Life Sciences Grade 12 Term 2 Vocabulary

Vocabulary flashcards for Life Sciences Grade 12 Term 2 revision booklet, covering topics such as the nervous system, endocrine system, homeostasis, plant responses, and genetics.

Nervous System

Detects stimuli and allows the body to react to changes; coordinates body activities.

Central Nervous System

Consists of the brain and spinal cord, enclosed by the skull and vertebral column respectively, and protected by the meninges.

Brain

Organ protected by the skull, part of the central nervous system.

Spinal Cord

Pathway for nerve impulses to and from the brain; centre for reflex actions, protected by the vertebral column.

Peripheral Nervous System

Includes all nervous tissue outside the central nervous system, consisting of cranial and spinal nerves; it conducts impulses to and from the central nervous system.

Cranial Nerves

12 pairs of nerves that conduct impulses to and from the brain.

Spinal Nerves

31 pairs of nerves that conduct impulses to and from the brain and spinal cord.

Somatic Nervous System

Conducts nerve impulses from the central nervous system to voluntary muscles (e.g., running).

Autonomic Nervous System

Conducts nerve impulses from the central nervous system to involuntary muscles and glands (e.g., sneezing, blinking).

Sympathetic Division

Prepares the body for an emergency (e.g., increases heart rate, dilates pupils).

Parasympathetic Division

Allows the body to return to normal after an emergency (e.g., decreases heart rate, constricts pupils).

Neuron

Basic unit of the nervous system; sends and carries signals throughout the body.

Dendrites

Conduct nerve impulses to the cell body of a neuron.

Axons

Conduct nerve impulses away from the cell body of a neuron.

Myelin Sheath

Insulates nerve fibres and accelerates the transmission of nerve impulses; formed by Schwann cells.

Sensory Neurons

Transmit impulses from the receptors to the spinal cord (afferent).

Motor Neurons

Transmit impulses from the spinal cord to the effector organs (muscles/glands) (efferent).

Interneurons

Occur in the spinal cord and transmit impulses from the sensory neurons to the motor neurons.

Reflex Action

A quick, automatic response to a stimulus that does not involve the brain; protects the body from harm.

Reflex Arc

The pathway along which nerve impulses are conducted from a receptor to an effector to bring about a reflex action.

Synapse

Functional connection between the axon of one neuron and the dendrites of another neuron.

Alzheimer's Disease

A disorder where healthy neurons become less efficient, causing memory loss and confusion.

Multiple Sclerosis

Occurs when the body's immune system destroys the myelin sheaths of neurons, leading to loss of muscle control.

Binocular Vision

Combining two images from the left and right eye to form a single three-dimensional image.

Accommodation

Changes in the shape of the lens and eyeball to focus on objects at different distances.

Pupillary Mechanism

A reflex action that controls the amount of light entering the eye by adjusting the size of the pupil.

Short-sightedness

Near objects can be seen clearly, but distant objects appear blurred.

Long-sightedness

Distant objects can be seen clearly, but near objects appear blurred.

Astigmatism

Uneven curvature of the lens or cornea, resulting in distorted images.

Cataracts

Clouding of the lens, causing blurred vision.

Middle Ear Infection

Excess fluid in the middle ear caused by pathogens, leading to pain and potential tympanic membrane rupture.

Endocrine System

A coordinating system that uses hormones.

Endocrine Glands

Ductless glands that release hormones directly into the bloodstream.

Hormones

Organic compounds and chemical messengers secreted by endocrine glands.

Homeostasis

Maintaining a constant internal environment in the human body.

Negative Feedback Mechanisms

Detect changes in the internal environment and work to restore balance.

Thyroxin

Hormone regulated by TSH in a negative feedback mechanism.

Goitre

Enlargement of the thyroid gland due to iodine deficiency.

Insulin

Hormone that stimulates the conversion of excess glucose into glycogen.

Glucagon

Hormone that stimulates the conversion of stored glycogen into glucose.

Diabetes Mellitus

Metabolic disease characterized by high glucose levels in the blood.

Thermoregulation

Regulation of body temperature by the hypothalamus and skin structures.

Auxins

Plant hormones that stimulate cell elongation and cause tropisms.

Gibberellins

Plant hormones that stimulate stem elongation and promote flowering.

Abscisic Acid

Plant hormone that causes dormancy of buds and inhibits germination.

Phototropism

Growth movement of a plant in response to a unilateral light stimulus.

Geotropism

Growth movement of a plant in response to a gravitational stimulus.

Chromatin

Thread-like structures in the nucleus of a cell that form the chromosomes.

Chromatid

Each of the two threads of a replicated chromosome.

Gene

A segment of DNA in a chromosome that contains the code for a particular characteristic.

Alleles

Different forms of a gene which occur at the same locus on homologous chromosomes.

Dominant Allele

An allele that is expressed in the phenotype when found in heterozygous and homozygous conditions.

Recessive Allele

An allele that is masked in the phenotype when found in the heterozygous condition; only expressed in the homozygous condition.

Phenotype

The physical appearance of an organism determined by the genotype.

Genotype

Genetic composition (makeup) of an organism.

Homozygous

Two identical alleles for a particular characteristic (e.g., TT or tt).

Heterozygous

Two different alleles for a particular characteristic (e.g., Tt).

Monohybrid Cross

Genetic cross showing only one characteristic or trait.

Dihybrid Cross

Genetic cross showing two different characteristics.

Karyotype

The number, shape, and arrangement of all the chromosomes in the nucleus of a somatic cell.

Complete Dominance

One allele is dominant and the other is recessive, masking the effect of the recessive allele in the heterozygous condition.

Incomplete Dominance

None of the two alleles of a gene is dominant over the other, resulting in an intermediate phenotype in the heterozygous condition.

Co-dominance

Both alleles of a gene are equally dominant whereby both alleles express themselves in the phenotype in the heterozygous condition.

Sex Chromosomes

One pair of chromosomes that determine sex (gonosomes).

Autosomes

22 pairs of chromosomes in humans that are not sex chromosomes.

Multiple Alleles

More than two alternative forms of a gene at the same locus.

Genetic Lineages/Pedigrees

Traces the inheritance of characteristics over many generations.

Mutation

A permanent change to the DNA of a cell.

Gene Mutation

A change in the sequence of nitrogenous bases/nucleotides in a gene and can occur during DNA replication, transcription and crossing over.

Chromosomal Mutation

Occurs when meiosis does not occur normally, resulting in a change in the number or structure of chromosomes.

Genetic Engineering

The manipulation or transfer of genes from one organism to another to make products that satisfy human needs.

GMOs

Genetically modified organisms are the result of genetic engineering.

Stem Cells

Undifferentiated cells that have the ability to grow into any tissue in the body.

Cloning

The process where genetically identical organisms are produced.