Week 3

Vascular Plant

Plants with conducting tissue which allows for movement of water and nutrients between and through the root and stem system.

Two Main Vascular Tissues

Xylem and Phloem.

Xylem

Function is to transport water and dissolved minerals from the going to upper part of the and to provide mechanical support for the plant.

Phloem

Function is to transport sugar from areas where it is stored or produced to areas where it is used.

Flowering Plants

Angiosperms have a flower as their reproductive structure. They can be divided into 2 groups: Monocotyledon (monocot) and Dicotyledon (dicot).

Monocotyledon (Monocot)

The flowering plants whose seeds have only one see leaf or cotyledon. Seed will not split into two halves when the seed coat is removed. Eg. Corn.

Dicotyledon (Eudicot)

Flowering plants whose seeds have 2 seed leaves or cotyledons. If you pull the seed coat off the surface the 'seed' falls into 2 halves. Eg. Peas, Beans.

Tissue

Group of cells that are similar in structure and function.

Root System

The subterranean part of the plant. It has several functions which it is structurally adapted for. Tiny, one-celled extensions (root hairs) function to absorb water and minerals from soil. Other functions: to conduct water and minerals, to store food that is produced above ground by photosynthesis and to anchor the plant to the ground.

Shoot System

The aerial part of the plant. Consists of stems, leaves and reproductive structures (ie. the flower). Three major functions: photosynthesis, transport of water and nutrients, and reproduction.

Node

Place on stem where the leaf attaches.

Internode

The region between successive nodes.

Leaf

In a typical flowering plant this structure consists of a flattened blade that is attached either directly to the stem or by way of a leaf stem called a petiole. In the blade the vascular tissue is evident by the 'venation' of the leaf.

Axillary Buds

Found in the angle between a leaf (or petiold) and a stem, and produce lateral branches.

Terminal Buds

Found at the Tips of Stems.

Meristematic Tissue

In the buds of the shoot system and at the tip of the roots in the root system this tissue is found. It consists of cells that are constantly dividing.

Apical Meristem

Meristematic tissue located at the tips of stems (in buds) and roots. Results in the elongation of the structure.

Primary Growth

The elongation of the structure. Addition of cells to the 'tips' of the root, lateral branch, main stem etc. Via meristematic tissue.

Primary Cell Wall

All plants have this, which is made up of material produced and secreted by the cell. It is thin and stretches easily as the cell grows. It protects the cell and helps maintain it's shape. Cellulose, a long chain-like carbohydrate, is a major component of this.

Secondary Cell Wall

Some plant cells produce this when they mature. It is only secreted after the primary cell wall, and lies between the primary wall and the plasma membrane. It contains even more cellulose than does the primary wall and also contains lignin for strength and rigidity. Next to cellulose lignin is the most abundant, large organic molecule in plants.

Middle Lamella

Between the walls of adjacent cells is this thin layer of sticky substances called pectins, that glue the cells together.

Epidermis

The outer covering around the entire plant. This covering can be made up of one or more layers of cells. It can be specialized for organs such as leaves and stems ball all of these cells perform a similar function; protection from physical damage as well as pathogens. The leaf covering is specialized in secreting a non-cellular waxy cuticle overlaying the cells to prevent water loss.

Parenchyma Cells

Living cells, with thin, stretchy primary cell cell walls. They carry out functions such as photosynthesis and storage of food.

Collenchyma Cells

Living cells, lacking secondary cell walls but their primary cell walls are irregularly thickened at the corners to give additional strength while still remaining stretchy to allow for growth. They are often arranged in supportive columns in young, growing stems.

Sclerenchyma Cells

The most common form of these cells consist of long, slender cells with tapered ends. These cells, also known as fibres, are usually dead at maturity and have thick, lignified secondary cell walls. They provide support in plant parts that are no longer growing.

Xylem

Consists of tracheids and vessel elements which are both water conducting cells. they are dead and hollow at maturity and have secondary walls. For both cells, the lignified walls provide support to the plant.

Tracheids

Long, tapered cells similar to the fibers of sclerenchyma. Water passes from one cell to the next through pits that penetrate the cell walls. These cells make up part of the xylem.

Vessel Elements

More efficient than their counter-part tissues in conducting water because they have a larger diameter and, at maturity, the end walls between adjacent cells have disintegrated. These cells make up part of the xylem.

Sieve-Tube Members

The conducting cells of the phloem, function mainly to transport sugars and other organic materials. They are alive at maturity and have only primary cell walls. They are quite similar to parenchyma, but LACK a nucleus and certain other organelles.

Cambium Cells

Meristematic cells that are capable of dividing to produce new specialized cells (eg. xylem and phloem), allowing the plant stem to grow in diameter. These cells appear 'brick-shaped'. They are alive and have a thin primary cell wall.

Plan Drawing

Outline particular regions, or tissues of the plant organ.

Vascular Bundle

Contains sclerenchyma, phloem cambium and xylem on the inside.

Secondary Growth

Growth by vascular cambium tissue.

Plants

Multicellular eukaryotes that are photosynthetic autotrophs.

4 Major Events in Plant Evolution

1. Movement onto land. 2. Evolution of vascular plants. 3. Evolution of seed plants. 4. Evolution of the angiosperms.

Plant Movement onto Land

Problems faced by the first plants on land was desiccation or Drying out. The evolutionary responses to this included 1. Production of a waxy water-proof cuticle covering the above-ground parts of the plant body. 2. Development of pores in the cuticle for gas exchange. 3. Development of a protective, water-resistant jacket of cells around embryos.

