Download Plants notes - WordPress.com

Seed Plants
Seed Plants­Subphylum Spermopsida
The evolutionary story is that now seed plants are free from the dependence on water and can successfully live on land. Over hundreds of millions of years the ancestors of seed plants evolved new adaptations so that they could survive in places that mosses and ferns could not. They evolved well developed vascular systems and also roots, stems, leaves and structures that would enable them to live almost everywhere on earth. Seed plants have evolved seeds, which is the key adaptation in a new form of sexual reproduction that frees these plants from living in or near wet environments.
Roots, Stems & Leaves
The 3 organs of a plant are: roots, stems, leaves. Each of these shows adaptations that have enabled plants to be better suited to survive on land.
Roots: • Absorb water and dissolved nutrients from moist soil
• Anchor plants to the ground
• Hold plants upright and prevent them from being knocked over in the wind/rain
• As they grow they make complex branching networks that penetrate the soil
Stems:
• Hold plant leaves up to the sun for photosynthesis
• Plants compete for the sun’s solar energy, many plants are tall and have long stems which need to be strong and sturdy to support their mass.
Leaves:
• The organs in which the plants capture the sun’s energy to perform photosynthesis
• Leaves evolved because plants that had broad, flat, surfaces were able to ‘capture’ more solar energy than plants that did not have these surfaces.
• These leaves have a waxy coating, called a cuticle, to prevent water loss to dry air.
Vascular Tissue
Xylem:
• Vascular tissue responsible for carrying water and dissolved nutrients from the roots to the stems and leaves.
• Have thick cell walls and therefore provide strength for the heavy limbs
• They only conduct water in one direction…UP
Phloem:
• Carry the products of photosynthesis from the leaves to all parts of the plant.
Gymnosperms
• Gymnosperms are characterized by seeds that develop exposed (or “naked”) on fertile leaves ‐
there are no ovary walls(fruit) surrounding the seeds. Gymnosperms do not have flowers.
• Leaves have evolved into specialized structures called scales (modified leaves) which are grouped into larger structures called male and female cones.
Male cones: Produce male gametophytes called pollen (pollen cones)
Female Cones: Produce female gametophytes called eggs (seed cones)
When the egg is fertilized by a sperm cell a seed is formed on a scale of the female cone. The seed is protected by a seed coat, but is not covered by the cone. It sits “naked” on the scale.
The gymnosperms are NOT a formal taxonomical category; the term is used casually by botanists. This informal group consists of the cycads, the ginkgoes, and conifers.
The Cycads
Palm like plants that thrived when dinosaurs roamed the earth
Today only 9 genera of cycads exist and they prefer warm, temperate climates
The Ginkgoes
• Were also common in the dinosaur era but now only one species remains, Ginkgo biloba
• Used in a lot of Chinese medicine ‐
thought to be a memory enhancer and prevent the onset of dementia
The Conifers (Evergreens)
Commonly called The Evergreens, the conifers are the most abundant gymnosperms. Eg. Pines, spruce, fir, cedars, sequoias, and redwoods.
Cover vast areas of North America, China, Europe, and Australia.
Adaptations in Conifers:
• Conifer leaves have adaptations that protect them against water loss in dry environments.
• Leaves are shaped like needles to reduce the surface area for evaporation
• Waxy cuticle covers leaves
• Stomata for gas exchange located in tiny pits on leaf surface.
Reproduction in Conifers:
• Most gymnosperms produce 2 kinds of cones
• The scales that form the cones carry sporangia that produce the male and female gametophytes (they are very small).
• Pollen cones (male cones) produce male gametophytes (produced by microspores) in the form of pollen grains and are released each spring and are carried by the wind.
• Seed cones (female cones) house the female gametophytes. Megasporocytes (megaspore mother cells) are cells contained within the ovule that produce four megaspores through meiosis. Only one of the megaspores survives. The remaining one develops into a female gametophyte from which eggs are produced.
• Pollen grains drift into female cones and are caught by a sticky secretion.
• Pollen grains (haploid) produce sperms by mitosis which burst out of the pollen grain and travel through a pollen tube to fertilize eggs in the ovules.
• Fertilized eggs (zygotes) develop into seeds on the surface of the scales that make up the female cone
• May take two years for the seeds to mature. If they land on good soil they may develop into a new conifer.
Conifer Life Cycle Diagram Angiosperms
• http://www.ted.com/talks/jonathan_drori_the_beautiful_tri
cks_of_flowers.html
• Angiosperms are flowering plants and they all reproduce sexually through their flowers in a process that involves pollination. They are different from gymnosperms in that the seeds of angiosperms are not carried naked on the flower parts. Angiosperm seeds are contained within a protective wall that develops into a structure called fruit (the scientific term fruit also refers to many structures also called vegetables).
Interesting fact:
• By definition of a fruit, apples, oranges, beans, pea pods, pumpkins, tomato and eggplant are all fruit
• Angiosperms are the most widespread of all the land plants and they have approximately a quarter of a million different types of species. They have also adapted to living in a variety of environments from frigid mountains to blazing deserts. Some angiosperms have evolved specialized tissues to withstand extreme hot or cold as well as long periods of drought.
2 subclasses of angiosperms: monocots & dicots
• Monocots examples include corn, wheat, lilies, daffodils, orchids, palms
‐ Dicots examples include roses, clover tomatoes, oaks, daisies.
• There are several differences between monocots and dicots but the simplest difference has to do with the number of leaves the embryo plant has when it first begins to grow/germinate. • The leaves of the embryo are called cotyledons
or seed leaves.
