Angiosperms Collective

What are angiosperms?

Flowering plants with seeds enclosed in a carpel that resembles a folded and fused leaf.

In angiosperms, where are seeds enclosed?

Within a carpel, a leaf-like structure folded over and fused at the margins

The seed of an angiosperm develops from the ______ within the ______.

Ovule; carpel.

What happens to the ovary after fertilization in angiosperms?

It matures into a fruit that encloses the seeds.

What is the scientific phylum name for flowering plants?

Phylum Magnoliophyta.

Into which two major classes is Phylum Magnoliophyta divided?

Magnoliopsida (dicots) and Liliopsida (monocots).

What has modern DNA and cladistic evidence revealed about dicots?

That there are two distinct groups of dicots, not one uniform class.

In angiosperms, the ______ is a modified stem bearing modified ______.

Flower; leaves.

What characteristics describe the most primitive flowers?

Long receptacle, many spirally arranged and unfused parts, parts not differentiated into sepals/petals, and numerous flattened stamens and carpels.

What are examples of primitive flowering plants?

Magnolias and other early-evolved species with simple, unfused floral structures.

Are angiosperms homosporous or heterosporous?

Heterosporous — they produce two types of spores (microspores and megaspores).

Which life stage dominates in angiosperms, sporophyte or gametophyte?

Sporophyte is dominant.

The female gametophyte in angiosperms is completely enclosed within ______ tissue and reduced to only a few ______.

Sporophyte; cells.

Describe the mature male gametophyte in angiosperms.

A germinated pollen grain containing three nuclei (one vegetative and two sperm nuclei).

What cell initiates the formation of the female gametophyte? (Phylum Magnoliophyta gametophyte production)

The diploid megasporocyte within the ovule.

The diploid megasporocyte undergoes ______, producing ______ haploid megaspores. (Phylum Magnoliophyta gametophyte production)

Meiosis; four.

What happens to the four megaspores produced by meiosis? (Phylum Magnoliophyta gametophyte production)

Three degenerate; one remains functional and enlarges.

What happens to the nucleus of the surviving megaspore following degeneration? (Phylum Magnoliophyta gametophyte production)

It divides repeatedly (by mitosis) to form eight nuclei within one large cell (no cell walls yet)

What structure does this 8-nucleate cell develop into following the mitosis of the single remaining cell? (Phylum Magnoliophyta gametophyte production)

The megagametophyte, also called the embryo sac.

What do the two outer layers of the ovule differentiate into following the creation of the megagametophyte? (Phylum Magnoliophyta gametophyte production)

The integuments, which develop into the seed coat.

What is the micropyle, and why is it important?

A small opening in the ovule of a seed plant and the seed coat of a mature seed. It guides the pollen tube to the egg cell during fertilization and it acts as the entry point for water and oxygen during seed germination.

How are the eight nuclei arranged inside the embryo sac/megagametophyte? (Phylum Magnoliophyta gametophyte production)

Into two groups of four—one group near each end of the cell.

What happens when one nucleus from each group migrates to the center within the megagametophyte? (Phylum Magnoliophyta gametophyte production)

They form the central cell, which will later participate in double fertilization to form endosperm.

Following the migration of nuclei, cell walls form around six of the nuclei, forming an ______, two ______, and three ______. (Phylum Magnoliophyta gametophyte production)

Egg; synergids; antipodals.

Where are synergids and antipodals located relative to the micropyle? (Phylum Magnoliophyta gametophyte production)

The egg and two synergids are near the micropyle; the three antipodals are at the opposite end.

What is the full structure of a mature female gametophyte?

A large sac containing 8 nuclei in 7 cells (3 antipodals, 2 synergids, 1 egg, and 1 central cell with 2 nuclei).

What is the primary function of synergids?

To help guide the pollen tube toward the egg for fertilization.

What is the function of antipodal cells in the embryo sac?

Their function is unclear or minimal; they may provide nutritional support early on.

Where does the formation of male gametophytes occur?

Inside the anthers of the flower.

How many microsporocyte patches typically form in an anther?

Four, corresponding to the four pollen sacs.

What happens to each microsporocyte?

It undergoes meiosis to form four haploid microspores.

What are the three key changes that occur in developing microspores?

(1) Mitosis to form a generative and tube cell, (2) separation of microspores, (3) wall formation.

The smaller cell inside the pollen grain is the ______ cell, and the larger surrounding cell is the ______ cell.

Generative; tube.

What is the nucleus of the tube cell called?

The vegetative nucleus.

What happens to the generative nucleus later in development?

It divides to produce two sperm cells.

What is the outer wall of the pollen grain called?

The exine.

What is special about the exine?

It is sculptured and contains species-specific chemicals that can interact with the stigma’s surface during pollination.

The mature male gametophyte (pollen grain) contains ______ nuclei and is capable of forming a ______ tube.

Three; pollen.

Pollination

The transfer of pollen grains from the anther (male structure) to the stigma (female structure) of a flower.

Anther and stigma

The two main reproductive organs involved in pollination.

Self-pollination

When pollen from a flower lands on the stigma of the same flower.

Cross-pollination

Transfer of pollen between different plants of the same species, increases genetic variation.

Pollination agents

The main agents in angiosperms include insects, wind, water, animals, and gravity.

