Photosynthesis

• The Sun

  • the Sun is the source of most of the energy on Earth
  • it provides heat to keep our planet warm
  • it also provides energy in the form of light (solar energy)
• Factors Affecting Photosynthesis

  • Light
  • Carbondioxide
  • Water
  • Chlorophyll
  • Temperature
• Light - Photosynthesis

  Plants get light from the sun

  • sunlight is absorbed by leaves
  • leaves have large flat surfaces to allow them to absorb as much light as possible
  • light provides the energy needed to form food (or glucose)
• Effects of Light Intensity

  • At low light intensities, increasing the light intensity will increase the rate of photosynthesis (as shown in part A of the graph).
  • Above a certain light intensity, the rate of photosynthesis remains constant (as shown in part B of the graph). This is because the plant cannot get enough of a necessary factor, e.g. carbon dioxide.

  
• Photosynthesis

  • a biochemical process
  • the process by which plants use solar energy to make food
  • in this way, they convert energy from one form (light) to another form (the chemical energy in food):
  • one of the main differences between plants and animals is that plants can make their own food, while animals cannot

  
• Word Equation for Photosynthesis


  Photosynthesis can be summarised by the word equation:

  
• Carbon Dioxide - Photosynthesis

  Plants get carbon dioxide from the air or from respiration in the plant.

  • Carbon dioxide passes from the air into leaves through tiny openings called stomata.
  • Stomata are mainly found on the lower surface of a leaf.
  • If plants are short of carbon dioxide the rate of photosynthesis will slow down.
  • Increasing the concentration of carbon dioxide increases the rate of photosynthesis.
  • Above a certain concentration of carbon dioxide the rate of photosynthesis remains constant. This is because the plant cannot get enough of another factor, such as light.
• Water - Photosynthesis

  • Plants get water from the soil. Water from the soil enters the roots and then passes from the roots up through the stem to the leaves.
  • Water is needed to allow glucose to be made, and it allows enzymes to work so that photosynthesis can take place.
• Chlorophyll - Photosysthesis

  • Plants make chlorophyll.
  • Chlorophyll is a green dye or pigment that is mostly found in chloroplasts in the leaves (and other green parts) of a plant. It absorbs light and allows photosynthesis to take place.

  Chlorophyll is not used up in the process of photosynthesis. In this way it acts as a catalyst (a catalyst speeds up a reaction without being used up in the reaction).

  Plants lacking chlorophyll are often yellow(ish) and have reduced rates of photosynthesis.
• Temperature - Photosynthesis

  Photosynthesis is an enzyme-controlled reaction. This means it is affected by temperature.

  The ideal temperature for photosynthesis in most plants is between 20°C and 30°C.
• Other Factors - Photosynthesis

  • The surface area of the leaves
  • The number of leaves
  • The distribution of leaves (i.e. whether they are blocking light from each other)
  • The number of tiny openings (called stomata) on the leaves
• Glucose - Photosynthesis

  The food made by a plant is called glucose. Glucose made in a leaf may be used:

  • To provide energy in respiration
  • To form starch in different parts of the plant
  • To form new cells and allow for growth.
  • (to make cell walls, i.e. it is converted to cellulose)
• Oxygen - Photosynthesis

  The gas made by photosynthesis is oxygen. The oxygen made in this way may be:

  • Used for aerobic respiration, to provide energy in the leaf
  • Released out of the leaf and into the air (passes out through stomata)
  • oxygen released by photosynthesis is important as it then becomes available to all other plants and animals for respiration
• Chemical Equation for Photosynthesis