Life Processes is a fundamental chapter that explores the essential biological activities organisms perform to sustain life. From obtaining and utilising food (nutrition) to releasing energy (respiration), moving substances throughout the body (transportation), and eliminating waste products (excretion), these processes are crucial for survival, growth, and maintenance. Understanding them helps us appreciate the intricate machinery of living beings, from the simplest bacteria to complex humans, and how they interact with their environment.

Nutrition

Nutrition is the process by which an organism obtains and utilises nutrients (food) for growth, repair, and energy.

Types of Nutrition

1. Autotrophic Nutrition: Organisms synthesise their own food using simple inorganic substances.

• Photoautotrophs: Use light energy (e.g., plants, algae, cyanobacteria).
• Chemoautotrophs: Use chemical energy from inorganic reactions (e.g., some bacteria).

2. Heterotrophic Nutrition: Organisms obtain food from other organisms.

• Holozoic Nutrition: Involves ingestion, digestion, absorption, assimilation, and egestion (e.g., humans, animals).
• Saprophytic Nutrition: Organisms obtain nutrients from dead and decaying organic matter (e.g., fungi, some bacteria).
• Parasitic Nutrition: Organisms live on or in another organism (host) and derive nutrients from it, often harming the host (e.g., Cuscuta, ticks, tapeworms).

Autotrophic Nutrition: Photosynthesis

Photosynthesis is the process used by green plants and some other organisms to convert light energy into chemical energy that, through cellular respiration, can later be released to fuel the organism's metabolic activities. This chemical energy is stored in carbohydrate molecules, such as sugars.

Equation for Photosynthesis: $6CO_2 + 6H_2O \xrightarrow{Sunlight, Chlorophyll} C_6H_{12}O_6 + 6O_2$ (Carbon dioxide + Water $\xrightarrow{Sunlight, Chlorophyll}$ Glucose + Oxygen)

Site of Photosynthesis: Chloroplasts in plant cells, which contain the green pigment chlorophyll.

Main Events of 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. This process is called photolysis of water.
3. Reduction of carbon dioxide to carbohydrates (glucose).

Stomata: Tiny pores on the surface of leaves primarily responsible for the exchange of gases ($CO_2$ and $O_2$) and loss of water vapour (transpiration). Each stoma is guarded by two guard cells which regulate its opening and closing.

Heterotrophic Nutrition in Humans

Humans exhibit holozoic nutrition, involving five steps:

1. Ingestion: Taking food into the body.
2. Digestion: Breaking down complex food into simpler, soluble molecules.
3. Absorption: Absorbing digested food into the blood.
4. Assimilation: Utilising absorbed food for energy, growth, and repair.
5. Egestion: Eliminating undigested food from the body.

Human Digestive System: A long tube called the alimentary canal and associated digestive glands.

• Mouth:
• Teeth: Chew food (mechanical digestion).
• Salivary glands: Secrete saliva, containing salivary amylase (also called ptyalin), which begins the digestion of starch.
• Tongue: Mixes food with saliva and helps in swallowing.
• Pharynx: Common passage for food and air.
• Oesophagus (Food Pipe): Carries food from the pharynx to the stomach by rhythmic contractions called peristalsis.
• Stomach:
• Muscular organ that churns food.
• Gastric glands secrete gastric juice containing:
• Hydrochloric acid (HCl): Creates an acidic medium, kills bacteria, and activates pepsin.
• Pepsin: Enzyme that digests proteins into peptones.
• Mucus: Protects the stomach lining from HCl.
• Small Intestine: The longest part of the alimentary canal (about 6.5 m), where complete digestion and absorption occur.
• Receives secretions from:
• Liver: Secretes bile juice, which emulsifies fats (breaks large fat globules into smaller ones) and makes the medium alkaline for pancreatic enzymes. Bile is stored in the gallbladder.
• Pancreas: Secretes pancreatic juice containing:
• Trypsin: Digests proteins.
• Lipase: Digests emulsified fats.
• Pancreatic amylase: Digests starch.
• Intestinal glands: Secrete intestinal juice containing enzymes that complete the digestion of carbohydrates, proteins, and fats into:
• Carbohydrates $\rightarrow$ Glucose
• Proteins $\rightarrow$ Amino acids
• Fats $\rightarrow$ Fatty acids and Glycerol
• The inner lining has finger-like projections called villi, which increase the surface area for absorption of digested food.
• Large Intestine: Absorbs excess water from undigested food.
• Rectum: Stores undigested waste temporarily.
• Anus: Egests faecal matter from the body.

