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Western Cape Education Department
Directorate: Curriculum FET
LIFE SCIENCES
REVISION BOOKLET
2026 TERM 2
Grade 12
This revision program is designed to assist you in revising the critical
content and skills covered during the 2 nd^ 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
Life Sciences revision booklet 202 6 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:
- 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. 1 .3 The human nervous system:
- 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. 1.3.1 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.
Life Sciences revision booklet 202 6 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:
- Provides a pathway for nerve impulses to and from the brain
- The spinal cord serves as a centre for reflex actions 1.3.2 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.
Life Sciences revision booklet 202 6 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 Parasympathetic division Increases heart rate Decreases heart rate Dilates pupils Constricts pupils Increases blood pressure 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.
Life Sciences revision booklet 202 6 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 Significance of a reflex action:
- A reflex action is rapid to protect the body from injury 1.5.3 What is a synapse?
- A synapse is the functional connection between the axon of one neuron, and the dendrites of another neuron. 1.5.4 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. 1.6 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.
Life Sciences revision booklet 202 6 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.
Life Sciences revision booklet 202 6 Grade 12 Term 2 1.7.5 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 Corrective measures Short- sightedness – 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 Wearing glasses with biconcave lenses Long- sightedness – 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 Glasses with lenses shaped to correct the distortion, contact lenses, laser surgery Cataracts • Lens becomes cloudy and opaque
- Light cannot reach the retina and causes blurred vision Surgery to replace lens with a synthetic lens **1.8 The Human Ear:
- 8 .1 Structure and functions of different parts of the ear** 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
Life Sciences revision booklet 202 6 Grade 12 Term 2 Figure 7: Diagrams of the human ear showing the different parts and their functions
Life Sciences revision booklet 202 6 Grade 12 Term 2
2. THE HUMAN ENDOCRINE SYSTEM: 2.1 Differentiate between endocrine and exocrine glands: - 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 2.2 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.
Life Sciences revision booklet 202 6 Grade 12 Term 2
3. 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 When thyroxin level increase below 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
- 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.
Life Sciences revision booklet 202 6 Grade 12 Term 2 3.1.4 Table 7 : Negative feedback mechanism controlling the concentration of water When the blood has more water than normal When the blood has less 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 - 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 3.1.5 Table 8 : Negative feedback mechanism controlling the concentration of salts: When the salt level in the blood increases When the salt level in the blood decreases
- 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
- 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
Life Sciences revision booklet 202 6 Grade 12 Term 2 3.1.6 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:
- 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
Life Sciences revision booklet 202 6 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:
- 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 4.4 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 EXPLANATION DIAGRAM/ NOTES Chromatin Thread-like structures in the nucleus of a cell that form the chromosomes
Life Sciences revision booklet 202 6 Grade 12 Term 2 CONCEPT EXPLANATION DIAGRAM/ NOTES 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 (position) on homologous chromosomes Dominant allele (T) – tall plant Recessive allele (t) – short plant Dominant allele An allele that is expressed (shown) in the phenotype when found in the heterozygous (Tt) and homozygous (TT) condition. Recessive allele 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 Phenotype The physical appearance of an organism determined by the genotype, e.g. tall, short. Genotype Genetic composition (makeup) of an organism.
