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Biology Master Notes (2025-26)

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CHAPTER 1: LIFE PROCESSES

Definition: The basic maintenance functions performed by living organisms to sustain life are called life processes (Nutrition, Respiration, Transportation, Excretion).
Why is diffusion insufficient? In multicellular organisms (like humans), all cells are NOT in direct contact with the environment. Simple diffusion cannot meet the oxygen requirement of all cells.

1. Nutrition (The Source of Energy)

A. Types of Heterotrophic Nutrition

Type	Definition	Examples
Holozoic	Organisms take in whole food and digest it inside the body.	Humans, Animals, Amoeba.
Saprophytic	Organisms feed on dead and decaying matter (break down outside body).	Fungi (Bread moulds, Yeast, Mushrooms).
Parasitic	Organisms live on/in host and derive nutrition without killing it.	Cuscuta (Amar-bel), Ticks, Lice, Leeches, Tapeworm.

B. Nutrition in Amoeba (Holozoic)

Figure 1.0: Nutrition in Amoeba (Phagocytosis)

Steps (Phagocytosis):

Pseudopodia: Finger-like extensions fuse over the food particle.
Food Vacuole: Food is trapped inside. Complex substances are broken down into simpler ones.
Diffusion: Simple substances diffuse into cytoplasm (Absorption).
Egestion: Undigested material moves to surface and is thrown out.

C. Autotrophic Nutrition (Plants)

            Chemical Equation (Must Memorize):

            6CO2 + 12H2O —(Sunlight/Chlorophyll)→ C6H12O6
            (Glucose) + 6O2 + 6H2O
        

Figure 1.1: Stomatal Pore: Open (Turgid) vs Closed (Flaccid)

Detailed Mechanism (3 Steps):

Absorption: Chlorophyll traps solar energy.
Conversion & Splitting: Light energy → Chemical energy. Water molecules split (H₂O → H₂ + O₂). (Note: O₂ is a by-product).
Reduction: CO₂ is reduced to Carbohydrates (using Hydrogen).

Desert Plants Exception (CAM Pathway):
Desert plants take up CO₂ at night (when stomata are open to save water) and prepare an intermediate. This is acted upon by energy absorbed by chlorophyll during the day (when stomata are closed).

B. Nutrition in Humans (Detailed)

Figure 1.2: Human Digestive System

Alimentary Canal (9 meters long tube):

Organ	Secretions	Action/Function
Mouth	Saliva (Salivary Amylase)	• Teeth: Chew/Grind. • Tongue: Tasting/Rolling. • Amylase: Starch (Complex) → Sugar/Maltose.
Oesophagus	No Enzymes	Peristalsis: Rhythmic contraction and relaxation of muscles to push food down.
Stomach (J-shaped)	Gastric Glands secrete: 1. HCl 2. Pepsin 3. Mucus	• HCl: Acidic medium (pH ~1.8) for Pepsin; Kills bacteria. • Pepsin: Digests Proteins (Partial). • Mucus: Protects inner lining from acid (prevents ulcers).
Small Intestine (Longest part)	Receives secretions from Liver & Pancreas	Site of Complete Digestion. • Liver (Bile Juice): 1. Makes medium Alkaline. 2. Emulsification (Large fat globules → Small globules). • Pancreas (Pancreatic Juice): - Trypsin: Proteins → Amino Acids. - Lipase: Emulsified Fats → Fatty Acids + Glycerol. - Amylase: Remaining Starch → Glucose.

Dental Caries (Tooth Decay):
Bacteria acting on sugars produce acids that soften or demineralise the enamel. Mass of bacterial cells together with food particles stick to the teeth to form Dental Plaque. Saliva cannot reach the tooth surface to neutralize the acid as plaque covers the teeth.

Absorption in Small Intestine:
Inner lining has millions of finger-like projections called Villi. They increase surface area for absorption and are richly supplied with blood vessels to take food to every cell.

Why is the Small Intestine longer in herbivores?
Herbivores eat grass containing cellulose, which takes a long time to digest (needs symbiotic bacteria). Carnivores eat meat, which is easier to digest, so they have shorter intestines.

2. Respiration (Energy Release)

A. Glucose Breakdown Pathways (The Most Repeated PYQ)

Figure 1.2b: Breakdown of Glucose by Various Pathways

Key Exam Point (Muscle Cramps):
When there is a lack of oxygen in muscle cells (sudden activity), Pyruvate converts to Lactic Acid. Accumulation of lactic acid causes muscle cramps.

ATP (Adenosine Triphosphate):
The energy released during respiration is used to make an ATP molecule from ADP and inorganic phosphate. ATP is known as the energy currency of the cell.

Feature	Aerobic Respiration	Anaerobic Respiration
Presence of Oxygen	Takes place in the presence of oxygen.	Takes place in the absence of oxygen.
Site	Mitochondria.	Cytoplasm.
End Products	CO₂ and H₂O.	Alcohol/Lactic Acid and CO₂.
Energy Released	More energy.	Less energy.

B. Human Respiratory System

Figure 1.3: Human Respiratory System

Why Trachea has Cartilaginous Rings? To prevent collapse when there is no air.
Role of Alveoli: Balloon-like structures where gas exchange occurs. They provide a massive surface area (80m²) and are covered in blood capillaries.

Mechanism of Breathing:
1. Inhalation: Ribs lift up, Diaphragm flattens → Chest cavity expands → Air rushes in.
2. Exhalation: Ribs move down, Diaphragm domes up → Chest cavity contracts → Air pushed out.
*Exchange of gases takes place in Alveoli via diffusion.

Aquatic vs Terrestrial Organisms (Breathing Rate):
Aquatic animals (like fish) breathe faster than terrestrial animals because the amount of dissolved oxygen in water is fairly low compared to the amount of oxygen in the air.

Respiratory Pigment:
In humans, Haemoglobin (present in RBCs) carries oxygen from lungs to tissues. It has a high affinity for oxygen. (CO₂ is more soluble in water and is mostly transported in dissolved form).

3. Transportation (Circulation)

A. Human Heart (Double Circulation)

Figure 1.4: Sectional View of Human Heart

Oxygenated and Deoxygenated blood travel in separate circuits.

Step-by-Step Blood Flow:

Vena Cava brings CO₂-rich blood from body to Right Atrium.
Right Atrium relaxes (fills) → Contracts → Blood goes to Right Ventricle.
Right Ventricle pumps blood to Lungs via Pulmonary Artery (for oxygenation).
Pulmonary Veins bring O₂-rich blood from Lungs to Left Atrium.
Left Atrium contracts → Blood goes to Left Ventricle.
Left Ventricle (Thickest wall) pumps blood to body via Aorta.

(Valves ensure unidirectional flow).

Why is separation of Oxygenated and Deoxygenated blood necessary?
Separation allows for a highly efficient supply of oxygen to the body. This is useful for animals that have high energy needs, such as birds and mammals, which constantly use energy to maintain their body temperature (Warm-blooded/Endothermic).

Why do Ventricles have thicker walls?
Because they have to pump blood to distant organs (Lungs/Whole Body) at high pressure, whereas atria only push blood to the next chamber.

Figure 1.4b: Schematic of Double Circulation

            Double Circulation Explained:

            Blood passes through the heart twice in one complete cycle.

            1. Pulmonary Circulation: Blood moves from Heart → Lungs → Heart (Oxygenation).

            2. Systemic Circulation: Blood moves from Heart → Body Organs → Heart (Supply O2).

B. Blood Vessels

Arteries	Veins
Carry blood Away from heart.	Carry blood Towards heart.
Thick, Elastic walls (High pressure).	Thin walls.
No Valves.	Valves present (prevent backflow).

C. Other Circulatory Components (Must Know)

            Platelets (Thrombocytes): Maintenance cells. They help in clotting of
                        blood at the point of injury to prevent loss of blood and pressure.
Lymph (Tissue Fluid): A fluid similar to blood plasma but colourless
                        and
                        contains less protein.

                    Function:

                    1. Carries digested and absorbed fat from intestine.

                    2. Drains excess fluid from extracellular space back into the blood.

C. Transportation in Plants

Xylem (Water/Minerals)	Phloem (Food)
Vessels & Tracheids (Dead cells).	Sieve Tubes & Companion Cells (Living).
Motion: Unidirectional (Up).	Motion: Bidirectional.
Mechanism: Transpiration Pull (Physical).	Mechanism: Translocation (Active, uses ATP).

4. Excretion (Waste Removal)

A. Human Excretory System

Figure 1.5a: Human Excretory System

            Components of Excretory System:
            1. Kidneys (Pair): Bean-shaped organs in abdomen. Filter blood to remove
                    nitrogenous waste (Urea/Uric acid).
2. Ureters (Pair): Tubes carrying urine from kidneys to bladder.
3. Urinary Bladder: Muscular sac where urine is stored until urge to pass.
4. Urethra: Channel through which urine passes out.

