Focused Biology chapters — Life Processes, Control, Reproduction, Heredity.
Nutrition, Respiration, Transportation, Excretion
Nervous system, Hormones, Brain, Spinal cord
Asexual reproduction, Sexual reproduction
Mendel's laws, Inherited traits, Sex determination
In multicellular organisms, the body is large and complex. Diffusion can only work over short distances. Oxygen cannot reach all parts of the body by diffusion alone. Therefore, multicellular organisms need specialized organs (like lungs, heart, blood vessels) for efficient transport of oxygen and nutrients.
The raw materials for photosynthesis are:
• Carbon dioxide (CO₂) — from the atmosphere through stomata
• Water (H₂O) — absorbed from soil through roots
• Sunlight — energy source for the reaction
Respiration:
• Biological process in living cells
• Enzyme-catalysed
• Releases energy gradually
• Produces ATP
Combustion:
• Chemical process (burning)
• No enzymes involved
• Releases energy suddenly as heat and light
• No ATP production
The heart is a pumping organ that:
• Pumps deoxygenated blood to the lungs for oxygenation
• Pumps oxygenated blood to all body parts
• It is a four-chambered muscular organ
• Beats about 72 times per minute
• Ensures continuous flow of blood through double circulation
Arteries:
• Carry oxygenated blood (except pulmonary artery)
• Carry blood away from heart
• Thick walls, no valves
• Blood flows under high pressure
Veins:
• Carry deoxygenated blood (except pulmonary vein)
• Carry blood towards heart
• Thin walls, have valves
• Blood flows under low pressure
Nephrons are the functional units of the kidney. They:
• Filter blood to remove waste products
• Form urine through filtration and reabsorption
• Maintain water and salt balance in the body
• Reabsorb useful substances like glucose, amino acids
• Each kidney has about 1 million nephrons
Aerobic respiration:
• Requires oxygen
• Complete breakdown of glucose
• Produces CO₂ + H₂O + 38 ATP
• Takes place in mitochondria
Anaerobic respiration:
• Does NOT require oxygen
• Incomplete breakdown of glucose
• Produces ethanol + CO₂ + 2 ATP (in yeast)
• Takes place in cytoplasm
Plants transport through two types of tissues:
• Xylem: Transports water and minerals from roots to leaves (unidirectional — upward)
• Phloem: Transports food (sugars) from leaves to other parts (bidirectional — downward and upward)
Xylem transport is driven by root pressure and transpiration pull.
Reflex action:
• Involuntary and automatic
• Does not involve the brain
• Very fast response
• Controlled by spinal cord
Thinking:
• Voluntary and conscious
• Involves the cerebral cortex
• Slow process
• Involves memory, analysis, and decision-making
Parts of the brain:
• Cerebrum: Controls thinking, memory, reasoning, voluntary actions
• Cerebellum: Controls balance, posture, and coordination of movements
• Medulla oblongata: Controls involuntary actions — breathing, heartbeat, blood pressure
• Hypothalamus: Controls hunger, thirst, sleep, body temperature
• Pons: Relays messages between parts of the brain
A neuron (nerve cell) is the structural and functional unit of the nervous system.
Structure:
• Cell body: Contains nucleus and cytoplasm
• Dendrites: Short, branched extensions that receive signals
• Axon: Long extension that carries impulses away from cell body
• Myelin sheath: Insulating layer around axon for faster signal transmission
• Synapse: Gap between two neurons where neurotransmitters are released
Hormones: Chemical messengers secreted by endocrine glands that regulate body functions.
Differences:
• Nervous control: Fast, short-lived, through electrical impulses, specific target
• Hormonal control: Slow, long-lasting, through blood, widespread effects
Hormones control growth, metabolism, reproduction, mood, and development.
Major endocrine glands:
• Pituitary gland: "Master gland" — controls other glands
• Thyroid gland: Produces thyroxine (metabolism)
• Adrenal glands: Produce adrenaline (emergency hormone)
• Pancreas: Produces insulin (blood sugar regulation)
• Testes: Produce testosterone (male hormones)
• Ovaries: Produce estrogen and progesterone (female hormones)
When frightened:
• Adrenaline is secreted by adrenal glands
• Heart rate increases
• Blood pressure rises
• Blood is directed to muscles
• Pupils dilate to see more
• Breathing rate increases
• This prepares the body for "fight or flight" response
The human eye works by:
• Light enters through the cornea
• Iris controls the size of the pupil
• Lens focuses light on the retina
• Retina has rod and cone cells — rods for dim light, cones for colour
• Image is formed inverted on retina
• Optic nerve sends signals to brain
• Brain interprets the image as erect
Plant hormones:
• Called phytohormones
• Produced in growing regions
• No specific glands
• Examples: Auxin, Gibberellin, Cytokinin, Abscisic acid, Ethylene
Animal hormones:
• Produced by endocrine glands
• Transported through blood
• Have specific target organs
• Examples: Insulin, Adrenaline, Thyroxine
Reproduction is important because:
• Ensures continuation of species
• Introduces variation in population
• Variation helps in adaptation to changing environment
• Without reproduction, species would become extinct
Asexual reproduction:
• Only one parent involved
• No gamete formation
• No fertilization
• Offspring are identical (clones)
• Examples: Budding, fragmentation, binary fission
Sexual reproduction:
• Two parents involved
• Gametes are formed
• Fertilization occurs
• Offspring show variation
• More genetic diversity
Binary fission is a type of asexual reproduction where a single parent cell divides into two equal halves.
