Western Cape Education Department Directorate: Curriculum FET LIFE SCIENCES REVISION BOOKLET 2025 TERM 2 Grade 12 This revision program is designed to assist you in revising the critical content and skills covered during the 2nd term. The purpose is to prepare you to understand the key concepts and to provide you with an opportunity to establish the required standard and the application of the knowledge necessary to succeed in the NCS examination. The revision program covers the following topics: • Responding to the environment (humans) – 54 marks in Paper 1 of Final Examination • Human endocrine system and homeostasis– 34 marks in Paper 1 of Final Examination • Responding to the environment (plants) – 13 marks in Paper 1 of Final Examination • Genetics and inheritance – 48 marks in Paper 2 of Final Examination 2 Life Sciences revision booklet 2025 Grade 12 Term 2 TERM 2 CONTENT Study the core content below on the topics responding to the environment (humans), human endocrine system, homeostasis in humans and responding to the environment (plants). 1. RESPONDING TO THE ENVIRONMENT (HUMANS) 1.1 Introduction: Organisms need to detect and respond to stimuli to survive in a continuously changing environment. There are two coordinating systems in humans: • Nervous system and • Endocrine system Study the following key concepts: 1.2 The need for a nervous system in humans: • • 1.3 The nervous system detects stimuli (changes in the environment) and allow the body to react to these changes. Stimuli can be external and internal. The nervous system coordinates the various activities of the body e.g. walking, hearing etc. The human nervous system: • 1.3.1 • • • The human nervous system is subdivided into two main systems i.e. ➢ Central nervous system – consisting of the brain and spinal cord ➢ Peripheral nervous system – consisting of nerves that conduct impulses to and from the brain and spinal cord. It includes 12 pairs of cranial nerves and 31 pairs of spinal nerves. The Central nervous system: The central nervous system consists of the brain and spinal cord. The brain is enclosed by the skull and the spinal cord by the vertebral column Both the brain and spinal cord are enclosed by the meninges. 3 Life Sciences revision booklet 2025 Grade 12 Term 2 1.3.1.1 The brain: Use the diagram (Figure 1) below to study the structure and functions of the following parts of the brain: • • • • Cerebrum Cerebellum Corpus callosum Medulla oblongata Figure 1: Diagram showing parts of the brain and their functions 1.3.1.2 The spinal cord: The spinal cord consists of: • • a central canal that is filled with cerebrospinal fluid grey matter and white matter 4 Life Sciences revision booklet 2025 Grade 12 Term 2 Figure 2: Cross section of the spinal cord Spinal nerves arise from both sides of the spinal cord. Each spinal nerve has a dorsal root and a ventral root. The dorsal root consists of sensory neurons and the ventral root consists of motor neurons. Functions of the spinal cord: • • 1.3.2 Provides a pathway for nerve impulses to and from the brain The spinal cord serves as a centre for reflex actions The Peripheral nervous system: Describe the location and functions of the peripheral nervous system (cranial and spinal nerves): • • • • • The peripheral nervous system includes all the nervous tissue situated outside the central nervous system i.e. 12 pairs of cranial nerves and 31 pairs of spinal nerves. It consists of sensory nerves and motor nerves. The motor nerves are subdivided into the somatic nervous system and the autonomic nervous system The somatic nervous system conducts nerve impulses from the central nervous system to the voluntary muscles and controls voluntary actions e.g. running etc. The autonomic nervous system conducts nerve impulses from the central nervous system to the involuntary muscles and glands and controls involuntary actions e.g. sneezing, blinking of eyes etc. 5 Life Sciences revision booklet 2025 Grade 12 Term 2 Functions of the peripheral nervous system: • • Conduct impulses from the receptors to the central nervous system Conduct impulses from the central nervous system to the effectors Location and functions of the autonomic nervous system (sympathetic and parasympathetic sections): • • • The autonomic nervous system has two subdivisions i.e. the sympathetic and the parasympathetic divisions. The sympathetic division prepares the body for an emergency The parasympathetic division allows the body to return to normal Examples of responses of the autonomic nervous system: Sympathetic division Increases heart rate Dilates pupils Increases blood pressure Parasympathetic division Decreases heart rate Constricts pupils Decreases blood pressure 1.4 Structure and functioning of a nerve: • • • • • • • Nerves send and carry signals to and from all parts of the body and are made up of neurons (sensory and motor) A neuron has a cell body consisting of cytoplasm and a nucleus. The cytoplasm contains granules, the Nissl granules, which are rich in RNA and are involved in protein synthesis. Two types of outgrowths extend from the cell body i.e. dendrites and axons. Dendrites conduct nerve impulses to the cell body. Axons conduct nerve impulses away from the cell body. Most of the nerve tissue outside the central nervous system are enclosed by a myelin sheath which is formed by cells, called the Schwann cells. The myelin sheath insulates nerve fibres and accelerates the transmission of nerve impulses. There are three types of neurons: • • • Sensory (afferent) neurons: transmit impulses from the receptors to the spinal cord. Motor (efferent) neurons: transmit impulses from the spinal cord to the effector organs (muscles/glands). Interneurons: occur in the spinal cord and transmit impulses from the sensory neurons to the motor neurons. 