Kerala SSLC Biology cheat sheet

Prokaryotic cells lack a membrane-bound nucleus and membrane-bound organelles; eukaryotic cells have both; ribosomes occur in both.

Cell theory: all living things are made of cells, the cell is the basic unit of life, and all cells arise from pre-existing cells.

Plant cells have a cellulose cell wall, a large central vacuole, and plastids; animal cells have centrioles and lack a cell wall.

Mitochondria are the site of aerobic respiration; chloroplasts carry out photosynthesis; ribosomes synthesise proteins; the Golgi apparatus packages and secretes materials.

Mitosis produces two genetically identical diploid daughter cells and maintains chromosome number; meiosis produces four haploid cells and halves it.

Meiosis has two divisions: homologous chromosomes separate in meiosis I, sister chromatids separate in meiosis II.

Crossing over occurs at chiasmata during prophase I of meiosis and increases genetic variation.

In plant mitosis cytokinesis occurs by cell plate formation; in animal cells it occurs by cleavage furrow formation.

A gene is a segment of DNA that codes for a protein or trait; alleles are alternative forms of a gene at the same locus.

Genotype is the allele combination; phenotype is the observable trait produced by genotype and environment.

Mendel's law of segregation: the two alleles of a gene separate during gamete formation, so each gamete carries one allele.

Monohybrid cross of two heterozygotes (Tt x Tt) gives a 3:1 phenotypic ratio and a 1:2:1 genotypic ratio.

A test cross with a homozygous recessive individual reveals whether a dominant phenotype is homozygous or heterozygous.

Sex-linked traits in humans are usually carried on the X chromosome; males (XY) express X-linked recessive traits more often than females.

DNA structure: double helix of two antiparallel strands, adenine pairs with thymine (two hydrogen bonds), guanine with cytosine (three).

In a DNA sample the percentage of adenine equals that of thymine, and guanine equals cytosine (Chargaff's rule).

Osmosis is the movement of water across a semipermeable membrane from low solute concentration to high solute concentration.

Root hair cells absorb water by osmosis and mineral ions by active transport; the Casparian strip forces water through the symplast pathway.

Transpiration pull, root pressure, and capillary action together move water up the xylem.

Stomata open when guard cells take up water and become turgid; they close when guard cells lose water and become flaccid.

Phloem transports sucrose and amino acids bidirectionally by translocation, driven by pressure flow from source to sink.

Turgor pressure in plant cells provides mechanical support; plasmolysis occurs when cells lose water in a hypertonic solution.

Human body temperature is regulated near 37 °C by the hypothalamus through sweating, vasodilation, shivering, and vasoconstriction.

Photosynthesis equation: 6CO2 + 6H2O → C6H12O6 + 6O2, requiring light energy absorbed by chlorophyll.

Light-dependent reactions occur in the thylakoid membranes and release oxygen by photolysis of water; the Calvin cycle occurs in the stroma.

Digestion of starch begins in the mouth by salivary amylase at pH near 7; protein digestion begins in the stomach by pepsin at pH 1.5–2.

Bile from the liver, stored in the gallbladder, emulsifies fats and neutralises acidic chyme; lipase then digests fats in the small intestine.

The ileum absorbs glucose and amino acids into blood capillaries and fatty acids and glycerol into lacteals of villi.

Enzymes are specific biological catalysts; their activity is reduced by extremes of temperature or pH due to denaturation.

Deficiency diseases: vitamin C deficiency causes scurvy, vitamin D deficiency causes rickets, iron deficiency causes anaemia.

Balanced diet components: carbohydrates and fats supply energy, proteins supply amino acids for growth and repair, vitamins and minerals regulate body processes.

Aerobic respiration equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + energy (about 38 ATP per glucose in theory).

Anaerobic respiration in muscle produces lactic acid with little energy; in yeast it produces ethanol and carbon dioxide.

Glycolysis occurs in the cytoplasm; the Krebs cycle and electron transport chain occur in the mitochondria.

Inhalation: diaphragm contracts and flattens, intercostal muscles raise the ribs, thoracic volume increases, pressure falls, air enters.

Alveoli provide a large surface area, thin walls, moist surface, and rich blood supply for efficient gas exchange.

Gaseous exchange in plants occurs through stomata in leaves and lenticels in stems.

Haemoglobin in red blood cells combines with oxygen in the lungs and releases it in respiring tissues.

