Qp

• Arrangement of cellulose molecules and secondary thickening in xylem vessels

  1. Cellulose molecules can be organised into microfibrils

  2. Cellulose/microfibrils arranged in different directions/a mesh

  3. Hydrogen bonds in cellulose molecules/microfibrils/layers (of microfibrils)/lignin secondary thickening/pectate add strength/support/stability

  4. Cellulose microfibrils/mesh held together by pectin/pectate

  5. Lignin makes outside of xylem vessels/cell wall impermeable (to water)
• Active mRNA is formed after post-transcriptional modification of pre-mRNA
• Skin colour


  • Example of continuous variation
  • Polygenic trait controlled by 3 genes: A, B, and C
• More dominant alleles present in the zygote

  Increases the darkness of the skin
• Titan arum


  • Critically endangered plant that flowers once every 10 years and the flowers last for 2-3 days
  • Can reproduce asexually or sexually, relies on insects to transfer pollen to other titan arum plants
• Hawaii palila honeycreeper is found only in the mountainous forest on one island
• How a stem cell in a plant can become a sclerenchyma cell

  1. Differential gene expression

  2. Epigenetic modification/histone modification/DNA methylation

  3. Proteins/enzymes synthesised from active genes which permanently modify the cell (e.g. synthesis of cellulose/microfibrils/lignin, secondary thickening, lignification of cell walls)
• Chromosome


  • Chromosome number 1
  • Chromosome number 4
• The diagram shows the location of genes on sweet pea chromosomes
• Genes shown on the chromosomes

  • Gene for flower colour
  • Gene for pollen grain length
  • Gene for pea pod shape
• Role of meiosis in the inheritance of these traits

  1. Meiosis increases genetic variation

  2. Crossing over and (random/independent) assortment occur in meiosis

  3. Alleles for colour and grain length are linked, so unlikely to be separated during crossing over

  4. Alleles for pea pod wrinkles and (colour/grain length) are not linked, so inherited independently due to independent assortment
• These bacteria.
• Description that includes two of the following points:

  • analysis of an aspect of phenotype
  • analysis of (the sequences in) biological molecules
  • (to see if) there are (many) differences (to existing types of bacteria)
• Phenotype


  Physical appearance / growth characteristics/biochemical tests
• Biological molecules


  DNA, genetic material, proteins
• accept compare named aspect of structure / named organelle / ribosomes
• accept see if other bacteria survive in those conditions
• ignore behaviour
• accept molecular phylogeny / genetic profiling / create genetic fingerprint
• ignore compare to other bacteria species unqualified
• ignore similarities
• The percentage survival of bacteria C reduced by over 70% after one day and no bacteria survived after 9 days / the percentage survival of mutated bacteria C reduced by 10% after one day and 60% bacteria C survived after 15 days
• error bars overlap so no significant difference
• Another treatment method could be stem cell therapy using either embryonic stem cells or human induced pluripotent stem cells (hiPSC).
• The hiPSCs are sourced from skin cells from a person without AD.
• Describe how a double-blind clinical trial would be performed with this cancer drug.
• Cells in the pancreas use amino acids to synthesise polypeptides.
• These cells also secrete enzymes and glycoproteins into the small intestine.
• Cells from the pancreas, containing amino acids labelled with a fluorescent marker, were used in an investigation. The fluorescent marker looked green when seen with a special microscope.
• The percentage of green fluorescence inside and outside the cells was measured at the start and after 60 minutes.
• The results of this investigation are shown in the table.
• Time / min


  • Inside the cells
  • Outside the cells
• • 0
  • 100
  • 0
• • 60
  • 38
  • 62
• At start, the amino acids are picked up by tRNA. ERNA carry individual amino acids to the surface of the mRNA for translation to take place. Hence, the polypeptide is formed at ribosomes, enters into cisternae of RER where it is folded to tentiary structure and is packaged into viesicles. these vesicles fuse with golgi apparatus where the protein is modified ex activation of enzyme. All these processes happen inside cell. So percentage of amino acid inside Ill is 100%
• There are still amino acids protein (amino acid) in the RER or golgi apparatus so Percentage of fluorescere is still there inside cells.
• The ironwood tree has wood containing chemical compounds called naphthoquinones. These compounds have antibacterial properties.
• Scientists are investigating whether these compounds could be used to develop a drug to treat people infected with Y. pestis.
• Processing and secretion of proteins

  1. Folded into tertiary structure in the rough endoplasmic reticulum

  2. Protein are packed into vesicles at the end of rough endoplasmic reticulum

  3. Proteins are modified in the Golgi apparatus

  4. Glycosides or carbohydrates are added

  5. Modified protein is packed into secretory vesicles by Golgi apparatus

  6. Proteins leave the cell by exocytosis
• Changes that occur in the prophase


  1. Nucleolus disappears

  2. Nuclear membrane breaks down

  3. Centrioles move to opposite poles

  4. Spindle fibres form

  5. Chromosomes become visible as pair of sister chromatids

  6. Centromeres hold chromatids together