Parts of a Seed

1
Parts of a Seed

• Mature embryo was formed by mitosis root tip,
  shoot tip, cotyledon(s)
• Seed coat formed from maternal flower tissue,
  encloses embryo and endosperm to protect seed.
• Endosperm surround embryo and provides
  nourishment
• Cotyledon not true leaves (also called seed
  leaves) but may be capable of photosynthesis.
  Two major groups of plants monocots and dicots

2
Seed Germination

• Germination - the sprouting of seeds when
  conditions are favorable
• Seed increases metabolic rate, water absorbed
  restores turgor pressure
• Seed coat fractures and embryo emerges
• Many seeds have interesting adaptations. What
  examples did you read about?

3
Plant Structure

• Shoot tip - location of apical meristem
• Root tip- location of apical meristem
• Node - point where leave attach
• Internode- space between nodes

4
Plant Meristems

• Apical meristems - in herbaceous in woody plants
• Responsible for primary growth, growth in length
  of roots and shoots
• Lateral meristems - in woody plants
• Responsible for secondary growth increasing the
  width (girth) of a plant in regions of plant
  where primary growth has stopped
• Contains two layers- the vascular cambium and
  cork cambium

5
Primary Growth in Roots

• What is happening at each root zone?
• As the apical meristem divides, some daughter
  cells remain part of the meristem. Some daughter
  cells specialize into other tissues
• The location of the cells often determines how
  they will specialize because plant cells are
  locked in position by cell walls (cells on the
  outside become dermal tissue etc.)
• Primary growth in roots produces new dermal,
  ground and vascular tissue.

6
Primary Growth in Shoots

• Apical meristem located at tip of terminal bud
• Axillary buds develop from meristem tissue left
  by apical meristem
• Elongation of shoot caused by elongation of cells
  of slightly older internodes

7
Secondary growth

• Occurs in the lateral meristems of woody plants
• The lateral meristem includes two layers of cells
  that form two columns around the plant. The
  vascular cambium and the cork cambium

8
Vascular Cambium

• The vascular cambium produces secondary layers of
  xylem and phloem (recall that primary growth made
  the primary xylem and phloem)
• As the lateral meristem divides, some daughter
  cells remain part of the meristem. Some daughter
  cells specialize into secondary xylem and
  secondary phloem
• Xylem cells are made inside the vascular cambium
  and phloem cells are found outside

9
Vascular Cambium

• The secondary xylem is concentrated in the center
  of the plant in multiple layer
• The old secondary phloem layers are incorporated
  into the cork cambium as the tree increases in
  width

10
Secondary Growth

• Cork Cambium - produces cork cells on the outside
  of the cambium
• As these cells mature they produce suberin and
  water proof layer that protects the plant
• Layers of cork are sloughed off as the tree grows
  in girth