6.Plant nutrition

• Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water, at the same time oxygen is made and released as a waste product
• photosynthesis is the process by which plants manufacture carbohydrates from raw materials using energy from light
• photosynthesis requires energy which is obtained by the pigment chlorophyll trapping light from the Sun
• the raw materials required for photosynthesis is carbon dioxide and water
• Photosynthesis Word Equation

  
• carbon dioxide + water ----->glucose +oxygen

  chlorophyll
• water is taken up by the roots and transported through the xylem to the leaves
• carbon dioxide diffuses into the leaf through the stomata
• the glucose produced in photosynthesis is used to make substances needed in the plants
• oxygen diffuses out the leaf through the stomata and is used in respiration
• Chlorophyll is a green pigment that is found in chloroplasts within plant cells.It reflects green light, giving plants their characteristic green colour
• Chlorophyll absorbs light energy; its role is to transfer energy from light into energy in chemicals, for the synthesis of carbohydrates, such as glucose
• Photosynthesis will not occur in the absence of chlorophyll
• The carbohydrates produced by plants during photosynthesis can be used in the following ways:

  • Converted into starch molecules which act as an effective energy store
  • Converted into cellulose to build cell walls
  • Glucose can be used in respiration to provide energy
  • Converted to sucrose for transport in the phloem
  • As nectar to attract insects for pollination
• Plants can also convert the carbohydrates made into lipids for an energy source in seeds and into amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots
• Photosynthesis produces carbohydrates, but plants contain many other types of biological molecule; such as proteins, lipids and nucleic acid (DNA),As plants do not eat, they need to make these substances themselves
• Carbohydrates contain the elements carbon, hydrogen and oxygen but proteins, for example, contain nitrogen as well (and certain amino acids contain other elements too)
• Other chemicals in plants contain different elements as well, for example chlorophyll contains magnesium and nitrogen
• This means that without a source of these elements, plants cannot photosynthesise or grow properly
• Plants obtain these elements in the form of mineral ions actively absorbed from the soil by root hair cells
• ‘Mineral’ is a term used to describe any naturally occurring inorganic substance
• Mineral deficiencies in plants

  
• magnesium is needed to make chlorophyll in plants and is caused by the yellowing between the veins of the. leaves (chlorosis)
• nitrates are a source of nitrogen needed to make make amino acids which build proteins, they cause the stunted growth in plants
• Testing a variegated leaf for starch. Care must be taken when carrying out this practical as ethanol is extremely flammable, so at that stage of the experiment the Bunsen burner should be turned off.The safest way to heat the ethanol is in an electric water bath rather than using a beaker over a Bunsen burner with an open flame.

  
• Investigating the Need for Light

  1. Destarching plant by placing in dark cupboard for 24 hours

  2. Partially cover leaf with aluminium foil

  3. Place plant in sunlight for a day

  4. Remove leaf and test for starch using iodine
• Photosynthesis is the process by which plants manufacture carbohydrates from raw materials using energy from light
• Limiting factor is something present in the environment in such short supply that it restricts life processes
• When sunlight falls on chlorophyll, some of the light is absorbed. Chlorophyll molecule then releases energy to make CO2 combine with H2O so in this process light energy converted to chemical energy and is stored in the form of carbohydrates
• Cellulose ‐ which strengthens the cell wall
• Proteins ‐ such as enzymes and chlorophyll
• Glucose


  A simple sugar that is soluble in water and can be quite reactive
• Glucose is not a good storage molecule because it is reactive and can get involved in unwanted chemical reactions
• Glucose is not a good storage molecule because it would dissolve in water, decreasing the water concentration in the cell, causing the cell to be damaged
• Conversion of glucose to carbohydrates (starch)

  1. Glucose is converted to a large, non-reactive molecule

  2. Glucose is made into granules

  3. Glucose is stored inside chloroplast
• Chlorophyll is necessary for photosynthesis
• Light is essential for photosynthesis Process

  • Take a potted plant.
  • Destarch the plant by keeping it in complete darkness for about 48 hours.
  • Test one of it leaves for starch, to check that is does not contain any.
  • Fix a leaf of this plant in between two strips of a thick paper on leaf.
  •  Place the plant in light for a few days.

  Remove the cover from the leaf and test it for starch.

  Observations

  Positive starch test will be obtained only in the portion of the leaf exposed to light and negative test in parts with paper strip.
• leaf photosynthesis adaptation: supported by stem and petiole

  function: to expose as much of the leaf to the sunlight and air
• leaf photosynthesis adaptation: large surface area

  function: to expose as large an area as possible to the sunlight and air
• leaf photosynthesis adaptation: thin

  function: allows sunlight to penetrate to all cells to allow carbon dioxide to diffuse in and oxygen to diffuse out asap