Terms and Definitions (Grade 12 NSC Matric Life Sciences): Revision Notes
Terms and Definitions
This comprehensive glossary contains essential biological terms and definitions for your Grade 12 Life Sciences studies. The terms are organized by topic-based sections to help you understand how concepts relate to one another and to make revision more efficient.
Molecular biology and DNA
Understanding the structure and function of DNA is fundamental to Life Sciences. These terms explain how genetic information is stored, copied, and used to make proteins. The double helix structure of DNA and the processes of replication, transcription, and translation form the foundation of molecular biology.
Nucleotide: The building blocks (or monomers) of nucleic acid.
Double Helix: The Natural shape of DNA
Base pair: linking of nitrogen bases on the complementary strand of the DNA by hydrogen bond
Complementary: Nitrogenous bases that always pair with each other joined by hydrogen bond in a DNA molecule.
Hydrogen bond: The bonds formed between two nitrogen bases.
The complementary base pairing in DNA follows a strict rule: Adenine (A) pairs with Thymine (T), and Cytosine (C) pairs with Guanine (G). This pairing is held together by hydrogen bonds, which are relatively weak bonds that can be easily broken during replication or transcription.
DNA Replication: The process during which a DNA molecule makes an exact copy (replica)
Interphase: The phase of meiosis through which DNA replication takes place.
DNA profile: An arrangement of black bars representing DNA fragments of the person.
mRNA: A bar code pattern formed from DNA
Protein synthesis is a two-step process:
- Transcription - DNA code is copied to mRNA in the nucleus
- Translation - mRNA code is used to assemble amino acids into proteins at the ribosome
Understanding the difference between these processes is crucial for exam success.
Protein synthesis: The process by which proteins are made in each cell of an organism.
Transcription: Process through which the mRNA makes a copy of the DNA code to form new proteins.
Translation: The process through which the tRNA brings specific amino acids to the mRNA.
Codon: The nitrogen base triplets on the mRNA.
Anticodon: The nitrogen base triplet on the tRNA.
Ribosome: The site for protein synthesis.
Nuclear pore: Openings in the nuclear membrane that allow mRNA to leave the nucleus
Peptide bond: The bonds formed between amino acids
Template: Strand of DNA upon which another strand of DNA is built from during replication or mRNA during Transcription
During protein synthesis, codons on mRNA pair with anticodons on tRNA, ensuring that the correct amino acids are brought to the ribosome in the proper sequence. Each set of three bases codes for one specific amino acid.
Cell division
Cell division is essential for growth, repair, and reproduction. Understanding the fundamental difference between mitosis and meiosis is crucial for your studies: mitosis produces two identical diploid cells, while meiosis produces four genetically different haploid cells.
Mitosis: Cell division in which a diploid cell undergoes cell division to form two identical cells
Meiosis: Cell division whereby a diploid cell undergoes two cell division to form four different cells.
Somatic cell: All cells in the body other than the sex cell (sperm cell/egg cell)
Diploid: A cell with two set of chromosomes.
Haploid: A cell with a single set of chromosome.
Key distinction: Mitosis occurs in somatic (body) cells for growth and repair, producing genetically identical cells. Meiosis occurs only in sex cells (gametes), producing genetically different cells for sexual reproduction. This difference is essential for understanding inheritance patterns.
Cytokinesis: Division of the cytoplasm.
Karyokinesis: Division of the nucleus.
Chromosome: The structure that is made up of two chromatids joined by a centromere
Chromatid: One half of a double-stranded chromosome
Centromere: The structure that joins the two halves of a double-stranded chromosome
Daughter chromosome: A single-stranded chromosome formed during Anaphase
Homologous chromosome: A pair of chromosomes, one inherited from each parent, that have the same genes at the same Locus
Understanding chromosome structure: A chromosome consists of two chromatids joined at the centromere. During cell division, these chromatids separate to form individual daughter chromosomes. Homologous chromosomes are pairs - one from each parent - that carry genes for the same characteristics.
Prophase I: The phase in meiosis where crossing over occurs
Anaphase I: The phase of meiosis during which homologous chromosomes separate and start moving towards opposite poles
Chiasma: point of contact between two chromosomes of a homologous pair during crossing over
Karyotype: The number, shape and the arrangement of all the chromosomes in a nucleus of a somatic cell.
