Unit6

• photosynthesis- the process by which plants synthesize carbohydrates from raw materials using energy from light
• equation for photosynthesis-

  • carbon-dioxide + water = glucose + oxygen
  • 6CO2 + 6H2O light and chlorophyll = C6H12O6 + 6O2
• chlorophyll is a green pigment found in chloroplast
• chlorophyll transfers energy from light into energy in chemicals, for synthesis of carbohydrates
• substances used and storage for carbohydrates :

  • starch as energy store
  • cellulose to build walls
  • glucose used in respiration to provide energy
  • sucrose for transport in phloem
  • nectar to attract insects for pollination
• Requirements for photosynthesis

  ●     Light​ - provides energy for the process

  ●     Chlorophyll​ - traps light energy

  ●     Carbon dioxide​ - diffuses into leaves from the air

  ●     Water​ - absorbed by roots of the plant
• TESTING A LEAF FOR STARCH

  ●   Place in boiling water 

  ●   Place in ethanol for 5-10 min

  ●   Place in a water bath 

  ●   Remove and wash in cold water 

  ●   Spread leaf on a tile and if present it will turn blue-black
• IMPORTANCE OF LIGHT

  • de-starch a plant by keeping it in the dark for 2-3days
  • take a leaf and cover some parts of with with black paper and leave it in light for a 6-8hrs
  • Test for starch - covered part should be brown the uncovered part is blue-black
• IMPORTANCE OF CHLOROPHYLL

  • de-starch the plant by keeping it in the dark for 2-3days
  • take out the plant and keep it in sunlight for 6-8hrs
  • Starch test one normal leaf, and variegated leaf
  • Normal leaf - blue black
  • Variegated leaf - brown where white
• IMPORTANCE OF CO2

  • de-starch the potted plants by keeping in the dark for 2-3days
  • take out both of them and place a bell jar above it
  • tie a polythene bag over the pot and the stem of the plant
  • place a small beaker containing sodium hydroxide in one of the jars
  • cover the other plant with label B
  • place both of them in sunlight for 6-8hrs
  • starch test it, leaf from A stains brown while the blue-black
• OXYGEN TEST

  • take water to a beaker of and add little Sodium Hydrogen Carbonate to supply CO, to the plant.
  • take the water plant. Place it in funnel and insert the funnel into the beaker containing water.
  • take a test tube, fill it with water and place it inverted on the stem of the funnel.
  • Keep the apparatus in sunlight for 2-3 hours
  • Air bubbles can be seen in the experiment set up. After 2-3 hours an air space will be seen in the test tube of experimental set up.
  • Remove the test tube and insert a glowing splint into the test tube.
  • gas collected will relight the glowing splint
• apparatus for oxygen test

  • water plant
  • sodium hydrogen carbonate (NaHCO3)
  • beaker
  • funnel
  • test tube
  • splint
• apparatus for CO2 test

  • well watered potted plants
  • sodium hydroxide solution
  • polythene or transparent bag
  • iodine solution
  • alcohol
  • test tube
  • beaker
  • Bunsen burner
• apparatus for light test

  • well watered plant
  • black paper
  • alcohol
  • iodine
  • Bunsen burner
  • test tube
• apparatus for chlorophyll test

  • a potted plant with variegated leaves
  • alcohol
  • iodine
  • test tube
  • Bunsen burner
• apparatus for starch test

  • alcohol
  • iodine
  • test tube
  • Bunsen burner
• investigate

  • light intensity- moving a lamp different distance away from the beaker containing pondweed
  • temperature- by changing the temperature of the water
  • CO2- by dissolving different amounts of sodium hydrogen carbonate in the water in the beaker
• investigate rate of photosynthesis

  • The plants usually used are Elodea or Camboba -types of pondweed
  • As photosynthesis occurs, oxygen gas produced is released
  • As the plant is in water, the oxygen released can be seen as bubbles leaving the cut end of the pondweed
  • The number of bubbles produced over a minute can be counted to record the rate
  • The more bubbles produced per minute, the faster the rate of photosynthesis
• factors effecting the rate of photosynthesis are light intensity, CO2 concentration and temperature
• temperature

  As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes

  • However, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases
• light intensity

  • The more light a plant receives, the faster the rate of photosynthesis
  • This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply
• CO2 concentration

  the more carbon dioxide that is present the faster the reaction can occur

  This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply

  The factors which could be limiting the rate when the line on the graph is horizontal include temperature not being high enough or not enough light
• magnesium is needed for chlorophyll, lack of it causes yellowing between the veins of leave aka chlorosis
• nitrate are sources of nitrogen needed to make amino acids to build proteins, lack of it will cause stunt growth and yellowing of leaves
• • The leaf is broad and flat to increase surface area for the maximum absorption of sunlight and carbon dioxide.
  • Most of the leaves are very thin. This allows CO2 to diffuse into the leaf quickly and light to penetrate easily to all the cells.
  • The lower surface of the leaf has many stomata. This enables the leaf to have efficient gaseous exchange.
  • The leaves of eth plant are positioned at different angles so that they all receive maximum amount of sunlight without over lapping or overshadowing each other
• label leaf

  A) lamina

  B) apex

  C) vein

  D) midrib

  E) petiole

  F) stem

  G) axillary bud

  H) stipule

  
• label internal structure of leaf

  A) cuticle

  B) upper epidermis

  C) palisade mesophyll

  D) bundle sheath

  E) xylem

  F) phloem

  G) lower epidermis

  H) spongy mesophyll

  I) guard cell

  J) stomata

  K) vein

  L) cuticle

  
• cuticle- a waxy non-cellular thin layer to protect the leaf.

  • prevent water loss
  • transparent to allow light to enter
• upper epidermis- this is a single layer of closely packed cells

  • contain no chloroplast to allow light to enter the cells beneath
  • protect the next layer of cell
• palisade mesophyll- they are usually one layer of long cylindrical cells closely packed together

  • contain large number of chloroplast compared to other cells(most photosynthesis occur here)
• chloroplast- it is an organelle containing chlorophyll pigment which traps energy from sunlight for photosynthesis and is the site for photosynthesis
• spongy mesophyll cells- are irregular in shape

  • contains fewer chloroplast which also carries photosynthesis
  • many air spaces to allow gaseous to diffuse freely
• lower epidermis- one cell thick layer covered by waxy cuticle

  • contains many stomata
  • no chloroplast only guard cell
• guard cells-

  • adjust the size of stomata
  • controls opening and closing of stomata
• stomata- allow 3 substances(CO2,O2,H2O) to move in and out of the leaf
• thin- allows CO2 to diffuse into palisade mesophylls quickly
• large surface area- increases surface area for the diffusion of CO2 and absorption of light for photosynthesis
• vascular bundle- thick cell walls of tissue in the bundles help to support the stem and leaf
• xylem-

  • supplies water needed for photosynthesis from root to photosynthesizing cells
  • lignified to give support to plant
• phloem- these are tubes which transport food made by photosynthesis from the leaf to all the plants of the plant as sucrose