Evolution of Vascular Plants

Plant with tissues specialized for transport. There are 2 vascular (transport) tissues: xylem, which transports water and minerals and phloem which transports sugars and other organic materials.

Evolution of Seed Plants

Represented by two major groups. The gymnosperms (such as conifers) and the angiosperms (flowering plants) Seeds not only protect plant embryos from desiccation and other dangers, but also contain a supply of food.

Evolution of Angiosperms

Evolution of flowers and fruits. Some of the flowering plants rely on the wind to carry pollen or have seeds in cones eg. Gymnosperms. While some attract animals as pollinating agents. Seeds enclosed in fruits. Eg. Angiosperms.

Non Vascular Plants

1. No True* roots, stems, leaves. 2. No vascular tissue. 3. Usually not more than a few cm tall. 4. Lack of vascular tissue restricts to moist environment.

Vascular Plants

1. Roots, stems and leaves present. 2. Vascular tissue. 3. More than a few cm tall. 4. Wide range of habitats.

Mosses

Nonvascular plants, xylem and phloem absent. Have an upright posture with stem-like and leaf-like structures and are anchored to the ground by root-like structures called rhizoids. Most common in wet habitats but also in tundra ecosystems.

Liverworts

Nonvascular plants, lacking xylem and phloem. Have a simple body that is flattened to the ground and lack stem-like and leaf like structures. However, sometimes confused with their counterpart of non-vascular plants.

Seedless Plants

Produce spores as single-celled reproductive units. Four main groups of this type of plant: Ferns, horsetails, club mosses and whisk ferns.

Ferns

Have large flattened leaves that are divided into leaflets. This characteristic is used to distinguish these plants from the other seedless plant groups. In many of these plants, spores, the single-celled reproductive units that are carried away by the wind, are produced on the underside of the leaves. In addition to spores, these plants also produce flagellated sperm for reproduction. Like mosses and liverworts these plants are most common in moist habitats.

Gymnosperms

About 700 species (mostly conifers). Nearly all species woody. Usually needle-like or scale-like leaves. Naked seeds. Pollen transport by wind.

Angiosperms

Nearly 250 thousand species. Both woody and non-woody (herbaceous) species. Usually flattened leaves ('broad-leaved' plants). Seeds enclosed in fruit. Pollen transport by wind in some species (eg. grasses), by animals in many others.

Monocots

Within angiosperms, these make up about 70 thousand of the species. Their leaves have parallel veins, flower parts are in multiples of 3's, vascular bundles are scattered in the stem and lack vascular cambium, the root system is fibrous and lacks a main axis and the seed has a single cotyledon (seed leaf). Common Egs. Grasses, bamboos, corn, wheat, barley, palms, lilies, irises, orchids, tulips and daffodils.

Eudicots

Within angiosperms, these make up about 200 thousand of the species. Their leaves have netted veins, flower parts are in multiples of 4's and 5's, vascular bundles are usually in a ring in the stem and contain vascular cambium, have a taproot system with a main axis and the seed has to cotyledons. Common Egs. Most trees, shrucs, small non-woody species like peas, roses and sunflowers.

Adaptations of Land Plants to Terrestrial Environments

Problem 1. Obtaining water and mineral nutrients when they no longer surround the entire plant. Adaptation- Roots. P2. Transporting water within the plant A-Xylem. P3. Transporting food from sites of manufacture to sites of use. A-Phloem. P4. Preventing evaporation from surfaces exposed to air A-Cuticle. P5. Obtaining gases for photosynthesis and respiration. A-Stomata. P6. Obtaining sunlight for photosynthesis A-Leaves. P7. Supporting body in medium lacking buoyancy. A-Xylem. P8. Coordinating plant growth and plant response to changes in environment. A-Hormones. P9. Getting gametes together without reliable supply of water for sperm. A-Pollen. P10 Dispersing new individuals to suitable locations. A-Airbourne spores, then seeds.

Adaptations that Land Plants have Evolved as a Result of a Requirement For Light.

Bipolar Habit and Mechanical Support.

Bipolar Habit

Adaptive response to the two directional distribution of essential resources.

Mechanical Support

Problem with aerial mass against gravity- this adaptation allows the development of specialized cells and tissues, as well as patterns of growth and behavior in response to the problem.

Secondary Growth For Mechanical Support

The cells of cambium divide to produce new cells and form secondary xylem toward the inside and secondary phloem towards the outside. Evident in sapwood and hardwood- conifers, apple trees etc.

Adaptations Evolved by Terrestrial plants as a Result of the Competition for Light.

Stratification, extreme height, shade tolerance, epiphyty, climbing, ability to colonize disturbed habitats.

Stratification

Layering produced when each species of tree achieves a characteristic height. All members of species occupy 1 of the 2 strata by growing to, and maturing at, a specific height. Each species of trees contributes to vertical separation, into discreet layers within the system.

Extreme Height

Photosynthetic trees with this adaptation have a great advantage as their is no shading.

Shade Tolerance

The ability to grow and reproduce in dim light. The understory layer, ground level of species don't compete for light and have this adaptation. They are vascular and non woody plants as well as non vascular mosses and liverworts.

Epiphyty

A plant that attaches itself to a tree therefore gaining the advantage of height without having to do the work of producing height. Eg. orchids and ferns do this.

Climbing

Method of reaching for light. Adaptations include: tendrils (eg found in garden peas), twining stems (eg found in runner beans), adventitious roots (english ivy), spines/thorns (blackberries and roses).

Colonizing of bare land

Disturbed habitats (tree falls=exposed light)- plants with this adaptation are shade intolerant and arrive as wind-blown seeds, they grow rapidly and reproduce before being "shaded-out".