Examples:
• Amoeba — divides into two
• Leishmania — longitudinal binary fission
• Bacteria — divide by binary fission
• Plasmodium — multiple fission
Budding is a type of asexual reproduction where a new organism develops from an outgrowth (bud) on the parent.
Examples:
• Hydra — bud grows and detaches
• Yeast — reproduces by budding
• Sponge — can reproduce by budding
Fragmentation is a type of asexual reproduction where the body of an organism breaks into two or more fragments, each developing into a new organism.
Examples:
• Spargana (flatworm)
• Starfish — can regenerate from arm fragments
• Spirogyra — filament breaks into fragments
Vegetative propagation is a type of asexual reproduction in plants where new plants are produced from roots, stems, leaves, or buds.
Advantages:
• Faster growth than seed propagation
• Plants are genetically identical (uniform quality)
• Plants can be produced year-round
• Useful for plants that don't produce viable seeds
Examples: Potato (tuber), Ginger (rhizome), Sugarcane (stem), Bryophyllum (leaf buds)
Methods of contraception:
• Barrier method: Condoms, diaphragm (prevent sperm entry)
• Oral contraceptive pills: Prevent ovulation
• IUD (Intrauterine Device): Copper-T prevents implantation
• Surgical methods: Vasectomy (male), Tubectomy (female)
• Natural methods: Periodic abstinence, withdrawal
• Emergency contraception: Morning-after pill
Boys:
• Voice becomes deeper
• Muscles develop
• Facial hair grows
• Testosterone increases
• Shoulders broaden
Girls:
• Menstruation begins
• Breasts develop
• Hips widen
• Estrogen increases
• Body becomes more rounded
Reproductive health is important because:
• Prevents sexually transmitted diseases (STDs)
• Ensures safe pregnancy and childbirth
• Reduces maternal and infant mortality
• Helps in family planning
• Promotes physical and mental well-being
• Awareness helps prevent unwanted pregnancies
Mendel crossed tall pea plants (TT) with dwarf pea plants (tt). In the F₁ generation, all plants were tall (Tt). This showed that:
• The tall trait is dominant (expressed even when one copy is present)
• The dwarf trait is recessive (expressed only when two copies are present)
When F₁ plants were self-crossed, F₂ generation showed both tall and dwarf in ratio 3:1.
Mendel's dihybrid cross showed independent inheritance:
• He crossed plants with two different traits (round-yellow vs wrinkled-green seeds)
• In F₂ generation, he got four types of offspring in ratio 9:3:3:1
• This showed that the inheritance of one trait (shape) is independent of another trait (colour)
• This is called the Law of Independent Assortment
A gene is a unit of heredity that is transferred from parent to offspring. It is a segment of DNA that codes for a specific trait.
Role:
• Determines physical characteristics
• Controls enzyme production
• Responsible for inherited traits
• Genes exist in pairs (alleles) on chromosomes
• Each parent contributes one allele for each trait
Types of variation:
• Somatic variation: Occurs in body cells, not inherited (e.g., scars, muscles)
• Germinal/Gametic variation: Occurs in reproductive cells, inherited
• Continuous variation: Gradual differences (e.g., height, skin colour)
• Discontinuous variation: Distinct categories (e.g., blood group, eye colour)
• Mutation: Sudden, heritable changes in DNA
Sex determination in humans:
• Humans have 23 pairs of chromosomes (46 total)
• 22 pairs are autosomes, 1 pair is sex chromosomes
• Females have XX chromosomes
• Males have XY chromosomes
• The father determines the sex of the child
• If X sperm fertilizes egg → Girl (XX)
• If Y sperm fertilizes egg → Boy (XY)
• Probability is 50:50 for each child
Mendel's laws:
• Law of Dominance: In a pair of contrasting traits, one is dominant and the other recessive
• Law of Segregation: Two alleles of a gene separate during gamete formation, each gamete gets only one allele
• Law of Independent Assortment: Genes of different traits are inherited independently of each other
A Punnett square is a diagram used to predict the outcome of a genetic cross. It shows all possible combinations of alleles from two parents.
For example, Tt x Tt cross:
It shows the genotypic ratio (1:2:1) and phenotypic ratio (3:1).
Genotype: The genetic makeup of an organism (the alleles it carries). Example: TT, Tt, tt.
Phenotype: The observable physical characteristics of an organism. Example: Tall, Dwarf.
Genotype determines phenotype, but environment can also influence phenotype.