Life Processes: Comprehensive University Study Guide

Distinguishing Life and the Necessity of Molecular Movement

• Criteria for Life: Commonly, movement is seen as evidence of life. This includes visible movements like a dog running, a cow chewing cud, or a human shouting. Growth-related movement in plants is also a key indicator.

• Limitations of Visible Movement:

  • Plants that are not visibly growing are still considered alive.

  • Some animals breathe without visible body movement.

  • Visible movement is insufficient as a defining characteristic of life.

• Molecular Movements: Professional biologists assert that invisible molecular movements are necessary for life.

  • The Virus Controversy: Viruses do not show molecular movement until they infect a host cell, leading to debate over whether they are truly "alive."

  • Why Molecular Movement Matters: Living organisms are highly organized structures (tissues, cells, organelles). The environment constantly causes this order to break down. To survive, organisms must constantly repair and maintain these structures using molecular movement.

Defining Life Processes

• Definition: Life processes are the functions that collectively perform the maintenance of a living organism, even when the organism is inactive (e.g., sleeping or sitting).

• Energy Requirement: Maintenance and prevention of breakdown require energy. This energy must come from outside the organism in the form of food.

• Key Processes:

  1. Nutrition: The process of transferring an external energy source (food) to the inside of the body.

  2. Respiration: The process of acquiring oxygen from outside to break down food sources for cellular energy.

  3. Transportation: The system for moving food and oxygen to all parts of a complex organism.

  4. Excretion: The removal of harmful, useless by-products created by chemical reactions for energy generation.

Nutrition and Feeding Strategies

• General Energy Needs: Required for maintaining order, growth, development, and protein synthesis.

• Autotrophic Nutrition:

  • Organisms use simple inorganic materials (carbon dioxide and water) to synthesize complex organic material using sunlight.

  • Examples: Green plants and some bacteria.

  • Photosynthesis: The process by which stored energy is created. The reaction involves:

    • Absorption of light energy by chlorophyll.

    • Conversion of light energy to chemical energy.

    • Splitting of water molecules into hydrogen and oxygen.

    • Reduction of carbon dioxide to carbohydrates.

    • Note: Desert plants may take up $CO_2$ at night and process it during the day.

  • Energy Storage: Plants store unused carbohydrates as starch; humans store energy as glycogen.

• Heterotrophic Nutrition:

  • Organisms depend directly or indirectly on autotrophs.

  • Examples: Animals and fungi.

  • Strategies:

    • External Breakdown: Fungi like bread moulds, yeast, and mushrooms break down food outside the body and then absorb it.

    • Internal Breakdown: Most animals take in whole food and break it down internally.

    • Parasitism: Organisms like Cuscuta (amar-bel), ticks, lice, leeches, and tape-worms derive nutrition without killing the host.

Human Alimentary Canal and Digestion

• The Digestive Tract: A long tube from the mouth to the anus.

• The Mouth:

  • Teeth: Crushing food into small particles of uniform texture.

  • Saliva: Secreted by salivary glands; contains the enzyme salivary amylase, which breaks starch ($complex$) into sugar ($simple$). Food is wetted to ease passage.

  • Tongue: Mixes food with saliva during chewing.

• Oesophagus: Transports food to the stomach via peristaltic movements (rhythmic muscle contractions).

• The Stomach:

  • A large organ that expands with food. Muscular walls mix food with digestive juices.

  • Gastric Glands: Located in stomach walls; release Hydrochloric acid ($HCl$), pepsin ($protein-digesting enzyme$), and mucus.

  • Function of HCl: Creates an acidic medium for pepsin activation.

  • Function of Mucus: Protects the stomach lining from acid.

• Small Intestine:

  • The longest part of the canal, coiled compactly.

  • Herbivore vs. Carnivore: Herbivores (e.g., cows) have longer small intestines for cellulose digestion; carnivores (e.g., tigers) have shorter ones.

  • Major Functions: Site of complete digestion of carbohydrates, proteins, and fats.

  • Liver Secretion: Bile juice makes the acidic food alkaline and emulsifies fats (breaks large globules into smaller ones).

  • Pancreas Secretion: Pancreatic juice contains trypsin (digests proteins) and lipase (breaks down emulsified fats).

  • Final Breakdown: Proteins to amino acids; Complex carbohydrates to glucose; Fats to fatty acids and glycerol.

  • Absorption: The inner lining has villi (finger-like projections) which increase surface area and are rich in blood vessels to carry nutrients to cells.

• Large Intestine and Anus: Unabsorbed food moves to the large intestine for water absorption before being expelled via the anus, regulated by the anal sphincter.

Respiration: Pathways and Gas Exchange

• First Step: Breakdown of glucose ($6$-carbon) into pyruvate ($3$-carbon) in the cytoplasm.

