Chapter 2: Life Processes in Living Organisms — Part 1
Chapter Flow
Living Organisms & Life Processes Energy Production in Cells Nutrients & Energy Efficiency Cell Division (Mitosis & Meiosis)
Can you recall?
- Why is a balanced diet essential?
- Role of digestive juices & enzymes?
- How do muscles help in daily work & sports?
- Which system removes body wastes?
- How does the circulatory system aid energy supply?
- How are body processes controlled (nervous & endocrine)?
- What is cellular respiration?
Living Organisms & Life Processes
In all organisms (including humans), organ systems like digestive, respiratory, circulatory, excretory, nervous and endocrine work in coordination. Cells need a continuous supply of energy; this is derived mainly from carbohydrates, lipids (fats) and sometimes proteins, using oxygen in the mitochondria. The circulatory system delivers nutrients and oxygen to every cell; control systems keep everything in sync.
Energy from diet (quick view)
| Nutrient | Examples | Energy Yield | Special Notes |
|---|---|---|---|
| Carbohydrates | Milk, fruits, jaggery, sugar, cereals, potatoes | ~ 4 kcal/g | Main fuel; stored as glycogen in liver & muscles |
| Proteins | Pulses, milk, eggs, fish, meat, soy | ~ 4 kcal/g | Builds tissues; excess not stored (deaminated) |
| Lipids (Fats) | Oils, ghee, nuts, butter, seeds | ~ 9 kcal/g | Stored in adipose; membrane & hormone synthesis |
Living Organisms & Energy Production
Cellular respiration oxidizes food (mostly glucose) to produce ATP, the cell’s energy currency. It occurs in two broad ways:
Aerobic Respiration (with O2) Anaerobic Respiration (without O2)
Overall aerobic equation
The three stages (Aerobic)
1) Glycolysis (Cytoplasm)
- Glucose → 2 Pyruvic acid
- Net gain: 2 ATP, 2 NADH2
- No O2 needed
2) Link & TCA (Krebs) Cycle (Mitochondria)
- Pyruvate → Acetyl-CoA (+ CO2, NADH2)
- Acetyl-CoA fully oxidized → CO2, NADH2, FADH2, small ATP (as GTP)
3) Electron Transport Chain (Mitochondria)
- NADH2/FADH2 donate electrons
- Drives ATP synthesis
- Water formed at the end
Total from complete aerobic oxidation of one glucose: up to \(\; \approx 38\;\) ATP (organism & conditions dependent).
Anaerobic Respiration (Fermentation)
When oxygen is absent/low (some microbes, germinating seeds in water-logged soil, vigorously working muscles), cells switch to fermentation:
- Alcoholic fermentation (e.g., yeast): Pyruvate → Ethanol + CO2
- Lactic acid fermentation (e.g., muscle cells, some bacteria): Pyruvate → Lactic acid
Less energy is produced because glucose is incompletely oxidized.
When carbs run low…
If dietary carbohydrates are insufficient (fasting, prolonged exercise):
- Lipids → Fatty acids → Acetyl-CoA → enter Krebs cycle
- Proteins → Amino acids → (deaminated) some → intermediates → Krebs cycle
Some Nutrients & Energy Efficiency
Proteins
Proteins are polymers of amino acids. After digestion and absorption, cells assemble the amino acids into specific proteins needed by the body:
- Blood: Haemoglobin, antibodies
- Muscles: Actin, myosin
- Skin/Hair: Keratin, melanin
- Hormones/Enzymes: Insulin, trypsin, pituitary hormones
- Bones: Ossein (matrix protein)
- Cell membranes: various transport & receptor proteins
Excess amino acids are not stored; they are deaminated and the nitrogen is excreted (e.g., as urea). Carbon skeletons can be used for energy or converted (e.g., to glucose via gluconeogenesis).
Lipids (Fats & Oils)
Lipids are made by bonding fatty acids with alcohol (e.g., glycerol). After digestion into fatty acids, cells use them to build:
- Phospholipids (key components of plasma membranes)
- Myelin sheaths around axons
- Steroid hormones: progesterone, estrogen, testosterone, aldosterone
Excess lipids are stored in adipose tissue.
Vitamins & Water
| Vitamin | Type | Notes |
|---|---|---|
| A, D, E, K | Fat-soluble | Stored in body; excess can be harmful |
| B-complex, C | Water-soluble | Not stored; need regular intake |
Coenzymes like FAD (from Vit B2 riboflavin) and NAD (from Vit B3 niacin) are essential in glycolysis & TCA.
ORS (salt–sugar solution) helps restore fluids & electrolytes.
Dietary fibre (from fruits, vegetables, cereals) aids digestion and regular bowel movement though it is not digested itself.
Glycolysis elucidated by Embden, Meyerhof & Parnas (EMP pathway). TCA Cycle discovered by Sir Hans Krebs (Nobel 1953).
Cell Division — A Life Process
Cell division is fundamental for growth, repair (healing wounds), replacement and reproduction. Two types:
Mitosis (equational) — Somatic & stem cells Meiosis (reductional) — Germ cells (gametes/spores)
Chromosome Basics
- Diploid (2n): pairs of each chromosome type.
