Biology & Health

Nutrients are the substances in food that the body needs. The body needs carbohydrates, proteins and fats in large amounts, so they are called macronutrients. They give energy and help growth. Vitamins and minerals are needed in small amounts; they are micronutrients. Add fibre and water, and food has seven components.

Water gives no energy, yet every body process needs it. It carries nutrients, removes wastes in urine and sweat, and keeps body temperature steady by sweating (thermoregulation). About two-thirds of the body is water. A dry mouth and headache are common early signs of mild dehydration.

Trans fats raise 'bad' (LDL) cholesterol and harm the heart. Small amounts occur naturally in dairy products and the meat of cows, buffaloes and goats. Most trans fat, though, comes from vanaspati and other partly hydrogenated oils used in fried snacks and bakery items.

Every protein is made of repeating units called amino acids. Only 20 kinds of amino acids join in long chains, in different orders, to make every protein in the body. It is like 35 Gurmukhi letters making countless words. Digestion breaks food proteins back into amino acids, and the body reuses them.

Protein facts asked in Constable 2025 papers

Fat-soluble vitamins: A, D, E, K — remember the word 'ADEK'. All the others (the eight B vitamins and C) dissolve in water.

Our skin makes vitamin D in sunlight, and gut bacteria make vitamin K. Vitamin B12 comes almost only from animal foods such as milk, curd and eggs, so strict vegetarians must watch it. Vegetables and fruits are called protective foods: they help the body fight infections and diseases.

A balanced diet gives every nutrient in the right amount for a person's age, work and health, with enough fibre and water. Optimal nutritional status comes from balanced nutrients — not from too little, and not from too much. Food choices also depend on individual likes/dislikes, cost, season and custom.

Good physical health is best shown by a person who can perform routine daily tasks efficiently, experiences minimal fatigue and has strong immunity — not by body weight alone, and not by exercise alone. The WHO defines health as complete physical, mental and social well-being.

Diet for players. Constable 2025 papers asked each of these.

• Water is essential, but it is not a source of energy.
• Fat gives the most energy per gram (9 kcal), but carbohydrate is the main fuel, also for players.
• Rice and bread are complex carbohydrates; sugar and fruit sugars are simple.
• Vitamin K is for clotting; vitamin C is for gums. B12 lack gives anaemia; B3 lack gives pellagra.
• Iron lack lowers haemoglobin; iodine lack lowers thyroxine and gives goitre.
• Too little fluoride = tooth decay; too much = mottled teeth (fluorosis).
• Kwashiorkor = protein only; marasmus = protein and calories.
• Haemoglobin and insulin are globular; myosin and keratin are fibrous.

A player has a race at 9 am. What should she eat for breakfast, and why?

• Macronutrients: carbohydrates, proteins, fats
• Energy per gram: fat 9 kcal; carbohydrate and protein 4 kcal each
• Proteins: 20 amino acids, 9 essential; milk has the best mix
• Fat-soluble vitamins: A, D, E, K
• Sodium: nerve signals; calcium: teeth, nerves and muscles
• Fluoride: tea and fish, spinach
• Obesity = energy imbalance
• Milk is perishable; sugar, pulses and oil are not

The pancreas is both a digestive gland and a hormone gland. It pours pancreatic juice into the small intestine. Small groups of cells in it, the islets of Langerhans, release the hormone insulin into the blood. Insulin lowers blood sugar; too little insulin causes diabetes.

Villi — millions of finger-like folds in the small intestine — give a huge surface for absorbing digested food. An adult has 32 teeth (8 incisors, 4 canines, 8 premolars, 12 molars); a child has 20 milk teeth.

Breathing is the physical act of taking air into the lungs and pushing it out. Respiration is the chemical breakdown of food (glucose) inside cells that releases energy. Breathing supplies the oxygen that respiration uses.

Group AB has no anti-A or anti-B antibody, so it can receive red cells of any ABO group. Group O cells carry no marker, so they can be given to anyone. Normal adult blood pressure is about 120/80 mm Hg, measured with a sphygmomanometer.

