2.1 Identify organelle 3 - NSC Life Sciences - Question 2 - 2024 - Paper 2

Molecule 1, which is an mRNA molecule, carries the genetic code from the DNA in the nucleus to the ribosome, where it acts as a template for synthesizing the protein. The ribosome reads the sequence of nucleotides on the mRNA to assemble the appropriate amino acids to form a protein.

(a) The sequence of nitrogenous bases at position 2 is CCU.
(b) On the DNA molecule that coded for histidine, the sequence is GTA.

The change in the amino acid sequence, from alanine to tryptophan, may result from a mutation in the DNA sequence, specifically a point mutation where a nucleotide is substituted, leading to an alteration in the mRNA coding sequence. This could change the tRNA's corresponding amino acid, affecting the protein's structure and function.

Transcription is the process by which the genetic information encoded in DNA is transcribed into messenger RNA (mRNA). During transcription, the DNA double helix unwinds, and one strand serves as a template to synthesize a complementary mRNA strand using RNA nucleotides. This mRNA strand then carries the genetic instructions from the DNA to the ribosome for protein synthesis.

Part B represents the centromere, which is essential for the movement of chromosomes during cell division.

Part A functions as the spindle fibers, which help in the alignment and segregation of chromosomes during meiosis.

Metaphase I contributes to natural selection by allowing for genetic variation through the random assortment of homologous chromosomes. This leads to different combinations of alleles in gametes, promoting diversity within a population. Individuals with favorable traits are more likely to survive and reproduce, hence potentially passing on those traits.

Cell D should accurately depict the structure of chromosomes, including a straight shape for the missing 4th chromosome, reflecting the proper configuration and arrangement typical of a haploid cell formed at the end of meiosis.

The diagram represents three generations.

The genotype of individual 9 is Bb, indicating that they are heterozygous with one allele for cystic fibrosis.

Both individuals 5 and 6 must be heterozygous (Bb) for cystic fibrosis because they do not exhibit the condition, yet they have offspring (individuals 8 and 9) that do have the disorder. Since cystic fibrosis is caused by a recessive allele, both parents must carry at least one recessive allele to have affected children.

P1 generation:

• Parental genotypes: Bb x Bb
  F1 generation:
• Genotype: BB, Bb, Bb, bb
• Phenotype: 1 with cystic fibrosis (bb) and 3 without cystic fibrosis (BB or Bb). This illustrates that there is a chance (25%) of offspring inheriting cystic fibrosis.

Genetic engineering of Bt corn was done by isolating a gene for insect resistance from bacteria, specifically Bacillus thuringiensis. This gene was inserted into the corn's DNA, allowing the plant to express a protein that is toxic to specific pests, thereby reducing the need for chemical insecticides.

As the percentage of land used to grow Bt corn increased from 1995 to 2010, the amount of insecticide used decreased significantly. This inverse relationship suggests that Bt corn's genetic modifications effectively reduced the reliance on chemical insecticides due to its inherent pest resistance.

1. Longer shelf-life, which reduces food waste and extends storage options.
2. Improved crop yield, which ensures a higher production rate and helps meet food demand.

The bar graph should clearly display the percentage of land allocated for Bt corn, showing a steady increase from 0% in 1995 to 60% in 2010, with correctly labeled axes and a title to denote the information presented.