Respiration

Respiration is the process by which organisms obtain energy from the food they eat. It involves the breakdown of organic molecules (like glucose) to release energy, which is then stored in ATP (Adenosine Triphosphate) molecules.

ATP: The energy currency of the cell. Energy is released when the terminal phosphate bond of ATP is broken, forming ADP (Adenosine Diphosphate) and inorganic phosphate ($\text{P}_i$). $\text{ATP} \rightarrow \text{ADP} + \text{P}_i + \text{Energy}$

Types of Respiration

1. Aerobic Respiration: Occurs in the presence of oxygen.

• Equation: $C_6H_{12}O_6 + 6O_2 \rightarrow 6CO_2 + 6H_2O + \text{Energy (38 ATP)}$ (Glucose + Oxygen $\rightarrow$ Carbon dioxide + Water + Energy)
• Steps:

1. Glycolysis: Glucose (6-carbon molecule) is broken down into two molecules of pyruvate (3-carbon molecule) in the cytoplasm. This step does not require oxygen.
2. Krebs Cycle (Citric Acid Cycle) and Electron Transport Chain: Pyruvate is completely broken down into carbon dioxide and water in the mitochondria, releasing a large amount of energy.

• Energy yield: High (38 ATP molecules per glucose molecule).

2. Anaerobic Respiration: Occurs in the absence of oxygen.

• Steps:

1. Glycolysis: Glucose is broken down into pyruvate in the cytoplasm.
2. Fermentation: Pyruvate is converted into other products without using oxygen.

• Products:
• In yeast: Pyruvate $\rightarrow$ Ethanol + Carbon dioxide + Energy (2 ATP) (Alcoholic fermentation)
• In muscle cells (during strenuous exercise): Pyruvate $\rightarrow$ Lactic acid + Energy (2 ATP) (Lactic acid fermentation). Accumulation of lactic acid causes muscle cramps.
• Energy yield: Low (2 ATP molecules per glucose molecule).

Comparison of Aerobic and Anaerobic Respiration:

Feature	Aerobic Respiration	Anaerobic Respiration
Oxygen	Required	Not required
Site	Cytoplasm (glycolysis), Mitochondria	Cytoplasm
Products	$CO_2$, $H_2O$	Ethanol & $CO_2$ (yeast) or Lactic acid (muscles)
Energy Released	High (38 ATP)	Low (2 ATP)
Complete Breakdown	Yes	No

Respiration in Humans

The human respiratory system ensures efficient exchange of gases.

• Nostrils: Air enters, filtered by fine hairs and mucus, warmed and moistened.
• Pharynx $\rightarrow$ Larynx (voice box) $\rightarrow$ Trachea (windpipe): Air passes through. Trachea has C-shaped cartilaginous rings to prevent collapse.
• Bronchi: Trachea divides into two bronchi, entering each lung.
• Bronchioles: Bronchi further divide into smaller tubes.
• Alveoli (air sacs): Bronchioles terminate in tiny balloon-like structures. These are the primary sites of gaseous exchange.
• Alveoli have thin walls and a rich network of blood capillaries, providing a large surface area for efficient exchange of $O_2$ and $CO_2$.
• Oxygen diffuses from alveoli into the blood, and carbon dioxide diffuses from blood into alveoli.
• Diaphragm and Rib Cage: Muscles that help in breathing movements (inhalation and exhalation).

