Life Processes — Notes

WHAT ARE LIFE PROCESSES?

Life processes are the fundamental maintenance functions performed by living organisms to sustain life. These processes are essential for survival and operate continuously, even when the organism is at rest or asleep, to prevent damage and breakdown of its organized structures.

To carry out these maintenance functions, living organisms require energy. This energy is derived from food, which is a source of energy obtained from outside the organism's body. The process of obtaining and utilizing this food is called nutrition.

In addition to energy, organisms also need raw materials for growth and repair. Most of these raw materials are carbon-based, as life on Earth is built upon carbon molecules. Different organisms employ various nutritional processes to break down or build up these carbon-based food sources into a usable form of energy and essential molecules.

To convert food sources into energy, organisms often use oxygen, typically sourced from the environment. The process of taking in oxygen and using it to break down food molecules for energy is known as respiration.

In single-celled organisms, the entire cell surface is in contact with the environment, allowing for direct exchange of materials like food and oxygen, and waste removal. However, in multi-cellular organisms, the complexity and increased size of the body mean that not all cells are in direct contact with the external environment. This makes simple diffusion insufficient to meet the needs of all cells for essential substances like food and oxygen.

Therefore, multi-cellular organisms have developed specialized tissues and body parts to perform specific functions. This leads to the need for a transportation system to carry absorbed food and oxygen from the sites of intake to all parts of the body where they are needed.

Furthermore, the chemical reactions involved in energy generation produce waste by-products. These by-products can be useless or even harmful to the organism. To maintain a stable internal environment and prevent harm, these wastes must be removed from the body through a process called excretion. This process also often involves the transportation system to move wastes from cells to specialized excretory tissues.

The key maintenance functions that collectively constitute life processes include:

• Nutrition: Obtaining and utilizing food for energy, growth, and repair.
• Respiration: Breaking down food molecules to release energy, often using oxygen.
• Transportation: Moving essential substances like food and oxygen throughout the body, and carrying waste products away from cells.
• Excretion: Removing metabolic waste products from the body.

Remember

Life processes are essential for maintaining the organized structure and preventing the breakdown of living organisms. They require energy, which is derived from external sources like food.

Exam-smart

Questions might ask you to identify the common thread linking various biological activities (like eating, breathing, moving) as life processes. You may also be asked to explain why diffusion is not enough for larger organisms, leading into the necessity of transport systems.

NUTRITION

Nutrition is the process by which an organism obtains and utilizes food substances. Food provides energy and raw materials needed for growth, repair, and other life processes.

Organisms can be broadly classified based on their mode of nutrition: autotrophs and heterotrophs.

Autotrophic Nutrition

Autotrophic nutrition is a mode of nutrition where organisms produce their own food using simple inorganic substances. These organisms are called autotrophs.

• How it works: Autotrophs use photosynthesis to convert carbon dioxide ($C{O}_2$) and water ($H_{2}O$) into carbohydrates (like glucose) in the presence of sunlight and a pigment called chlorophyll.

• Carbon dioxide is obtained from the atmosphere through small pores on leaves called stomata.
• Water is absorbed from the soil by the roots.
• Sunlight provides the energy for the reaction.
• Chlorophyll, present in chloroplasts, absorbs light energy.
• Raw Materials: Besides $C{O}_2$ and $H_{2}O$, autotrophs also require other raw materials like nitrogen, phosphorus, iron, and magnesium for synthesizing proteins and other essential compounds. These are absorbed from the soil.
• Energy Storage: Carbohydrates not immediately used are stored as starch in plants, serving as an internal energy reserve. In animals, excess energy is stored as glycogen.
• Stomata Control: Stomata are pores on leaves that open and close to regulate gas exchange ($C{O}_2$ intake and $O_2$ release) and transpiration. The opening and closing are controlled by guard cells which swell when water enters them, opening the pore, and shrink when water leaves, closing it.

Remember

The opening and closing of stomata is crucial for balancing gas exchange with water conservation.

Exam-smart

Questions may involve designing experiments to prove the necessity of light, $C{O}_2$, or chlorophyll for photosynthesis, often using a potometer or testing for starch with iodine solution.

Heterotrophic Nutrition

Heterotrophic nutrition is a mode of nutrition where organisms cannot produce their own food and depend directly or indirectly on autotrophs for their sustenance. These organisms are called heterotrophs.

