10.1 Life Processes: Nutrition & Respiration

10.1 Life Processes: Nutrition & Respiration

Why It Matters

Every living organism must keep itself alive by performing certain basic functions — obtaining food, releasing energy from it, carrying materials around the body and getting rid of waste. These are called life processes: nutrition, respiration, transportation, excretion, control and coordination, growth, and reproduction. RRB Group D questions test the names, locations and end-products of these processes, so you should be able to recognise each step and the organ or cell part responsible.

Nutrition: Two Main Modes

Nutrition is the process by which organisms obtain food (energy) and use it. There are two main modes:

• Autotrophic nutrition — organisms make their own food from simple inorganic substances. Green plants, blue-green algae and some bacteria are autotrophs. They use photosynthesis: sunlight energy trapped by chlorophyll in chloroplasts converts carbon dioxide and water into glucose, releasing oxygen as a by-product. The overall equation is: 6CO2 + 12H2O → C6H12O6 + 6O2 + 6H2O (in the presence of light and chlorophyll).
• Heterotrophic nutrition — organisms depend on other organisms for food. Animals, fungi and most bacteria are heterotrophs. Three sub-types are important for the exam:
  • Saprophytic — feed on dead/decaying matter (e.g., bread mould Rhizopus, yeast, many fungi). They secrete digestive enzymes onto the food and absorb the soluble products.
  • Parasitic — live on or in a living host and harm it (e.g., Plasmodium causing malaria, Cuscuta (Amarbel), tapeworm).
  • Holozoic — ingest solid food and digest it internally (most animals, including humans).

The leaf is the food factory of the plant. Stomata (pores guarded by guard cells) allow CO2 to enter and O2/water vapour to exit. Chlorophyll absorbs mainly red and blue wavelengths and reflects green, which is why leaves look green.

Human Digestive System

The human alimentary canal is a long tube running from the mouth to the anus, with associated glands (salivary glands, liver, pancreas). Digestion has two steps — ingestion and then breakdown by enzymes:

The liver secretes bile, which is NOT an enzyme — it emulsifies fats (breaks large fat globules into smaller droplets) so that lipase can act efficiently, and makes the small intestine alkaline so pancreatic enzymes work. The inner lining of the small intestine has villi (finger-like projections) that massively increase the surface area for absorption of digested food into the blood. The large intestine mainly absorbs water; undigested matter is egested through the anus.

A common trap: students think bile digestes fats. It does NOT — it only emulsifies them. The actual digestion of fats is done by lipase.

Respiration: Releasing Energy

Respiration is the biochemical oxidation of food (mainly glucose) inside cells to release energy, stored in ATP (adenosine triphosphate) molecules. ATP is the energy currency of the cell.

• Aerobic respiration — uses oxygen; glucose is completely broken down:
  • C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (~38 ATP)
• Anaerobic respiration — without oxygen; glucose is partially broken down:
  • In muscle cells (during heavy exercise when O2 supply is short): C6H12O6 → lactic acid + energy (2 ATP). The cramps you feel after sprinting are due to lactic acid build-up.
  • In yeast (fermentation): C6H12O6 → ethanol + CO2 + energy (2 ATP). This is used in brewing and baking.

The site of aerobic respiration inside the cell is the mitochondria (the powerhouse of the cell). Anaerobic respiration in plants produces ethanol, while in human muscle cells it produces lactic acid — a favourite RRB distinction.

Human Respiratory System

Air enters through the nostrils, passes through the nasal cavity (filtered, warmed, moistened), then the pharynx, larynx (voice box), trachea (windpipe), the two bronchi (one per lung), which branch into bronchioles and end in alveoli (air sacs). The alveoli are surrounded by a network of thin blood capillaries where gas exchange happens: O2 diffuses into the blood and CO2 diffuses out.

Breathing mechanism:

• Inhalation: diaphragm contracts and flattens, ribs move up and out, chest cavity expands, lungs expand, air pressure inside falls, air rushes IN.
• Exhalation: diaphragm relaxes and becomes dome-shaped, ribs move down and inward, chest cavity shrinks, lungs are compressed, air pressure rises, air rushes OUT.

In an adult human at rest, the normal breathing rate is about 15–18 times per minute. Haemoglobin in red blood cells carries oxygen (as oxyhaemoglobin); CO2 is mostly transported dissolved in blood plasma.

Exam Traps

1. Bile vs lipase — bile emulsifies, lipase digests.
2. End-products of anaerobic respiration differ between yeast (ethanol + CO2) and human muscle (lactic acid).
3. Site of photosynthesis vs respiration — chloroplast for photosynthesis (only in green parts), mitochondria for respiration (in all living cells, including plant cells).
4. Alveoli vs nephron — alveoli are the functional units of lungs; nephrons are the functional units of kidneys (see 10.2). Mixing them up is a classic error.