Life Processes

Introduction: Defining Life

Living beings can be identified by observing movements like running (dog), chewing (cow), or shouting (man).
Breathing is an indicator of life, even when asleep.
Plants are identified as living through their green color or growth over time.
Movement, whether growth-related or not, is generally considered evidence of life.
However, visible movement isn't sufficient as a defining characteristic.
Invisible molecular movement is considered necessary for life by professional biologists.
Viruses lack molecular movement until they infect a cell, leading to debate about whether they are truly alive.
Living organisms possess well-organized structures that tend to break down over time due to environmental effects.
Maintenance processes are essential for repairing and maintaining these structures.
Molecular movements are necessary to move molecules around for repair and maintenance.

What are Life Processes?

Maintenance functions must occur even when organisms are not actively doing anything.
Life processes perform maintenance, requiring energy.
Energy comes from outside the organism's body (food).
Nutrition is the process of transferring energy from outside the body (food) to inside.
Additional raw materials are needed from outside for body size growth.
Life on earth depends on carbon-based molecules, so most food sources are carbon-based.
Different organisms use different nutritional processes based on the complexity of carbon sources.
Outside energy sources vary and need to be broken down/built up into a uniform source of energy.
Energy is used for molecular movements to maintain living structures and for growth.
Chemical reactions, such as oxidizing-reducing reactions, are necessary to break down molecules.
Many organisms use oxygen from outside the body for breakdown processes (respiration).
Respiration is the acquisition of oxygen from outside the body for use in the breakdown of food sources for cellular needs.
Single-celled organisms don't need specific organs for food intake, gas exchange, or waste removal because their entire surface is in contact with the environment.

Complexity in Multi-cellular Organisms

Multi-cellular organisms: all cells may not be in direct contact with the environment, so simple diffusion is insufficient.
Multi-cellular organisms have specialized body parts for specific functions.
Uptake of food and oxygen is the function of specialized tissues.
A transportation system is needed to carry food and oxygen throughout the body because they are taken up at one place.
Chemical reactions create by-products that are useless or harmful and need removal (excretion).
Excretion is the process of removing waste by-products from the body.
A specialized tissue for excretion is developed, requiring the transportation system to move waste to the excretory tissue.

Nutrition

Energy is used when walking or riding a bicycle.
Energy is needed to maintain order in our body even when not active.
Materials from outside are needed to grow, develop, and synthesize proteins.
Food provides energy and materials.
All organisms have a common requirement for energy and materials fulfilled in different ways.

Autotrophic Nutrition

Some organisms use simple food material from inorganic sources (carbon dioxide and water).
Autotrophs include green plants and some bacteria.
Autotrophs carbon and energy requirements are fulfilled by photosynthesis.
Photosynthesis converts substances from the outside into stored forms of energy.
Carbon dioxide and water are converted into carbohydrates in the presence of sunlight and chlorophyll.
Carbohydrates provide energy to the plant.
Unused carbohydrates are stored as starch for later use.
Humans store energy derived from food as glycogen.

Photosynthesis equation: 6CO2 + 6H2O + (light energy) \rightarrow C6H{12}O6 + 6O2

Photosynthesis Process

Absorption of light energy by chlorophyll.
Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen.
Reduction of carbon dioxide to carbohydrates.
These steps don't necessarily happen immediately one after the other.
Desert plants take up carbon dioxide at night and use energy absorbed during the day.
Chlorophyll is essential for photosynthesis.
Chloroplasts, found in cells, contain chlorophyll.
Stomata are tiny pores on the surface of leaves for gaseous exchange during photosynthesis.
Gaseous exchange also occurs across stems, roots, and leaves.
Plants close stomata when carbon dioxide is not needed to prevent water loss.
Guard cells control the opening and closing of stomatal pores: they swell when water flows in (opening) and shrink when water flows out (closing).
Water used in photosynthesis is taken up from the soil by roots in terrestrial plants.
Other materials like nitrogen, phosphorus, iron, and magnesium are taken up from the soil.
Nitrogen is essential for protein synthesis and is taken up as inorganic nitrates or nitrites or as organic compounds prepared by bacteria.

