Plant Diversity – Part 2

Chapter 22, sections 4-5

Seed Plants• When you picture a plant, you probably think

of it growing from a seed. However, seeds are actually a relatively new innovation, which has allowed plants to become as successful as they have worldwide.

Seed Plants

Seed plants are divided into two groups:•Gymnosperms - plants where seeds are found relatively exposed, in cones– Includes conifers such as pines and spruces, as well as

cycads, ginkoes, and gnetophytes•Angiosperms - flowering plants, where the seeds are covered by a layer of tissue, such as a fruit, to protect them– Includes grasses, flowering trees and shrubs, and all

flowers

Reproduction

• Seed plants do not require water for fertilization to occur, which allows them to live in a much broader range of habitats than ferns and mosses can.

• The adaptations which allow fertilization to occur without water include: flowers or cones, the transfer of sperm by pollination, and the protection of embryos in seeds.

Cones and Flowers

• The gametophytes of seed plants grow inside reproductive structures of the sporophyte generation.

Cones

• In gymnosperms these structures are cones, which are the seed bearing structures of these plants.

Flowers• In angiosperms, the gametophytes are found

in the reproductive structures - flowers.

Pollen

• In seed plants the entire male gametophyte is found inside a tiny structure called a pollen grain.

• The sperm of these plants do not need to swim through water to fertilize the eggs. – The entire pollen grain is carried to the female

reproductive structure by wind, water, insects, or small animals – this is known as pollination.

Seeds

• A seed is the embryo of the plant, which is encased in a protective coating and surrounding by a food supply.

Seeds

• The embryo is a very early stage of development of the diploid sporophyte. The embryo stops growing while it is still very small, and remains dormant in this condition for weeks, months, or even years, only germinating when conditions are right again.

Seed Banks

Food Supply

• The food supply in the seed provides food to the embryo as it grows. When the seed germinates and the embryo begins to grow again, it uses the nutrients and energy from the stored food supply, until it can produce it’s own food through photosynthesis.

Seed Coat

• A seed coat surrounds and protects the embryo and prevents it from drying out.

Seed Structures

• Some seeds also have special structures to help it to be dispersed to new habitats. This can include “wings” to help it blow in the wind, textures or tiny hooks so the seed can attach to the fur or feathers of animals, or the seeds are contained in fleshy tissues (fruit) to encourage animals to eat them and disperse the seeds.

How Seeds Travel

Evolution of Seed Plants

• Mosses and ferns thrived and were diversifying, 300-400 million years ago. At this time many habitats were much wetter than they are today.

• Over time the climate changed however, becoming drier, making it harder for seedless plants to survive and reproduce.

• Many species of mosses and ferns became extinct, and were replaced by seed plants that could live in drier conditions.

Evolution of Seed Plants

• The earliest seed plants resembled ferns – we have fossils of these plants from 360 million years ago.

Gymnosperms

• Gymnosperms all reproduce with seeds that are exposed; the word gymnosperm means “naked seed.” Current groups of gymnosperms include conifers, cycads, ginkgoes, and gnetophytes.

Conifers

• Conifers are the most common gymnosperms, with over 500 species alive today. This group includes pines, spruces, firs, cedars, sequoias, redwoods, junipers, and yews.

Conifers

• Some can live to be very old (the bristlecone pine can live for more than 4000 years), and some can grow to be extremely tall (redwoods can grow to over 100m).

Cycads• Cycads are unique palm-like plants, which use large

cones to reproduce. They first appeared in the Triassic period (225 million years ago), and huge forests of cycads were common during the age of dinosaurs.

Cycads

• Today only 9 groups of cycads still exist, and most are much smaller than those ancient varieties.

• Cycads make good houseplants, and they are found naturally in tropical and subtropical locations such as Mexico, the West Indies, Florida, and parts of Asia, Africa, and Australia.

Ginkoes

• Ginkgo trees were also very common during the age of dinosaurs, but there is only 1 species left today: Ginkgo biloba. Ginkgos may be some of the oldest seed plants, and they seem to have changed very little over time.

Ginkgoes• Ginkgoes were often cultivated in ancient China,

where they were planted near temples. Today they are commonly used as shade trees in urban areas in the US and Canada, since they are quite resistant to air pollution.

Gnetophytes

• Gnetophytes are fairly odd plants, which seem to be the most closely related to angiosperms of all the gymnosperm groups. There are about 70 species of this group alive today, though they were common in the Cretaceous period (145 mya).

Gnetophytes• One of the best-known gnetophytes is the plant

Welwitschia, which grows in the Namibian desert, and has only 2 leaves which grow continuously throughout its lifespan.

Ecology of Conifers

• Conifers thrive in a wide variety of habitats in many biomes – from mountains and boreal forests, in sandy soils, and in temperate rainforests.

• Conifer leaves have special adaptations for dry conditions. Scientists suggest that when conifers were evolving 250 million years ago, the climate conditions were dry and cool.

Adaptations for Dry Conditions

• To deal with these conditions, conifers evolved long, thin leaves that we call needles. – This shape reduces the surface area where water

can be lost through evaporation. • There is also a thick, waxy coating on the

needles, to further reduce water loss. • The openings (stomata) that allow for gas

exchange, are found in cavities below the surface of the leaves.

Evergreens

• Most conifers are “evergreens” – trees that retain their leaves throughout the year. The needles stay on the tree for 2-14 years, and new ones gradually replace older needles, rather than turning over all at once.

