Science 226

Lab 4: Plant & Animal diversity

 

The purpose of lab this week is to get an idea of the different important kinds of plants and animals that are commonly encountered in the world. Young people have an enormous interest in the living world, and wish to understand this fantastic variation all around them. This yearning has been suggested to be a fundamental feature of human development and has been described as such by E.O.Wilson in his biophilia hypothesis. Appreciation of Wilson’s Biophilia hypothesis can give you, as a teacher, a valuable insight into why conservation of earth’s biodiversity is such an important activity, and why your students have such an innate interest in different living things.

An overview of the classification of life: the five kingdoms. Classically, living things have been organized into 5 great groups or kingdoms. A kingdom includes a great number of different organisms, all with certain basic features in common. There have been several attempts to organize life into different numbers of kingdoms over the years. Actually the 5 kingdom scheme will soon be replaced by an 8 kingdom grouping. But for know lets settle on the 5 kingdoms. In terms of our daily encounters with life, we most commonly see members of 2 kingdoms: Animalia and Plantae

 

Plants

Plants are the most conspicuous form of life on earth. Variation in the types of plants, their density and distribution can be easily seen from outer space, and have much to do with the apparent colors of terrestrial surfaces. In general, plant can be defined as multicellular, photosynthetic organisms that have evolved adaptations (more or less) for life on land. This “life on land” part of the definition is important, because there are very large, multicellular, photosynthetic organisms only found in aquatic environments (the algae) that are not “plants” in the true sense of the word. Foremost among the adaptations to life on land found in plants, is a structure associated with reproduction termed an archegonium. The archegonium serves 2 functions: it produces an egg (later fertilized by a sperm), and serves to protect and support the young embryonic plant that develops from the fertilized egg. No algae have this “mothering” capacity as found in true plants, a capacity that helps get the young plant started in potentially hostile terrestrial environments.

Although all plants have archegonia, they differ in other adaptations to life on land. The other important adaptations to life on land include things like roots, internal conducting cells (a vascular system for moving water and nutrients from one part of the plant to another), seeds, flowers and fruits. The most simple of the plants, the bryophytes, lack most adaptation for life on land except for the archegonium, while the other three groups of plants show increasing adaptation for life on land, with the angiosperms being the most successful.

In today’s lab you will learn to recognize representatives of each of the four main groups of plants. Remember: you can find plants just about anywhere, they stay put, and so they are excellent choices for teaching about nature and cultivating observational skills in your students.

Main groups of plants. As indicated in the above diagram there are four main groups of plants: bryophytes, seedless vascular, gymnosperms and angiosperms. The charophytes (regarded as algae, Kingdom Protista) are shown only because they are the presumed ancestors of true plants.

Bryophytes (mosses)

The simplest of plants, mosses can be found growing in many unexpected places like the roof of a house, a rock wall, a tree truck, etc. Mosses grow also on soil and forest litter. They get all their water and nutrients through the leaf surfaces (not through roots) so they do fine on sites where there isn’t any soil. When they reproduce, they produce spores in tiny structures called sporangia. The sporangia (capsule) is typically attached to the end of a long filament called a seta. The capsule + seta represents a stage in the life cycle of a moss termed the sporophyte. The spores are easily carried by the wind, and if they land in the right place, will grow into a new moss plant. What we usually recognize as a moss is only part of the organism. This little green plant is sometimes termed the gametophyte stage in the life cycle, because it is responsible for producing gametes (sperm and egg). Water must be present for the sperm to swim to the egg (this is true also for the seedless vascular plants, but not the gymnosperms and angiosperms). The sperm and egg produced by the gametophyte fuse to form the sporophyte. Sporophytes growing from gametophytes are clearly seen in the above photograph as the cylinder-shaped structures at the ends of fine stalks. In bryophytes the gametophyte stage is said to be dominant in the life cycle, in the sense that it is the more obvious, larger and commonly encountered stage; this is not so for the other groups of plants as we’ll see.