Autosomes: All the chromosomes of an organism other than the sex chromosomes.
Gonosome: Sex chromosomes (XY or XX)
Non disjunction: The defect in cell division that leads to Down syndrome
Crossing over during Prophase I of meiosis is crucial for genetic variation. At the chiasma, genetic material is exchanged between homologous chromosomes, creating new combinations of alleles.
Genetics and inheritance
Genetics explains how characteristics are passed from parents to offspring. These terms help you understand inheritance patterns and genetic variation. The relationship between genotype (genetic makeup) and phenotype (physical appearance) is central to understanding heredity.
Gene: A small portion of the DNA coding for a particular characteristics.
Alleles: Different forms of genes which occur at the same locus.
Locus: The position of gene on the chromosome.
Genotype: Genetic make-up (composition) of an organism.
Phenotype: The physical appearance of an organism determined by the genotype.
Understanding genetic terminology:
- Gene - a section of DNA coding for a characteristic
- Alleles - different versions of the same gene
- Locus - the specific position of a gene on a chromosome
For example, the gene for eye colour has different alleles (brown, blue, green) all located at the same locus.
Dominant allele: The allele that is expressed (shown) in the phenotype eg Tt.
Recessive allele: An allele that does not influence the phenotype when found in the heterozygous condition.
Heterozygous: Two different alleles for a particular characteristics eg.Tt
Homozygous: Two identical allele for a particular characteristics eg. TT or tt
Dominant vs Recessive:
- Dominant alleles are expressed even when only one copy is present (Tt shows the dominant trait)
- Recessive alleles are only expressed when two copies are present (tt)
- In heterozygous individuals (Tt), only the dominant trait appears in the phenotype
This is why two parents without a recessive trait can have children who express it - both parents can be heterozygous carriers.
Complete dominance: A genetic cross were the dominant allele masks (blocks) the expression of the recessive allele.
Incomplete dominance: A genetic cross between two phenotypically different parents produces offsprings that are different from both parents but with an intermediate offspring.
Co-dominance: A genetic cross in which both alleles are expressed equally in the phenotype.
Multiple alleles: More than two alternative forms of genes at the same locus.
Types of Dominance Patterns:
- Complete dominance: Red flower (RR) × White flower (rr) → All pink flowers (Rr show only red)
- Incomplete dominance: Red flower (RR) × White flower (rr) → All pink flowers (Rr shows blend)
- Co-dominance: Both alleles expressed equally (e.g., AB blood type shows both A and B antigens)
Sex-linked characteristics: Characteristics or trait that are carried on the sex chromosome.
Monohybrid cross: Only one characteristic or trait is being shown in the genetic cross.
Hybrid cross: Two characteristics or trait shown in the genetic cross.
Pedigree diagram / Family tree: Is used to study the inheritance of the characteristics in a family over generations.
Variation: Genotype and phenotype differences among organisms of the same species.
Continuous variation: variation were there is wide range of phenotype eg shoe size, height or skin colour.
Discontinuous variation: variation where there is no wide range of phenotype eg blood groups or eye colour.
Gene pool: the sum total of all the alleles that are present in a breeding population of a particular species
Types of variation:
- Continuous variation shows a range of phenotypes (height from very short to very tall)
- Discontinuous variation shows distinct categories (blood type A, B, AB, or O)
Continuous variation is usually controlled by multiple genes, while discontinuous variation is typically controlled by one or a few genes.
Genetic conditions and technologies
Modern genetics helps us understand inherited conditions and develop technologies to diagnose and treat them. These terms cover both natural genetic conditions and human interventions in genetics.
Albinism: The condition that results from the absence of skin pigmentation
Melanin: Pigment that gives skin its colour.
Colour blindness: Absence of a protein that make up either the red or green cones/photoreceptors in the eye.
Haemophilia: A sex-linked condition where blood fails to clot properly.
Sex-linked conditions like haemophilia and colour blindness are carried on the X chromosome. Males (XY) are more likely to express these conditions because they only have one X chromosome - if that X carries the recessive allele, they will have the condition. Females (XX) need two copies of the recessive allele to express the condition.