6 Life Sciences revision booklet 2025 Grade 12 Term 2 Figure 3: Structure of a motor neuron Figure 4: Structure of a sensory neuron 1.5 The simple reflex arc: 1.5.1 • • Differentiate between a reflex arc and a reflex action: Reflex action: a quick, automatic response to a stimulus and does not involve the brain. Protects the body from harm e.g. blinking of eyes, coughing etc. Reflex arc: the pathway along which nerve impulses are conducted from a receptor to an effector to bring about a reflex action. 7 Life Sciences revision booklet 2025 Grade 12 Term 2 Figure 5: Diagram of a simple reflex arc to show the different parts and functions of the parts The path of a reflex arc: Receptor (A) → Sensory neuron (B) → Interneuron (C) → Motor neuron (D) → Effector (E) 1.5.2 • 1.5.3 • 1.5.4 • • • 1.6 Significance of a reflex action: A reflex action is rapid to protect the body from injury What is a synapse? A synapse is the functional connection between the axon of one neuron, and the dendrites of another neuron. Significance of a synapse: Synapses ensure that impulses can only move in one direction. Impulses can be transmitted to more than one neuron at a synapse. A synapse determines which impulse will be transmitted to the next neuron. Disorders of the Central Nervous System: You need to know the causes and symptoms of the following disorders i.e. Alzheimer's disease and multiple sclerosis. 8 Life Sciences revision booklet 2025 • • Grade 12 Term 2 Alzheimer’s disease – occurs when healthy neurons become less and less efficient. Symptoms include memory loss and confusion. Multiple sclerosis – occurs when the body’s own immune system destroys the myelin sheaths of neurons. (Remember the myelin sheath insulates the nerve fibres and accelerates the transmission of nerve impulses). Symptoms include loss of muscle control and coordination in all parts of the body. 1.7 The Human Eye: 1.7.1 Structure and functions of different parts of the eye You should be able to use a diagram of the human eye and provide labels and functions of the different parts of the eye. Figure 6: Diagram of the human eye showing the different parts and their functions 1.7.2 • • • • Binocular vision and its importance: The left and right eye each forms its own image of an observed object. The brain combines the two images to form a single three-dimensional image of the object Binocular vision provides a wider field of vision and creates a perception of depth. The ability to see in 3D is known as stereoscopic vision. 9 Life Sciences revision booklet 2025 1.7.3 • Grade 12 Term 2 Accommodation: Accommodation is the series of changes that take place in the shape of the lens and the eyeball in response to the distance of an object from the eye. Table 1: Accommodation Distant vision (objects further than 6m) Ciliary muscles relax Ciliary body moves further away from the lens Suspensory ligaments tighten (becomes taut) Tension on lens increases Lens is less convex Light rays are refracted less Light rays are focused on the retina and image falls on the retina 1.7.4 • • Near vision (objects closer than 6m) Ciliary muscles contract Ciliary body moves closer to the lens Suspensory ligaments slacken Tension on lens decreases Lens becomes more convex Light rays are refracted more Light rays are focused on the retina and image falls on the retina Pupillary mechanism: The pupillary mechanism is a reflex action The size of the pupil controls the amount of light that enters the eye Table 2: Pupillary mechanism In bright light Radial muscles of the iris relax Circular muscles of the iris contract Pupil constricts (becomes smaller) Less light enters the eye In dim light Radial muscles of the iris contract Circular muscles of the iris relax Pupil dilates (enlarges) More light enters the eye 10 Life Sciences revision booklet 2025 1.7.5 Grade 12 Term 2 Visual defects: You should know the nature and treatment of the following visual defects. You should also be able to use diagrams to identify different visual defects. Table 3: Visual defects Visual defect Nature of the defect Shortsightedness – near objects can be seen clearly • Inability of the lens to become more flat/eyeball is longer than normal • Lens bends the light rays too much • Focal point of distant objects lies in front of the retina • Causing the image to be blurred Longsightedness – distant objects can be seen clearly • Inability of the lens to become more convex/eyeball is shorter than normal • Lens does not bend light rays enough • Focal point of nearby objects lies behind the retina • Causing the image to be blurred Wearing glasses with biconvex lenses Astigmatism • The curvature of the lens or cornea is uneven, resulting in distorted images Cataracts • Lens becomes cloudy and opaque • Light cannot reach the retina and causes blurred vision Glasses with lenses shaped to correct the distortion, contact lenses, laser surgery Surgery to replace lens with a synthetic lens 1.8 The Human Ear: 1.8.1 Structure and functions of different parts of the ear Corrective measures Wearing glasses with biconcave lenses You should be able to use a diagram of the human ear and provide labels and functions of the different parts of the ear. The human ear consists of three parts: • • • Outer ear Middle ear Inner ear 11 Life Sciences revision booklet 2025 Grade 12 Term 2 Figure 7: Diagrams of the human ear showing the different parts and their functions 12 Life Sciences revision booklet 2025 1.8.2 Grade 12 Term 2 Functioning of the human ear: Hearing: • • • • • • • The pinna traps and directs the sound waves into the external auditory canal/ear canal/meatus This causes the tympanic membrane to vibrate The vibrations are transmitted to the auditory ossicles The ossicles amplify the vibrations and transmit it to the oval window The oval window vibrates creating pressure waves in the fluid/endolymph of the cochlea This stimulates the organ of Corti to convert the wave into an impulse The impulse travels along the auditory nerve to the cerebrum where it is interpreted Balance: • • • • • 1.8.3 The maculae in the utriculus and sacculus are stimulated by changes in the position of the head. The cristae in the semi-circular canals are stimulated by changes in the direction and speed of movement. When