Respiration in Plants

• Plants exchange gases through stomata on leaves, lenticels on stems, and the general surface of roots.
• They respire throughout the day and night.
• During the day, $CO_2$ produced during respiration is used for photosynthesis. $O_2$ released during photosynthesis is used for respiration or released.
• At night, only respiration occurs, so $CO_2$ is released.

Transportation

Transportation is the process by which substances absorbed or synthesised in one part of an organism are carried to other parts.

Transportation in Humans

The circulatory system is responsible for transport. It consists of the heart, blood, and blood vessels.

1. Heart: A muscular pumping organ, roughly the size of a clenched fist.

• Structure: Four chambers:
• Right Atrium and Right Ventricle: Receive and pump deoxygenated blood to the lungs.
• Left Atrium and Left Ventricle: Receive and pump oxygenated blood to the rest of the body.
• Septum: A wall separating the right and left sides, preventing mixing of oxygenated and deoxygenated blood.
• Valves: Ensure unidirectional flow of blood.
• Double Circulation: Blood passes through the heart twice in one complete cycle.
• Pulmonary Circulation: Blood from the right ventricle goes to the lungs and returns to the left atrium.
• Systemic Circulation: Blood from the left ventricle goes to the body and returns to the right atrium.
• This ensures efficient supply of oxygen to the body.

2. Blood: A fluid connective tissue.

• Components:
• Plasma: Fluid matrix, transports food, $CO_2$, nitrogenous wastes, salts, hormones.
• Red Blood Cells (RBCs): Contain haemoglobin, a red pigment that binds with oxygen and transports it to tissues.
• White Blood Cells (WBCs): Fight infections and provide immunity.
• Platelets: Help in blood clotting.
• Functions: Transport of $O_2$, $CO_2$, nutrients, hormones, waste products, and regulation of body temperature.

3. Blood Vessels:

• Arteries: Thick-walled, elastic vessels that carry oxygenated blood away from the heart to various body parts (except pulmonary artery, which carries deoxygenated blood to lungs).
• Veins: Thin-walled vessels with valves that carry deoxygenated blood towards the heart from various body parts (except pulmonary vein, which carries oxygenated blood from lungs to heart).
• Capillaries: Extremely thin, single-celled vessels connecting arteries and veins. They are the site of exchange of gases, nutrients, and wastes between blood and tissues.

4. Lymph: A yellowish fluid that leaks out of blood capillaries into intercellular spaces.

• Composition: Similar to plasma but with less protein.
• Functions:
• Carries digested and absorbed fat from the intestine.
• Drains excess fluid from extracellular space back into the blood.
• Part of the immune system (contains lymphocytes).

Transportation in Plants

Plants have specialised vascular tissues for transport.

1. Xylem: Transports water and dissolved minerals from roots to all parts of the plant.

• Composed of tracheids, vessels, xylem parenchyma, and xylem fibres.
• Transpiration pull: The main driving force for water movement. Water evaporates from the leaves through stomata (transpiration), creating a suction force that pulls water up from the roots.
• Movement is largely unidirectional (upwards).

2. Phloem: Transports prepared food (sugars) from leaves (site of photosynthesis) to other parts of the plant, including storage organs and growing regions.

• Composed of sieve tubes, companion cells, phloem parenchyma, and phloem fibres.
• Translocation: The process of transporting food in the phloem. It occurs by utilising ATP energy, moving sugars into sieve tubes, which increases osmotic pressure, causing water to move in and push the food.
• Movement is bidirectional (upwards and downwards).

Excretion

Excretion is the biological process of removing harmful metabolic waste products from the body.

Excretion in Humans

The human excretory system consists of a pair of kidneys, a pair of ureters, a urinary bladder, and a urethra.

1. Kidneys: Bean-shaped organs located in the abdomen.

• Function: Filter blood to remove nitrogenous waste products like urea, uric acid, and excess salts and water, forming urine.
• Each kidney contains millions of filtering units called nephrons.

