B3. FOOD AND ECOSYSTEMS

• a plant is a producer that makes its own food in the form of glucose
• the glucose is made from carbon dioxide and water by photosynthesis
• the glucose made in plants is the source of biomass for most ecosystems
• a series of chemical reactions in the cells of producers where carbon dioxide and water are used to make glucose and oxygen that require light from the sun

  photosynthesis
• all the tissues that make up an organism

  biomass
• some biomass of an organism is transferred to another organism when eaten
• oxygen is a by-product of photosynthesis
• plants use some of the oxygen for cellular respiration and the rest is released into the atmosphere
• humans depend on oxygen for aerobic respiration
• two stages of photosynthesis

  • first stage: water molecules are split into hydrogen and oxygen; oxygen Is released into the air
  • second stage: hydrogen is combined with carbon dioxide from the air to make glucose
• a green pigment that absorbs light and splits water into hydrogen and oxygen during photosynthesis

  chlorophyll
• organelle that contains chlorophyll; where reactions of photosynthesis happen

  chloroplast
• some of the glucose is converted into starch
• equation model of photosynthesis

  name the parts

  A) carbon dioxide

  B) water

  C) oxygen

  D) glucose

  
• transfers energy (absorbs heat) from its surroundings, making it cooler

  endothermic process
• transfers energy to its surroundings, making it warmer

  exothermic process
• a biological catalyst that speeds up a chemical reaction

  enzyme
• enzymes catalyse reactions that help larger molecules to break down into smaller ones, and smaller molecules to join together to make larger molecules
• an enzyme's shape is very important to how it works
• enzymes are specific and can only work with one substrate
• the molecule that is changed by an enzyme

  substrate
• a part of the enzyme where the substrate fits in

  active site
• at higher temperatures, speed of reactions are increased
• higher temperatures damage living cells
• enzymes in humans work best at about 37 degrees celcius
• enzyme reactions get faster if temperature increases from a low value
• the temperature at which an enzyme works best

  optimum temperature
• above the optimum temperature, the enzyme slows down
• as temperature rises, an enzyme's shape changes and does not work well
• the enzyme is denatured at very high temperatures
• other organisms have enzymes that adapt to different temperatures to suit the environment they are in
• as the temperature rises, the rate of reaction increases up to the optimum temperature. at the optimum temperature, the reaction rate is at its highest. above the optimum temperature, the reaction rate starts to decrease because the active site changes and the substrate no longer fits. at very high temperatures, the reaction rate falls to zero as the enzyme becomes denatured.
• yield is the amount of product the farmer has to sell
• increasing the amount of light increases the plant's rate of photosynthesis
• limiting factor is the factor that prevents the rate of reaction or process from increasing
• the four limiting factors of photosynthesis

  temperature, carbon dioxide, water availability, light intensity
• when molecules collide with one another, change direction, and then spread out

  diffusion
• diffusion does not need any more energy thus it is a passive process
• tiny holes in leaves are called stomata that allow carbon dioxide to enter the leaf and for oxygen to diffuse out
• the movement of carbon dioxide and oxygen in and out of the leaf is an example of gas exchange