Life Processes

All living organisms carry out seven life processes (MRS GREN): Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, Nutrition.

Nutrition:

• Autotrophs (plants): make their own food via photosynthesis. 6CO₂ + 6H₂O + sunlight → C₆H₁₂O₆ + 6O₂. Chlorophyll (green pigment) captures light; site is chloroplasts.
• Heterotrophs (animals, fungi): consume other organisms.
• Herbivores eat plants; carnivores eat meat; omnivores eat both.

Human digestive system — from mouth to anus:

1. Mouth: teeth grind food; saliva (with amylase) starts starch breakdown.
2. Oesophagus: tube pushes food to stomach via peristalsis (rhythmic muscle contractions).
3. Stomach: HCl kills bacteria; pepsin digests protein.
4. Small intestine: bile (from liver) emulsifies fats; pancreatic enzymes complete digestion. Villi absorb nutrients into blood.
5. Large intestine: water absorption.
6. Rectum/Anus: waste expelled.

Respiration:

• Aerobic: glucose + O₂ → CO₂ + H₂O + 36-38 ATP energy.
• Anaerobic (no O₂): glucose → lactic acid (in muscles during heavy exercise) or alcohol (in yeast fermentation) + 2 ATP only.

Human respiratory system:
Nose → Pharynx → Larynx → Trachea (windpipe) → Bronchi → Bronchioles → Alveoli (air sacs in lungs).

• Diaphragm and intercostal muscles power breathing.
• Gas exchange happens at alveoli: O₂ in, CO₂ out.
• Haemoglobin in red blood cells carries O₂.

Transport — human circulatory system:

• Heart: 4 chambers (right atrium, right ventricle, left atrium, left ventricle). Pumps blood.
• Arteries (away from heart): thick walls, high pressure. Carry oxygenated blood except pulmonary artery.
• Veins (back to heart): thinner walls, low pressure, valves. Carry deoxygenated blood except pulmonary vein.
• Capillaries: thin-walled; exchange O₂, CO₂, nutrients with tissues.

Double circulation (humans): blood passes through heart twice per cycle — once for lungs (pulmonary), once for body (systemic).

Plant transport:

• Xylem: carries water and minerals from roots up (one-way).
• Phloem: carries sugars from leaves (source) to other parts (sink), both ways.

Photosynthesis details:

• Site: chloroplasts (mainly in leaves; some in stems).
• Pigments: chlorophyll a, chlorophyll b, carotenoids.
• Two stages:
  1. Light reactions (in thylakoid membranes) — split water (photolysis), produce ATP and NADPH; release O₂.
  2. Dark reactions / Calvin cycle (in stroma) — fix CO₂ into sugars using ATP and NADPH.
• Factors affecting rate: light intensity, CO₂ concentration, temperature, water availability.

Excretion removes metabolic waste.

• Humans: kidneys filter blood, producing urine (water + urea + salts). Each kidney has ~1 million nephrons.
• Filtration → Reabsorption → Secretion → Excretion: nephron stages.
• Urea is the main nitrogenous waste in humans (formed in liver from protein breakdown).
• Plants: excrete via stomata (transpiration), shedding of leaves and bark, storing waste in vacuoles.

Hormones (human endocrine system):

• Insulin (pancreas): lowers blood glucose. Deficiency → diabetes.
• Adrenaline (adrenal): fight-or-flight response.
• Thyroxine (thyroid): metabolism. Deficiency → goitre; excess → hyperthyroidism.
• Growth hormone (pituitary): regulates growth. Excess in childhood → gigantism; deficiency → dwarfism.
• Oestrogen / Testosterone: sexual development.

Reflex action: involuntary, rapid response (e.g. pulling hand from a hot pan). Signal travels: stimulus → receptor → sensory neuron → spinal cord (relay) → motor neuron → muscle. Brain is bypassed for speed.

Nervous system:

• CNS: brain + spinal cord.
• PNS: nerves connecting CNS to body.
• Brain regions: cerebrum (thinking), cerebellum (balance/coordination), medulla (involuntary actions like heartbeat).

Quick facts:

• Human heart beats ~72 times/min, ~100,000 times/day.
• Adult has ~5 L of blood, ~600 muscles, 206 bones.
• Largest organ: skin. Largest internal organ: liver.
• Smallest bone: stapes (in ear).
• Strongest muscle: masseter (jaw).
• Red blood cells live ~120 days; white blood cells fight infection.

Vitamins — essential micronutrients; deficiency causes specific diseases:

• A (retinol): night blindness if low. Carrots, milk, eggs.
• B1 (thiamin): beriberi. Whole grains.
• B12: pernicious anaemia. Meat, eggs.
• C (ascorbic acid): scurvy. Citrus, amla.
• D: rickets/osteoporosis. Sunlight, fish.
• K: bleeding. Green vegetables.