• Types of Heterotrophic Nutrition:
• Saprotrophic Nutrition: Organisms feed on dead and decaying organic matter (e.g., fungi like bread moulds, yeast, mushrooms). They break down food outside their body and then absorb it.
• Parasitic Nutrition: Organisms obtain nutrients from living hosts without killing them (e.g., cuscuta (amar-bel), ticks, lice, leeches, tapeworms).
• Holozoic Nutrition: Organisms ingest complex food material, digest it internally, and then absorb the nutrients. This is common in animals.

Remember

All heterotrophs depend on autotrophs, either by eating them or by eating other organisms that eat autotrophs.

Exam-smart

You might be given examples of organisms and asked to identify their mode of nutrition or the strategy they use to obtain food.

How do Organisms obtain their Nutrition?

The method of obtaining food varies greatly among organisms depending on their complexity and environment.

• Unicellular Organisms:
• Amoeba: Engulfs food particles using temporary extensions called pseudopodia, forming a food vacuole. Digestion occurs within the food vacuole by enzymes. Undigested food is expelled from the cell.
• Paramoecium: Has a definite shape and takes in food through a specific spot using the coordinated movement of cilia that sweep food particles into the cell.
• Multicellular Organisms: Possess specialized organs for ingestion, digestion, absorption, and egestion.

Remember

The complexity of the digestive system generally increases with the complexity of the organism.

Exam-smart

Diagrams of unicellular organisms like Amoeba showing the process of phagocytosis might be presented, asking to identify the structures involved.

Nutrition in Human Beings

Human beings exhibit holozoic nutrition, involving the ingestion, digestion, absorption, assimilation, and egestion of food through a specialized alimentary canal.

• Alimentary Canal: A long, muscular tube extending from the mouth to the anus, with specialized organs:

1. Mouth: Food is ingested and chewed by teeth, increasing its surface area. Salivary glands secrete saliva, which contains the enzyme salivary amylase that begins the breakdown of starch into simpler sugars. The tongue helps in mixing food with saliva and swallowing.
2. Oesophagus (Food Pipe): A muscular tube that transports food from the mouth to the stomach through rhythmic contractions called peristalsis.
3. Stomach: A muscular sac where food is mixed with gastric juices. Gastric glands secrete:

• Hydrochloric Acid (HCl): Creates an acidic medium (pH 1.5-3.5) essential for pepsin's action and kills bacteria.
• Pepsin: A protein-digesting enzyme that breaks down proteins into simpler peptides in an acidic medium.
• Mucus: Protects the stomach lining from the acidic environment.

4. Small Intestine: The longest part of the alimentary canal, highly coiled. It is the primary site for the complete digestion of carbohydrates, proteins, and fats.

• Receives secretions from the liver and pancreas.
• Liver secretes bile juice, which emulsifies fats (breaks large fat globules into smaller ones), and neutralizes the acidic food from the stomach, making it alkaline for pancreatic enzymes.
• Pancreas secretes pancreatic juice containing enzymes like trypsin (for protein digestion) and lipase (for fat digestion).
• The walls of the small intestine also secrete intestinal juice containing enzymes that complete the digestion of carbohydrates to glucose, proteins to amino acids, and fats to fatty acids and glycerol.
• The inner lining of the small intestine has millions of finger-like projections called villi, which vastly increase the surface area for absorption of digested food.
• The absorbed nutrients are transported by blood vessels to all cells of the body.

5. Large Intestine: Absorbs water and some salts from the remaining undigested food material.
6. Anus: The undigested waste material (faeces) is expelled from the body through the anus, regulated by an anal sphincter.

• Dental Caries (Tooth Decay): Occurs when bacteria in the mouth act on sugars, producing acids that demineralize tooth enamel. Plaque formation prevents saliva from neutralizing the acid.

Remember

The villi in the small intestine are specialized for absorption by having a large surface area and a rich blood supply.

Exam-smart

Case studies might present a patient's symptoms related to digestion (e.g., indigestion, acidity, issues with fat metabolism) and ask to identify the affected organ or enzyme, or explain the role of a specific secretion like bile. Questions could also involve tracing the path of food and the chemical changes occurring at each stage.

RESPIRATION

Respiration is a process that breaks down food molecules, like glucose, to release energy for various life processes. This energy is captured in the form of ATP (Adenosine Triphosphate), which acts as the energy currency of the cell.

Types of Respiration

Organisms use different pathways for respiration, depending on the availability of oxygen.

Aerobic Respiration Equation

The overall process of aerobic respiration can be summarized as:

Anaerobic Respiration Pathways

1. In Yeast (Fermentation): Glucose is broken down into ethanol and carbon dioxide. This occurs in the absence of oxygen.

