nutrition and transport in plants

• photosynthesis is a process in green plants where light energy is absorbed by chlorophyll and transformed into chemical energy, used in the synthesis of carbohydrates from water and carbon dioxide.
• autotrophic describes organisms which can make complex nutritive compounds from simple inorganic substances by photosynthesis 
• chemical and word equation for photosynthesis:

  6CO2 + 6H20 —> C6H12O6 + 6O2

  carbon dioxide + water —light—> glucose + oxygen
• • photolysis is the use of light energy to split water into hydrogen and oxygen
  • when water molecules are split, 2H+, 2e-, and oxygen are formed during photosynthesis
• light dependent reactions require light, while the light independent reactions proceed in both light and darkness
• the molecular formula of glucose is C6H12O6. carbon and oxygen come from carbon dioxide obtained via leaves. hydrogen comes from water obtained via the roots. oxygen molecules released from photosynthesis comes from the photolysis of water during the light reaction
• • plants undergo both respiration and photosynthesis, respiration occurs 24/7, while photosynthesis only occurs in the presence of light.
  • compensation point is when the rate of photosynthesis and rate of respiration are the same 
  • respiration and photosynthesis are opposites, as shown from the reactions:
  • photosynthesis: 

          6CO2 + 6H20 —> C6H12O6 + 6O2

  • respiration:

          C6H12O6 + 6O2 —> 6CO2 + 6H20
• • the action spectrum of light is highest at blue and red light
  • plants can die due to overexposure to sunlight but not fluorescent light, as sunlight includes infra-red light which can cause overheating in plant cells, resulting in denaturing of enzymes. 
• role of chlorophyll

  • mesophyll cells are full of chloroplasts which contain chlorophyll 
  • chlorophyll is a green chemical substance which contains magnesium
  • the role of chlorophyll is to capture light energy and convert it into chemical energy
  • chlorophyll mostly absorbs red and blue wavelengths, while green wavelengths are reflected, making chlorophyll appear green
• intake of water into the plant

  • root hairs absorb water from the soil via osmosis
  • water travels from cell to cell by osmosis and from cell wall to cell wall by diffusion until it reaches the xylem
  • water is transported up the xylem by transpiration pull, capillary action, and root pressure
  • water moves into mesophyll cells in leaves in response to an osmotic gradient
• what is the path of intake of water into a plant?

  root hair > xylem > mesophyll cells
• intake of CO2 into the plant

  • carbon dioxide enters the leaf by diffusion through stomata into intercellular air spaces 
  • carbon dioxide dissolves into a thin film of moisture found on mesophyll cells
  • dissolved carbon dioxide diffuses from cell to cell until it reaches chloroplasts of mesophyll cells
  • availability of carbon dioxide often limits rate of photosynthesis 
• what is the path of intake of CO2 into plant?

  stoma > intercellular air spaces > mesophyll cells
• product of photosynthesis: glucose

  for regular use in cell:

  • broken down during respiration to produce energy for vital activities 
  • used in synthesis of cell wall (cellulose)
  • converted to amino acids and proteins 
  • converted into fats

  in excess:

  • converted to sucrose for translocation 
  • stored as starch in chloroplasts
  • stored as starch in cytoplasm of storage organs such as tubers
• glucose molecules are converted to sucrose which is a water soluble disaccharide which can be transported via phloem to other parts of the plant, and stored in the vacuole of plant cells. sucrose is less reactive than glucose and can be broken down into glucose for energy or built into starch for storage 
• glucose that is not required for respiration will diffuse into the cytoplasm from chloroplasts, causing cytoplasm to have high glucose concentration. this slows down enzyme activity, therefore excess glucose is converted into insoluble carbohydrates such as starch granules stored in chloroplasts or cytoplasm.
• oxygen produced and released during photosynthesis is considered a waste product, as oxygen is a metabolic waste product of photosynthesis. oxygen released can be measured to measure rate of photosynthesis by rate of oxygen production
• importance of photosynthesis

  • chemically converts carbon dioxide to carbohydrate for plants, which in turn are consumed by animals as part of the carbon cycle
  • replenishes oxygen in the atmosphere, which is required for aerobic respiration by all living organisms 
  • maintains carbon dioxide levels in the atmosphere (~0.04%) and reduces global warming
• what are other minerals that are important for plants?

  nitrogen for making protein and magnesium for making chlorophyll
• • magnesium ions are soluble in water and are absorbed through root hairs by diffusion and active transport
  • plants that lack nitrogen will have stunted growth (less leaves and shorter stem) and chlorosis (leaves lose chlorophyll)
  • plants that lack magnesium will have chlorosis and yellowing between veins of leaves
  • plants lacking phosphorus will have shorter and unhealthy roots
• excess glucose in the plant can be converted to protein in the presence of nitrogen. plants cannot obtain nitrogen from the air, instead nitrate ions are absorbed by root hairs via diffusion and active transport, and combine with glucose to produce amino acids
• autotrophic organisms can make ___?

  complex nutritive compounds from simple inorganic substances by photosynthesis