Life Science Grade 12 | Essential Revision 2

Life Science Grade 12

QUESTION 1.1

1.1.1 The function of the epididymis is to:

A) Produce semen.
B) Transport sperm to the urethra.
C) Produce sperm.
D) Store sperm until maturation.

The answer is: D

1.1.2 Which ONE of the following is an exocrine gland?

A) Pituitary
B) Prostate
C) Adrenal
D) Thyroid

The answer is: B

1.1.3 A list of the functions of the brain is provided below:

(i) Interprets sensation
(ii) Regulates involuntary actions
(iii) Controls higher thought processes
(iv) Controls voluntary actions

Which ONE of the following combinations are the functions of the cerebrum?

A) (ii) and (iii) only
B) (i), (ii), (iii) and (iv)
C) (i), (iii) and (iv) only
D) (i) and (ii) only

The answer is: C

1.1.4 An acrosome has:

A) Mitochondria to produce energy for the movement of sperm.
B) A chromatin network that carries genes.
C) Enzymes needed to penetrate the ovum.
D) A tail to facilitate the movement of sperm.

The answer is: C

1.1.5 Ovulation is stimulated by an increase in the levels of:

A) Progesterone
B) LH
C) FSH
D) Oestrogen

The answer is: B

1.1.6 Barotrauma is a common condition that occurs when pressure builds up in the middle ear. This causes the tympanic membrane to bulge. It is most common among deep-sea divers. Divers are advised against diving when they have a middle-ear infection because the:

A) Auditory canal cannot equalize the pressure in the middle ear.
B) Eustachian tube is blocked and air cannot enter the middle ear.
C) Tympanic membrane is hardened and cannot pass the vibrations onto the middle ear.
D) Ossicles are fused together and cannot vibrate freely in the middle ear.

The answer is: B

1.1.7 Which ONE of the following shows the correct combination of the hormone with its target organ?

A) Prolactin – Pituitary gland
B) Glucagon – Pancreas
C) LH – Uterus
D) TSH – Thyroid gland

The answer is: D

1.1.8 Oogenesis takes place in the:

A) Uterus
B) Ovary
C) Cervix
D) Vagina

The answer is: B

1.1.9 An investigation was done in which a potted plant was placed horizontally on a clinostat, as shown in the diagram. The plant was exposed to uniform light from all directions. The stem grew vertically upwards, which indicates that the clinostat was:

A) Stationary and the stem showed negative geotropism.
B) Rotating and the stem showed positive geotropism.
C) Stationary and the stem showed negative phototropism.
D) Rotating and the stem showed positive phototropism.

The answer is: A

1.1.10 An investigation was done to determine the effect of caffeine on reaction time. Which ONE of the following increased the reliability of the results obtained?

A) Gender of the volunteers
B) Age of the volunteers
C) 50 volunteers used
D) Type of caffeine used

The answer is: C

Give the correct biological term for each of the following descriptions.

QUESTION 1.2

1.2.1 The planting of the same crop on the same land repeatedly:

The answer is: Monoculture

1.2.2 The permanent removal of trees and vegetation from an area:

The answer is: Deforestation

1.2.3 A part of the male reproductive system used to transfer semen to the female:

The answer is: Penis

1.2.4 The part of the nervous system that is made up of spinal and cranial nerves:

The answer is: Peripheral

1.2.5 A type of vision in which both eyes are used together to focus on an object:

The answer is: Binocular vision / Stereoscopic vision

1.2.6 The structure that the Graafian follicle develops into after ovulation:

The answer is: Corpus luteum

1.2.7 A functional gap between two consecutive neurons:

The answer is: Synapse

1.2.8 An underground permeable rock that stores water:

The answer is: Aquifer

1.2.9 The hormone that stimulates puberty in females:

The answer is: Oestrogen

QUESTION 1.3

Indicate whether each of the descriptions below applies to A ONLY,B ONLY, BOTH A AND B or NONE

1.3.1 A factor that reduces food security:

A) Floods
B) Drought

The answer is: Both A and B

Both floods and droughts are environmental factors that can severely impact food security. Floods can destroy crops and infrastructure, while droughts can lead to water shortages, reducing crop yields and food availability.

1.3.2 The part of a neuron that speeds up the transmission of an impulse:

A) Myelin sheath
B) Axon

The answer is: A only

The myelin sheath is a protective covering around the axon of a neuron that acts as an insulator, allowing electrical impulses to travel more quickly along the nerve cell. The axon transmits the impulse, but the speed is enhanced by the presence of the myelin sheath.

