Life Sciences Grade 12 | Study Guide | Past Papers | Notes & Revision 1
Life Sciences Grade 12
Question
Which ONE of the following statements is CORRECT for oogenesis in humans?
A One diploid mature ovum is formed
B One haploid mature ovum is formed
C Four diploid mature ova are formed
D Four haploid mature ova are formed
The correct answer is B: One haploid mature ovum is formed.
Only one functional haploid ovum is produced during oogenesis as the other three cells formed (polar bodies) are non-functional and eventually disintegrate.
Question
A structure in the eye that contains a high concentration of blood vessels and provides oxygen and nutrients to the retina is the …
A sclera
B choroid
C conjunctiva
D lens
The correct answer is B: choroid.
The choroid is the vascular layer of the eye lying between the retina and the sclera, rich in blood vessels that nourish the retina.
Question
The vagina …
A transports urine to the outside
B is the place where the foetus develops
C produces progesterone
D acts as a birth canal
The correct answer is D: acts as a birth canal.
The vagina functions as the passage through which the baby is delivered during childbirth, also serving as the canal for menstrual flow.
Question
The list below gives the characteristics of some young birds immediately after hatching:
(i) Eyes are open
(ii) Can move around
(iii) Cannot feed themselves
(iv) No feathers
Which ONE of the following combinations represents the characteristics of precocial development?
A (ii) and (iii) only
B (iii) and (iv) only
C (i) and (ii) only
D (ii) and (iv) only
The correct answer is C: (i) and (ii) only.
Precocial birds hatch with open eyes and are mobile soon after birth, although they may still need parental care for feeding and protection.
Question
The cornea and the lens are both …
A opaque
B transparent
C elastic
D inelastic
The correct answer is B: transparent.
Both the cornea and lens are transparent structures that allow light to pass through and focus it onto the retina for clear vision.
Question
Which ONE of the following is TRUE for a person who has an underactive thyroid gland? The TSH levels will be …
A high and the metabolic rate low
B high and the metabolic rate high
C low and the metabolic rate low
D low and the metabolic rate high
The correct answer is A: high and the metabolic rate low.
In hypothyroidism, the thyroid gland produces insufficient thyroid hormones, causing the pituitary to release more TSH to stimulate the thyroid, resulting in low metabolism.
Question
The diagram below represents a visual defect.
Which ONE of the following is the correct treatment of the visual defect shown above?
A Glasses with biconvex lenses
B Glasses with biconcave lenses
C Surgery to replace the cornea
D Surgery to replace the retina
The correct answer is B: Glasses with biconcave lenses.
The defect depicted is myopia (short-sightedness), which is corrected using concave lenses to help focus distant objects onto the retina.
Question
A list of some components of the nervous system is provided below. Which ONE of the following combinations applies to the central nervous system?
(i) Brain
(ii) Cranial nerves
(iii) Spinal nerves
(iv) Spinal cord
A (i), (ii), (iii) and (iv)
B (i) and (iv) only
C (ii), (iii) and (iv) only
D (iii) and (iv) only
The correct answer is B: (i) and (iv) only.
The central nervous system comprises the brain and spinal cord, while cranial and spinal nerves are part of the peripheral nervous system.
Question
Which ONE of the following is the part of the eye with the highest concentration of cones?
A Cornea
B Lens
C Yellow spot
D Iris
The correct answer is C: Yellow spot.
The yellow spot (fovea) contains the highest density of cones, making it the area of sharpest vision and best color discrimination.
Question
Which ONE of the following maintains the shape of the eyeball?
A. Cornea
B. Lens
C. Vitreous humour
D. Retina
The correct answer is C: Vitreous humour.
The vitreous humour is a clear, jelly-like substance that fills the eye and provides internal pressure, helping the eyeball maintain its round shape.
Question
The choroid …
A. is richly supplied with blood vessels.
B. contains photoreceptors.
C. refracts the light rays.
D. sends impulses to the brain.
The correct answer is A: is richly supplied with blood vessels.
The choroid is the middle layer of the eye containing many blood vessels that nourish the outer layers of the retina and other eye tissues.
Question
Which ONE of the following occurs immediately after fertilisation?
