What are PlantsAlternation of Generations
Plant Adaptations to Land
Special Adaptations of Angiosperms
Morphology of a Typical Angiosperm
Plants are multicellular photosynthetic organisms that are believed to have evolved from green algae. Both groups have chlorophylls a and b and betacarotene as their photosynthetic pigments, both store reserve food as starch, and both have cellulose containing cell walls.
Distinguishing Features of all plants
The plant life cycle is sporic. This involves an alternation between a multicellular diploid sporophyte which, through meiosis produces haploid spores which in turn undergo mitosis to form a multicellular gametophyte which makes, what else, gametes.
The multicellular diploid embryo is housed within a multicellular gametophyte (in algae the embryo is separate from the haploid tissue).
Plants are divided into two major groups based on the presence (in vascular plants) or absence (in nonvascular plants) of an internal vascular system for transporting water and dissolved particles.
The nonvascular plants -- bryophytes -- require a constantly moist environment. They include:
Vascular plants or tracheophytes include:seedless vascular plants such as -
seed- bearing forms. The success of seed plants (gynmosperms and angiosperms may be attributed to:
- development of an extensive root system
- an efficient vascular system (xylem and phloem)
- reproductive structure in which the gametophyte is protected inside sporophyte tissue (the seed)
The seed plants include:
- naked-seed plants (such as conifers), known as gymnosperms and
- flowering plants, the angiosperms.
flowering plants may be divided into the
- monocots (parallel veins in blade-like leaves and flower parts in multiples of 3)
- dicots (cotyledon divided into two parts, flower parts in multiples of 4 or 5)
Some of the adaptations of plants to a terrestrial existence include a waxy cuticle, surface pores (stomata) that enable gas exchange, protected reproductive structures, and the retention of the embryonic sporophyte within the female gametophyte. Review the table below for more adaptations for life on dry land.
Roots Leaves and Stems Adaptations to Dryness Seeds Pollen Dominance of Sporophyte
Minerals in the soil and
Light and CO2 in the
prevents vertical growth
reinforces cellulose. This
skeletal support allows turgor pressure to increase to
help maintain rigidity.
requires mechanism to prevent
water loss and conduction of water more
allows plants to grow taller in
order to reach light. The vascular system is made of
microscopic pipes, the xylem and phloem. Xylem is
lignified adding to the other supporting tissues.
help disperse plants and are
able to survive the harshest conditions. Some can survive
for years waiting for just the right conditions to
Pollen, the male gametophyte, is
designed to travel great distances by wind or
The diploid condition exhibits
all the specialized tissues described above.
Leaves and Stems
Adaptations to Dryness
Dominance of Sporophyte Generation
Flowering plants are the most numerous of the modern plants. Many of their flowers, designed to attract pollinators, are the product of coevolution with insects (and other animals) resulting in an efficient means of uniting sperm and egg. Their fruits are often designed to aid in the dispersal of their seeds.
Flower SpecializationHow -
- colors, nectar, and fragrances
- radial vs. bilateral symmetry
- incomplete vs. complete flowers
- perfect vs. imperfect flowers
- single vs. composite flowers
- prevents self fertilization
- reduces or minimizes energy needs
- attracts insect pollinators
PollinationPollen grains may be transferred from anther to stigma without the help of moisture.
- wind and millions of tiny, buoyant pollen grains
- coevolution between flowers and pollinators such as bees
- A tube emerges from the coat of the pollen grain (male gametophyte) and
- digests its way through the style.
- Generative and tube nuclei become sperm.
- The sperm enter egg sac via pollination tube through micropyle
- one sperm unites with egg forming the zygote
- the other sperm nucleus unites with a polar cell containing two nuclei- endosperm is formed (triploid tissue).
The plant body is divided into a root system and a shoot or stem system, connected by vascular tissue that is continuous throughout the plant. The root system of this dicot consists of a taproot and several lateral roots. Shoots consist of stems, leaves, and flowers. The blade, the expanded portion of a leaf, is attached to a stem by a petiole. Nodes, the regions of a stem where leaves attach, are separated by internodes. At a shoot's tip is the terminal bud, the main growing point of the shoot. Axillary buds are located in the upper angles of leaves. Most of these axillary buds are dormant, but they have the potential to develop into vegetative (leaf-bearing) branched or flowers.