Heterotrophic Nutrition

Each organism is adapted to its environment.
Nutrition differs based on food type, availability, and how it's obtained.
Food source (stationary or mobile) affects how food is accessed and the nutritive apparatus used.
Some organisms break down food outside the body and then absorb it (e.g., fungi, yeast, mushrooms).
Others take in whole material and break it down inside their bodies.
Some derive nutrition from plants or animals without killing them (parasitic strategy, e.g., cuscuta, ticks, lice, leeches, tapeworms).

How Organisms Obtain Nutrition

Digestive systems differ depending on food and how it's obtained.
Single-celled organisms take in food through their entire surface.

Amoeba

Amoeba uses finger-like extensions to engulf food forming a food vacuole.
Inside the vacuole, complex substances are broken down into simpler ones that diffuse into the cytoplasm.
Undigested material is moved to the cell surface and expelled.

Paramoecium

Paramoecium has a definite shape and takes in food at a specific spot using cilia movement.

Nutrition in Human Beings

The alimentary canal is a long tube from the mouth to the anus with different parts specialized for different functions.
Food has to be processed into small particles with the same texture.
Food is crushed by teeth and wetted with saliva for smooth passage.
Saliva, secreted by salivary glands, contains salivary amylase.
Salivary amylase breaks down starch into simple sugar.
The muscular tongue mixes food with saliva and moves it around.
Peristaltic movements push food along the digestive tube.
Food moves from the mouth to the stomach through the oesophagus.
The stomach expands when food enters and mixes it with digestive juices.
Gastric glands release hydrochloric acid, pepsin, and mucus.
Hydrochloric acid creates an acidic medium for pepsin to act.
Mucus protects the stomach lining from the acid.
A sphincter muscle regulates the exit of food from the stomach into the small intestine.

Small Intestine

The food enters the small intestine from the stomach.
The small intestine is the longest part of the alimentary canal (compact space due to coiling).
The length varies depending on the food eaten (longer in herbivores).
The small intestine is the site of complete carbohydrate, protein, and fat digestion.
The small intestine receives secretions from the liver and pancreas.
The food from the stomach is acidic and needs to be made alkaline for pancreatic enzymes.
Bile juice from the liver makes the food alkaline and acts on fats by breaking down fats into smaller globules.
Pancreas secretes pancreatic juice containing trypsin (for proteins) and lipase (for emulsified fats).
The walls of the small intestine contain glands that secrete intestinal juice.
Intestinal juice enzymes convert proteins to amino acids, carbohydrates into glucose, and fats into fatty acids and glycerol.
Digested food is taken up by the walls of the intestine.
Villi (finger-like projections) increase the surface area for absorption.
Villi are supplied with blood vessels that transport absorbed food to cells for energy, tissue building, and repair.
Unabsorbed food is sent to the large intestine where water is absorbed.
The remaining material is removed from the body via the anus, which is regulated by the anal sphincter.

Respiration

Food material taken in during nutrition provides energy for life processes.
Diverse organisms use different ways to break down food.
Some use oxygen to break-down glucose completely into carbon dioxide and water, while some use other pathways that do not involve oxygen.

Glucose Breakdown

The first step in all cases is to break down glucose (a six-carbon molecule) into pyruvate (a three-carbon molecule) in the cytoplasm.
Pyruvate can be converted into ethanol and carbon dioxide during fermentation in yeast (anaerobic respiration, occurs without oxygen).
Break-down of pyruvate using oxygen occurs in the mitochondria (aerobic respiration).
- This process breaks up the three-carbon pyruvate molecule to give three molecules of carbon dioxide and water, along with a high quantity of energy.
Aerobic respiration releases more energy than anaerobic respiration.
In muscle cells, pyruvate can be converted into lactic acid (a three-carbon molecule) when there is a lack of oxygen, causing cramps.

