Life Processes Part 1 Class 10 Notes, Formulas, Questions | SSC

This chapter explains how the life processes of the body work together to produce energy. It covers cellular respiration in detail: glycolysis, the Krebs cycle and the electron transfer chain, along with anaerobic respiration and fermentation. It then looks at how carbohydrates, proteins, lipids, vitamins, water and fibres serve the body. Finally it describes cell division by mitosis and meiosis.

Summary

All organ systems such as the digestive, respiratory, circulatory, excretory and control systems work in coordination and need a continuous supply of energy. Carbohydrates and fats are the main energy sources, and the energy is harvested by mitochondria in each cell. Food alone is not enough; oxygen is also needed, and both are carried to cells by the circulatory system. Carbohydrates come from cereals, milk, fruits, jaggery, cane sugar, potatoes and similar foods and give 4 kcal of energy per gram.

Respiration occurs at two levels. At body level, oxygen and carbon dioxide are exchanged with the surroundings. At cellular level, food is oxidised with or without oxygen to release energy as ATP; this is cellular respiration. In aerobic respiration glucose is oxidised in three steps. In glycolysis, which takes place in the cytoplasm, one glucose molecule gives two molecules each of pyruvic acid, ATP, NADH2 and water. The pyruvic acid is then converted into acetyl-coenzyme A, releasing two NADH2 and two CO2.

The two acetyl-CoA molecules enter the mitochondria, where the tricarboxylic acid (Krebs) cycle completely oxidises the acetyl part, giving CO2, H2O, NADH2 and FADH2. In the electron transfer chain, also in the mitochondria, each NADH2 gives 3 ATP and each FADH2 gives 2 ATP, and water is formed. Thus glucose is completely oxidised to CO2 and water with release of energy. Glycolysis is also called the EMP pathway after Embden, Meyerhof and Parnas, and the Krebs cycle is named after Sir Hans Krebs, who received the Nobel Prize in 1953.

ATP (adenosine triphosphate) contains adenine, ribose sugar and three phosphate groups. Energy is stored in the bonds between phosphate groups and released when a phosphate bond breaks, so ATP is called the energy currency of the cell. NAD and FAD are coenzymes used in respiration. During fasting, lipids are broken into fatty acids and proteins into amino acids, which are converted into acetyl-CoA and oxidised through the Krebs cycle.

Anaerobic respiration occurs without oxygen in two steps: glycolysis and fermentation. Glucose is only partly oxidised and less energy is released; pyruvic acid is converted into alcohol or other organic acids by enzymes. Many bacteria respire only this way. Seeds in waterlogged soil and our muscle cells during exercise also respire anaerobically; lactic acid builds up in muscles and we feel tired.

Excess carbohydrates are stored as glycogen in the liver and muscles. Proteins are made of amino acids, give 4 kcal per gram, and animal proteins are called first class proteins. Cells use amino acids to build proteins like keratin, haemoglobin, insulin, actin and myosin. Excess amino acids are not stored; they are broken down and the ammonia is removed, or converted into glucose by gluconeogenesis. RUBISCO in chloroplasts is the most abundant protein in nature. Lipids are formed from fatty acids and alcohol, give 9 kcal per gram, are used to make phospholipids of the plasma membrane, hormones and nerve coverings, and the excess is stored in adipose tissue.

Vitamins are heterogeneous compounds needed for body processes; A, D, E and K are fat-soluble and B and C are water-soluble. Riboflavin (B2) and nicotinamide (B3) are needed to make FADH2 and NADH2. The body has 65 to 70 percent water, each cell about 70 percent and blood plasma about 90 percent, so water is an essential nutrient. Fibres cannot be digested but help digestion and egestion; they come from leafy vegetables, fruits and cereals.

Cell division allows new organisms to form, growth and repair of the body. Before division the chromosome number doubles from 2n to 4n. Mitosis occurs in somatic and stem cells in two steps: karyokinesis (prophase, metaphase, anaphase, telophase) and cytokinesis. Meiosis occurs in germ cells in two stages: in meiosis I, crossing over occurs between homologous chromosomes, which then separate to form two haploid cells; meiosis II is like mitosis and separates sister chromatids. One diploid cell gives four genetically different haploid cells, which form gametes and spores.