Because mosses don’t have roots and depend on the atmosphere directly for water, they face the problem of occasionally drying out. But amazingly, mosses can recover (i.e., they can begin to photosynthesize and grow) after very long periods of being completely dry when they become wet again. This is something that the “vascular” plants have lost the ability to do, because they have become dependent on the water supplied by roots.

The moss gametophyte

Leaves. Moss leaves are always very tiny and usually arranged in a spiral fashion on stem. Prepare

a wet mount of some leaves of the mosses in lab (scrape them off of stem with scalpel) and view

with the compound scope. Note the leaves are very thin, so no cell is ever far from water when rain

hits the leaf. The mosses in lab may have leaves that terminate in a clear tip termed an awn; the awn

helps absorb water. Remember that leaves are found on the stage in the moss life cycle termed the

gametophyte.

The moss sporophyte

As introduced above, the sporophyte of a moss produces spores, which can blow away on the wind

and grow into new moss plants. The internal region of the capsule is where the spores are made.

The photograph below shows moss sporophytes.

Examine moss sporophytes with the compound scope. With a scalpel, make a longitudinal

slice through the capsule and locate the spores. Also examine prepared slides of moss capsules.

Study the life cycle of a moss in the below diagram as well as in posters in class. There are

numerous other terms in the below diagram that you are not responsible for learning. However, note

the relationship of the sporophyte and gametophyte stages. In nature, sporophytes are usually

produced in the fall or spring.

Seedless vascular plants (ferns and related forms)

These are relatively primitive plants, but they have certain advantages over the mosses when it comes to life on land. This is primarily an internal vascular system of tubes for water transport from the soil throughout the plant. As the name of the group implies however, they have not figured out how to make seeds, a further adaptation to life on land. The seedless vascular plants are found throughout the world, but they are rarely abundant. In the past however (especially during the Carboniferous period of the Paleozoic era), they formed the major forests of the world, forests that ultimately became the coal deposits we use today. Ferns and other seedless vascular plants left very good fossils, that we will study in later labs.

In lab today we will study features of two common types of living seedless vascular plants: ferns and horsetails.

Ferns

Ferns are the most successful and widespread of the seedless vascular plants; there are more than 10,000 species living today, largely tropical. They are characterized by a dominant sporophyte stage with large, often divided leaves (the small leaflets are termed pinnae). What you see of the plant when growing in the forest or a pot is mainly the divided leaves, as the stems and branches are normally underground.

fern sporophyte

Study the ferns on display in lab, noting leaves and pinnae. Since what you are looking at represents the sporophyte stage in the fern life cycle, they are responsible for spore formation. Look on the undersides of pinnae for small brownish bumps. These are sori: clusters of tiny sporangia similar to the single capsule+filament of a moss. Remove a leaflet with sori and study under the dissecting scope. Note that each sorus is covered by a little lid (termed an indusium). On a given plant, sori will be in various stages of development. Refer to the posters in lab to orient you to your specimen. Also refer to the life cycle of a fern and relate to that of a moss. Note that the gametophyte stage (that which grows from a spore) is relatively small and rarely seen in ferns. Thus unlike bryophytes, ferns are said to have a dominant sporophyte stage (as is also true for all other groups of plants except the bryophytes).

fern gametophyte

Examine the preserved specimens of fern gametophytes in lab. The tiny little gametophytes grow on the ground, where they produce sperm and eggs. Sperm fertilize eggs, and a new fern plant (sporophyte) will grow from the gametophyte archegonium. Again, consult posters in lab that outline the life cycle of ferns.

Horsetails

These plants are common but there are only about 15 species living on earth today. They are very common in our area, usually near stream banks. Horsetails are constructed in a very different fashion compared to ferns. Examine the horsetails in lab. They consist of an upright stem with worls of thin, hair-like branches that emerge from distinct positions termed nodes. Horsetails accumulate SiO2 (silica dioxide, the same material comprising quartz crystals) in their cells, giving them a course texture. In the past horsetails were used to clean pots and pans by pioneers, hence they are sometimes called “scouring rushes”. Sporangia are clustered in cone-like structures at the stem tips. The gametophyte stage of a horsetail is even smaller than that of a fern, and they are very hard to find in nature. Refer to the horsetail life cycle posters in lab.