- Haploid (n): one set (e.g., gametes).
- Before any division, DNA replicates so that chromosomes (2n) effectively become 4n in content (sister chromatids joined at centromere).
Mitosis (Karyokinesis → Cytokinesis)
Prophase
- Chromosomes condense (short & thick; visible as sister chromatids)
- Centrioles duplicate; move to poles
- Nuclear membrane & nucleolus begin to disappear
Metaphase
- Nuclear envelope gone; chromosomes fully condensed
- Align on equatorial plane
- Spindle fibres attach centromeres ↔ centrioles
Anaphase
- Centromeres split; sister chromatids separate
- Daughter chromosomes move to opposite poles (banana-like appearance)
Telophase & Cytokinesis
- Chromosomes decondense; nuclear envelopes reform (two nuclei)
- Cytokinesis: cleavage furrow in animals / cell plate in plants
Meiosis (I & II)
Meiosis I: homologous chromosomes pair, crossing over (recombination) occurs; homologues separate → two haploid (n) cells.
Meiosis II (like mitosis): sister chromatids separate → four haploid (n) daughter cells, all genetically different.
Try this (Microscopy Activity)
Observe mitosis in onion root tip — grow roots in water 4–5 days, stain tips with iodine, squash on slide, and view under compound microscope. Identify phases like prophase, metaphase, anaphase, telophase.
Quick Checks & Key Ideas
- Complete oxidation of glucose occurs only in aerobic respiration in mitochondria.
- Fermentation is anaerobic and yields less ATP; products differ (ethanol/CO2 vs lactic acid).
- Proteins are not stored; excess → deamination → excretion; carbon skeletons used for energy or conversion.
- Vitamins act as coenzymes; water & fibre are essential for homeostasis and digestive health.
- Mitosis = growth & repair; Meiosis = gametes & variation.
Chapter 2 — Exercise: Perfect Solutions
1) Fill in the blanks (with reasoning)
a) After complete oxidation of a glucose molecule, 38 ATP molecules are formed.
b) At the end of glycolysis, two molecules of pyruvic acid are obtained.
(+ Net 2 ATP and 2 \(\mathrm{NADH_2}\))
c) Genetic recombination occurs in pachytene phase of prophase-I of meiosis.
d) All chromosomes are arranged parallel to the equatorial plane in metaphase of mitosis.
e) For formation of plasma membrane, phospholipid molecules are necessary.
f) Our muscle cells perform anaerobic (lactic acid) respiration during heavy exercise.
1c) Prophase-I of Meiosis — Five Sub-stages (with neat labelled sketches)
Names & key events
- Leptotene — Chromosomes begin to condense; appear as thin threads.
- Zygotene — Synapsis: homologous chromosomes pair via synaptonemal complex.
- Pachytene — Crossing over: genetic recombination between non-sister chromatids.
- Diplotene — Synaptonemal complex dissolves; homologues start separating; chiasmata visible.
- Diakinesis — Maximal condensation; terminalization of chiasmata; spindle forms; nuclear envelope breaks down.
2) Definitions
- Nutrition: Process by which organisms obtain and utilize food for energy, growth, repair and regulation.
- Nutrients: Chemical substances in food (carbohydrates, proteins, lipids, vitamins, minerals, water, fibre) that nourish the body.
- Proteins: Large biomolecules made of amino acids linked by peptide bonds; perform structural, enzymatic, transport, hormonal and defensive roles.
- Cellular respiration: Enzyme-controlled oxidation of food (mainly glucose) in cells to release energy as ATP.
- Aerobic respiration: Complete oxidation of substrates using oxygen as final electron acceptor to yield CO\(_2\), H\(_2\)O and large ATP.
- Glycolysis: Cytoplasmic pathway that converts one glucose into two pyruvate with a net gain of 2 ATP and 2 \(\mathrm{NADH_2}\).
3) Distinguish between
a) Glycolysis vs TCA (Krebs) Cycle
| Glycolysis | TCA (Krebs) Cycle |
|---|---|
| Occurs in cytoplasm | Occurs in mitochondrial matrix |
| Glucose → 2 Pyruvate | Acetyl-CoA → CO\(_2\) |
| O\(_2\) not directly required | Indirectly depends on O\(_2\) (via ETC regenerating NAD\(^+\)/FAD) |
| Net 2 ATP + 2 \(\mathrm{NADH_2}\) | Per acetyl-CoA: 3 \(\mathrm{NADH_2}\), 1 \(\mathrm{FADH_2}\), 1 ATP (as GTP) |
| No CO\(_2\) released | CO\(_2\) released in multiple steps |
b) Mitosis vs Meiosis
| Mitosis | Meiosis |
|---|---|
| One division → 2 daughter cells | Two divisions → 4 daughter cells |
| Chromosome number maintained (2n → 2n) | Chromosome number halved (2n → n) |
| No pairing/crossing over | Homologous pairing & crossing over (Prophase-I) |
| Daughters genetically identical | Daughters genetically different |
| Somatic & stem cells (growth/repair) | Germ cells (gametes/spores) |
c) Aerobic vs Anaerobic Respiration
| Aerobic | Anaerobic |
|---|---|
| Requires O\(_2\) | Occurs without O\(_2\) |
| Complete oxidation (CO\(_2\)+H\(_2\)O) | Incomplete (lactate / ethanol + CO\(_2\)) |
| High ATP yield (up to ~38) | Low ATP yield (net 2 per glucose) |
| ETC in mitochondria | No mitochondrial ETC involvement |
| Occurs in most cells | Yeast, some bacteria, muscle under exertion, water-logged seeds |
4) Give scientific reasons
- a) Oxygen is necessary for complete oxidation of glucose.