Mind map

Aerobic respiration of one glucose molecule

Important definitions

Formulas

Key points to remember

• Glycolysis occurs in the cytoplasm; the Krebs cycle and electron transfer chain occur in the mitochondria.
• Oxygen is needed for complete oxidation of glucose; mitochondria are the organelle needed.
• Glycolysis was discovered by Embden, Meyerhof and Parnas (EMP pathway).
• Sir Hans Krebs discovered the TCA cycle and got the Nobel Prize in 1953.
• The Krebs cycle is also called the citric acid cycle because citric acid, a tricarboxylic acid, is formed in it.
• ATP contains adenine, ribose and three phosphate groups.
• NAD stands for nicotinamide adenine dinucleotide and FAD for flavin adenine dinucleotide.
• Muscle cells respire anaerobically during exercise and lactic acid accumulates, causing tiredness.
• Excess carbohydrate is stored as glycogen in liver and muscles; excess fat in adipose tissue; excess amino acids are not stored.
• RUBISCO is the most abundant protein in nature.
• Vitamins A, D, E, K are fat-soluble; B and C are water-soluble.
• Metaphase: chromosomes line up on the equatorial plane. Anaphase: chromatids separate and look like a bunch of bananas.
• Plant cells form a cell plate in cytokinesis; animal cells form a notch.
• Prophase I of meiosis has five sub-stages (leptotene, zygotene, pachytene, diplotene, diakinesis); crossing over occurs in pachytene.

Solved examples

Example 1. Calculate the total number of ATP molecules formed by complete aerobic oxidation of one glucose molecule.

Step 1, glycolysis: 2 ATP directly plus 2 NADH2 x 3 = 6 ATP, giving 8 ATP. Step 2, pyruvic acid to acetyl-CoA: 2 NADH2 x 3 = 6 ATP. Step 3, Krebs cycle (two turns, one per acetyl-CoA): 6 NADH2 x 3 = 18 ATP, 2 FADH2 x 2 = 4 ATP and 2 ATP formed directly, giving 24 ATP. Total = 8 + 6 + 24 = 38 ATP.

Example 2. How much energy is obtained from a meal containing 50 g carbohydrate, 20 g protein and 10 g fat?

Carbohydrate: 50 x 4 = 200 kcal. Protein: 20 x 4 = 80 kcal. Fat: 10 x 9 = 90 kcal. Total = 200 + 80 + 90 = 370 kcal.

Example 3. A cell has 2n = 46 chromosomes. How many chromosomes will be present (a) after doubling before division, (b) in each daughter cell after mitosis, (c) in each cell after meiosis?

(a) Doubling gives 4n = 92. (b) Mitosis keeps the number the same, so each daughter cell has 2n = 46. (c) Meiosis halves the number, so each of the four cells has n = 23.

Example 4. How many daughter cells are formed when 5 diploid cells undergo meiosis, and what is their ploidy?

Each diploid cell gives 4 haploid cells by meiosis. 5 x 4 = 20 haploid (n) daughter cells.

Example 5. How many ATP molecules are produced in the electron transfer chain from 10 NADH2 and 2 FADH2?

NADH2: 10 x 3 = 30 ATP. FADH2: 2 x 2 = 4 ATP. Total = 34 ATP.

Important questions and answers

Q1. Fill in the blanks: (a) At the end of glycolysis ____ molecules are obtained. (b) Our muscle cells perform ____ respiration during exercise. (c) For formation of plasma membrane ____ molecules are necessary.

(a) Pyruvic acid. (b) Anaerobic. (c) Phospholipid.

Q2. Distinguish between glycolysis and the TCA cycle.

Glycolysis occurs in the cytoplasm; the TCA cycle occurs in the mitochondria. Glycolysis breaks glucose into pyruvic acid; the TCA cycle completely oxidises the acetyl part of acetyl-CoA. Glycolysis occurs in both aerobic and anaerobic respiration; the TCA cycle occurs only in aerobic respiration. Glycolysis is a linear pathway; the TCA cycle is cyclic and releases CO2.

Q3. Distinguish between mitosis and meiosis.

