plant structures and their functions

• what are photosynthetic organism

  • plants and algae
  • they are the main producers of food, which they synthesise from sunlight in a process called photosynthesis
  • this means they are also the primary producers of biomass in food webs and chains
• what is the photosynthesis reaction

  • it is an endothermic reactions, as it takes more energy in than it releases
  • the light energy from the environment is transferred to chloroplasts in leaves
  • equation:
  • carbon dioxide + water - glucose + oxygen
  • 6CO2 + 6H20 - C6H12O6 + 6O2
• what are the limiting factors of photosynthesis

  • temperature
  • light intensity
  • carbon dioxide concentration
• how is temperature a limiting factor of photosynthesis

  • increase temp = increases rate of temperature
  • this is because the enzymes work faster due to increase in KE
  • although if the temperature increases too high, the enzymes will denature and the rate of reaction decreases
• how is light intensity a limiting factor of photosynthesis

  • increasing light intensity = increasing rate of reaction
  • this is because the plant has more light energy to carry out the reaction
  • if the rate of reaction is increasing then light intensity is still a limiting factor as reaction wasn't as fast as it could have have been
  • eventually if light intensity keeps increasing the photosynthesis will no longer increases
  • this means light intensity is no longer the limiting factor
• how is carbon dioxide concentration a limiting factor

  • increasing carbon dioxide = increasing rate of reaction
  • this is because CO2 is needed for the plants to take in during photosynthesis
  • although if the rate is still increasing, carbon dioxide is a limiting factor but at a certain point photosynthesis no longer increase so CO2 is no longer a limiting factor
• what is the core practical to investigate the effect of light intensity on the rate of photosynthesis

  • place a sealed flask with 100ml of water and a small amount of pondweed 15cm away from the lamp
  • leave the apparatus for around 10 minutes to allow pondweed to adjust
  • connect the gas syringe to the flask and record the number of bubbles produced over a period of time
  • the rate of reaction is the no. of bubbles produced per minute
  • move the lamp 10cm away and repeat experiment
• what are the variables in Core Practical: Investigate the effect of light intensity on the rate of photosynthesis

  • independent variable - distance from the light source/light intensity
  • dependent variable - the number of bubbles produced per minute
  • control variables - using the same piece of pondweed each time, same volume of water
• how is the rate of photosynthesis directly proportional to light intensity

  • as light intensity increases, rate of reaction increases
  • this is because there is more light energy to hit chloroplasts in the leaf
• what is light intensity inversely proportional to

  • distance$^2$
  • inverse square law : $\frac{1}{dis\tan ce^2}$
  • this because if rate of reaction decreases, light intensity decreases
  • so if distance increases, rate of reaction decreases
• how is the root hair cells is adapted to absorb water and mineral ions

  • has a large surface area: means more water can move in
  • large permanent vacuole: affects speed of movement of water from the soil to cell and allows more water to be stored
  • mitochondria: provides energy from respiration for active transport of mineral ions into root hair cells
• how is the xylem adapted to their function

  • they are specialised to transport water and mineral ions up the plant from the roots to the shoots
  • a chemical called lignin is deposited which causes the cells to die (become lignified).
  • They become hollow and are joined end-to-end to form a continuous tube so water and mineral ions can move through
  • lignin is deposited in spiral which helps the cells withstand the pressure from the movement of water
• how is the phloem adapted to their function

  • they are specialised to carry the products of photosynthesis to all part of the plants
  • cell walls of each cell form structure called sieve plates when they break down, allowing the movement of substances from cell to cell
  • the energy need for these cells to be alive is supplied by the mitochondria of the companion cells
  • these cells use this energy to transport sucrose (sugar) around the plant
• how do farmers use the rate of reaction of photosynthesis to improve crop yield

  • increasing the rate of photosynthesis = an increase in yield of crops
  • so farmers light and heat their greenhouses and also add extra carbon dioxide
  • some even use oil burners as it releases heat and CO2 at the same time
  • although this is expensive
• how is water and mineral ions transported through the plant

