Igniting the Spark of Knowledge

Life Processes in Living Organisms – Part 1

Complete study guide with questions and answers

1
Fill in the blanks and rewrite the statements.

Answer:

a. After the complete oxidation of one glucose molecule, ______ ATP molecules are produced.
38
b. At the completion of glycolysis, ______ molecules are formed.
2 pyruvic acid, 2 ATP, and 2 NADPH2
c. Genetic recombination takes place during the ______ stage of prophase of meiosis-I.
third (pachytene)
d. All chromosomes align parallel to the equatorial plane of the cell during the ______ stage of mitosis.
metaphase
e. For the formation of the plasma membrane, ______ molecules are required.
lipid (phospholipid)
f. During exercise, our muscle cells carry out ______ respiration.
anaerobic
2
Write definitions.

Answers:

Nutrition

All living organisms need food for growth, repair and maintenance. The process by which an organism consumes and utilizes food is known as nutrition.

Nutrients

Nutrients are substances that organisms obtain from food to support growth, survival and reproduction. These include carbohydrates, fats, proteins, vitamins and minerals.

Proteins

Proteins are large and complex biomolecules made up of amino acids joined together by peptide bonds. Structures such as muscles, hair and nails are composed mainly of proteins.

Cellular Respiration

Cellular respiration is the biochemical process through which cells release energy from food in the form of ATP, either in the presence or absence of oxygen.

Aerobic Respiration

Aerobic respiration is the process of releasing energy by oxidizing glucose in the presence of oxygen. This multistep process produces 38 ATP molecules.

C6H12O6 + 6O2 → 6CO2 + 6H2O + Energy
Glycolysis

Glycolysis is the initial stage of cellular respiration that occurs in the cytoplasm, where one glucose molecule is broken down into two molecules of pyruvic acid.

3
Distinguish between the following:

Answers:

Glycolysis
  • Occurs in the cytoplasm
  • First stage of cellular respiration
  • Anaerobic process (does not require oxygen)
  • Breaks down glucose into pyruvate
  • Produces 2 ATP molecules net
TCA Cycle (Krebs Cycle)
  • Occurs in mitochondrial matrix
  • Second stage of aerobic respiration
  • Aerobic process (requires oxygen)
  • Oxidizes acetyl-CoA to CO2
  • Produces more ATP (24-28) indirectly via electron carriers
Mitosis
  • Occurs in somatic cells
  • One division cycle
  • Produces 2 diploid daughter cells
  • Daughter cells are genetically identical
  • Used for growth, repair, and asexual reproduction
  • No crossing over occurs
Meiosis
  • Occurs in germ cells
  • Two division cycles (Meiosis I & II)
  • Produces 4 haploid daughter cells
  • Daughter cells are genetically different
  • Used for gamete formation and sexual reproduction
  • Crossing over occurs in prophase I
Aerobic Respiration
  • Requires oxygen
  • Occurs in mitochondria
  • Complete oxidation of glucose
  • Produces CO2 and H2O
  • Yields 38 ATP molecules per glucose
  • More efficient energy production
Anaerobic Respiration
  • Does not require oxygen
  • Occurs in cytoplasm
  • Incomplete oxidation of glucose
  • Produces lactic acid or ethanol + CO2
  • Yields only 2 ATP molecules per glucose
  • Less efficient energy production
4
Give scientific reasons.

Answers:

(A) Oxygen is essential for the complete oxidation of glucose.

All living organisms need energy to perform life activities. This energy is obtained from food such as carbohydrates. Complete breakdown of glucose into simpler substances releases maximum energy and requires oxygen. Therefore, oxygen is necessary for complete oxidation of glucose.

(B) Fibres are important nutrients.

Along with carbohydrates, proteins, fats, vitamins and minerals, dietary fibres are essential nutrients. Although fibres are not digested, they help in digestion and assist in the elimination of undigested food from the body.

(C) Cell division is an important characteristic of cells and organisms.

Cell division results in the formation of new cells. It is essential for growth, repair and reproduction. In unicellular organisms like Amoeba, cell division produces new individuals, while in multicellular organisms it helps in growth and healing.

(D) Sometimes higher plants and animals also perform anaerobic respiration.

When oxygen supply is insufficient, higher plants and animals switch to anaerobic respiration. For example, during seed germination in waterlogged soil and during vigorous exercise in humans, cells respire anaerobically and release less energy.

(E) Krebs cycle is also called the citric acid cycle.

The Krebs cycle was discovered by Sir Hans Krebs. The first stable compound formed in this cycle is citric acid, a six-carbon molecule. Hence, the Krebs cycle is also known as the citric acid cycle.

