B2

• Organelles


  Also called subcellular structures, the parts that make up a cell like the nucleus, ribosomes and mitochondria
• Organelles


  • Each individual organelle has a specific role to play
  • When combined, multiple organelles will form a single cell
• Cells


  Come in all sorts of shapes and sizes and contain different combinations and numbers of organelles
• Specialized cells


  Different types of cells like epithelial cells, muscle cells and glandular cells
• Tissues


  A group of similar cells that work together to carry out a particular function
• Tissues


  • Epithelial tissue
  • Muscle tissue
  • Glandular tissue
• Organs


  A group of different tissues that work together to perform a particular function
• Organ systems


  A group of organs that work together to perform a particular function
• Organism


  The highest level, with multiple organ systems working together
• Enzymes


  Catalysts made by living organisms
• Enzymes

  • They are large proteins made up of long chains of amino acids
  • They can fold into different shapes, each shape catalyzing a particular chemical reaction
• How enzymes work


  1. Enzyme has an active site with a unique shape

  2. Substrate fits into active site

  3. Enzyme speeds up the chemical reaction
• Substrate


  Reactant in a chemical reaction
• Products


  Smaller pieces that a substrate is broken into
• Enzymes speed up the process of chemical reactions
• Enzyme active site

  • It has a shape complementary to the substrate
  • If substrate doesn't fit, reaction won't be catalyzed
• Lock and key model


  Original model where substrate fits perfectly into active site
• Induced fit model


  More realistic model where enzyme changes shape slightly to better fit the substrate
• why we can't just make our cells even warmer to increase the rate of reactions


  1. Heating our cells more would require a lot of energy
  2. Higher temperatures could damage our cells
  3. Higher temperatures would also speed up non-useful reactions 
• A catalyst is a substance that increases the speed of a chemical reaction without being used up or changed in the process.

  enzymes are a biological catalyst
• what's circled in blue

  active site

  
• In order for an enzyme to catalyse a reaction, the active site of the enzyme must be complementary to the substrate
• Optimum temperature


  The temperature at which the rate of reaction is highest
• pH


  A measure of acidity
• How pH affects enzymes

  1. pH gets too high or too low

  2. Bonds holding the enzyme together start to break

  3. Active site starts to change shape

  4. Substrate can't fit the active site anymore

  5. Enzyme becomes denatured
• Optimal pH

  The pH at which the enzyme works best
• Most enzymes in our body work best at neutral pHs of around 7
• Enzymes that work in the stomach have an optimal pH of around 2 because they need to function in the stomach's acidic environment
• Explain how increasing the temperature can cause an enzyme to denature. (3 marks)

  1. High temperatures start to break the bonds holding the enzyme together 
  2. This causes the enzyme and it's active site to change shape
  3. This means the enzymes active site will no longer be complementary to the substrate 
• carbohydrates - provides energy for chemical reactions
• lipids - provide energy for chemical reactions AND insulation for body cells AND body temperature regulation
• why is iron important in our diet (2 marks)

  Iron is an important component of haemoglobin 

  Haemoglobin is the protein in red blood cells that allows them to transport oxygen around the body

  A lack of iron (and hence haemoglobin), can lead to anaemia, where we can't transport enough oxygen to our tissues. 
• fibre -  helps to move food through our intestines 
• 3 main ways by which we lose water from the body

  1. breathing
  2. urination
  3. sweating
• Enzymes


  Essential for helping us break down the large molecules that we eat into the much smaller soluble molecules that we can absorb through our intestinal lining
• Main groups of nutrients to be broken down

  • Carbohydrates
  • Proteins
  • Fats
• Carbohydrates


  Found mainly in foods like pasta, potatoes and rice, used by the body mainly as an energy source
• Starch


  The main type of carbohydrate
• Breakdown of starch

  Broken down by the enzyme amylase into smaller sugars such as maltose
• Places where amylase is made

  • Salivary glands
  • Pancreas
  • Small intestine