A. The blastula, which is a hollow ball of cells, is formed by meiosis.
B. The morula, which is a hollow ball of cells, is formed by meiosis.
C. The blastula, which is a solid ball of cells, is formed by mitosis.
D. The morula, which is a solid ball of cells, is formed by mitosis.
The correct answer is D: The morula, which is a solid ball of cells, is formed by mitosis.
After fertilisation, the zygote divides by mitosis to form a solid ball of cells called the morula, marking the early stage of embryonic development.
Question
On a hot day …
A. less blood flows to the surface of the skin.
B. the sweat glands become inactive.
C. more blood flows to the surface of the skin.
D. vasoconstriction takes place.
The correct answer is C: more blood flows to the surface of the skin.
To help cool the body on a hot day, blood vessels near the skin dilate, allowing more blood to flow to the surface to release heat.
Question
The normal site of fertilisation in a human female is the …
A. uterus.
B. ovary.
C. vagina.
D. Fallopian tube.
The correct answer is D: Fallopian tube.
Fertilisation typically takes place in the Fallopian tube, where the sperm meets and fuses with the ovum before moving to the uterus for implantation.
Question
Which ONE of the following best describes the events of accommodation when a person is viewing an object that is less than 6 m away?
A. Ciliary muscle: Relaxes | Suspensory ligaments: Tighten | Tension on the lens: Increases
B. Ciliary muscle: Contracts | Suspensory ligaments: Slacken | Tension on the lens: Decreases
C. Ciliary muscle: Relaxes | Suspensory ligaments: Slacken | Tension on the lens: Decreases
D. Ciliary muscle: Contracts | Suspensory ligaments: Tighten | Tension on the lens: Increases
The correct answer is B: Ciliary muscle contracts, suspensory ligaments slacken, tension on the lens decreases.
When focusing on a nearby object, the ciliary muscle contracts, reducing tension on the suspensory ligaments, allowing the lens to become more convex for better near vision.
THE FOLLOWING 2 QUESTIONS ARE BASED ON THE DIAGRAM OF THE NEURON BELOW.
Question
The axon is represented by structure …
A. 1
B. 2
C. 3
D. 4
The correct answer is D: 4.
The axon is the long, thin part of a neuron that conducts electrical impulses away from the cell body toward other neurons or muscles.
Question
Which labelled part affects the speed of impulse transmission?
A. 1
B. 2
C. 3
D. 4
The correct answer is C: 3.
The myelin sheath, represented by structure 3, speeds up nerve impulse transmission by allowing impulses to jump between the gaps (nodes of Ranvier) in the sheath.
FOR THE NEXT TWO QUESTIONS REFER TO THE DIAGRAM BELOW THAT SHOWS AN INVESTIGATION DONE TO DETERMINE THE EFFECT OF AUXINS ON TROPISM.
The procedure was as follows:
- A pot plant was placed on a stationary clinostat.
- The plant was exposed to light from all directions.
- The growth was then observed after few days.
The diagram below shows the set-up of the investigation.
The results after a few days showed the stem growing upwards
Question
Which ONE of the following is an explanation of the results?
A. Phototropism occurred because the auxins moved towards light, which inhibited growth on the lower side of the stem.
B. Geotropism occurred because the auxins moved downwards, which stimulated growth on the lower side of the stem.
C. Phototropism occurred because the auxins moved away from light, which stimulated growth on the upper side of the stem.
D. Geotropism occurred because the auxins moved upwards, which inhibited growth on the upper side of the stem.
The correct answer is B: Geotropism occurred because the auxins moved downwards, which stimulated growth on the lower side of the stem.
In this setup, the stem grows upwards because auxins accumulate on the lower side due to gravity, promoting cell elongation and causing the stem to bend upward.
Question
A control for the same investigation was set up by putting an identical pot plant on a rotating clinostat. Which ONE of the following would be the expected results observed after a few days?
A. There will be no growth.
B. The stem will grow upwards.
C. The stem will grow downwards.
D. The stem will grow horizontally.
The correct answer is D: The stem will grow horizontally.
When a plant is placed on a rotating clinostat, the continuous rotation neutralizes the effect of gravity on one side of the plant. This prevents auxins from accumulating unevenly, resulting in no directional growth toward or away from gravity. As a result, the stem grows horizontally because growth hormones are distributed evenly.
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Give the correct biological term for each of the following descriptions.
Question
The part of the skull that protects the brain.
The correct term is Cranium.