Final electron acceptor in the ETC is O\(_2\). Accepting electrons & protons forms H\(_2\)O, regenerating NAD\(^+\)/FAD that keep TCA & glycolysis running to fully oxidize substrates and maximize ATP. - b) Fibres are important nutrients.
Though indigestible, dietary fibre increases bulk, promotes peristalsis, supports gut microbiota, improves glycaemic control and helps lower LDL cholesterol by bile acid binding. - c) Cell division is a key property of cells & organisms.
Enables growth (mitosis), tissue repair & replacement, asexual reproduction, and formation of gametes (meiosis) ensuring genetic continuity & variation. - d) Higher plants & animals sometimes perform anaerobic respiration.
Under low O\(_2\) (e.g., water-logged germinating seeds; vigorously contracting muscles), fermentation regenerates NAD\(^+\) so glycolysis can continue and supply limited ATP. - e) Krebs cycle is also called the citric acid cycle.
The first stable product is citrate (citric acid), formed by condensation of acetyl-CoA with oxaloacetate.
5) Answer in detail
a) Explain glycolysis in detail.
- Investment phase: Glucose → glucose-6-P → fructose-6-P → fructose-1,6-bisphosphate (uses 2 ATP).
- Cleavage: F-1,6-BP → DHAP + GAP; DHAP ↔ GAP.
- Payoff: Each GAP → 1,3-BPG → 3-PG → 2-PG → PEP → Pyruvate (produces total 4 ATP & 2 \(\mathrm{NADH_2}\); net 2 ATP).
b) With suitable diagrams, explain mitosis.
- Prophase: Chromosomes condense; spindle begins; nuclear envelope & nucleolus fade.
- Metaphase: Chromosomes align at the equator attached to spindle fibres.
- Anaphase: Centromeres split; sister chromatids pulled to opposite poles.
- Telophase: Chromosomes decondense; nuclear envelopes re-form (two nuclei).
- Cytokinesis: Cleavage furrow (animal) / cell plate (plant) → two identical 2n cells.
d) How do all life processes contribute to growth & development?
- Nutrition & Digestion: Supply building blocks (amino acids, sugars, fatty acids) & energy.
- Respiration: Converts substrates to ATP powering biosynthesis, transport, division, movement.
- Circulation: Distributes O\(_2\), nutrients, hormones; removes CO\(_2\), wastes.
- Excretion: Maintains internal chemical balance by removing nitrogenous & metabolic wastes.
- Coordination (nervous/endocrine): Regulates rates and timing of processes (e.g., growth hormone).
- Cell division: Adds cells (growth), repairs damage, and renews tissues (skin, blood, gut lining).
e) Explain the Krebs (TCA) cycle with reaction.
Per Acetyl-CoA (TCA):
\( \text{Acetyl-CoA} + 3\,\mathrm{NAD^+} + \mathrm{FAD} + \mathrm{GDP} + \mathrm{P_i} + 2\,\mathrm{H_2O} \rightarrow 2\,\mathrm{CO_2} + 3\,\mathrm{NADH_2} + \mathrm{FADH_2} + \mathrm{GTP} + \mathrm{CoA} \)
Key steps: Citrate synthase (citrate), isomerization (isocitrate), oxidative decarboxylations (α-ketoglutarate), succinyl-CoA → succinate (GTP/ATP), FADH\(_2\) at succinate dehydrogenase, NADH\(_2\) at malate dehydrogenase; oxaloacetate regenerated.
6) How is energy formed from oxidation of carbohydrates, fats & proteins?
- Carbohydrates: Glucose → Glycolysis (→ pyruvate) → Acetyl-CoA → TCA → \(\mathrm{NADH_2}\)/\(\mathrm{FADH_2}\) → ETC → ATP.
- Fats: Lipids → fatty acids + glycerol; glycerol enters glycolysis; fatty acids undergo β-oxidation → multiple Acetyl-CoA + \(\mathrm{NADH_2}\) + \(\mathrm{FADH_2}\) → TCA → ETC → lots of ATP.
- Proteins: Proteins → amino acids → deamination; carbon skeletons → pyruvate/acetyl-CoA/TCA intermediates → TCA → ETC → ATP (nitrogen excreted as urea, etc.).
7) Correct the diagram (Energy pathways)
Correct flow from carbohydrates, fats and proteins to ATP via central metabolism: