CHAPTER 13PAGES 267-294

Introduction to Plants

Introduction

Most of the plants you are familiar with produce flowers.

Recall not every plant produces flowers, some have seeds or cone, others have neither.

What are Plants?

Plants are multicellular eukaryotes with cell walls made of cellulose.

Plant cells also have chloroplasts.Plants have specialized reproductive organs.Male and Female reproductive organs may be

found on the same plant or on different plants.

How do plants obtain food?

Almost all plants make food by photosynthesis.About 1% of plants are consumers: ex Venus FlytrapThe Venus Flytrap plant, unlike most plants, actively

seeks insects, not to pollinate, but to feed on! You see, Venus Flytrap plants grow in soils that are poor in nutrients. And Venus Flytraps catch insects and digest them for the nutrients that they cannot get from soil. Venus Flytrap plants do not eat meat. (Don’t feed them hamburger!)

Venus Flytrap plants catch and digest insects. Venus Flytrap plants even catch and digest small frogs.

Each trap is only good for 4 to 6 catches. After that, the trap withers, turns brown, and falls off.

What do plants need?

Plants need temperatures above freezing while they are actively growing and photosynthesizing.

They need sunlight, carbon dioxide, and water for photosynthesis.

Plants need oxygen for cellular respiration and minerals to build proteins and other organic molecules.

Most plants need roots to grow down into the soil to absorb water and nutrients.

The importance of plants.

Read and highlight this part on page 268.

Weeds are plants that grow where people do not want them, such as gardens and lawns.

When people introduce new plants to an area or habitat and that plant does not have natural predators or parasites it called invasive.

The introduced plants may spread rapidly and drive out the native plants.

Vascular and Non-vascular plants

Nonvascular Plants examples: Green Algae, Mosses, liverworts and hornworts. Called bryophytes.

Vascular Plants are seed and non-seed plants.Seed: Conifers and Flowering plantsNon Seed: Ferns

Non Vascular Plants

Mosses are non-vascular plants that do not have flowers or seeds.

These simple plants typically grow in damp areas such as forests or wetlands. 

You may have seen large patches of moss growing on a tree or rock or even on the forest floor.

While we may think of mosses as small, forgettable plants, they actually serve several vital roles.

For example, peat moss can be used as a fuel, carbon sink, and habitat for many unique organisms.

You may also see moss used in flower arrangements or hanging flower baskets.

Mosses are also useful to many ecosystems because they can survive in very high or low temperatures and can even help make soil.

As for the life cycle of these plants, mosses are unique because they spend most of their lives with only one set of genetic material rather than the normal two sets.

This would be like living the majority of your life cycle with only half of your genetic information.

Unlike more advanced plants, mosses have a dominant haploid stage.

Moss gametophytes are generally either male or female.

Male gametophytes contain antheridia, which produce and release the male gamete - sperm.

Female gametophytes contain archegonia, which produce the female gamete – eggs..

This newly formed diploid sporophyte will grow within the archegonia, eventually developing a foot that attaches to the gametophyte, a stalk, and a capsule that contains sporangium. 

Sporocytes within the sporangium undergo meiosis in order to create spores that are released to continue this alternation of generations.

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Seedless Vascular Plants

Ferns are able to reproduce without using seeds.

Ferns are seedless vascular plants. Ferns were the first type of vascular plant

and are generally considered to be simpler than vascular plants that make seeds.

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Introduction To Gymnosperms

Gymnosperms are vascular plants that produce seeds but not flowers.

These plants are more advanced than ferns but not quite as complicated as flowering plants.

Common examples of gymnosperms include ginkgos and pine trees.

These all produce seeds but do not make flowers.

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Flowering Vascular plants

Angiosperms (flowering plants) have two alternative life cycles because they undergo sexual and asexual reproduction.

Asexual reproduction creates a clone of the original plant.

The advantage to asexual reproduction is that an individual plant can propagate the species.

Sexual reproduction creates genetic diversity.

The seeds produced by sexual reproduction can also help distribute plants to far away areas.

Thus, there are two advantages to sexual reproduction. The next slide Figure 1 shows the angiosperm life cycle.

Meristems

The growing tip of a plant is called the meristem.

You can see this at the tip of a branch, and it is where new leaves form.

Angiosperms shift between a vegetative growth phase (no flowers) and a reproductive growth phase (flowers).

Diploid vs. Haploid

Like most other higher organisms, plants are diploid. This means that they have two copies of each gene in their nucleus.

Once copy comes from each parent, which is how we get genetic diversity.

Each parent is genetically different, thus the combination of their genetic material (DNA) creates a new variation.

Sperm and egg cells (gametes or gametophytes) are haploid.

This means that they have half of the genetic material of a diploid cell.

Sexual reproduction requires that the diploid organism halves its DNA.

If it did not, then the offspring would inherit all of each parent's genetic material.

They would have twice as much DNA as necessary.

So, developing gametes undergo two stages of cell division, mitosis (cell division with DNA replication) and meiosis (cell division without DNA replication).

The resulting mature gamete is haploid.

The Angiosperm Sexual Reproduction Organ: The Flower

When you look at a flowering plant, the part you can see is called a sporophyte.

The flower contains the male and/or female gametophytes.