1.3.3 A factor that impacts on biodiversity:

A) Poaching
B) Habitat destruction

The answer is: Both A and B

Both poaching and habitat destruction negatively affect biodiversity. Poaching reduces species populations by illegal hunting, often leading to extinction. Habitat destruction removes the natural environment that species rely on, leading to a decline in biodiversity.

QUESTION

1.4 The diagram below represents a part of the human ear.

1.4.1 Identify part:
(a) A
(b) B

1.4.1 Identify part:

(a) Part A is: Semi-circular canals
The semi-circular canals are part of the inner ear responsible for maintaining balance. They detect rotational movements of the head and help in coordinating balance and spatial orientation.

(b)Part B is: Auditory nerve
The auditory nerve, also known as the cochlear nerve, carries sound information from the cochlea in the inner ear to the brain. It plays a crucial role in transmitting auditory signals for sound perception.

1.4.2 Give the LETTER and NAME of the part that:

• (a) Creates pressure waves in the fluid of the inner ear: The letter representing the part is E and the name is – Oval window: The oval window is a membrane-covered opening that leads from the middle ear to the cochlea of the inner ear. When the stapes bone vibrates against the oval window, it creates pressure waves in the fluid inside the cochlea, which are essential for hearing.
• (b) Absorbs excess pressure waves in the inner ear to prevent the formation of an echo: The letter representing the part is D – and the name is Round window
  The round window is another membrane-covered opening in the inner ear. It acts as a pressure release valve, allowing the fluid in the cochlea to move properly when the oval window creates pressure waves. This prevents the build-up of pressure that could distort sound transmission or create echoes.

1.4.3 Name the:
(a) Part of the brain that interprets impulses from part F
(b) Receptors found at C

• (a) Part of the brain that interprets impulses from part is called Cerebellum
  The cerebellum is the part of the brain that processes information related to balance and coordination. It interprets the signals from the semi-circular canals (part F) to help maintain balance and coordinate movements.
• (b) Receptors found at C: They are called Hair cells / Organ of Corti
  The hair cells in the Organ of Corti, located in the cochlea (part C), are the sensory receptors for hearing. They convert mechanical vibrations from sound waves into electrical signals that can be interpreted by the brain as sound.

1.5 A boy steps on a nail and pulls his leg away suddenly. The diagram below shows the pathway taken to create this reaction.

1.5.1 Name the pathway represented by the diagram.

The pathway represented in the diagram is called the reflex arc
The reflex arc is the neural pathway that controls an immediate, involuntary response to a stimulus, such as pulling your leg away after stepping on a nail. It bypasses the brain, allowing for a faster reaction to prevent injury.

1.5.2 Give ONE advantage of this type of reaction.

This type of reaction helps to minimize injury
The main advantage of a reflex action is that it allows the body to respond quickly to potentially harmful stimuli. By minimizing the time it takes to react, reflex actions help protect the body from injury, such as pulling away from a sharp object before it can cause significant damage.

1.5.3 Identify part:

(a) B
(b) C
(c) E

• a) B is the Interneuron/connector
  The interneuron, or connector neuron, is located in the spinal cord and serves as a link between the sensory neuron and the motor neuron in the reflex arc. It processes the incoming sensory information and triggers an immediate response by activating the motor neuron.
• (b) C is the Ventral root
  The ventral root is the part of the spinal nerve that carries motor signals from the spinal cord to the muscles. In the reflex arc, the motor neuron exits the spinal cord through the ventral root to stimulate the effector muscle.
• (c) E: is the Effector/muscle
  The effector in a reflex arc is typically a muscle or gland that carries out the response to the stimulus. In this scenario, the effector muscle contracts to pull the leg away from the nail, completing the reflex action.

Religious studies grade 12 Revision 3

1.5.4 Give the LETTER and NAME of the neuron that transports impulses towards the spinal cord:

The letter is A and the name is Sensory neuron
The sensory neuron (A) detects the stimulus (stepping on a nail) and transmits the nerve impulse towards the spinal cord. This neuron is responsible for conveying information from the receptors in the skin to the central nervous system, where the reflex response is initiated.

QUESTION 2
2.1 The diagram below shows a phase during meiosis in an animal cell.