The cranium is the bony structure that encloses and safeguards the brain, forming the main part of the skull and providing protection against injury.
Question
The homeostatic process whereby temperature is controlled in the body.
The correct term is Thermoregulation.
Thermoregulation is the process by which the body maintains a stable internal temperature despite external changes, using mechanisms like sweating or shivering to achieve balance.
Question
The visual defect characterised by a cloudy lens.
The correct term is Cataract.
A cataract occurs when the lens of the eye becomes cloudy or opaque, reducing the amount of light that reaches the retina and leading to blurred or impaired vision.
Question
The blood vessel that transports deoxygenated blood from the foetus towards the placenta.
The correct term is Umbilical artery.
The umbilical artery carries oxygen-poor blood and waste products from the developing foetus to the placenta, where exchange with the mother’s blood takes place.
Question
The part of the brain that controls body temperature.
The correct term is Hypothalamus.
The hypothalamus is a small region of the brain responsible for regulating vital functions, including body temperature, by triggering responses like sweating or shivering.
Question
A branch of the nervous system that is made up of spinal and cranial nerves.
The correct term is Peripheral nervous system.
The peripheral nervous system consists of all the nerves outside the brain and spinal cord, connecting the central nervous system to limbs and organs.
Question
Finger-like projections that develop from the outer membrane of an embryo after implantation.
The correct term is Chorionic villi.
Chorionic villi are small, finger-like projections that extend into the uterine lining, helping to anchor the embryo and facilitate the exchange of nutrients and gases between mother and foetus.
Question
A hormone that regulates the salt levels in blood.
The correct term is Aldosterone.
Aldosterone is a hormone produced by the adrenal glands that increases sodium reabsorption in the kidneys, helping to control blood salt concentration and fluid balance.
Question
The fluid that protects the developing foetus against mechanical injury.
The correct term is Amniotic fluid.
Amniotic fluid surrounds the foetus inside the amniotic sac, cushioning it from physical shocks and allowing free movement for proper development.
Question
The area of the retina that contains the highest concentration of cones.
The correct term is Fovea centralis (or yellow spot).
The fovea centralis is the small central pit in the retina where cone cells are densely packed, enabling sharp, detailed vision especially in bright light.
Question
A structure in the ear that absorbs excess pressure waves from the inner ear.The correct term is Round window (or Fenestra rotunda).
The round window is a membrane-covered opening in the cochlea that helps dissipate excess sound vibrations, preventing damage and allowing fluid movement in the inner ear.
Question
The structure in a sperm that contains enzymes.The correct term is Acrosome.
The acrosome is a cap-like structure at the head of the sperm containing enzymes that help break down the outer layers of the egg to enable fertilisation.
Question
The site of fertilisation in the human female.The correct term is Fallopian tube.
The fallopian tube is the part of the female reproductive system where the sperm meets the ovum, and fertilisation typically takes place before the zygote moves to the uterus.
Question
A visual defect caused by the uneven curvature of the cornea.The correct term is Astigmatism.
Astigmatism is a condition where the cornea or lens has an irregular shape, leading to blurred or distorted vision because light rays are not focused evenly on the retina.
Question
The nerve that transmits impulses from the eye to the brain.The correct term is Optic nerve.
The optic nerve carries visual information in the form of electrical impulses from the retina to the brain, where the signals are processed into images.
Question
A disease characterised by the degeneration of brain cells and memory loss.The correct term is Alzheimer’s disease.
Alzheimer’s disease is a progressive neurological disorder that causes the death of brain cells, leading to memory loss, confusion, and decline in cognitive abilities.
Question
The inner layer of the uterus that thickens during the menstrual cycle.The correct term is Endometrium.
The endometrium is the mucous membrane lining the uterus, which becomes thicker each month to prepare for a possible pregnancy and sheds during menstruation if fertilisation does not occur.
Question
A hollow ball of cells that forms during embryonic development.The correct term is Blastula (or blastocyst).
The blastula is an early stage in embryonic development, consisting of a hollow sphere of cells that will later differentiate into various tissues and organs.
Question
The period of development of secondary sexual characteristics in humans.The correct term is Puberty.
Puberty is the stage in human development when the body undergoes physical changes such as growth of hair, breast development, and voice deepening, leading to sexual maturity.
Question
The type of vision where both eyes are used to focus on an object.The correct term is Binocular vision (or stereoscopic vision).