Gene mutation: Mutations that affect a single or a few base pairs in just a single gene
Chromosomal mutations: Refer to changes in the normal structure or number of chromosomes.
Clone: A copy of an organism that is genetically identical to the original organism
Cloning: The process through which a copy of an organism that is genetically identical is formed.
Genetic engineering: The process whereby the genes on the DNA are changed, transferred or manipulated To produce a different organism.
Genetic modification: Manipulation of a genetic material to get desired changes.
Human genome: The mapping of exact position of all the genes in all the chromosomes of a human.
Genome: an organism's entire hereditary information (genes) encoded either on the DNA or RNA.
Genetic technologies have important applications:
- Cloning produces genetically identical organisms
- Genetic engineering can create organisms with desired traits (e.g., disease-resistant crops)
- Human genome mapping helps identify genetic disorders and develop treatments
Reproduction and development
These terms cover both sexual and asexual reproduction, as well as the development of offspring in different organisms. Understanding the different reproductive strategies helps explain how organisms are adapted to their environments.
Gametogenesis: Process by which sex chromosomes are produced.
Spermatogenesis: Process by which sperm cells are produced in the testes.
Oogenesis: The process by which egg cells or ova are produced in the ovary.
Fertilization: Fusion of the sperm and an egg cell.
External fertilization: The sperm fertilises the egg cell outside the body of the female usually in water.
Internal fertilization: Fertilization occurs inside the female's reproductive organs.
Gametogenesis is the general term for sex cell production, which includes:
- Spermatogenesis (sperm production in males)
- Oogenesis (egg production in females)
Both processes involve meiosis to produce haploid gametes.
Ovipary: Reproductive strategy in which eggs are laid and hatching takes place outside the Female's body.
Vivipary: The young develops inside the uterus of the mother after the eggs are fertilised internally.
Ovovivipary: Young develop from the eggs that are fertilised internally and retained inside the mothers After fertilisation until they hatch.
Three reproductive strategies:
- Ovipary - eggs laid outside body (birds, most reptiles)
- Vivipary - young develop inside mother's body (mammals)
- Ovovivipary - eggs retained inside mother until hatching (some sharks, snakes)
Each strategy has advantages depending on the environment and parental care capabilities.
Amniotic egg: The embryo protected by the shell of the egg laid by oviparous animals.
York sac: The structure that provides nutrition to the embryo in an amniotic egg.
Allantois: Structure for excretion/collects waste from the embryo in an amniotic egg.
Chorion: The outermost extra-embryonic membrane surrounding the embryo acts as a surface for gas exchange.
Altricial development: Hatchlings/offsprings are usually: poorly developed on hatching,
- Eyes are closed,
- Unable feed on their own,
- brain size and intelligence increases a lot after hatching. .
Precocial development: Hatchlings/offsprings are usually: well developed when they hatch,
- Eyes are open,
- Able to move,
- Able to feed, brain size and intelligence remains the same throughout their life.
Developmental strategies:
- Altricial young require extensive parental care (most songbirds, humans)
- Precocial young are independent soon after birth (chickens, horses)
Altricial development allows for larger brain development after birth but requires more parental investment.
Parental care: Offered through building of nests, protecting the eggs, protecting the young or teaching the young.
Gestation: The period of development of an embryo in the uterus, between fertilisation and birth
Male reproductive system
The male reproductive system is designed for the production and delivery of sperm cells. Understanding the function of each structure helps explain how fertilization occurs.
Testes: Produces sperm cells and the hormone testosterone.
Epididymis: provide storage and maturation of sperms cells
Sperm duct/ vas deferens: Transport sperms from the epididymis to the urethra.
Urethra: Transport semen and urine out of the body.
Sperm pathway: Testes (production) → Epididymis (storage/maturation) → Sperm duct → Urethra → Outside body
Remember that the urethra has a dual function - it transports both semen and urine (but not at the same time).
Seminal vesicle: A gland that produces a nutrient rich fluid that provides energy for the sperm cells.
Prostate gland: Produces an alkaline fluid that neutralises the acid from the vagina, which would kill the sperms.