stimulated, the cristae and maculae convert the stimuli into nerve impulses The nerve impulses are transmitted through the auditory nerve to the cerebellum where they are interpreted The cerebellum then sends impulses via the motor neurons to the skeletal muscles to restore balance Hearing defects: You should know the causes and treatment of the following hearing defects: Table 4: Hearing defects Hearing defect Middle ear infection Deafness Causes • Excess fluid in the middle ear caused by pathogens e.g. viral infection. The tympanic membrane bulges and this causes pain • Injury to parts of the ear, nerves or parts of the brain responsible for hearing • Accumulation and hardening of wax • Hardening of ear tissues such as ossicles Treatment • Inserting of grommets • Antibiotics • Hearing aids • Cochlear implants 13 Life Sciences revision booklet 2025 2. THE HUMAN ENDOCRINE SYSTEM: 2.1 Differentiate between endocrine and exocrine glands: • • 2.2 Grade 12 Term 2 Endocrine glands: ductless glands that release their secretions (hormones) directly into the bloodstream. Endocrine glands – glands that release their secretions through ducts to a body cavity or to the outside e.g. salivary glands that secrete saliva through ducts that open in the mouth cavity What are hormones? • • • • • Hormones are organic compounds and chemical messengers. Most hormones are proteins. Hormones are secreted by endocrine glands in small quantities directly into the bloodstream Hormones are then transported to target organs where they have specific effects. Hormones have a regulatory function that can be stimulating or inhibiting. You should be able to use a diagram to indicate the location of the endocrine glands, the hormones they secrete and function(s) of each hormone. Figure 8: Diagram showing the location of different endocrine glands, the hormones that they secrete and the functions of the hormones. 14 Life Sciences revision booklet 2025 3. Grade 12 Term 2 HOMEOSTASIS: • • The process of maintaining a constant internal environment in the human body Negative feedback mechanisms operate in the human body to detect changes of imbalances in the internal environment and to restore the balance. 3.1 Negative feedback mechanisms: 3.1.1 Negative feedback involving TSH and thyroxin: Figure 9: Flow diagram to show negative feedback mechanism involving TSH and thyroxin Table 5: Negative feedback mechanism involving TSH and thyroxin When thyroxin levels in the blood increase above normal • Hypophysis is stimulated • Hypophysis produces less TSH • Low TSH level stimulates the thyroid gland • The thyroid gland secretes less thyroxin • The thyroxin level decreases and returns to normal When thyroxin level increase below normal • Hypophysis is stimulated • Hypophysis produces more TSH • High TSH level stimulates the thyroid gland • The thyroid gland secretes more thyroxin • The thyroxin level increases and returns to normal Thyroid disorder: The element iodine is essential for the production of thyroxin. A shortage of iodine can cause the thyroid gland to enlarge, known as a goitre. 15 Life Sciences revision booklet 2025 3.1.2 Grade 12 Term 2 Negative feedback mechanism involving insulin and glucagon: Table 6: Negative feedback involving insulin and glucagon: When glucose level in the blood increases above normal levels • The islets of Langerhans in the pancreas are stimulated • and secrete insulin into the blood • Insulin is transported to the liver • where it stimulates the conversion of excess glucose into glycogen which is then stored • The glucose level in the blood decreases and returns to normal • 3.1.3 • • • • • • • • When glucose level in the blood decreases below normal levels • The islets of Langerhans in the pancreas are stimulated • and secrete glucagon into the blood • Glucagon is transported to the liver • where it stimulates the conversion of stored glycogen into glucose • The glucose level in the blood increases and returns to normal Diabetes mellitus: a metabolic disease that is characterized by high glucose levels in the blood. Negative feedback mechanism controlling the concentration of carbon dioxide (CO2): When the carbon dioxide concentration in the blood increases above normal levels e.g. after or during an exercise Chemoreceptors in the wall of the aorta and in the carotid arteries are stimulated The chemoreceptors send nerve impulses to the respiratory and cardiovascular centres in the medulla oblongata of the brain The medulla oblongata sends nerve impulses to the diaphragm and intercostal muscles These muscles contract more actively and this increases the rate and depth of breathing and more carbon dioxide -rich air is exhaled The cardiovascular centre sends impulses to the heart and the heart beats faster. Carbon dioxide is transported faster to the lungs and exhaled The carbon dioxide concentration in the blood returns to normal. 16 Life Sciences revision booklet 2025 3.1.4 Table 7: Negative feedback mechanism controlling the concentration of water When the blood has more water than normal • The hypothalamus is stimulated • and sends impulses to the hypophysis to secrete less or stop secreting the hormone ADH • Less ADH/no ADH is transported in the blood to the kidneys • The collecting ducts and distal convoluted tubules of the kidney become less permeable to water • Less water is re-absorbed and passed to the surrounding blood vessels • More water is excreted in the urine and the water level in the blood returns to normal 3.1.5 Grade 12 Term 2 When the blood has less water than normal • The hypothalamus is stimulated • and sends impulses to the hypophysis to secrete more of the hormone ADH • ADH is transported in the blood to the kidneys • The collecting ducts and distal convoluted tubules of the kidney become more permeable to water • More water is re-absorbed and passed to the surrounding blood vessels • Less water is excreted in the urine and the water level in the blood returns to normal Table 8: Negative feedback mechanism controlling the concentration of salts: