Paper 2

• Function of the nucleus (other than storing genetic information)

  Controls cellular activities
• Structure of the cytoplasm

  Fluid component of the cell, contains organelles, enzymes and dissolved ions and nutrients
• Function of the cytoplasm

  Site of cellular reactions e.g. first stage of respiration, Transport medium
• Function of the cell membrane


  Controls the entry and exit of materials into and out of the cell
• Function of the ribosomes


  Joins amino acids in a specific order during translation for the synthesis of proteins
• Sexual reproduction


  • Type of reproduction
  • Involves the production of gametes by meiosis
  • A gamete from each parent fuses to form a zygote
  • Genetic information from each gamete is mixed so the resulting zygote is unique
• Meiosis


  1. Form of cell division involved in the formation of gametes (non-identical haploid cells) in reproductive organs

  2. Chromosome number is halved

  3. Involves two divisions
• First stage of meiosis

  1. Chromosome pairs line up along the cell equator

  2. The pair of chromosomes are separated and move to opposite poles of the cell (the side to which each chromosome is pulled is random, creating variation)

  3. Chromosome number is halved
• Second stage of meiosis

  1. Chromosomes line up along the cell equator

  2. The chromatids are separated and move to opposite poles of the cell

  3. Four unique haploid gametes are produced
• Importance of meiosis for sexual reproduction

  • It increases genetic variation
  • It ensures that the zygote formed at fertilisation is diploid
• Materials cycling through living and non-living components of an ecosystem

  Organisms take in elements from their surroundings, elements converted to complex molecules which become biomass, elements transferred along food chains, elements returned to environment during excretion and decomposition of dead organisms
• Molecules cycled through ecosystems

  • Oxygen
  • Carbon dioxide
  • Water
• Carbon cycle


  Plants fix carbon dioxide into organic molecules during photosynthesis, the organic carbon-containing molecules are passed onto organisms that eat the plants, carbon dioxide is released back into the atmosphere by respiration from animals and plants, burning fossil fuels also releases carbon dioxide into the atmosphere
• Importance of carbon cycle

  Carbon-containing molecules such as glucose are important for living organisms to grow and provide energy for vital functions within cells
• Water cycle


  Water from lakes and oceans evaporates, the evaporated water condenses into clouds and returns to earth as precipitation, the water from precipitation is useful for life on land, the water then returns to rivers and oceans through surface runoff
• Importance of water cycle

  Living organisms require water and the water cycle provides organisms on land with a continuous supply of water
• Metabolism

  the sum of all reactions happening in a cell or organism, in which molecules are made or broken down
• What is tissue culture?

  A group of cells are grown in a lab into a new tissue or organism
• General steps of selective breeding

  .

  • Breed 2 individuals with the desired characteristics together  
  • Select offspring with the desired characteristics  
  • Breed the offspring together  
  • Repeat the process over many generations
• Describe how muscles in the iris help help the person to see clearly when moving from a dimly-lit area to a brightly lit area

  muscles contract, reducing size of pupil, reduces light entering
• what is a tissue culture?

  a group of cells are grown into a new organism
• Explain why the pH changes more quickly in milk when the temperature is higher:

  Enzymes are more active, lipids are broken down more quickly, and fatty acids are produced more quickly (which change pH)
• Explain how the production of thyroxine causes an increase in body temperature

  thyroxine increases metabolic rate, respiration releases heat
• Explain how the decrease in the concentration of ADH would cause changes to the urine:

  Tubules less permeable to water, less water is reabsorbed, more water in urine causing increased rate of production of urine, more water in urine causing lower concentration of dissolved substances.
• Describe how meiosis produces cells that are genetically different.

  Random chromosomes from each pair, moves to one end of the cell