Bio Tutorial 31 Q/a

Front 1

How old do we estimate the plant kingdom to be?

Back 1

Fossil plant remains that clearly show features of true plants date back to 475 million years ago. Because it can take millions of years for evolutionary changes to become established, and because it is more rare than common for fossilization to occur, scientists estimate that the earliest plants began to evolve prior to the first evidence of plants in the fossil record. Some evidence indicates that land plants appeared 700 million years ago.

Front 2

What groups of algae are most closely related to the plant kingdom?

Back 2

Modern land plants have much in common with the group of green algae called charophytes, and charophytes are the closest relatives of the plant kingdom. It is thought that the first true plants were derived from a charophyte. This means that the ancestor species of all modern plants was actually a green algae living in an aquatic environment.

Front 3

List all the common characteristics shared between plants and green algae. What has DNA analysis shown about the similarities and closeness of the two?

Back 3

Chlorophyll a is common to other photosynthetic organisms, but chlorophyll b is shared only by green algae and plants. Characters such as a cell wall composed primarily of cellulose, storage of carbon in the form of starch, and formation of a cell plate at cytokinesis are not limited to green algae and plants; however, these shared characters provide further evidence of their relatedness. Molecular evolutionary analyses of RNA and DNA sequence data from green algae and plants also clearly place these two groups closely together.

Front 4

What are the main distinguishing characteristics between plants and algae?

Back 4

The features that distinguish members of the plant kingdom from charophytes are their adaptations to a terrestrial environment

Front 5

Describe the particular environments which would have fostered the evolution of plants from green algae.

Back 5

Plants evolved from green algae during a time when the Earth's climate was changing. Likely, those areas where plants evolved was subject to periods of saturation and periods of drying, and characteristics that enabled some species to better survive during the dry periods evolved slowly. Adaptation to the drier conditions eventually enabled early plants to colonize the land.

Front 6

What advantages did a terrestrial environment give photosynthetic organisms?

Back 6

Photosynthetic organisms growing on land receive the full amount of light energy radiated from the sun, unlike those underwater. Photons emitted from the sun can directly strike light absorbing surfaces and the full range of useful wavelengths are available for photosynthesis. Secondly, a terrestrial environment provided a less competitive environment—because sunlight is abundant on land, there was no competition for access to light when early plants colonized land.

Front 7

What challenges did early plants encounter as a result of moving to a terrestrial environment?

Back 7

The major challenge for early plants first migrating onto land was the lack of water. The ancestors of early plants were highly dependent on water, not only to maintain their moisture content, but also for structural support. The buoyancy of water supports upright growth of giant marine seaweeds (e.g., kelp). Consider the seaweeds that can often be found washed up on the beach. Although these algae are no longer alive, when held beneath the water their upright form is restored. In a terrestrial environment, the surrounding media is air rather than water. Air does not provide any support for upright growth.

Front 8

List the adaptations which allowed early plants to survive on land.

Back 8

These adaptive features include: cuticles, stomata, vascular tissue, gametangia, and seeds.

Front 9

Why do plants have stomata?

Back 9

Stomata are also an important adaptive feature to the terrestrial environment. Because the cuticle is impermeable, it is necessary for plants to have pores through which gasses can be exchanged with the environment. Carbon dioxide is required for photosynthesis, and oxygen is produced during this process. These gasses enter and exit the plant through the stomata.

Front 10

Discuss the major advantages to terrestrial plants of having vascular tissue. Explain how vascular tissue allowed plants to survive on land.

Back 10

Specialized cells of vascular tissue allow transport of water and nutrients throughout the plant. This adaptation enables water, absorbed by the roots of the plant, to reach the stem and leaves, and the sugars from photosynthesis, produced in the shoots, to be transported to the roots. Plants with vasculature are less dependent on a very moist environment to maintain hydration throughout the plant.

Secondly, cells of the vascular tissue have secondarily reinforced cell walls that make the tissue rigid. The vascular tissue that runs throughout the plant body, circulating water and nutrients, also forms a "skeleton" that strengthens the roots, shoots, and leaves. Vascular tissue enables plants to grow upright (some to very great heights), while maintaining moisture levels in all parts of the plant.

