SSC Biology Visual Guide

Chapter 0 · Foundation

Cell recap (कोशिका)

The cell is the structural and functional unit of life (जीव जीवन की संरचनात्मक एवं कार्यात्मक इकाई). All life processes — nutrition, respiration, transport, excretion — happen inside cells or by organised groups of cells (tissues and organs).

Cell — smallest living unit that can carry out life processes Organelle — specialised structure inside a cell Tissue — group of similar cells

Plant cell vs animal cell

Chapter 1 · NCERT Life Processes

Life processes (जीवन प्रक्रियाएँ)

Living organisms must maintain life by taking in materials, releasing energy, transporting substances and removing wastes. These maintenance functions are life processes: nutrition (पोषण), respiration (श्वसन), transportation (परिवहन) and excretion (उत्सर्जन). Growth and reproduction also occur, but maintenance comes first — a machine that is not maintained stops working.

Nutrition (पोषण)

Nutrition is the process of taking in food and converting it into energy and body materials. Two broad modes:

Photosynthesis

Green plants use chlorophyll (in chloroplasts), sunlight, water and carbon dioxide to make glucose and release oxygen.

Light reactions (grana / thylakoid, need light):

• Chlorophyll absorbs sunlight; water splits (photolysis) → H⁺, e⁻ and O₂ (oxygen is released).
• Energy is stored as ATP.
• Hydrogen is accepted as NADPH (reducing power) for the dark reaction.

Dark reactions (stroma, do not need light directly, but need ATP + NADPH from light reaction):

• CO₂ is taken in through stomata and fixed into a carbon compound.
• ATP and NADPH reduce the carbon compound.
• Glucose (C₆H₁₂O₆) is formed; it may be stored as starch.

Do not write the full Calvin-cycle names in SSC unless asked — “CO₂ reduced to glucose using ATP and NADPH” is enough.

Stomata (रंध्र) and transpiration (बाष्पोत्सर्जन)

Stomata are pores, mainly on the lower epidermis of dicot leaves. Each pore is guarded by two kidney-shaped guard cells that contain chloroplasts. When K⁺ ions enter guard cells, water follows by osmosis; cells become turgid and the pore opens. When K⁺ and water leave, cells become flaccid and the pore closes. Opening in day allows CO₂ in; closing at night or in drought reduces water loss.

Transpiration is loss of water vapour from aerial parts, mainly through stomata. It creates a transpiration pull that helps xylem (दारु) lift water. It also cools the plant.

Nutrition in Amoeba

Amoeba shows holozoic nutrition. It captures food with pseudopodia (false feet) by phagocytosis. A food vacuole forms; enzymes digest the food; undigested remains are egested.

Human alimentary canal and enzymes (उत्प्रेरक)

Humans show holozoic nutrition: ingestion → digestion → absorption → assimilation → egestion. Digestion is mostly enzymatic and extracellular in a long tube — the alimentary canal — helped by glands.

Respiration (श्वसन)

Food is broken down to release energy that is stored as ATP. Do not confuse breathing (mechanical intake/outflow of air) with cellular respiration (biochemical oxidation of food in cells, mainly mitochondria).

Transportation (परिवहन)

In plants

Translocation (pressure flow) in 3 steps:

• Loading: sucrose is actively loaded into phloem at the source (leaf). Water follows by osmosis → high pressure.
• Flow: pressure pushes the sap through sieve tubes towards the sink (root, fruit, growing tip).
• Unloading: sucrose is removed at the sink; pressure falls. Water may return to xylem.

Human heart (sectional)

The heart is a muscular pump with four chambers. The septum stops oxygenated and deoxygenated blood mixing. Valves keep one-way flow. In Indian board diagrams the heart is drawn as if facing you: anatomical left is on the right side of the page.

Blood vessels

Excretion (उत्सर्जन)

Excretion is the removal of metabolic wastes (urea, extra water, salts, CO₂). The main nitrogenous waste in humans is urea, made in the liver (ornithine cycle — name not required for SSC) and filtered by kidneys.

Nephron (नेफ्रॉन)

The nephron is the structural and functional unit of the kidney. Each kidney has about one million nephrons. A nephron has a filtering head (Bowman’s capsule + glomerulus = Malpighian body) and a long tubule (PCT, loop of Henle, DCT) opening into a collecting duct.

• Ultrafiltration: high blood pressure in the glomerulus forces water, urea, salts and glucose into Bowman’s capsule. Blood cells and proteins stay in blood (too large).
• Selective reabsorption: useful substances (all glucose, most amino acids, much water and salts) are reabsorbed from the tubule, mainly in the PCT, back into blood. Amount of water reabsorbed depends on body need (ADH).
• Secretion: extra ions, drugs and remaining wastes may be secreted into the tubule. Remaining fluid is urine, which flows to the collecting duct → pelvis → ureter.

