biology p1- organisation

• specialised cells


  As an organism develops, cells differentiate to form different types of cells- they become specialised.

  Most types of animal cells can differentiate at an early stage, but many types of plant cell can differentiate throughout their life.

  Once mature, an animals cells divide only for cell division and repair.

  As a cell differentiates: it may change shape, different sub-cellular structures develop to let it carry out a specific function.

  Specialised animal cells include sperm, nerve and muscle cells.
• Sperm cell

  • Tail: to propel the sperm to fertilise the egg
  • Mitochondria: sperm have many of these cell components, which are the major site of respiration, to provide energy for their journey.
  • Nucleus: contains only one set of genetic material
  • Acrosome: contains enzymes to allow the sperm to penetrate the outer layer of the egg
• Motor neurone (types of nerve cell)

  • Dendrites
  • Cell body
  • Axon
  • Sheath
• A muscle cell

  • Nucleus
  • Mitochondria
  • Protein fibres that can contract
• Xylem


  Xylem cells are arranged end to end but the end walls break down to form hollow tubes.

  The cell wall of the cells is strengthened by a substance called lignin.
• Phloem


  The end walls of cells allow sugars through but support the tubes.

  Phloem cells are arranged end to end into tubes.

  Companion cell.
• Root hair cell


  Lots of mitochondria for active transport of minerals.

  Long projection to increase the surface area to absorb water and minerals.
• tissues

  In most organisms, cells are arranged into tissues.

  Tissue- a group of cells with a similar structure and function, which all work together to carry out a role eg: muscle tissues contacts and relaxes to produce movement, glandular tissue produces substances such as enzymes and hormones, epithelial tissue covers organs.
• organs

  Organs are a group of different tissues, which all work together to preform a specific job.

  Each organ may contain several tissues.

  For example the stomach is an organ that contains: muscle tissue that contracts to churn the contents, glandular tissue to produce digestive juices and acid to sterilise food, epithelial tissue to cover the outside and inside of the stomach.
• Organ systems


  Organs are organised into organ systems, which are groups of organs working together to do a particular job.

  The digestive system is an example of an organ system, in which several organs work together to digest and absorb food.

  All the organ systems work together to make an organism.
• Digestive system

  • Mouth
  • Oesophagus- which pushes food down to the stomach
  • Liver
  • Stomach
  • Gall bladder
  • Pancreas
  • Large intestine
  • Small intestine
  • Rectum
  • Anus
• Enzymes

  Enzymes are biological catalysts.

  They have a number of properties: they are all large proteins, there is a space within the proteins molecule called the active site, each enzyme catalyses a specific reaction, they work best at a specific temperature and pH called the optimum.
• Lock and key theory


  A model used to explain how enzymes work: the chemical that is called the substrate (key) and it fits into the enzymes active site (lock).
• Denaturing


  High temperatures and extremes of pH can cause the active site to change shape.

  High temp cause an irreversible and permanent change- this is called denaturing.

  If the active site has temporarily changed shape or is denatured, the enzyme will not work. The substrate will no longer fit into the active site
• Enzymes in digestion

  Produced by specialised cells in glands and in the lining of the gut:

  1. The enzymes pass out of the cells into the digestive system
  2. They come into contact with food molecules
  3. They catalyse the breakdown of large insoluble food molecules into smaller soluble molecules
• Enzymes in digestion

  The digestive enzymes, protease, lipase, amylase, digest proteins, lipids (fats and oils) and carbohydrates to produce smaller molecules that can be easily absorbed into the bloodstream.

  The products of digestion are then transported and used as building blocks for new carbohydrates, lipids and proteins.

  Some of the glucose is used in respiration.
• Food tests

  1. To test for sugars, eg glucose, add benedicts reagent and heat in a water bath for 2 minutes, if sugar is present it will turn red
  2. To test for starch add iodine solution, if starch is present it will turn blue-black
  3. To test for protein add biuret reagent, if protein is present it will turn lilac/ purple.
• Food test- considerations,mistakes and errors

  Do not boil the mixture for a long time, because any starch present might break down into sugar and test positive.

  Refer to iodine solution, not 'iodine'

  Sometimes the purple colour is difficult to see, try holding the test tube in front of a sheet of white paper
• Amylase

  Is produced in the salivary glands and the pancreas.

