Nutrition and transportation in flowering plants

• External structure of a leaf:

  • Veins:

  * Veins allow the transport of water and dissolved mineral salts to the cells in the lamina

  * They transport manufactured food from the leaves to other parts of the plant

  • Lamina:

  * The lamina has a large surface area to maximize absorption of light energy

  * It allows for rapid diffusion of carbon dioxide molecules into the inner cells of the leaf

  • Petiole:

  * The petiole positions the lamina for maximum absorption of sunlight and gaseous exchange
• Upper epidermis:

  • Single layer of closely packed cells
  • Covered in a layer of waxy cuticle to prevent excessive water flow
  • Transparent to let light energy pass through
• Palisade mesophyll:

  • Long and cylindrical closely packed cells
  • Contains many chloroplasts for maximum absorption of light energy
• Spongy mesophyll:

  • Irregularly shaped with many large intercellular air spaces
  • Allows for rapid diffusion of gases
  • Contains fewer chloroplasts compared with palisade mesophyll
• Stoma:

  • Opening controlled by the guard cells
• Guard cells:

  • Control the opening and closing of the stoma
  • Contain some chloroplasts
• Vascular bundle:

  • Contains the xylem and the phloem
  • Xylem transports water, phloem transports food
  • Allows the transport of food, water, and minerals
• Lower epidermis:

  • Single layer of closely packed cells
  • Guard cells and stomata are found here
• Xylem transports water and minerals from the roots to other parts of the plant through long and narrow hollow tubes without cross walls or protoplasm, strengthened by lignin
• Phloem transports manufactured food bidirectionally from leaves to other plant parts, with sieve tube cells allowing rapid flow of substances and companion cells providing energy for sugar loading
• Root hair cells absorb water and mineral salts from the soil, utilizing a high surface area to volume ratio, many mitochondria for energy release, and pumping mineral salts into the roots against the concentration gradient
• Water entering plants involves pumping water and mineral ions into the roots, where the cell sap is more concentrated, leading to a net movement of water into the roots by osmosis until reaching the xylem
• Photosynthesis equation: Carbon dioxide + water (with light energy and chlorophyll) produces glucose and oxygen
• Glucose in the leaf is used for cellular respiration, stored as starch, converted into sucrose for transport, and reacts with nitrates and mineral salts to form amino acids or store fat
• Photosynthesis is crucial as most life depends on it, with plants as producers in food chains storing chemical energy and releasing oxygen while removing carbon dioxide
• Factors affecting photosynthesis include light intensity, temperature, and carbon dioxide concentration, with each being a limiting factor that affects the process
• Transpiration is the loss of water vapor from plant parts, mainly through stomata, driven by transpirational pull moving water up the xylem
• Transpiration rate is measured using a photometer, and factors like air movement, temperature, humidity, and light intensity affect the rate
• Wilting occurs when the rate of water loss exceeds absorption, leading to drooping leaves, reduced photosynthesis, closed stomata, and decreased carbon dioxide intake
• Factors affecting transpiration rate:

  • Air movement/wind:

  * Transpiration rate increases when wind increases

  * Wind blows away the water vapor around the leaf, maintaining a steeper concentration gradient for diffusion of water vapor out of the leaf through the stomata

  • Temperature:

  * Transpiration rate increases when temperature increases

  * Rate of evaporation increases of the water of thin moisture around the mesophyll

  • Humidity:

  * Transpiration rate increases when humidity decreases

  * Lower concentration of water vapor around the leaf maintains a steeper concentration gradient for diffusion of water vapor out of the leaf through the stomata

  • Light intensity:

  * Transpiration rate increases when light intensity increases

  * Stomata open during the day when light intensity is higher and close at night when light intensity is lower
• Process of water movement in the leaf:

