Std. 9
Biology

The cell is the basic structural and functional unit of life. Cell theory explains that living organisms are made of cells and that new cells arise from pre-existing cells.

Protoplasm is the living content of a cell. Cytoplasm is the material between the cell membrane and nucleus; the nucleus controls cell activities and contains genetic material.

Mitochondria release usable energy; endoplasmic reticulum helps in synthesis and transport; ribosomes make proteins; Golgi bodies modify and package materials; lysosomes contain digestive enzymes; plastids occur in plant cells; vacuoles store materials; centrosome helps in cell division.

The cell membrane is selectively permeable and regulates movement of substances. The plant cell wall is a rigid supporting layer outside the membrane.

Prokaryotic cells lack a true membrane-bound nucleus and membrane-bound organelles. Eukaryotic cells possess a true nucleus and membrane-bound organelles.

Plant cells generally have a cell wall, plastids and a large vacuole; animal cells lack a cell wall and plastids and characteristically possess a centrosome.

Tissues are groups of similar cells performing a particular function. Plant tissues include meristematic and permanent tissues; animal tissues include epithelial, connective, muscular and nervous tissues.

A bisexual flower contains both male and female reproductive structures. The essential whorls are androecium and gynoecium; sepals and petals are accessory whorls.

Sepals protect the bud; petals often attract pollinators; stamens produce pollen; the carpel consists of stigma, style and ovary, with ovules inside the ovary.

Inflorescence is the arrangement of flowers on a floral axis. Placentation describes how ovules are arranged inside the ovary.

Pollination is transfer of pollen from anther to stigma. Self-pollination occurs within the same flower or plant; cross-pollination occurs between flowers of different plants of the same species.

Insects, wind and water can transfer pollen. Flower structure, colour, scent, nectar, pollen characteristics and stigma position may show adaptations to a particular agent.

After compatible pollen reaches the stigma, the pollen tube grows toward the ovule and delivers male gametes. Fusion of male and female gametes forms the zygote.

In flowering plants, one male gamete fuses with the egg while the other fuses with the polar nuclei. The latter fusion is called triple fusion; the two events together are called double fertilisation.

Root hairs provide a large surface area for absorption of water and mineral salts. Water enters mainly by osmosis while mineral ions may enter by active transport.

Osmosis is movement of water molecules through a selectively permeable membrane from a region of higher water potential to lower water potential.

Transpiration is loss of water vapour from aerial parts of a plant, mainly through stomata. It contributes to transpiration pull and mineral transport.

Cobalt chloride paper changes from blue to pink when it becomes moist, demonstrating water loss. A potometer estimates water uptake associated with transpiration.

6CO₂+6H₂O→C₆H₁₂O₆+6O₂. Green plants manufacture food from carbon dioxide and water using light and chlorophyll, with oxygen released.

Light intensity, carbon dioxide concentration, temperature and chlorophyll availability affect the rate of photosynthesis within suitable limits.

Respiration releases energy from food. Aerobic respiration uses oxygen and releases more energy; anaerobic respiration occurs without oxygen and produces different end products.

The syllabus includes experiments related to carbon dioxide, oxygen, chlorophyll, starch and light as requirements or products of photosynthesis.

Classification groups organisms according to similarities and differences so that their characteristics and relationships can be studied systematically.

The five-kingdom system includes Monera, Protista, Fungi, Plantae and Animalia. Each kingdom differs in cellular organisation, nutrition and other major characteristics.

Monerans are prokaryotic organisms. Bacteria may differ in shape, nutrition and respiration; useful and harmful examples illustrate their importance.

Protists are mainly unicellular eukaryotes. Amoeba, Paramecium and Euglena illustrate different modes of nutrition and movement.

Fungi are non-green heterotrophs that obtain nutrients by absorption. Yeast and mushroom are familiar examples; many fungi act as decomposers.

Plants are multicellular eukaryotes with chlorophyll in most members and generally make food by photosynthesis.

Animals are multicellular eukaryotes that obtain food from other organisms and generally show active movement at some stage.

Viruses are acellular infectious particles that reproduce only inside host cells. Lichens represent a close association between a fungus and an alga/cyanobacterium.

Nutrition is the process by which organisms obtain and use nutrients. Humans require carbohydrates, proteins, fats, vitamins, minerals, water and roughage.

The digestive tract includes mouth, pharynx, oesophagus, stomach, small intestine, large intestine, rectum and anus. Each region has a specialised function.

Digestion breaks large, insoluble food molecules into smaller soluble molecules that can be absorbed and used by cells.

Amylase begins starch digestion; pepsin acts on proteins in the stomach; pancreatic and intestinal enzymes complete digestion in the small intestine.

Bile is produced by the liver and stored in the gall bladder. It emulsifies fats and provides an alkaline medium for intestinal digestion.

Villi increase the surface area of the small intestine. Digested nutrients enter blood or lymph and are then used by cells for energy, growth and repair.

A balanced diet provides nutrients in appropriate amounts according to age, activity and physiological needs. Nutrient deficiency can cause deficiency diseases.

Breathing is physical movement of air into and out of the lungs. Respiration is the cellular chemical process that releases energy from food.

Air passes through the nostrils, nasal cavity, pharynx, larynx, trachea and bronchi to the lungs, where bronchioles end in alveoli.