Front 11

How do most aquatic algae reproduce? What do they rely on to transport their gametes?

Back 11

In the charophyte ancestor of modern plants, processes such as gamete production, fertilization, and development of the embryo were highly dependent on the aquatic environment. Gametes were dispersed by water currents and were maintained in a hydrated state until fertilization occurred. The zygote and growing embryo developed free from the parent organism because there was no threat of desiccation.

Front 12

How did land plants evolve to be able to reproduce without the help of water? What special structure was developed?

Back 12

The major adaptation of plants to the terrestrial environment (with respect to reproduction) was the production of gametes and the development of embryos within gametangia. The female gametangium produces egg cells and the male gametangium produces sperm. A protective chamber, formed by a single layer of sterile cells, prevents the gametes from drying out by reducing or eliminating their exposure to air. Egg cells are maintained in the female gametangium, but the sperm must leave the male gametangium for fertilization to occur.

Front 13

How has the process of fertilization and reproduction evolved and changed in plants? Are there still plants that use water? Why?

Back 13

Some groups of modern plants have retained the primitive characteristic of flagellated sperm and still are dependent on water for dispersal of male gametes; however, the majority of modern plants do not have motile sperm and have developed non-water-based methods of dispersal (e.g., wind and insect pollination). In all plants, fertilization occurs within the female gametangium, where the zygote begins to develop into the embryo.

Front 14

Explain why plants are referred to as embryophytes. Why do they require this protection?

Back 14

ecause all plants retain the developing embryo within the gametangium, they are referred to as embryophytes. Protection of the growing embryo is especially important in the terrestrial environment because the waxy cuticle, stomata, and vascular tissue present in mature plants are not well developed in the embryonic plant.

Front 15

How are the ways of protecting embryos different in different plant lineages? What is the most primitive way? In what ways has this been advanced and what advantages do these advancements have?

Back 15

The most primitive group of plants retains the developing embryo through sexual maturity. The diploid embryo is completely dependent on the haploid gametophyte generation. This life cycle is typical of the non-vascular plants. The more derived plant lineages have further adapted to the terrestrial environment by producing specialized structures for protection and nutrition of the developing embryo. The embryo is enclosed in a seed, which is dispersed from the parent plant long before the embryo reaches maturity. In the derived plant lineages, the haploid gametophyte is greatly reduced because it no longer plays a dominant role in protecting the embryo; in these groups of plants, the haploid gametophyte has become completely dependent on the diploid generation.

Front 16

Why are seeds an adaptive advantage?

Back 16

Seeds are a highly successful adaptation to the variable environmental conditions on land. Independent of the parent plant, the seed-enclosed embryo can withstand drying and temperature fluctuations, even the digestive tract of some animals, until conditions are suitable for germination and growth of the embryo to maturity. Seed production enabled plants to reproduce more successfully, because the embryos had a much better chance of surviving the dry terrestrial environment than did the embryos of more primitive plants that were still dependent on the parent plant body.

Front 17

Why are flowering plants considered to be the most “advanced” plants? What techniques have they developed to protect and disperse offspring?

Back 17

Flowering plants produce their seeds within a fruit that provides a functional "packaging" around the seed(s). The fruit can be edible, such that the digested seeds are then deposited with the feces of the animal that consumed the fruit. Other fruits are designed for transport on air currents, water currents, or on the fur of different animals. Fruit production by flowering plants is a more specialized adaptation to life on land, because it reflects not only the environment, but also the other life forms that exist there.

Front 18

Explain the basis on which plants are classified.

Back 18

The relationships indicated by the branching pattern of the phylogenetic tree reflect the current character states and the evolutionary history of these groups of plants. The base of each of the plant lineages is defined by a significant adaptation to life on land (e.g., the development of vascular tissue, production of seeds, and flowering). As mentioned earlier, there are many more specialized adaptations to the terrestrial environment found among modern plants; however, these adaptations are found in only a small group of plants. The major adaptations that define each lineage are characteristic of hundreds and thousands of species of plants. The ancestral forms of these plants and those in which the adaptive features first evolved are no longer living, but their remains are present in the fossil record and provide a basis for dating the origin of each lineage. Continuous adaptations to an ever-changing environment over the history of plant life has led to the diversity of species currently in existence.