2. In Muscle Cells: During sudden strenuous activity, when oxygen supply is limited, pyruvate is converted into lactic acid. This build-up causes muscle cramps.

Energy Release and ATP

The energy released during respiration is not directly used. Instead, it's used to synthesize ATP from ADP (Adenosine Diphosphate) and inorganic phosphate. ATP then acts as a readily usable energy source for cellular activities. Breaking the terminal phosphate bond in ATP releases about 30.5 kJ/mol of energy.

Remember

ATP is often called the "energy currency" of the cell because it stores and releases energy in a usable form for various cellular functions.

Respiration in Plants

• Plants, like all living organisms, respire to get energy.
• They perform gas exchange (taking in oxygen and releasing carbon dioxide) through stomata.
• Inter-cellular spaces in plant tissues ensure that all cells are in contact with air.
• Diffusion is the primary mechanism for gas movement.
• At night, when photosynthesis doesn't occur, carbon dioxide elimination is the major exchange.
• During the day, the $C{O}_2$ produced during respiration is used up in photosynthesis, so there is no net $C{O}_2$ release; instead, oxygen release is dominant.

Exam-smart

Questions might describe scenarios where a plant is kept in a closed environment during the day versus at night, asking about gas exchange patterns. You need to recall that photosynthesis uses $C{O}_2$ and releases $O_2$, while respiration uses $O_2$ and releases $C{O}_2$.

Respiration in Animals

Animals have evolved specialized organs for respiration to meet their oxygen demands.

Aquatic Animals

• Animals living in water must use dissolved oxygen.
• The amount of dissolved oxygen is much lower than in the air, so aquatic animals have a faster rate of breathing.
• Fishes, for example, take in water through their mouths and pass it over their gills. Gills have a large surface area and are rich in blood vessels, allowing efficient uptake of dissolved oxygen.

Terrestrial Animals

• Terrestrial animals use atmospheric oxygen.
• They have structures that increase the surface area for gas exchange, which are usually delicate and protected inside the body. Passages lead air to these surfaces.

Respiration in Human Beings

1. Pathway of Air: Air enters through the nostrils, which filter it with fine hairs and line it with mucus to trap dust and germs.

2. The air then passes through the throat and into the lungs.

3. The trachea (windpipe) has rings of cartilage to prevent its collapse.

4. Inside the lungs, the trachea branches into smaller tubes called bronchioles, which end in tiny balloon-like structures called alveoli (singular: alveolus).

5. Alveoli provide a large surface area for gas exchange. Their walls are thin and surrounded by a dense network of blood vessels.

6. Mechanism of Breathing:

• Inhalation: The ribs lift up and the diaphragm flattens. This increases the volume of the chest cavity, reducing pressure inside the lungs, causing air to be sucked in.
• Exhalation: The ribs move down and inwards, and the diaphragm relaxes (moves up). This decreases the chest cavity volume, increasing pressure inside, forcing air out.
• Residual Volume: Lungs always contain some air, even after exhalation, to allow sufficient time for gas exchange.

7. Gas Exchange:

• Oxygen from the inhaled air in the alveoli diffuses into the blood in the surrounding capillaries.
• Carbon dioxide from the body's tissues diffuses from the blood into the alveoli to be exhaled.

8. Transport of Gases:

• Oxygen is transported by haemoglobin, a respiratory pigment present in red blood corpuscles. Haemoglobin has a high affinity for oxygen.
• Carbon dioxide is more soluble than oxygen and is mostly transported in the blood in a dissolved form.

Remember

The presence of cartilage rings in the trachea is crucial to keep the airway open, while the alveoli's thin walls and extensive blood supply are vital for efficient gas exchange.

Exam-smart

A question might provide a diagram of the human respiratory system and ask to identify parts or explain the role of specific structures like alveoli or diaphragm in breathing. You might also be asked to compare breathing rates of aquatic vs. terrestrial animals based on oxygen availability.

TRANSPORTATION

Transportation in Human Beings

Blood is a fluid connective tissue that acts as the primary transport medium in humans. It circulates throughout the body, carrying essential substances and removing waste products. Blood consists of two main components:

1. Plasma: The liquid matrix, which transports dissolved food substances, carbon dioxide, nitrogenous wastes, salts, hormones, and heat.
2. Blood Cells: Suspended in plasma, these include:

• Red Blood Cells (RBCs): Contain haemoglobin, a pigment that binds to oxygen and transports it from the lungs to tissues. RBCs are also a key factor in the colour of blood.
• White Blood Cells (WBCs): Part of the immune system, defending the body against infections.
• Platelets: Small cell fragments responsible for blood clotting, which prevents excessive blood loss at injury sites.

