NATIONAL
SENIOR CERTIFICATE
GRADE 12
JUNE 2022
LIFE SCIENCES
MARKING GUIDELINE
MARKS: 150

SECTION A

QUESTION 1

1.1

1.1.1 D ✓✓
1.1.2 B ✓✓
1.1.3 A ✓✓
1.1.4 A ✓✓
1.1.5 C ✓✓
1.1.6 B ✓✓
1.1.7 A ✓✓
1.1.8 C ✓✓
1.1.9 A ✓✓
1.1.10 C ✓✓   (10 x 2) (20)

1.2

1.2.1 Internal ✓ fertilisation
1.2.2 Umbilical vein ✓
1.2.3 Mitochondrion ✓/Mitochondria
1.2.4 Pinna ✓
1.2.5 Acrosome ✓
1.2.6 Puberty ✓
1.2.7 Chromatin ✓ network
1.2.8 Amniotic ✓egg (8 x 1) (8)

1.3

1.3.1 A only ✓✓
1.3.2 B only ✓✓
1.3.3 None ✓✓ (3 x 2) (6)

1.4

1.4.1 DNA profiling ✓ (1)
1.4.2 Adult C ✓ (1)
1.4.3 

• All bands of adult B and C together ✓
• match all the children’s bands ✓
  OR
• He is the only adult that can provide all the DNA bands ✓ with adult B that the children have ✓ (2)

1.4.4

• Child 1 and 2 ✓✓ (2)

1.4.5

• Tracing missing persons ✓
• Identify crime suspects ✓
• Identification of genetic disorders ✓
• Establishing family relations ✓
• Matching tissues for organ transplants ✓
• Identifying dead persons ✓/animals
  (Mark first TWO only) (2)

1.5

1.5.1 

1. Dihybrid cross ✓ (1)
2. Involves the inheritance of two characteristics ✓ (1)

1.5.2   1 ✓ (1)
1.5.3    FfBb ✓ (1)
1.5.4

1. Fluffy tails and brown fur ✓ (1)
2. ffBb ✓ (1)

1.5.5 ¹²/₁₆  ✓✓ OR ¾ OR 75% (2)
TOTAL SECTION A: 50

QUESTION 2

2.1

2.1.1

1. Deoxyribose ✓ (1)
2. Nucleotide ✓ (1)

2.1.2 

• The DNA (double helix) unwinds✓and
• unzips ✓/hydrogen bonds break
• to form two separate strands ✓
• Both DNA strands serve as templates ✓
• to build a complementary DNA ✓/(A to T and C to G) using free (DNA) nucleotides from the nucleoplasm
• This results in two identical (DNA) molecules ✓
• Each molecule consists of one original strand and one new strand ✓             (Any 6 x 1) (6)

2.1.3 Met ✓- Phe ✓- Cys ✓ (3)
2.1.4

• Codon AUG (on the mRNA) changed to AAG ✓
• Anticodon UAC (on tRNA) changed to UUC ✓
• which resulted in Lys ✓ being picked by tRNA and
• a different protein was formed ✓ (4)

2.2.1 

1. Locus ✓ (1)
2. Centromere ✓ (1)

2.2.2 Heterozygous ✓ (1)
2.2.3 The alleles/letters representing the gene are different. ✓ (1)
2.2.4
Similarity:

• They carry the same genes at the same loci ✓/positions/locations

Difference:

• They carry different alleles ✓
• because of crossing over ✓ during meiosis and
• mutations ✓/copying errors during DNA replication
  1 similarity + Any 2 differences (3)

2.3

2.3.1

1. Zygote ✓ (1)
2. Morula ✓/ Blastula (1)

2.3.2 Fertilisation ✓ (1)
2.3.3 In the fallopian tubes ✓/Oviducts (1)
2.3.4

• The process is oogenesis ✓
• Diploid cells in the ovary undergo mitosis ✓
• to form numerous follicles ✓
• At the onset of puberty ✓
• and under the influence of FSH ✓
• one cell inside a follicle enlarges and undergoes meiosis ✓
• Of the four cells that are produced, only one survives ✓
• to form a mature, haploid ovum ✓ (Any 6 x 1) (6)