  Is a carbohydrase that breaks starch into maltose (a sugar).

  Maltose is later broken down into glucose.
• Protease

  Is produced in the stomach, pancreas and small intestine.

  Breaks down proteins into amino acids.
• Lipase

  Is produced in the pancreas and small intestine.

  Breaks down lipids (fats) into fatty acids and glycerol
• Bile and digestion

  Bile is a liquid made in the liver and stored in the gall bladder.

  It is alkaline to neutralise hydrochloric acid from the stomach.

  It also emulsifies fat to form small droplets, increasing the surface area for enzymes to act on.

  The alkaline conditions and large surface area increase the rate at which fat is broken down by lipase.
• Required practical- to investigate the effectnofnpH on the rate of reaction of amylase enzyme

  1. Put a test tube containing starch solution and a test tube containing amylase into a water bath at 37°
  2. After 5 mins add the amylase solution to the starch
  3. Every 30 secs take a drop from the mixture and test it for starch using iodine solution
  4. Record how long it takes for the starch to be digested
  5. Repeat the experiment at different pH values using different buffer solutions
• Variables for effect of pH on the rate of reaction of amylase enzyme

  • Independant- the pH
  • Dependant- time taken for the starch to be digested
  • Control- temp, concentration and volume of starch and amylase
• Considerations, mistakes and errors- amylase practical

  • The solutions need to be left in the water bath for a while to reach the correct temp before they are mixed
  • After mixing, the tube must be kept in the water bath
  • A buffer solution must be used to keep the reaction mixture at a certain fixed pH
• Blood

  Blood is a tissue.

  It is made up of a liquid called plasma, which has 3 different components suspended in it: red blood cells, white blood cells and platelets.

  Plasma transports various chemical substances around the body, such as the products of digestion, hormones, antibodies, urea and carbon dioxide.
• Red blood cells

  • Contain haemoglobin which binds to oxygen to transport it from the lungs to the tissue and cells, where it is needed for respiration.
  • Do not contain a nucleus, so there is maximum capacity for haemoglobin.
  • Very small, so they can fit through tiny capillaries.
  • Are shaped like bioconcave discs, providing a large surface area for oxygen to quickly diffuse through.
• White blood cells

  • Are essential to protect the body against infection.
  • Can change shape, squeezing out of the blood vessels into the tissues or to surround and engulf microorganisms.
• Platelets

  • Fragments of dead cells, which collect at wounds and trigger blood clotting
• Blood vessels

  Blood passes around the body in Blood vessels.

  The body contains 3 different types of Blood vessel
• Arteries

  • Transport Blood from the heart to your organs
  • Thick walls made from muscle and elastic fibres
• Veins

  • Transport blood from the organs to your heart
  • Thinner walls with valves to prevent backlfow
• Capillaries

  • Allow substances produced by the cells to pass into the blood
  • Allows substances needed by the cells to pass out of the blood
  • Narrow, thin walled blood vessels
• The heart

  The heart pumps blood around the body in a double circulatory system.

  Blood passes through the heart twice on each circuit.

  There are four Chambers in the heart: the left and right atria, which relieved blood from veins and the left and right ventricles which pump the blood out into arteries.

  Blood enters the heart through the atria.

  The atria contract and force blood out of the heart.

  The ventriclesthen contract and force blood out of the heart.

  Valves make sure the blood flows in the correct direction
• The heart pt.2

  The natural resting heat rate is controlled by a group of cells located in the right atrium, which act as a pacemaker.

  Artificial pacemakers are devices that use electric currently mimic the natural pacemaker. They can correct irregularities in the heart rate.
• Pacemakers

  Devices that use electric current to mimic the natural pacemaker and correct irregularities in the heart rate
• Gaseous Exchange


  1. Air obtained by breathing reaches the lungs through the trachea

  2. The trachea divides into two tubes - the bronchi

  3. The bronchi divide to form bronchioles

  4. The bronchioles divide until they end in tiny air sacs called alveoli
• Alveoli

  • They have a large, moist surface area
  • They have a very rich blood supply
  • They are very close to the blood capillaries, so the distance for gases to diffuse is small
• The heart sends blood to the lungs

  Via the pulmonary artery
• The blood is taken back to the heart

  Through the pulmonary vein