        

How Urine is Formed (Step-by-Step):
Blood enters Kidney -> Filtration in Glomerulus -> Reabsorption in Tubular part -> Urine collection in Ureter.

Nephron (Filtration Unit) Structure & Function:

Figure 1.5b: Structure of a Nephron

Glomerulus & Bowman's Capsule: Filtration under high pressure. Glucose, Amino acids, Water, Urea filter out.
Tubular Part (PCT/DCT): Selective Reabsorption. All Glucose, Amino acids, and most water are taken back into blood.
Collecting Duct: Remaining fluid is Urine (Urea + Excess salts + Water).

Hemodialysis (Artificial Kidney):
Blood is pumped into a dialyser (tubes with semi-permeable lining in dialysing fluid). Fluid has same osmotic pressure as blood but NO nitrogenous waste. Urea diffuses from blood to fluid.
Difference from Nephron: No Reabsorption occurs in dialysis.

B. Excretion in Plants

How do plants get rid of waste?
1. Oxygen: Released as waste during day (Photosynthesis).
2. Water: Lost via Transpiration.
3. Dead Cells: Stored in leaves that fall off.
4. Resins/Gums: Stored in old Xylem.
5. Into Soil: Some waste is excreted into soil around roots.

🎯 TRICKY PRACTICE ZONE (Life Processes)

In the breakdown of glucose, a student confuses the pathway that occurs in Yeast vs Muscle cells. Can you clarify the end products for both? Hint: Yeast produces Ethanol + CO2 (Fermentation); Muscles produce Lactic Acid (Cramps).
A patient has low blood pressure. Which vessel carries blood back to the heart under low pressure, and what structure prevents backflow? Hint: Veins have thin walls and valves.
Plants do not have a heart to pump. How do they move water up to the top of tall trees like Eucalyptus? Hint: Think of "Suction" created by evaporation from leaves (Transpiration Pull).

🧪 NCERT EXPERIMENT ZONE (Life Processes)

1. Chlorophyll is necessary for Photosynthesis:
• Plant: Variegated leaf (Money plant/Croton) has green and white parts.
• Test: Boil in alcohol (remove chlorophyll) → Dip in Iodine.
• Result: Only green parts turn Blue-Black (Starch present). White parts remain colourless.

Figure 1.E1: Chlorophyll is necessary for Photosynthesis (a) before starch test (b) after starch test

2. CO₂ is necessary for Photosynthesis (Mohl's Half-Leaf):
• Setup: One plant inside bell jar with KOH (Potassium Hydroxide).
• Role of KOH: Absorbs CO₂.
• Result: Leaf with KOH does NOT turn Blue-Black with Iodine (No Starch formed), proving CO₂ is essential.

Figure 1.E2: CO₂ is necessary for Photosynthesis (a) with potassium hydroxide (b) without potassium hydroxide

3. CO₂ is released during Respiration:
• Test: Blow air into Lime Water.
• Observation: Lime Water turns Milky.
• Conclusion: Exhaled air contains Carbon Dioxide.

Figure 1.E3: CO2 is released during Respiration

4. Action of Saliva on Starch:
• Test Tube A: Starch + Saliva. Test Tube B: Starch only.
• Result: After 20 mins, Tube A does NOT turn blue-black (Starch digested by Amylase). Tube B turns blue-black.

CHAPTER 2: CONTROL & COORDINATION

1. Animal Nervous System

A. The Neuron (Structural Unit)

Figure 2.1: Structure of Neuron

            Structure & Function:
            Dendrite: Acquires information. (Tips of nerve cells).
Cell Body (Cyton): Information travels as an Electrical Impulse.
Axon: Longest fibre. Transmits impulse away from cell body.
Nerve Ending: Converts Electrical Impulse → Chemical Signal (Neurotransmitter).
                

        

The Synapse (Crucial Definition):
It is the microscopic gap between the nerve ending of one neuron and the dendrite of the next.
Mechanism: At the nerve ending, the electrical impulse releases chemicals (Neurotransmitters like Acetylcholine). These chemicals diffuse across the gap and start a similar electrical impulse in the dendrite of the next neuron.

Why do we need Chemical Communication (Hormones) if we have Nerves?
Limitations of Electrical Impulses:
1. They reach only those cells connected by nervous tissue.
2. Once an impulse is generated, the cell takes time to reset (cannot continuously create impulses).
Chemical communication (Hormones) overcomes this by reaching every cell and acting steadily.

