Biology

• Photosynthesis


  The process by which plants manufacture carbohydrates from raw materials using energy from light

  
• Photosynthesis

  Carbon dioxide + Water → Glucose + Oxygen

  
• Chlorophyll


  A green pigment found in chloroplasts within plant cells that absorbs light energy and transfers it into chemical energy for the synthesis of carbohydrates
• Uses of carbohydrates produced by photosynthesis


  • Converted into starch for energy storage
  • Converted into cellulose to build cell walls
  • Used in respiration to provide energy
  • Converted to sucrose for transport in the phloem
  • Used as nectar to attract insects for pollination
  • Converted into lipids and amino acids

  
• Minerals in plants

  • Plants obtain mineral ions from the soil to make substances like proteins, lipids and nucleic acids that they cannot obtain by eating
  • Mineral deficiencies can prevent proper growth and photosynthesis
• Care must be taken to keep other variables constant when investigating one condition
• Care must be taken when investigating a condition to keep all other variables constant in order to ensure a fair test
• Plants are respiring all the time and so plant cells are taking in oxygen and releasing carbon dioxide as a result of aerobic respiration

  
• Plants also photosynthesise during daylight hours, for which they need to take in carbon dioxide and release the oxygen made in photosynthesis

  
• At night, plants do not photosynthesise but they continue to respire, meaning they take in oxygen and give out carbon dioxide

  
• During the day, especially when the sun is bright, plants are photosynthesising at a faster rate than they are respiring, so there is a net intake of carbon dioxide and a net output of oxygen

  
• Balanced chemical equation for photosynthesis

  6CO2 + 6H2O → C6H12O6 + 6O2

  
• The light energy is converted into chemical energy in the bonds holding the atoms in the glucose molecules together
• The photosynthesis equation is the exact reverse of the aerobic respiration equation

  
• Limiting factor

  Something present in the environment in such short supply that it restricts life processes
• Main factors which limit the rate of photosynthesis

  • Temperature
  • Light intensity
  • Carbon dioxide concentration

  
• Temperature

  • As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes
  • However, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases

  
• Light intensity

  • The more light a plant receives, the faster the rate of photosynthesis
  • This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply

  
• Carbon dioxide concentration

  • The more carbon dioxide that is present, the faster the reaction can occur
  • This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply

  
• Leaf structures to identify in a dicotyledonous plant


  • Chloroplasts
  • Cuticle
  • Guard cells
  • Stomata
  • Upper and lower epidermis
  • Palisade mesophyll
  • Spongy mesophyll
  • Air spaces
  • Vascular bundles (xylem and phloem)
• Pathway of carbon dioxide from the atmosphere to chloroplasts by diffusion: atmosphere → air spaces around spongy mesophyll tissue → leaf mesophyll cells → chloroplast

  
• Taxonomy


  A way of grouping organisms based on their anatomy (internal features) and morphology (external features)
• Cladistics


  A way of grouping organisms based on their common DNA base sequences
• Taxonomy and cladistics are methods of classification
• Binomial system


  A system of naming organisms using two names - the genus and the species
• Dichotomous keys


  A tool used to identify organisms by asking a series of questions with two possible answers
• The binomial system and dichotomous keys are used to describe how organisms are classified
• Scientists now use cladistics to classify organisms
• Species


  A group of organisms that can interbreed to produce fertile offspring
• If species are not closely related, it is often impossible for individuals of the different species to breed</b>
• If members of two closely related species do interbreed and produce offspring, the hybrids will be sterile (e.g. mules)