Biological Diversity: Plant Classification and Structures

Thallophytes

Simplest form of a plant with no specialized vascular system.

Bryophytes

Aquatic and land habitats; Dominant gametophyte stage (haploid-n); E.g., Mosses, liverworts, hornworts.

Tracheophytes

Grow vertically and tall; Dominant sporophyte stage (diploid-2n); E.g., Ferns and Pine trees.

Angiosperms

Most diverse land-based plant; Produce flowers and have pollen; Bear their seeds in fruits.

Pollen

Undergo double fertilization; Contains non-flagellated male gametes.

Microsporocytes

Diploid (2n) cells that undergo meiosis to produce four microspores (n).

Megasporocyte

Diploid (2n) cell in the ovary that undergoes meiosis to produce four megaspores (n).

Double Fertilization

One male gamete (n) fuses with the female egg gamete (n) to form an embryo/zygote (2n) & another male gamete fuses with polar nuclei to form endosperm (3n).

Endosperm

Triploid (3n) tissue formed from the fusion of a male gamete with polar nuclei.

Zygote

Diploid (2n) cell formed from the fusion of a male gamete and a female egg gamete.

Embryo

Develops from the zygote (2n) after fertilization.

Monocots

Plants with one cotyledon, parallel veins, scattered vascular bundles, and flower parts in multiples of 3; E.g., Lilies and Kentucky bluegrass.

Dicots

Plants with two cotyledons, net-like veins, ringed vascular bundles, and flower parts in multiples of 4 or 5; E.g., Oak trees.

Synergid Cells

Two cells that help attract/guide pollen tube to the female gametophyte.

Antipodal Cells

Cells with an unknown function in the embryo sac.

Cotyledon

The first leaf or leaves that appear from a germinating seed.

Seed Coat

Protective outer covering of a seed, which is diploid (2n).

Ovary

Part of the flower that contains the ovules and where fertilization occurs.

Stigma

The part of the flower that receives pollen.

Style

The stalk that connects the stigma to the ovary.

Embryo Sac

The female gametophyte that develops within the ovule.

Pollen Tube

Structure that grows from the pollen grain to deliver sperm to the ovule.

Gametophyte

The haploid stage in the plant life cycle that produces gametes.

Sporophyte

The diploid stage in the plant life cycle that produces spores.

Dermal Tissue

Epidermal cells covering outside of plant parts → secrete waxy protective substance (cuticle) in aerial (above ground) portions of plant.

Seed Coat

Tough outer covering of seed that protects embryo/seed content.

Phototropism

Bending of a plant in response to light.

Gravitropism

Bending of a plant in response to gravity.

Thigmotropism

Growth response to mechanical stimuli.

Vascular Tissue

Conducts water and minerals throughout plant.

Xylem

Transports water and minerals throughout plant.

Phloem

Transports sugar throughout plant.

Endosperm

Primary storage tissue.

Auxin

Influences plant's response to light + gravity to stimulate growth/elongation.

Gibberellins

Promote flower + stem elongation.

Cytokinins

Stimulate cytokinesis (cell division).

Abscisic Acid

Inhibits growth and promotes seed dormancy.

Ethylene Gas

Promotes fruit ripening, flower production, and leaf abscission.

Epidermis

Protective layer covered w/ cuticle to reduce transpiration (water loss through evaporation).

Spongy Mesophyll

Intracellular spaces allow for gas travel.

Palisade Mesophyll

Has cells w/ chloroplasts and is the primary site for leaf photosynthesis.

Stomata

Microscopic pore in epidermis that allows for gas exchange between plant and external environment.

Photoperiodism

A plant's response to changes in length of day and night (photoperiod).

Vascular Bundles

Consist of xylem and phloem - surrounded by bundle sheath cell.

Axillary bud

Bud that can develop into a flower or shoot.

Short-day plants

Flower when sunlight is less than half the day.

Long-day plants

Flower when sunlight is more than half the day.

Guard Cells

Specialized epidermal cells to control opening of stomata and permit gas exchange.

Epicotyl

Part of the embryo above the cotyledons.

Hypocotyl

Part of the embryo below the cotyledons.

Radicle

Part of the embryo that develops into the root.

Cotyledon

Provide mechanical support and transfer nutrients from endosperm to embryo.

Bean seed

Example of a dicot seed.

Cord seed

Example of a monocot seed.