Plant Evolution and Categories

Plant Evolution and Categories

Introduction

• Plants nicely represent evolutionary advancements from aquatic to terrestrial environments.

• Algae are still present today, signifying they weren't an evolutionary dead end.

• The ancestor of modern plants diverged from aquatic algae around 500 million years ago.

• Terrestrial adaptations accumulated over tens of millions of years, leading to the first land plants.

Categories of Plants

1. Bryophytes

   • Includes mosses.

   • First plants to move onto land, forming mat-like structures.

   • Lack a vascular system.

2. Seedless Vascular Plants

   • Represented by ferns.

   • Developed a vascular system but do not have seeds.

3. Gymnosperms

   • Means "first seeds".

   • Includes conifers and pine trees.

4. Angiosperms

   • Most prevalent type of plant today.

   • Develop flowers and fruits.

Bryophytes

• Dependent on moist environments.

• Bryophytes were the first plant that was to move on to land and kind of form these these mat like structures that we still see today.

• Absorb moisture through their leaves.

• Examples: liverworts, hornworts, and mosses.

• Small enough to grow upright without a vascular system.

• Anatomical Developments:

  • Waxy cuticle to prevent moisture evaporation.

  • Protection for vulnerable reproductive cells from drying out.

  • Lack structural support like lignin.

Alternation of Generations

• Plants have different life stages (sporophyte and gametophyte) that take turns producing each other.

  • Sporophyte produces spores (asexual reproduction).

    • Spores germinate into a gametophyte.

  • Gametophyte produces gametes (egg and sperm cells) for sexual reproduction.

• The gametophyte stage is more obvious in ancient plants like mosses.

• Mosses have stalks with caps that release spores for dispersal.

• The leafy photosynthesizing structure of moss is the gametophyte stage.

Vascular Seedless Plants (Ferns)

• Developed a vascular system, allowing them to grow taller.

• Dependent on moist environments since they don't have seeds.

• Ferns of today still don't reproduce using seeds.

• Vascular system enables nutrient transport from the ground up.

Vascular Tissue

• Xylem:

  • Performs transpiration by pulling water from the soil up through the plant.

  • Water molecules cohere due to hydrogen bonds; as one molecule evaporates, it pulls the next one up.

  • Passive process through dead, hollow cells.

• Phloem:

  • Living cells with two-way flow.

  • Transports sugars from photosynthetic tissues (leaves) to sinks (roots, stem).

• Plants produce hormones for signaling between tissues, including alarm signals to warn nearby plants of pests or infections.

Gametophyte and Sporophyte Stages of Ferns

• The gametophyte of a seedless vascular plant looks kinda like this. Just a like a very, very small little plant, kinda heart shaped.

• Gametophyte produces eggs and sperm cells released into the soil.

• Sporophyte is the dominant life stage.

• Spores are produced asexually underneath the leaves (fronds).

• Spores germinate into a gametophyte.

Carboniferous Forests

• Ferns were the dominant life form on Earth about 300 million years ago.

• Vascular system adaptation led to huge forests of large ferns and palm-like trees.

• Coal deposits formed from these forests due to lack of saprophytic fungi to decompose the organic matter.

Gymnosperms

• Evolutionary advancement: development of seeds.

• Allowed movement further inland to drier habitats.

• Separate egg and sperm (cones).

• Ovule: the egg.

• Pollen: the sperm.

• Reproductive cells are protected, enabling survival in drier environments.

• Pollen is released and transports genetic information to the ovule.

• After fertilization, a seed develops, containing an embryo, food, and protective packaging.

• Gametophytes are cones that produce eggs and pollen.

Pollination

• Pollen is released in large quantities.

• Self-fertilization can occur, but cross-pollination from different trees is ideal for sexual reproduction.

• Fertilized cones continue to develop and eventually drop off the tree.

Angiosperms

• Flowering plants that evolved about 40 million years ago.

• Flowers entice pollinators with nectar (sugar).

• Pollinators accidentally transfer pollen between plants.

Flower and Fruit Development

• Flowers are reproductive organs with an ovary.

• After fertilization, the flower develops into a fruit.

• A seed in angiosperms is a fertilized plant egg.

• Fruits entice animals to disperse the seeds.

• Examples of fertilized flowers developing into fruits: strawberry, tomatoes, cucumbers, peppers.

Anatomy of a Flower

• Sepals protect the developing flower bud.

• Petals attract pollinators.

• Stamen: male reproductive structure.

  • Anther: contains pollen.

  • Filament: stalk supporting the anther.

• Pistil: female reproductive organ.

  • Carpel: produces eggs (ovules).

  • Stigma: platform for pollen to land on.

  • Style: tube that sperm travels down to reach the egg.

  • Ovary: protects the eggs.
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Cellular Development

• Embryos have a period of vulnerable cell division and need nutrients.

• Ovules and seeds are protected within each respective structures.

Seed Dispersal

• Fruits, which are swollen ovaries, develop to assist in animal dispersion for the seeds contained.

• Fruit contains water and sugar to entice animals.

• Plants, in that case, put an investment of sugar and energy towards generating fruits and pollination.

The Seed

• A seed is the embryo that sprouts from the plant.

• Protection and the environment are key to the long-term survival of a seedling.

• There are known cases of seeds being viable for thousands of years, such as those found of ancient palm trees.

True Fruits and False Fruits

• In a true fruit, the entire fruit is a swollen ovary with seeds inside.

• In a false fruit, the ovary is at the core, and other parts of the flower form the fruit.

Reproductive Designations of Flowering Plants

• Pollen is male gametophyte and the ovule is considered a female gametophyte.

• Designations are based less on a full male-female construct since the pollen and ovule are just variants of genetic data.

• Sporophyte is more widely dispersed throughout the plant.

Parts of a Flower found on a Fruit

• Stigma rests on top the fruit.

• Sepals remain on the bottom portion of the fruit.

• The majority of the fruit is the ovary.

Plant Categories

• Monocots and dicots are two major types of angiosperms.

• Division can be told by, number of seed leaves, or structures in the vascular bundles.

Differences between Monocots and Dicots

Plant Designations

• Anything derived from the flower that contains seeds is a considered a fruit, such as a cucumber or tomato.

• Roots, stems, and leaves used for consumptions are considered vegetables, such as potatoes or carrots.

Plant Lifespan & Growth

• Plants for the most part will grow as long as they live.

Plant Lifespan

• Annuals live for one year, reproduce, and die in one growing season.

• Biennials flower and produce seeds in their second year.

• Perennials reproduce for years.

Plant Growth

• Primary growth leads to lengthening via meristems with growing tissue.

• Secondary growth involves thickening via accumulation of dead xylem.