Photosynthesis & Respiration

• All green plants can prepare their food and are therefore called autotrophs. This method of nutrition is known as autotrophic nutrition.
• The following raw materials are required:

  Water(soil)

  Carbon dioxide (air)

  Chlorophyll (leaf)

  Energy/Sunlight (Sun)
• External factors affecting photosynthesis

  Light Intensity

  Carbon dioxide

  Temperature

  Water
• Internal factors affecting photosynthesis

  Chlorophyll

  Structure of leaf
• Photosynthesis is the process by which green plants capture solar energy and use it to convert carbon dioxide and water into simple sugars.
• The process is completed in the mesophyll cells of the plant.
• Mesophyll cells contain numerous plastids called chloroplasts which contain a green pigment called chlorophyll
• On the lower side of the leaf are numerous pores called stomata, which open up the air cavity inside the leaf.


  CO2 diffuses into the leaf through the stomata.
• The guard cells regulate the opening and closing of the stomata. This is due to water movement in and out of the guard cells.
• Thick inner wall -  Thin outer wall of stomata.
• In the presence of sunlight, water diffuses in guard cells, making them swell. The outer inner wall of the guard cell bulges outward. This makes the inner thin walls draw apart from each other, which helps in the opening of the stomata. 


  Without sunlight, water is drawn out of guard cells which shrinks them. Hence the inner thick walls of the guard cells get frightened to close the stomata.
• Photosynthesis produces food for sustaining life on Earth. All the oxygen in the atmosphere is the result of photosynthesis. 


  Photosynthesis maintains the balance of oxygen and carbon dioxide in the atmosphere.
• Respiration is the process by which oxidisation of organic compounds releases energy in the form of ATP adenosine triphosphate. 


  It is of two types - Aerobic and Anaerobic.
• Aerobic Respiration -

  Enzymes

  Glucose + Oxygen ----------> Carbon dioxide + Water + Energy (38 ATP)


  Anaerobic respiration -

  Enzymes

  Glucose --------> Ethanol + Carbon dioxide + Energy (2 ATP)
• Aerobic respiration - The excess energy gets stored in the cells an ATP.


  In Anaerobic respiration the food is broken down into ethanol and carbon dioxide, but the energy given out is less (only 2 ATP).
• Respiration in Plants:

  Absorption of oxygen from the atmosphere.

  Oxidation of stored food.

  Release of energy as a result of oxidization.

  CO2 and H2O are end products which are released from the plant.
• Photosynthesis is the process by which green plants and certain other autotrophic organisms manufacture their own food material in the form of carbohydrates from carbon dioxide and water in the presence of chlorophyll and sunlight
• Photosynthesis converts light energy to chemical energy
• Photosynthesis takes place inside cellular organelles called chloroplasts which contain abundant photosynthetic pigments called chlorophyll
• Chloroplasts are found in abundance in green leaves and are therefore the major site of photosynthesis in plants
• Gaseous oxygen is a major byproduct of the process of photosynthesis
• Photosynthesis occurs in two major steps within the chloroplasts: a light reaction and a dark reaction
• Starch is eventually formed as a reserve food by plants at the end of the photosynthetic process
• If a plant is stripped of any vital factors necessary for photosynthesis, the process ceases to occur and the plant starts utilizing its existing reserve food stored as starch
• A de-starched plant cannot remain alive for long unless it is provided with the vital factors necessary for photosynthesis to occur
• The absence or presence of starch and thereby photosynthesis is determined using iodine solution, which turns blue-black in the presence of starch and retains its original brown color in the absence of starch
• Chlorophyll is an absolute essential for photosynthesis to take place in a plant
• Photosynthesis is the process by which green plants and certain other autotrophic organisms manufacture their own food material in the form of carbohydrates from carbon dioxide and water in the presence of chlorophyll and sunlight
• Photosynthesis takes place inside cellular organelles called chloroplasts which contain abundant photosynthetic pigments called chlorophyll
• Chloroplasts are found in abundance in green leaves and are therefore the major site of photosynthesis in plants
• Gaseous oxygen is a major byproduct of the process of photosynthesis
• Photosynthesis occurs in two major steps within the chloroplasts: a light reaction and a dark reaction
• A plant without stored starch due to lack of photosynthesis is known as a d starch plant
• If a plant is stripped of any vital factors necessary for photosynthesis, the process ceases to occur in that plant
• Starch is eventually formed as a reserve food by plants at the end of the photosynthetic process
• A starch plant cannot remain alive for long unless it is resupplied with the vital factors necessary for photosynthesis to occur.
• The absence or presence of starch and thereby photosynthesis is determined using iodine solution, which turns blue-black in the presence of starch and retains its original brown color in the absence of starch
• This experiment demonstrates that light is an essential external component for photosynthesis to occur in a plant
• During night too respiration continues. Plants take in oxygen and give out carbon dioxide. Hence, there is some truth under the belief that one shouldn't sleep under the trees at night. 


  But sleeping under the tree during hot midday is good as one gets both the oxygen due to photosynthesis and coolness, good transpiration.
• Photosynthesis

  1. Food is synthesized.
  2. Oxygen is released as a by-product.
  3. Occurs during the day.

  Respiration

  1. Food is broken down.
  2. CO2 is released as a by-product.
  3. Occurs both during the day and the night.