Cowper's gland: Produces mucus that helps with the movement of the sperm.
Three accessory glands contribute to semen:
- Seminal vesicle - provides nutrients (energy) for sperm
- Prostate gland - produces alkaline fluid to neutralize vaginal acidity
- Cowper's gland - produces mucus for lubrication and sperm movement
These secretions together with sperm form semen.
Acrosome: The structure in the head of a sperm cell that contains enzymes which break down the membrane surrounding the ovum
Testosterone: The hormone responsible for secondary sexual characteristics in males.
Female reproductive system
The female reproductive system has two main functions: producing egg cells and providing an environment for embryo development during pregnancy.
Ovary:
- Produces egg cells,
- Secrets progesterone and oestrogen.
Fallopian tube:
- connects the ovaries to the uterus,
- transports egg cells from the ovary,
- it is the site of fertilisation.
Uterus/womb: Carries the embryo during and foetus during pregnancy.
Endometrium:
- Inner lining of the uterus place;
- Place where the embryo implants and the placenta forms.
Cervix:
- Lower, narrow part of the uterus.
- It stretches to allow the baby through during child birth.
Vagina:
- Receives the penis and semen during sexual intercourse,
- The passage through which the baby is born.
Mucus plug: The structure that form on the cervix that prevents entrance of bacteria.
Path of the egg: Ovary (production) → Fallopian tube (fertilization occurs here) → Uterus (implantation and development)
The fallopian tube is the site where fertilization normally occurs, not the uterus.
Ovulation: The process when the Graafian follicle burst to release the egg cell.
Graafian follicle: produced by the primary follicle and contains the egg cell.
Oestrogen: The hormone released by new follicles in the ovary.
Progesterone:
- A hormone that further thickens the endometrium when secreted.
- Inhibits the secretion of FSH
Corpus Lateum: The structure that releases progesterone during pregnancy.
Key hormones in the female reproductive system:
- Oestrogen - released by developing follicles, thickens endometrium, triggers ovulation
- Progesterone - released by corpus luteum, maintains endometrium, inhibits FSH
These hormones work in a negative feedback system to regulate the menstrual cycle.
Pregnancy and development
Once fertilization occurs, a series of precisely coordinated events leads to pregnancy and the development of a new individual.
Implantation:
- The process in which the embryo settles on the endometrium and sinks into it,
- Embryo embedded itself in the endometrium
Chorion: The finger-like structures from the outer membrane formed by the embryo.
Amnion: The fluid-filled sac enclosing the embryo.
Umbilical vein: The blood vessel in the umbilical cord that carries blood rich in oxygen and nutrients
Umbilical artery: Carry deoxygenated blood towards the placenta.
Remember the umbilical blood vessels:
- Umbilical vein - carries oxygenated, nutrient-rich blood FROM placenta TO baby
- Umbilical artery - carries deoxygenated blood FROM baby TO placenta
Note: This is opposite to the normal artery/vein pattern in the body!
Nervous system
The nervous system coordinates and controls body functions through electrical impulses transmitted along specialized cells called neurons. Understanding the structure and function of neurons and the brain is essential for explaining how the body responds to stimuli.
Sensory (afferent) neuron: Transmits impulses from the sense organs or receptors to the spinal cord and brain.
Motor (efferent) neuron: Transmits impulses from the brain or spinal cord to sense organs or receptors muscles and glands, the effectors bring about a response.
Interneuron (connector): Links the sensory neuron to the motor neuron.
Three types of neurons work together:
- Sensory neurons - carry impulses FROM receptors TO CNS
- Interneurons - connect sensory and motor neurons in CNS
- Motor neurons - carry impulses FROM CNS TO effectors
Remember: Sensory = Towards brain, Motor = Away from brain
Dendrites: The structures that sends impulse towards the cell body.
Axon: the structure that sends impulse away from the cell body
Myelin sheath: a layer fat around the axon that prevents the loss of impulse.
Synapse: the functional connection between the axon and one neuron and the dendrites of another neuron.
Receptor: The structure that receives stimulus and converts it into an impulse.
Effector: A structure which responds to a stimulus.