Front 19

Draw a phylogenetic tree, and explain the traits that differ between each of the lineages.

Back 19

Draw a phylogenetic tree, and explain the traits that differ between each of the lineages.

Front 20

What are the four major lineages of plants? Give a description of each, and name some examples. State the major adaptation and the common structures and characteristics.

Back 20

(1) non-vascular plants, (2) seedless vascular plants (3) non-flowering seed plants, and (4) flowering seed plants

Non-vascular plants do not have vascular tissue (or if present it is very reduced). Because they lack substantial vasculature, plants in this lineage are generally small in size, lack significant structural support, grow close to the ground in moist areas, and lack significant water-conducting cells. Plants first evolved in environments that were transitional between the land and the sea, and although modern non-vascular plants are dependent on water to complete their life cycle, they are able to withstand long periods of desiccation. Non-vascular plants include mosses, liverworts, and hornworts.

Seedless vascular plants have a waxy cuticle, stomata, and well-developed vascular tissue. Their vasculature allows them to grow to larger sizes than the non-vascular plants, but they still generally occupy moist habitats. This lineage is more highly derived from the common ancestor of all plants than are the non-vascular plants; however, they do not produce seeds. Although the developing diploid embryo is dependent on the haploid gametophyte for survival (like mosses), the diploid sporophyte is more conspicuous and is the prominent generation of seedless vascular plants. Phylogenetically, seedless vascular plants are basal to the seed plants. The seedless vascular plants include species such as ferns and horsetails.

Vascular plants without flowers are also known as gymnosperms, which means "naked seed" and refers to the lack of flowers and fruits in all members of this lineage, as compared to the more highly derived lineage with flowers. The ancestor of modern non-flowering seed plants evolved once plants were already well established on land. Adaptations of a well-developed vasculature and seeds indicate a strictly land-based existence. With the production of seeds, the gametophyte generation is highly reduced in this lineage and the sporophyte generation is most prominent. Non-flowering seed plants include conifers (e.g., pine, hemlock, spruce, and fir trees) and cycads.

Flowering vascular plants are also known as angiosperms. Although this group of plants evolved more recently than non-vascular plants, seedless vascular plants, and non-flowering seed plants, it includes the greatest number of species currently in existence. The great success of this group is due to their highly evolved and specialized methods for gamete dispersal (many species have insect or other animal pollinators) and seed dispersal (various types of fruits aid in the dispersal and successful germination of their seeds). The adaptations found in this taxonomic group are linked to the great diversity of animal life existing in the terrestrial environment. All of the agricultural crops we depend on for food, the fiber plants we depend on for clothing, and the plants we grow to beautify our surroundings are from this lineage.

Front 21

Explain the reproductive process mosses undergo. How does their environment allow them to survive?

Back 21

Mosses require a moist environment for successful fertilization. They do not produce pollen grains; hence, this group of plants has retained the primitive condition of a flagellated sperm. The male gametes are motile in water and must be released into a moist environment so that the sperm can swim to the female gametangium where the egg cells are located.

Front 22

Outline the alternation of generations observed in moss. Draw this process out and include all the proper terminology. It is important to be able to distinguish the different forms and know the ploidy state of each.

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Back 22

Outline the alternation of generations observed in moss. Draw this process out and include all the proper terminology. It is important to be able to distinguish the different forms and know the ploidy state of each.

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Front 23

What is the dominant form of the moss life cycle? What is the ploidy number?

Back 23

The prominent form of the moss is the gametophyte, which is haploid (1n).

Front 24

What adaptations have mosses developed to streamline the process of reproduction and ensure its successfulness?

Back 24

An important feature of the moss life cycle is that the developing embryo is retained on the gametophyte plant body. This is an adaptation to the terrestrial environment, because the embryo is protected from desiccation throughout its development into the sporophyte.