Binocular vision allows both eyes to focus on a single object, providing depth perception and a three-dimensional view of the environment.
Indicate whether each of the descriptions in COLUMN I apply to A ONLY, B ONLY, BOTH A AND B or NONE of the items in COLUMN II.
| COLUMN I | COLUMN II | ANSWER |
|---|---|---|
| 1. The plant hormone that stimulates the germination of seeds | A: Gibberellins B: Abscisic acid | A ONLY |
| 2. The part of the brain that connects the left and the right hemispheres | A: Corpus luteum B: Corpus callosum | B ONLY |
| 3. The liquid found in front of the lens in the eye | A: Vitreous humor B: Aqueous humor | B ONLY |
Explanation for 1
Gibberellins stimulate seed germination by breaking seed dormancy and promoting enzyme production for growth. Abscisic acid, by contrast, inhibits germination and maintains dormancy.
Explanation for 2
The corpus callosum is a bundle of nerve fibers that connects the left and right cerebral hemispheres, allowing communication between them. The corpus luteum is part of the ovary, unrelated to brain function.
Explanation for 3
The aqueous humor is the fluid located in front of the lens, helping maintain eye pressure and nourishing the cornea and lens. The vitreous humor is found behind the lens, filling the large cavity of the eyeball.
| COLUMN I | COLUMN II | ANSWER |
|---|---|---|
| 2.1 A plant hormone that inhibits the germination of seeds | A: Gibberellins B: Abscisic acid | B ONLY |
| 2.2 The functional connection between two consecutive neurons | A: Synapse B: Effector | A ONLY |
| 2.3 A hormone that stimulates puberty | A: Testosterone B: Oestrogen | BOTH A AND B |
Explanation for 2.1:
Abscisic acid is the plant hormone that inhibits seed germination by maintaining dormancy, while gibberellins promote germination by breaking dormancy.
Explanation for 2.2
A synapse is the functional connection between two consecutive neurons, enabling communication via neurotransmitters. An effector is a muscle or gland that responds to neural stimulation but is not involved in neuron-to-neuron communication.
Explanation for 2.3
Both testosterone and oestrogen are hormones that stimulate puberty. Testosterone is responsible for male secondary sexual characteristics, while oestrogen primarily influences female puberty.
The diagrams below show the condition of the eyes for different light intensities when viewing the same object.
Question
Give the LETTER and NAME of the part that contains muscles.
The correct answer is: B – Iris
The iris is the colored part of the eye that contains circular and radial muscles. These muscles control the size of the pupil to regulate how much light enters the eye, helping protect the retina and adjust to different lighting conditions.
Question
Give the LETTER and NAME of the part that is made up of tough white fibrous tissue.
The correct answer is: A – Sclera
The sclera is the tough, white outer layer of the eye made of dense fibrous tissue. It maintains the shape of the eyeball, protects internal structures, and provides attachment points for the muscles that move the eye.
Question
Which diagram (1, 2, or 3) represents the eye of a person in a very bright area?
The correct answer is: Diagram 2
In bright light, the circular muscles of the iris contract to make the pupil smaller, reducing the amount of light entering the eye. Diagram 2 shows a constricted pupil, indicating exposure to a very bright environment.
Question
Which diagram (1, 2, or 3) represents the eye of a person where the rods are stimulated the most?
The correct answer is: Diagram 3
Rods are photoreceptor cells that work best in dim light. Diagram 3 shows a dilated pupil, which allows more light into the eye, thereby stimulating the rods the most in low-light conditions.
Question
Which muscles are contracted in diagram 2?
The correct answer is: Circular muscles
In diagram 2, the circular muscles of the iris are contracted to constrict the pupil in response to bright light, protecting the eye from excessive light exposure.
Question
Which muscles are relaxed in diagram 3?
The correct answer is: Circular muscles
In diagram 3, the circular muscles are relaxed, allowing the pupil to dilate so that more light enters the eye, enhancing vision in a dim environment.
The diagram below shows the interaction between two endocrine glands.
Question
Name the type of interaction that occurs between hormone A and gland B.
Answer: Negative feedback mechanism
The negative feedback mechanism is a regulatory process where increased levels of thyroxine (hormone C) in the blood signal the pituitary to reduce TSH (hormone A) secretion. This maintains hormone balance and prevents overstimulation of the thyroid gland.
