B3

• Photosynthesis equation:

  carbon dioxide + water → glucose + oxygen
• Producers:

  • Plants and other producers make glucose during photosynthesis
  • Some glucose is used as a fuel in cells for respiration, and some is stored as starch until needed
• Enzymes:

  • Biological catalysts that speed up the rate of chemical reactions
  • The rate of photosynthesis is controlled by enzymes
• Stages of photosynthesis:

  • Light stage - light energy splits water into hydrogen and oxygen
  • Dark stage - hydrogen bonds with carbon dioxide to form glucose

  Photosynthesis absorbs energy from the surroundings - it is an endothermic reaction
• Chloroplasts:

  • sub cellular structure only found in plant cells
  • stores chlorophyll
  • absorbs light energy for photosynthesis
• Photosynthesis experiment (testing for starch):

  • Place one plant in a dark room and one in light.
  • Carry out test for starch on each plant
  • Leaves store glucose in their leaves as starch
  • Starch is insoluble (doesn't dissolve)

  1. Heat leaf in boiling water
  2. Add leaf to ethanol and heat
  3. Rinse leaf in water
  4. Lay leaf on tile
  5. Add iodine to leaf
  6. Observe if leaf turns black/purple, then there is starch present
• Factors affecting enzymes:

  • High temperature and pH can denature enzymes decreasing rate
  • Low temperatures decrease enzyme energy decreasing the rate
  • Concentration of substance can affect the rate
• Limiting factors of photosynthesis:

  • environmental conditions can affect the rate of photosynthesis such as:
  • Light intensity
  • Carbon dioxide concentration
  • Temperature
• Investigating the rate of photosynthesis:

  1. Use a lamp and change the distance of the lamp from the plant
  2. Use heat shield to limit impact of the temperature
  3. Use the same volume of water/concentration of carbon dioxide
  4. Count number of bubbles produced/volume of gas using syringe
• Enzyme mechanism (lock and key model):

  • Scientists model how enzymes work using the lock and key model
  • Enzymes have an active site (lock), they are a specific shape to allow a substrate (key) to bind to them
  • An enzyme-substrate reaction occurs and a product is formed

  
• Denaturing enzymes:

  • If a temperature is higher than the enzymes optimum temperature then the enzyme will start to change shape on its active site, therefore the substrate won't fit correctly slowing down the rate of reactions

  
• Light intensity - inverse square law 1/d²
• Rate calculations:

  • Volume of gas/time it has taken
  • Number of bubbles/time it has taken
  • How long it takes for a colour to occur/ time it has taken
• Diffusion:

  • movement of particles from a higher concentration to a lower concentration

  
• Diffusion:

  • Carbon dioxide and oxygen are exchanged through the stomata in plant leaves by diffusion

  
• Osmosis - movement of water from a higher concentration to a lower concentration across a partially permeable membrane
• Investigating Osmosis:

  • Potato cylinders can be placed in different sucrose concentrations
  • Mass of potato is taken before and after

  % change in mass/original mass X 100
• Investigating Stomata:

  • Stomata are holes underneath a leaf and are controlled by guard cells.
  • Observe them by putting nail varnish and iodine on the under of a leaf
• Flow of Biomass - energy is transferred through tropic levels

  Tertiary consumer (4th tropic level)

  ↑

  Secondary consumer (3rd tropic level)

  ↑

  Primary consumer (2nd tropic level)

  ↑

  Producer (1st tropic level)
• Carbon Cycle:

  • Carbon dioxide in the atmosphere gets absorbed by plants for photosynthesis
  • Plants decompose and then are used for fossil fuels
  • Plants get eaten by animals
  • Carbon dioxide is released through respiration
  • Carbon dioxide is released when fossil fuels are burned

  
• Water Cycle:

  • Water is released through organisms breathing, sweating and excreting

  A) Condensation

  B) Evaporation

  C) Precipitation

  D) Transpiration

  E) Ground water flow

  
• Decomposition:

  • Process of biomass breaking down
  • Dead organisms and waste products are all decomposed in the carbon cycle
  • Two types of decomposers: bacteria, fungi
  • Decomposers use enzymes to break down material
• Factors affecting population:

  • Pesticides are an abiotic factor, they contain toxic chemicals. Pesticides are not broken down by enzymes in organisms. They are transferred between tropic levels when feeding occurs. The organisms at the top of the food chain die as a result, this is called bioaccumulation
• Abundance method:

  1. Choose and measure an area (25m x 25m)
  2. Randomly throw a quadrat in the area
  3. Count number of organisms of a species
  4. Repeat at least 9 times
  5. Calculate the mean number of species across the 10 samples
• Distribution:

  • Transect - used to mark out a straight line across a sample area
  • Light meter - used to measure light intensity
• Sampling animals:

  • Population size = number in 1st sample X number in 2nd sample

  -------------------------------

  number in second sample previously marked
• Interdependence - when changes in population of one species affect the population of another. Populations are reliant on each other for survival
• Biomass - a store of chemical energy