When the salt level in the blood increases • Receptor cells in the afferent and efferent arterioles of the kidney detects the high salt/sodium ion level • The adrenal gland is stimulated • to stop secreting aldosterone/to secrete less aldosterone • The re-absorption of sodium ions from the renal tubules in the kidney into the blood vessels decreases • The sodium ion concentration in the blood decreases and returns to normal When the salt level in the blood decreases • Receptor cells in the afferent and efferent arterioles of the kidney detects the low salt/sodium ion level • The adrenal gland is stimulated • to secrete more aldosterone • The re-absorption of sodium ions from the renal tubules in the kidney into the blood vessels increases • The sodium ion concentration in the blood increases and returns to normal 17 Life Sciences revision booklet 2025 3.1.6 • • Grade 12 Term 2 Thermoregulation/Temperature regulation: Use your textbook and study the structure of the skin, using a diagram, with an emphasis on the parts involved in thermoregulation. Body temperature is regulated by the hypothalamus in the brain and the blood vessels and sweat glands in the skin. Figure 10: Diagram showing the negative feedback mechanism for controlling temperature/thermoregulation: 4. RESPONDING TO THE ENVIRONMENT(PLANTS) 4.1 • • • • • General functions of the following: Auxins: Stimulate cell elongation Cause tropisms in stems and roots Stimulate the development of fruit Stimulate the development of adventitious roots in stem cuttings Inhibit the growth of lateral branches - apical dominance • • • • Gibberellins: Stimulate stem elongation Stimulate root growth Promote flowering Stimulate the germination of seeds Abscisic acid: • • • Causes dormancy of terminal and lateral buds in winter Contributes to the dormancy of seeds by inhibiting germination Promotes the abscission of leaves and fruit 18 Life Sciences revision booklet 2025 4.2 Grade 12 Term 2 The control of weeds using plant hormones • • Some weed killers contain high concentrations of auxins that accelerate the metabolism of broad-leaved dicotyledonous weeds. The weeds grow so fast that their water absorption and food production are insufficient and they weaken and die. 4.3 Role of auxins in phototropism and geotropism: Tropisms are growth movements of a plant in response to a stimulus. 4.3.1 Phototropism Phototropism is the growth movement of part of a plant in response to a unilateral light stimulus. Stems and leaves usually grow towards the light to absorb maximum light for photosynthesis. What happens when the growing tip of a stem receives unilateral light? • • • • 4.3.2 Auxins move away from the light and accumulate towards the shaded side Auxins stimulate cell elongation on shaded side Shaded side grows faster Stem curves in the direction of the light. Geotropism Geotropism is the growth movement of a plant or part of the plant in the response to a gravitational stimulus. When a pot plant is placed horizontally the roots will curve downwards and the stem will curve upwards. Explain why the root and the stem grow of a pot plant grow in different directions when the plant is placed horizontally on the ground and receive light equally from all directions. Figure 11: Diagram showing tropism 19 Life Sciences revision booklet 2025 • • Grade 12 Term 2 Auxins will accumulate on the lower side of the stem and root because auxins are attracted by gravity. This leads to uneven distribution of auxins in the stem and root In the stem: • • • • There will be a higher concentration of auxins on the lower side of the stem. Growth on the lower side of the stem is stimulated. The lower side of the stem grows faster. This causes the stem to grow/bend upwards away from gravity. In the root: • • • • 4.4 There will be a higher concentration of auxins on the lower side of the root. Growth on the lower side of the root is inhibited. This causes the upper side of the root to grow faster This will cause it to bend downwards towards gravity Role of chemicals and thorns as plant defence mechanisms: Chemicals: • • Many plants produce chemicals that play a role in the defence against herbivores Some of these chemicals are toxic or influence the digestibility of plant material Thorns: • Some plants e.g. cacti have thorns and spines that discourage herbivores from eating them. 5. GENETICS AND INHERITANCE 5.1 Concepts in inheritance: CONCEPT Chromatin EXPLANATION Thread-like structures in the nucleus of a cell that form the chromosomes DIAGRAM/ NOTES 20 Life Sciences revision booklet 2025 CONCEPT Chromatid EXPLANATION 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 (position) on homologous chromosomes An allele that is expressed (shown) in the phenotype when found in the heterozygous (Tt) and homozygous (TT) condition. An allele that is masked (not shown) in the phenotype when found in the heterozygous (Tt) condition. It is only expressed in the homozygous (tt) condition The physical appearance of an organism determined by the genotype, e.g. tall, short. Genetic composition (makeup) of an organism. Dominant allele Recessive allele Phenotype Genotype Grade 12 Term 2 DIAGRAM/ NOTES Dominant allele (T) – tall plant Recessive allele (t) – short plant 21 Life Sciences revision booklet 2025 CONCEPT Homozygous Heterozygous Monohybrid cross Dihybrid cross Karyotype 5.2 EXPLANATION Two identical alleles for a particular characteristic, e.g. TT or tt. Two different alleles for a particular characteristic, e.g. Tt. Only one characteristic or trait is shown in the genetic cross Two different characteristics shown in genetic cross The number, shape and arrangement of all the chromosomes in the nucleus of a somatic cell Grade 12 Term 2 DIAGRAM/ NOTES Types of dominance: • Complete dominance – one allele is dominant and the other is recessive, such that the effect of the recessive allele is masked by the dominant 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 22 Life Sciences revision booklet 2025 5.3 Grade 12 Term 2 Monohybrid crosses: Mendel's principle of segregation: • The pair of alleles on homologous chromosomes separate during meiosis/gamete formation, so that only one allele of each pair is present in the gamete. Mendel's principle of independent assortment: • Alleles of a gene for one characteristic segregate independently of the alleles of a gene for another characteristic. The alleles for each gene will therefore come together randomly during gamete formation. Mendel's Law of Dominance: • When two organisms with pure breeding contrasting traits are crossed all the individuals of the F1 generation will display the dominant trait. 