Bio paper 1 struggle

• Mitosis


  The process by which a cell divides into two or more cells
• Body cells


  • Contain 23 pairs of chromosomes
• Gametes


  • Contain unpaired chromosomes
• Chromosomes

  Carry a large number of genes that determine many of our features
• Cell cycle including mitosis

  1. DNA replication

  2. Mitosis

  3. Cytoplasm and cell membrane division
• Mitosis copies one cell into two
• Functions of mitosis


  • Essential for growth and development of multicellular organisms
  • Repairs organisms
  • Occurs during asexual reproduction
• Stem cell


  An undifferentiated cell which can give rise to more cells of the same type and can differentiate into other types of cells
• Fertilization


  1. Sperm cell joins with ovum

  2. Fertilized ovum undergoes mitosis

  3. Forms a ball of cells called an embryo

  4. Cells continue to undergo mitosis

  5. Cells begin to form specialized cells
• Differentiation


  The process where cells specialize
• Embryonic stem cells


  Undifferentiated cells in the early stage embryo that can differentiate into any type of body cell
• Adult stem cells


  Stem cells found in adult organisms that cannot differentiate into any other type of cell
• Adult stem cells


  • Bone marrow stem cells that differentiate into blood cells
• Bone marrow transplant


  1. Patient's bone marrow is destroyed

  2. Patient receives transplant of donor bone marrow

  3. Stem cells divide and form new bone marrow

  4. Stem cells differentiate and form blood cells
• Problems with bone marrow transplants

  • Donor must be compatible
  • Risk of viruses being passed from donor to patient
• Therapeutic cloning


  1. Embryo is produced with same genes as patient

  2. Stem cells from embryo can be transplanted into patient without rejection

  3. Stem cells can differentiate to replace malfunctioning cells
• Therapeutic cloning could be useful for a range of medical conditions
• Some people have ethical or religious objections to therapeutic cloning
• Plant stem cells


  • Found in meristem tissue at root tips and buds
  • Can differentiate into any type of plant tissue
• Using plant stem cells

  1. Can clone rare plants to prevent extinction

  2. Can produce cloned crop plants resistant to diseases
• Circulatory system in fish

  Deoxygenated blood is pumped from the heart to the gills where it collects oxygen and becomes oxygenated, the oxygenated blood then passes straight from the gills to the organs where the oxygen diffuses out of the blood and into the body cells, the blood now returns to the heart
• Problem with single circulatory system in fish

  The blood loses a lot of pressure as it passes through the gills before reaching the organs, this means the blood travels to the organs relatively slowly so it cannot deliver a great deal of oxygen
• Circulatory system in humans


  Deoxygenated blood is pumped from the heart to the lungs where it collects oxygen, this oxygenated blood then returns to the heart, the heart now pumps the oxygenated blood to the organs where the blood transfers its oxygen to the body cells, the blood now returns back to the heart
• Benefit of double circulatory system in humans

  Because the blood passes through the heart twice, it can travel rapidly to the body cells delivering the oxygen that the cells need
• Heart


  • An organ consisting mainly of muscle tissue
  • The job of the heart is to pump blood around the body
• Heart chambers


  4 chambers - left atrium, right atrium, left ventricle, right ventricle
• Valves


  Separate the atria from the ventricles
• Blood vessels entering/leaving the heart

  • Vena cava (brings in oxygenated blood from the body)
  • Pulmonary artery (blood passes from the heart to the lungs)
  • Pulmonary vein (oxygenated blood passes from the lungs to the heart)
  • Aorta (blood is pumped from the heart to the body)
• Pattern of blood flow through the heart


  1. Blood enters the left and right atria

  2. Atria contract, forcing blood into the ventricles

  3. Ventricles contract, forcing blood out of the heart

  4. Valves prevent backflow into the atria
• Left ventricle


  • Has a thicker muscular wall than the right ventricle, as it pumps blood around the entire body and needs to provide greater force
• Coronary arteries


  Branch out of the aorta and spread into the heart muscle, their purpose is to supply oxygen to the muscle cells of the heart
• Pacemaker


  A group of cells found in the right atrium that control the natural resting heart rate
• Artificial pacemaker


  A small electrical device implanted by doctors to correct irregularities in the heart rate when the natural pacemaker stops working correctly
• Arteries


  Carry very high pressure blood from the heart to the organs in the body
• Arteries


  • Have very thick muscular walls to withstand the very high pressure of the blood
  • Contain elastic fibers that stretch when the surge of blood passes through and then recoil in between the surges to keep the blood moving
• Capillaries


  Where substances such as glucose and oxygen diffuse from the blood to the cells, and carbon dioxide diffuses from the cells back to the blood
• Capillaries


  • Have very thin walls so the diffusion pathway is very short, allowing substances to diffuse rapidly between the blood and the body cells
• Veins


  Carry blood back to the heart
• Veins


  • Have thin walls because the blood pressure is low
  • Contain valves that stop blood flow backwards when the blood is flowing in the correct direction
• Blood travels through the arteries and surges every time the heart beats, which can be felt as a pulse in the wrist