structure of plants ch23

• 3 types of roots

  tap

  fibrous

  adventitious
• tap (primary roots)

  one main root

  develop from radicle

  lateral roots grow out of main root

  root hairs incr surface area

  e.g. dandelion
• fibrous root

  many similar sized roots

  common in monocots e.g. grass
• adventitious roots

  roots don't develop from radicle

  e.g. ivy root
• functions of roots

  anchor plant in the ground

  absorb water and minerals from soil

  transport absorbed materials

  store food
• zones

  zone of protection

  meristematic zone

  zone of elongation

  zone of differentiation
• zone of protection

  root cap protect cells as root moves through soil
• meristematic zone


  rapid cell division by mitosis
• zone of elongation

  auxins (growth regulators) stimulate the cells to grow in size
• zone of differentiation

  cells develop into dermal vascular and ground tissues
• herbaceous plants - the stem is soft and green
• woody plants - stem is hard brown and woody
• stems

  node - where the leaf attaches

  internode - between two nodes

  apical bud - growing point at the tip of a shoot

  lateral bud -sideways growth of the plant

  axil - angle between leaf and stem
• stem in winter

  leaf scar - where a leaf fell from the stem

  scale scar - where the previous apical bud was located

  lenticles - pores for gas exchange
• functions of stems

  supports aerial parts of plant

  transports water & food

  photosynthesis

  store food
• leaves structure

  petiole -stalk of the leaf

  midrib -central vein in a leaf

  veins -branch off the midrib
• leaves venation

  parallel (monocots)

  net (dicots)
• functions of leaves

  make food

  gas exchange

  transpiration

  store food
• dermal tissue


  protects plant (epidermis)

  root hairs are extensions of dermal tissue in roots to help absorb water and minerals

  epidermis coated in a waxy layer to prevent transpiration
• ground tissue


  make up space between dermal & vascular tissue

  function = photosynthesis, storage of food, strength and support to the plant
• vascular tissue

  xylem & phloem
• xylem


  carries water and minerals

  non living

  has lignin

  no companion cells
• xylem vessels


  tubular

  transport water and minerals from roots to leaves

  contains lignin that reinforces xylem giving support

  join end to end
• xylem tracheids


  long and tapered

  primitive tissue
• phloem


  carries food

  living

  has no lignin

  has companion cells
• sieve tubes


  walls are porous

  each sieve tube has a companion cell
• companion cell


  contains a nucleus which controls the activities of the sieve tube
• function of phloem

  transports food
• tissue location in roots

  vascular tissue in the centre of root

  xylem makes an X shape phloem fills the corners
• tissue location in stems

  in a dicot stem vascular bundles are ring shaped

  xylem towards the centre

  phloem towards the outside

  in monocot stem Vascular bundles are scattered all around
• cotyledon is a seed leaf
• monocots


  one cotyledon

  mostly herbaceous

  leaves have parallel veins

  vascular bundles are scattered

  flower parts are arranged in 3's

  e.g. grass
• dicots


  two cotyledons

  may be herbaceous

  flower parts arranged in multiples of 5 or 4

  net venation

  vascular bundles in ring