B2 TOPIC 3- ORGAN SYSTEMS

B2 TOPIC 3- ORGAN SYSTEMS

1. Evolution

   • Fossils
     • Fossil formation
       • 1. Gradual replacement by minerals- teeth, shell and bone don't decay (last ages when buried). Eventually replaced by minerals forming a rock-like substance shaped like the original hard part (fossil stays distinct inside rock)
       • 2. Casts and impressions- when an organism is buried in a soft material (eg. clay) it hardens arounds it and organism decays- leaving a cast.
       • 3. Preservation- no decay happens because conditions are not suitable for microbes to work
     • What do fossils in rock layers tell us?
       • 1. What creatures and plants looked like
       • 2. How long ago they existed- deeper the rock the older the fossil
       • 3. How they evolved- studying similarities and differences between differently aged rocks can show how species have developed
     • Why is the fossil record incomplete?
       • Very few dead plants/animals turn into fossils- most decay away
       • Some body parts (soft tissue) decay completely
       • Some fossils are yet to be discovered
   • Pentadactyl limb- a limb with 5 digits
     • Evident in many species eg. mammals, reptiles and amphibians
     • In each species, limb has similar structure but different function
     • Similarity in bone structure means that species with the limb evolved from common ancestor

2. Growth and development

   • How to measure an organism
     • Size- height, length, width or circumference
     • Wet mass- mass including the water in its body- can vary a lot
     • Dry mass- mass of an organism with no water in its body- doesn't vary but can only be measured when organism's dead
   • Cell differentiation, elongation and division
     • Differentiation- when a cell changes to become specialised for its job
     • Division- by mitosis
     • Elongation- where a plant cell expands, making cell bigger and therefor the plant grows.
     • Plants and animals grow differently
       • Animals- happens by cell division. Grow when they're young, reach full growth and stop growing. When young- cells divide at fast rate but once reaching adulthood, cell division is only for repair meaning that cell differentiation is lost at an early age.
       • Plants- grow continuously, continue to differentiate and develop new parts. Growth in height mainly due to cell elongatin- happens at tips of roots and shoots

3. Cell organisation

   • Tissues- a group of similar cells that work together to carry out a particular function
   • Organs- a group of different tissues that work together to perform a particular function

4. The Heart

   • 1) Right atrium- receives deoxygenated blood from body (through vena cava)
   • 2) Right ventricle- deoxygenated blood moves to here and is pumped into lungs (via pulmonary artery
   • 3) Left atrium- receives oxygenated blood from lungs (through pulmonary vein)
   • 4) Left ventricle- oxygenated blood moves through here and is pumped through body (via aorta)
   • Left ventricle has thicker wall than right ventricle because it needs more muscle to pump blood around whole body. Right ventricle only pumps to lungs
   • Valves prevent backflow of blood

5. The blood

   • Red blood cells
     • Carry oxygen from lungs to all cells in body
     • Biconcave disc (donut shape)- large surface area to absorb oxygen
     • Contain haemoglobin (contains lots of iron). In lungs- combines with oxygen to become oxyhaemoglobin. In body tissues- releases oxygen into cells
     • Don't have a nucleus- more room for haemoglobin
     • Lack of iron in diet- anaemia where blood can't carry enough oxygen
   • White blood cells
     • Change shape to gobble up bad microorgansims
     • Produce antibodies to fight microorganisms and antitoxins to neutralise toxins produced by microorgansims
     • Low WBC count- increased risk of infection
     • High WBC count- indicates infection/leukaemia
   • Platelets (small fragments of cells)
     • Help blood clot at a wound- stop blood coming out and microorganisms getting in
     • Lack of them- excessive bleeding/bruising
   • Plasma
     • What does it transport?
       • Red and white blood cells, and platelets
       • Nutrients (glucose and amino acids)
       • Carbon dioxide- transported in blood to lungs and is then removed
       • Urea (waste product formed in liver) blood transports to kidneys
       • Hormones- from glands to target organs
       • Antibodies and antitoxins produced by WBC

6. Blood vessels

   • Arteries (carry blood away from heart)
     • Heart pumps blood at high pressure- artery walls strong and elastic
     • Walls are thick compared to lumen- thick layers of muscle to make them strong
   • Capillaries (exchange materials with tissues)
     • Arteries branch into capillaries
     • Tiny
     • Carry blood close to every cell in body to exchange substances with them
     • Permeable walls- substances diffuse in and out
     • Supply food and oxygen. Take away wastes (carbon dioxide)
     • Walls only 1 cell thick- increases rate of diffusion by decreasing distance over which it occurs
   • Veins
     • Capillaries join up to form veins
     • Lower pressure blood- walls aren't as thick as arteries
     • Larger lumen than arteries to help blood flow
     • Have valves to keep blood flowing in right direction

7. Breaking down food

   • Starch, protein and fat- too big to pass through walls of digestive system
   • Sugars, amino acid, glycerol and fatty acids can
   • Digestive system enzymes break them down into smaller
     • Carbohydrases- digest starch to sugars
     • Proteases- digest proteins to amino acids
     • Lipase- digest fat into fatty acids and glycerol

8. Digestive system

   • Mouth
     • Food moistened with saliva from salivary glands
       • Salivary glands produce amylase enzyme- breaks down starch
     • Food chewed to form a bolus before being swallowed
   • Oesophagus
     • Takes food from mouth to stomach
     • Lined with muscles- contract to help bolus move along by peristalsis
   • Stomach
     • Pummels food with muscular walls
     • Produces protease enzyme- pepsin
     • Produces HCl to kill bacteria and give pepsin right pH to work (pH 2)
   • Liver
     • Bile produced to neutralise stomach acid and emulsify fats
   • Small intestine
     • Produces protease, amylase and lipase enzymes to complete digestion
     • Food absorbed out of digestive system into body
   • Gall bladder
     • Bile stored before being released into small intestine
   • Pancreas
     • Produces protease, amylase and lipase enzyme- released into small intestine
   • Large intestine
     • Excess water is absorbed from food

9. Digestion cont.

   • Peristalsis
     • There are longitudinal muscles down the length of the gut and circular muscles running around the gut
       • They squeeze the food along
     • Circular muscle contractions- push food along gut
     • Longitudinal muscle contractions- run slightly ahead to keep food in a ball
   • Bile
     • HCl in stomach makes pH too acidic for enzymes in small intestine to work
     • Its alkaline & neutralises acid to make conditions alkaline
       • Enzymes in small intestine work best in these conditions
     • Also emulsifies fats- gives a bigger surface area for lipase to work on
       • Makes digestion faster
   • Villi
     • Make absorbing food into bloodstream efficient
     • Big surface area- digested food absorbed quickly into blood
     • Single layer of surface cells- digested food diffuses quickly over short distance
     • Good blood supply via capillary-assist quick absorption of food

10. Functional foods

    • Probiotics (live bacteria)
      • Good bacteria- similar to those found naturally in gut
      • Added to yoghurt, soya milk and dietary supplements (can be pre-existing/ added by manufacturer