When both kidneys fail, a dialysis machine cleans the blood. Blood flows past a thin membrane with a clean fluid on the other side. Urea and extra salts move across by diffusion, from where there is more of them to where there is less. Clean blood goes back to the body.

Fresh urine hardly smells. On standing, bacteria turn its urea into ammonia, which gives the sharp smell. Plants have no excretory organs: they lose gases through stomata, shed wastes with old leaves and bark, and store some as gums and resins.

• Bile has no enzyme and comes from the liver; the pancreas gives pancreatic juice and insulin.
• Breathing is physical; respiration is chemical and happens in every cell.
• Not all arteries carry oxygen-rich blood — the pulmonary artery does not.
• O is the universal donor; AB is the universal recipient.
• Dialysis works by diffusion, not osmosis.
• Nephron (kidney) and neuron (nerve) sound alike — do not mix them.

Why is the small intestine lined with villi?

• Saliva acts on starch; pepsin on protein; lipase on fat
• Bile: liver, stored in gall bladder, no enzyme
• Aerobic: CO2 + water + energy; yeast makes ethanol
• Heart: 4 chambers, double circulation, about 72 beats a minute
• Blood: plasma, RBC, WBC, platelets — no 'blue' cells
• O donor, AB recipient; histamine is a vasodilator
• Xylem: water up; phloem: food both ways
• Nephron filters blood; dialysis uses diffusion

Bone is a hard connective tissue. Its hard matrix is made mainly of calcium phosphate, with some calcium carbonate. Teeth are also mostly calcium phosphate. An adult has 206 bones. The longest is the femur (thigh bone). The smallest is the stapes in the middle ear. Each middle ear has 3 tiny bones, so both ears together have 6.

The earthworm's body is made of rings (segments), but it has no jointed legs and no hard outer skeleton. It moves with tiny bristles called setae. So it is an annelid, like the leech.

• The earthworm has segments but no jointed legs: it is an annelid, not an arthropod. Silkworm, honey bee and king crab are arthropods.
• Bones are mainly calcium phosphate, not calcium carbonate.
• Ear bones: 3 in each ear, 6 in all. Read whether the question asks one ear or 'total'.
• Tendon joins muscle to bone; ligament joins bone to bone.
• Hooke (1665) saw dead cork cells; Leeuwenhoek first saw living cells.
• Ribosomes make proteins; mitochondria release energy. Do not swap them.
• Blood is a connective tissue, even though it is a liquid.

Why is the earthworm not put in Arthropoda, though its body has segments?

• Cell → tissue → organ → organ system → organism
• Hooke 1665 named the cell; Brown 1831 found the nucleus
• Mitochondria = powerhouse; ribosomes = proteins; lysosomes = suicide bags
• Only plant cells: cell wall, plastids, one big vacuole
• Mitosis: 2 identical cells; meiosis: 4 cells with half the chromosomes
• 206 bones; 6 ear bones; bones mainly calcium phosphate
• Arthropods have jointed legs; the earthworm is an annelid

Ways to keep food safe. Fresh, moist foods such as milk, meat and fruit are perishable.

HIV (Human Immunodeficiency Virus) attacks white blood cells called lymphocytes (helper T-cells). As they are destroyed, the body's defence becomes weak. Then common infections become deadly. This last stage is AIDS — Acquired Immuno Deficiency Syndrome.

In 1347–1351 a plague pandemic swept Europe and killed a very large share of its people — often given as a third to a half or more. Plague is caused by a bacterium (Yersinia pestis) carried by fleas on rats.

A vaccine contains dead or weakened germs, or just a harmless part of them such as a protein. It makes the body produce antibodies and remember the germ. A real infection later is fought off quickly. So vaccination is preventive medicine. Smallpox has been wiped out worldwide, and India was certified polio-free in 2014.

An antibiotic is a medicine, first made by microbes, that kills or stops bacteria. It blocks processes that only bacteria have. Viruses live inside our own cells, so antibiotics are useless against the cold, flu or chickenpox. Taking them when not needed helps bacteria become resistant.

