Plant nutrition and transport

• Parts of a typical leaf

  • Waxy cuticle
  • Upper epidermis
  • Palisade mesophyll layer
  • Spongy mesophyll layer
  • Lower epidermis
  • Stomata
  • Guard cells
• Photosynthesis

  1. Takes place in the leaves

  2. Takes place in chloroplasts

  3. Chlorophyll absorbs light energy

  4. Converts carbon dioxide and water into glucose and oxygen
• Photosynthesis is an endothermic reaction, where energy is transferred from the environment to chloroplasts by light
• Carbon dioxide and water supply for photosynthesis

  1. Carbon dioxide diffuses into leaves through stomata

  2. Water is taken up from soil by roots and transported to leaves via xylem
• Glucose


  The main product plants want from photosynthesis
• Uses of glucose by plants

  • Cellular respiration
  • Making cellulose
  • Making starch
  • Making amino acids
  • Making oils and fats
• Plant growth rate often depends on the rate of photosynthesis
• Factors affecting the rate of photosynthesis are light intensity, temperature, carbon dioxide concentration, and the amount of chlorophyll
• Factors affecting photosynthesis

  • Light intensity
  • Temperature
  • Concentration of carbon dioxide in the air
  • Amount of chlorophyll in plants
• Chlorophyll

  Pigment within chloroplasts that absorbs the light energy needed for photosynthesis
• Plants have less chlorophyll

  They won't be able to carry out as much photosynthesis
• Different plants naturally have different amounts of chlorophyll
• The level of chlorophyll within an individual plant can vary due to disease, environmental stress, or lack of nutrients like water
• Factors normally referred to as limiting factors for photosynthesis are light, carbon dioxide, and temperature
• Graphing factors affecting photosynthesis

  1. Plot light intensity on x-axis, rate of photosynthesis on y-axis

  2. As light intensity increases, rate of photosynthesis increases up to a point where it plateaus

  3. This plateau means another factor is limiting, such as carbon dioxide or temperature
• Graphing carbon dioxide effect on photosynthesis

  Rate of photosynthesis increases with carbon dioxide concentration up to a plateau
• Graphing temperature effect on photosynthesis

  Rate increases initially as enzymes work faster, then decreases as enzymes denature at higher temperatures
• Graphs can show multiple limiting factors by comparing curves at different conditions
• Farmers can artificially create conditions for high photosynthesis rates, e.g. using greenhouses, artificial lighting, carbon dioxide injection, and fertilizers
• Providing optimal conditions for photosynthesis can be costly for farmers, so they have to weigh the extra costs against the expected yield increase
• Active transport

  The movement of molecules across a cell membrane from a region of lower concentration to a region of higher concentration, requiring energy from cellular respiration
• Active transport

  • Occurs across a membrane
  • Requires special proteins in the membrane to transfer molecules
• Cellular respiration

  Provides the energy for active transport
• ATP

  Molecules that store the energy from cellular respiration and transport it to different parts of the cell
• Root hair cells

  • Have a large surface area for absorption
  • Have many mitochondria to provide energy for active transport
• Active transport in root hair cells

  1. Absorb water and mineral ions from the soil

  2. Against their concentration gradient

  3. Using energy from cellular respiration
• Root hair cells need to absorb minerals like magnesium and nitrates at a higher concentration inside the cell than outside in the soil
• Transpiration


  The process of water constantly evaporating from the surfaces of leaves
• Transpiration process

  1. Water evaporates from cells inside the leaf

  2. Water vapor diffuses through air spaces in spongy mesophyll

  3. Water vapor exits the leaf through stomata

  4. Water passes from xylem into leaf to replace lost water

  5. Water drawn into root hair cells and up xylem vessels to leaf
• Importance of transpiration

  • Brings water to the leaf for photosynthesis
  • Transports dissolved mineral ions
  • Cools the leaf down in warm weather
• Factors affecting rate of transpiration

  • Higher temperatures
  • Drier conditions (low humidity)
  • Windy conditions
  • Higher light intensity
• Stomata opening and closing

  1. Guard cells swell and change shape in high light, causing stomata to open

  2. Plant closes stomata in hot conditions to reduce water loss
• Closed stomata means the plant cannot photosynthesize
• Multicellular Organisms Need Transport Systems
• The cells in all living organisms need a variety of substances to live. Plant cells need things like water, minerals and sugars. They also need to get rid of waste substances.
• In unicellular organisms, these substances can diffuse directly into and out of the cell across the cell membrane. The diffusion rate is quick because of the short distances substances have to travel.
• In multicellular organisms (like animals and plants) direct diffusion from the outer surface would be too slow - that's because substances would have to travel large distances to reach every single cell.
• So multicellular organisms need transport systems to move substances to and from individual cells quickly.
• Plants Have Two Main Transport Systems

  Water and Xylem tubes transport water and minerals

  Phloem tubes transport food
• Xylem tubes

  Carry water and mineral salts from the roots up the shoot to the leaves in the transpiration stream