2. Nephron: The structural and functional unit of the kidney.

• Structure:
• Bowman's Capsule: A cup-shaped structure containing a cluster of capillaries called the glomerulus.
• Renal Tubule: A long, coiled tube extending from Bowman's capsule.
• Function (Urine Formation):

1. Glomerular Filtration: Blood enters the glomerulus under high pressure. Water, salts, glucose, amino acids, and nitrogenous wastes are filtered from the blood into Bowman's capsule, forming the filtrate. Large molecules like proteins and blood cells are retained.

2. Tubular Reabsorption: As the filtrate flows through the renal tubule, useful substances like glucose, amino acids, most salts, and a large amount of water are selectively reabsorbed back into the blood capillaries surrounding the tubule.

3. Tubular Secretion: Some waste products and excess ions are actively secreted from the blood capillaries into the renal tubule.

4. The remaining fluid, now called urine, contains urea, uric acid, excess salts, and water.

5. Ureters: Tubes that carry urine from the kidneys to the urinary bladder.

6. Urinary Bladder: A muscular sac that stores urine temporarily.

7. Urethra: A tube that carries urine from the bladder out of the body.

Artificial Kidney (Dialysis):

• In case of kidney failure, an artificial kidney (dialysis machine) is used to remove nitrogenous waste products from the blood.
• The patient's blood is passed through a dialysing unit containing a semi-permeable membrane. The unit contains dialysing fluid with the same composition as plasma, except for nitrogenous wastes.
• Waste products from the blood diffuse into the dialysing fluid, while useful substances are retained in the blood. The cleaned blood is then returned to the patient.

Excretion in Plants

Plants use different strategies to remove waste products:

• Gaseous wastes ($O_2$ during photosynthesis, $CO_2$ during respiration) are removed through stomata and lenticels.
• Excess water is removed by transpiration.
• Other waste products are stored in cellular vacuoles, leaves that fall off, or as resins and gums (especially in old xylem) or as crystals in bark.
• Some wastes are excreted into the soil around them.

Board Exam Examples

Example 1: Photosynthesis and Stomata

Question: (a) List the three major events that occur during photosynthesis. (b) How does the opening and closing of stomata regulate the exchange of gases in plants? (c) Name two raw materials required for photosynthesis.

Solution: (a) The three major events that occur during photosynthesis are:

1. Absorption of light energy by chlorophyll.
2. Conversion of light energy to chemical energy and splitting of water molecules into hydrogen and oxygen (photolysis of water).
3. Reduction of carbon dioxide to carbohydrates (glucose).

(b) The opening and closing of stomata are regulated by the guard cells surrounding them.

• Opening: When water enters the guard cells, they swell and become turgid, causing their outer walls to bulge out and the inner walls to pull apart, opening the stomatal pore. This allows $CO_2$ to enter for photosynthesis and $O_2$ to exit.
• Closing: When guard cells lose water, they shrink and become flaccid, causing the stomatal pore to close. This prevents excessive water loss through transpiration, especially during dry conditions.

(c) Two raw materials required for photosynthesis are:

1. Carbon dioxide ($CO_2$)
2. Water ($H_2O$)

Example 2: Human Digestion and Respiration

Question: (a) Where does the digestion of fat take place in the human alimentary canal? Name the enzyme involved and its role. (b) Differentiate between aerobic and anaerobic respiration based on their end products and energy yield. (c) Why is the left ventricle thicker than the right ventricle in the human heart?

Solution: (a) The digestion of fat primarily takes place in the small intestine.

• The enzyme involved is lipase (secreted by the pancreas and intestinal walls).
• Role of lipase: It breaks down emulsified fats (large fat globules broken down by bile) into fatty acids and glycerol. Bile juice, secreted by the liver, plays a crucial role in emulsification of fats, making it easier for lipase to act.

