Life Processes – Notes by Home Academy
Introduction
Life processes are the basic activities that all living organisms perform to maintain and sustain life. These processes are essential for survival, growth, repair, and reproduction. Without life processes, an organism cannot remain alive.
The major life processes include nutrition, respiration, transportation, and excretion.
1. Nutrition
Definition
Nutrition is the process by which organisms obtain food and utilize it to get energy, grow, repair tissues, and maintain body functions.
Types of Nutrition
Autotrophic Nutrition
In this mode, organisms prepare their own food using simple inorganic substances.
Example: Green plants, algae
Photosynthesis Equation:
6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂ (in presence of sunlight and chlorophyll)
Steps of Photosynthesis
Absorption of light energy by chlorophyll
Conversion of light energy into chemical energy
Reduction of carbon dioxide to carbohydrates
👉Important Points for Exam
Chlorophyll is present in chloroplast
Stomata help in gaseous exchange
Xylem transports water to leaves
Heterotrophic Nutrition
Organisms depend on others for food.
Types include
Holozoic nutrition – humans, animals
Saprophytic nutrition – fungi
Parasitic nutrition – Cuscuta, tapeworm
Human Digestive System
Main Organs and Functions
Mouth – ingestion, salivary amylase digests starch
Oesophagus – transport of food
Stomach – HCl kills bacteria, pepsin digests proteins
Small intestine – digestion and absorption
Large intestine – absorption of water
Rectum – storage of waste
Bile emulsifies fats and is produced by liver.
2. Respiration
Definition
Respiration is the process of breaking down food to release energy.
Types of Respiration
Aerobic Respiration
Occurs in presence of oxygen
Produces more energy
End products are CO₂ and H₂O
Equation:
C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + Energy (ATP)
Anaerobic Respiration
Occurs in absence of oxygen
Less energy released
In yeast:
Glucose → Alcohol + CO₂ + Energy
In muscles:
Glucose → Lactic acid + Energy
| Basis of Comparison | Aerobic Respiration | Anaerobic Respiration |
|---|---|---|
| Definition | Respiration that occurs in the presence of oxygen | Respiration that occurs in the absence of oxygen |
| Oxygen Requirement | Oxygen is required | Oxygen is not required |
| Breakdown of Glucose | Complete breakdown of glucose | Incomplete breakdown of glucose |
| End Products | Carbon dioxide and water | Alcohol and carbon dioxide (in yeast) or lactic acid (in muscles) |
| Energy Released | Large amount of energy | Small amount of energy |
| ATP Produced | About 36–38 ATP molecules | About 2 ATP molecules |
| Site of Occurrence | Mitochondria | Cytoplasm |
| Efficiency | Highly efficient | Less efficient |
| Occurrence | Most plants and animals | Yeast, bacteria, human muscle cells during heavy exercise |
| Effect on Body | No harmful by-products | Lactic acid causes muscle fatigue |
Plant Respiration – Cycle
Plant respiration is the process by which plants break down glucose to release energy required for growth, repair, and maintenance. Unlike photosynthesis, respiration occurs day and night in all living plant cells.
Plants respire mainly through three interconnected cycles:
Glycolysis
Krebs Cycle (Citric Acid Cycle)
Electron Transport Chain (ETC)
1. Glycolysis (EMP Pathway)
Definition
Glycolysis is the first stage of respiration in which glucose is partially broken down into pyruvic acid.
Key Features
Occurs in the cytoplasm
Does not require oxygen
Common to both aerobic and anaerobic respiration
Main Events
One molecule of glucose (6-carbon) is converted into two molecules of pyruvic acid (3-carbon).
Small amount of energy is released.
Energy Yield
2 ATP (net gain)
2 NADH
Importance for Exam
Glycolysis is also called Embden–Meyerhof–Parnas pathway.
It is the only stage common to all living organisms.
2. Krebs Cycle (Citric Acid Cycle)
Definition
Krebs cycle is the second stage of aerobic respiration in which pyruvic acid is completely oxidized.
Site
Occurs in the mitochondrial matrix.
Key Events
Pyruvic acid is converted into Acetyl-CoA.
Carbon dioxide is released.
Energy-rich compounds are formed.
Energy Yield (per glucose)
2 ATP
6 NADH
2 FADH₂
Important Exam Points
Krebs cycle is also called TCA cycle.
CO₂ released during respiration comes mainly from this cycle.
Named after Hans Krebs.
3. Electron Transport Chain (ETC)
Definition
ETC is the final stage of respiration where maximum ATP is produced.
Site
Occurs on the inner mitochondrial membrane (cristae).
Key Events
Electrons from NADH and FADH₂ pass through carriers.
Oxygen acts as the final electron acceptor.
Water is formed.
Energy Yield
About 34 ATP molecules.
Importance
This stage produces maximum energy.
Without oxygen, ETC cannot function.
Overall Energy Yield in Plant Respiration
| Stage | ATP Produced |
|---|---|
| Glycolysis | 2 ATP |
| Krebs Cycle | 2 ATP |
| ETC | 34 ATP |
| Total | 38 ATP |
Anaerobic Respiration in Plants
When oxygen is absent, plants undergo fermentation.
Example
In germinating seeds and waterlogged plants.
Equation
Glucose → Ethyl alcohol + CO₂ + Energy
Key Point
Much less energy is released compared to aerobic respiration.
