Grade 12 Biology: Nervous System, Genetics, Angiosperms, and Sense Organs

Comprehensive vocabulary flashcards covering nervous system organization, DNA and genetics, angiosperm plant biology, and human sensory structures based on Grade 12 Biology lecture notes.

Neuron

The fundamental cellular unit of the nervous system responsible for transmitting information or nerve impulses.

Nerve Impulse

The electrochemical message carried by a neuron, originating in the dendrites, traveling across the cell body, and descending along the axon to the axon terminal.

Unipolar Neuron

A neuron that possesses a single short extension branching directly from its cell body.

Bipolar Neuron

A neuron characterized by two parallel extensions emerging from opposite poles of the cell body: one dendrite and one axon.

Multipolar Neuron

A neuron possessing multiple slender dendrites extending from the cell body and a single long, large axon, commonly functioning as a motor neuron.

Sensory Neuron

A neuron that conducts nerve impulses from sensory receptors toward the central nervous system.

Motor Neuron

A neuron that transmits commands and nerve impulses from the central nervous system outward to effector organs such as muscles and glands.

Interneuron

A specialized neuron located within the central nervous system that relays impulses between sensory neurons and motor neurons.

Central Nervous System (CNS)

The division of the nervous system composed of the brain and spinal cord, functioning to receive, interpret, and integrate sensory information.

Peripheral Nervous System (PNS)

All nervous tissues situated outside the brain and spinal cord, comprising $12$ pairs of cranial nerves and $31$ pairs of spinal nerves.

Cerebrum

The largest brain division, split by a deep central groove into left and right hemispheres (each featuring frontal, parietal, temporal, and occipital lobes), responsible for sensory interpretation, reasoning, intelligence, and conscious responses.

Cerebellum

A structure located beneath the posterior cerebrum consisting of two hemispheres; it monitors voluntary movements, controls certain involuntary actions, and coordinates motor balance.

Brainstem (Medulla Oblongata)

The lower stalk-like region of the brain responsible for regulating autonomic, involuntary vital activities within the body.

White Matter

Nervous tissue composed primarily of myelinated nerve fibers (axons) within the brain and spinal cord.

Gray Matter

Nervous tissue composed primarily of interneurons and motor neuron cell bodies located within the central nervous system.

Reflex Action

A rapid, involuntary, automatic motor response to a stimulus executed via the spinal cord without immediate conscious participation of the brain.

Somatic Nervous System

A subdivision of the peripheral nervous system that connects the central nervous system to skeletal (striated/voluntary) muscles to regulate conscious activities like running and writing.

Autonomic Nervous System

A subdivision of the peripheral nervous system connecting the central nervous system to smooth muscles and cardiac muscle, partitioned into the sympathetic and parasympathetic systems.

Sympathetic Nervous System

The division of the autonomic nervous system activated during stress or emergency conditions, acting to accelerate heart rate and elevate blood pressure.

Parasympathetic Nervous System

The division of the autonomic nervous system that opposes the sympathetic system by returning bodily functions to their baseline resting state.

Cerebrospinal Fluid

A protective fluid occupying the subarachnoid space and ventricles that absorbs physical shocks and transports nutrients, oxygen, glucose, white blood cells, and hormones to neural tissues.

DNA (Deoxyribonucleic Acid)

The hereditary molecular carrier composed of nucleotide sequences that preserve and transmit genetic information across generations.

Chromosome

A dense nuclear network of fine chromatin fibers composed of DNA and associated proteins that houses hereditary instructions.

Pneumococcus

A pathogenic bacterium causing pneumonia that exists in two distinct forms: a virulent encapsulated $S$ (smooth) strain and a non-virulent unencapsulated $R$ (rough) strain.

Griffith's Experiment

The historical experiment where mice died after being injected with a mixture of heat-killed virulent $S$ bacteria and living non-virulent $R$ bacteria, discovering the transformation of genetic material.

Avery, MacLeod, and McCarty Experiment

The biochemical study establishing that DNA extracted from virulent $S$ bacteria transformed non-virulent $R$ bacteria into the $S$ type, identifying DNA as the transforming molecule.

Hershey and Chase Experiment

An experiment utilizing bacteriophages labeled with radioactive sulfur ($^{35}\text{S}$) on protein coats and radioactive phosphorus ($^{32}\text{P}$) on DNA, proving viral DNA enters host cells to direct reproduction.

Nucleotide

The basic monomeric building block of DNA, consisting of one molecule of phosphoric acid, one deoxyribose sugar, and one nitrogenous base.

Purines

Double-ring nitrogenous bases found in nucleic acids, specifically Adenine ($A$) and Guanine ($G$).

Pyrimidines

Single-ring nitrogenous bases found in DNA, specifically Thymine ($T$) and Cytosine ($C$).

Chargaff's Rules

Base pairing principles establishing that within double-stranded DNA, the percentage of $A = T$ and $C = G$, meaning purines ($A + G = 50\%$) equal pyrimidines ($T + C = 50\%$).

