confident

• What are similar cells organized into?

  Tissues
• What are tissues organized into?

  Organs
• What are organs organized into?

  Organ systems
• What are enzymes?

  Catalysts produced by living things
• What is a catalyst?

  A substance that speeds up reactions
• Why do enzymes have special shapes?

  To catalyse reactions effectively
• What do digestive enzymes break down?

  Big molecules
• What conditions do enzymes need to avoid denaturation?

  Optimum pH and temperature
• What happens in the alveoli?

  Gas exchange takes place
• What is the composition of blood passing next to alveoli?

  Lots of carbon dioxide and little oxygen
• What happens to oxygen in the alveoli?

  It diffuses into the blood
• What happens to carbon dioxide in the alveoli?

  It diffuses into alveoli to be breathed out
• What happens when blood reaches the cells?

  Oxygen is released and diffuses into cells
• What happens to carbon dioxide in the cells?

  It diffuses out into the blood
• What do arteries do?

  Carry blood away from the heart
• Why are artery walls strong and elastic?

  Due to blood at high pressure
• What do capillaries do?

  Involved in the exchange of materials
• What is unique about capillary walls?

  Typically one cell thick
• What do veins do?

  Carry blood to the heart
• Why do veins have thinner walls?

  Due to blood at lower pressure
• What do veins have to prevent backflow?

  Valves
• What do white blood cells do?

  Defend against infection
• How do some white blood cells engulf microorganisms?

  Through phagocytosis
• What do other white blood cells produce?

  Antibodies and antitoxins
• cancer is the result of changes in cells that lead to uncontrolled growth and division
• Benign tumours are growths of abnormal cells which are contained in one area - they do not invade other areas of the body
• Malignant tumour cells are cancers. They invade neighbouring tissues and spread to different parts of the body in the blood where they form secondary tumours