Nutrition: The process of taking nutrients in the body and utilizing them by an organism is known as nutrition.
b. Nutrients.
Answer:
Nutrients: The substances like carbohydrates, proteins, lipids, vitamins, minerals etc. which are components of the food are called nutrients.
c. Proteins.
Answer:
Proteins: Protein is a macromolecule which is formed by many amino acids which are joined by peptide bonds.
d. Cellular respiration.
Answer:
Cellular respiration: Oxidation of glucose and other food components which takes place inside the cell in presence or absence of oxygen, is known as cellular respiration.
e. Aerobic respiration.
Answer:
Aerobic respiration: Cellular respiration taking place in presence of oxygen is known as aerobic respiration.
f. Glycolysis.
Answer:
Glycolysis: The process occurring in the cell where a molecule of glucose is oxidized in step by step process forming two molecules of each of pyruvic acid, ATP, NADH2 and water, is called glycolysis.
Question 3.
Distinguish between
a. Glycolysis vs. TCA Cycle
| Feature | Glycolysis | TCA Cycle (Krebs Cycle) |
|---|---|---|
| Definition | The process of breaking down one glucose molecule into two pyruvic acid molecules to produce energy. | A series of cyclic reactions that further oxidize acetyl-CoA to produce energy and other molecules. |
| Location | Occurs in the cytoplasm of the cell. | Occurs in the mitochondria (specifically in the mitochondrial matrix). |
| Starting Material | Glucose (6-carbon molecule). | Acetyl-CoA (formed from pyruvic acid after glycolysis). |
| End Products | 2 Pyruvic acid, 2 ATP (net), 2 NADH, 2 H₂O. | CO₂, H₂O, 2 NADH₂, 1 FADH₂ (per acetyl-CoA; 2 cycles per glucose). |
| Oxygen Requirement | Does not require oxygen (occurs in both aerobic and anaerobic conditions). | Requires oxygen indirectly (part of aerobic respiration). |
b. Mitosis vs. Meiosis
| Feature | Mitosis | Meiosis |
|---|---|---|
| Definition | Cell division that produces two identical daughter cells for growth and repair. | Cell division that produces four genetically different haploid cells for reproduction. |
| Occurrence | Occurs in somatic cells (body cells) and stem cells. | Occurs in germ cells (cells that form gametes like sperm and eggs). |
| Number of Divisions | One division (includes karyokinesis and cytokinesis). | Two divisions (Meiosis-I and Meiosis-II). |
| Daughter Cells | Produces 2 daughter cells. | Produces 4 daughter cells. |
| Chromosome Number | Daughter cells are diploid (2n), same as the parent cell. | Daughter cells are haploid (n), with half the chromosome number of the parent cell. |
| Genetic Variation | Daughter cells are genetically identical to the parent cell. | Daughter cells are genetically different due to crossing over and recombination. |
| Purpose | Essential for growth, repair, wound healing, and formation of blood cells. | Essential for gamete production (sperm, eggs) and spore formation, ensuring genetic diversity. |
c. Aerobic vs. Anaerobic Respiration
| Feature | Aerobic Respiration | Anaerobic Respiration |
|---|---|---|
| Definition | Complete oxidation of glucose using oxygen to produce energy. | Incomplete oxidation of glucose without using oxygen to produce energy. |
| Oxygen Requirement | Requires oxygen. | Does not require oxygen. |
| Location | Occurs in cytoplasm (glycolysis) and mitochondria (Krebs cycle, ETC). | Occurs only in the cytoplasm (glycolysis followed by fermentation). |
| Steps Involved | Glycolysis, Krebs cycle, Electron Transport Chain (ETC). | Glycolysis followed by fermentation (e.g., lactic acid or ethanol production). |
| End Products | CO₂, H₂O, and a large amount of ATP (up to 38 ATP per glucose). | Lactic acid (in animals) or ethanol and CO₂ (in yeast), with 2 ATP per glucose. |
Question 4.
Give scientific reasons.
a. Oxygen is necessary for complete oxidation of glucose.
Answer:
- When glucose is completely oxidized in aerobic cellular respiration, it produces 38 molecules of ATP.