Watson-Crick Model

The structural representation of DNA as an antiparallel double helix with a diameter of $2\,\text{nm}$, stabilized by complementary hydrogen bonds ($A=T$ with $2$ bonds, $C\equiv G$ with $3$ bonds).

DNA Polymerase

The enzyme responsible for unwinding double-stranded DNA and attaching free complementary nucleotides to each template strand during replication.

Semiconservative Replication

The DNA synthesis mechanism where each newly formed daughter molecule conserves one intact parental strand and incorporates one newly synthesized complementary strand.

Angiosperms

Flowering vascular plants whose seeds develop enclosed within an ovary or protective fruit tissue.

Monocotyledons (Monocots)

Angiosperms characterized by a single cotyledon, parallel leaf venation, trimerous ($3$-part) floral organs, fibrous root systems, and scattered vascular bundles in stems.

Dicotyledons (Dicots)

Angiosperms possessing two cotyledons, net-veined (reticulate) leaves, tetramerous or pentamerous ($4$ or $5$-part) flowers, a primary taproot system, and ring-arranged stem vascular bundles.

Xylem

Vascular plant tissue responsible for conducting water and dissolved mineral nutrients upward from roots to stems and leaves.

Phloem

Vascular plant tissue specialized for transporting synthesized organic food materials (sugars) from photosynthesizing leaves to all living plant cells.

Vascular Cambium

The meristematic cellular layer located between xylem and phloem in vascular bundles that divides to generate secondary xylem and phloem.

Palisade Layer

A densely packed layer of elongated leaf mesophyll cells containing numerous chloroplasts rich in chlorophyll, serving as the primary site of photosynthetic carbohydrate production.

Stamen

The male reproductive organ of a flower consisting of the anther, which produces pollen grains, supported by the filament.

Pistil (Carpel)

The female reproductive structure of a flower comprising a sticky stigma to catch pollen, an elongated style, and an ovary enclosing ovules.

Pollination

The transfer of mature pollen grains from the anther to the receptive sticky surface of the stigma, occurring either by self-pollination or cross-pollination.

Sporophyte

The diploid ($2n$) spore-producing generation in the plant alternation of generations lifecycle that originates from the mitotic development of a zygote.

Gametophyte

The haploid ($n$) gamete-producing generation in plants that develops through mitotic division from haploid microspores or megaspores.

Double Fertilization

A specialized angiosperm fertilization event wherein one sperm cell ($n$) unites with the egg cell ($n$) to form a diploid zygote ($2n$), while the second sperm cell ($n$) fuses with two polar nuclei to yield triploid endosperm ($3n$).

Endosperm

A nutrient-rich triploid ($3n$) tissue formed in angiosperm seeds that nourishes the developing embryo until it can photosynthesize independently.

Sclera

The tough, opaque, white outer fibrous tunic of the eyeball that maintains eye geometry and protects interior intraocular structures.

Choroid

The thin, darkly pigmented, vascular middle layer of the eyeball that absorbs scattered light rays and supplies oxygen and nutrients to the retina.

Retina

The innermost sensory layer of the eye containing photoreceptor cells (rods and cones), bipolar neurons, and ganglion cells that convert light energy into nerve impulses.

Cone Cells

Retinal photoreceptors concentrated in the central retina that function in bright light conditions to provide high visual acuity and color vision.

Rod Cells

Sensitive photoreceptor cells in the retina containing rhodopsin that mediate peripheral and monochromatic vision in low-light environments.

Macula (Yellow Spot)

The most sensitive central region of the retina, populated primarily by cones, responsible for distinct and colored visual perception.

Blind Spot

The region of the optic disc where the optic nerve exits the eyeball, entirely devoid of photoreceptors and thus incapable of image detection.

Aqueous Humor

The transparent fluid filling the anterior and posterior chambers between the cornea and lens, providing structural internal pressure and nourishment.

Vitreous Humor

The gelatinous transparent substance situated behind the crystalline lens in the vitreous cavity that maintains spherical eyeball shape.

Cochlea

The spiral, snail shell-shaped chamber within the inner ear containing auditory fluid and microscopic sensory hair cells that transduce sound vibrations into neural impulses.

Semicircular Canals

Three fluid-filled bony rings oriented perpendicularly in the inner ear that detect rotational acceleration to maintain body equilibrium.

Taste Buds

Chemosensory structures embedded in the mucosal papillae of the tongue that detect sweet, salty, sour, and bitter taste sensations.

Olfactory Epithelium

The specialized chemoreceptive mucous tissue in the upper nasal cavity containing supporting cells, basal cells, and olfactory receptor cells that detect gaseous chemical compounds.

Sebaceous Glands

Exocrine glands associated with hair follicles that secrete sebum, a lipid-rich protective barrier that limits moisture loss and inhibits bacterial and fungal proliferation.

Sweat Glands (Sudoriferous Glands)

Coiled tubular glands distributed across the dermis that secrete $500\text{--}600\,\text{mL}$ of sweat daily (composed of water, minerals, and urea) to achieve thermoregulation via evaporative cooling.

Melanin

The dark organic pigment synthesized by melanocytes located in the basal epidermis that dictates hair and skin coloration.