5
Answer in detail.

Detailed Answers:

(A) Explain glycolysis.

Glycolysis is the first stage of cellular respiration.

  • It occurs in the cytoplasm of the cell.
  • It is common to both aerobic and anaerobic respiration.
  • In this process, one molecule of glucose is gradually oxidized to form two molecules each of pyruvic acid, ATP, NADH2 and water.
  • The process involves 10 enzymatic reactions.
  • It requires an initial investment of 2 ATP but yields 4 ATP, resulting in a net gain of 2 ATP molecules.
  • Glycolysis does not require oxygen and can occur under anaerobic conditions.
(B) Explain mitosis with the help of suitable diagrams.

Mitosis is completed in two main stages:

I. Karyokinesis (division of the nucleus)

Karyokinesis occurs in four phases:

  • Prophase: Chromosomes become short and thick due to condensation. Each chromosome consists of two sister chromatids. Centrioles move to opposite poles, and the nuclear membrane and nucleolus begin to disappear.
  • Metaphase: Chromosomes align at the equatorial plane of the cell. Spindle fibres attach to the centromeres of chromosomes.
  • Anaphase: Centromeres divide, and sister chromatids separate and move toward opposite poles. These separated chromatids are called daughter chromosomes.
  • Telophase: Chromosomes uncoil and become thin. Nuclear membranes reform around each set of chromosomes, resulting in two daughter nuclei.
II. Cytokinesis (division of the cytoplasm)

In animal cells, the cytoplasm divides by the formation of a cleavage furrow, while in plant cells a cell plate forms at the center, producing two daughter cells.

Refer to textbook for diagrams showing the different stages of mitosis.
(C) Explain the five stages of prophase-I of meiosis with diagrams.

Meiosis is a type of cell division occurring in germ cells during sexual reproduction and includes Meiosis-I and Meiosis-II.

The five stages of prophase-I are:

  • Leptotene: Chromosomes begin to condense and become visible as long, thin threads.
  • Zygotene: Homologous chromosomes pair closely to form bivalents or tetrads (synapsis).
  • Pachytene: Crossing over occurs between non-sister chromatids, resulting in genetic recombination.
  • Diplotene: Homologous chromosomes start separating but remain connected at chiasmata.
  • Diakinesis: Chromosomes condense further, chiasmata terminalize, and the nuclear membrane disintegrates.
Refer to textbook for diagrams showing the five stages of prophase-I.
(D) How do life processes contribute to growth and development?

Life processes are essential activities that maintain body functions and ensure survival. These include:

Nutrition

Provides raw materials and energy for growth and repair.

Respiration

Releases energy from food for cellular activities.

Transportation

Distributes nutrients, oxygen and hormones throughout the body.

Metabolism

Chemical reactions that build up and break down substances for growth.

Excretion

Removes toxic wastes that could hinder growth and development.

Reproduction

Ensures continuity of species and genetic diversity.

Together, these coordinated processes lead to growth, development, and maintenance of the organism.

(E) Explain the Krebs cycle with reaction.

The Krebs cycle, also known as the TCA or citric acid cycle, takes place in the mitochondrial matrix.

  • It begins when acetyl-CoA (2C) combines with oxaloacetate (4C) to form citric acid (6C).
  • Through a series of reactions, citric acid is broken down, releasing carbon dioxide and regenerating oxaloacetate.
  • For each acetyl-CoA molecule, the cycle produces three NADH, one FADH2 and one ATP (or GTP).
  • The NADH and FADH2 produced enter the electron transport chain to generate more ATP.
  • The cycle turns twice for each glucose molecule (since glycolysis produces 2 pyruvate molecules).
Acetyl CoA + 3 NAD+ + FAD + ADP + Pi → 2 CO2 + 3 NADH + FADH2 + ATP + CoA

Overall, the Krebs cycle is a central metabolic pathway that connects carbohydrate, fat, and protein metabolism.

6
How is energy released from carbohydrates, fats and proteins? Correct the given diagram.

Answer:

Please refer to the textbook for the diagram and detailed explanation of energy release from carbohydrates, fats, and proteins.
Key Points:
  • Carbohydrates: Broken down into glucose, which enters glycolysis and cellular respiration to produce ATP.
  • Fats: Broken down into fatty acids and glycerol. Fatty acids undergo beta-oxidation to form acetyl-CoA, which enters the Krebs cycle.
  • Proteins: Broken down into amino acids. After deamination, the carbon skeletons enter various stages of cellular respiration.