Cheat Sheet — Life Processes

🌿 Nutrition — Autotrophic vs Heterotrophic

Feature	Autotrophic	Heterotrophic
Food source	Inorganic raw materials (CO₂, H₂O)	Other organisms (organic matter)
Energy source	Sunlight / Chemical reactions	Oxidation of ingested food
Examples	Green plants, algae, cyanobacteria	Animals, fungi, most bacteria
Types	Photoautotroph, Chemoautotroph	Holozoic, Saprophytic, Parasitic
Key organ	Chloroplast (chlorophyll)	Digestive system / cell membrane

☀️ Photosynthesis — Key Facts

6CO₂ + 6H₂O →(chl/sunlight)→ C₆H₁₂O₆ + 6O₂

TWO STAGES:

Light Reaction (Thylakoid): H₂O splits → O₂ released, ATP + NADPH formed. Needs light.

Dark Reaction / Calvin Cycle (Stroma): CO₂ + ATP + NADPH → Glucose. Does NOT need light directly.

        Factors affecting photosynthesis: Light intensity, CO₂ conc., Temperature, Water availability

        Chlorophyll absorbs RED + BLUE; reflects GREEN → leaves look green

🍽️ Human Digestion — Summary

Mouth

→

Oesophagus

→

Stomach

→

Small Intestine

→

Large Intestine

Key enzymes and secretions:

Mouth: Salivary amylase → starch to maltose (pH 7)

Stomach: HCl (pH 2) + Pepsin → protein to peptides

Small intestine: Bile (emulsifies fats); Trypsin, Lipase, Amylase (pancreatic); Villi absorb nutrients

Large intestine: Water reabsorption; faeces formation

💨 Respiration — Aerobic vs Anaerobic

Feature	Aerobic	Anaerobic
Oxygen needed?	Yes	No
Location	Mitochondria (+ Cytoplasm for glycolysis)	Cytoplasm only
End products	CO₂ + H₂O	Lactic acid (muscles) OR Ethanol + CO₂ (yeast)
ATP yield	38 ATP per glucose	2 ATP per glucose
Complete oxidation?	Yes (complete)	No (partial)
Common in	All higher organisms	Yeast, muscle cells under exertion

C₆H₁₂O₆ + 6O₂ → 6CO₂ + 6H₂O + 38 ATP (Aerobic)

C₆H₁₂O₆ → 2C₂H₅OH + 2CO₂ + 2 ATP (Yeast — Fermentation)

C₆H₁₂O₆ → 2CH₃CHOHCOOH + 2 ATP (Muscle cells)

Aerobic (38)

Anaerobic (2)

⚡ Stages of Aerobic Respiration

STAGE 1 — Glycolysis (Cytoplasm)

Glucose (6C) → 2 Pyruvate (3C) + 2 ATP + 2 NADH
No O₂ needed · Common to aerobic + anaerobic

STAGE 2 — Krebs Cycle (Mitochondrial Matrix)

Pyruvate → Acetyl CoA → 2 ATP + CO₂ + NADH + FADH₂

STAGE 3 — ETC (Inner Mitochondrial Membrane)

NADH + FADH₂ + O₂ → H₂O + 34 ATP
O₂ = final electron acceptor · Max energy here

🫁 Human Respiratory System

Nose

→

Pharynx

→

Larynx

→

Trachea

→

Bronchi

→

Alveoli

~300 million alveoli per lung; total area ≈ 70 m²

Walls 1 cell thick; O₂ diffuses IN; CO₂ diffuses OUT (passive diffusion)

Haemoglobin (Hb) + O₂ ⇌ Oxyhaemoglobin (HbO₂)

Breathing rate: ~15–18 breaths/min at rest

🌱 Transport in Plants — Xylem vs Phloem

Feature	Xylem	Phloem
Transports	Water + Dissolved Minerals	Food (Sucrose, Amino acids)
Direction	Unidirectional: Roots → Stem → Leaves	Bidirectional: Source ↔ Sink
Driving force	Transpiration pull (Cohesion-Tension) + Root pressure	Active transport (needs ATP) — Translocation
Cell type	Dead cells; hollow; no cytoplasm	Living: Sieve tubes + Companion cells
Process name	Ascent of Sap	Translocation
Energy needed?	No (passive)	Yes (active)

❤️ Human Circulatory System

DOUBLE CIRCULATION (heart pumped twice per circuit):