Differences Important for Exam
Photosynthesis vs Respiration
Photosynthesis stores energy; respiration releases energy.
Photosynthesis occurs only in green parts; respiration occurs in all living cells.
Aerobic vs Anaerobic Respiration
Aerobic uses oxygen and releases more energy.
Anaerobic occurs without oxygen and releases less energy.
Very Important Exam Facts
Respiration occurs day and night.
Oxygen is not always required in initial stages.
Mitochondria are called the powerhouse of the cell.
ATP is the energy currency of the cell.
Human Respiratory System
Nostrils → Trachea → Bronchi → Bronchioles → Alveoli
Alveoli are the site of gaseous exchange.
They have thin walls and rich blood supply.
3. Transportation
Transportation in Plants
Xylem transports water and minerals from roots to leaves.
Phloem transports food from leaves to other parts.
Transpiration helps in upward movement of water.
| Basis of Comparison | Xylem | Phloem |
|---|---|---|
| Function | Transports water and minerals | Transports food (sugars) |
| Direction of Transport | Unidirectional (roots to leaves) | Bidirectional (source to sink) |
| Type of Material | Water and mineral salts | Prepared food |
| Nature of Cells | Mostly dead cells | Mostly living cells |
| Main Elements | Tracheids, vessels, xylem fibres, xylem parenchyma | Sieve tubes, companion cells, phloem fibres, phloem parenchyma |
| Energy Requirement | Does not require energy | Requires energy (ATP) |
| Thickness of Walls | Thick and lignified | Thin and non-lignified |
| Support Function | Provides mechanical support | Does not provide much support |
| Position in Vascular Bundle | Inner side | Outer side |
| Speed of Transport | Fast | Slow |
Transportation in Humans
Blood Components
Red Blood Cells – carry oxygen
White Blood Cells – immunity
Platelets – clotting
Plasma – transport of nutrients
Heart
Four-chambered organ
Right side carries deoxygenated blood
Left side carries oxygenated blood
Double circulation ensures efficient oxygen supply.
4. Excretion
Definition
Excretion is the process of removal of metabolic waste products from the body.
Excretion in Humans
Excretory Organs
Kidneys – filter blood
Ureters – carry urine
Urinary bladder – storage
Urethra – removal
Nephron is the functional unit of kidney.
Steps of Urine Formation
Ultrafiltration
Selective reabsorption
Tubular secretion
Excretion in Plants
Excess oxygen removed through stomata
Waste stored in leaves, bark, fruits
Resins and gums are excretory products
Excretion in Animals –
Excretion is the biological process by which animals remove metabolic waste products such as nitrogenous wastes, excess salts, and water from their body to maintain internal balance (homeostasis).
Why Excretion is Necessary
Removal of toxic wastes prevents cell damage.
Maintains water and salt balance.
Regulates body temperature and pH.
Essential for survival of animals.
Types of Nitrogenous Wastes
Ammonotelic Animals
Excrete ammonia.
Examples include fishes and aquatic invertebrates.
Ammonia is highly toxic and requires more water for removal.
Ureotelic Animals
Excrete urea.
Examples include mammals, adult amphibians, and cartilaginous fishes.
Urea is less toxic than ammonia.
Uricotelic Animals
Excrete uric acid.
Examples include birds, reptiles, and insects.
Uric acid is least toxic and conserves water.
Excretory Organs in Different Animals
Protozoa
Excretion occurs through cell membrane by diffusion.
Contractile vacuole removes excess water.
Annelids (Earthworm)
Excretion by nephridia.
Nephridia regulate water and salts.
Arthropods (Insects)
Excretion by Malpighian tubules.
Uric acid is excreted.
Molluscs
Excretion by kidneys (metanephridia).
Vertebrates (Human example)
Excretion by kidneys.
Human Excretory System
Main Organs
Kidneys
Ureters
Urinary bladder
Urethra
Structure and Function of Kidney
Kidney
Bean-shaped organs located in abdominal cavity.
Filter blood and remove waste products.
Nephron
Functional unit of kidney.
Parts of Nephron
Glomerulus – filtration
Bowman’s capsule – collects filtrate
Proximal convoluted tubule – reabsorption
Loop of Henle – concentration of urine
Distal convoluted tubule – secretion
Collecting duct – urine formation
Steps of Urine Formation
Ultrafiltration
Occurs in glomerulus.
Blood is filtered under high pressure.
Selective Reabsorption
Useful substances reabsorbed into blood.
Tubular Secretion
Excess ions and wastes added to urine.
Role of Other Organs in Excretion
Lungs
Remove carbon dioxide and water vapour.
Skin
Sweat removes water, salts, and urea.
Liver
Converts ammonia into urea.
Detoxifies harmful substances.
Excretion in Aquatic vs Terrestrial Animals
Aquatic animals excrete ammonia due to availability of water.
Terrestrial animals excrete urea or uric acid to conserve water.
Important Exam Points
Nephron is the functional unit of kidney.
Urea is formed in liver.
Dialysis is artificial purification of blood.
Excretion maintains homeostasis.
Kidneys regulate water balance.
Very Important Exam Points
ATP is the energy currency of the cell
Small intestine is the longest part of alimentary canal
Kidneys maintain water balance
Alveoli increase surface area for gas exchange
Life processes are essential for survival
Frequently Asked Exam Questions
Why is small intestine long and coiled
What is the role of bile
Define double circulation
Explain anaerobic respiration in muscles
What is transpiration