23 Life Sciences revision booklet 2025 5.4 Grade 12 Term 2 Sex determination: • • • 5.5 22 pairs of chromosomes in humans are autosomes and one pair of chromosomes are sex chromosomes/gonosomes A human male has X and Y gonosomes and a female has two X gonosomes Half of the sperm of males will have 22 + X chromosomes, and the other half will have 22 + Y chromosomes. Depending on which sperm reaches the egg, there is a 50% chance of the zygote being male and a 50% chance of the zygote being female. Karyotypes: • A karyotype is the number, shape and arrangement of all the chromosomes in the nucleus of a somatic cell. 24 Life Sciences revision booklet 2025 5.6 Grade 12 Term 2 Sex-linked inheritance: • • Although most of the bodily characteristics are carried on the 22 pairs of autosomes, there are a few characteristics carried on the gonosomes only. Certain sex-linked genetic disorders are carried on the allele found on the X chromosome only. Two of these disorders are colour blindness and haemophilia. Colour blindness: • • Colour blindness is a visual defect resulting in an inability to distinguish between certain colours. The allele for colour-blindness is recessive (e.g. Xb) and is carried on the Xchromosome Haemophilia: • • Haemophilia is the inability of the blood to clot due to lack of a blood clotting factor. The allele for haemophilia is recessive (e.g. Xh) and is carried on the Xchromosome. Genotype Phenotype H H X x Normal female H h X X Normal female h h XX Haemophiliac female H X Y Normal male h XY Haemophiliac male 25 Life Sciences revision booklet 2025 5.7 Grade 12 Term 2 Blood grouping: • • • • • There are four blood types in humans: A, B, AB or O. These phenotypes are controlled by three alleles (IA, IB and i) but each person only inherits two alleles. Multiple alleles – refers to more than two alternative forms of a gene at the same locus. Allele IA and allele IB is dominant over allele i. Allele IA and allele IB are codominant. Blood group (phenotype) A B AB O 5.8 Genotype IAIA or IAi IBIB or IBi I AI B ii Dihybrid crosses: • A genetic cross involving two characteristics Example of a dihybrid cross • In pea plants, the allele for tallness (T) is dominant and the allele for shortness (t) is recessive. The allele for purple flowers is dominant (P) and the allele for white flowers is recessive (p). Two plants, heterozygous for both tallness and purple flowers were crossed. Use a genetic cross to show all the possible genotypes and phenotypes of their offspring. 26 Life Sciences revision booklet 2025 5.9 Grade 12 Term 2 Genetic lineages/pedigrees: • A genetic lineage/pedigree traces the inheritance of characteristics over many generations Example: The pedigree diagram below shows inheritance of eye colour in humans over three generations of a family. Brown eye colour (B) is dominant over blue eye colour (b). 27 Life Sciences revision booklet 2025 • • • • • • • • • • 5.10 • • • • Grade 12 Term 2 Squares represent males and circles represent females. The horizontal line between a square (Joshua) and a circle (Ronel) shows that they have mated. The vertical line flowing from the horizontal line represents the offspring (Sarah and Peter) of the two parents (Joshua and Ronel). Remember the following steps when interpreting pedigree diagrams: Step 1: Study any key and opening statement/s and look for dominant and recessive characteristics and phenotypes. Brown eye colour (B) is dominant over blue eye colour (b) – as stated in the problem Step 2: Write in the phenotypes of all the individuals as given in the problem. Joshua, Jack and John are males with blue eyes. Veronica and Marlena are females with blue eyes. Peter and Frank are males with brown eyes. Ronel, Sarah and Gayle are females with brown eyes. Step 3: Fill in the genotype of all the individuals with the recessive condition – it must have two recessive alleles (two lower case letters, e.g. bb). Joshua, Veronica, Marlena, Jack and John will have the genotype ‘bb’. The recessive characteristic only shows up in the homozygous condition Step 4: For every individual in the diagram that has the recessive condition, it means that each allele was obtained from each of the parents. Work backwards and fill in one recessive allele for each parent. Step 5: If the parents showed the dominant characteristic, fill in the second letter which represents the dominant allele (a capital letter, e.g. B). The genotype of Peter is ‘Bb’ – working backwards from the offspring Marlena or Jack or John who are homozygous recessive. This means that one of the recessive alleles of Marlena, Jack and John, i.e. ‘b’, must have come from parent Peter and the other one from parent Veronica Step 6: Any other individual showing the dominant characteristic will most likely be homozygous dominant (BB) or heterozygous dominant (Bb). Ronel could be homozygous dominant (BB) or heterozygous dominant (Bb) Mutations: A mutation is caused by a permanent change to the DNA of a cell. Harmful mutations cause changes in DNA that can cause errors in protein sequencing, that can result in partially or completely non-functional proteins. Harmless mutations occur in the non-coding DNA and have no effect on the structure or functioning of the organism. Useful mutations can be advantageous to the organism and they are passed on from parent to offspring. These mutations also change the DNA responsible for the production of a specific protein. If the protein made increases the organism’s chance of survival, it would be seen as a useful mutation. 