- In cellular respiration, three processes take place one after the other, these are glycolysis, Krebs cycle and electron transport chain reactions.
- In absence of oxygen only glycolysis can occur but further two reactions will not take place.
- If glycolysis occurs in absence of oxygen, it produces alcohol.
- By anaerobic glycolysis only two molecules of ATP are produced.
- This results in less energy supply to the body. Therefore, oxygen is necessary for complete oxidation of glucose.
b. Fibres are one of the important nutrients.
Answer:
- Fibres are indigestible substance.
- They are thrown out along with other useless and undigested matter.
- This aids in egestion. Some fibres also help in digestion of other substances.
- Green leafy vegetables, fruits, cereals, etc. are considered as important in diet as they supply nutritious fibres.
- Thus, fibres are considered as one of the important nutrients.
c. Cell division is one of the important properties of cells and organisms.
Answer:
- Cell division is very essential for all the living organisms.
- The growth and development is possible only due to cell division.
- The emaciated body can be restored only through the cell division which adds new cells.
- Offspring is produced only through the cell division that take place in parents.
- In asexual reproduction, mitosis helps to give rise to new generation.
- In sexual reproduction, meiosis helps to form haploid gametes.
- 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.
Answer:
- When there is deficiency of oxygen in the surrounding, the aerobic respiration is not possible.
- In such case, to survive, higher plants switch over to anaerobic respiration.
- In some animal tissues in case of oxygen deficiency cells perform anaerobic respiration.
e. Krebs cycle is also known as citric acid cycle.
Answer:
- Sir Hans Kreb proposed this cycle and hence it is called Krebs cycle.
- These are series of cyclic chain reactions which begins with acetyl-coenzyme-A molecules which act with molecules of oxaloacetic acid.
- The reactions are catalysed with the help of specific enzymes.
- The first molecule formed in this reaction is called citric acid. Therefore, Krebs cycle is also called citric acid cycle.
Question 5.
Answer in detail.
a. Explain the glycolysis in detail.
Answer:
Glycolysis is an important process in living organisms where one molecule of glucose (a type of sugar) is broken down into two molecules of pyruvic acid. This process happens in the cytoplasm of cells and is the first step in cellular respiration, which helps produce energy for the body. Glycolysis is a universal process that occurs in both plants and animals, whether oxygen is present (aerobic) or not (anaerobic).
b. With the help of suitable diagrams, explain the mitosis in detail.
Answer:
(1) There are two stages of mitosis. These are
(a) Karyokinesis or nuclear division and
(b) Cytokinesis or cytoplasmic division. Karyokinesis takes place in further four phases, viz prophase, metaphase, anaphase and telophase.
(a) Karyokinesis:
(i) Prophase: During prophase, condensation of chromosomes starts. The thin and thread like chromosomes start thickening. They are seen with their pair of sister chromatids. In animal cells the centrioles are seen to duplicate and move to opposite poles of the cell. Nuclear membrane and nucleolus disappear.
(ii) Metaphase: Chromosomes complete their condensation and each one is seen with its sister chromatids. The chromosomes are seen in equatorial plane of the cell. The spindle fibres are formed from polar region, where centrioles are present, and they attach themselves to the centromere of each chromosome. Nuclear membrane now disappears completely.
(iii) Anaphase: The centromeres of the chromosomes now divide forming two daughter chromosomes. The spindle fibres pull apart the chromosomes from equatorial region to the opposite poles. Chromosomes moving to the poles appear like bunch of bananas. One set of chromosomes reach each pole by the end of the anaphase.
(iv) Telophase: Telophase is reverse of events that occurred in prophase. The thickened chromosomes decondense. They again assume the thin and thread like appearance. Nuclear membrane and nucleolus appear again. The spindle fibres are completely lost. The cell looks as if it has two nuclei in one cytoplasm.
(b) Cytokinesis: In animal cells a notch develops in the middle of the cell. This notch goes on deepening down and later the cytoplasm divides into two. In plant cells, cell plate formation takes place and then cytokinesis takes place.
c. With the help of suitable diagrams, explain the five stages of prophase-I of meiosis.
Answer:
Prophase-I: Prophase – I of meiosis is much longer phase of the meiosis.