Neuron structure and impulse direction:
- Dendrites → Cell body → Axon
- Impulses always travel in this direction
- The myelin sheath insulates the axon and speeds up impulse transmission
- Impulses jump from one gap to the next in myelinated neurons
Reflex action: A quick automatic action that involves the spinal cord and does not involve the brain.
Reflex arc: The path along which the impulse is transmitted to bring about a response to a stimuli.
Reflex arcs provide rapid, automatic responses to stimuli without involving the brain. This is crucial for protective responses (e.g., pulling hand away from hot object).
Pathway: Receptor → Sensory neuron → Interneuron (in spinal cord) → Motor neuron → Effector
Peripheral nervous system: The nervous system which consists of cranial and spinal nerves
Parasympathetic system: The nervous system which consists of cranial and spinal nerves
Cranial nerves: nerves arising from the brain.
Meninges: The membranes which protect the central nervous system.
Brain structure and function
The brain is divided into different regions, each with specific functions. Understanding these regions helps explain how different body functions are controlled and coordinated.
Cerebrum:
- Control voluntary actions.
- Receive and interprets sensations from sense organs.
- Centre for higher mental process.
Cerebellum:
- Coordinates all voluntary movements.
- Controls muscle tension to maintain balance.
Medulla oblongata:
- Transmits nerve impulses between the spinal cord and the brain.
- Controls involuntary actions such as heartbeat and breathing.
Hypothalamus: The control centre for hunger, thirst, sleep, body temperature and emotions.
Corpus callosum: Connects the right and left hemisphere of the brain- allows communication between the two sides of the brain.
Key Brain Regions and Functions:
- Cerebrum - Voluntary actions, sensory interpretation, thinking, memory
- Cerebellum - Coordination, balance, muscle control
- Medulla oblongata - Involuntary actions (breathing, heartbeat)
- Hypothalamus - Homeostasis control centre (temperature, hunger, thirst)
- Corpus callosum - Communication between brain hemispheres
The eye
Understanding the structure of the eye helps explain how we see and what can go wrong with vision. The eye works like a camera, focusing light onto the retina where it is converted into nerve impulses.
Cornea: The transparent front part of the eye (though not explicitly defined in the source, it's implied by related terms)
Pupil: Opening in the eye that allows light to enter the eye.
Iris: The coloured part of the eye.
Lens: Holds the lens in position.
Aqueous humour: Watery fluid that supports the cornea and the front chamber
Vitreous humour: A jelly-like substance which gives the shape to the lens.
Ciliary muscles: Muscles whose contraction and relaxation alters the shape of the lens bring about accommodation.
Ciliary body: Thickened circular rim of the choroid which contains ciliary muscles.
Retina: The light-sensitive layer at the back of the eye (implied by related terms)
Choroid: Layer behind the retina that supplies nutrients and oxygen to the retina.
Yellow spot: Area on the retina containing lots of rods and cones, and is responsible for bright light and colour vision.
Blind spot:
- The area with no rods and cones;
- Therefore there is no vision at this spot.
Optic nerve: Carries nerve impulses from the retina to the brain (cerebrum)
Path of light through the eye: Cornea → Aqueous humour → Pupil → Lens → Vitreous humour → Retina → Optic nerve → Brain
The lens can change shape to focus light, while the pupil size changes to control how much light enters.
Accommodation: The adjustment of the shape of the lens to see the objects clearly near or far.
Pupillary mechanism: Regulates the amount of light entering the eye by adjusting the size of the pupil.
Accommodation is controlled by the ciliary muscles:
- To see near objects: ciliary muscles contract → lens becomes thicker/more curved
- To see far objects: ciliary muscles relax → lens becomes thinner/flatter
This allows the eye to focus on objects at different distances.
Vision problems
Common vision problems occur when the eye cannot properly focus light onto the retina. Understanding these conditions helps explain how corrective lenses work.
Short sightedness (Myopia): A condition were near objects can be seen clearly inability of the lens to become more flat/eyeball is longer than normal object falls in front of the retina Cannot see distant objects clearly.
Astigmatism: A condition were the curvature of the lens or cornea is uneven resulting in distorted image.
