Plant structures and their functions

• Photosynthetic organisms


  During photosynthesis, photosynthetic organisms use energy from the sun to make glucose. Some of the glucose is used to make larger, complex molecules that the plant or algae need to grow. These make up the organisms biomass (the mass of living material). The energy stored in the organisms biomass then works its way through the food chain as animals eat them and each other. So photosynthetic organisms are the main producers for food for nearly all life on earth
• Photosynthesis in plants and algae

  Photosynthesis in plants and algae is an endothermic reaction (energy is taken in) that uses light energy to react carbon dioxide and water to produce glucose and oxygen
• Rate of photosynthesis factors

  The rate of photosynthesis is affected by the light intensity, the concentration of carbon dioxide, and the temperature. These factors can become a limiting factor meaning its stopping photosynthesis from happening any faster.
• Light intensity 


  Light transfer the energy needed for photosynthesis. At first, the light intensity and rate of photosynthesis are directly proportional, meaning the light intensity is limiting the rate of photosynthesis however eventually the rate of photosynthesis stops increasing.

  
• Inverse square law (light intensity)

  The distance from the lamp and light intensity are inversely proportional to each other- this means as the distance increases, the light intensity decreases. However, light intensity decreases in proportion to the square of the distance. This is the inverse square law.

  Equation: Light intensity is proportional to 1/d^2
• Temperature


  If temperature is the limiting factor its because its too low. The enzymes needed for photosynthesis work slower at lower temperatures. If a plant gets too hot the enzymes will denature. This happens at 45 degrees

  
• Carbon dioxide


  Increasing the CO2 concentration increases the rate of photosynthesis up to a point meaning it is limiting the rate of photosynthesis. After this the graph flattens out meaning CO2 is no longer the limiting factor.

  
• Photosynthesis equation


  Carbon Dioxide + Water >(light)> glucose + oxygen
• Investigating the effect of light intensity on photosynthesis

  1. Apparatus set up (gas syringe, conical flask with water and pondweed, light source, ruler)
  2. Sodium hydrogencarbonate is added to water to make sure plant has enough CO2
  3. A source of white light is placed at a specific distance from the pondweed, which is left to photosynthesise for a set amount of time.
  4. Oxygen released is collected in the gas syringe
  5. Repeat experiment with light source at different distances. The rate of oxygen production can then be calculated (volume/time)
• Investigating the effect of light intensity on photosynthesis

  Control variable- temperature, CO2 concentration, volume of water

  Independent variable- Distance of light source from pondweed

  Dependent variable- Rate of oxygen production by pondweed
• Root hair cell

  Label diagram:

  A) cell membrane

  B) cell wall

  C) root hair

  D) vacuole

  E) cytoplasm

  F) nucleus

  G) mitochondria

  H) ribosomes

  
• Root hair cell adaptations

  • Each branch of a root will be covered in millions of microscopic hairs
  • This gives the plant a large surface area for absorbing water and mineral ions from the soil
• Xylem and Phloem tubes

  Xylem tubes are used to take water and mineral ions from the roots to the stem and leaves.

  Phloem tubes are used to take food substances (mainly sucrose) made in the leaves the the rest of the plant for immediate use or storage.
• Xylem adaptations to use

  Xylem tubes are made of dead cells joined end to end with no end walls between them and a hole down the middle. Theyre strengthened with a material called lignin. This means they are able to carry water and mineral ions.
• Phloem adaptations 


  Phloem tubes have living cells with small pores in the end walls to allow food to flow through.
• Transpiration


  Transpiration is caused by evaporation and diffusion of water from a plants surface, mainly leaves. The loss of water creates a shortage of water in the leaves and so more water is drawn up from the rest of the plants by xylem vessels to replace it. This means more water is drawn in from the roots and so theres a constant transpiration stream of water through the plant. The stream carried mineral ions that are dissolved in the water.
• Stomata 


  Stomata are tiny pores on the surface of a plant. They allow CO2 and oxygen to diffuse directly in and out of a leaf. They are also allow water vapour to escape during transpiration. Stomata are surrounded by guard cells which change shape to control the size of the pore- when the guard cells are turgid (swollen with water) the stomata are open and when the guard cells are flaccid (low on water) the stomata are closed
• Transpiration and Stomata 


  Transpiration is a side effect of the way leaves are adapted for photosynthesis. They have stomata so that gases can be exchanged easily. Because theres more water inside the plant than in the air outside, the water escapes from the leaves through the stomata by diffusion.
• Turgid

  When guard cells are swollen with water
• Flaccid


  When guard cells are low on water and limp
• Stomata structure

  Label the diagram

  A) nucleus

  B) chloroplasts

  C) vacuole

  D) guard cell

  E) cell wall

  F) stoma

  
• Translocation

  Glucose produced by photosynthesis is turned into sucrose. The sucrose is transported around the plant in phloem vessels. It needs to be able to reach all cells in the plant so that the sucrose can be converted back into glucose for respiration. The movement of sucrose and other substances like amino acids is called translocation. This happens between where these substances are made and where they are used or stored: from sources in the root to sinks in the leaves in early spring time or from sources in the leaves to sinks in the root in the summer
• Environmental factors on water uptake- light intensity

  The brighter the light, the greater the transpiration rate . The stomata begin the close as it gets darker. Photosynthesis cant happen in the dark so they dont need to be open to let CO2 in.
• Environmental factors on water uptake- temperature

  The warmer it is, the faster transpiration is. When its warm the water particles have more energy to evaporate diffuse out of the stomata.
• Environmental factors on water uptake- air movement

  The better the air flow around a leaf (e.g strong wind) the greater the transpiration rate. If the air flow is poor, the water vapour just surrounds the leaf and doesnt move away. This means the water concentration is high so diffusion doesnt happen as quickly. If theres good air flow the water vapour is swept away maintaining a low concentration of water.
• Rate calculations for transpiration

  A potometer estimates transpiration rate. It measures water uptake by the plant but its assumed water uptake is related to transpiration.
• How to use a potometer

  1. Set up apparatus ( beaker of water, a capillary tube with a scale, a reservoir of water and a tap, and a plant)
  2. Record the starting position of the air bubble
  3. Start a stopwatch and record the distance moved by the bubble per unit time. Calculating the speed of air bubble movement gives an estimate of the transpiration rate.