B2 Cell Organisation

• Explain, using an example, why the digestive system is considered as an ‘organ system’.

  The digestive system is considered an organ system because it consists of a group of organs that work together to perform the common function of digesting and absorbing our food. For example the pancreas releases digestive enzymes which help break down the food molecules,
• Tissue

  A group of specialised cells with a similar structure and function, can be made of more than one type of cell
• Tissue examples

  • Muscular tissue
  • Epithelial tissue
• Organ

  Formed from a number of different tissues, working together to produce a specific function
• Organ system

  Organs organised to work together to perform a certain function
• Organs in the digestive system

  • Glands (salivary glands, pancreas)
  • Stomach
  • Small intestine
  • Liver
  • Gall bladder
  • Large intestine
  • Rectum
  • Anus
• Enzymes

  Biological catalysts that increase the rate of reaction without being used up
• Enzymes

  • They can both break up large molecules and join small ones
  • They are protein molecules and the shape of the enzyme is vital to its function
  • Each enzyme has its own uniquely shaped active site where the substrate binds
• Lock and Key Hypothesis

  1. Substrate shape is complementary to active site shape, forming enzyme-substrate complex

  2. Reaction takes place and products are released
• Optimum pH

  The pH at which an enzyme works best, usually around 7 but some have a low optimum pH
• Optimum temperature

  The temperature range around 37 degrees Celsius (body temperature) at which an enzyme works best
• As temperature increases

  The rate of reaction increases up to the optimum, then rapidly decreases and the enzyme denatures
• Types of enzymes

  • Carbohydrases (convert carbohydrates into simple sugars)
  • Proteases (convert proteins into amino acids)
  • Lipases (convert lipids into fatty acids and glycerol)
• Soluble glucose, amino acids, fatty acids and glycerol pass into the bloodstream to be carried to all the cells around the body
• Tests for biological molecules

  • Benedict's test (for sugars)
  • Iodine test (for starch)
  • Biuret test (for protein)
  • Emulsion test (for lipids)
  • Sudan III test (for lipids)
• Bile

  Produced in the liver, stored in the gallbladder, released into the small intestine. It is alkaline to neutralise stomach acid and emulsifies fats.
• Investigating effect of pH on enzyme controlled reaction

  1. Use iodine to detect presence of starch

  2. Warm amylase, starch and buffer solution

  3. Take samples at regular intervals and test with iodine

  4. Time when starch is completely broken down

  5. Calculate rate using 1000/time
• Circulatory system

  Carries oxygen and nutrients to every cell in the body and removes waste products
• Double circulatory system

  Two circuits - deoxygenated blood to lungs, oxygenated blood around body
• Parts of the heart

  • Right atrium
  • Right ventricle
  • Left atrium
  • Left ventricle
  • Muscular walls
  • Valves
  • Coronary arteries
• Blood flow through the heart

  1. Blood flows into right atrium and right ventricle, pumped to lungs

  2. Blood flows into left atrium and left ventricle, pumped around body

  3. Valves prevent backflow
• Pacemaker

  Group of cells in right atrium that provide electrical stimulation to control heart rate
• Artificial pacemaker

  Electrical device that produces a signal causing the heart to beat at a normal speed
• Types of blood vessels

  • Arteries (carry blood away from heart)
  • Veins (carry blood towards heart)
  • Capillaries (allow close contact between blood and cells)
• Lungs

  Supply oxygen to blood and remove carbon dioxide
• Parts of the gas exchange system

  • Trachea
  • Intercostal muscles
  • Bronchi
  • Bronchioles
  • Alveoli
  • Diaphragm
• Ventilation

  Ribcage moves up and out, diaphragm moves down, increasing chest volume and decreasing pressure, drawing in air
• Gas exchange

  Oxygen diffuses from alveoli into blood, carbon dioxide diffuses from blood into alveoli
• Alveoli

  • Small and arranged in clusters for large surface area
  • Capillaries provide large blood supply
  • Thin walls for short diffusion pathway
• Blood

  Made up of plasma, red blood cells, white blood cells and platelets
• Components of blood

  • Plasma
  • Red blood cells
  • White blood cells
  • Platelets
• Red blood cells

  • Biconcave disc shape for large surface area
  • No nucleus for more space to carry oxygen
  • Contain haemoglobin to bind oxygen
• White blood cells

  Part of the immune system, defend against pathogens
• Alveoli

  Very thin, meaning there is a short diffusion pathway
• Calculating breathing rate

  Divide the number of breaths by the number of minutes
• Components of blood

  • Plasma
  • Red blood cells
  • White blood cells
  • Platelets
• Plasma

  Liquid that carries the components in the blood: red blood cells, white blood cells, platelets, glucose, amino acids, carbon dioxide, urea, hormones, proteins, antibodies and antitoxins
• Red blood cells

  • Carry oxygen molecules from the lungs to all the cells in the body
  • Biconcave disc shape provides a large surface area
  • No nucleus allowing more room to carry oxygen
  • Contain the red pigment haemoglobin, which binds to oxygen and forms oxyhaemoglobin
• White blood cells

  • Part of the immune system, which is the body's defence against pathogens (microorganisms that can produce disease)
  • Have a nucleus
  • Types: those that produce antibodies against microorganisms, those that engulf and digest pathogens, those that produce antitoxins to neutralise toxins produced by microorganisms
• Platelets

  • Help the blood clot form at the site of a wound
  • The clot dries and hardens to form a scab, which allows new skin to grow underneath while preventing microorganisms from entering
  • Small fragments of cells
  • No nucleus
  • Without them, cuts would result in excessive bleeding and bruising