  • Water moves out of the mesophyll by osmosis to form a thin film of moisture around the cell
  • Water from the thin film of moisture evaporates to form water vapor in the intercellular air spaces
  • Concentration of water vapor in the intercellular air spaces is higher than the surrounding
  • Net movement of water vapor molecules out of the leaf through the stomata by diffusion (transpiration)
  • Movement of water out of the leaf to replace the film of moisture that has evaporated
  • Mesophyll cells absorb water by osmosis
  • Cells absorb water from the xylem vessels in the leaf
  • Transpirational pull
• Limiting factor: a factor that affects a process
• Light intensity:

  • As light intensity increases, the rate of photosynthesis increases until a certain light intensity
• Temperature:

  • As temperature increases, the rate of photosynthesis increases until a certain temperature
  • Graph shows rate of photosynthesis is highest at optimal temperature
• Carbon dioxide concentration:

  • As carbon dioxide concentration increases, the rate of photosynthesis increases
• During the day when there is light, carbon dioxide reaches the mesophyll and is used rapidly during photosynthesis
• Carbon dioxide concentration is lower in the intercellular air spaces in the spongy mesophyll than in the atmosphere
• The net movement of carbon dioxide into the leaf occurs by diffusion through the stomata
• Carbon dioxide dissolves into the film of water around the mesophyll cells and further dissolves into the cells
• Process of water entering plants:

  • Water and mineral ions from the soil are pumped into the roots and transported to the xylem
  • Cell sap in the roots is more concentrated, so the cell has a lower water potential than the soil
  • There is a net movement of water into the roots by osmosis
  • Entry of water dilutes the root hair cell sap
  • Root hair cell has a higher concentration than the next cell
  • Water can pass by osmosis
  • This process continues until the xylem
• Characteristics of a root hair cell:

  • Absorbs water and dissolved mineral salts from the soil
  • Long and narrow extension
  • Increases surface area to volume ratio, enhancing absorption of water and mineral salts
  • Contains many mitochondria for energy release during respiration
  • Functions to pump mineral salts into the roots against the concentration gradient
• Characteristics of phloem:

  • Sieve tube cells
  • Very little protoplasm
  • Arranged to form a continuous column
  • Pores in the sieve cells allow for rapid flows of manufactured food substances
  • Companion cells have many mitochondria to release energy for loading of sugars
  • Each sieve tube has a companion cell to ensure survival
• External structure of a leaf:

  • Veins:
  • Veins allow the transport of water and dissolved mineral salts to the cells in the lamina
  • Veins transport manufactured food from the leaves to other parts of the plants
• Lamina:

  • Has a large surface area to maximize absorption of light energy
  • Allows for rapid diffusion of carbon dioxide molecules into the inner cells of the leaf
• Petiole:

  • Positions the lamina for maximum absorption of sunlight and gaseous exchange
• Xylem:

  • Transports water and minerals from the roots to the other parts of the plant
  • Structure: long and narrow hollow tube
  • Characteristics: does not have a cross wall or protoplasm
  • Contains lignin which strengthens the xylem walls
• Process of water entering plants:

  • Water and mineral ions from the soil are pumped into the roots and transported to the xylem
  • Cell sap in the roots is more concentrated, with a lower water potential than the soil
  • Net movement of water into the roots occurs by osmosis
  • Entry of water dilutes the root hair cell sap
  • Root hair cell has a higher concentration than the next cell
  • Water can pass by osmosis
  • This process continues until the xylem
• Process of water movement in the leaf:

  • Water moves out of the mesophyll by osmosis to form a thin film of moisture around the cell
  • Water from the thin film of moisture evaporates to form water vapor in the intercellular air spaces
  • The concentration of water vapor in the intercellular air spaces is higher than the surrounding
  • There is a net movement of water vapor molecules out of the leaf through the stomata by diffusion (transpiration)
  • Water moves out of the leaf to replace the film of moisture that has evaporated
  • Mesophyll cells absorb water by osmosis
  • Cells absorb water from the xylem vessels in the leaf
  • This process is driven by transpirational pull