bioenergetics

• Cellular respiration is an exothermic reaction that transfers energy from glucose and occurs continuously in living cells
• Energy for organisms is used for:

  • Building up larger molecules from smaller ones (e.g., combining amino acids to form proteins)
  • Muscular contraction for movement
  • Maintaining body temperature to stay warm in colder environments
• Metabolism is the combination of all reactions in cells, including those catalyzed by enzymes, and it includes processes that do not require energy
• There are two types of respiration:

  • Aerobic respiration: occurs in the presence of oxygen, is the most efficient way to transfer energy from glucose, takes place in mitochondria, word equation: glucose + oxygen → carbon dioxide + water
  • Anaerobic respiration: occurs without oxygen, less efficient due to incomplete breakdown of glucose and lactic acid buildup, word equation: glucose → lactic acid
  • In plants and yeast, anaerobic respiration can produce ethanol and carbon dioxide, known as fermentation
• Effects of exercise on the human body
• During exercise, our bodies need to carry out more cellular respiration
• Muscular contraction during exercise requires a lot of energy obtained from respiration, which requires oxygen
• To supply more oxygen to muscles, the rate of breathing and the volume of each breath increase
• Increased effort during exercise allows us to supply enough oxygen to all muscles and continue using aerobic respiration
• During intense activities like sprinting or fast cycling, when there is not enough oxygen, cells resort to anaerobic respiration
• Anaerobic respiration is less efficient than aerobic respiration but is used when oxygen demand exceeds supply
• Anaerobic respiration produces lactic acid, leading to a burning sensation in muscles after exercise
• After exercise, the body needs to eliminate lactic acid by reacting it with oxygen, creating an oxygen debt
• Blood carries lactic acid to the liver where it is converted back to glucose by reacting with oxygen
• Investigating the effects of exercise on the body
• Main measurements: breathing rate and heart rate
• Breathing rate can be measured by counting how many times the chest rises and falls in a given time period, usually one minute
• Heart rate can be measured by feeling the pulse on an artery in the wrist or neck
• Questions may involve measuring these parameters before and after exercise and explaining the changes
• Photosynthesis is the process where plants convert carbon dioxide and water into glucose and oxygen using light energy in the chloroplasts
• Equation for photosynthesis: 6 CO2 + 6 H2O → C6H12O6 + 6 O2
• Photosynthesis is an endothermic reaction, meaning it requires light energy to take place
• Plants obtain carbon dioxide through stomata in leaves and water is absorbed from the soil by roots and transported to leaves via xylem
• Glucose is the main product of photosynthesis and is used for:

  • Cellular respiration to release energy
  • Making cellulose to strengthen cell walls
  • Making starch for long-term storage
  • Making amino acids by combining glucose with nitrate ions from the soil to make proteins
  • Making oils and fats for future energy resources, especially for seeds
• Plants store starch to break it down into glucose when photosynthesis is not active, like during the night or winter
• Plant growth rate is dependent on the speed of photosynthesis, influenced by factors like light intensity, temperature, carbon dioxide concentration, and chlorophyll amount
• Plants need to carry out photosynthesis to survive
• Four main factors that affect photosynthesis:

  • Light intensity
  • Temperature
  • Concentration of carbon dioxide in the air
  • Amount of chlorophyll in the plants
• Chlorophyll is the pigment within chloroplasts that absorbs light energy needed for photosynthesis
• Factors that can affect the amount of chlorophyll in plants:

  • Different plants naturally have different amounts of chlorophyll
  • Levels within an individual plant can vary due to disease, infection with tobacco mosaic virus, environmental stress, or lack of nutrients like water
• Limiting factors for photosynthesis are usually light, carbon dioxide, and temperature
• Graphs used to show the relationship between factors and rate of photosynthesis:

  • Light intensity on the x-axis and rate of photosynthesis on the y-axis
  • As light intensity increases, the rate of photosynthesis increases until it plateaus
  • Similar graphs can be drawn for carbon dioxide and temperature
• Temperature graph:

  • Rate rises with temperature initially
  • Rate starts to drop as enzymes denature, fully denaturing at about 45 degrees
• More than one limiting factor can be shown in a single graph:

  • Comparing curves can identify which factor is limiting photosynthesis
• Farmers can artificially create optimal conditions for photosynthesis:

  • Place crops in greenhouses to increase temperature
  • Provide artificial light for continuous photosynthesis
  • Pump carbon dioxide into the greenhouse
  • Use paraffin heaters for heat and carbon dioxide release
  • Greenhouses also protect plants from pests and pathogens
  • Use fertilizers for essential minerals and pesticides for unwanted bugs
• Farmers need to consider the cost of creating optimal conditions versus the expected yield from crops
• Plants have different levels of organization:

  • Similar cells combine to form tissues
  • Different types of tissues combine to form organs
  • Multiple organs combine to form organ systems
• A leaf is an organ that, along with a stem and roots, forms an organ system for the transport of substances around the plant
• Leaves are the site of photosynthesis, requiring carbon dioxide and water to make sugars
• Water for photosynthesis comes from the soil and is transported to the leaves by the roots and xylem