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
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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.
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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
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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.
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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.
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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.
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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.
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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.
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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
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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
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Life Sciences revision booklet 2025
Grade 12 Term 2
Figure 7: Diagrams of the human ear showing the different parts and their functions
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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
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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.
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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.
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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.
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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
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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
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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
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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
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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
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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
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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.
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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.
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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
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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.
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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).
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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.
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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).
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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
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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
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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.
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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)
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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)
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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)
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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)
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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)
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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.
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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)
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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)
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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)
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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)
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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