B. Reflex Action & Reflex Arc

Figure 2.2: Reflex Arc Pathway

Why are Reflex Arcs formed in the Spinal Cord?
Thinking processes in the brain are complex and slow. To save time and prevent tissue damage during emergencies, nerves connect directly in the spinal cord for a quicker response. (The signal still goes to the brain later for memory).

The Pathway (Reflex Arc):

Stimulus (Heat)

→

Receptor (Skin)

→

Sensory Neuron

→

Spinal Cord (Relay Neuron)

→

Motor Neuron

→

Effector (Muscle)

→

Response (Movement)

2. The Human Brain (The Thinking Center)

Figure 2.3: Human Brain

Region	Part	Function (Matches PYQ 2025)
Forebrain (Main thinking part)	Cerebrum	• Voluntary actions. • Sensory processing (Hearing, Smell, Sight). • Seat of Intelligence, Memory, Learning. • Hypothalamus: Satiety Center (Hunger/Thirst).
Midbrain	-	Involuntary reflexes of head/neck/eyes. (e.g., Pupil size change).
Hindbrain	Cerebellum	• Precision of voluntary actions (e.g., Threading a needle). • Maintains Posture and Balance (e.g., Riding a bike). (Damage leads to loss of balance, drunk-like walk).
	Medulla	Controls Involuntary life processes: Blood Pressure, Heartbeat, Salivation, Vomiting.
	Pons	Regulates Respiration (Rate of breathing).

C. Protection of the CNS

How are these delicate organs protected?
1. Brain: sits inside a bony box (Cranium/Skull). Inside the box, the brain is contained in a fluid-filled balloon (Cerebrospinal Fluid) for shock absorption.
2. Spinal Cord: Protected by the Vertebral Column (Backbone).

3. Coordination in Plants

Plants use Electrical-Chemical means to convey information from cell to cell, but lack specialized tissue.

A. Types of Movements

Feature	Nastic Movements	Tropic Movements
Direction	Non-directional.	Directional.
Growth	Growth Independent.	Growth Dependent.
Speed	Immediate/Fast.	Slow.
Mechanism	Change in Turgor Pressure.	Cell division/elongation (Auxin).
Example	Mimosa pudica (Touch-me-not).	Shoot bending to light (Phototropism).

B. Mechanism of Phototropism (Auxin Action)

How does a plant bend towards light?
1. Auxin is synthesized at the shoot tip.
2. When light comes from one side, Auxin diffuses towards the shady side of the shoot.
3. High concentration of Auxin stimulates cells on the shady side to grow longer.
4. As one side grows longer than the other, the plant appears to bend towards light.

C. Various Tropic Movements

Movement	Stimulus	Response (Example)
Phototropism	Light	Shoot bends towards light (Positive). Root bends away (Negative).
Geotropism	Gravity	Roots grow down (Positive). Shoots grow up (Negative).
Hydrotropism	Water	Roots grow towards water (Positive).
Chemotropism	Chemicals	Growth of Pollen Tube towards Ovule.
Thigmotropism	Touch	Growth of Tendrils around a support (climbing plants).

D. Plant Hormones (Phytohormones)

Hormone	Function
Auxin	Helps cells to grow longer (Phototropism).
Gibberellins	Helps in the growth of the stem.
Cytokinins	Promotes cell division. Rapid in fruits and seeds.
Abscisic Acid	Inhibits growth. Causes wilting of leaves.

4. Animal Hormones (Endocrine System)

Figure 2.4: Endocrine Glands in Humans

Gland	Hormone	Function/Deficiency Disease
Pituitary	Growth Hormone	Regulates growth. Deficiency: Dwarfism. Excess: Gigantism.
Thyroid	Thyroxin	Regulates Metabolism. Deficiency: Goitre. Requires Iodine.
Adrenal	Adrenaline	"Fight or Flight": Increases heart rate, breathing, alert.
Pancreas	Insulin	Lowers blood sugar. Deficiency: Diabetes.
Testes	Testosterone	Sperm production + Puberty changes.
Ovary	Oestrogen	Egg production + Puberty changes.

Feedback Mechanism (Example):
Blood sugar rises → Detected by Pancreas → More Insulin secreted → Sugar falls → Insulin secretion reduced.