Pulmonary: Right ventricle → Lungs → Left atrium
(Deoxygenated → Oxygenated)

Systemic: Left ventricle → Body → Right atrium
(Oxygenated → Deoxygenated)

Arteries: Carry blood AWAY from heart; thick walls; high pressure; NO valves

Veins: Carry blood TO heart; thin walls; low pressure; HAVE valves

Capillaries: Exchange site; 1 cell thick walls; no valves

Heartbeat: ~70 beats/min; Left ventricle has thickest walls

🩸 Blood — Composition & Functions

Component	%	Function
Plasma	55%	Carries nutrients, hormones, CO₂, plasma proteins (fibrinogen, antibodies)
RBC (Erythrocytes)	40%	Haemoglobin carries O₂ as oxyhaemoglobin; no nucleus in mature human RBC
WBC (Leucocytes)	~1%	Immune defence; phagocytosis; antibody production
Platelets (Thrombocytes)	<1%	Blood clotting; no nucleus; fragments of megakaryocytes

🫘 Urine Formation — 3 Steps

1. Ultrafiltration

Glomerulus + Bowman's capsule; High pressure; Small molecules filtered out

↓

2. Reabsorption

Proximal tubule + Loop of Henle; ALL glucose + amino acids; most water reabsorbed

↓

3. Secretion

Distal tubule + Collecting duct; H⁺, K⁺, NH₃ secreted; ADH regulates water

        ~180 L filtrate/day → only 1.5–1.8 L urine (99%+ reabsorbed!)

        Urine: 95% water · 2% urea · 3% salts/uric acid/creatinine

🗑️ Organs of Excretion in Humans

Kidneys

Urea, uric acid, creatinine, salts

Via urine through ureter → bladder → urethra

Lungs

CO₂ + H₂O vapour

Exhaled through alveolar diffusion

Skin (Sweat glands)

Water, NaCl, traces of urea

Also helps in thermoregulation

Liver

Bile pigments (bilirubin)

Broken-down RBCs; urea cycle converts NH₃ → urea

Dialysis: Semi-permeable cellophane tube; urea diffuses out into isotonic fluid; RBC + proteins retained.

📊 Life Processes — Big Picture Comparison

Process	What it does	Key organ / site	Output
Nutrition	Obtains energy-rich molecules	Chloroplast (plants) · Digestive system (animals)	Glucose, amino acids, fats
Respiration	Releases energy from food as ATP	Mitochondria (aerobic) · Cytoplasm (anaerobic)	ATP + CO₂ + H₂O
Transportation	Moves materials to/from cells	Heart + Blood vessels (animals) · Xylem + Phloem (plants)	Nutrients, O₂, hormones delivered; CO₂, waste removed
Excretion	Removes metabolic wastes	Kidneys · Lungs · Skin (animals) · Stomata (plants)	Urine, CO₂, sweat, bile pigments

🎯 Exam Tips & Memory Tricks

NRTE Mnemonic

Life Processes: Nutrition → Respiration → Transportation → Excretion. All essential — no organism survives without all four.

38 vs 2 ATP

Aerobic = 38 ATP (mitochondria + cytoplasm). Anaerobic = 2 ATP (cytoplasm only). Aerobic is 19× more efficient.

Xylem = Dead, Phloem = Living

Xylem cells are dead (hollow) — no cytoplasm. Phloem uses living sieve tubes + companion cells. Phloem needs ATP; Xylem does not.

180 L → 1.8 L

Kidneys filter 180 L/day but produce only 1.8 L urine. 99%+ is reabsorbed. Always mention this in 3-mark excretion questions.

Pulmonary vs Systemic

Pulmonary: Heart → Lungs → Heart (short loop, O₂ pick-up). Systemic: Heart → Body → Heart (long loop, O₂ delivery). Blood passes through the heart TWICE per cycle.

Glycolysis = Both

Glycolysis is the FIRST step in BOTH aerobic AND anaerobic. It occurs in the cytoplasm and does NOT require oxygen. Common starting point!

Amoeba digestion order

Engulf (pseudopodia) → Food vacuole → Lysosomes add enzymes → Digestion → Diffusion into cytoplasm → Egestion. All inside ONE cell!

Left ventricle = Thickest

Left ventricle pumps blood to the entire body (systemic) → needs highest pressure → thickest muscular walls. Right ventricle only pumps to the lungs.