Biology

• Palisade cell

  Function: Absorb sunlight and make nutrients

  Adaptation: Regular in shape, closely packed with chloroplasts to form a continuous layer for efficient absorption of sunlight for photosynthesis

  Found: Below the epidermis of leaf
• Root hair cell


  Function: Take in water and mineral ions from the soil, transport water and mineral salts from roots to stem, leaves, flowers and fruits, provide support for parts of plant above the ground

  Adaptation: Have finger-like projection that increases surface area for more water intake, have large number of mitochondria to provide energy for active transport, have concentrated vacuole to help absorb water by osmosis

  Structure: No nucleus and cytoplasm so water can pass freely, no end walls so can form a continuous tube, have thick cell wall containing lignin to resist bending strains
• Cell membrane


  Description: Elastic thin layer that allows the cell to change its shape, made of proteins and fats, partially permeable

  Function: Prevents cell contents from escaping, controls what substances enter and leave the cell
• Cytoplasm


  Description: Jelly-like, made of water (70%), salts and proteins

  Function: Contains cell organelles, site of chemical reactions
• Nucleus


  Description: Circular or oval structure containing DNA in the form of chromosomes

  Function: Controls cell division, development and activities
• Inheritance


  The transmission of genetic information from generation to generation
• Chromosomes


  • Long threads, made of DNA & proteins
  • Can be seen clearly when the cell is dividing
  • Each species has its own chromosome number
  • The chromosomes contain genes
• Genes


  Length of DNA that codes for a protein
• Homologous chromosomes


  The chromosomes are always found in pairs, one from the male gamete and the other from the female gamete
• Diploid cell


  Cell which contains the full number/two sets of chromosomes characteristic for the species (2N)
• Haploid cell


  Cell which contains the half number of chromosomes/one set of chromosomes characteristic for the species (N)
• Alleles


  Any versions/forms of a gene
• Dominant allele


  Stronger than recessive allele, always shows if present
• Recessive allele


  Weaker than dominant allele, only shows if both present
• Dominant and recessive alleles

  • F=freckles (dominant)
  • f=no freckles (recessive)
• Genotype


  Genetic make-up/constitution of an individual/allele content
• Phenotype


  Outward appearance of an individual/feature/characteristic
• Homozygous/pure


  Organism whose alleles for a characteristic are the same e.g. BB and bb
• Heterozygous/hybrid


  Organism whose alleles for a characteristic are different e.g. Bb
• Dominant allele


  Allele which shows its effect in the phenotype of a heterozygote
• Recessive allele


  Allele which doesn't show its effect in the phenotype of a heterozygote
• Genetic ratios


  The ratio 3:1
• Parent's phenotype


  • Brown eyed
  • Brown eyed
• Gametes


  1. B

  2. b
• Offspring genotype


  • BB
  • Bb
  • Bb
  • bb
• Offspring phenotype


  • Brown eyed
  • blue eyed
• The ratio 3:1 is expected when 2 heterozygote parents are mated
• Punnett square