The transport system in humans comprises:

• Heart: A muscular pumping organ that propels blood throughout the body. It has four chambers: two atria (upper) and two ventricles (lower).
• The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs.
• The left side of the heart receives oxygenated blood from the lungs and pumps it to the rest of the body.
• Valves within the heart prevent backflow of blood.
• Ventricles have thicker muscular walls than atria because they pump blood to more distant parts of the body.
• Blood Vessels: A network of tubes through which blood circulates.
• Arteries: Carry blood away from the heart to various organs. They have thick, elastic walls to withstand the high pressure of blood pumped from the heart.
• Veins: Collect blood from organs and return it to the heart. They have thinner walls than arteries and possess valves to ensure unidirectional blood flow, as blood pressure is lower.
• Capillaries: Extremely narrow vessels with walls only one-cell thick. They connect arteries and veins and form a network throughout tissues, allowing for the exchange of gases, nutrients, and waste products between blood and cells.

Double Circulation: In mammals and birds, blood passes through the heart twice during each complete cycle of circulation. This double circulation ensures that oxygenated and deoxygenated blood do not mix, leading to a highly efficient supply of oxygen to meet high energy demands for maintaining body temperature.

• Pulmonary Circulation: Blood from the right side of the heart goes to the lungs and returns to the left side of the heart.
• Systemic Circulation: Blood from the left side of the heart is pumped to the rest of the body and returns to the right side of the heart.

Blood Pressure: The force exerted by blood against the walls of blood vessels.

• Systolic Pressure: The pressure in arteries during ventricular contraction. Normal value is about 120 mm Hg.
• Diastolic Pressure: The pressure in arteries during ventricular relaxation. Normal value is about 80 mm Hg.
• It is measured using a sphygmomanometer.
• Hypertension (high blood pressure) is caused by constricted arterioles, increasing resistance to blood flow and potentially leading to arterial rupture.

Lymph (Tissue Fluid): A fluid that circulates in the lymphatic system. It is formed when plasma, proteins, and some blood cells escape from capillaries into the intercellular spaces.

• Functions: Drains excess fluid from extracellular spaces, absorbs digested fats from the intestine, and plays a role in immune responses.

Remember

Haemoglobin's high affinity for oxygen is crucial for efficient oxygen transport. Carbon dioxide is mostly transported dissolved in plasma due to its higher solubility in water.

Exam-smart

Case studies might present scenarios of patients with heart conditions, blood pressure issues, or problems with blood clotting, requiring students to apply their knowledge of the heart's structure, function, and the roles of blood components. For instance, a question could describe someone with very low blood pressure after an injury, asking why platelets are vital in that situation.

Transportation in Plants

Plants have a sophisticated transport system to move water, minerals, and food. Unlike animals, plants have low energy needs due to their sedentary lifestyle and large proportion of dead cells, allowing for slower transport mechanisms.

Xylem: This vascular tissue is responsible for the transport of water and dissolved minerals from the soil, absorbed by the roots, to the rest of the plant, including the leaves.

• Mechanism of Water Transport:

1. Active Ion Uptake: Root cells actively absorb ions from the soil, creating a concentration gradient.
2. Osmosis: Water moves from the soil into the root xylem by osmosis to equalize this concentration difference.
3. Root Pressure: The upward movement of water creates a positive pressure that pushes water up the xylem. This is more significant at night when transpiration is low.
4. Transpiration Pull: This is the major driving force for water movement during the day. Evaporation of water from leaf surfaces through stomata (a process called transpiration) creates a negative pressure or "pull" that draws water up from the roots through the continuous network of xylem vessels and tracheids. Transpiration also helps in regulating plant temperature.

Phloem: This vascular tissue is responsible for the translocation of food (primarily sugars like sucrose) produced during photosynthesis in the leaves to other parts of the plant where it is needed for growth or storage (e.g., roots, fruits, seeds, developing buds).

• Mechanism of Food Transport:

1. Loading into Phloem: Sugars are transferred into the phloem tissue using energy from ATP.
2. Increased Osmotic Pressure: This increases the osmotic pressure within the phloem.
3. Water Movement: Water moves from surrounding xylem into the phloem by osmosis, creating turgor pressure.
4. Bulk Flow: This pressure gradient drives the movement of phloem sap (containing sugars, amino acids, etc.) from regions of higher pressure (source, usually leaves) to regions of lower pressure (sink, e.g., roots, storage organs, growing parts).