🎯 TRICKY PRACTICE ZONE (Control & Coordination)

A person is walking in a drunken manner (loss of balance). Which part of the brain is likely affected? How is this part different from the part that helps you think? Hint: Balance = Cerebellum (Hindbrain); Thinking = Cerebrum (Forebrain).
Why does a tendril circle around a support? Explain the role of Auxin in this specific case. Hint: Auxin diffuses to the side AWAY from support, causing it to grow faster, making the tendril bend/coil.
In a Reflex Arc, what happens at the Synapse? Why can't the signal travel backwards? Hint: Electrical signal converts to Chemical. Receptors for chemicals are only on the next dendrite, ensuring one-way flow.

🧪 NCERT EXPERIMENT ZONE (Control & Coordination)

1. Phototropism (Response to Light):
• Setup: Conical flask with water, wire mesh covering, germinating bean seeds. Keep in cardboard box open from one side.
• Observation: Shoots bend towards light (Positive Phototropism). Roots bend away (Negative Phototropism).

Figure 2.E1: Phototropism (Response to Light)

2. Geotropism (Response to Gravity):
• Setup: Potted plant laid horizontally.
• Observation: Shoot bends Upwards (Negative Geotropism). Root bends Downwards (Positive Geotropism).

Figure 2.E2: Geotropism (Response to Gravity)

CHAPTER 3: HOW DO ORGANISMS REPRODUCE?

1. Asexual Reproduction (One Parent)

Production of offspring from a single parent without gametes.

Figure 3.1: Modes of Asexual Reproduction

Mode	Definition & Examples
Fission	Cell divides into offspring. • Binary: Amoeba (any plane), Leishmania (specific plane). • Multiple: Plasmodium (Malaria parasite) - one cell divides into many.
Fragmentation	Multicellular organism breaks into pieces; each grows into new individual. Example: Spirogyra (Algae).
Regeneration	Regrowth of lost parts or whole organism from cut parts via specialized cells. Example: Planaria, Hydra.
Budding	Outgrowth (bud) forms due to repeated cell division at one site. Example: Hydra (External), Yeast.
Vegetative Propagation	New plants from root, stem, leaf. • Leaf: Bryophyllum. • Artificial: Layering (Jasmine), Grafting (Rose), Tissue Culture.
Spore Formation	Reproductive parts (Sporangia) burst releasing spores. Example: Rhizopus (Bread Mould).

Why can't complex organisms (Humans/Dogs) reproduce by Regeneration?
Complex organisms are not just a collection of random cells. They have organized tissues and organs. A piece of skin cannot grow into a whole human because it lacks the specialized stem cells and organization required to form all other organs. Regeneration is meant for repair, not reproduction in higher animals.

Advantages of Vegetative Propagation:
1. Plants that have lost capacity to produce seeds (Banana, Orange, Rose) can reproduce.
2. Genetically identical offspring (clones).
3. Bear flowers and fruits earlier than seed-grown plants.

Tissue Culture: New plants are grown by removing tissue or separating cells from the growing tip of a plant. The cells are placed in an artificial medium where they divide rapidly to form a small group of cells or callus. The callus is transferred to another medium containing hormones for growth and differentiation.

2. Sexual Reproduction in Flowering Plants

A. Structure of a Flower

Figure 3.2: L.S. of a Flower

            Stamen (Male): Filament + Anther (Produces Pollen Grains/Yellow powder).
Pistil/Carpel (Female):
                    
• Stigma: Sticky tip to receive pollen.
                    
• Style: Tube leading down.
                    
• Ovary: Swollen base containing Ovules (Egg).

B. Process of Seed Formation

Figure 3.3: Germination of Pollen on Stigma

Pollination: Transfer of pollen from Anther to Stigma.
• Self: Same flower.
• Cross: Different flower (Agents: Wind, Water, Bees).
Fertilization: Pollen tube grows through style to ovary. Male germ cell enters ovule.
• Male gamete (n) + Female gamete (n) → Zygote (2n).
Post-Fertilization Changes:
• Zygote → divides to form Embryo.
• Ovule → hardens to form Seed.
• Ovary → ripens to form Fruit.
• Petals/Sepals wither and fall off.

Structure of a Seed (Germination):
Comparison of parts:
• Cotyledon: Food Store.
• Plumule: Future Shoot.
• Radicle: Future Root.

Conditions for Germination:
1. Water (Moisture): To soften seed coat and activate enzymes.
2. Air (Oxygen): For respiration.
3. Warmth (Temperature): Optimum temperature for enzymes.

Steps of Germination:
1. Seed absorbs water (swells up).
2. Seed coat bursts.
3. Radicle comes out first (Functions as Root).
4. Plumule comes out next (Functions as Shoot).

