Plants + Photosynthesis

• Photosynthesis

  The process that 'produces food' in green plants and other photosynthetic organisms (e.g. algae)
• Photosynthesis

  • Takes place in the green parts of plants – mostly in leaves
  • Chlorophyll (found in the chloroplasts) absorbs light energy
  • This energy is used to convert carbon dioxide and water into glucose
  • Oxygen is produced as a by-product
• Photosynthesis

  1. Carbon dioxide + Water

  2. Glucose + Oxygen
• Enzymes

  Control the chemical reactions of photosynthesis
• Oxygen

  Given off during photosynthesis, its rate of production can be used to measure the rate of photosynthetic activity
• Investigating the Conditions Needed for Photosynthesis

  1. Measure the volume of oxygen produced per minute

  2. Measure the number of oxygen bubbles produced per minute
• Investigation – Effect of Light Intensity on the Rate of Photosynthesis

  1. Measure and record the distance of the lamp from the plant

  2. Count the number of bubbles given off every minute

  3. Measure volume of gas produced every minute
• Factors that can be investigated

  • Carbon dioxide concentration
  • Temperature
  • Distance of light
• Temperature

  Affects the enzymes controlling photosynthesis
• Light intensity

  Provides energy for photosynthesis. Increasing light intensity will increase rate of photosynthesis up to a point when another factor will be limiting
• Carbon dioxide concentration

  Increasing carbon dioxide concentration will increase rate of photosynthesis up to a point when another factor will be limiting
• Limiting factor

  The factor that is controlling the rate of photosynthesis at a given time. Increasing this factor will increase the rate of photosynthesis.
• Testing a Leaf for the Presence of Starch

  1. Place leaf in boiling water for 1 minute

  2. Remove leaf and put into boiling ethanol for 10 minutes

  3. Remove leaf, wash in water, place on white tile and cover in iodine
• Glucose produced during photosynthesis

  Cannot be stored and is either used up or stored as insoluble starch
• It is difficult to set up an experiment to prove that water is needed for photosynthesis because you cannot easily remove water from the system
• Uses of glucose produced in photosynthesis

  • Used to release energy in respiration
  • Changed to starch and stored
  • Used to make cellulose which make up the body of plants
  • Used to make proteins and oils
• Structure of a leaf

  • Epidermis
  • Palisade layer
  • Spongy layer
  • Epidermis
  • Stoma
  • Guard cells
  • Xylem
  • Phloem
  • Cuticle
• To follow how water is used in photosynthesis you need to use water containing radioactive isotopes of hydrogen or oxygen
• Uses of glucose produced in photosynthesis

  • Glucose is used to release energy in respiration
  • Glucose can be changed to starch and stored
  • Glucose can be used to make cellulose which make up the body of plants (e.g. cell walls)
  • Glucose can be used to make proteins, which also make up the body of plants, and also oils
• Respiration is taking place all the time in plant cells
• Trans section (T.S.) of a leaf

  • Epidermis
  • Palisade layer
  • Spongy layer
  • Epidermis
  • Stoma (plural = stomata)
  • Guard cells
  • Xylem
  • Phloem
  • Air space
  • Cuticle
• The transpiration stream

  1. Water enters the plant through root hair cells by osmosis

  2. Water moves from cell to cell in the root by osmosis

  3. Water moves into the xylem by osmosis

  4. Water is carried through the plant by the xylem

  5. Water evaporates from the leaf through the stomata

  6. Water moves from cell to cell in the leaf by osmosis

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

  8. Water diffuses from the air spaces in the spongy layer out of the stomata into the air
• Observation of root hair cells

  • Water enters the plant from an area of high concentration of water in the soil to an area of lower water concentration inside the root hair cell, through it's selectively permeable membrane, by osmosis
  • The increased surface area of the root hair cell allows the plant to take in more water faster by osmosis
• Plant Transport Systems

  • Phloem vessels (tubes) - transport sugar and other substances that are produced by cells to all the other parts of the plant
  • Xylem vessels (tubes) – transport water and mineral ions from the roots to the rest of the plant
  • Phloem and xylem vessels usually run together side by side
  • Groupings of phloem and xylem vessels are called vascular bundles
• Phloem Vessels

  • Phloem carries sugar from the photosynthetic areas to other parts of the plant
  • Sugar is moved to other parts of the plant for use in respiration and converted into starch for storage
  • The transport of sugar is not fully understood so plant scientists are still investigating it
• Xylem Vessels

  • Transport of water – from the roots to the rest of the plant
  • Transport minerals – minerals such as nitrates phosphates and potassium are transported by xylem around the plant dissolved in water
  • Support the plant - the xylem vessels in the shoots and roots of mature plants are inflexible and strong and give support to the plant
• Investigation into the movement of a dye through a flowering plant

  1. Take a white flower with a long stalk, e.g. a chrysanthemum and cut the stalk carefully lengthwise

  2. Put each half of the stalk into a measuring cylinder (or boiling tube) containing either plain water or water to which food dye has been added

  3. Tape the measuring cylinders to a plastic tray so that they don't fall over

  4. Leave the flower for a few hours

  5. Observe where the dye ends up in the flower head
• • Water and dye are pulled up through xylem vessels
  • When they reach the flower petals the water evaporates from pores in the petal surface but the dye remains in the cells of the petals
  • The petals become coloured as dye accumulates in them
  • This procedure could be useful for producing quantities of unusually coloured flowers
• The Importance of Water

  • Use in photosynthesis
  • Transport of minerals
  • Support
• How does water support the structure of plant?

  Water provides support due to the pressure of the vacuoles pushing against the cell walls and this keeps the cells turgid and prevents cells becoming flaccid and plants wilting
• Using a Potometer to Measure Transpiration Rate

  1. An air bubble is introduced into the capillary tube at the start of the investigation

  2. As water evaporates through the stomata of the leaves water is drawn up the capillary tube causing the bubble to move

  3. The investigation makes the assumption that water uptake is equal to the transpiration rate

  4. Measure the time taken for the bubble to move a set distance

  5. Measure how far the bubble moves in a set period of time
• Environmental factors that affect water loss from a plant

  • Temperature as temperature increases water molecules have more kinetic energy and therefore move faster. This increases transpiration
  • Humidity increasing humidity reduces the concentration gradient of water between the air and the intercellular spaces in the spongy layer of the leaf this decreases the diffusion of water out of the stomata
  • Wind speed increasing wind speed carries away more water vapour from near the leaf surface and increases the rate of diffusion of water vapour out of the stomata
• • Plants can only grow well if they are in a soil rich in mineral nutrients
  • Plant roots absorb the minerals from the soil and use them to produce materials that they need to grow
• Three main minerals are needed

  • Nitrates
  • Potassium
  • Phosphates
• Investigating Plant Nutrient Requirements

  1. Three healthy plants of the same species and age are grown in an equal volume of aerated mineral solutions

  2. After eight weeks the growth of the plants are observed
• Plant Descriptions

  • Healthy growth
  • Poor growth
  • Yellowing of leaves
  • Poor root growth
• NPK fertilisers that contain nitrates, phosphates and potassium can be added to soil to increase the mineral content