After complete oxidation of a glucose molecule, 38 number of ATP molecules are formed.

Explanation: In aerobic respiration, one glucose molecule undergoes glycolysis (producing 8 ATPs net), formation of acetyl-CoA (producing 6 ATPs), and the Krebs cycle with electron transport chain (producing 24 ATPs), totaling 38 ATP molecules.

At the end of glycolysis, pyruvate (pyruvic acid) molecules are obtained.

Explanation: During glycolysis occurring in cytoplasm, a 6-carbon glucose molecule is broken down step-by-step into two 3-carbon molecules of pyruvic acid, along with 2 ATP, 2 NADH₂, and 2 water molecules.

Genetic recombination occurs in pachytene phase of prophase of meiosis-I.

Explanation: During the pachytene sub-stage of prophase-I, crossing over occurs between non-sister chromatids of homologous chromosomes, resulting in genetic exchange and recombination.

All chromosomes are arranged parallel to equatorial plane of cell in metaphase phase of mitosis.

Explanation: In metaphase, chromosomes complete their condensation, the nuclear membrane dissolves, and spindle fibres pull the chromosomes to align at the central equatorial plate.

For formation of plasma membrane, phospholipid molecules are necessary.

Explanation: The cell plasma membrane is chemically a phospholipid bilayer, made from fatty acids and glycerol, which provides structural integrity and semi-permeability.

Our muscle cells perform anaerobic type of respiration during exercise.

Explanation: During vigorous exercise, oxygen demand exceeds oxygen supply in muscle tissues. Muscles temporarily switch to anaerobic respiration, producing lactic acid which causes muscle fatigue.

The process of intake and utilization of food nutrients by living organisms for obtaining energy, growth, maintenance, and repair of tissues is called nutrition.

Chemical substances present in food—such as carbohydrates, proteins, lipids (fats), vitamins, mineral salts, and water—that provide energy and support life processes are called nutrients.

Biological macromolecules formed by many amino acid units linked together by peptide bonds are called proteins. They provide 4 kcal of energy per gram and serve as body-building materials.

The enzymatic breakdown and oxidation of food components (mainly glucose) inside living cells to release biologically usable energy in the form of ATP is called cellular respiration.

The cellular respiration in which glucose is completely oxidized in the presence of molecular oxygen to produce carbon dioxide, water, and 38 ATP molecules is called aerobic respiration.

The step-by-step breakdown of one molecule of glucose in the cell cytoplasm into two molecules of pyruvic acid, ATP, NADH₂, and water is called glycolysis (EMP pathway).

1. Complete cellular oxidation of glucose involves three stages: Glycolysis, the Krebs cycle, and the Electron Transfer Chain (ETC).
2. In the absence of oxygen, only glycolysis can take place in the cytoplasm, yielding only 2 ATP molecules and converting pyruvic acid into alcohol or lactic acid (incomplete oxidation).
3. Molecular oxygen acts as the final electron acceptor in the Electron Transfer Chain within mitochondria, which drives the production of 34 additional ATP molecules.
4. Therefore, oxygen is absolutely necessary for the complete breakdown of glucose into CO₂, water, and full energy yield (38 ATPs).

1. Dietary fibres are indigestible plant carbohydrates (cellulose) that our digestive enzymes cannot break down.
2. However, fibres add bulk to the digested food in the intestines and help in smooth peristaltic movement of bowels.
3. Fibres assist in the proper digestion of other food substances and prevent constipation by facilitating easy egestion of undigested waste.
4. Hence, green leafy vegetables, fruits, and whole grains rich in dietary fibres are considered essential nutrients.

1. All living organisms begin life as a single cell (zygote). Growth and physical development are only possible through continuous mitotic cell division.
2. Wounds are healed and dead or damaged cells are replaced daily by the production of new cells via mitosis.
3. Asexual reproduction in unicellular organisms (amoeba, yeast) depends entirely on cell division.
4. In sexual reproduction, meiotic cell division produces haploid gametes (sperm and ova), ensuring genetic continuity across generations.
5. Therefore, cell division is a vital and fundamental property of all living systems.

1. Normally, higher plants and animals carry out aerobic respiration.
2. However, if oxygen levels in the environment become severely depleted—such as seeds submerged under waterlogged soil during germination—plants switch to anaerobic respiration to survive.
3. Similarly, during vigorous running or intense exercise, oxygen supply to human muscle cells falls short of the energy demand. Muscle cells temporarily perform anaerobic respiration, accumulating lactic acid.

