Chapter 30 Plant Diversity: The Evolution of Seed Plants

Characteristics of Seed Plants 1.) Reduced Gametophytes a.) Gametophytes are microscopic and are retained in the parental sporophyte. i.) Protects the female gametophytes from environmental stress & enables them to obtain nutrients from the sporophyte.

Characteristics of Seed Plants 2.) Heterospory: female gametophytes are produced by megaspores and male gametophytes are produced by microspores a.) Megasporangia (which is the tissue that produces megaspores) are protected by tissue called integument.

Characteristics of Seed Plants b.) Microspores develop into pollen grains which contain the male gametophytes & sperm nuclei. i.) Pollen can be carried by wind or on the body of other animals. This is an important adaptation of seed plants. ii.) The transfer of pollen to a plant containing the ovules (eggs) is called pollination.

Characteristics of Seed Plants 3.) When pollination occurs, the ovule develops into a seed which consists of the plant embryo, a food supply & a protective coat derived from the integuments. Why are seeds an advantage? a.) Resist harsh conditions – can remain dormant until conditions are favorable for growth (germination) b.) Able to be dispersed into a larger area

Characteristics of Seed Plants 4.) There are 2 types of seed plants: a.) Gymnosperms b.) Angiosperms

Gymnosperms 1.) Have “naked” seeds that are not enclosed in ovaries. a.) Seeds are usually on modified leaves that form cones. 2.) Include trees such as pines/firs & redwoods.

Gymnosperms 3.) 1 st seed plants to appear in fossil record. 4.) Heterosporous: male & female spores are produced by separate cones. a.) Pollen cones: produce microspores which develop into a pollen grain containing the male gametophyte (i.e. sperm) b.) Ovulate cones: produce megaspores which which develop into female gametophytes (containing egg).

This is a simplified diagram of a typical gymnosperm life cycle.

Angiosperms (Flowering Plants) 1.) Produce flowers & fruits 2.) Are the most diverse & widespread plant group.

Angiosperms (Flowering Plants) 3.) Flower structure: a.) Sepals: at base of flower which are usually green & enclose the flower before it opens b.) Petals: brightly colored to aid in attracting pollinators c.) Stamens: produce microspores that give rise to pollen grains. Has 2 parts: i.) Filament: stalk ii.) Anther: sac at end of filament where pollen is produced

Angiosperms (Flowering Plants) d.) Carpels: make megaspores which produce ovules (eggs). Consists of… i.) Stigma: sticky end that receives pollen ii.) Style: tube/stalk that leads to the ovary iii.) Ovary: located at base of carpel & contains one or more ovules which will develop into seeds. The ovary will mature into a fruit.

Angiosperms (Flowering Plants) 4.) Fruit: consists of a mature ovary containing seeds. a.) Fruit develops after pollination. Ovary grows and its wall becomes the pericarp: the thickened wall of the fruit. b.) Fruits can be fleshy (grape, oranges, tomatoes, strawberries) or dry (beans, nuts, grains – wheat, corn, rice)

Angiosperms (Flowering Plants) 5.) Fruit adaptations help disperse seeds: a.) Maples & dandelions are wind adapted b.) Coconuts float for water dispersal c.) Burrs that cling to fur/clothing d.) Fleshy, edible fruits are eaten but seeds are not digested – deposited with animal species far from parent plant.

Angiosperm Life Cycle 1.) The flower of the sporophyte produces microspores that form male gametophytes & megaspores that form female gametophytes. a.) Male gametophytes are IN pollen grains. Each pollen grain consists of 2 sperm cells & a cell that will produce a pollen tube.

Angiosperm Life Cycle b.) Inside the flower’s ovary, are ovules which contains the female gametophyte - consists of a few cells (one of which is the egg). 2.) Pollen (released from the anther) sticks to the stigma of a carpel. a.) Some flowers self-pollinate but most cross-pollinate 3.) The pollen grain germinates on the stigma & grows a pollen tube down the style of the carpel.

Angiosperm Life Cycle 4.) The pollen grain then discharges its sperm down the pollen tube & into an ovule. a.) One sperm fertilizes the egg & the other fuses with other cells in the female gametophyte. b.) This is known as double fertilization.

Angiosperm Life Cycle 5.) The ovule now matures into a seed. a.) The nucleus of a cell in the gametophyte divides repeatedly and forms endosperm tissue which is the food for the embryo.

Concept Check 1.) It could be said that an oak is an acorn’s way of making more acorns. Write an explanation of this statement that includes these terms: sporophyte, gametophyte, ovule, seed, ovary and fruit.

Angiosperm Diversity 1.) Most angiosperms are divided into 2 groups: a.) Monocots b.) Eudicots 2.) These names refer to the # of seed leaves (called cotyledons) that surround the developing embyro in a seed.

Comparing Monocots & Eudicots MonocotsEudicots # of Coyledons12 Leaf VenationParallelVeins fan out Vascular TissueScattered throughout stem Arranged in a ring around stem RootsRoots are fibrous Taproot (main root) FlowersFloral organs are in multiples of 3 Floral organs are in multiples of 4 or 5

Angiosperm Diversity 3.) There are 2 other groups of angiosperms called the basal angiosperms and the magnoliids.

Angiosperms & Animals 1.) Have had a strong evolutionary influences on each other. 2.) Plant & pollinator relationships have probably increased both plant & animal diversity and can be described as mutualistic partnerships.

Angiosperms & Humans 1.) Most of our food comes from angiosperms… a.) Corn, wheat, rice, potatoes…spices, chocolate, coffee, tea b.) We either eat these foods directly (or in processed foods) or we feed them to livestock that we then consume.

Angiosperms & Humans 2.) Seed plants (this would also include gymnosperms) are our source of wood too. 3.) We also depend on both gymnosperms & angiosperms for many of our medicines – from basic pain relievers to cancer fighting compounds. 4.) Remember to tie this back to ecology – plant diversity is part of biodiversity and it is rapidly disappearing.