It is subdivided into 5 substages, namely leptotene, zygotene, pachytene, diplotene, and diakinesis.
(1) Leptotene: Initially the chromosomes start condensation and they become compact during leptotene.
(2) Zygotene: In zygotene, homologous chromosomes start pairing. This pairing is called synapsis. The structure called synaptonemal complex develops to hold chromosomes in place during this pairing. Each chromosome’s chromatid arm divides and forms structure called bivalent or tetrad.
(3) Pachytene: During pachytene stage, crossing over of non-sister chromatids of homologous chromosomes takes place. Genetic recombination is produced due to such exchange. The homologous chromosomes still remain paired together at the sites of crossing over.
(4) Diplotene: During diplotene, synaptonemal complex dissolves and the homologous chromosomes of the bivalents separate except at the point of crossing over. Thus, it looks like X-shaped structures called the chiasmata.
(5) Diakinesis: The last phase of prophase is for termination of chiasmata. The spindle fibres originate, and the cross-over homologous chromosomes are now separated. The nucleQlus disappears, and the nuclear envelope breaks down.
d. How do all the life processes contribute to the growth and development of the body?
Answer:
- Different systems work in co-ordination with each other in the body of the living organisms. In human body the homoeostasis is very advanced.
- Digestive system, respiratory system, circulatory system, excretory system, nervous system and all the external and internal organs in the bodywork independently but in coordination with each other.
- The digested and absorbed nutrients of the food are transported to various cells with the help of circulatory system due to pumping of the heart. Simultaneously, the oxygen absorbed in the blood by lungs is also transported to each cell by RBCs.
- Mitochondria in every cell brings about oxidation of nutrients and produce energy required for all of these functions.
- The control is exercised by the nervous system on all these actions. This keeps the organism alive and helps in growth and development of the same.
e. Explain the Krebs cycle with reaction.
Answer:
- Krebs cycle was proposed by Sir Hans Kreb. This cycle is named after him. It is also called tricarboxylic acid cycle or citric acid cycle.
- The acetyl-coenzyme-A molecules enter the mitochondria located in the cytoplasm.
- They participate in the chemical reactions taking place in Krebs cycle.
- In the cyclic chemical reactions, acetyl- coenzyme-A is completely oxidised
- It yields molecules of CO2, H2O, NADH2, FADH2 and ATP upon complete oxidation.
Question 6.
How energy is formed from oxidation of carbohydrates, fats and proteins?
Correct the dagram below.
Answer:
(1) First of all the dietary carbohydrates are digested in the digestive system with the help of various enzymes and converted into glucose. Similarly, proteins are converted into amino acids and fats are broken down into fatty aid and glycerol (alcohol).
(2) Oxidation of carbohydrates takes place during cellular respiration. Glucose is oxidized by three steps during aerobic respiration, viz. glycolysis, tricarboxylic acid cycle or Krebs cycle and electron transfer chain.
(3) From one molecule of glucose two molecules of each pyruvic acid, ATP, NADH2 and water are formed during glycolysis. Pyruvic acid which is formed in this process is converted into Acetyl-Coenzyme-A along with release of two molecules each of NADH2 and CO2.
(4) In the next step, i.e. in TCA cycle, molecules of Acetyl-Co-A enter the mitochondria and a cyclic chain of reactions take place. Acetyl part of Acetyl- Co-A is completely oxidized through this cyclical process. The molecules CO2, H2O, NADH2, FADH2 are released in this process.
(5) In third step, i.e. in ETC reaction, NADH2 and FADH2 formed during first two steps are used for obtaining ATP molecules. 3 molecules of ATP are obtained from each NADH2 molecule and 2 molecules of ATP from each FADH2.
(6) Thus, one molecule of glucose upon complete oxidation in presence of oxygen yields 38 molecules of ATP. This is how from carbohydrates, energy is obtained.
(7) If carbohydrates are insufficient in diet, then proteins or lipids are used for energy production. Fatty acids derived from fats and amino acids derived from proteins are converted into Acetyl- Co-A. Acetyl-Co-A once again can yield energy through TCA cycle.
Corrected diagram:
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