28 Life Sciences revision booklet 2025 Grade 12 Term 2 Gene mutation: • • • • A gene mutation is a change in the sequence of nitrogenous bases/nucleotides in a gene and can occur during DNA replication, transcription and crossing over. Examples of gene mutations are haemophilia and colour-blindness. Haemophilia – absence of blood-clotting factors Colour-blindness – due to absence of the proteins that comprise either the red or green cones/photoreceptors in the eye. Chromosomal mutation: • • 5.11 • • • Chromosomal mutations occur when meiosis does not occur normally. It may result in a change in the number or structure of chromosomes e.g. during Anaphase I if the chromosomes do not separate. Both chromosomes go to the same pole, and thus the chromosome number of the gametes changes. An example of a chromosome mutation is Down syndrome - due to an extra copy of chromosome 21 as a result of non-disjunction during meiosis Genetic engineering: Genetic engineering is the manipulation or transfer of genes from one organism to another to make products that satisfy human needs. Genetically modified organisms (GMOs) are the result of genetic engineering. Example (genetic engineering in medicine): Synthetic insulin is used to treat diabetes and is produced by genetic engineering technology (see diagram and explanation below). 29 Life Sciences revision booklet 2025 • • • • • • • • Grade 12 Term 2 The DNA with the gene coding for the production of insulin is removed from healthy human pancreatic cells Enzymes are used to cut the DNA into segments to isolate the specific gene. A plasmid/ circular DNA is removed from a bacterial cell. The plasmid is cut using enzymes. The human insulin gene is inserted into the plasmid to form recombinant DNA The recombinant DNA is placed back into the bacterial cell. The bacteria are placed in a fermentation tank where they reproduce rapidly to produce many copies of the insulin gene. The insulin is extracted from the bacteria and purified. Advantages of genetic engineering: • • • • • • • • Produce crops that are resistant to adverse conditions/ drought/disease/pests Increase crop yield Change the time for the ripening of fruit Increase shelf life of plant products Improve nutritional value of food Improve the taste of food Developing fruit/plants with desirable characteristics Production of drugs or hormones (e.g. insulin) which have fewer side-effects and is cheaper Stem cell research: • • Stem cells are undifferentiated cells that have the ability to grow into any tissue in the body. They may be harvested from the placenta, embryos, bone marrow and from blood in the umbilical cord. Use of stem cells: • • Bone marrow has been used for a long time to treat cancers Stem cells are used to replace dead cells in the heart after a heart attack or growing skin tissue to treat burn victims or growing nerve cells to treat spinal cord injuries and Parkinson’s disease Cloning: • Cloning is the process where genetically identical organisms are produced 30 Life Sciences revision booklet 2025 Grade 12 Term 2 Process of cloning in animals: • • • The nucleus of an ovum is removed and replaced with the nucleus of a somatic donor cell/ diploid donor cell The zygote is stimulated for mitosis to occur The embryo is then placed into the uterus of an adult female Process of cloning in plants: • • • 5.12 Plants may be cloned by vegetative reproduction/asexual reproduction /tissue culture/grafting A plant with the desired characteristics is selected A vegetative part of the “parent” plant structure is removed and placed inside a growth medium and allowed to grow. Paternity testing: Blood grouping: • • • • The blood group of a child is determined by the alleles received from both parents The blood group of the mother, the child and the possible father is determined If the blood group of the mother and possible father cannot lead to the blood group of the child, the man is not the father If the blood group of the mother and the possible father can lead to the blood group of the child the man might be the father but this is not conclusive because many men have the same blood group DNA profiles: • • • • A child received DNA from both parents The DNA profiles of the mother, child and the possible father are determined A comparison of the DNA bands of the mother and the child is made The remaining DNA bands are compared to the possible father’s DNA bands 31 Life Sciences revision booklet 2025 • • 6. Grade 12 Term 2 If all the remaining DNA bands in the child’s profile match the possible father’s DNA bands then the possible father is the biological father If all the remaining DNA bands in the child’s profile does not match the possible father’s DNA bands then the possible father is not the biological father. REVISION QUESTIONS: • • • • Answer the questions below. Work through the questions in the Term 3 lessons. Work through questions in past examination papers The instructional verbs (in italics) e.g. name, give, describe, explain etc. and the mark allocation per question give an indication of what and how much information you should provide in your answer. Examples of some of the instructional verbs used in test and examination questions: Instructional verb Name Differentiate Tabulate Describe Explain Compare • Meaning Give the name of something Use differences to qualify between two or more categories Draw a table and indicate the answers as direct pairs. State in sentences the main points of a process Give your answer in a cause-effect or statement and reason sequence Give similarities and differences between concepts Please note that HIGHER ORDER questions are in BOLD and marked with a (*) QUESTIONS ON RESPONDING TO THE ENVIRONMENT (HUMANS): 1. The diagram below represents the central nervous system in a human. 32 Life Sciences revision booklet 2025 1.1 1.2 1.3 Grade 12 Term 2 Identify part: (a) A (b) C (c) D State THREE functions of part B. Describe the structure and the functioning of the autonomic nervous system. (1) (1) (1) (3) (4) 2. Study the diagram of a reflex arc below. 