chap 10 nutrition and transport in flowering plants

• where can the chloroplasts mostly be found ?

  most found in palisade mesophyll and spongy mesophyll, with there being more chloroplast in the palisade mesophyll
• what are the external features of a leaf ?

  network of veins, leaf blade, leaf arrangement and leaf stalk
• function of the network of veins

  veins carry water and mineral salts to the cells in the leaf blade, and carry manufactured food such as sucrose from these cells to other parts
• function of leaf arrangement

  • organised in a regular pattern around stem
  • leaves grow in pairs or singly in alternate arrangement

  this ensures the leaves are not blocking one another from light and so each leaf receives sufficient light
• function of leaf blade

  has a large flat surface relative to volume so obtain maximum amount of light for photosynthesis

  large, thin leaf blade so CO2 can reach the inner cells of leaf at higher rate
• function of leaf stalk

  it holds the leaf blade away from the stem so leaf blade can obtain sufficient light and air
• what adaptation does a plant without a leaf stalk have ?

  long leaf blades like in grasses and maize
• the upper epidermis is covered on the outside by a waxy transparent cuticles to reduce water loss through evaporation of the leaf and is transparent to allow light to enter to the leaf
• palisade mesophyll has layers of closely packed, long and cylindrical cells to maximise light absorption for photosynthesis
• palisade mesophyll contains numerous chloroplasts for maximum light absorption for photosynthesis
• spongy mesophyll has an irregular shape
• spongy mesophyll has numerous large intercellular air spaces among the cells
• spongy mesophyll cells are loosely packed
• spongy mesophyll contains chloroplasts to carry out photosynthesis but has less than that of palisade mesophyll
• spongy mesophyll are covered with a thin film of moisture for diffusion of gases
• upper palisade mesophyll cells contain more chloroplast so more light can be absorbed near the upper leaf surface
• With presence of light, photosynthesis occurs, rapidly using up the carbon dioxide in the leaf. This causes the carbon dioxide concentration in the leaf to decrease and be lower than that in the atmospheric air. Hence, a diffusion gradient is formed. This causes CO2 to diffuse from a region of higher concentration, in the atmosphere, through the stomata to a region of lower concentration, the intercellular air spaces in the leaf
• The surface of the mesophyll cells are always covered by a thin film of water so CO2 can dissolve in it, which then diffuses into the cells
• how is xylem adapted for its function ?

  hollow tube made up of dead cells, reducing resistance to water flowing through the xylem

  its walls are lined with a tough substance called lignin which provides mechanical support and prevents the xylem vessels from collapsing
• phloem is made up of 2 types of cells : sieve tube elements and companion cells
• sieve tube elements contain cytoplasm but not other organelles like nucleus and vacuole, hence allowing sucrose to pass through the cells easily
• each sieve tube element has a companion cell connected to it that carries out metabolic processes to provide nutrients to keep the sieve tube element alive and help it transport manufactured food
• movement of substances in xylem is only upwards from the roots to the leaves while the movement in phloem is bidirectional, allowing sucrose to be transported up or down the phloem
• each sieve tube element is a narrow thin- walled cell with many mitochondria, cytoplasm and a nucleus, where the mitochondria provide energy needed for the companion cells to load sugar from the mesophyll cells into the sieve tubes via active transport
• vascular bundles in stems are arranged so that xylem is located closer inside which the phloem lies outside it with the cambium between them
• what is a waxy, waterproof cuticle for ?

  reduce evaporation of water from that area
• where is this vascular bundle in ?

  stem

  
• where is this vascular bundle in ?

  leaves

  
• vascular bundles is leaves are arranged such that the xylem is closer to the upper surface of the leaf and phloem closer to the lower surface of the leaf
• the epidermis of the root is the outermost layer of the cells in which it bears root hairs
• each root hair has a long and narrow protrusion which increases surface area to volume ratio of the root hair cell, increasing the rate of absorption of water and mineral salts
• where is this vascular bundle in ?

  roots

  
• what is the chemical equation of photosynthesis ?

  6CO2 + 6H2O -light + chlorophyll-> C6H12O6 + 6O2
• glucose is formed more quickly than it is used up, the excess glucose is converted to starch for storage
• when there is a plastic bag around a plant during an experiment, it is to ensure that no CO2 is produced due to the microorganisms like bacteria which may respirate to produce CO2, being present in the soil

  it is to also ensure that no water can be evaporated from the soil which can affect the mass of the plant
• photosynthesis is the process by which plants synthesise carbohydrates (eg. glucose) from water and carbon dioxide where oxygen will be released during the process
• during photosynthesis, chlorophyll absorbs energy from light and transfers it to chemical stores of energy (eg. glucose) which are synthesised from water and carbon dioxide, with oxygen being released as a by-product
• rate of photosynthesis can be affected by light intensity, concentration of carbon dioxide and temperature
• glucose can be used immediately, converted to starch, converted to sucrose, converted to amino acids or form fats
• the glucose that is used immediately is for cellular respiration to provide energy for cellular activities or form cellulose cell walls