Biology Year 10 semester 1

• Cell theory


  • All living things are composed of one or more cells
  • The cell is the basic structural and functional unit of living organisms
  • All cells arise from pre-existing cells
• Ten life processes for an organism to qualify as 'living'

  • Maintaining a stable environment
  • Controlled exchange of materials
  • Response to stimuli
  • Obtaining energy and chemical elements
  • Transport of materials
  • Removal of waste
  • Cell division
  • Growth and development
  • Reproduction
  • Independent movement
• DNA


  • Deoxyribonucleic acid (DNA) is the molecule that stores and transmits genetic information that determines the characteristics of all living things
  • These characteristics are heritable
  • It has double helix structure and is located in the nucleus of eukaryotic cells
• James Watson and Francis Crick described the structure of DNA in 1953, due to the work of Rosalind Franklin
• Complementary base pairing

  • Each of the four bases in a nucleotide have their own chemical structure that are complementary to another base
  • A pairs with T
  • G pairs with C
  • This allows DNA to replicate itself accurately
• Nucleotide


  • DNA is made up of nucleotides
  • A nucleotide consists of a deoxyribose sugar, a phosphate group, and one of the four nitrogenous bases (Adenine, Thymine, Guanine, Cytosine)
  • The phosphate attaches to the sugar of the next nucleotide, creating a 'backbone' of alternating phosphates and sugars, forming a strand of DNA
• Genes


  • A gene is a section of DNA along a chromosome
  • Each gene will code for a specific protein
  • Genes are the basic functional unit of heredity (the transmission of genetic traits from one generation to the next)
  • Different genes vary in length from each other (the number of bases)
• Chromosomes


  • A chromosome is a thread-like structure composed of DNA and proteins found in the nucleus of a cell
  • Chromosomes carry genetic information in the form of genes, which are segments of DNA that code for specific traits of functions
  • Every cell of an organism has the same number of chromosomes
  • Generally, members of the same species also have the same number of chromosomes
• Human chromosomes


  • In humans the chromosome number is 46, but it is often expressed as 13 pairs because each chromosome has a partner
  • Pairs of chromosomes are the same in size, shape, banding pattern, and provide information for the same characteristics
  • The number of chromosomes generally determines the species
• Chromosome types


  • Non-sex chromosomes (autosomes)
  • Sex chromosomes (XX for females, XY for males)
• Proteins


  • Genes code for specific proteins
  • Proteins are large molecules composed of chains of amino acids
  • They perform a wide variety of functions in the body
• Examples of proteins


  • Haemoglobin
  • Insulin
  • Collagen
• DNA Replication


  • DNA replication is the mechanism for copying (doubling) the DNA
  • It occurs in the nucleus of the cell
  • DNA replication is semi-conservative because each double strand of DNA consists of an old temple strand and a new complementary strand
  • DNA replication occurs before cell division to ensure each new cell (daughter cell) has a complete copy of the genetic material from the parent cell
• DNA replication process


  1. Helicase breaks the hydrogen bonds between the complementary bases

  2. Each strand serves as a template for making a new complementary strand

  3. DNA nucleotides base-pair to the exposed bases A-T or G-C

  4. Enzymes (DNA polymerases) link the nucleotides to the newly forming strand

  5. Each new double stranded DNA molecule rewinds into a double helix
• Mitosis


  • Mitosis is a type of cell division that occurs in somatic cells (non sex cells)
  • During mitosis, a single cell divides into two identical daughter cells
  • This process is essential for growth, repair, and maintenance of tissues and organs in multicellular organisms
• Mitosis stages


  1. Interphase

  2. Prophase

  3. Metaphase

  4. Anaphase

  5. Telophase

  6. Cytokinesis
• Meiosis


  • Meiosis is the process of cell division that produces the gametes - sex cells (sperm and eggs)
  • Meiosis creates daughter cells with exactly half as many chromosomes as the starting cell
  • Meiosis is the division process of going from a diploid cell to a haploid cell
• In humans, the haploid cells are sperms and eggs. When a sperm fuses with an egg during fertilisation, the two haploid sets of chromosomes form a diploid set.
• Genetic variation


  • Sexual reproduction results in nearly infinite possibilities of genetic variation, which is vital to the survival of species
  • This occurs mainly due to crossing over and independent assortment
• Crossing over


  • Crossing-over is the exchange of genetic material between homologous chromosomes
  • It results in new combinations of genes on each chromosome
  • The points where homologous chromosomes cross over and exchange genetic material is random
• Independent assortment


  • When cells divide during meiosis, homologous chromosomes are randomly distributed to daughter cells
  • This results in gametes that have unique combinations of chromosomes (i.e. some from the father of the original organism, some from the mother)
• Mendelian genetics - alleles


  • The inherited traits are determined by genes that are passed from parents to children
  • A child inherits two sets of genes—one from each parent
  • A trait may not be observable, but its gene can be passed to the next generation
  • Every organism inherits two copies of every gene
  • The variations in a gene - different traits, are known as alleles
  • A capital letter represents a dominant trait, a lowercase letter represents a recessive trait
• Phenotype and Genotype


  • Phenotype is the allele that is expressed (observed)
  • Genotype is the genetic information inherited from both parents for that gene, which results in a phenotype
• Homozygous vs Heterozygous


  • Homozygous genotypes refers to an individual that has inherited the same allele from both parents
  • Heterozygous genotypes are when the individual has inherited a different allele from each parent