‐ Monocots have one seed leaf
‐ Dicots start off with 2 seed leaves
• In some plants the cotyledons are filled with food for the plant and in others, the cotyledon is the first leaf to carry out photosynthesis.
Monocot
Leaves
Flowers
Veins in leaves of most monocots are parallel to each other
Flower parts in threes or multiples of threes
Dicot
Veins in leaves form a branching network
Flower parts in fours or fives or multiples of fours/fives
Vascular Bundles in stem
Vascular bundles are scattered Vascular bundles are arranged in a cross section of a stem
in a ring in a cross section of a stem
Vascular Bundles in root
Bundles of xylem and phloem A single mass of xylem forms alternate with one another in a an “X” in the center of the root
circle
Phloem bundles are located between the arms of the “X”
Stem Thickness
Stems of most monocots do not grow thicker from year to year
Stems can grow thicker from year to year
Flower Pollination in Angiosperms
• Pollination is essential for reproduction in flowering plants. • Some angiosperms pollinate using wind, they usually have small, plain flowers with little to no fragrance.
• Most flowering plants are pollinated by insects, birds or animals that carry pollen from one flower to another, in return, plants provide pollinators with food (ex‐
nectar)…this is called vector pollination because both the plant and the pollinator benefit.
• Beautiful and fragrant flowers evolved so that the honeybee could easily recognize them and know that they have food for them (blue and yellow flowers)
• Markings on flowers point to the center of the plant are like landing pads and directions for bees to help them find the nectar.
• Moths also pollinate but they don’t see well so the color of the flower is not of importance, they have a great sense of smell and are attracted to flowers that are fragrant such as jasmine.
• Hummingbirds have great sight but little to no sense of smell, they are attracted to bright red and orange flowers that have little fragrance
Structure of a Flower
• A typical flower will produce both male and female gametes but often the plant will produce them in different areas of the plant or on completely different plants.
• Flowers are from modified stems that produce four specialized leaves: sepals, petals, stamens, and carpels.
• Sepals – outermost and enclose the flower bud before it opens to protect it while it develops. All sepals together form the calyx
• Petals – found just inside the sepals and are often brightly coloured. All of the petals together form the corolla. What is the evolutionary benefit to having brightly coloured petals?
• Because petals and sepals produce no gametophytes, they are considered to be sterile leaves.
Fertile Leaves
• Contain the structures that produce male and female gametophytes
• Stamen – contains a long thin filament that supports the anther. Inside the anther are microsporangia in which the microspores (male gametophytes) are produced
• Carpels – at the very center of the flower and are produced from fertile leaves that have rolled up which places megasporangia
(produce female gametophytes) inside female leaves. One or more carpels form the pistil
• Pistil – consists of a base called an ovary, a stalk called the style, and a stigma located at the top of the style.
Pollen is deposited on the stigma by wind or pollinators.
Female Gametophyte
• Inside each ovary is one or more megasporangia
called ovules
• Megaspore produces female gametophyte.
• 1. megaspore mother undergoes meiosis producing 4 haploid cells
• 2. The surviving one undergoes mitosis to produce 8 nuclei which is surrounded by a membrane to form the embyro sac
• 3. The nuclei move until two sit in the center (polar nuclei) and three combine at each end. • 4. One of the three nuclei in the group closest to the opening enlarges to become the egg nucleus. The three at the opposite end die.
Male Gametophyte
• Inside the athers, microsporangia called pollen chambers
produce many diploid microspore mother cells which divides by mitosis to produce 4 haploid microspores. Each microspore becomes a pollen grain. The wall of each grain thickens to protect it from damage.
• The nucleus of the grain undergoes one mitotic division producing two haploid nuclei. One is called the tube nucleus
and the other is the generative nucleus.
• The tube nucleus disintegrates and the generative nucleus divides to form two sperm cells
Fertilization
• When a pollen grain lands on a stigma of an appropriate flower it begins to grow a pollen tube. The generative nuclei divides to form two sperm nuclei. The pollen tube has tube nucleus and two sperm nuclei.
• The sperm nuceli travel down the pollen tube to the embryo sac to undergo double fertilization. One sperm fuses with the egg nucleus to form the zygote and the other fuses with the polar nuclei to make a triploid endosperm which supplies the food for the embryo during its growth.
Task for today
• Get a big 11X17 page and divide it in two.
• On one side outline and draw the steps involved in gymnosperm gametophyte development and eventual fertilization
• On the other side do the same for Angiosperms.
• Each should also show the formation of the seed/fruit and explain how and where they form.
Seed Dispersal
• Flowers have adapted ways to ensure pollination. Angiosperm fruit has also adapted ways to ensure that their seeds are scattered away from the parent plant. This is called seed dispersal.
• Why is seed dispersal so important?
• If the seeds are dropped near the parent there will be a competition for nutrients, water and sunlight and could decrease the chance of survival
• Allows plants to colonize other environments
How is this done?
• Some plants have barbs so that an animal that rubs against it may pick up seeds that will fall off the animal at a later date and in a different environment
• Some fruits are so tasty that animals eat them and the seeds are inside, the animals then deposit the seeds in a new environment through their waste (a natural fertilizer)
Interesting Fact: Why does unripened fruit taste so bad?
• The seeds are still maturing, the fruit doesn’t want to be eaten because its seeds are not ready to be dispersed so it makes itself taste bad so that animals are only attracted to the ripened fruit which contain the seeds ready to be dispersed.