structure of flowering plant

• ➢ Dermal Tissue forms and protects the surfaces of the

  plant, e.g. epidermis of the leaf is a cuticle, which is a

  layer of waxes that coat the outermost cell wall,

  reducing the loss of water and providing a barrier to

  attacks by germs or insects.

  ➢ A leaf’s veins are vascular tissue—xylem transports

  water and phloem carries sugars.

  ➢ Ground Tissue is photosynthetic, with large air spaces

  between the cells, to allow rapid diffusion of gases
• the dermal layer is the outer layer, is for protection and reduces water loss
• ground tissue is the bulk of the plant and is for storage and support
• the vascular tissue is divided into two parts: the xylem and the phloem

  the xylem transports H2O and the phloem transports sugars
• adaptations of the leaf:

  • network of veins
  • lots of chlorophyll
  • large surface area
  • thin surface
• low CO2 in guard cells makes potassium ions (K+) move into the guard cells

  water then moves into the guard cells by osmosis

  guard cells expand and stoma open
• stomata are found on the underside of the leaf to avoid excess water loss from the sun
• there is a thick cuticle (wax feel) on the leaf to decrease transpiration
• • high CO2 in guard cells means potassium ions move out of the cells
  • water moves out of the cells by osmosis
  • guard cells shrink and stoma close
• • plants photosynthesise when it’s light using CO2 and produces O2 during the day
  • plants respire continuously using O2, producing CO2, all the time
• transpiration

  the evaporation of water from leaves (and stems)
• • over 90% of the water that enters a leaf goes right through it and evaporates into the air
• how to reduce transpiration:

  • waxy cuticle
  • closing stomata

  lots of water = turgid plant cells

  water loss = plasmolysis
• transpiration rates are determined by:

  1. temperature (high temperature higher rates)
  2. humidity (higher humidity lower rate)
  3. wind (high wind higher rate)
• transpiration stream is the movement of water from the roots to the stem to the leaf
• lenticel

  small opening in bark of woody plants where gas exchange occurs
• cotyledon:

  an embryonic seed leaf
• monocot example: daffodil

  dicot example : rose
• monocot:

  seed - one cotyledon

  root - fibrous root

  vascular - scattered

  leaf - parallel veins

  flower - multiples of three petals
• dicot:

  seed - two cotyledon

  root - tap roots

  vascular - ringed

  leaf - net like veins

  flower - 4 or 5 multiples
• water uptake in roots:

  • water enters the root hair cells by osmosis when the concentration of solutes inside the plant is greater than the concentration of the soil
  • root hair cells are adapted to this by:

  thin walls

  large surface area
• Root Types:

  • Tap roots - one main long root that comes from the radicle of the seed, usually have root hairs, common in dicots
  • fibrous roots - formed when radicle dies and leaves equal sized roots coming out of stem, common in monocots
  • Adventitious - don’t grow from the radicle and found in strange places , ex. ivy
• functions of the root:

  • anchor plant in soil
  • absorb H2O + minerals
  • transport absorbed substances to shoots
  • some roots store food e.g carrots, turnip, radishes
• Zones of the root: DEMP

  • Differentiation - unspecified cells become specialised into tissues, water absorbed through root hairs
  • Elongation - area of root affected by growth regulated cells increase in size
  • Meristematic - rapid division of cells by mitosis create new root tissue
  • Protection - consists of root cap allowing the root to push its way through the ground
• meristematic tissue

  area of rapid mitosis leading to growth

  • found in shoot + root these are called apical meristems
  • lateral meristems found at the side of the plant and make it thicker
• stems

  • the tip of the stem has a terminal or apical bud - causes the stem to keep growing at the tip - upwards
  • lateral buds or auxiliary buds are located along the side of the stem - grow sidewards branches
  • lenticels are found on stems and are openings for gas exchange
• functions of the stem:

  • support
  • transport water and minerals
  • photosynthesis
  • storage (food)
• differences between the stem and the root:

  • no root hair in the stem
  • xylem shaped like an x in the root
• function of xylem: transports water and mineral ions from the roots to the leaves
• function of phloem: transports sugars and amino acids from the leaves to the rest of the plant, transports food
• xylem tracheid structure:

  • long cells tapered at both ends
  • pits in the walls - allow water and minerals to move sideways from cell to cell
  • walls thickened with lignin for support
• xylem vessels structure:

  • elongated cells
  • spiral lignin for strength
  • no end walls - form a continuous tube like a straw
  • pits to allow sideways movement of water
• xylem vessels on maturity are dead, hollow and contain no cytoplasm which makes them strong
• phloem structure:

  1. sieve tube cells: mature cells have no nucleus, have sieve plates, cytoplasm extends from cell to cell through the sieve plate
• phloem structure:

  2. companion cells

  • nucleus controls activities of both companion and sieve tube cells
• water uptake by roots:

  • root hairs absorb water by osmosis. water passes from the epidermis across the ground tissue to the xylem where it rises due to transpiration
• transport of water is caused by root pressure and transpiration
• root pressure

  forced upward movement of water and mineral salts from the root up through the stem
• transpiration

  the loss of water vapour from a plant, mainly through the stomata of the leaves.
• cohesion tension model was made by who

  Dixon and Joly, Dublin 1895