4- Bioenergetics

• Limiting Factor: A limiting factor is a condition, that when in shortage, slows down the rate of a reaction
• Photosynthesis Factors

  
  

  Light (energy source), takes in energy:  and endothermic reaction 

  • Takes place in the leaves, contain chlorophyll -can absorb light energy
  • Amount of chlorophyll in the leaf- can strap less light so low rate of photosynthesis    
  • If we increase the light intensity, the rate of photosynthesis also increases- this tells us the light intensity was limiting  (photosynthesis was not as fast because there was not enough light) 
  • When light intensity stops increasing (levels off) this means another factor is short in supply 

  
• Photosynthesis Factors

  Carbon Dioxide: 

  • As you increase the C02, rate of photosynthesis increase- this is the limiting factors, but at a certain point it levels off and its no longer the limiting factor (light and temp becomes limiting factor)

  
• Photosynthesis Factors

  Temperature:

  • As you increase the temperature, the enzymes involved in photosynthesis work faster- so rate increases, if you keep increasing temperature the enzymes denature and photosynthesis falls  

  
• Stages:

  Carbon dioxide + water → (Light- into chlorophyll) glucose + oxygen 

  C02 + H20 → C6H12O6 + O2

  1. Plant takes carbon dioxide and water into the leaf 
  2. Light is absorbed by chlorophyll- then convert carbon dioxide + water into glucose and oxygen is produced 
• uses of glucose from photosynthesis

  1. Produce insoluble starch- can be converted back to glucose when needed  
  2. Stored energy as fats and oils 
  3. Cellulose is made out of glucose- provides strength for the cell 
  4. Produce amino acids- to synthesise proteins, to make amino acids from glucose plant absorbs nitrate ions from soil
• Required Practical: Photosynthesis

  • Use boiling tube and place it 10cms away from a LED source (doesn't release too much heat- won't affect the temp)
  • Fill tube with sodium hydrogen carbonate solution (release CO2-needed for photosynthesis) 
  • Put a piece of pondweed into the tube with end and top cut, leave for 5 minutes to allow it to acclimate to the conditions of boiling tube  
  • Bubble will produce- this gas is oxygen produced by photosynthesis 
  • use stopwatch- count number of bubbles produced in one minute, repeat two more times and calculate mean numbers 
  • Repeat over a range of lengths
• Required Practical: Photosynthesis

   Problems: 

  Numbers of bubbles can be too fast to count accurately 

  Size of bubbles may be different

  • To solve: measure volume of oxygen produced- 
  • Place pondweed under a funnell and catch bubbles in a measuring cylinder filled with water, then use measuring cylinder to measure volume of oxygen gas produced 

  Inverse square law: light intensity = 1 / distance (squared)   

  • Double distance = bubble per minute falls by four (eg, 40cms to 20cms, bubbles fall 4) 
  • Need light for photosynthesis, that causes number of oxygen bubbles to fall by four

  
• Respiration is an exothermic reaction because it releases energy, and takes place continually in all living cells  
• Aerobic respiration

  • releases lots of energy because glucose molecule has been fully oxidised
  • chemical formula: C6H1206 + O2 → CO2 + H2O

  A) glucose

  B) oxygen

  C) water

  D) energy

  E) carbon dioxide

  
• Anaerobic respiration

  Muscle respiration: need energy for contraction 

  • Shortage of oxygen- muscle cells respired anaerobically 

  Anaerobic release less energy than aerobic, this is because the oxidation of glucose is incomplete 

  A) glucose

  B) lactic acid

  
• In Plants: Anaerobic respiration in yeast cells (fermentation)

   - Used to make alcoholic drinks- the alcohol in drinks is ethanol 

  • Bread: carbon dioxide produced by fermentation is useful, creates bubbles in dough making it rise  

  A) glucose

  B) ethanol

  C) carbon dioxide

  
• During exercise your body needs energy for muscle contraction- aerobic respiration increases, this means the body cells require more oxygen

  • The provide extra oxygen the breathing rate and volume increase (frequent and deeper breaths) this gets more oxygen into the bloodstream
  • Heart Rate increase to pump oxygenated blood around the body
• When there's not enough oxygen anaerobic respiration takes place in the muscles 

  •  in anaerobic respiration the oxidation of glucose is incomplete- this leads to build up of lactic acids and this causes muscles to become fatigued- muscles stop contracting efficiently 
  • Body has to remove lactic acids and this creates oxygen debt   
  • Lactic acids is taken  to liver and concerted back to glucose through chemical reactions- to remove from cells this requires oxygen  
• Oxygen debt: amount of extra oxygen body needs after exercise to deal with accumulated lactic acid
• Uses of Metabolism: 

  • Conversion of glucose to cellulose in plants to build and strengthen cell walls
  • Conversion of glucose into glycogen in animals and starch in plants for storage

  Lipid synthesis

  • The formation of lipid molecules from a molecule of glycerol and three molecules of fatty acids to form triglycerides which are used for energy storage and as insulation in animals
  • found in the cell membrane
• metabolism in plants: the use of glucose and nitrate ions to form amino acids which in turn are used to synthesise proteins required by cells (such as enzymes)

  • Glucose is broken down in the process of respiration to release energy in all cells
• [metabolism] glucose in plants

  • cellulose: strengths the plant cell wall
  • starch- storage form of glucose
  • reacts with nitrate ions to create amino acids: used to synthesise proteins
• [metabolism] glucose in humans

  • glycogen: storage form of glucose