 

The seed forming plants: Gymnosperms & Angiosperms

The remaining two groups of plants make seeds during their life cycles. A seed encloses a tiny, embryonic (partially developed) plant. Seeds were a big break through in the evolution of plants, since they allow the organism to persist during periods unfavorable for growth. For instance many desert plants grow to maturity and make seeds within a very short period of time during spring or winter rains. The adult plant dies, but the seeds wait it out in the soil until rains come again (these are called “annual plants”). Seeds are also very good ways of dispersing plants throughout the world, as they can be transported long distances while protecting the little plant within. Seed plants also have very advanced vascular systems, so they can grow very large, much taller than ferns and other primitive plants.

Like all plants except the bryophytes, the seed bearing plants have a life cycle with sporophyte and gametophyte stages, with the sporophyte being the dominant stage. In the seed bearing plants however, the gametophyte stage is even further reduced than in the seedless vascular plants. The life cycle of seed bearing plants is much more complex than that of the previous groups we have studied. In lab today we will focus only on the seed forming structures of these plants: cones and flowers.

Gymnosperms (mainly conifers; pines, firs, etc)

Gymnosperms are seed bearing plants that produce seeds in structures termed cones or stroboli. A pine cone is good example of a strobilus. To complex things a little, there are male and female cones. Male cones make pollen grains that enclose sperm cells. The pollen grains are blown on the wind and land, with a little luck, at the archegonium of a female cone (each female cone has many archegonia). The sperm emerge from the pollen grain, fertilize the egg within the archegonium, and an embryonic plant begins to develop. Tissues from the female archegonium make the characteristic layers of the seed. Thus a pine cone, with seeds enclosed is the female cone, as shown in the photograph. The male cones of a pine tree are much smaller.

 

The term gymnosperm means “naked seed”. This means that seeds are not themselves enclosed in any special tissue. They simply form on the surface of the appendages comprising the cone (termed scales). In angiosperms the seeds are enclosed in a special tissue called the fruit. Not all fruits are sweet and large like apples and oranges however.

 

Examine male and female pine cones in lab and relate the life cycle of a pine tree to these

structures. Pull off female cone bracts and see if there are any seeds attached. If not you will still be

able to find a slight depression on the upper surface of the bract where the seen formed. For the

male cones, examine with the dissecting scope. Pollen grains form in the delicate little sacs under the

male cone bracts. Because gymnosperms do not make flowers, and consequently do not attract

pollinators, they rely on the wind alone for pollen transfer to female cones. Therefore gymnosperms

make an amazing amount of pollen, with the hope that by chance some will get to female cones. This

is why if you live near a pine tree you’ll find lots of yellowish pollen grains on your car windows or

other local surfaces in the springtime.

Angiosperms

The most successful group of plants are the angiosperms: flowering plants. Angiosperms make seeds, but they also make flowers and fruits. Flowers serve two primary functions: they attract pollinators and they protect the seed within a fruit. Pollinators are usually animals that are attracted to a flower by its color, shape or odor. While visiting a flower, an animal may inadvertently get some pollen on its body, and when visiting another flower the pollen is directly transferred to the female portion of the second flower. Flowers are remarkably varied in design.

Anatomy and function of the angiosperm flower. Following are the main features of angiosperm

flowers. Not all features are found in all flowers, as there has been considerable evolution and

modification of this basic pattern.

Sepals. These are the outermost tissues of the flower; they are what you see of a flower when in the

bud stage, before it opens. Usually the sepals are green in color and photosynthetic. Collectively the

sepals (there may be 3 or more) are termed the calyx.

Petals. These are the usually colored tissues that make flowers attractive to us and other animals.