Question
Identify:
(a) Gland B
Answer: Thyroid gland
The thyroid gland is an endocrine gland located in the neck. It is stimulated by TSH (thyroid-stimulating hormone) from the pituitary to release thyroxine, a hormone that regulates metabolism and other important bodily functions.
(b) Hormone A
Answer: TSH (Thyroid-Stimulating Hormone)
TSH is secreted by the pituitary gland. It stimulates the thyroid to produce and release thyroxine, ensuring proper metabolic function and maintaining hormonal balance.
(c) Hormone C
Answer: Thyroxine (T4)
Thyroxine is the hormone released by the thyroid gland in response to TSH stimulation. It plays a critical role in controlling metabolism, regulating energy production, and maintaining body temperature.
Question
Name the disorder that results when gland B is overstimulated and becomes enlarged.
Answer: Goitre
Goitre occurs when the thyroid gland enlarges due to overstimulation, often caused by iodine deficiency. Without enough iodine, the thyroid cannot make sufficient thyroxine, leading to increased TSH production, which causes the thyroid to grow abnormally.
Question
Which hormone (A or C) will be expected to be high in the blood of the person with the Goitre disorder ?
Answer: Hormone A (TSH)
In the case of goitre caused by iodine deficiency, thyroxine (hormone C) production is low. The pituitary responds by releasing more TSH (hormone A) in an attempt to stimulate the thyroid, resulting in elevated TSH levels in the blood.
The diagrams below show part of the eye under different conditions.
Question
Name the process that occurs when the:
(a) Curvature of the lens changes to focus on a near or distant object
Answer: Accommodation
Accommodation is the process by which the lens changes shape—becoming more rounded to focus on nearby objects or flatter to focus on distant objects—allowing the eye to adjust its focus depending on distance.
(b) Pupil size changes to regulate the amount of light entering the eye
Answer: Pupillary mechanism (or Pupillary reflex)
The pupillary mechanism refers to the reflex action that adjusts the size of the pupil to control how much light enters the eye, helping protect the retina from too much light and improving vision in dim or bright conditions.
Question
Give the LETTERS of TWO diagrams (A, B, C, or D) that represent the condition of the eye of a person:
(a) In dim light
Answer: B and D
In dim light, the pupil dilates to allow more light into the eye for better vision. Diagrams B and D show a widened pupil, indicating the eye’s adaptation to low-light conditions.
(b) Focusing on a distant object
Answer: A and B
When focusing on a distant object, the lens becomes thinner and the ciliary muscles relax. Diagrams A and B reflect this condition by showing a flatter lens shape, allowing clear focus on far objects.
Question
Give the LETTERS of TWO diagrams (A, B, C, or D) that represent the eye of a person whose:
(a) Ciliary muscles are contracted
Answer: C and D
Contracted ciliary muscles reduce tension on the suspensory ligaments, making the lens rounder for near vision. Diagrams C and D illustrate this rounded lens shape for close focusing.
(b) Radial muscles are relaxed
Answer: A and C
Relaxed radial muscles result in a constricted pupil (smaller opening), helping limit light entry in bright conditions. Diagrams A and C show a smaller pupil, indicating relaxed radial muscles.
Diagram 1 below represents part of a reflex arc and diagram 2 represents a neuron.
Question
(a) Identify Layer E
Answer: Myelin sheath
The myelin sheath is the insulating layer around the axon that speeds up the transmission of nerve impulses.
(b) Identify Structure F
Answer: Axon
The axon is the long fiber that carries electrical impulses away from the neuron’s cell body toward other neurons or effectors.
Question
(a) Which neuron (A, B, or C) represents the type of neuron shown in diagram 2?
Answer: A
Neuron A is a sensory neuron, just like the neuron shown in diagram 2, which carries impulses from receptors to the central nervous system.
(b) Which neuron is damaged when a person can feel the stimulus but cannot respond?
Answer: C
Neuron C is the motor neuron, which carries impulses from the central nervous system to effectors like muscles. If it’s damaged, the person feels the stimulus but cannot produce a response.
Question
Give the LETTER and NAME of the part that ensures one-directional flow of the impulse.
Answer: D – Synapse
The synapse (D) ensures impulses travel in one direction only by passing chemical signals from one neuron to the next across the gap.