Flowers are actually modified leaves. Each flower contains four different types of

modified leaves: carpels, petals, stamens, and sepals.

The Female Gametophyte

The carpel is the female sex organ. Female gametophytes develop within the carpel.

The carpel (megametophyte) is comprised of a stigma, style, ovary, and ovule.

The megaspores (egg cells or female gametophytes) reside within the ovule (macrospore).

An individual macrospore will undergo meiosis twice to produce four haploid macrospores.

The Male Gametophyte

Male gametophytes are called microspores. They develop within the male sex organ

(anther). They also undergo two rounds of meiosis to

produce four haploid cells. However, all four haploid cells will develop

into pollen grains (microgametophytes).

Fertilization

Pollen grains are released from the anther and travel to the stigma.

Once bound to the stigma, the tube cell forms a pollen tube which delivers the sperm to the egg.

Only one sperm nucleus fuses with the egg. An embryo then begins to develop within the

ovary. The ovary becomes a seed. If the angiosperm

develops fruit, then the ovary wall thickens and creates the edible portion of the fruit.

Germination, Growth, And Asexual Reproduction

A seed develops into a seedling upon germination.

The seedling will develop into a fully mature diploid organism.

The adult organism can reproduce sexually, as described above.

It can also reproduce asexually.This involves sending out a runner (as with

strawberries), which can travel some distance from the parent plant.

A seedling develops where the runner makes contact with the soil.

The seedling is a clone of the parent since there was no introduction of DNA from another plant.

The seedling and runner cells are also diploid.

Angiosperms (flowering plants) have two alternative life cycles because they can reproduce sexually or asexually. Sexual reproduction creates haploid gametes, which allows for genetic diversity. It also allows for seed dispersal far from the parent plant.

Either sexual or asexual reproduction will complete the life cycle of an angiosperm.

Summary video: http://education-portal.com/academy/lesson/an-angiosperm-life-cycle-flowering-plant-reproduction.html#lesson

An Angiosperm Life Cycle: Flowering Plant Reproduction approx. 6:19

Tropisms: Phototropic, Geotropic and Thigmotropic Plant Growth

In plants, the response to a stimulus is known as a tropism.

This plant movement toward or away from a stimulus can come in many forms.

Like many words in science, tropism comes from a Greek word. Tropos means 'to turn'.

Therefore, a tropism is a turn towards or away from a stimulus.

Phototropism

Phototropism is generally the tropism that makes the most sense.

We know that plants grow towards the sun, so they can make food through photosynthesis.

This movement in response to sunlight is called phototropism.

Geotropism

Geo many sound familiar because of words such as 'geography' and 'geology.' Geo means earth; therefore, geotropism is movement towards or away from the earth.

Examples of geotropism include the downward growth of roots and the upward growth of shoots.

Roots have specialized cells that sense gravity and therefore have a positive tropism by growing toward the pull of gravity.

Opposite of this is the growth of the shoot, which is the aboveground portion of the plant.

The shoot exhibits negative geotropism by growing away from the earth.

You can see these growth patterns with lateral roots and branches: lateral roots will curve down, while lateral branches will curve up.

Thigmatropism

Thigma means 'touch' and again, tropos means 'to turn.'

Therefore, thigmatropism is the movement towards or away from touch.

Plants can be affected by touch both positively and negatively.

We can also see a response to touch in vines and other climbing plants.

Seasonal Growth Cycles: Perennial, Annual and Biennial Plants

Seasonal growth cycles can be influenced by several factors, including temperature, amount of water and amount of daylight.

Plants regulate their developmental processes depending on these factors.

Seasonal growth cycles are determined by where plants live, how they reproduce and the role they play in their environments.

Many common garden plants only grow for one season and then need to be replanted the next. These plants are called annuals.

Biennials are plants whose entire life cycle occurs within two years. In the first year, these plants are only vegetative, meaning that they don't produce reproductive structures.

Some plants do not die every year or every other year.

These are commonly trees and shrubs. These perennials persist for many growing

seasons. Perennial plants must have structures that

allow for them to survive through different seasons.

Perennials can be broken into two main categories: woody and herbaceous.

Classification of Vascular, Nonvascular, Monocot & Dicot Plants

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Ground TissueThe shoot system includes the aboveground

structures of plants. That means it includes the leaves, buds, stems, flowers and fruits of plants.

The plant stem is best identified as the part of the plant above ground that provides support for other structures.

Some of these other structures include leaves and flowers. Within the stem, there are several types of tissue.

The meristem is the tissue of the stem capable of cell division.

Plants also need something to protect their inner structures from outside elements. On the stem, this is the epidermis, which contains wax-coated cells for protection.

Previously, the concept of vascular tissue was addressed.

Remember that vascular tissue is the tissue used to transport water and nutrients throughout a plant.

It acts like roads and plumbing, moving around nutrients and water needed by the plant.

There are two types of vascular tissue: xylem and phloem.

Xylem transports water and dissolved minerals, while phloem transports food.

Previously it was pointed out that an easy way to remember which vascular tissue is which is that 'phloem' and 'food' both start with the same sound.

This may help you remember that phloem moves food and that the other tissue, xylem, moves water.

Root System

Roots serve many purposes for plants, including the storage of food and the intake of water.

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