• Ringworm is a fungus, not a worm.
• Malaria is caused by a protozoan; the female Anopheles mosquito only carries it.
• Dengue is a virus carried by Aedes, which bites by day. Anopheles carries malaria.
• AIDS: the 'D' is Deficiency, not Disease. HIV destroys lymphocytes, not red cells.
• Pneumonia is the usual 'not viral' answer: it is mostly bacterial.
• Food lasts longer with low water activity, not high moisture.
• 'Bad air' = miasma theory; germs = germ theory (Pasteur, Koch).
• Antibiotics kill bacteria, not viruses. Streptomycin → TB; chloramphenicol → 1947.

Why does a doctor not give antibiotics for a common cold?

• Five microbe groups: bacteria, fungi, protozoa, algae, viruses
• TB, typhoid, cholera, plague: bacteria; ringworm: fungus
• Cold, chickenpox, polio, AIDS, dengue: viruses
• Malaria: Plasmodium via female Anopheles
• Low water activity = long shelf life; Salmonella = food poisoning
• Vaccines prevent; no approved HIV vaccine yet
• Penicillin 1928, streptomycin 1943 (TB), chloramphenicol 1947

Identical twins come from one zygote that splits into two. Non-identical twins come from two eggs. In IVF, egg and sperm are joined outside the body ('test-tube baby'). In some reptiles, the temperature of the eggs decides the sex.

Mendel crossed pure tall pea plants with pure dwarf ones. All first-generation (F1) plants were tall. So tallness is dominant and dwarfness is recessive. When F1 plants bred among themselves, the F2 plants were tall and dwarf in the ratio 3 : 1. With two traits at once, the F2 ratio is 9 : 3 : 3 : 1.

Some genes sit on the X chromosome. Colour blindness and haemophilia (blood that does not clot) are caused by recessive genes on the X. A man has only one X, so one faulty gene shows its effect. A woman has two X's, so a normal X usually hides the faulty one. That is why these problems are more common in men.

Down's syndrome comes from an extra copy of chromosome 21, not from the X. Skin colour is controlled by many genes on other chromosomes.

Parts of every person's DNA are unique, except in identical twins. DNA fingerprinting compares these parts. Police use it to identify criminals from blood, hair or skin left at a crime scene. It also settles questions about who a child's parents are. Alec Jeffreys of Britain developed it in 1984.

AB has nothing to fight (no antibodies), so it accepts all. O has nothing on its cells, so it can be given to all.

• The pericarp is part of the fruit, not the flower. Saffron is the stigma, not the petal.
• Body cells have 46 chromosomes; sperm and egg have 23.
• The father, not the mother, decides the sex of the child.
• Colour blindness is on the X chromosome, not the Y.
• Green seed is recessive, but green pod is dominant. Terminal flower is recessive.
• AB is the universal recipient; O is the universal donor.
• Darwin = natural selection; Lamarck = acquired characters (use and disuse).

Why do children of the same parents look different from each other?

• Asexual: fission, budding, fragmentation, regeneration, spores, vegetative
• Ovary → fruit; ovule → seed; ovary wall → pericarp
• 46 chromosomes; XX girl, XY boy; father decides
• Mendel: 3 : 1 and 9 : 3 : 3 : 1
• Colour blindness, haemophilia: X-linked, more in men
• DNA: A T G C; RNA: A U G C
• AB universal recipient; O universal donor
• Darwin 1859: natural selection; Lamarck: acquired characters

Green plants make glucose from carbon dioxide and water. The energy comes from sunlight, trapped by the green pigment chlorophyll. Oxygen is given off. This happens in the chloroplasts of leaf cells, so leaves are the food factories of the plant. Extra glucose is stored as starch.

To test a leaf for starch, boil it in alcohol to remove the chlorophyll. Then add iodine: it turns blue-black. A leaf kept in the dark for two days gives no blue-black colour. This shows that light is needed.

Kharif crops need heat and plenty of water. Rabi crops need a cool season to grow and a warm, dry spell to ripen. Zaid crops are short summer crops grown between the two.