Cataract: A condition were the lens becomes cloud and opaque.
Common vision defects:
- Myopia (short-sightedness) - eyeball too long, image forms in front of retina, can see near but not far objects
- Astigmatism - uneven cornea/lens curvature causes distorted images
- Cataract - cloudy lens blocks light passage
Each can be corrected: myopia with concave lenses, astigmatism with cylindrical lenses, cataracts with surgery.
The ear
The ear is responsible for hearing and balance. Sound waves are converted into nerve impulses that the brain interprets as sound.
Auditory canal: transmits sound waves to the ear drum/tympanum.
Eustachian tube: a tube that equalises pressure on either side of the ear drum/ tympanic membrane.
Cochlea: spirally coiled portion of the inner ear responsible for the reception of sound.
Glomet: A device that is used to drain excess fluids from the middle ear.
The eustachian tube connects the middle ear to the throat, allowing pressure equalization. This is why your ears "pop" when changing altitude - the tube opens to equalize pressure on both sides of the eardrum.
Homeostasis and hormones
Homeostasis is the maintenance of a constant internal environment despite external changes. Hormones play a key role in this process through negative feedback mechanisms.
Homeostasis: A process of maintaining a constant internal environment.
Negative feedback: Detect changes or imbalances in the internal environment and to restore the balance.
Negative feedback is the key mechanism for maintaining homeostasis:
- A change is detected (e.g., temperature rises)
- A response is triggered to counteract the change (e.g., sweating)
- The system returns to normal
- The corrective response stops
This prevents overcorrection and maintains balance.
Endocrine gland: a grand that pours its secretions (hormones) into the blood streams
Exocrine grand: a grand that has its secretions transported by means of ducts
ADH: The hormone that regulates the amount of water in the human body
Aldosterone: The hormone that regulates the salt concentration in the human body
Thyroid stimulating hormone/TSH: The hormone inhibited by an increased level of thyroxin
Gibberellin: A plant growth hormone that stimulates seed germination
Key homeostatic hormones:
- ADH (Antidiuretic hormone) - controls water reabsorption in kidneys
- Aldosterone - regulates salt (sodium) levels
- TSH - regulates thyroid hormone production through negative feedback
- Gibberellin - plant hormone for growth and germination
Evolution and human origins
Evolution explains how life on Earth has changed over time through natural selection. These terms help you understand the evidence for evolution and human origins, from fossil records to biogeography.
Theory: An explanation for something that has been observed in nature and which can be supported by facts, laws and tested hypotheses
Hypothesis: A tentative explanation of a phenomenon that can be tested
In science, a theory is not just a guess - it's a well-supported explanation backed by extensive evidence. A hypothesis is a testable prediction that can be supported or rejected through experimentation.
Species: A group similar organism that can interbreed and produce fertile offspring.
Population: A group of organism of organisms of the same species that occupy the same habitat.
Speciation: the formation of new species from existing species.
Natural selection: the environment or nature is the selective force.
Artificial selection: The deliberate breeding of organisms for desirable characteristics selected by humans
Natural selection is the mechanism of evolution:
- Variation exists in a population
- Organisms with favorable traits survive better
- These organisms reproduce more successfully
- Favorable traits become more common in the population
This process, over many generations, leads to evolution and adaptation.
Biogeography: The distribution of species in different parts of the world
Fossils: remains of organisms that have existed in the past.
Palaeontology: The study of remains of organisms that have existed in the past.
Punctuated equilibrium: The explanation that species experience long periods without physical change, followed by short periods of rapid physical change
Homologous: Similar structure in different organisms indicating common ancestry.
Phylogenetic tree/ Cradogam/ evolutionary tree: represents the possible evolutionary relationship among a set of organisms or groups of organisms.
Evidence for evolution comes from multiple sources:
- Fossils - preserved remains showing change over time
- Homologous structures - similar bone structures in different species (e.g., human arm, whale flipper, bat wing)
- Biogeography - distribution patterns of species
- Phylogenetic trees - show evolutionary relationships based on shared characteristics
Human evolution
Understanding human evolution involves studying both fossil evidence and anatomical features that distinguish different species in our evolutionary lineage.