Chapter 2 · NCERT Control and Coordination

Control and coordination (नियंत्रण एवं समन्वय)

Animals coordinate with a nervous system (fast, electrical + chemical) and an endocrine system (slower, hormones in blood). Plants coordinate mainly with hormones (हार्मोन) and tropisms (अनुवर्तन). A stimulus is detected by a receptor; a response is produced by an effector (muscle or gland).

Neuron (तंतुकोशिका)

The neuron is the structural and functional unit of the nervous system. Information travels as an electrical impulse along the axon, then as a chemical signal at the synapse (सैनैप्स).

Synapse — gap between axon terminal of one neuron and dendrite of the next; neurotransmitter (e.g. acetylcholine) crosses it

Reflex arc (प्रतिवर्तन चाप)

A reflex is a sudden, involuntary response to a stimulus (knee-jerk, pulling hand from a hot object). It is protective and often processed in the spinal cord, so the brain is informed but not required for the first action.

Path: receptor → sensory neuron → spinal cord (association / relay neuron) → motor neuron → effector.

Human brain

The brain is protected by the cranium, meninges and cerebrospinal fluid. It is the main coordinating centre along with the spinal cord (CNS).

Plant tropisms (अनुवर्तन) and hormones

A tropism is a directional growth movement in response to a stimulus. Shoots are generally positively phototropic and negatively geotropic; roots are positively geotropic and hydrotropic.

Auxin (ऑक्सिन) and phototropism: light from one side causes auxin to accumulate on the shaded side of the shoot tip. Cells there elongate more, so the shoot bends towards the light.

Endocrine glands

Endocrine glands are ductless; they pour hormones into blood. Hormones are chemical messengers that act on target organs.

Chapter 3 · NCERT How do organisms reproduce?

How do organisms reproduce (जीव कैसे प्रजनन करते हैं)

Reproduction makes new individuals of the same species so that life continues. Before a cell divides, it must make a copy of its DNA so that the offspring get a blueprint similar to the parent. DNA copying is not always perfect — small differences create variation (विभिन्नता), which is useful for survival of the population if the environment changes.

Asexual modes

Sexual reproduction in flowering plants

The flower is the reproductive organ. Stamen = male (anther + filament). Pistil / carpel = female (stigma + style + ovary with ovules).

Pollination (परागण) is transfer of pollen from anther to stigma (self or cross; wind, water, insects). Fertilisation (निषेचन) is fusion of male gamete with the egg to form a zygote.

Human reproductive systems (board-exam outlines)

Humans reproduce sexually. Gametes are produced by meiosis so that chromosome number is restored at fertilisation (23 + 23 = 46).

If sperm meets the egg in the oviduct, a zygote forms, divides into a ball of cells, and implants in the uterus. If the egg is not fertilised, the thick uterine lining sheds — menstruation — about once in 28 days from puberty to menopause. This is a normal biological cycle, not an illness.

Reproductive health

Reproductive health means physical, emotional and social well-being in matters of reproduction. Preventing unwanted pregnancy and sexually transmitted infections is part of the SSC syllabus.

Chapter 4 · NCERT Heredity

Heredity (अनुवंशिकता)

Heredity is the passing of traits from parents to offspring through genes. Variation is the difference between individuals of a species. Traits are carried by genes on chromosomes (DNA). Sexual reproduction mixes genes, so siblings are not identical (except identical twins).

Do not describe evolution as a ladder from “lower” to “higher” life. Populations change because variation already exists and natural selection filters which variants leave more offspring in a given environment. That is not progress towards a goal; it is survival and reproduction in that place and time.

Mendel and the pea plant

Gregor Mendel used garden pea (Pisum sativum) because: (1) many clear contrasting traits (tall/dwarf, round/wrinkled, yellow/green cotyledon…), (2) short life cycle and many offspring, (3) bisexual flowers that can be self- or cross-pollinated, (4) true-breeding lines were available.

Dominant — trait that appears in F₁ (T, tall) Recessive — hidden in F₁, reappears in F₂ (t, dwarf) Genotype — genetic make-up (Tt) Phenotype — visible trait (tall) Homozygous — TT or tt Heterozygous — Tt

Monohybrid cross (one trait): F₂ phenotype ratio 3 : 1. Dihybrid (two traits): F₂ phenotype ratio 9 : 3 : 3 : 1. Independent assortment: alleles of different genes separate independently during gamete formation (true when genes are on different chromosomes).

Sex determination in humans

Humans have 23 pairs of chromosomes: 22 pairs of autosomes + 1 pair of sex chromosomes. Females are XX; males are XY. The mother always contributes an X. The father contributes either X or Y — so the sperm decides the sex, each with a 50% chance. There is no scientific basis for blaming the mother for the child’s sex.

Chapter 5 · NCERT Our Environment

Our environment (हमारा पर्यावरण)

An ecosystem (परिस्थितिकी तंत्र) is a community of living organisms (biotic) interacting with non-living surroundings (abiotic: sunlight, temperature, water, soil, air) in a given area. A garden, a pond, a forest and even an aquarium are ecosystems.

Ozone (ओज़ोन), waste and the 3Rs