y10 science semseter exam

• DNA is a double helix structure and has a sugar phosphate backbone
• The base pairs are A-T and G-C
• A gene is a short stretch of DNA. This is 'packaged' into a chromosone when the cell divides.
• DNA is a molecule that contains the genetic code that is inherited.
• Genes contains a particular sequence and number of bases, providing a code for a particular protein.
• A chromosome contains a strand of DNA inside the nucleus of the cell.
• Humans have 46 chromosomes or 23 pairs.
• Mitosis occurs in somatic cells for cell repair, replacement and growth.
• During mitosis, one parent cell will divide into genetically identical daughter cells.
• Meiosis occurs in reprodctive cells to produce gametes.
• During meiosis, one parent cell will divide twice to produce 4 genetically non-identical daughter cells.
• Nitrogenus base pairs are connected by weak hydrogen bonds.
• Percipitation reactions form an insoluable solid (called a precipitate) when two clear solutions or a gas are mixed.
• Acid Based Reactions/Netrualisation

  Acid + Base --> salt + water
• Group 7 (Halogens) reactivity increases as you move up the group.
• The reacitivity of metals increases as you move down the group.
• Combustion reactions occur when a substance is burned in oxygen, it is always a recantant.
• Ionic bonds are a transfer of electrons between metals and non-metals. Metals lose electrons and non-metals gain electrons to gain a full outer shell.
• Naming of ionic compounds, the suffix -ide to the end of the anion.
• A chemical reaction only occurs when recantants collide with sufficent energy to break the bonds.
• The speed of a chemical reaction can be altered by changing temperature, concentration, agitation and surface area if the recantants, or adding a catalyst.
• Catalysts increase the rate of a reaction without being used up themselves.
• Changing the temperature = independant variable

  Time Taken = dependent variable
• Acid pH can either be strong, moderate or weak.
• Base/Alkali has a pH from 8-14
• HCl is a strong acid with a pH of 1 and Acetic Acid (vinegar) is a weak acid with a pH of 4
• Metallic structures are made up of cations and delocalised electrons. The sea of electrons give metals their unique properties as the electrons can transfer energy and move freely.
• Mitosis


  1. Cell repair and replacement

  2. Growth

  3. Asexual reproduction (cloning) in bacteria
• Meiosis


  Production of gametes - sperm and egg/ova cells in the sex organs
• Gametes


  Fertilisation = fusion of sperm and egg cell to produce a zygote
• Mutations


  Initial change in DNA
• Mutations allow for evolution to occur
• Alleles


  Variations of genes
• Gregor Mendel (Monk) explained that each inherited trait is due to two alleles being inherited - one from the father and one from the mother
• Natural selection


  1. Overproduction

  2. Variation

  3. Competition

  4. Survival of the fittest (best suited to the environment)

  5. Reproduction

  6. Inheritance of traits from parents to offspring
• Variation and adaptations contribute to natural selection
• Variation amongst bacteria can lead to some being resistant to antibiotics
• Artificial selection


  Important mechanism for change driven by humans in (the evolution of) species
• Selective breeding of animals by humans can slowly produce animals with traits believed to be desirable by humans
• Analogous Structures are structures that have similar functions but are not identical.