2.1 What is a reflex action? (2) 2.2 Label the functional connection at D and the neuron B. (2) 2.3 State ONE significance of the functional connection at D. (1) (*)2.4 Write down, in the correct order, the LETTERS ONLY of the neurons involved from the time a stimulus is received until a response takes place. (2) (*)2.5 Explain the consequences for a reflex action if neuron C is damaged. (2) (*)2.6 The nerve pathway in the above response is about 1,5 metres in length. A nerve impulse travels at 75 m.s-1. Use this information to calculate the time taken for this reflex action to occur. Show all working. (3) 2.7 Draw a labelled diagram to represent the structure of neuron A. (5) 33 Life Sciences revision booklet 2025 Grade 12 Term 2 3. Study the diagram of the human ear below. 3.1 3.2 Identify parts: (a) B (b) D Which part of the brain will receive impulses from part C? (1) (1) (1) 3.3 Describe the role of the semi-circular canals in maintaining balance. (5) (*)3.4 Describe how an increased production of mucus in the nose and throat may lead to the bursting of part E. (3) (*)3.5 Explain why fusion of the structures at A may lead to hearing loss. (2) (*)3.6 Explain the effect if the receptors in region C are damaged. (3) (*)3.7 Describe how the parts of the middle ear, including the membranes, assist with amplifying sounds. (3) 34 Life Sciences revision booklet 2025 Grade 12 Term 2 4. The diagram below represents the structure of the human eye. 4.1 State ONE function of part: (a) (b) A C (1) (1) (*)4.2 Nocturnal animals sleep during the day and are active at night. Explain how part: (a) 4.3 B of nocturnal animals will differ from that found in animals that are active during the day (2) (b) C of nocturnal animals will differ from that found in animals that are active during the day (2) Describe how the iris controls the amount of light entering the eye when a person is exposed to bright light. (4) (*)4.4 Explain why long-sighted people need to wear glasses with biconvex lenses as a corrective measure. (4) 35 Life Sciences revision booklet 2025 Grade 12 Term 2 QUESTIONS ON THE HUMAN ENDOCRINE SYSTEM AND HOMEOSTASIS: 5. The diagram below represents a negative feedback mechanism. X and Y represent hormones secreted by the respective glands. 5.1 What is the role of any negative feedback mechanism in the human body? (1) Identify hormone X. (1) 5.2 (*)5.3 Explain the consequences for a person if hormone Y remained abnormally high for extended periods of time. (3) 6. People with Type I diabetes mellitus are usually insulin-dependent (must inject themselves with insulin to control their blood glucose levels). During a stressful situation adrenalin is secreted, which has the same effect as glucagon on the blood glucose levels. An investigation was conducted to determine the influence of adrenalin on the blood glucose levels of Type I diabetics who were also glucagon deficient. The investigation was conducted as follows: • • • • • • 6.1 100 male patients with Type I diabetes mellitus, who were also glucagon deficient, participated in the investigation. They were then given the same amount of food and water at the same time for a period of three days. Their blood glucose levels were measured on the morning of the third day. A solution with a low concentration of adrenalin was then administered intravenously (injected). After 20 minutes, the blood glucose concentration in each person was measured again. The blood glucose levels before and after administering adrenalin were compared. Name the gland that secretes glucagon. (*)6.2 Identify the independent variable in the investigation. (1) (1) 36 Life Sciences revision booklet 2025 Grade 12 Term 2 (*)6.3 State THREE other factors that should have been kept constant during the investigation. (3) (*)6.4 Explain why the blood glucose levels were measured before injecting adrenalin on the third day. (2) (*)6.5 Explain why the adrenalin was injected instead of given orally. (2) (*)6.6 Explain what would be the expected results after adrenalin was injected into the patients. (2) (*)6.7 Give a reason for the use of 100 patients in the investigation instead of only 10 patients. (1) 7. Study the flow diagram below of a homeostatic mechanism used to regulate the concentration of salts in the human body. 7.1 Give the name of the following: (a) (b) (c) 7.2 Organ A Gland B Hormone C Describe the response by the effector at D (1) (1) (1) (2) 37 Life Sciences revision booklet 2025 8. Grade 12 Term 2 The table below shows the change in the concentration of carbon dioxide (CO2) in a person's veins, as exercise levels increase. The person in the investigation was asked to ride a bicycle which generated electricity, measured in watts. The faster the person cycled, the more watts he generated. 8.1 EXERCISE (Watt) CO2 CONCENTRATION IN VENOUS 0 50 100 150 200 250 0,50 0,51 0,53 0,55 0,55 0,54 BLOOD (mol/mℓ) What is a normal carbon dioxide concentration in the venous blood for this person? (1) (*)8.2 Explain the significance of measuring the carbon dioxide concentration in the blood when the person is not doing any exercise. (2) (*)8.3 Explain why the carbon dioxide concentration in the veins increased during strenuous exercise. (2) 8.4 Describe the homeostatic response that takes place in the body to reduce the carbon dioxide concentration when exercising between 200 and 250 watts. (6) QUESTION ON RESPONDING TO THE ENVIRONMENT (PLANTS): 9. Diagram A shows an upright pot plant. Diagram B shows the same pot plant one week after falling over. The plant was exposed to uniform light from all directions before and after falling over. 38 Life Sciences revision booklet 2025 9.1 Grade 12 Term 2 Name the type of tropism that is illustrated in diagram B? (1) (*)9.2 Explain why the stem of the plant bent upwards, as illustrated in diagram B. (4) (*)9.3 Explain the advantage that the upward bending of the stem could have for the