plant structures and their functions

• Photosynthesis


  carbon dioxide + water -> glucose + oxygen

  Photosynthesis is a endothermic reaction which means it takes in energy from its surroundings

  The products have more energy than the reactants

  Glucose can link together to form starch which can then be broken down to form sucrose.

  Glucose is used in respiration in cells.
• Factors that affect the rate of photosynthesis


  Temperature:

  • photosynthesis is controlled by enzymes which means temperature affects the rate
  • photosynthesis works best at higher temperatures

  Carbon dioxide concentration:

  • the higher the concentration of carbon dioxide around a plant the faster the rate of photosynthesis

  Light intensity:

  • light intensity varies with the distance according to the inverse square law
  • if you double the distance, the light intensity is 1/4
• Plant adaptions 


  Plants have adapted for extreme conditions to minimise water loss.

  Broad leaved deciduous lose their leaves in winter, preventing water loss when the soil water may be frozen.

  Conifers do not do this, they have needle-shaped leaves (small surface area and very thick cuticle). This shape creates less wind resistance and also means they collect less snow.

  Plants can also reduce water loss by trapping water vapour close to their leaves. Conifers stomata are in small pits, water vapour less exposed to wind movements. Other plants use tiny hairs to trap water vapour.
• Plant hormones


  Stimulus - a change in the environment that causes a response by an organism

  Tropism - a respond to a stimulus by growing towards / away from it.

  Auxins are produced in the tips of shoots, where they causes elongation.

  If a shoot has light coming from one side, the auxins move to the shaded side, making the cell elongate more, which causes the cell to point in the direction of the light.

  Auxins are also found in the roots, where they have the opposite effect to that in the shoots, they cause cells to stop elongating and this causes gravitropism.
• Uses of plant hormones (gibberellins)


  Plant hormones called gibberellins are naturally released inside a seed to start germination.

  Some seeds need darkness/cold before they start germination but plant growers can use gibberellins to start germination.

  Photoperiodism - response to the number of daylight hours

  Some flowers use this to flower at a certain time (pollinators/not too cold). Flower growers can override this using gibberellins.

  Many plants only produce plants after being pollinated. Gibberellins can be used to produce fruits without pollination, giving seedless fruits.
• Uses of plant hormones (artificial auxins)


  Artificial auxins make some plants grow uncontrollably, which cam kill them.

  Selective weedkillers contain artificial auxins to kill plants with broad leaves but not those with narrow leaves. Farmers use these in their fields

  Auxins are also found in rooting powders, causing plant cuttings to develop roots quickly.

  Large numbers of identical plants can be produced quicker this way compared to germinating seeds.
• uses of plant hormones (ethene gas)


  Ethene gas can be used to transport unripe fruit easier without damaging them as well as making them able to be stored for longer before going off.

  It can also be used to ripen fruits to make sure they arrive in shops in a just ripened condition.
• Transpiration 


  Transpiration is the loss of water by evaporation from the leaves. The movement of water from the roots to the leaves is called the transpiration stream.

  1. causes water to enter the roots by osmosis
  2. draws water up the stem through the xylem from the roots
  3. draws water out of the leaf cells and xylem
  4. water vapour evaporates from the leaves mainly through the stomata
• Factors that affect the transpiration rate


  • wind - moves water molecules away from the stomata
  • humidity level - water vapour in the air depends on this
  • temperature -higher the temperature, the faster the particles move and diffuse
  • light intensity - the more light, the more photosynthesis occurs and stomata are open wider
• Translocation


  Translocation is the transport of sucrose around a plant.

  Phloem:

  • plants produce sucrose from glucose and starch made by photosynthesis
  • sucrose is translocated, in the sieve tubes of the phloem tissue
  • the sieve cells are connected to neighbouring sieve cells by holes, so the sucrose solution can pass through
  • companion cells actively pump sucrose into or out of the sieve cells
  • as sucrose is pumped into sieve tubes the increased pressure cause the sucrose solution to flow up to growing shoots or down to the storage organs
• Light intensity and photosynthesis (core practical) Pt.1

  Aim - to investigate how light intensity affects the rate of photosynthesis

  Apparatus - screw top bottles, algal balls, universal indicator solution, measuring cylinder, foil/black paper, bright lamp, small tank of water, metre ruler
• Light intensity and photosynthesis (core practical) Pt.2

  Method:

  1. Place 20 algal balls and the same volume of indicator solution in each tube, and replace the screw tops.
  2. Check the colour of the indicator and record the pH.
  3. If you are using a hot lamp, place the water tank next the lamp.
  4. Use the metre ruler to place the tubes at specific distances from the lamp, on the opposite side of the tank.
  5. Leave the tubes for 1-2 hours.
  6. Calculate the rate of change in pH per hour for each tube.
• Photosynthesis

  Carbon dioxide + water$\rightarrow$ glucose + oxygen

  Photosynthesis is endothermic so it takes in energy from the surroundings.

  Glucose can link together to form starch.

  Starch can then be broken down to form sucrose.

  Sucrose can make other molecules for plants, such as cellulose, lipids or proteins.

  Glucose is used in respiration in cells.
• Limiting factors in photosynthesis

  With the la of limiting factors, each factor does not work in isolation. Several factors may interact, and it may be any one of them that is limiting photosynthesis.