The petals may be equipped with nectar glands near their base, an attraction and reward for

pollinators. Collectively the petals are termed the corolla.

Stamen. The stamens can be regarded as the male part of the flower. A stamen consists of 2 parts:

filament and anther. The anther is where pollen is made. Pollen grains are tiny male

gametophytes in the life cycle of angiosperms. Pollen grains therefore are important because they are

the source of sperm in the angiosperm life cycle.

Carpel. The carpel is the female part of a flower (not all flowers have male and female parts, but

most do). A carpel consists of three parts: stigma, style and ovary. The stigma is a sticky surface

where pollen grains land and attach. The pollen grain bursts open and sends a sperm cell down

through the style into the ovary. Within the ovary are the eggs = ovules. When fertilized, an egg

becomes the seed. The ovary walls, which surround the eggs/seeds becomes the fruit of the flower.

Thus an apple is really the expanded and enlarged ovary of the apple flower.

Examine the flowers on display in lab

Note variation in flower parts between different kinds of flowers.

Flower dissection.

Working impairs, dissect a fresh flower. Beginning with the calyx, separate the flower parts as listed

and illustrated above. Make longitudinal sections of an anther and the ovary. Note pollen grains

within the anther and ovules within the ovary. Remember it is the ovary, surrounding the ovules/eggs

that will form the fruit.

 

Animals

Most of us think of animals as organisms like mammals, birds, fishes or reptiles. But in fact the kingdom of animals (sometimes called the metazoans) includes not only these very familiar creatures but a host of other organisms as well. The definition of an animal goes this way: a multicellular, eukaryotic organism that is capable of movement (at least at some point of its life cycle) and obtains chemical energy (premanufactured “food”) from the environment by ingestion. The kinds of organisms that fit this description are fantastically diverse. In fact there are more kinds (species) of animals than all other groups of organisms combined. Animals range in size from microscopic, aquatic organisms such as rotifers, nematodes and tardigrades to the blue whales largest of all animals. While this disparity in form is considerable, animals are thought to be all related, in the sense that they all evolved from a single ancestral animal more than half a billion years ago. There are currently 25 major groups (phyla) of animals recognized by biologists.

In a very general sense, animals can be separated out into two main groups: invertebrates and vertebrates, animals without and with backbones, respectively. In this portion of lab you will study some of the wildly different kinds of organisms that make up the animal kingdom. Study each of the following animal groups with compound or dissecting scopes, as required.

Invertebrates

Microscopic invertebrates

Two good examples of very successful tiny invertebrates are rotifers and tardigrades. Although

quite small, they are structurally quite complex. Both rotifers and tardigrades can be found in streams

and other places in our area.

Rotifers.

First examine with compound scope using a depression slide. Rotifers are tiny animals, although they

might be mistaken for single celled organisms. They are among the smallest of animals and are found

mainly in fresh water but can also be found in wet soil and plant debris. They feed by creating a

water current with a ring of cilia around the mouth area. With careful observation you can see this

motion of the cilia. They digest whatever small bits of organic debris they might obtain. You can

think of them as tiny vacuum cleaners in aquatic systems.

Tardigrades.

These little animals are commonly known as water bears. They can be found in many habitats

though, aquatic as well as terrestrial. They have the amazing ability to survive long periods of

complete dessication (drying). When dessicated, the tardigrade turns into an almost unrecognizable

structure known as a tun. Tardigardes feed on organic debris, like rotifers.

Annelids.

Annelids are a distinctive and common group of animals. Some are microscopic, but most are easily

seen without microscopes. Commonly called worms, annelids are distinguished by many

segmented body, without much difference or specialization among the segments. There are other

types of animals that are “worm like” (for instance nematodes), but they are not annelids for they

lack the distinctive segmentation. Annelids can be found in soils throughout the world, but also in

fresh and marine aquatic systems.

