B4 - Bioenergetics

  • Created by: Snowy271
  • Created on: 12-05-18 18:13


Photosynthesis is a chemical process by which plants produce glocose and oxygen to harvest energy

Image result for balanced equation for photosynthesis

Leaves use chlorophyll (a green pigment found in chloroplasts, palisade cells and spongey mesophyll cells) to absorb sunlight, which is required for photosynthesis.

  • Carbon dioxide is taken in from the air; it enters through the stomata on the leaves
  • Water is absorbed from the soil by the roots, and is transpoted to the leaves via the xylem
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Factors Affecting the Rate of Photosynthesis

There are four major factors affecting the rate of photosynthesis:

  • Light intensity
  • Carbon dioxide concentration
  • Temperature
  • Water

A plant requires all four in order to carry out photosynthesis. If one of these factors is in short supply (called the limiting factor), the rate of photosynthesis willl decrease.

  • Increasing light intensity, carbon dioxide concentration or water will each increase the rate until another factor is limiting
  • Increasing temperature will increase the rate until the optimum temperature is reached, where the enzymes begin to denature and the rate then decreases.
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Uses of Glucose in Plants

  • Synthesis: Glucose combines with nitrate from the soil to make compunds. Glucose combines with mineral ions, such as nitrate ions, to produce amino acids. The amino acids can then be built up into proteins to be used in various ways.
  • Storage: Glucose can be stored as starch in the leaves as an energy store. Starch is insoluble in water, so does not affect osmosis in the plant's cells.
  • Cellolose: Glucose molecules join together to make cellulose, a tough fibrous carbohydrate molecule.It is used to make the cell wall in plant cells and is used for support.
  • Respiration: Glucose is broken down using oxygen to release energy for the plant's cells.This energy can then be used to make molecules for growth.
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Aerobic Respiration

Respiration is a chemical process by which energy is release from the breakdown of glucose. It is an exothermic reaction.

  • Aerobic respiration is a type of respiration used when oxygen is asufficient
  • It takes place in the mitochondria and releases lots of energy
  • The energy produced can be used for life processes such as growth, homeostasis, movement ect.

Glucose + oxygen → carbon dioxide + water

C6H12O6 + 6O2→ 6CO2 + 6H2O

  • Aerobic respiration requires oxygen. During respiration, food is broken down into smaller molecules to release energy,
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Anaerobic Respiration

  • Anaerobic respiration does not require oxygen, but releases less energy than aerobic respiration.
  • It takes place in the cell's cytoplasm

Glucose --> Lactic acid


  • Lactic acid can cause muscle pains
  • In aerobic repiration, glucose is broken down withouth oxygen. Energy is transferred to the cell and the lactic acid is broken down in the liver.
  • To do this, the liver needs oxygen- this is known as oxygen debt.
  • When a sufficient oxygen supply is available, the liver is able to break down the lactic acid into harmless waste products.
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Metabolism is the sum of all the chemical reaction is the body

They are enzyme catalysed and either break down or build up molecules

Some metabolic reactions include:

  • Respiration - aerobic and anaerobic
  • Photosynthesis
  • Conversion of glucose into starch, cellulose and glycogen
  • Formation of lipids 
  • Breakdown of excess proteins in the liver to produce urea for excretion 
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