Alveoli are tiny air sacs with thin moist walls and a rich blood supply. Their large surface area makes gas exchange efficient.

During inspiration, the diaphragm contracts and thoracic volume increases, lowering pressure so air enters. During expiration, the reverse changes occur.

Oxygen diffuses from alveolar air into blood; carbon dioxide diffuses from blood into alveoli because of concentration/partial-pressure differences.

Most oxygen is carried by haemoglobin in red blood cells. Carbon dioxide is transported mainly in dissolved or chemically combined forms in blood.

Smoking and air pollution can damage respiratory surfaces and reduce efficient gas exchange. Avoiding tobacco smoke and maintaining clean air protect respiratory health.

Blood consists of plasma, red blood cells, white blood cells and platelets. Plasma transports dissolved substances; blood cells perform specialised functions.

RBCs contain haemoglobin and transport oxygen. Their biconcave shape and lack of a nucleus in mature human RBCs aid their function.

WBCs protect the body against infection through mechanisms including phagocytosis and antibody-related responses.

Platelets help blood clotting and reduce blood loss after injury.

The heart is a muscular organ with four chambers: right and left atria and right and left ventricles. Valves help keep blood flowing in one direction.

Humans have pulmonary circulation between heart and lungs and systemic circulation between heart and body. Blood passes through the heart twice in one complete circuit.

Arteries carry blood away from the heart, veins carry blood toward it, and capillaries allow exchange between blood and tissues.

Blood pressure is the force of blood against vessel walls; pulse is the rhythmic expansion of arteries caused by heartbeats.

Excretion removes metabolic waste products from the body. It is different from egestion, which is removal of undigested food.

Kidneys filter blood and form urine while regulating water, salts and other substances.

A nephron is the functional unit of the kidney. Filtration occurs at the glomerulus and Bowman's capsule, followed by selective reabsorption along the renal tubule.

Useful substances and much water are reabsorbed from the filtrate according to the body's needs. Remaining waste forms urine.

Urine passes from kidneys through ureters to the urinary bladder and leaves the body through the urethra.

Lungs remove carbon dioxide and water vapour; skin removes sweat; the liver processes various substances and contributes to detoxification.

Adequate hydration, balanced nutrition and timely medical care support urinary-system health. Kidney stones and renal failure are important disorders.

Coordination allows different organs to work together and enables the body to respond appropriately to internal and external changes.

A neuron is the structural and functional unit of the nervous system. Dendrites receive impulses, the cell body processes them and the axon carries impulses away.

The brain and spinal cord form the central nervous system. The brain interprets information and coordinates responses.

Nerves connecting the central nervous system with receptors and effectors form the peripheral nervous system.

A reflex action is a rapid, automatic response to a stimulus. The reflex arc commonly involves receptor, sensory neuron, relay neuron, motor neuron and effector.

Eyes, ears, nose, tongue and skin contain receptors that detect stimuli such as light, sound, chemicals, temperature and touch.

The skull, vertebral column, meninges and cerebrospinal fluid protect the central nervous system.

Hormones are chemical messengers released by endocrine glands into the blood. They act on target organs or tissues and help coordinate body functions.

The pituitary is an important endocrine gland whose hormones influence growth and the activity of other endocrine glands.

The thyroid produces thyroxine, which influences metabolism. Iodine is needed for normal thyroid hormone production.

The endocrine part of the pancreas produces insulin and glucagon, which help regulate blood glucose.

Adrenal hormones help the body respond to stress and influence metabolism and salt-water balance.

Nervous control is generally rapid; hormonal control is generally slower but can last longer. Together they coordinate body functions.

Asexual reproduction involves a single parent and usually produces genetically similar offspring. Sexual reproduction involves fusion of male and female gametes and creates variation.

The testes produce sperm and male sex hormones. Sperm travel through ducts and are released with secretions forming semen.

The ovaries produce ova and female sex hormones. The oviduct, uterus, cervix and vagina have specialised roles in reproduction.

The menstrual cycle involves maturation of an ovum, changes in the uterine lining and hormonal regulation. If fertilisation does not occur, the lining is shed.

Fertilisation is fusion of male and female gametes to form a zygote, usually occurring in the oviduct.

The developing embryo implants in the uterine lining. The placenta allows exchange of nutrients, gases and wastes between maternal and foetal blood without their blood directly mixing.

Puberty involves hormonal changes that produce physical and reproductive maturity. Personal hygiene and responsible health practices are essential.

A population is a group of individuals of the same species living in a particular area. Population size changes through births, deaths, immigration and emigration.

An ecosystem consists of living organisms interacting with one another and with non-living components such as air, water, soil and light.

A food chain shows transfer of food and energy from producers to consumers. A food web links several food chains and shows interdependence.

Air, water, soil, forests, minerals and wildlife are resources used by organisms and humans. Sustainable use prevents depletion.

Air, water, soil and noise pollution can disturb ecosystems and harm health. Prevention and control are more effective than relying only on cleanup.

Conservation protects biodiversity and natural resources through habitat protection, afforestation, reduced waste and responsible use.

Reducing unnecessary consumption, pollution and habitat destruction supports sustainable living and ecological balance.