Life Processes: Comprehensive University Study Notes and Study Guide
Introduction to Life and Life Processes
Criteria for Life: Being alive is often associated with movement, such as a dog running, a cow chewing cud, or a human shouting. Even in sleep, breathing indicates life. In plants, growth is a key indicator, though some plants with non-green leaves or those with invisible growth are still alive. Therefore, visible movement is insufficient as a defining characteristic of life.
Molecular Movement: Professional biologists assert that invisible molecular movement is essential for life. Viruses do not show molecular movement until they infect a cell, which leads to controversy regarding their status as living or non-living entities.
Need for Maintenance: Living organisms are highly organized (tissues, cells, organelles). Environmental factors tend to break down this order. Since order is necessary for life, organisms must perform continuous repair and maintenance. These molecular processes are collectively called life processes.
Definition of Life Processes: The processes which together perform the maintenance job of keeping the organism alive, even during inactivity (like sitting or sleeping), are called life processes.
Energy and Nutrition: Maintenance requires energy, which is acquired from outside the body as food. Nutrition is the process of transferring this external energy source to the inside of the body. Most food sources on Earth are carbon-based molecules.
Development and Growth: If an organism's size is to increase, it requires additional raw materials from the environment, primarily carbon-based sources.
Basic Requirements of Life Processes
Respiration: Energy from external sources must be broken down or built up in the body and converted into a uniform energy source for molecular movements. This often involves oxidizing-reducing reactions. Respiration is the process of acquiring oxygen from outside the body and using it to break down food sources for cellular needs.
Need for Transportation: In single-celled organisms, the entire surface is in contact with the environment, allowing simple diffusion for gas exchange, food intake, and waste removal. In multi-cellular organisms, diffusion is insufficient because most cells are not in direct contact with the environment. Thus, specialized tissues and transportation systems are needed to move food and oxygen to all parts of the body.
Excretion: Chemical reactions producing energy also generate harmful or useless by-products (like nitrogenous waste). Excretion is the process of removing these wastes from the body. Multicellular organisms develop specialized excretory tissues, supported by the transportation system which brings waste to these tissues.
Nutrition and Feeding Strategies
Energy and Material Source: Energy is required for activity and maintaining a state of order in the body. Raw materials are also needed for growth, development, and protein synthesis. These are obtained from food.
Autotrophic Nutrition: Organisms that use simple inorganic sources ( and water) are called autotrophs. This includes green plants and some bacteria.
Heterotrophic Nutrition: Organisms that utilize complex substances, which must be broken down by bio-catalysts called enzymes, are heterotrophs. Their survival depends directly or indirectly on autotrophs. Examples include animals and fungi.
Heterotrophic Strategies: * Saprotrophic: Breaking down food material outside the body and then absorbing it (e.g., bread moulds, yeast, mushrooms). * Holozoic: Taking in whole material and breaking it down inside the body (e.g., humans, lions, cows). * Parasitic: Deriving nutrition from plants or animals without killing them (e.g., Cuscuta/amar-bel, ticks, lice, leeches, tape-worms).
Autotrophic Nutrition and Photosynthesis
Definition: The process by which autotrophs convert external substances ( and ) into stored forms of energy (carbohydrates) using sunlight and chlorophyll.
Chemical Equation of Photosynthesis:
Main Events in Photosynthesis: 1. Absorption of light energy by chlorophyll. 2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen. 3. Reduction of carbon dioxide to carbohydrates.
Timing of Steps: Steps do not always occur sequentially. Desert plants take up at night and prepare an intermediate, which is acted upon by energy absorbed by chlorophyll during the day.
Chloroplasts: Cell organelles containing chlorophyll, visible as green dots in a leaf cross-section.
Starch Storage: Plants store excess carbohydrates as starch (internal energy reserve). Humans store energy as glycogen.
Stomata and Gas Exchange: Stomata are tiny pores on leaf surfaces. While the majority of gas exchange happens through these, it also occurs across stems, roots, and leaves. To prevent excessive water loss via transpiration, the plant closes these pores.
Guard Cells: The opening and closing of stomata are regulated by guard cells. They swell when water flows into them (opening the pore) and shrink when water is lost (closing the pore).
Raw Materials for Plants: Water is taken from soil by roots. Nitrogen, phosphorus, iron, and magnesium are also essential. Nitrogen is used for protein synthesis and is taken as inorganic nitrates/nitrites or organic compounds prepared by bacteria.