Limewater turns milky with carbon dioxide; this tests for CO2 produced in respiration.

Human heart: right side pumps deoxygenated blood to the lungs, left side pumps oxygenated blood to the body; the left ventricle wall is thicker.

Double circulation means blood passes through the heart twice per complete circuit, which maintains high pressure to body tissues.

Arteries carry blood away from the heart under high pressure with thick elastic walls; veins carry blood to the heart and have valves.

Capillaries are one cell thick to allow exchange of gases, nutrients, and wastes between blood and tissues.

Blood components: plasma transports dissolved substances, red cells carry oxygen, white cells defend against infection, platelets clot blood.

The SA node (pacemaker) initiates the heartbeat; the cardiac cycle includes atrial systole, ventricular systole, and diastole.

Blood groups: A has A antigen, B has B antigen, AB has both (universal recipient), O has neither (universal donor).

Transpiration stream in xylem moves water and minerals upward; root pressure and cohesion-tension explain its ascent.

The nephron is the functional unit of the kidney; it includes the glomerulus, Bowman's capsule, proximal tubule, loop of Henle, distal tubule, and collecting duct.

Ultrafiltration in the glomerulus removes water, glucose, salts, and urea from blood; proteins and blood cells remain.

Selective reabsorption in the proximal tubule returns all glucose, most water, and useful salts to the blood; urea remains for excretion.

ADH from the posterior pituitary increases water reabsorption in the collecting duct, producing concentrated urine.

The kidney regulates blood water potential, salt balance, pH, and blood pressure, and removes urea and excess salts.

Dialysis removes urea and excess salts using a selectively permeable membrane; it does not replace the endocrine functions of the kidney.

Plants excrete wastes by shedding leaves, storing resins and gums in old xylem, and releasing CO2 and water through stomata.

A reflex arc pathway: receptor → sensory neurone → relay neurone in spinal cord → motor neurone → effector.

The synapse is a junction between neurones; the impulse crosses via neurotransmitters released into the synaptic cleft.

The cerebrum controls voluntary action, memory, and intelligence; the cerebellum controls balance and coordination; the medulla controls heartbeat and breathing.

The myelin sheath insulates axons and speeds up impulse conduction.

Endocrine glands secrete hormones into the blood; the pituitary is the master gland controlling other glands.

Insulin from the pancreas lowers blood glucose by promoting uptake and glycogen storage; glucagon raises it.

Adrenaline from the adrenal glands raises heart rate and breathing rate and prepares the body for 'fight or flight'.

Thyroxine from the thyroid gland regulates metabolic rate; iodine is required for its synthesis.

Tropisms: phototropism is growth towards light, geotropism is growth in response to gravity; auxin mediates both.

Mitosis produces growth and repair cells; meiosis produces gametes with half the chromosome number.

Human male gamete is the sperm (haploid, motile); the female gamete is the ovum (haploid, large, non-motile).

Fertilisation forms a diploid zygote; implantation occurs in the uterus wall after cleavage to a blastocyst.

The placenta allows exchange of nutrients, oxygen, and wastes between mother and fetus; the umbilical cord connects them.

Menstrual cycle: FSH stimulates follicle development, LH triggers ovulation around day 14, progesterone maintains the uterine lining.

Pollination is transfer of pollen to stigma; fertilisation in plants forms a zygote and a triploid endosperm.

Double fertilisation occurs in angiosperms; one sperm fertilises the egg, the other fuses with polar nuclei.

Asexual reproduction produces genetically identical offspring (clones); examples include binary fission, budding, and vegetative propagation.

A food chain begins with producers; energy flows from producers to consumers and is lost as heat at each trophic level.

Only about 10% of energy passes to the next trophic level; this limits food chain length.

Decomposers break down dead matter and return nutrients to the soil; they are essential for nutrient cycling.

Biotic factors include predators and competitors; abiotic factors include light, temperature, and water.

Biodiversity is the variety of species and ecosystems; loss is caused by habitat destruction, pollution, overexploitation, and invasive species.

Carbon cycle: photosynthesis removes CO2, respiration and combustion release it; excess CO2 contributes to the greenhouse effect.

Nitrogen cycle: nitrogen fixation by bacteria such as Rhizobium, nitrification, assimilation, and denitrification.

Ecological pyramids of numbers, biomass, and energy represent trophic relationships; the pyramid of energy is always upright.