(b) Differentiation between aerobic and anaerobic respiration:

Feature	Aerobic Respiration	Anaerobic Respiration
End Products	Carbon dioxide ($CO_2$) and Water ($H_2O$)	Ethanol and $CO_2$ (in yeast) or Lactic acid (in muscle cells)
Energy Yield	High (38 ATP molecules per glucose)	Low (2 ATP molecules per glucose)

(c) The left ventricle is thicker than the right ventricle because it has to pump oxygenated blood to the entire body (systemic circulation) against high resistance and pressure. The right ventricle, on the other hand, only needs to pump deoxygenated blood to the lungs (pulmonary circulation), which is a much shorter distance and requires less pressure. The thicker muscular wall of the left ventricle generates the necessary force for efficient blood circulation throughout the body.

Common Mistakes

1. Confusing Photosynthesis and Respiration: Students often mix up the reactants and products or the energy changes (photosynthesis stores energy, respiration releases energy).
2. Incorrect Chemical Equations: For both photosynthesis and respiration, getting the balanced equations wrong or misidentifying products/reactants is common.
3. Location of Processes: Forgetting that glycolysis occurs in the cytoplasm for both aerobic and anaerobic respiration, or that the Krebs cycle and ETC occur in mitochondria for aerobic respiration.
4. Role of Enzymes: Not knowing which enzyme acts on which nutrient (e.g., amylase on starch, pepsin/trypsin on protein, lipase on fat) or their optimal pH.
5. Function of HCl in Stomach: Thinking HCl digests food directly, instead of activating pepsin and killing bacteria.
6. Direction of Blood Flow in Heart: Confusing which side carries oxygenated vs. deoxygenated blood, or the path of blood through the chambers.
7. Arteries vs. Veins: Incorrectly stating that all arteries carry oxygenated blood or all veins carry deoxygenated blood (pulmonary artery/vein are exceptions).
8. Xylem vs. Phloem: Mixing up their functions (water vs. food transport) or direction of transport.
9. Nephron Functions: Not understanding the distinct steps of filtration, reabsorption, and secretion in urine formation.
10. Stomata Regulation: Simply stating stomata open/close without explaining the role of guard cells and water movement.

Quick Revision

• Life Processes: Essential activities for survival (nutrition, respiration, transport, excretion).
• Nutrition:
• Autotrophic: Plants (photosynthesis: $6CO_2 + 6H_2O \xrightarrow{Sunlight, Chlorophyll} C_6H_{12}O_6 + 6O_2$). Stomata for gas exchange.
• Heterotrophic: Humans (holozoic). Alimentary canal: Mouth (salivary amylase), Stomach (HCl, pepsin), Small Intestine (bile, pancreatic enzymes, intestinal enzymes; complete digestion, absorption via villi).
• Respiration: Breakdown of food to release energy (ATP).
• Aerobic: With $O_2$. Glucose $\rightarrow$ Pyruvate (cytoplasm) $\rightarrow$ $CO_2 + H_2O + 38 \text{ ATP}$ (mitochondria).
• Anaerobic: Without $O_2$. Glucose $\rightarrow$ Pyruvate (cytoplasm) $\rightarrow$ Lactic acid ($2 \text{ ATP}$) or Ethanol + $CO_2$ ($2 \text{ ATP}$).
• Human Respiration: Nostrils $\rightarrow$ Pharynx $\rightarrow$ Larynx $\rightarrow$ Trachea $\rightarrow$ Bronchi $\rightarrow$ Bronchioles $\rightarrow$ Alveoli (gas exchange).
• Transportation:
• Humans: Heart (4 chambers, double circulation), Blood (plasma, RBCs, WBCs, platelets), Blood Vessels (arteries, veins, capillaries), Lymph.
• Plants: Xylem (water, minerals - transpiration pull, unidirectional), Phloem (food - translocation, bidirectional).
• Excretion: Removal of metabolic wastes.
• Humans: Kidneys (filter blood), Nephron (glomerular filtration, tubular reabsorption, tubular secretion). Urine $\rightarrow$ Ureters $\rightarrow$ Bladder $\rightarrow$ Urethra. Dialysis for kidney failure.
• Plants: Stomata/lenticels (gases), transpiration (water), storage in vacuoles/falling leaves/gums/resins.