Mitosis occurs in somatic and stem cells; meiosis in germ cells. Mitosis has one division and forms two cells; meiosis has two divisions and forms four cells. Mitosis keeps the chromosome number same (2n); meiosis halves it (n). In mitosis daughter cells are identical; in meiosis crossing over makes them genetically different. Mitosis helps growth and repair; meiosis forms gametes and spores.

Q4. Distinguish between aerobic and anaerobic respiration.

Aerobic respiration uses oxygen; anaerobic does not. In aerobic respiration glucose is completely oxidised to CO2 and water; in anaerobic it is incompletely oxidised to alcohol or organic acids. Aerobic releases much more energy. Aerobic includes glycolysis, Krebs cycle and electron transfer chain; anaerobic includes glycolysis and fermentation.

Q5. Give reasons: Oxygen is necessary for complete oxidation of glucose.

Without oxygen, glucose is only broken down to pyruvic acid and then fermented to alcohol or organic acids, so oxidation is incomplete. Complete oxidation to CO2 and water occurs only through the Krebs cycle and electron transfer chain in the mitochondria, which run in aerobic respiration.

Q6. Give reasons: Sometimes higher plants and animals also perform anaerobic respiration.

When oxygen in the surroundings runs short, they switch to anaerobic respiration to get energy. Seeds germinating in waterlogged soil and our muscle cells during heavy exercise are examples.

Q7. Give reasons: Fibres are an important nutrient.

Though fibres cannot be digested, they help in the digestion of other foods and in the egestion of undigested matter. Hence they are essential and are obtained from leafy vegetables, fruits and cereals.

Q8. Give reasons: Cell division is an important property of cells and organisms.

Through cell division a new organism forms from an existing one, a multicellular organism grows, and worn-out or injured tissues are restored, as in wound healing and formation of blood cells.

Q9. Why is ATP called the energy currency of the cell?

ATP stores energy in the bonds joining its phosphate groups. Whenever a cell needs energy, a phosphate bond is broken and energy is released. Thus ATP stores and supplies energy as needed, like currency.

Q10. Explain mitosis in detail.

Mitosis has karyokinesis and cytokinesis. Prophase: chromosomes condense and show sister chromatids, centrioles move to opposite poles, nuclear membrane and nucleolus start disappearing. Metaphase: nuclear membrane disappears fully, chromosomes line up on the equatorial plane and spindle fibres attach to centromeres. Anaphase: centromeres split and sister chromatids move to opposite poles. Telophase: chromosomes decondense, nuclear membrane and nucleolus reappear, forming two nuclei, and spindle fibres disappear. Cytokinesis: a notch in animal cells or a cell plate in plant cells divides the cytoplasm into two daughter cells.

Q11. How is energy obtained from carbohydrates, fats and proteins?

Carbohydrates are broken into glucose, which forms pyruvic acid by glycolysis and then acetyl-CoA. Fats are converted to fatty acids and proteins to amino acids, which are also converted to acetyl-CoA. Acetyl-CoA is completely oxidised in the Krebs cycle, and through the electron transfer chain CO2, H2O and energy are produced.

Exam tips

• Remember where each step happens: glycolysis in cytoplasm, Krebs cycle and electron transfer chain in mitochondria.
• Learn the product counts of glycolysis (2 pyruvic acid, 2 ATP, 2 NADH2, 2 H2O) for fill-in-the-blank items.
• In mitosis diagrams label chromosomes, spindle fibres, centrioles and the equatorial plane.
• For difference questions write at least four clear points in a two-column format.
• Use the energy values 4, 4 and 9 kcal per gram correctly for carbohydrate, protein and lipid.

FAQs

How many ATP are formed from one glucose molecule?

Complete aerobic oxidation gives 38 ATP, counting 3 ATP per NADH2 and 2 ATP per FADH2.

Why do we feel tired after heavy exercise?

Muscle cells respire anaerobically, less energy is produced and lactic acid accumulates.

Where does meiosis occur?

In germ cells, to form gametes and spores.

Which vitamins are needed to make NADH2 and FADH2?

Nicotinamide (vitamin B3) for NADH2 and riboflavin (vitamin B2) for FADH2.

These notes were prepared with AI help from the Balbharati Science and Technology Part 2 textbook (2026-27) and checked against it.