• Translocation can occur in both upward and downward directions, depending on the plant's needs.

Remember

Transpiration creates a crucial "pull" that drives water and mineral transport upwards in the xylem, a process vital for plant survival. Phloem transport uses energy and can move substances both up and down.

Exam-smart

Questions might involve diagrams of plant roots, stems, or leaves, asking students to identify the tissues responsible for water and food transport or to explain how environmental factors (like drought or high humidity) affect these processes. A case might describe a plant wilting despite adequate root water, prompting an explanation related to impaired transpiration.

EXCRETION

Excretion is the biological process involved in the removal of harmful metabolic wastes from the body. These wastes are often nitrogenous materials produced by various metabolic activities. Different organisms have evolved diverse strategies for excretion.

• Unicellular organisms typically remove wastes through simple diffusion from their body surface into the surrounding water.
• Complex multicellular organisms employ specialised organs to carry out excretion efficiently.

Excretion in Human Beings

The human excretory system is responsible for filtering waste products, primarily nitrogenous compounds like urea, from the blood and eliminating them from the body in the form of urine.

Components of the Human Excretory System:

1. Kidneys (a pair): Located in the abdomen, on either side of the backbone. These are the primary filtering organs.
2. Ureters (a pair): Tubes connecting the kidneys to the urinary bladder, carrying urine.
3. Urinary Bladder: A muscular sac that stores urine.
4. Urethra: The tube through which urine is expelled from the body.

Formation of Urine:

Urine formation is a process of filtering waste from the blood. This occurs in microscopic functional units within the kidneys called nephrons.

• Filtration: Each kidney contains millions of nephrons. The basic filtration unit is a cluster of thin-walled blood capillaries (glomerulus) enclosed within a cup-shaped structure called the Bowman's capsule. Blood entering the glomerulus is filtered, and the initial filtrate collects in the Bowman's capsule.
• Re-absorption: As the filtrate passes through the coiled tubules of the nephron, essential substances like glucose, amino acids, salts, and a significant amount of water are selectively re-absorbed back into the blood. The extent of water re-absorption is regulated based on the body's water balance and the concentration of waste products.
• Secretion: Further waste products can be secreted from the blood into the tubule.

The final fluid, now concentrated urine, travels through the ureters to the urinary bladder for storage. The release of urine is controlled by a muscular sphincter under nervous control.

Artificial Kidney (Haemodialysis):

In cases of kidney failure, where the kidneys cannot adequately filter waste, an artificial kidney is used. This device performs dialysis, a process to remove nitrogenous wastes from the blood.

• The artificial kidney contains tubes with a semi-permeable lining through which the patient's blood is passed.
• These tubes are immersed in a dialysing fluid that has the same osmotic pressure as blood but is free of waste products.
• Waste products diffuse from the blood into the dialysing fluid, while purified blood is returned to the patient.
• Crucially, unlike the natural kidney, dialysis involves no selective re-absorption.

Key Facts about Urine Production:

• The initial filtrate in a healthy adult is about 180 litres per day.
• However, only 1-2 litres are actually excreted daily due to extensive re-absorption.

Remember

The nephron is the functional unit of the kidney, responsible for filtering blood and producing urine. Re-absorption in the kidney tubules is crucial for conserving water and essential nutrients.

Exam-smart

Case study questions might describe a patient with symptoms of waste accumulation (e.g., fatigue, swelling) and ask to identify the affected organ system or the process needed to correct it. Understanding the role of kidneys and dialysis is key.

Excretion in Plants

Plants also produce waste products, but their strategies for excretion differ significantly from animals.

• Oxygen: Oxygen, a byproduct of photosynthesis, can be considered a waste product for the plant. Plants manage this excess oxygen by releasing it into the atmosphere.
• Excess Water: Plants get rid of excess water through transpiration, a process where water vapor is released from aerial parts, primarily leaves.
• Other Wastes:
• Many plant tissues, such as xylem, consist of dead cells, providing a structural framework and also a means to store some waste products.
• Waste substances can be stored in cellular vacuoles.
• Some wastes are stored as resins and gums, particularly in older xylem.
• Plants can shed parts like leaves, effectively discarding accumulated waste.
• Some waste products are released into the surrounding soil.

Remember

Plants have simpler excretory mechanisms compared to animals. They utilize processes like transpiration, shedding of leaves, and storage of wastes in dead tissues or vacuoles.

Exam-smart

A question might present a scenario describing how a plant loses certain substances and ask to identify the excretory process involved. Understanding that transpiration removes excess water and falling leaves remove stored wastes is important.