Nutrition in Simple Organisms
Amoeba: Uses temporary finger-like extensions of the cell surface (pseudopodia) to engulf food, forming a food-vacuole. Complex substances are broken down inside the vacuole and diffuse into the cytoplasm. Undigested material is moved to the cell surface and expelled.
Paramoecium: A unicellular organism with a definite shape. Food is taken at a specific spot. Cilia covering the entire surface move the food to this spot.
Human Digestive System (Alimentary Canal)
Mouth: Food is crushed by teeth and wetted with saliva to make passage smooth. Salivary glands secrete saliva containing the enzyme salivary amylase, which breaks down starch (complex molecule) into simple sugar. The muscular tongue mixes food with saliva.
Oesophagus: Food moves via peristaltic movements (rhythmic muscle contractions) to the stomach.
Stomach: A large organ that expands to accommodate food. Muscular walls mix food with digestive juices secreted by gastric glands. These glands release: 1. Hydrochloric Acid (): Creates an acidic medium for pepsin action. 2. Pepsin: A protein-digesting enzyme. 3. Mucus: Protects the inner stomach lining from acid.
Small Intestine: The longest part of the alimentary canal, extensively coiled. Site of complete digestion of carbohydrates, proteins, and fats. * Differences in Length: Herbivores have longer small intestines to digest cellulose; carnivores like tigers have shorter ones because meat is easier to digest. * Liver Secretion: Produces bile juice. It makes the acidic food from the stomach alkaline for pancreatic enzymes and emulsifies fats (breaking large globules into smaller ones). * Pancreas Secretion: Produces pancreatic juice containing trypsin (for protein digestion) and lipase (for breaking down emulsified fats). * Intestinal Juice: Enzymes finally convert proteins to amino acids, complex carbohydrates into glucose, and fats into fatty acids and glycerol. * Absorption: The inner lining has villi (finger-like projections) which increase surface area. Villi are richly supplied with blood vessels that transport nutrients to all cells for energy, repair, and tissue building.
Large Intestine: Absorbs water from unabsorbed food. The remaining waste is removed via the anus.
Sphincters: The exit of food from the stomach is regulated by the sphincter muscle; the anus is regulated by the anal sphincter.
Dental Caries: Tooth decay caused by bacteria producing acid from sugar, demineralizing enamel and dentine. Dental plaque (mass of bacteria and food) prevents saliva from neutralizing acid.
Respiration Pathways
Cytoplasmic Step: The first step in all organisms is the break-down of glucose (-carbon molecule) into pyruvate (-carbon molecule), taking place in the cytoplasm.
Anaerobic Respiration: Occurs in the absence of oxygen. In yeast during fermentation, pyruvate is converted into ethanol and carbon dioxide.
Lactic Acid Fermentation: In our muscle cells during sudden activity and lack of oxygen, pyruvate is converted into lactic acid (-carbon molecule), causing cramps.
Aerobic Respiration: Occurs in the presence of oxygen in the mitochondria. Pyruvate is broken down into three molecules of and water. The energy release is far greater than in anaerobic respiration.
ATP (Adenosine Triphosphate): The energy currency for cellular processes. Respiration energy is used to make ATP from ADP and inorganic phosphate. Breaking the terminal phosphate linkage using water releases of energy. ATP fuels muscle contraction, protein synthesis, and nervous impulses.
Human Respiratory System
Structure: Air enters through nostrils (filtered by hair and mucus), passes through the throat (protected by rings of cartilage to prevent collapse), and enters the lungs.
Alveoli: The passage ends in balloon-like structures called alveoli. They provide a surface for gas exchange. If spread out, the alveolar surface would cover about .
Mechanism of Breathing: Inhalation involves lifting ribs and flattening the diaphragm, making the chest cavity larger. This sucks air into lungs. Oxygen is taken up from alveoli by haemoglobin in red blood corpuscles. is brought from the body and released into alveoli.
Gas Exchange Efficiency: Haemoglobin has a high affinity for oxygen. Diffusion alone is too slow; oxygen would take years to reach the toes from the lungs without it.
Residual Volume: Lungs always retain a volume of air so exchange can continue during the breathing cycle.
Tobacco and Health: Tobacco use (smoking or chewing) is a major risk factor for oral cancer, lung cancer, heart attacks, and strokes. Cilia in the upper respiratory tract are destroyed by smoking, allowing germs into the lungs.
Transportation in Human Beings
Blood: A fluid connective tissue consisting of plasma (transports food, , nitrogenous wastes, salts) and red blood corpuscles (transport oxygen).
