Plants and photosynthesis

• Importance of photosynthesis


  Green plants and other photosynthetic organisms use chlorophyll to absorb light energy and convert carbon dioxide and water into glucose, producing oxygen as a by-product
• Word equation


  Carbon dioxide + water --> glucose + oxygen
• How does temperature affect photosynthesis

  . Higher temperature provides more kinetic energy for enzymes involved in photosynthesis so rate increases as temperature rises

  . The optimum temperature is usually 25°c

  . If temperature is too high (around 45) enzymes become denatured and rate of photosynthesis decreases

  . When it drops too low on cold winter days
• How does light intensity affect photosynthesis

  . The rate of photosynthesis is directly proportional to light intensity, as light intensity increases, the rate of photosynthesis increases

  . Rate will eventually plateau as temperature becomes limiting

  . When its night in the winter
• How does carbon dioxide affect photosynthesis

  . As carbon dioxide concentration increases, the rate of photosynthesis increases

  . Rate will eventually plateau as light intensity becomes limiting

  . When light intensity and temperature are not limiting
• Use of sodium hydroxide


  Absorbs carbon dioxide in air
• How to test for starch

  . Leaf is placed in a beaker of boiling water for 1 minute - to kill leaf

  . The leaf is removed from water and put into a boiling tube half full of ethanol - to remove chlorophyll

  . The boiling tube containing the leaf and ethanol is placed in the hot water for 10 minutes

  . Leaf is placed on a white tile and covered in iodine - if its black blue starch is present
• Uses of glucose


  Respired to release energy

  Converted to starch for storage

  Used to make cellulose, proteins and oils
• Able to label


  Cuticle, epidermis, stomata, palisade layer, spongy layer, xylem and phloem
• Structure of stomata


  Pores found in the lower epidermis that allows gas exchange
• Why does the stomata open and close

  To regulate transpiration and allows gas exchange
• Importance of water in plants

  Used in photosynthesis

  Transports minerals
• Significance of root hairs in increasing the area for absorption in a root hair cells

  Water enters the plant from an area of high to low concentration of water in the soil to an area of lower water concentration inside the root hair cells, through its selectively permeable membrane, by osmosis. The increased surface are allows the plant to take in more water faster by osmosis
• Role of osmosis in the uptake and movement of water through a plant

  . Water enters plant through root hair by osmosis

  . Water moves from cell to cell

  . Water moves into the xylem by osmosis

  . Water molecules stick together causing water to be pulled up from xylem as column

  . Water moves from cell to cell by osmosis

  .Water evaporates from some leaf cells causing more water to be pulled up the xylem

  . Water diffuses from the air in spongy layer out of stomata into the air
• Uptake of mineral ions into root

  Lower concentration of mineral ions in the soil than in root. Root hair cells take up mineral ions by active transport (uses energy)
• Role of xylem


  Transports water and minerals up the plant from roots to the leaves via the transpiration stream
• Role of transpiration in the movement of water through a plant

  . Water evaporates from mesophyll layer and diffuses out of stomata

  . Water molecules are drawn up the xylem vessels to replace water that as been lost

  . This causes more water molecules to be absorbed from the soil into root hair cells
• How does temperature effect rate of transpiration

  As temperature increases water molecules have more kinetic energy so rate of diffusion increases. More water vapor diffuses out of stomata, rate of transpiration increases.
• How does humidity effect rate of transpiration

  As humidity increases the water concentration gradient between air spaces in the leaf and atmosphere decreases. Decreased rate of diffusion of water molecules out of stomata, rate of transpiration increases.
• How does air movement effect rate of transpiration

  As air movement increases a high water concentration gradient is maintained between air spaces in leaf and atmosphere. Increased rate of diffusion of water molecules out of stomata, rate of transpiration increases
• Phloem function


  Transports sugars up and down the plant from photosynthesis tissues to non photosynthetic tissues
• Lack of nitrates


  Results in poor growth
• Deficiency of potassium 


  Yellowing of the leaf
• Deficiency of phosphate


  Poor root growth
• Use of NPK fertilizers

  Contains nitrogen, phosphorus and potassium. They can be used artificially increase the concentrations of mineral ions in the soil.