Note on Cotyledons:
• Monocots: One Cotyledon (e.g., Maize, Wheat).
• Dicots: Two Cotyledons (e.g., Gram, Pea, Bean). (Gram seeds are used in lab activities).

3. Human Reproduction

Humans use sexual reproduction. Puberty is the age when reproductive maturity begins.

A. Male Reproductive System

Figure 3.4: Male Reproductive System

Part	Function
Testes (Pair)	1. Produce Sperms. 2. Secrete Testosterone (Puberty changes).
Scrotum	Pouch outside body. Keeps testes temp 2-3°C lower than body temp (Required for sperm formation).
Vas Deferens	Tube carrying sperm from testes to urethra.
Prostate & Seminal Vesicles	Secrete fluids that: 1. Provide nutrition to sperms. 2. Make transport easier (Fluid medium).

B. Female Reproductive System

Figure 3.5: Female Reproductive System

Part	Function
Ovary (Pair)	1. Produce Eggs (Ova). 2. Secrete Oestrogen/Progesterone.
Oviduct (Fallopian Tube)	Site of Fertilization (Sperm meets Egg here). Carries egg to uterus.
Uterus (Womb)	Bag-like structure where baby grows (Implantation).

C. The Placenta (Very Important PYQ)

            Structure: A disc-embedded special tissue in the uterine wall.

            • Embryo side: Contains Villi (Finger-like projections).

            • Mother side: Blood spaces surrounding villi.

            Function: Provides large surface area for:

            1. Glucose & Oxygen to pass from Mother → Embryo.

            2. Wastes to pass from Embryo → Mother.

D. Menstruation (What if fertilization fails?)

The uterus prepares itself every month with a thick, spongy lining rich in blood to nourish a potential embryo.
If no fertilization: The lining breaks down and comes out through the vagina as blood and mucus. This cycle takes ~28 days.

4. Reproductive Health

A. Sexually Transmitted Diseases (STDs)

Bacterial: Gonorrhoea, Syphilis.
Viral: Warts, HIV-AIDS.

B. Contraception (Avoiding Pregnancy)

Method	Example	Pros/Cons
Mechanical Barrier	Condoms, Diaphragm	Prevents sperm meeting egg. Condoms also prevent STDs.
Chemical	Oral Pills	Change hormonal balance so egg is not released. Side effects possible.
IUCD	Copper-T	Placed in uterus. Prevents implantation.
Surgical	Vasectomy (Male) Tubectomy (Female)	Blocking Vas Deferens/Fallopian Tube. Permanent.

🎯 TRICKY PRACTICE ZONE (Reproduction)

Why is the use of a condom considered better than oral pills or Copper-T? Hint: Condoms are the ONLY method that protects against STDs (like HIV/Syphilis).
A flower is pollinated but seeds are not formed. Where did the process likely fail? Hint: Failure of the Pollen Tube to reach the Ovary or failure of gamete fusion (Fertilization).
If a woman undergoes tubectomy, will menstruation stop? Explain. Hint: No. Menstruation depends on the Uterus lining and Hormones (Ovary), which are still active. Tubectomy only blocks the egg from meeting sperm.

            🧪 NCERT EXPERIMENT ZONE (Reproduction)

            1. Budding in Yeast:

            • Observation under Microscope: Small protuberance (bud) appears on parent cell.
            Nucleus
            divides. Bud detaches to form new cell.

            2. Spore Formation (Rhizopus):

            • Observation: Cottony white mass on wet bread slice. Black dots (Sporangia) contain
            spores.
            
• Condition: Moisture and warmth favor fungal growth.

            3. Binary Fission in Amoeba:

            • Observation: Nucleus elongates → Nucleus divides (Karyokinesis) → Cytoplasm
            constricts →
            Two daughter cells formed (Cytokinesis).

            4. Parts of a Dicot Seed (Gram/Pea):

            • Procedure: Soak seeds overnight. Peel off seed coat.

            • Observation:

            - Cotyledons: Fleshy part (food store).

            - Plumule: Future Shoot.

            - Radicle: Future Root.

CHAPTER 4: HEREDITY

Why did Mendel choose Garden Peas?
1. Short life cycle (can study many generations).
2. Distinct contrasting characters (Tall/Short, Round/Wrinkled).
3. Self-pollinating (easy to get pure lines) but can be cross-pollinated artificially.