Bt stands for Bacillus thuringiensis, a soil bacterium. A gene from it is put into the cotton plant. The plant then makes a protein that kills bollworm caterpillars that eat it. Such a plant with a gene from another organism is called transgenic (genetically modified).

Ethylene is a plant hormone and a gas. Ripening fruit gives it off. Ripening chambers use ethylene gas to ripen green bananas and mangoes evenly. Using calcium carbide, which gives off acetylene, is unsafe and banned for this.

From the mid-1960s, India used high-yielding varieties (HYV) of wheat and rice, with irrigation, chemical fertilisers and pesticides. Grain output rose fast, and Punjab led the change. It worked best for wheat. Crop insurance was not part of this package.

• Chlorophyll has magnesium; haemoglobin has iron.
• At night trees give off carbon dioxide, not carbon monoxide.
• Nitrogen-fixing bacteria live in the root nodules of legumes, not in leaves.
• Maize, paddy, cotton are kharif; wheat, barley, mustard, gram are rabi.
• Monocropping = one crop every year; catch crop = short crop between two main crops.
• Bt is a bacterium (Bacillus), not a fungus; Bt cotton fights bollworm.
• Fruit is ripened with ethylene, not ethane or acetylene.
• Green = grain, White = milk, Blue = fish, Yellow = oilseeds, Round = potato, Grey = fertilisers.

Why is it good to grow moong between two cereal crops?

• 6CO2 + 6H2O → C6H12O6 + 6O2, with sunlight and chlorophyll
• Chlorophyll: magnesium; starch test: iodine turns blue-black
• Rhizobium in root nodules of legumes
• Kharif: paddy, maize, cotton; rabi: wheat, barley, mustard
• Ploughing loosens soil; catch crop fills the gap
• Bt = Bacillus thuringiensis; pink bollworm = cotton
• Green: Swaminathan; White: Kurien
• PAs: Boraginaceae, Asteraceae, Fabaceae

Two neurons do not touch. A tiny gap, the synapse (synaptic cleft), lies between them. The electrical impulse reaching the end of the axon releases a chemical. The chemical crosses the gap and starts a new impulse in the next neuron. So messages move only one way.

An adult human brain weighs about 1.3–1.4 kg, roughly 3 pounds. It is about 2 percent of body weight but uses about a fifth of the body's energy at rest.

People with diabetes may need insulin injections. Today human insulin is made by genetically modified E. coli bacteria. In 1983 the company Eli Lilly made human insulin this way.

Adolescence is the time, roughly from 11 to 19 years, when body and mind change from child to adult. Puberty is the part of it when the body becomes able to reproduce. Testosterone in boys and oestrogen in girls bring these changes, under the control of the pituitary.

Active oil glands cause acne (pimples) in many teenagers. A balanced diet, exercise and cleanliness keep adolescents healthy. Menstruation stops at about 45–50 years of age; this is menopause.

• The gap between neurons is the synapse (synaptic cleft), not the dendrite or axon.
• Reflex actions are run by the spinal cord, not the brain.
• Cerebrum = thinking; cerebellum = balance; medulla = heartbeat and breathing.
• Growth hormone comes from the pituitary; the pineal makes melatonin.
• Sweat, salivary and tear glands are exocrine (they have ducts).
• Insulin lowers blood sugar; it is now made by E. coli, not Rhizobium.
• Para-heliotropism avoids the sun; heliotropism follows it.
• Bhang, ganja and charas come from Indian hemp, not poppy.

Why does your heart beat faster when a dog suddenly chases you?

• Neuron: dendrite → cell body → axon; gap = synapse
• Reflex arc runs through the spinal cord
• 12 pairs cranial, 31 pairs spinal nerves; brain about 3 pounds
• Pituitary: growth hormone; pineal: melatonin; pancreas: insulin
• Sweat gland = exocrine; human insulin from E. coli
• Phototropism: to light; paraheliotropism: away from strong sun
• Ethylene ripens fruit; abscisic acid stops growth
• Morphine: painkiller from poppy; bhang, ganja, charas: Indian hemp