• Three Pathways for Pyruvate:

  1. Absence of Oxygen (Anaerobic): In yeast (fermentation), pyruvate converts to ethanol, $CO_2$, and energy.

  2. Lack of Oxygen: In human muscle cells during sudden activity, pyruvate converts to lactic acid ($3$-carbon) and energy. Lactic acid build-up causes cramps.

  3. Presence of Oxygen (Aerobic): In the mitochondria, pyruvate breaks into three molecules of $CO_2$, water, and a high amount of energy.

• ATP (Adenosine Triphosphate):

  • The energy currency for cellular processes.

  • Formed from ADP and inorganic phosphate.

  • Breaking the terminal phosphate linkage releases $30.5\,kJ/mol$.

• Plant Respiration:

  • Exchange occurs via stomata by diffusion.

  • At night: $CO_2$ elimination is main activity.

  • During day: $CO_2$ is used for photosynthesis; $O_2$ release is the major event.

• Aquatic vs. Terrestrial Organisms:

  • Aquatic organisms (e.g., fish) use dissolved oxygen. Since dissolved oxygen levels are low, their breathing rate is much faster than terrestrial organisms.

  • Fish force water past gills where blood takes up oxygen.

• Human Respiratory System:

  • Passage: Nostrils (filtered by hair and mucus) → Throat (with rings of cartilage to prevent collapse) → Lungs.

  • Alveoli: Balloon-like structures at the end of the bronchioles providing maximal surface area (approx. $80\,m^2$) for gas exchange.

  • Transport: Haemoglobin in red blood corpuscles carries $O_2$. $CO_2$ is more soluble in water and is mostly transported in dissolved form in plasma.

Transportation in Humans and Plants

• The Heart (Human):

  • A muscular organ the size of a fist.

  • Four Chambers: Left atrium, left ventricle (oxygenated blood); Right atrium, right ventricle (de-oxygenated blood).

  • Left side receives oxygenated blood from lungs and pumps to the body. Right side receives de-oxygenated blood from the body and pumps it to the lungs.

  • Ventricles: Have thicker walls than atria to pump blood further.

  • Double Circulation: Blood passes through the heart twice in one cycle (common in mammals/birds for efficiency and body temp maintenance).

• Blood Vessels:

  • Arteries: Carry blood away from the heart; thick, elastic walls.

  • Veins: Bring blood back; thin walls; have valves to prevent backflow.

  • Capillaries: One-cell thick walls for material exchange.

• Blood Pressure: Measured by a sphygmomanometer. Normal: $120/80\,mm\,Hg$ (Systole/Diastole).

• Other Fluids:

  • Platelets: Circulate to clot blood and plug leaks.

  • Lymph (Tissue Fluid): Colourless, lower protein than plasma. Drains excess fluid from extracellular space and carries fats.

• Plant Transport:

  • Xylem: Transports water and minerals from soil to leaves. Uses root pressure (at night) and transpiration pull (during day).

  • Phloem: Transports products of photosynthesis (translocation), amino acids, and nutrients from leaves to storage/growing organs. Requires energy (ATP).

Excretion in Humans and Plants

• Human Excretory System: Consists of Kidneys, Ureters, Urinary Bladder, and Urethra.

• Nephron: The basic filtration unit.

  • Bowman’s Capsule: Collects filtrate from capillary clusters.

  • Selective Re-absorption: Glucose, amino acids, salts, and water are re-absorbed from the tubules into the blood.

  • Daily Filtrate: Normal initial filtrate is approx. $180\,L$ daily, but only $1-2\,L$ is excreted as urine.

• Artificial Kidney (Hemodialysis): A device used for patients with kidney failure to remove nitrogenous waste via diffusion through semi-permeable tubes in dialysing fluid.

• Plant Excretion:

  • Oxygen released as a waste product of photosynthesis.

  • Excess water lost through transpiration.

  • Waste stored in cellular vacuoles, leaves (which fall off), or as resins and gums in old xylem.

  • Some wastes excreted into the surrounding soil.

Supplementary Information

• Dental Caries: Softening of enamel caused by bacterial acid production; prevented by brushing to remove plaque.

• Tobacco Health Warning: Smoking and chewing tobacco (gutkha) are major causes of lung and oral cancer in India. Smoking destroys cilia in the respiratory tract.

• Organ Donation: A generous act whereby organs (kidneys, heart, liver, etc.) are harvested from deceased (or sometimes living) donors to save lives.

Questions & Discussion

• Question 1: Why is diffusion insufficient for humans?

• Response: The large body size and complexity mean not all cells are in contact with the environment; simple diffusion is too slow to reach internal cells (it would take 3 years for $O_2$ to reach the toes).

• Question 2: What criteria indicate life?

• Response: Various types of movement, growth, and invisible molecular maintenance processes.

• Question 3: What are raw materials used for?

• Response: Energy (carbon-based food), growth, and building body structures (water, minerals like nitrogen, phosphorus, iron, and magnesium).

• Question 4: Essential life processes?

• Response: Nutrition, Respiration, Transportation, and Excretion.