Life Processes Comprehensive University Study Guide
Characteristics of Life and Molecular Movement
Criteria for life include visible movements such as a dog running, a cow chewing cud, or humans shouting. However, visible movement is not a definitive characteristic since plants may not show visible growth and some animals breathe without outward movement.
Life depends on invisible molecular movements. Professional biologists assert that these movements are necessary for maintaining the highly organized structures of living organisms (tissues, cells, and organelles).
Environment-driven breakdown of organized structures leads to death unless repaired. Maintenance requires continuous movement of molecules.
Viruses are a point of controversy because they show no molecular movement until they infect a host cell.
Definition and Scope of Life Processes
Life processes are the collective maintenance functions of living organisms that must continue even during inactivity (like sitting or sleeping) to prevent damage.
Four primary essential processes are:
Nutrition: The process of transferring an external energy source (food) to the inside of the body.
Respiration: The process of acquiring oxygen from the environment and using it for the breakdown of food sources for cellular energy.
Transportation: The system used in complex multicellular organisms to carry food and oxygen to all parts of the body.
Excretion: The removal of harmful metabolic by-products from the body.
Nutrition and Energy Acquisition
Energy and raw materials for growth, development, and protein synthesis come from food.
Life on Earth depends on carbon-based molecules; therefore, most food sources are carbon-based.
Autotrophic Nutrition:
Used by green plants and some bacteria.
Involves the use of simple inorganic materials ( and ) and external energy (sunlight) to synthesize high-energy organic material.
Glucose not used immediately is stored as starch in plants; in humans, internal energy is stored as glycogen.
Heterotrophic Nutrition:
Used by animals and fungi.
Involves the intake of complex substances that must be broken down by bio-catalysts called enzymes.
Strategies include:
Breaking down food outside the body and then absorbing it (e.g., fungi like bread moulds, yeast, and mushrooms).
Taking in whole material and breaking it down internally (e.g., humans).
Parasite nutrition, where organisms derive nutrients without killing the host (e.g., cuscuta, ticks, lice, leeches, and tape-worms).
Mechanism of Photosynthesis
Photosynthesis involves converting carbon dioxide and water into carbohydrates using sunlight and chlorophyll.
Major events in photosynthesis:
Absorption of light energy by chlorophyll.
Conversion of light energy to chemical energy and the splitting of water molecules into hydrogen and oxygen.
Reduction of carbon dioxide to carbohydrates.
Desert plants adapt by taking up at night to create an intermediate, which is processed by chlorophyll-absorbed energy during the day.
Chloroplasts: Cell organelles seen as green dots in a leaf cross-section, containing chlorophyll.
Stomata: Tiny pores on the leaf surface for gaseous exchange. Opening and closing are regulated by guard cells which swell with water to open and shrink to close.
Other raw materials for plants include nitrogen, phosphorus, iron, and magnesium from the soil. Nitrogen is essential for protein synthesis and is taken as inorganic nitrates/nitrites or organic compounds from bacteria.
Nutrition in Unicellular Organisms
Amoeba: Uses temporary finger-like extensions (pseudopodia) to engulf food particles into a food-vacuole. Complex substances are broken down and diffuse into the cytoplasm; wastes are moved to the surface and expelled.
Paramoecium: Has a definite shape; food is moved to a specific spot by the movement of cilia covering the entire cell surface.
Human Digestive System
The alimentary canal is a long tube from the mouth to the anus consisting of specialized regions.
Mouth: Food is crushed by teeth and wetted by saliva. Salivary amylase (an enzyme) breaks down complex starch into simple sugar.
Oesophagus: Pushes food toward the stomach through rhythmic contraction of muscles known as peristaltic movements.
Stomach: A large, expandable muscular organ. Gastric glands secrete:
Hydrochloric acid (HCl): Creates an acidic medium for pepsin.
Pepsin: A protein-digesting enzyme.
Mucus: Protects the stomach lining from the acid.
Small Intestine: The longest part of the canal, highly coiled.
Herbivores have longer small intestines for cellulose digestion; carnivores like tigers have shorter ones.
Site of complete digestion of carbohydrates, proteins, and fats.
Receives bile juice from the liver (emulsifies fats and makes acidic food alkaline) and pancreatic juice (contains trypsin for proteins and lipase for emulsified fats).
Intestinal juices convert proteins to amino acids, complex carbohydrates to glucose, and fats to fatty acids and glycerol.
Villi: Finger-like projections that increase surface area for absorption into the blood.
Large Intestine: Absorbs more water from unabsorbed food; waste is expelled via the anus, regulated by the anal sphincter.
Respiration Pathways
The first step in all organisms is the breakdown of glucose (-carbon) into pyruvate (-carbon) in the cytoplasm.
Anaerobic Respiration: Happens in the absence of oxygen.
In yeast (fermentation): Pyruvate yields ethanol + + energy.