1. In this cyclic pathway inside the mitochondria, the 2-carbon Acetyl-CoA combines with 4-carbon oxaloacetic acid to initiate the reaction.
2. The very first stable chemical compound formed during this cycle is citric acid (a 6-carbon tricarboxylic acid).
3. Because citric acid is the first product synthesized in this pathway, the Krebs cycle is also called the Citric Acid Cycle or Tricarboxylic Acid (TCA) Cycle.

1. Glycolysis is the initial step of cellular respiration occurring in the cytoplasm of all living cells. It was discovered by Gustav Embden, Otto Meyerhof, and Jacob Parnas, hence named the EMP Pathway.
2. In this process, one molecule of 6-carbon glucose is broken down through a sequence of enzymatic steps into two molecules of 3-carbon pyruvic acid.
3. During glycolysis:
   • 4 ATP molecules are synthesized, and 2 ATP molecules are consumed (net gain = 2 ATP).
   • 2 molecules of NADH₂ and 2 molecules of water are formed.
4. In aerobic respiration, the two pyruvic acid molecules are converted into two molecules of Acetyl-Coenzyme-A, with the release of 2 molecules of CO₂ and 2 molecules of NADH₂. This Acetyl-CoA then enters the mitochondria for the Krebs cycle.

Mitosis occurs in somatic cells and consists of two main steps: Karyokinesis (nuclear division) and Cytokinesis (cytoplasmic division).

A. Karyokinesis (4 Stages):

1. Prophase: Chromatin threads condense into thick, distinct chromosomes with sister chromatids joined at the centromere. Centrioles duplicate and move to opposite poles. Spindle fibres begin to form, and the nucleolus and nuclear membrane disappear.
2. Metaphase: Nuclear membrane disappears completely. Chromosomes align clearly along the central equatorial plane of the cell. Spindle fibres attach to the centromeres.
3. Anaphase: Centromeres split, separating sister chromatids into daughter chromosomes. Spindle fibres pull daughter chromosomes toward opposite poles, appearing like bunches of bananas.
4. Telophase: Daughter chromosomes reach opposite poles and uncoil into fine chromatin threads. Nuclear membrane and nucleolus reappear. Spindle fibres vanish completely, forming two identical nuclei.

B. Cytokinesis: In animal cells, a cleavage furrow forms in the middle and deepens until the cell divides into two. In plant cells, a cell plate forms along the center to divide the cytoplasm.

Prophase-I of meiosis is lengthy and subdivided into 5 distinct substages:

1. Leptotene: Chromatin threads begin condensation and become visible as long, thin, bead-like threads.
2. Zygotene: Homologous chromosomes come together and pair up lengthwise. This pairing process is called synapsis, forming bivalents (tetrads).
3. Pachytene: Non-sister chromatids of paired homologous chromosomes twist over each other and exchange genetic material. This exchange is called crossing over, which produces genetic variations.
4. Diplotene: The force of attraction dissolves; homologous chromosomes begin to repel and separate, remaining attached only at crossing-over contact points called chiasmata (X-shaped structures).
5. Diakinesis: Chiasmata shift toward chromosome ends (terminalization). Spindle fibres form, the nucleolus completely disappears, and the nuclear membrane breaks down.

1. Digestive System: Breaks down complex dietary foodstuffs into simple nutrients like glucose, amino acids, and fatty acids.
2. Respiratory System: Absorbs oxygen from atmospheric air into the bloodstream and expels waste carbon dioxide.
3. Circulatory System: Pumping action of the heart transports digested nutrients and oxygen to every living cell throughout the body.
4. Mitochondria: Inside each cell, mitochondria oxidize glucose with oxygen to produce energy (ATP) needed for all metabolic activities.
5. Excretory System: Eliminates toxic nitrogenous wastes generated by metabolism, maintaining body homeostasis.
6. Nervous and Endocrine Systems: Control and coordinate all body functions in harmony, ensuring healthy growth and cell division.

1. The Krebs cycle (also known as the Citric Acid Cycle or TCA cycle) was discovered by Sir Hans Krebs.
2. Step 1: In the mitochondrial matrix, 2-carbon Acetyl-CoA combines with 4-carbon Oxaloacetic acid to produce 6-carbon Citric acid.
3. Step 2: In a series of cyclical enzymatic reactions, the acetyl group is completely oxidized.
4. Products: For each molecule of Acetyl-CoA oxidized, the cycle yields molecules of CO₂, H₂O, 3 NADH₂, 1 FADH₂, and 1 ATP.