Topic 3 Living Together

• Photosynthesis


  1. Light absorption by chlorophyll

  2. Water splitting into hydrogen and oxygen

  3. Hydrogen combined with carbon dioxide to make glucose
• Photosynthesis


  Process of converting light energy to chemical energy
• Chloroplasts


  • Organelles in plant cells where photosynthesis occurs
  • High concentration in upper leaf cells where most sunlight hits
• Light-dependent stage


  Stage 1 of photosynthesis where light is absorbed and water is split
• Light-independent stage


  Stage 2 of photosynthesis where hydrogen from stage 1 is combined with carbon dioxide to make glucose
• Oxygen is a waste product of photosynthesis and is released from the plant
• Glucose produced in photosynthesis can be stored as starch and used for growth, repair, and synthesis of other molecules
• Enzymes


  Proteins that catalyse chemical reactions without being consumed or permanently altered
• Substrate


  Molecule that an enzyme binds to during a reaction
• Active site


  Place on an enzyme where the substrate binds
• Lock and key model

  Each enzyme is specific to one type of substrate, like how each lock requires a different key
• Factors that can change the rate of an enzyme-catalysed reaction

  • pH
  • Temperature
  • Substrate concentration
• Limiting factor


  The factor which is least available to the plant and limits the rate of photosynthesis
• As carbon dioxide concentration increases

  Rate of photosynthesis increases
• As temperature increases up to the optimum


  Rate of photosynthesis increases
• As light intensity increases

  Rate of photosynthesis increases
• Farmers can reduce the effects of limiting factors on photosynthesis by using greenhouses and artificial lighting
• Diffusion


  Passive process of molecules moving from high to low concentration
• Osmosis


  Passive movement of water molecules from high to low concentration through a partially permeable membrane
• Active transport


  Requires energy to move substances up a concentration gradient
• Root hair cells


  • Large surface area
  • High concentration of mitochondria for energy production
  • Thin cell membrane to speed up diffusion and active transport
• Stomata


  Pores on the lower leaf surface that allow diffusion of gases
• Guard cells


  Cells that surround the stomata and control their opening and closing
• Xylem


  Transports water from roots to leaves
• Phloem


  Transports sugars and nutrients from source to sink
• Transpiration


  1. Loss of water vapour from the leaf surface due to evaporation

  2. Water drawn up the xylem by transpiration pull
• High light intensity


  Increases rate of photosynthesis and transpiration
• High air movement


  Increases rate of transpiration and water uptake
• High temperature


  Increases rate of evaporation and water uptake
• Translocation


  Transport of amino acids and sucrose from source to sink in the phloem
• Leaves can act as both source and sink for translocated materials
• Low water uptake


  If there is lots of air movement, this moist air is blown away from the leaf, meaning that water uptake increases
• Temperature


  At warm temperatures, the rate of evaporation is high, so the rate of water uptake is high. In addition, the rate of photosynthesis is high, meaning that the stomata will be open, increasing transpiration
• Translocation


  1. Occurs in the phloem vessels

  2. Involves the transport of amino acids and sucrose

  3. Areas where amino acids and sucrose are produced are called sources

  4. Regions where they are stored or used for respiration and growth are called sinks

  5. Materials are always transported from source to sink

  6. Sucrose and amino acids are produced in the leaves, before being transported to the roots for storage

  7. They are later transported to regions where they are used in respiration and for growth

  8. Some parts of the plant, such as the leaves, can act as both source and sink within a plant's life as they synthesise molecules and use them in metabolic reactions
• Producer


  An organism that converts light energy to chemical energy in order to produce its own nutrients. Photosynthetic organisms are the main producers of food and hence biomass
• Consumer


  An organism which gets energy and biomass from feeding on other animals or plants
• Herbivore


  Organisms which feed on plants
• Carnivore


  Organisms which feed on animals
• Decomposer


  Organisms which break down decaying organic material (detritus)
• Ecosystem


  An ecosystem is made up from all the living organisms and abiotic components (such as soil, rocks and water) in a community. These interact with each other to function as one unit