Mendel's 7 Pairs of Contrasting Characters:

Character	Dominant Trait	Recessive Trait
Stem Height	Tall	Dwarf (Short)
Flower Colour	Violet	White
Flower Position	Axial	Terminal
Pod Shape	Inflated (Full)	Constricted
Pod Colour	Green	Yellow
Seed Shape	Round	Wrinkled
Seed Colour	Yellow	Green

1. Mendel’s Experiments

A. Terminologies (Must Know)

            Gene: Unit of heredity that controls a trait (segment of DNA).
Allele: Alternative forms of a gene (e.g., T for Tall, t for Short).
Genotype: Genetic makeup (TT, Tt, tt).
Phenotype: Physical appearance (Tall, Short).
Homozygous: Having two identical alleles for a trait (e.g., TT or tt).
                    (Pure).
                
Heterozygous: Having two different alleles for a trait (e.g., Tt).
                    (Hybrid).
                

        

B. Monohybrid Cross (One Trait: Height)

Parent: Pure Tall (TT) x Pure Short (tt)
Gametes: (T) and (t)
F1 Generation: All Tt (Tall) -> Law of Dominance.
F2 Generation (Selfing Tt x Tt):

Gametes	T	t
T	TT (Tall)	Tt (Tall)
t	Tt (Tall)	tt (Short)

Monohybrid Ratios:
• Phenotypic Ratio: 3 Tall : 1 Short (3:1)
• Genotypic Ratio: 1 TT : 2 Tt : 1 tt (1:2:1)

PYQ Trend (Animals):
In a cross between Black Fur (BB) and White Fur (bb) rabbits, F1 will be Black (Bb). In F2, 25% will be White (bb). Concept remains the same as plants.

C. Dihybrid Cross (Two Traits: Shape & Colour)

Parent: Round Yellow (RRYY) x Wrinkled Green (rryy)
F1 Generation: All Round Yellow (RrYy).
F2 Generation Ratio: 9:3:3:1

9 Round Yellow (Parental)
3 Round Green (New Combination)
3 Wrinkled Yellow (New Combination)
1 Wrinkled Green (Parental)

Conclusion: Law of Independent Assortment (Traits are inherited independently).

D. Mendel's Three Laws of Inheritance (Important Theory)

            
                    Law of Dominance:

                    In a cross between two parents with contrasting traits (e.g., TT x tt), only one characteristic
                    appears in the F1 generation. This expressed trait is called
                    Dominant (Tall), and the hidden one is Recessive (Dwarf).
                
                    Law of Segregation (Law of Purity of Gametes):

                    During gamete formation, the two alleles of a gene separate (segregate) from each other so that
                    each
                    gamete receives only one allele. This ensures gametes are pure for a trait.
                
                    Law of Independent Assortment:

                    In a Dihybrid cross (two pairs of traits), the inheritance of one pair of characters (e.g.,
                    Shape)
                    is independent of the other pair (e.g., Colour). (Example: Round can go with
                    Green
                    or Yellow).

2. Sex Determination in Humans

Figure 4.1: Sex Determination Flowchart

In humans, sex is determined by the sperm (Male Gamete).

Male: XY chromosomes. Produces two types of sperms (50% X and 50% Y).
Female: XX chromosomes. Produces only one type of egg (100% X).

Sperm (Father)	Egg (Mother)	Zygote	Child Sex
X	X	XX	Female (Girl)
Y	X	XY	Male (Boy)

Conclusion: There is a 50-50 chance of a boy or a girl. The sex of the child depends entirely on which sperm (X or Y) fertilizes the egg.

Humans have 23 pairs of chromosomes. 22 pairs are Autosomes. 1 pair is Sex Chromosome.

Mechanism:
• Mother produces eggs only with X chromosome.
• Father produces sperms with X (50%) or Y (50%).
• If Sperm (X) fertilizes Egg (X) → Girl (XX).
• If Sperm (Y) fertilizes Egg (X) → Boy (XY).

Who determines the sex of the child?
The Father. Because the mother provides only X chromosomes, while the father provides either X or Y, which decides the outcome. It is a matter of chance (50-50 probability).

3. Acquired vs Inherited Traits

Inherited Traits	Acquired Traits
Passed from parents to offspring.	Developed during lifetime of individual.
Cause change in DNA of Germ cells.	Involve changes in Somatic (Body) cells only. No DNA change.
Examples: Eye colour, Skin colour, Blood group.	Examples: Muscular body of a wrestler, Learning French, Cut tail of a mouse.

