chapter 2

• Cell

  The basic building block of a living organism
• Tissue

  A group of cells with a similar structure and function working together. For example, muscular tissue contracts to bring about movement.
• Organ

  A collection of tissues working together to perform a specific function.
• Organ system

  A group of organs working together to perform specific functions. For example, the digestive system contains organs such as the stomach, the small intestine and the large intestine.
• Epidermal tissue

  • Covers the entire plant
  • Has a waxy cuticle which helps reduce water loss from the leaf surface
• Palisade mesophyll tissue

  • Contains lots of chloroplasts which allows photosynthesis to progress at a rapid rate
• Spongy mesophyll tissue

  • Has lots of air spaces which allow gases (including oxygen and carbon dioxide) to diffuse in and out
• what is the Xylem

  • Made up of dead cells which form a continuous hollow tube - allows the movement of water and mineral ions from the roots to the leaves
  • Strengthened by lignin - makes the vessel strong and waterproof
  • Has bordered pits - allow minerals to be transported to specific places
• what is the Phloem

  • Made up of elongated living cells
  • Cells have sieve plates that connect them together - cell sap can move through plates into other cells
  • Sieve tube cells to allow the efficient transport of substances
  • transport simple sugars
• Meristem tissue

  • Made up of stem cells which can differentiate into many different cell types, allowing the plant to grow
• Tissues in the leaf organ

  • Epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Xylem
  • Phloem
  • Guard cells
• Guard cells

  Control the opening and closing of the stomata, according to the water content of the plant
• Stomata

  • Allow the control of gaseous exchange and water loss from the leaf
  • More stomata on the base of the leaf - minimises water loss as this side is cooler and shaded
  • Have guard cells which control their opening and closing
• adaptations of Root hair cells

  • Allow the uptake of water and mineral ions from the soil
  • Large surface area - maximises rate of absorption
  • Contain lots of mitochondria -- release energy for active transport of mineral ions
• Translocation

  The movement of dissolved sugars from the leaves to other parts of the plant
• Transpiration

  The evaporation of water vapour from the surface of a plant
• How transpiration works

  1. Water evaporates from the leaf surface via the stomata

  2. Water molecules cohere together - more water is pulled up the xylem in an unbroken column

  3. More water is taken up from the soil - creating a continuous transpiration stream
• Increasing temperatureaffect on transpiration

  Increases the rate of transpiration
• Increasing humidityaffect on transpiration

  Decreases the rate of transpiration
• Increasing wind speed/air movementaffect on transpiration

  Increases the rate of transpiration
• Increasing light intensity

  Increases the rate of transpiration
• Digestive system

  To digest food and absorb the nutrients obtained from digestion
• Pancreas and salivary gland

  Glands which produce digestive juices containing enzymes
• Stomach

  Produces hydrochloric acid - which kills any bacteria present and provides the optimum acidic pH for the protease enzyme to function
• Small intestine

  The site where soluble food molecules are absorbed into the bloodstream
• Liver

  Produces bile (stored in the gallbladder) which emulsifies lipids and allows the lipase enzyme to work more efficiently
• Large intestine

  Absorbs water from undigested food, producing faeces
• Enzymes

  Act as biological catalysts which speed up the rate of biological reactions (the breakdown of food) without being used up
• Enzyme shape

  Enzymes have a specific active site which is complementary to their substrate
• Metabolism

  The sum of all the reactions in a cell or an organism
• Types of metabolic reactions catalysed by enzymes

  • Building larger molecules from smaller molecules
  • Changing one molecule to another
  • Breaking down larger molecules into smaller molecules
• Lock and key hypothesis

  The shape of the enzyme active site and the substrate are complementary, so can bind together to form an enzyme-substrate complex
• Temperature effect on enzymes

  Up to a certain point, increasing temperature increases enzyme action, as molecules have a higher kinetic energy. Above a certain temperature, the shape of the active site is altered and the enzyme becomes denatured, so it can no longer catalyse the reaction. The optimum temperature is around 37°
• pH effect on enzymes

  The optimum pH for most enzymes is 7 (apart from proteases in the stomach). If the pH is too extreme, the shape of the active site may be altered and the enzyme may no longer work
• Locations of enzyme production

  • Carbohydrases: amylase - salivary gland and pancreas; maltase - small intestine
  • Proteases: pepsin - stomach; others - pancreas and small intestine
  • Lipases: pancreas and small intestine
• Role of carbohydrases

  Break down carbohydrates into monosaccharides and disaccharides. Amylase breaks down starch into maltose, and maltase breaks down maltose into glucose
• Role of proteases

  Break down proteins into amino acids
• Role of lipases

  Break down lipids into fatty acids and glycerol
• Use of digestion products

  They are used to build bigger molecules such as carbohydrates and proteins. Glucose is used as a substrate in respiration
• Bile production and storage

  Bile is made by the liver and stored in the gallbladder