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10.4. Spermatophytes

Division Spermatophyta

Spermatophytes are flowering plants , they produce pollen and seeds.

Spermatophytes are cormophytes, more evolved than pteridophytes, with well- developed rootstem, and leaves. Remember that pteridophytes are also cormophytes but without flowers or seeds.

The flower is the part of the plant responsible for reproduction. They produce gametes that are no longer dependent on water for fertilization to occur. Therefore, the flower is the organ that allowed the sexual reproduction of plants without the male gametes needing water to move to the female gamete, as happens in bryophytes (mosses) and pteridophytes (ferns), since the male gametes move , within pollen grains, through air.

The flower produces the male and female gametophytes :

  • Ovum. It contains the female gametophyte, which it protects and keeps moist.
  • Pollen grain. It contains the male gametophyte and protects it from desiccation.

Flowers and seeds protect the embryo from desiccation, which has allowed spermatophytes to colonize all ecosystems and to be the dominant plants.

Structure of the spermatophytes

Pteridophytes and spermatophytes have  conductive tissues , but spermatophytes have flowers. Cormophytes ( pteridophytes and spermatophytes) are characterized by having three organs:

Root

The root is an organ of the plant, generally underground, whose two main functions are:

  • Fix the plant to the ground.

  • Absorb water and mineral salts from the soil ( crude sap ) through their absorbent hairs.

  • Accumulate reserve substances, such as carrots.

There is usually a main root that grows into the earth, from which other secondary roots arise. Many absorbent hairs emerge from the roots , which are responsible for absorbing water and mineral salts.

The root cells do not carry out photosynthesis since they do not receive sunlight and do not have chlorophyll.

Roots can be of various types:

  • Axonomorphic or pivoting: several secondary roots emerge from the main root, which is thicker.

  • Fasciculated: the main root cannot be distinguished from the secondary ones, they all have a similar thickness.

  • Napiform: the root thickens by accumulating reserve substances, such as carrots, radishes or turnips.

  • Adventitious or aerial: they do not come from the embryo of the plant, but from another place, such as in the nodes of the stems. This type of root is used by some plants for climbing (such as ivy) or for spreading along the ground.

Algunos tipos de raíces son: axonomorfa o pivotante, fasciculada, napiforme, adventicias o aéreas

Interactive Activity: Root Types.

Stem

  • The stem is the axis of the aerial part of cormophytes.
  • It supports the leaves , the flowers and the fruits.
  • It contains in its interior the conductive vessels through which water and mineral salts (crude sap) are transported from the root to the leaves (through the xylem), and the organic matter (processed sap) produced in the leaves by photosynthesis from the leaves to the rest of the plant (through the phloem).
  • Stems grow by multiplying the cells that form their buds. The buds can be:
    • Terminal or apical buds: at the ends of the stems. They are responsible for the growth in length of the stems.
    • Axillary or lateral buds. They are responsible for the appearance of branches and leaves on the stems.
  • The stem has knots, thickenings where the axillary buds are found, from which the branches come out, and internodes, spaces without branches.
Tallo de una cormofita /gramínea)By Kelvinsong [CC BY-SA 3.0 ], from Wikimedia Commons
  • The types of stems can be classified according to several criteria:
    • According to its duration in time: annual or perennial.
    • According to his habit:
      • Epigeal or aerial. They grow above the ground.
      • Hypogea or underground. They grow below ground. For example, tubers , bulbs, rhizomes and corms.
      • Aquatics. They grow underwater.


 

  • According to its consistency:
    • Herbaceous: soft and green stems, such as scape, cane, calamus, climbers, etc.
    • Woody: rigid and hard stems, such as bushy, arboreal, stipe or stipe (palm trees).
    • Meaty or succulent.
Interactive Activity: Parts of a Stem.
Interactive activity: Recognize the different types of stems.

Leaves

The leaves are green organs, generally flattened, that come out of the stem and that perform basic functions for plants:

  • They carry out photosynthesis, transforming inorganic matter (CO2, water and mineral salts) into organic matter (carbohydrateslipidsproteins) using the sun's energy.
  • They perform evapotranspiration, removing water vapor through their stomata.
  • They perform gas exchange: they capture oxygen for respiration and COfor photosynthesis and expel gaseous waste substances.
  • The leaves can also be transformed to perform other functions, such as:
    • Some transform into scales to protect the buds.
    • Some become spines to protect themselves from desiccation and herbivores.
    • Some transform into fleshy leaves to store water.

Leaves have three parts:

  • Blade: is the flat part of the leaf. It is green in color because of the chlorophyll of the chloroplasts, the cellular organelles responsible for carrying out photosynthesis. In the limbus the conductive vessels (nerves) can be distinguished. The upper part of the limb is called the upper part, and the lower part, the lower part It contains the stomata, which carry out gas exchange .
  • Petiole: it is the corner that joins the blade with the stem.
  • Sheath: it is the widest part of the petiole, with which it joins the stem.

Partes de la hoja


The leaves can have very varied shapes , which can be classified according to different criteria:

  • Depending on the number of limbs: they can be simple (only one) or compound (several).
  • Depending on the shape of the blade: heart-shaped, rounded, acicular, etc.
  • Depending on the edge of the blade: serrated, toothed, whole, etc.
  • According to the arrangement of the nerves: uninervias, parallelinervias, palmatinervias, etc.
  • According to their arrangement along the stem: alternate, opposite.
  • Depending on whether or not it has a petiole: petiolate and seated.

Clasificación de los distintos tipos de hojas

Mushii [CC BY-SA 3.0], via Wikimedia Commons

Interactive Activity: Parts of a Leaf.

Interactive activity: Classify the leaves.

Classification of spermatophytes

Spermatophytes (seed plants) are classified into two groups:
  • Gymnosperms. They are the oldest. They are plants that produce seeds but are not contained within a fruit. Their ovules are naked , without an ovary, so after fertilization only the seed is produced and the fruit does not appear. For example, the pine.
  • Angiosperms. Its flower has an ovary that contains ovules that are fertilized with the arrival of the pollen grain. A seed is formed enclosed within that ovary which later develops into a fruit. For example, the almond tree.
    • Monocots (with a single leaf when the seed germinates).
    • Dicots (with two leaves when the seed germinates).

Interactive activity: Difference between a gymnosperm and an angiosperm.