🎯 TRICKY PRACTICE ZONE (Heredity)

A violet flower (VV) is crossed with a white flower (vv). Why do we not see ANY white flowers in the F1 generation? Hint: Law of Dominance. White (recessive) is hidden by Violet (dominant) in F1 (Vv).
"A wrestler's son is not born with muscular muscles." Explain scientifically. Hint: Muscles are an Acquired Trait (change in Somatic cells), which does not change the DNA of Germ cells (sperm/egg).
In a population of mice, does the environment select the survival of specific traits? (Give an example). Hint: Yes. If bushes turn brown, brown mice survive better than green mice (Natural Selection).

CHAPTER 5: OUR ENVIRONMENT

1. Ecosystem and its Components

Ecosystem: A self-sustaining system where biotic (living) and abiotic (non-living) components interact with each other. (e.g., Garden, Forest, Pond).

Component	Examples & Role
Abiotic	Temperature, Rainfall, Soil, Air, Light.
Biotic	1. Producers: Green plants/Blue-green algae (Make food). 2. Consumers: Herbivores, Carnivores, Omnivores, Parasites. 3. Decomposers: Bacteria, Fungi (Break down dead matter).

What is the role of Decomposers?
They break down complex organic matter (dead plants/animals) into simple inorganic substances that go into the soil and are used up once more by the plants. They act as natural cleansing agents of the environment.

2. Food Chain & Energy Flow

Food Chain: A series of organisms where one eats another to transfer energy. (Grass → Deer → Tiger).

Food Web vs Food Chain:
In nature, food chains are not isolated. One organism may be eaten by many others (e.g., a Frog eaten by Snake or Bird). This interconnected network is a Food Web. It provides stability to the ecosystem.

A. The 10% Law (Lindeman)

            Statement: Only 10% of energy entering a particular trophic level is
            available for transfer to the next higher trophic level. The remaining 90% is lost as
            heat/digestion/growth.

            *Note: Plants capture only 1% of Solar Energy.
        

Numerical Example (PYQ):
Sun (100,000 J) → Plant (1% = 1000 J) → Deer (10% = 100 J) → Lion (10% = 10 J).
Conclusion: Food chains generally consist of only 3 or 4 steps because very little energy is left for a 5th level.

B. Flow of Energy is Unidirectional

Energy captured by autotrophs does not revert back to the sun. Energy passed to herbivores does not come back to autotrophs. It moves progressively through trophic levels.

Figure 5.1: Trophic Levels Pyramid

3. Biological Magnification

Mechanism:
1. Harmful chemicals (Pesticides/DDT) are sprayed on crops.
2. They enter the soil/water bodies.
3. Absorbed by plants (Producers).
4. Passed on to Herbivores and then Carnivores.
5. Since these are non-biodegradable, they accumulate at each level.
Result: Concentration is maximum in Humans (Top level).

4. Ozone Layer Depletion

Ozone (O₃): A deadly poison at ground level, but a shield in the stratosphere. It protects earth from harmful UV radiation (causes skin cancer, cataracts).

A. Formation of Ozone

            UV splits Oxygen molecule: O2 —(UV)→ O + O
Free oxygen combines with Oxygen molecule: O + O2 → O3
                        (Ozone)

        

B. Depletion Cause

Synthetic chemicals like CFCs (Chlorofluorocarbons) used in Refrigerators and Fire Extinguishers reach the upper atmosphere and break down Ozone.
UNEP (1987): Forged an agreement to freeze CFC production at 1986 levels (Montreal Protocol).

5. Managing Garbage

Biodegradable	Non-Biodegradable
Broken down by biological processes (Bacteria/Enzymes).	Cannot be broken down biologically. Persist for long.
Example: Fruit peels, Paper, Wood, Cotton.	Example: Plastic, Glass, Metals, DDT.

Why replaced plastic cups with Kulhads (Clay cups) and then Paper cups?
• Plastic: Non-biodegradable waste.
• Kulhads: Biodegradable, but caused loss of fertile topsoil (to make clay).
• Paper Cups: Biodegradable and can be recycled. Best option.

🎯 TRICKY PRACTICE ZONE (Environment)

Calculate the energy available to the Tiger if the Plants absorb 20,000 J of energy from the Sun. Hint: Don't forget Plants take only 1% from Sun (200 J), then 10% passes to Deer (20 J), then 10% to Tiger (2 J).
Why do we find maximum chemical accumulation in Humans in a food chain? Hint: Humans are at the top trophic level. Chemicals are non-biodegradable and accumulate at every step (Biomagnification).
"Damage to the Ozone layer is a cause for concern." Justify this statement. Hint: Ozone protects from UV rays. UV rays cause Skin Cancer, Cataracts in humans, and damage to crops/ecosystems.