2.1.1 Identify part C:

Part C is the Centromere
The centromere is the region of a chromosome where the two sister chromatids are held together. During meiosis, the centromere plays a crucial role in ensuring the correct separation of chromosomes, as it attaches to spindle fibers that pull the chromatids apart.

2.1.2 Name the phase represented in the diagram:

The phase represented in the diagram is : Metaphase I
In Metaphase I of meiosis, homologous chromosomes align at the equator of the cell, preparing for separation. The centromeres attach to spindle fibers from opposite poles, positioning the chromosomes in a way that ensures the correct division of genetic material.

2.1.3 B represents homologous chromosomes. What are homologous chromosomes?

Homologous chromosomes are a pair of chromosomes that have the same structure, including the same location of the centromere and the same length. They also possess the same sequence of genes. One chromosome in this pair is of maternal origin, while the other is of paternal origin:

2.1.4 Explain the appearance of the chromosomes in the diagram.

Some chromatids have a mixture of genetic material from their homologous chromosomes, which indicates that crossing over took place. This genetic exchange occurs during prophase I of meiosis, where homologous chromosomes pair up and exchange segments of genetic material.

2.1.5 State the function of part A in the phase following the one represented in the diagram:

Part A Contracts to pull the chromosome to the pole

Part A represents the spindle fibers, which are responsible for separating the chromosomes during meiosis. In the next phase, Anaphase I, the spindle fibers contract, pulling the homologous chromosomes towards opposite poles of the cell, ensuring that each daughter cell receives one chromosome from each pair.

2.1.6 The total amount of DNA is 12 arbitrary units in each daughter cell at the end of this cell division. How much DNA (in arbitrary units) was in the parent cell at the beginning of the cell division?

48 arbitrary units was in the parent cell at the beginning of the cell division

In meiosis, the parent cell undergoes a reduction division, meaning the amount of DNA is halved as the cell divides. Meiosis produces four daughter cells, each containing half the genetic material of the parent cell. If each daughter cell has 12 arbitrary units of DNA at the end of meiosis, the parent cell must have initially contained 48 arbitrary units of DNA. This is because the total DNA is divided equally among the four daughter cells

2.2 The diagram below represents a part of the human skin

2.2.1 Identify part B.

Part B in the diagram represents the sweat gland, which is responsible for producing sweat. This gland plays a crucial role in regulating body temperature

2.2.2 Describe how structure A functions during thermoregulation on a cold day.

On a cold day, structure A, which is a blood vessel, constricts in a process known as vasoconstriction. This reduces the amount of blood flowing towards the surface of the skin, which in turn minimizes heat loss from the body. By restricting blood flow to the skin, the body retains more heat, helping to maintain its core temperature. As a result, this mechanism allows the body to conserve heat and bring the temperature back to a normal, stable level.

2.2.3 Explain why temperature needs to be kept constant in the human body.

Maintaining a constant temperature in the human body is essential because enzymes that facilitate various biochemical reactions function optimally at around 37°C. If the body temperature rises too high, these enzymes can denature, meaning they lose their shape and can no longer carry out their functions. on the other hand, if the temperature drops too low, the enzymes become inactive, slowing down vital processes. Therefore, keeping the body temperature stable ensures that all necessary enzymatic reactions continue efficiently to sustain life.

QUESTION 2.3

ADH plays a role in osmoregulation in the human body.

2.3.1 Name the gland that secretes ADH:

The gland responsible for secreting ADH (antidiuretic hormone) is the pituitary gland, also known as the hypophysis.

This gland plays a key role in the regulation of water balance in the body by controlling how much water is reabsorbed by the kidneys, ensuring that blood pressure and hydration levels remain within healthy ranges.

2.3.2 Describe osmoregulation on a cold day:

On a cold day, osmoregulation functions differently because the body loses less water through sweating. As a result, the water levels in the blood are higher than normal. Since the body does not need to conserve water, less or no ADH is secreted. This leads to the renal tubules in the kidneys becoming less permeable to water, meaning less water is reabsorbed back into the bloodstream. Consequently, the body produces more urine, as it no longer needs to retain as much water to maintain balance.

2.3.3 Explain why the ADH levels in the blood will always be higher than normal for a person with a medical condition that causes the renal tubules to become resistant to the effects of ADH:

In a person with a medical condition where the renal tubules are resistant to the effects of ADH, water cannot be reabsorbed into the blood effectively. As a result, the water levels in the blood remain lower than normal, which prompts the body to secrete more ADH in an attempt to correct the imbalance. However, because the renal tubules do not respond to the ADH, the body continuously produces higher levels of the hormone without achieving the desired effect of water reabsorption, leading to persistently elevated ADH levels in the blood.