The Heart: A muscular organ (size of a fist) with four chambers to prevent mixing of oxygenated and deoxygenated blood. 1. Left Atrium: Collects oxygenated blood from lungs. 2. Left Ventricle: Pumps oxygenated blood to the body (has thick muscular walls). 3. Right Atrium: Collects deoxygenated blood from the body. 4. Right Ventricle: Pumps deoxygenated blood to the lungs for oxygenation.
Valves: Ensure one-way blood flow.
Double Circulation: Blood passes through the heart twice in one cycle. Mammals and birds use this for efficient energy supply to maintain constant body temperature. Amphibians and reptiles (three-chambered hearts) tolerate some mixing of blood. Fish (two-chambered hearts) pump blood to gills, from which it goes directly to the body.
Blood Pressure: Measured by a sphygmomanometer. Normal systolic pressure (ventricular contraction) is and diastolic (relaxation) is . Hypertension (high blood pressure) is caused by arteriolar constriction.
Vessels: Arteries have thick elastic walls (carry blood from heart under high pressure). Veins have valves and thinner walls (collect blood for the heart). Capillaries are one-cell thick for material exchange.
Platelets: Circulate in blood to plug leaks and clot blood at injury sites.
Lymph: Also called tissue fluid. Plasma, proteins, and cells escape through capillary pores into intercellular spaces. It is colourless, contains less protein than blood, and drains into large veins. It carries digested fats and drains excess fluid from tissues.
Transportation in Plants
Need: Soil is the source of nitrogen, phosphorus, and minerals. Diffusion is sufficient only if distances between roots and leaves are small. Tall plants need transport systems.
Xylem: Transports water and minerals from soil. Roots actively take up ions, creating an osmotic gradient that moves water into roots (root pressure). In tall trees, transpiration pull is the main force.
Transpiration: Evaporation of water from leaf surface through stomata. It creates a suction pull, helps in upward moisture movement, and regulates temperature. Root pressure is more dominant at night.
Phloem: Transports soluble products of photosynthesis (translocation), amino acids, and other substances to storage organs (roots, fruits, seeds) and growing organs. Translocation occurs in sieve tubes with companion cells in both directions.
Mechanism of Phloem Transport: Utilizes energy (ATP). Material like sucrose is loaded into phloem, increasing osmotic pressure, causing water to move in and pushing material to tissues with lower pressure.
Excretion
Unicellular Organisms: Remove waste by simple diffusion from the body surface.
Human Excretory System: Pair of kidneys, pair of ureters, urinary bladder, and urethra. Kidneys are in the abdomen on either side of the backbone.
The Nephron: The basic filtration unit. Each kidney has millions. It starts with a cup-shaped Bowman's capsule surrounding a capillary cluster (glomerulus). * Selective Reabsorption: As filtrate flows through the nephron tube, glucose, amino acids, salts, and water are reabsorbed. Water reabsorption depends on body hydration and dissolved waste levels. * Volume: Initial filtrate is daily, but only of urine is excreted.
Artificial Kidney (Hemodialysis): A device containing semi-permeable tubes in dialysing fluid (no nitrogenous waste) used to filter blood for patients with kidney failure. Unlike real kidneys, there is no reabsorption.
Excretion in Plants: Plants use various strategies: * Release oxygen () as waste. * Lose excess water through transpiration. * Store waste in vacuoles or in leaves that fall off. * Store resins and gums in old xylem. * Excrete wastes into the surrounding soil.
Questions & Discussion
Question: Why is diffusion insufficient to meet the oxygen requirements of multi-cellular organisms like humans?
Answer: Multi-cellular organisms have large body sizes where most cells are not in direct contact with the environment, so diffusion is too slow to reach every cell.
Question: What criteria do we use to decide whether something is alive?
Answer: Movement (growth-related or not) and essential invisible molecular movements/maintenance processes.
Question: What are outside raw materials used for by an organism?
Answer: Energy source (food), growth, and body tissue building (nitrates, minerals).
Question: What is the role of acid in our stomach?
Answer: It creates an acidic medium for pepsin to function and kills bacteria.
Question: Why is it necessary to separate oxygenated and deoxygenated blood in mammals and birds?
Answer: To ensure an efficient supply of oxygen to maintain constant body temperature.
Question: How is the small intestine designed to absorb digested food?
Answer: It has numerous villi to increase surface area and a rich supply of blood vessels for transport.