2.3.5

•  Amniotic fluid acts as a shock absorber and protect the foetus from mechanical injury ✓ /temperature changes/dehydration
• The placenta serves as a barrier protecting the foetus from certain diseases ✓ (2)

2.4

*1 Compulsory + Any 5 (6)

2.5.1 Karyotype ✓ (1)
2.5.2 Autosomes ✓ (1)
2.5.3 Female ✓ (1)
2.5.4

• The last pair ✓/chromosome pair 23/gonosomes
• consist of two X chromosomes ✓/XX (2)

2.5.5 

• During Anaphase ✓ I/II
• Chromosome pair 21/chromosome failed to separate ✓/ nondisjunction occurred at position 21
• Resulting in a gamete (daughter cell) with an extra chromosome ✓ at position 21
• When this gamete was fertilised by a normal gamete ✓
• The zygote ended up with 3 chromosomes at position 21 ✓ (5)
  [50]

QUESTION 3

3.1

3.1.1 

1. Centriole ✓/ Centrosome (1)
2. Spindle fibre ✓ (1)

3.1.2 Anaphase I ✓ (1)
3.1.3 Each chromosome of each homologous pair is being pulled to the opposite poles ✓ (1)
3.1.4    3 ✓ (1)
3.1.5

• The chromosomes show swapped segments of genetic material ✓ (1)

3.1.6

• Introduces genetic variation ✓ in offspring thereby
• improving the chances of survival ✓ (2)

3.2

3.2.1 

1. Menstruation ✓ (1)
2. Ovulation ✓ (1)

3.2.2

1. Follicle stimulating hormone ✓/FSH (1)
2. Progesterone ✓ (1)

3.2.3

• Stimulates the development of primary follicles into mature Graafian follicle ✓ (1)

3.2.4

• The endometrial lining will no longer be maintained ✓
• This will result in the lining being broken down and shed ✓ during menstruation ✓
• preventing possible implantation of the fertilised egg ✓ and pregnancy ✓
• new follicle ✓ being formed (Any 5 x 1) (5)

3.3

3.3.1 

1. D ✓– Eustachian tube ✓ (2)
2. E ✓– Round window ✓ (2)

3.3.2 Transmits sound vibrations to the middle ear. ✓ (1)
3.3.3

• They lie on three different planes ✓
• to detect movement in any direction ✓
• fluid moves in at least one of the semi-circular canals ✓
• to stimulate receptors ✓                     (Any 3 x 1) (3)

3.4

• The receptor receives the stimulus ✓ and
• converts it into an impulse ✓
• which is transmitted by the sensory neuron ✓
• through the dorsal root ✓
• of the spinal nerve ✓
• to the spinal cord ✓
• where the impulse is transferred via the interneuron ✓
• to the motor neuron ✓
• which carries the impulse via the ventral root ✓
• to the effector ✓/muscle/gland
• The impulse is transferred from one neuron to the next via a synapse ✓
  (Any 7 x 1) (7)

3.5

3.5.1 X = 292 + 301 + 297 ✓
                          3
              = 297 ✓mm ✓ (Accept 296,67/ 296,7) (3)
3.5.2

1. Accommodation ✓ (1)
2.  
   • Ciliary muscles contract ✓
   • Suspensory ligaments slacken ✓/loosen
   • Tension on the lens decreases ✓
   • Lens becomes more convex ✓/more rounded/bulging
   • Light rays are focused on the retina ✓ (5 x 1) (5)

3.5.3

(6)
Guideline for assessing the graph

3.5.4 As the age of the volunteers increase, the longer is the average focusing distance. ✓✓
OR
As the age of the volunteers decreases, the shorter is the average focusing distance ✓✓ (2)
[50]
TOTAL SECTION B: 100
GRAND TOTAL: 150