2.4 Read the extract below.

REPRODUCTION IN GUPPY FISH Guppy fish have a very interesting method of breeding. During mating the male deposits packets of sperm inside the female’s reproductive opening using an organ called the ‘gonopodium’. This process takes place several times and the female stores some of the extra sperm. The fertilised eggs remain in the female’s body until they hatch and the young are born live. The gestation period is usually between 22 and 28 days.

2.4.1 Name the type of fertilisation in guppies:

The type of fertilisation that occurs in guppies is internal fertilisation. In this process, the male guppy deposits sperm inside the female’s reproductive opening, where fertilisation takes place within the female’s body.

2.4.2 Explain TWO ways in which the type of fertilisation named in QUESTION 2.4.1 increases reproductive success:

Internal fertilisation increases reproductive success in guppies in two important ways.

Firstly by depositing sperm directly into the female’s body, increases reproductive success and ensures that more sperm reach the eggs, resulting in a higher number of eggs being fertilised and develop into offspring.

Secondly, once the eggs (Gametes/zygotes) are fertilised, they remain inside the female’s body, which provides a safe environment where the developing embryos are shielded from predators and environmental dangers. This protection increases the chances of the young surviving to birth.

2.4.3 Why Are Guppies Considered Ovoviviparous?

 refers to species in which the embryos develop inside eggs that remain within the mother’s body until they are ready to hatch.

Guppies are regarded as ovoviviparous because their fertilised eggs develop and hatch inside the female’s body. The developing young are nourished by the yolk within the egg, not directly by the mother, but they are born live. There is no placenta involved as the young hatch within the mother and are then released into the environment as live offspring.

Premature delivery of babies (babies born between weeks 28 to 35 ofgestation) has been a concern in many countries. The care of premature
babies is very costly. Women with a history of premature delivery aresometimes given a progesterone treatment between weeks 16 to 20 of
pregnancy. However, this treatment is believed to lead to the development of gestational diabetes mellitus in the mother. An investigation was done to determine if progesterone treatment leads to the development of gestational diabetes mellitus.The procedure was as follows:

• 300 pregnant women with a history of premature delivery participated inthe investigation (those that had pre-existing diabetes mellitus were excluded).
• The women were divided into two equal groups (Group A and Group B).
• The women in Group A were injected once a week with 250 mg of progesterone between weeks 16 and 20.
• Their glucose levels were measured and recorded daily between week 16 and 36 of the pregnancy.
• Group B was the control

2.5.1 Why is the injection of progesterone a good treatment to prevent premature delivery?

The injection of progesterone is an effective treatment for preventing premature delivery because it helps to maintain or thicken the endometrium (the lining of the uterus). By keeping the endometrium intact and healthy, progesterone supports the continuation of pregnancy, reducing the risk of premature birth.

2.5.2 Identify the:

• (a) Independent variable:
  The independent variable in this investigation is the progesterone treatment.
• (b) Dependent variable:
  The dependent variable in this case is the development of gestational diabetes.

2.5.3 Describe how the investigators determined whether any of the participants in Group A had developed gestational diabetes mellitus:

The investigators monitored the glucose levels of the participants daily. If a participant’s glucose level remained consistently high over time, it indicated the development of gestational diabetes mellitus. This method allowed the researchers to track any changes in blood sugar levels that might suggest the onset of diabetes.

2.5.4 State TWO factors that were kept constant when the progesterone was administered in Group A:

Two key factors that were kept constant in the administration of progesterone were

• the same dosage (250 mg of progesterone per injection)
• and the same period of time over which the injections were given (injections were administered weekly between weeks 16 and 20 of pregnancy).

These controlled variables ensured that all participants in Group A received the same treatment under the same conditions.

2.5.5 Group B was the control. Explain the importance of group B in this investigation:

Group B served as the control group in this investigation because they did not receive progesterone injections. The role of this group was crucial, as it allowed the researchers to compare the results between women who received progesterone (Group A) and those who did not (Group B). If gestational diabetes developed in Group A but not in Group B, it would suggest that the progesterone treatment may have contributed to the development of the condition, helping to identify a potential link between the treatment and gestational diabetes.