Fertilization

The union of sperm and egg that immediately follows pollination.

Cross-fertilization

Occurs when pollen grain from a different plant or variety continues its development.

Pollen tube

A structure that grows through the stigma and style to reach the ovule’s micropyle.

Vegetative nucleus

The nucleus that stays at the tip of the pollen tube, guiding its growth.

Generative cell

The cell that lags behind the vegetative nucleus during pollen tube development and divides to form two sperm cells.

Female gametophyte

The structure into which the pollen tube enters, releasing two sperm cells through the micropyle.

Synergid cell

One synergid cell is destroyed during fertilization as the pollen tube discharges the sperm cells.

Mature male gametophyte

A germinated pollen grain containing one vegetative nucleus and two sperm cells inside a tube cell.

Double fertilization

A unique angiosperm process where one sperm fertilizes the egg and the other fuses with the two polar nuclei to form triploid endosperm.

Zygote

The embryo (new sporophyte) that forms after double fertilization.

Triploid endosperm nucleus

The result of the fusion of the other sperm with the two central cell nuclei, which develops into nutritive endosperm tissue.

Endosperm tissue

Provides nutrition to the developing embryo within the seed.

Monocots

Plants like corn and grasses, where endosperm becomes a major part of the mature seed.

Dicots

Plants in which the endosperm is absorbed into the cotyledons as the seed matures.

Staple crops

Wheat, rice, and corn, which provide major nutrition due to their endosperm content.

Seed

The transformation the ovule undergoes after fertilization.

Fruit

What the ovary becomes after fertilization, enclosing the seeds.

Seed coat

Formed from integuments, hardening to protect the embryo.

8-nucleate embryo sac

Not all flowering plants form this; some develop gametophytes with 4–16 nuclei.

Endosperm ploidy levels

5x, 9x, or 15x, depending on how many nuclei fuse.

Lily gametophyte

Unique development occurs when all four haploid megaspore nuclei remain functional.

Triploid nucleus in lilies

Formed when three of the four megaspore nuclei unite.

Apomixis

Seed or embryo formation without fertilization, often from diploid cells of the ovule.

Diploid cells

The type of cell that may give rise to an embryo in apomixis instead of a zygote.

Genetically identical plants

Results from apomixis since no meiosis or fertilization occurs.

Vegetative propagation

The result of apomixis, producing offspring that clone specific traits.

Parthenocarpy

Development of fruit from an unfertilized ovary, producing seedless fruits.

Seedless fruits examples

Navel oranges and bananas are examples of parthenocarpic fruits.

Agricultural advantage of parthenocarpy

Produces seedless varieties desirable for consumption and commercial production.

Trends of specialization

Evolutionary changes in floral structure that move from primitive to more specialized forms.

Inferior ovary

In an epigynous flower, where the receptacle and other floral parts appear attached at the top.

Superior ovary

Found in a hypergynous flower, with parts attaching below it.

Perigynous flower

Flower where parts are attached to a corolla tube but not fused to the ovary.

Complete flower

A flower having all four main parts: calyx, corolla, stamens, and pistil.

Incomplete flower

A flower missing one or more of the four main parts, like lacking petals or stamens.

Perfect flower

A flower that contains both stamens and pistil reproductive structures.

Imperfect flower

A flower that lacks either stamens or pistil, making it unisexual.

Monoecious

A plant species that has both male and female imperfect flowers on the same individual.

Dioecious

A plant species that bears only male flowers or only female flowers (on separate individuals).

Advantage of dioecious reproduction

Ensures outcrossing and genetic diversity by requiring two separate plants for fertilization.

Differences between flower types

Hypogynous has superior ovary, parts attached below; perigynous has parts around but not fused; epigynous has inferior ovary with parts attached above.

Primitive flowering plants characteristics

Simple leaves, numerous spirally arranged unfused floral parts, radial symmetry, complete and perfect flowers, superior ovary.

Radial symmetry

Floral parts arranged in a circular pattern, divisible into equal halves through multiple planes.

Numerous flower parts

Primitive flowers tend to have unfused and spirally arranged parts on a long receptacle.

Example of primitive flowering plant

Magnolia, characterized by numerous, separate, spiral floral parts.

Defining traits of specialized flowering plants

Fewer floral parts, definite in number, arranged in whorls, bilateral symmetry, fusion or reduction of parts, often incomplete or imperfect flowers, inferior ovary.

Bilateral symmetry

Specialized flowers can be divided into equal halves along only one plane.

Floral specialization

The process of flower parts fusing together or reducing in number through evolution.

Highly specialized flowering plant example

Orchid, which has fused and reduced floral parts with bilateral symmetry.

Specialization effect on pollination strategies

Specialized structures evolve to match specific pollinators, improving efficiency but reducing generality.

Herbarium

A collection of preserved, dried, and labeled plant specimens for scientific study.

Purpose of herbaria

To preserve plant specimens for taxonomy, research, reference, and education.

Herbarium singular

The singular term for herbaria.

Preserved organisms in herbaria

Vascular plants, algae, fungi, and sometimes bryophytes.

Fungi preservation method in herbaria

Dried and stored in small packets or envelopes.

Plant press

A tool used to flatten and dry vascular plant specimens.

Rag paper

100% rag paper is used for mounting herbarium specimens because it is acid-free and long-lasting.