Hominid/Hominidae: The group consisting of modern humans, chimpanzees, gorillas and orangutans plus all their immediate ancestors.
Hominin: The group consisting of modern humans, extinct human species and all our immediate ancestors (include members of the genera Homo, Australopithecus, Paranthropus and Ardipithecus).
Australopithecus: genus to which little foot, Mrs Ple, Karabo and Taung Child belong.
Homo Habilis: genus to which Homo habilis and Homo erectus belong
Homo Sapien: genus to which the human ancestor belong.
Understanding human classification:
- Hominid - broader group including great apes and humans
- Hominin - specifically the human lineage (including extinct human species)
- Australopithecus → Homo habilis → Homo erectus → Homo sapiens represents the progression of human evolution
Prognathous: Having pointed face because of projecting jaws and nose.
Foramen magnum: a hole in the skull though which the spine joins the skull.
Out of Africa hypothesis: states that modern humans originated in Africa and then migrated out of Africa.
The position of the foramen magnum indicates how an organism moves:
- Positioned at the base of the skull → upright walking (bipedalism)
- Positioned toward the back → quadrupedal (walking on all fours)
This is a key feature used to determine whether fossil species walked upright.
Sustainability and food security
Understanding how human activities affect the environment is crucial for creating a sustainable future. These terms relate to environmental impact and food production strategies.
Carbon footprint: Measure of the total amount of carbon dioxide emissions of an individual, a defined population or any company per year.
Food security: Access by all people at all the times, to adequate, safe and nutritious food for health and reproductive life.
Sustainable: The act of using natural resources without destroying the ecological balance.
Monoculture: The act of growing only type of crop over large areas of land year after year.
Sustainability means meeting current needs without compromising future generations' ability to meet their needs. This includes:
- Reducing carbon footprint
- Maintaining food security
- Avoiding destructive practices like excessive monoculture
- Preserving biodiversity and ecological balance
Biological control: The use of the natural enemy of a pest to control the pest population.
Chemical control: The use of chemical substance such as pesticides to control the pest population
Herbicides: Chemical preparation designed to kill plants, especially weeds, or to inhibit their growth.
Pesticides: Chemical substances used to eliminate the pests.
Eutrophication: the process whereby nutrients become highly concentrated in a body of water leading to algae bloom
Pest control methods:
- Biological control - uses natural predators (environmentally friendly, sustainable)
- Chemical control - uses pesticides/herbicides (effective but can harm environment)
Eutrophication often results from excessive fertilizer runoff, leading to oxygen depletion and death of aquatic organisms.
Scientific methodology
These terms are essential for understanding how to conduct scientific investigations. Proper experimental design requires identifying and controlling variables correctly.
Hypothesis: A propose solution to the problem that is yet to be tested.
Independent variable: The variable whose influence is tested in an investigation/ the variable that is manipulated in an investigation.
Dependent Variable: The factor that is influenced by the independent variable (the effect/result of an investigation)
Fixed/controlled variable: variables that are controlled so that they do not interfere with the purpose of the investigation
Understanding variables is crucial for valid experiments:
- Independent variable - what YOU change/manipulate
- Dependent variable - what you MEASURE (the result)
- Controlled variables - what you keep CONSTANT
Example: Testing effect of light on plant growth:
- Independent: light intensity (what you change)
- Dependent: plant height (what you measure)
- Controlled: water, temperature, soil type (what you keep the same)
Key Points to Remember:
- DNA replication creates exact copies of genetic material, which is essential for cell division and inheritance
- Mitosis produces two identical daughter cells, while meiosis produces four genetically different cells for sexual reproduction
- Dominant and recessive alleles determine which characteristics appear in offspring, with dominant alleles masking recessive ones in heterozygous individuals
- The nervous system coordinates body functions through neurons that transmit electrical impulses between receptors, the central nervous system, and effectors
- Homeostasis maintains constant internal conditions through negative feedback mechanisms
- Evolution through natural selection explains how species change over time, with only organisms having favorable characteristics surviving to reproduce
- Sustainable practices are essential for maintaining food security and protecting the environment for future generations
- Valid scientific investigations require proper identification and control of independent, dependent, and controlled variables