cone

Examples of cone in the following topics:

• Characteristics of Gymnosperms

  • Gymnosperms are seed plants that have evolved cones to carry their reproductive structures.
  • One type of cone is the small pollen cone, which produces microspores that subsequently develop into pollen grains .
  • The other type of cones, the larger "ovulate" cones, make megaspores that develop into female gametophytes called ovules .
  • This is the cone that produces pollen.
  • This is the cone that produces ovules.

• Transduction of Light

  • Some cones are maximally responsive to short light waves of 420 nm; they are called S cones ("S" for "short").
  • Other cones (M cones, for "medium") respond maximally to waves of 530 nm.
  • A third group (L cones, or "long" cones) responds maximally to light of longer wavelengths at 560 nm.
  • With only one type of cone, color vision would not be possible; a two-cone (dichromatic) system has limitations.
  • In the absence of light, the bipolar neurons that connect rods and cones to ganglion cells are continuously and actively inhibited by the rods and cones.

• Life Cycle of a Conifer

  • Pine trees are conifers (cone bearing) and carry both male and female sporophylls on the same mature sporophyte.
  • In the male cones (staminate cones), the microsporocytes give rise to pollen grains by meiosis.
  • Some gametophytes will land on a female cone.
  • Female cones (ovulate cones) contain two ovules per scale.
  • Pollen from male cones moves up into upper branches where it fertilizes female cones.

• Sexual Reproduction in Gymnosperms

  • The female cones are larger than the male cones and are positioned towards the top of the tree; the small, male cones are located in the lower region of the tree.
  • Upon maturity, the male gametophyte (pollen) is released from the male cones and is carried by the wind to land on female cones.
  • The scales of the cones are closed during development of the seed.
  • Pollen from male cones blows up into upper branches, where it fertilizes female cones.
  • Examples are shown for female and male cones.

• Anatomy of the Eye

  • There are two types of photoreceptors in the retina: rods and cones.
  • The fovea has a high density of cones.
  • In humans, cones far outnumber rods in the fovea.
  • Rods and cones are photoreceptors in the retina.
  • Cones respond in intense light and are responsible for color vision.

• Inorganic Nutrients and Other Factors

  • For example, the jack pine, a coniferous tree, requires heat from fire for its seed cones to open .
  • The mature cones of the jack pine (Pinus banksiana) open only when exposed to high temperatures, such as during a forest fire.

• Diversity of Gymnosperms

  • Gymnosperms are a diverse group of plants the protect their seeds with cones and do not produce flowers or fruits.
  • Cycads bear large cones and may be pollinated by beetles rather than wind, which is unusual for a gymnosperm ().
  • This Encephalartos ferox cycad has large cones and broad, fern-like leaves.

• Pollination and Fertilization

  • In gymnosperms, pollination involves pollen transfer from the male cone to the female cone.

• The First Law of Thermodynamics

  • Humans can convert the chemical energy in food, like this ice cream cone, into kinetic energy by riding a bicycle.

• Boreal Forests and Arctic Tundra

  • The long and cold winters in the boreal forest have led to the predominance of cold-tolerant, cone-bearing plants.