plant. (2) 9.4 State how the roots in diagram B would react. (1) QUESTIONS ON GENETICS AND INHERITANCE: 10. In dogs rough hair (H) is dominant to smooth hair (h). A heterozygous roughhaired dog is mated with a smooth-haired dog. Represent a genetic cross to show the phenotypic ratio of the puppies. (6) 11. You have two rose plants, both with pink flowers. You cross them and find that, while most of the offspring are pink, some are red and some are white. Use a genetic cross to show how breeding two pink flowering plants can result in pink, red and white flowering plants. Use the letter R for the red allele and W for the white allele. (6) 12. Fur colour in mice is controlled by a gene with two alleles. Black fur colour (B) is dominant over brown fur colour (b). Use a genetic cross to show the possible genotypes and phenotypes of the offspring if a mouse that is heterozygous for fur colour is crossed with a mouse with brown fur. (6) 13. A species of fish has three phenotypes for fin length: elongated, short and medium. Heterozygous fish have medium fins. The characteristic is under the control of one gene with two alleles: elongated (E) and short (S). 13.1 Name and describe the type of dominance shown here. (1) 13.2 Use a genetic cross to show the percentage chance of two fish with medium fins having offspring with short fins. (6) 14. A man is heterozygous for blood group A and marries a woman who has blood group O. Use a genetic cross to show the phenotypic ratio of their offspring. (6) 39 Life Sciences revision booklet 2025 15. Grade 12 Term 2 Haemophilia is a genetic disorder caused by a recessive allele on the X chromosome. A haemophiliac female marries a normal male. Explain why all their sons will be haemophiliacs. (4) 16. A rare form of rickets in humans is caused by a sex-linked dominant allele (R) which is carried on the X-chromosome. An affected female, whose father was unaffected, married an unaffected male. 16.1 Determine the possible genotypes and phenotypes of their offspring by representing a genetic cross. (6) What is the percentage chance that they will have a child who is an unaffected male? (2) Explain why this disorder, although it is sex-linked, does NOT affect males only. (2) 16.2 16.3 17. In dogs, coat appearance is controlled by two genes; one for coat colour and one for coat pattern (presence or absence of white patches). The alleles for each characteristic are shown in the table below. In a cross between two dogs, the four offspring, V, W, X and Y, had the phenotypes as shown in the diagram below. 17.1 What is the term given to a genetic cross involving two characteristics? 17.2 Give the phenotype of: (1) (a) The dominant coat colour (1) (b) Dog V (1) (c) A dog that is homozygous recessive for both characteristics. (1) 40 Life Sciences revision booklet 2025 17.3 17.4 18. Grade 12 Term 2 Explain why all dogs with the phenotype of dog W may not have the same genotype. (2) The two characteristics are inherited in accordance with Mendel's principle of independent assortment. State this principle. (3) In holly trees, red fruit (R) is dominant over white fruit (r) and spiny leaves (L) are dominant over smooth leaves (l). The Punnett square below shows the possible results of a cross between two individual plants. The genotype at X is not given. 18.1 18.2 18.3 Give the: (a) Genotype of X (1) (b) Phenotype of the parents (2) In a population of 128 plants, how many plants with red fruit and smooth leaves are expected from the Punnet square above? Show ALL working. (3) A farmer wanted to produce plants with only white fruit and spine leaves. Give the genotype of the plants that he should use in the cross. (2) 41 Life Sciences revision booklet 2025 19. Grade 12 Term 2 The pedigree diagram below shows the inheritance of colour-blindness (Daltonism) in a family. Colour-blindness is sex-linked and is caused by a recessive allele (d). The ability to see colour normally is caused by a dominant allele (D). (March 2015) 19.1 How many of the male offspring of parents 1 and 2 were normal? 19.2 State the genotype of: (a) (b) Individual 2 Individual 5 (1) (2) (2) 19.3 A person with a recessive allele for colour-blindness may not be colourblind. Explain why males with an allele for colour-blindness are always colour-blind. (4) 19.4 If individual 5 marries a normal male, what percentage of their daughters will have an allele for colour-blindness, but will NOT be colour-blind? (2) 42 Life Sciences revision booklet 2025 Grade 12 Term 2 20. Severe combined immune deficiency syndrome (SCID) is a disorder affecting the immune system. It is caused by a sex-linked recessive allele (Xd). The diagram below shows the inheritance of the disorder in a family. It is not known if individual 1 has the disorder or not. 20.1 Give the: (a) Phenotype of individual 2 (1) (b) Phenotype of individual 1 (1) (c) Genotype of individual 3 (2) 20.2 Explain how individual 5 inherited the disorder. (2) 21. Describe sex determination in humans. (10) 22. Explain how blood grouping are used in paternity testing. (8) 23. Explain how DNA profiling are used in paternity testing. (8) 43 Life Sciences revision booklet 2025 24. Read the extract below. 24.1 According to the extract, state ONE: 24.2 Grade 12 Term 2 (a) Advantage of cloning (1) (b) Disadvantage of cloning (1) State why the donor cell was taken from LMJC 865 and not from any other cow. (1) 24.3 State why an ear cell was used and not an ovum. (2) 24.4 Briefly describe the process of cloning. (4) 25. Synthetic insulin is used to treat diabetes and is produced by genetic engineering technology. The diagram below represents the process. (June 2019) 44 Life Sciences revision booklet 2025 Grade 12 Term 2 25.1 Define genetic engineering. (2) 25.2 Describe the steps involved in producing the recombinant DNA. (4) 25.3 Explain why bacteria are most suitable for genetic engineering. (2) 25.4 Suggest THREE objections that some people might have to genetic engineering. (3) END OF DOCUMENT
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