ATP: Energy Currency

Energy released during cellular respiration synthesizes ATP (adenosine triphosphate), which fuels cellular activities.
ATP is broken down to release a fixed amount of energy for endothermic reactions.
* ATP is made from ADP (adenosine diphosphate) and inorganic phosphate
* Energy released through breaking of the terminal phosphate linkage = 30.5 kJ/mol
ATP is used for muscle contraction, protein synthesis, and nerve impulse conduction.

Gas Exchange in Plants

Plants exchange gases through stomata, ensuring all cells are in contact with air.
Carbon dioxide and oxygen are exchanged by diffusion based on environmental conditions and plant requirements.
At night, carbon dioxide elimination is the major exchange activity.
During the day, carbon dioxide generated during respiration is used for photosynthesis, with oxygen release as the major event.
Animals have evolved different organs for oxygen uptake and carbon dioxide removal.

Respiration in Aquatic vs. Terrestrial Organisms

Terrestrial animals breathe oxygen in the atmosphere, while aquatic animals use oxygen dissolved in water.
Aquatic organisms breathe faster because dissolved oxygen levels are lower.
Fishes take in water and force it past gills where oxygen is taken up by blood.
Terrestrial organisms use different organs to absorb oxygen from the atmosphere; these organs increase the surface area for contact with oxygen.
The exchange surface is fine and delicate and usually placed within the body.
Passages take air to the exchange area, and a mechanism moves air in and out of this area.

Human Respiratory System

Air is taken in through the nostrils and filtered by fine hairs and mucus.
Air passes through the throat and into the lungs.
Rings of cartilage in the throat prevent collapse.
Within the lungs, the passage divides into smaller tubes terminating in alveoli.
Alveoli walls have an extensive network of blood vessels for gas exchange.
During inhalation, ribs lift, the diaphragm flattens, and the chest cavity enlarges, sucking air into the lungs and expanding the alveoli.
Blood brings carbon dioxide from the body for release into the alveoli and takes up oxygen for transport to all cells.
Lungs always contain a residual volume of air for sufficient oxygen absorption and carbon dioxide release.
Respiratory pigments (haemoglobin in humans) take up oxygen from the air in the lungs and carry it to tissues, releasing it where oxygen is deficient.

Transportation

Transportation in Human Beings

Blood transports food, oxygen, and waste materials.
Blood is a fluid connective tissue with plasma and suspended cells.
Plasma transports food, carbon dioxide, and nitrogenous wastes.
Red blood corpuscles carry oxygen.
Salts are also transported by blood.
A pumping organ (heart) pushes blood, a network of tubes (blood vessels) reaches tissues, and a repair system fixes damage.

The Heart

The heart is a muscular organ with different chambers to prevent mixing of oxygen-rich and carbon dioxide-rich blood.
Carbon dioxide-rich blood goes to the lungs for carbon dioxide removal, and oxygenated blood returns to the heart for pumping to the body.

Process of Circulation

Oxygen-rich blood from the lungs enters the left atrium.
The left atrium contracts, transferring blood to the left ventricle.
The left ventricle contracts, pumping blood to the body.
Deoxygenated blood from the body enters the right atrium.
The right atrium contracts, transferring blood to the right ventricle.
The right ventricle pumps blood to the lungs for oxygenation.
Ventricles have thicker muscular walls than atria.
Valves prevent backflow of blood.

Separation of Oxygenated and Deoxygenated Blood

Separation allows efficient oxygen supply.
Useful for animals with high energy needs (birds, mammals) to maintain body temperature.
Amphibians and reptiles have three-chambered hearts with some mixing of oxygenated and deoxygenated blood streams.
Fishes have two-chambered hearts; blood is pumped to the gills, oxygenated, and passed directly to the body (single circulation).
Other vertebrates have double circulation (blood passes through the heart twice in each cycle).

Blood Pressure

Blood pressure is the force blood exerts against vessel walls and is measured using a sphygmomanometer.
* Normal systolic pressure = 120 mm of Hg
* Normal diastolic pressure = 80 mm of Hg
Arteries: vessels carrying blood from the heart under high pressure, have thick, elastic walls.
Veins: collect blood and bring it back to the heart and have valves to ensure one-way flow.
Arterioles constriction results in high pressure, also called hypertension, which can lead to the rupture of an artery.

