biology paper 1

• Chromosomes


  DNA molecules combined with proteins that contain genes which provide the instructions for protein synthesis
• Gene


  A section of DNA which codes for a protein
• The nucleus of human body cells contains 46 chromosomes
• The nucleus of gametes contains 23 chromosomes
• Arrangement of chromosomes in body cell nucleus


  Arranged in pairs - 46 chromosomes form 23 pairs
• Cell cycle


  1. Replication of DNA and synthesis of organelles

  2. Mitosis

  3. Division of cell
• Mitosis


  • Produces identical cells which all have the same genetic information
  • Produces additional cells for growth and repair
• First stage of cell cycle

  Longest stage - cells grow and increase in mass, replicate DNA and synthesise more organelles (eg. mitochondria, ribosomes)
• Second stage of cell cycle


  Each chromosome in a pair is pulled to opposite poles of the cell, then the nucleus divides
• Third stage of cell cycle


  The cytoplasm and cell membrane divide - two identical daughter cells are produced
• Stem cell


  An unspecialised cell which is capable of differentiating into other cell types and of self-renewal
• Function of embryonic stem cells

  • Can replicate themselves and differentiate into many other types of cells
  • May be able to treat conditions such as paralysis and diabetes by dividing to replace damaged cells
• Function of adult stem cells in bone marrow

  • Can differentiate into several cell types to replace dead or damaged tissues
  • Bone marrow stem cells can form many different types of blood cell
• Function of stem cells in plant meristems


  • Retain the ability to differentiate into any type of plant cell throughout their lifespan - they can differentiate into any cell which is required by the plant
• Therapeutic cloning


  • A cloning method where an embryo is produced with the same genetic makeup as the patient
  • The stem cells which originate from the embryo will not be rejected by the patient's immune system, so can be used to treat certain medical conditions
• Advantages of cloning plants using meristem stem cells

  • Can prevent rare plants from becoming extinct
  • Can produce large numbers of plants with a favourable characteristic
  • Can produce identical plants for research
• Issues associated with the use of stem cells

  • Many embryonic stem cells are sourced from aborted embryos - some people have an ethical/religious objection
  • Development of stem cell therapies is slow, expensive and difficult
  • Adult stem cells infected with viruses could transfer infections to patients
  • If donor stem cells do not have a similar genetic makeup to the patient, an immune response could be triggered
• Eukaryotic cells


  Plant and animal cells
• Differences between eukaryotic and prokaryotic cells

  • Prokaryotic cells are much smaller than eukaryotic cells
  • Eukaryotic cells contain membrane bound-organelles and a nucleus containing genetic material, while prokaryotes do not
• Prokaryotic cell wall


  Composed of peptidoglycan
• Genetic information storage in prokaryotic cells


  Found free within the cytoplasm as: Chromosomal DNA (single large loop of circular DNA), Plasmid DNA
• Plasmids


  Small, circular loops of DNA found free in the cytoplasm and separate from the main DNA, carry genes that provide genetic advantages e.g. antibiotic resistance
• Order of magnitude


  A power to the base 10 used to quantify and compare size
• Centimetre (cm)


  1 x 10-2 metres
• Millimetre (mm)


  1 × 10-3 metres
• Micrometre (µm)


  1 × 10-6 metres
• Nanometre (nm)


  1 x 10-9 metres
• Difference in order of magnitude between a human hair (length = 100 µm) and the HIV virus (length = 100 nm)

  100 µm = 10-4 m, 100 nm = 10-7 m, -4-(-7) = -4 + 7 = 3
• Components of both plant and animal cells


  • Nucleus
  • Cytoplasm
  • Cell membrane
  • Mitochondria
  • Ribosomes
• Additional cell components found in plant cells

  • Chloroplasts
  • Permanent vacuole
  • Cell wall
• 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 mitochondria

  Site of later stages of aerobic respiration in which ATP is produced
• Function of the ribosomes


  Joins amino acids in a specific order during translation for the synthesis of proteins
• Function of the plant cell wall

  Provides strength, Prevents the cell bursting when water enters by osmosis
• Contents of the permanent vacuole

  Cell sap (a solution of salts, sugars and organic acids)
• Function of the permanent vacuole

  Supports the cell, maintaining its turgidity
• Function of chloroplasts


  Site of photosynthesis