Exceptions

• Larches (tamaracks) and bald-cypresses are exceptions – they lose their needles every fall.

Homework

• Textbook Reading– Section 22-4 (pgs 564-568)• Questions 1-3 (pg 568)

• Notebook Quiz on Chap 22 on Friday• We’ll watch the video of the Guest Speaker on

Friday

Demonstration

• Osmosis - a process by which molecules of a solvent (usually water) tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane.

• Diffusion - the gradual intermingling of substances by the natural movement of their particles.

Angiosperms

• Flowering plants first appeared during the Cretaceous period (135 million years ago), which makes them the youngest group of plants. They quickly dominated Earth’s plant life – flowering plants are the vast majority of living plant species.

Flowers

• Flowers are the unique reproductive organs used by Angiosperms. Flowers give angiosperms an advantage by attracting animals such as bees, moths, hummingbirds, or bats, who then transport pollen from flower to flower. This type of pollination is much more efficient than the wind pollination used by gymnosperms.

Flowers

• Flowers contain ovaries, which surround and protect seeds. This is what gives angiosperms their name – angiosperm means “enclosed seed.” The ovary develops into a fruit after pollination, protecting the seed and helping with its dispersal.

Fruit

• A fruit is a wall of tissue surrounding the seed, and it is another reason angiosperms have been so successful.

• When an animal eats the fruit, the seeds pass through the digestive system

Fruit

• The seeds pass through the digestive tract unharmed and are deposited far from the original plant– This helps to drastically increase the range of

flowering plants by spreading their seeds over hundreds of square kilometers.

Diversity of Angiosperms

• Angiosperms are an incredibly diverse group of plants. There are multiple ways to break up all angiosperms into groups. It’s important to remember that these different sets of categories overlap each other (example: an iris is a monocot, but also a herbaceous perennial).

Monocots & Dicots• The monocots and dicots are the two classes

within the angiosperms.• They are named for the number of seed

leaves in the plant embryo– Monocots have 1 cotyledon, dicots have 2

cotyledons

Monocots & Dicots• There are several other differences between

these two groups:• Vein arrangement in leaves– Monocots have parallel veins – Dicots have branched veins

Monocots & Dicots

• Flower parts– Monocots have multiples of 3– Dicots have multiples of 4 or 5

Monocots & Dicots

• Arrangement of vascular bundles in stems– Monocots – scattered throughout stem– Dicots – bundles in a ring

Monocots & Dicots

• Root-types– Monocots have fibrous roots– Dicots have a taproot

Monocots vs Dicots

Monocots & Dicots

• Examples:– Monocots: corn, wheat, lilies, orchids, palms– Dicots: roses, clover, tomatoes, oaks, and daisies

Woody & Herbaceous

• Another way to divide up angiosperms is by the characteristics of their stems – whether they are woody or not. Woody plants have cells with thick cell walls to support the plant body.

• Woody plants include shrubs, trees, and vines.

Woody

• Shrubs are smaller than trees and have multiple stems coming up form the roots, in contrast to one main stem (trunk) as in a tree. – Examples: blueberries,

roses, and hawthorn

Woody• Vines have long, flexible stems. – Examples: grapes and ivy

Herbaceous• Herbaceous plants have

stems that are smooth and non-woody, and these plants are generally much smaller than woody plants. – Examples: dandelions,

petunias, and sunflowers

Annuals, Biennials, & Perennials

• Some plants grow, flower, and die in a single year. Other types of plants will regrow the next spring.

• Plants can be categorized by their life spans into three groups – annuals, biennials, and perennials.

Annuals

• Annuals - flowering plants which grow from seed to maturity, flower, produce seeds, and die, all in one growing season– Examples: marigolds, petunias, pansies, wheat,

cucumbers

Biennials

• Biennials – flowering plants that complete their life cycle in two years.

• The first year they germinate and grow roots, short stems, and sometimes leaves.

• In the second year they grow new stems, leaves, then flowers and seeds. Once the flowers produce seeds, the plant dies.– Examples: evening primrose, parsley, celery,

foxglove

Perennials

• Perennials – any flowering plant that lives for more than two years.

• Most perennials live many years. • Some perennials are herbaceous (peonies,

asparagus, and many grasses), but most perennials are woody plants, such as palm trees, sagebrush, maple trees, and honeysuckle.

Demonstration

• Osmosis - a process by which molecules of a solvent (usually water) tend to pass through a semipermeable membrane from a less concentrated solution into a more concentrated one, thus equalizing the concentrations on each side of the membrane.

• Diffusion - the gradual intermingling of substances by the natural movement of their particles.

Homework

• Read Section 22-5 (pgs 569-572)– Questions 1-3

• Lots of Article Analyses are still missing!• Notebook Quiz tomorrow– This whole chapter

Great Summary Video

• https://www.youtube.com/watch?v=X4L3r_XJW0I (8 min)

Crash Course: Vascular Plants

• https://www.youtube.com/watch?v=h9oDTMXM7M8&noredirect=1 (12 min)

Notebook Quiz

• 15 min (timed)• Open book to your notes/logbook– No textbooks or photocopies of textbooks

• Remember your name!• Put in the yellow folder when finished• When done – do something SILENTLY!

Guest Speaker Videos

• Sub – please see folder of videos on the USB key