Capillaries

Arteries divide into smaller vessels (capillaries).
Capillaries are thin walls (one-cell thick).
Exchange of materials takes place here.
Capillaries join to form veins.

Platelets

Platelets are blood cells that circulate and help clot blood to plug leaks.
Lymph (tissue fluid) is another fluid involved in transportation.
Plasma, proteins, and blood cells escape into intercellular spaces to form lymph.
Lymph is similar to blood plasma but is colourless and contains less protein.
Lymph drains into lymphatic capillaries, joins to form lymph vessels, and opens into veins.
Lymph carries digested fat from the intestine and drains excess fluid from extracellular space back into the blood.

Transportation in Plants

Plants take in carbon dioxide and photosynthesize energy stored in leaves (chlorophyll-containing organs).
Plants also need nitrogen, phosphorus, and other minerals.
Minerals are absorbed through roots.
If the distances are small, energy and raw materials diffuse easily.
If distances are large, a transport system is essential.
Plants have low energy needs and slow transport systems.
Plant transport systems move energy stores from leaves and raw materials from roots, constructed as independent conducting tubes.

Xylem

Xylem moves water and minerals from the soil.
Xylem consists of vessels and tracheids in roots, stems, and leaves.
Cells in roots actively take up ions, creating a concentration difference between root and soil.
Water moves into the root to eliminate this difference, creating a column of water that is pushed upwards.
Transpiration is the loss of water in the form of vapour from the aerial parts of the plant.
The evaporation of water from leaf cells creates a suction that pulls water from xylem cells of roots.
Transpiration helps in absorption and upward movement of water and minerals and regulates temperature.
Root pressure is more important at night.
During the day, transpiration pull is the major force for water movement.

Phloem

Phloem transports products of photosynthesis from leaves to other parts of the plant (translocation).
Phloem also transports amino acids and other substances, delivers them to storage organs, fruits, seeds, and growing organs.
Translocation occurs in sieve tubes with adjacent companion cells, in both upward and downward directions.
Translocation in phloem uses energy.
Sucrose is transferred into phloem tissue using energy from ATP (adenosine triphosphate).
Increased osmotic pressure causes water to move into the tissue.
The movement of water moves materials in the pholem
In spring, sugar stored in root or stem tissue is transported to buds.

Excretion

Organisms get rid of gaseous wastes generated during photosynthesis or respiration.
Metabolic activities generate nitrogenous materials that need to be removed.
Excretion is the removal of harmful metabolic wastes.
Unicellular organisms remove wastes by simple diffusion.
Multi-cellular organisms use specialized organs.

Excretion in Human Beings

The excretory system includes a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.
Kidneys are located in the abdomen.
Urine is produced in the kidneys and passes through the ureters into the urinary bladder, where it is stored and released through the urethra.
Urine is produced to filter waste products from the blood.
Nitrogenous waste (urea, uric acid) is removed from blood in the kidneys.
The basic filtration unit is a cluster of thin-walled blood capillaries associated with Bowman’s capsule (nephrons).

Nephrons

Each kidney has a large number of nephrons.
Initial filtrate (glucose, amino acids, salts, water) are re-absorbed along the tube.
Water re-absorption depends on excess water in the body and the amount of dissolved waste to be excreted.
Urine enters the ureter, connecting the kidneys with the urinary bladder.
Urine is stored in the bladder until the pressure leads to the urge to urinate.
The bladder (muscular) is under nervous control.

Excretion in Plants

Oxygen is a waste product of photosynthesis.
Plants get rid of excess water by transpiration.
Many tissues consist of dead cells, and plants can lose parts such as leaves.
Plant waste products are stored in cellular vacuoles or leaves that fall off.
Other wastes are stored as resins and gums in old xylem.
Plants also excrete some waste substances into the soil.