  • mineral ions in the earth dissolve in water
  • water and mineral ions are transported by transpiration
  • TRANSPIRATION:
  • the evaporation of water from cells inside the leaf (cools leaf down)
  • water vapour diffuses through the air spaces in the spongy mesophyll and out of the cell through the stomata
  • water passes from the xylem into the leaf to replace water that has been lost
  • water is drawn into the root hair cells and up the xylem vessels to the leaf
• what is the structure and function of a stomata

  • surrounded by two guard cells
  • when light intensity is high, the guard cells swell and change shape, causing the stomata to open
  • this means that carbon dioxide is able to diffuse into the leaf (for photosynthesis) and water vapour to diffuse out
  • under hot conditions, plant closes stomata to reduce water loss by transpiration (water vapour cannot diffuse out)
• how is sucrose transported around the plant

  • by translocation in the phloem tubes
  • in phloem cell, cells are joined end to end and contain holes in the end of cell walls (called sieve plates)
  • this allows sucrose to flow from one plant cell to the next easier
• how is the structure of a leaf adapted for photosynthesis and gas exchange

  • thin and transparent epidermis: allow more light to reach palisade cells
  • thin cuticle made of wax: protect leaf from infection and prevent water loss
  • palisade cell layer at top of the leaf: absorb more light and increase rate of photosynthesis
  • spongy layer: air spaces allow gases to diffuse through leaf
  • palisade cells contain many chloroplasts: absorb all the available light
• what are the environmental factors that effect the rate of water uptake/transpiration

  • temperature: rate is greater at high temp. because it allows evaporation to be faster
  • humidity: rate is greater when air is not humid because evaporation is faster in dry conditions
  • air movement: rate increases in windy conditions because it removes water vapour and allows more water to evaporate
  • light intensity: rate increases when light increase because more light intensity increase rate of photosynthesis, meaning stomata will open and more water vapour will evaporate
• how could you calculate the rate of transpiration

  • measuring the distance travelled by an air bubble in a capillary tube for a given time
  • can do this using a potometer
• how are plants adapted to survive in extreme conditions

  • Desert plants:
  • stems can store water
  • widespread or deep root systems so can collect water for a large area or deep underground
  • spines are modified leaves meaning they can minimise surface area and so reduce water loss and also can protect plant
  • very thick, waxy cuticle to reduce water loss by evaporation
  • reduced number of stomata to reduce water loss by transpiration
• what are auxins

  • plant hormone in the tips of the shoots of a plant
• how does auxins control and coordinate plant growth and development(phototropism)

  • the distribution of auxin in the shoots is affected by light
  • if the plant is exposed to light on one side, the auxin moves to the shaded side of the shoot
  • the auxin stimulates cells to grow more here
  • this means the shoot bends towards the light
  • so the plant receives more light, meaning photosynthesis can occur at a faster rate
• how does auxins control and coordinate plant and growth development(gravitropism)

  • the distribution of auxins in the shoots and roots is affected by gravity
  • if a shoot is horizonal, the shoot will show negative gravitropism
  • auxin moves to the lower side
  • the cells of the shoot grow more on the side with most auxin, so it stimulates cells to grow more here
  • this makes the shoot bend and grow away from the ground
  • this is beneficial as light is likely to be further away from the ground
  • if a root is horizontal the root will show positive gravitropism
  • the auxin moves to the lower side
  • the cells of the root grow more on the side with less auxin, stimulates cell growth on the upper side
  • makes root bend and grow downwards
  • beneficial as can increase levels of water lower down
• what are the uses of auxins

  • weedkillers - auxin will make the cells grow too rapidly so will die
  • as rooting powders - new plant grows quickly
  • promote growth in tissue cultures - so cells begin to form roots and shoots
• what are the uses of gibberellins

  • gibberellins help cells with elongation(growth)
  • end seed dormancy (can help seeds germinate(grow))
  • encourage plants to flower at a faster rate
  • fruits can grow larger, increasing yields
• what are the uses of ethene

  • controls cell division and ripening of fruits
  • helps ripen fruits
  • so during transport it gets less bruised and damaged
  • reduces wastage