Biology 3

• Tissues


  A group of cells with similar structures and function working together
• Types of tissues


  • Muscular tissue
  • Glandular tissue
  • Epithelial tissue
• Muscular tissue


  • Contracts for movement
• Glandular tissue


  • Produces and releases substances e.g. enzymes
• Epithelial tissue

  • Covering of body and internal organs
• Organs


  Collections of tissues working together to form a specific function
• Organs


  • Stomach
  • Pancreas
• Stomach


  • Muscular tissue: Churns food and digestive juices
  • Glandular tissue: Produces digestive juices
  • Epithelial tissue: Covers inside and outside
• Pancreas


  • Makes hormones to control blood sugar (insulin, islets of Langerhans)
  • Makes enzymes to digest food (acinar cells)
• Organ systems


  A group of organs that work together to perform a specific function
• Adaptations for effective exchange

  • Large surface area
  • Rich blood supply
  • Short diffusion distance
  • Mechanisms to increase concentration gradients
• Digestive system


  A hollow muscular tube that squeezes food along between 6-9 metres
• Functions of the digestive system

  • Exchange substances with environment
  • Break down food from large insoluble molecules to smaller soluble molecules that can be absorbed by cells
• Mouth


  • Teeth and gums used to mechanically break down food into smaller sections
  • Alkaline pH
  • Salivary glands produce enzymes like amylase to digest starch
• Enzymes


  Biological catalysts that speed up the rate of chemical reactions
• Oesophagus


  • Muscular tube connecting mouth to stomach
  • Peristalsis - squeezing of muscles to move food
• Stomach


  • Main organ where food is digested
  • Breaks down large insoluble molecules into smaller insoluble ones
  • Produces protease to digest proteins
  • Acidic pH
• Liver


  • Large multi-lobed organ
  • Produces bile to neutralise pH in small intestine
• Gallbladder


  • Stores bile before it is released through the bile duct
• Pancreas


  • Produces insulin to control blood glucose
  • Produces enzymes like amylase, protease, lipase that flow into small intestine
• Small intestine


  • Main site of digestion and absorption
  • Produces protease and lipase
  • Main site of carbohydrate digestion using amylase from pancreas
  • Smaller soluble molecules absorbed into blood via diffusion and active transport
  • Villi increase surface area for absorption
• Large intestine


  • Absorbs water from undigested food
  • Material left forms faeces
  • Includes appendix
• Rectum


  • Stores faeces before being passed out through the anus
• Carbohydrates


  • Made up of carbon, hydrogen, oxygen units of sugar (e.g. sucrose, glucose)
  • Small carbohydrate units = simple sugars
  • Long chains of simple sugars = complex carbohydrates (starch)
• Carbohydrate tests


  • Benedict's test - blue solution turns brick red if sugars present
  • Iodine test - yellow-red solution turns blue-black if starch present
• Lipids


  • Made up of carbon, hydrogen, oxygen
  • Fats (solid) and oils (liquid)
  • Insoluble in water
  • 3 fatty acid molecules + 1 glycerol molecule
• Lipid test


  • Mix food sample with ethanol - gives a cloudy white layer if lipids present
• Proteins


  • Made up of long chains of different amino acids
  • Shape is important for function, can be denatured by changes in temperature or pH
• Protein functions


  • Building tissues, enzymes, hormones, antibodies
• Biuret test


  • Mix food sample with biuret reagent - turns purple if protein present
• Catalysts


  Speed up rate of chemical reactions without being consumed or permanently altered
• Enzymes


  Biological catalysts - proteins that interact with specific substrates
• Enzyme structure


  • Primary structure - amino acid chain
  • Secondary structure - folded amino acid chain
  • Tertiary structure - 3D folded shape with active site
• Lock and key model

  Substrate fits perfectly into the enzyme's active site due to complementary shapes
• Metabolic reactions


  1. Building large molecules from smaller ones
  2. Changing one molecule into a different molecule
  3. Breaking down large molecules into smaller ones
• Effect of temperature on enzymes

  • Increase in temperature increases reaction rate up to 40°C, then enzyme becomes denatured and reaction rate drops
• Effect of pH on enzymes

  • Enzymes work best at specific pH levels, changes in pH can denature the enzyme
• Digestive enzymes


  • Produced by specialised glands and work outside cells in the digestive system to break down food