  An example of how they may interact:

  • the rate of photosynthesis increases until factors become limiting
  • if carbon dioxide concentration is increased, the rate increases further, and another factor becomes limiting
  • the rate can be increased further if the temperature is increased
  • the rate increases again until another factor becomes limiting
• Factors affecting photosynthesis (light intensity)

  Without enough light, a plant cannot photosynthesise very quickly - even if there is plenty of water and carbon dioxide.

  Increasing the light intensity increases the rate of photosynthesis, until some other factor - a limiting factor - becomes in short supply.
• Factors affecting photosynthesis (carbon dioxide and temperature)

  Carbon dioxide:

  • If the concentration of carbon dioxide is increased. the rate of photosynthesis will therefore increase.

  Temperature:

  • At low temperatures, the rate of photosynthesis is limited by the number of collisions between enzymes and substances. As the temperature increases, the number of collisions increases. However, at high temperatures, enzymes are denatured and this will decrease the the of photosynthesis.
• Absorbing water and mineral ions

  Roots are used to absorb water and mineral ions from soil.

  Plants use water for:

  • carrying dissolved minerals
  • photosynthesis
  • keeping cells rigid
  • cooling the leaves

  The outer surface of roots are covered with root hir cells.

  The 'hairs' are long extensions that provide a large surface area so that water and mineral ions can be absorbed quickly. The hairs also have thin cell walls so that the flow of water into the cell is not slowed.

  Minerals salts are naturally occurring ionic compounds.

  Plants need ions to form new substances.
• Transpiration

  Transpiration is the loss of water by evaporation from the leaves. The movement of water from the roots to the leaves is called the transpiration stream.

  1. water vapour evaporates for leaves mainly through the stomata
  2. draws water out of the leave cells and xylem
  3. draws up the stem through the xylem from the roots
  4. causes water to enter the roots by osmosis
• Translocation

  During photosynthesis, plants produce glucose from simple inorganic molecules - carbon dioxide and water - using light energy. Some of the glucose produced by photosynthesis is used for respiration.

  Translocation is the movement of sugar produced in photosynthesis to all other parts of the plant for respiration and the other processes described above. This occurs in the phloem cells.
• Plant adaptations (tropical)

  Plants need to be adapted to wet conditions with low light intensity. These include:

  • large leaves to take in as much light as possible
  • stems and leaves that climb up trees to obtain more light, with the plant's roots still in the ground
  • leaves with 'drip tips' so water runs off them
• Plant adaptations (dry and waterlogged)

  Dry conditions:

  • stomata sunk in pits to reduce water loss
  • waxy cuticle to reduce water loss
  • leaf hairs to trap moist air round stomata
  • rolled leaf to reduce air movement around the stomata

  waterlogged soil - no air spaces:

  • spongy tissue in their roots that stores oxygen
  • fine surface roots that take in oxygen at the water surface
• Leaf adaptations

  Leaves are often broad and flat, giving them a large surface area. The palisade cells near the top of a leaf are packed with chloroplasts. These adaptations allow a leaf to absorb a great deal of light.

  Carbon dioxide for photosynthesis comes form the air. Leaves contain microscopic pores called stomata. Stomata allow carbon dioxide to diffuse into the leaf. The stomata are opened/closed by specialised guard cells. In the light, water flows into pairs of guard cells making them rigid. At night, water flows out of the guard cells. They lose their rigidity and stomata closes.
• Plant hormones

  Auxin is for phototropism and gravitropism. Auxins are produced in the tips of shoots, where they cause elongation of the cells. If a shoot has light coming from one side, the auxins move to the shaded side, making the cells to elongate more, which causes the cells to point in the direction of the light.

  Auxins are also found in the roots, where they have the opposite effect to that in the shoots, they cause cells to stop elongating and this causes gravitropism - towards gravity.

  Gibberellins - helps seeds germinate and grow shoots and roots

  Ethene gas - helps fruit to ripen
• Uses of plant hormones (gibberellins)

  Plant hormones called gibberellins are naturally released inside a seed to start germination. Some seeds need darkness/cold before they start to germinate, but plants can use gibberellins to start germination. Some plants use phototropism to flower at a certain time. Flower growers can override this by using gibberellins. Many plants only produce seeds after being pollinated. Gibberellins can cause some plants to produce fruits without pollination - gives seedless fruits. Gibberellins can be used on some plants to increase the size of fruits.
• Uses of plant hormones (auxins)

  Artificial auxins make some plants grow uncontrollably, which can kill them. Selective weedkillers contain these to kill plants with broad leaves but not those with narrow leaves. Farmers therefore kill weeds in a field but don't affect the crop. They are also found in rooting powders, causing plant cuttings to develop roots quickly. Large numbers of identical plants can be produced quicker compared to germinating seeds.

  Unripe fruits are easier to transport without damage and can be kept longer in cold storage without going off.

  The fruit can be ripened
• Uses of plant hormones (ethene gas)

  Unripe fruits are easier to transport without damage and can be kept longer in cold storage without going off.

  The fruit can be ripened using ethene gas to make sure the fruit arrives in shops in just ripened conditions.