Aerobic Respiration: Happens in the presence of oxygen in the mitochondria.
Produces + + energy (significantly higher energy release than anaerobic).
Muscle Cell Pathway: During a lack of oxygen, pyruvate is converted to lactic acid (-carbon). Lactic acid build-up causes cramps during sudden activity.
ATP (Adenosine Triphosphate): The energy currency of the cell.
Formed from ADP and inorganic phosphate using energy from respiration.
Breaking the terminal phosphate linkage using water releases .
Gas Exchange Mechanisms
Plants: Exchange gases via stomata and large intercellular spaces. Oxygen release is the major event during the day; elimination is the major activity at night.
Aquatic Organisms: Use oxygen dissolved in water. Since dissolved oxygen levels are low, the breathing rate is faster than in terrestrial animals (e.g., fish force water past gills).
Terrestrial Organisms: Use atmospheric oxygen. Human system includes:
Nostrils: Filter air using fine hairs and mucus.
Throat: Contains rings of cartilage to prevent collapse of the air-passage.
Lungs: Branch into smaller tubes terminating in alveoli (balloon-like structures for gas exchange).
Alveoli: Walls have extensive blood vessel networks. The total alveolar surface area is approximately .
Gas Transport:
Haemoglobin: Respiratory pigment in red blood corpuscles with high affinity for oxygen. Oxygen delivery by diffusion alone in large animals would take years to reach the toes.
: More soluble in water, transported mostly in dissolved form in the blood.
Human Circulatory System
The Heart: A muscular organ (fist-sized) with separated chambers to prevent mixing of oxygen-rich and carbon dioxide-rich blood.
Left Atrium/Ventricle: Deals with oxygenated blood from lungs to body.
Right Atrium/Ventricle: Deals with de-oxygenated blood from body to lungs.
Ventricles have thicker walls than atria. Valves prevent backflow.
Circulation Patterns:
Double Circulation: Blood passes through the heart twice per cycle (birds/mammals). Highly efficient oxygen supply for maintaining body temperature.
Single Circulation: Blood passes through the heart once in fish (two-chambered heart).
Amphibians/Reptiles: Three-chambered hearts; tolerate some mixing of blood.
Blood Vessels:
Arteries: Thick, elastic walls; carry blood away from heart at high pressure.
Veins: Thin walls with valves; carry blood back to heart.
Capillary: One-cell thick walls for material exchange.
Blood Pressure: Force against vessel walls.
Systolic: of Hg (ventricular contraction).
Diastolic: of Hg (ventricular relaxation).
Measured by a sphygmomanometer.
Platelets: Circulating cells that plug leaks by clotting blood at injury sites.
Lymph (Tissue Fluid): Colourless fluid escaped from capillaries into intercellular spaces. Contains less protein than plasma. Transports digested fats and drains excess fluid back to blood.
Transportation in Plants
Xylem: Transports water and minerals from soil.
Root Pressure: Active ion uptake creates concentration differences, pulling water in. More important at night.
Transpiration: Evaporation of water from leaves creates a suction (transpiration pull) that moves water upward during the day and helps in temperature regulation.
Phloem: Transports soluble products of photosynthesis (translocation), amino acids, and other substances.
Uses energy from ATP to transfer sucrose into phloem.
Osmotic pressure increases, moving material to tissues with lower pressure (e.g., sugar from roots to buds in spring).
Excretory Systems
Human Excretory System: Pair of kidneys, pair of ureters, urinary bladder, and urethra.
Nephron: The basic filtration unit. Consists of a cluster of thin-walled capillaries associated with a cup-shaped Bowman’s capsule.
Filtration process: Substances like glucose, amino acids, salts, and water are selectively re-absorbed from the initial filtrate ( daily, but only excreted as urine).
Urine path: Kidney → Ureters → Urinary bladder (muscular/under nervous control) → Urethra.
Artificial Kidney (Hemodialysis): A device to remove nitrogenous wastes from blood when kidneys fail. It uses semi-permeable tubes in dialysing fluid. Unlike real kidneys, no re-absorption occurs.
Plant Excretion:
Oxygen and are released as waste during specific times.
Excess water is lost via transpiration.
Wastes are stored in cellular vacuoles, old xylem (resins/gums), or in leaves that eventually fall off.
Some wastes are excreted into the soil.
Supplemental Information
Tobacco Use: Harmful in all forms (smoking or smokeless). Affects tongue, lungs, heart, and liver. High oral cancer incidence in India is linked to chewing tobacco (gutkha).
Smoking: Destroys respiratory cilia, leading to infection, cough, and lung cancer.
Dental Caries: Bacterial acid production demineralises enamel and dentine. Plaque (bacterial mass) prevents saliva from neutralizing acid.
Organ Donation: Organs (kidneys, heart, liver, etc.) can be donated with consent from the donor or family. Most occur after death or brain death, though some (kidney, part of lung/liver) can be donated by living donors.