Earthworms. Probably the most familiar of the annelids are the earthworms. Examine with a

dissecting scope (keep them moist and return to container). The many body segments should be

clearly visible. Earthworms move through the soil by pulling themselves with tiny bristles that emerge

from the sides of their bodies. If you gently pull an earthworm, from the rear end through your

fingers you can feel these tiny structures. Earthworms ingest soil, digesting whatever organic

materials available, such as bacteria, algae and single celled organisms. Through this process

earthworms aerate soils, increasing soil fertility and infiltration (we’ll study the nature of soils in a

later lab)

Leeches. You perhaps would not think that leeches are related to nice old earthworms, but they

are. The body segmentation is clearly visible, so they are annelids too. Most leeches have taken a

parasitic path: they drink vertebrate blood. In the past and still occasionally today, leeches are used

by doctors to relieve internal bleeding (edema), as the leeches “bite” it relatively benign and they

produce an anticoagulant as well. A leech attaches to its host with a sucker which surrounds its

mouth. Examine the leeches in lab.

Arthropods

In terms of diversity, arthropods are the most successful animal group; there are hundreds of thousands of species in nearly all habitats. Arthropods (including spiders, ticks, crabs, lobsters, and insects) are distinguished by a rigid exoskeleton, that is hinged in all the right places so the animals can move quite efficiently. In fact the term “arthropod” literally means “jointed foot”, but there are joints (hinged portions of the exoskeleton) all over the body. Arthropods also have a segmented body, but there has been considerable specialization among the segments (e.g., a distinct head and abdomen). Arthropods are thought to have evolved from an annelid-like ancestor in the early Paleozoic. There are 3 primary groups of arthropods: arachnids, crustaceans and insects.

Arachnids

These are the spiders, ticks and scorpions. They are primarily terrestrial. Arachnids are distinguished from other arthropods by details of their mouth anatomy and the fact that they have 8 legs. Furthermore, unlike the insects there are only two primary body segments (insects have three). Spiders, tick and mites are the most widespread of the arachnids. Although scorpions and spiders are the most “exciting”, the little ticks and mites are more important in many ways. Mites live in our homes as well as in the soil where they act as scavengers, although many mites are plant and animal parasites. Ticks, like leeches, are parasitic, again going for the blood of vertebrates. Unfortunately, ticks carry an array of bacteria and other internal parasites that can cause severe illness such as Rocky Mountain spotted fever and lyme disease.

 

Examine the arachnids on display in lab, both living and preserved. Spiders are a good example of the basic arachnid body form with 2 main segments: the abdomen and cephalothorax. The abdomen contains reproductive and digestive organs, while the cephalothorax supports the legs, mouthparts and eyes. Note the general similarity between ticks and spiders.

Crustaceans

Almost all crustaceans are aquatic, and life in the water has lead to many of their distinguishing characteristics. They are a very successful group of organisms including barnacles, lobsters, and crabs; many are found in freshwater too. On land the most familiar of the crustaceans are the Isopods (AKA pill bugs, sow bugs, potato bugs, etc.)

Examine the following living and preserved crustaceans:

Daphnia. Prepare a wet mount (depression slide) and examine with compound scope. This is an

important little crustacean found in fresh water ponds and lakes. Daphnia is primarily an herbivore

that eats algae. Daphnia is important food for small fish (like minnows) which in turn are food for

larger game fish such as trout and bass.

Isopods. The basic crustacean design is easily seen in isopods: many legs, many segmented body,

and, echoing their aquatic heritage, gills. Unlike other terrestrial arthropods, isopods breathe with

tiny gills located on their ventral surface (belly). See if you can make out the gills using a dissecting

scope; ask you lab instructor for assistance.

Insects

Insects are the most successful of the arthropods as well as all forms of animals: there are more species of insects than all other animal groups combined! Almost all insects are found on land. Insects include bees, ants, beetles, flies, water striders, butterflies and many more forms. All insects are characterized by 2 features: 1) a distinctly 3 segmented body (abdomen, thorax and head) and, 2) six legs (hence they are sometimes called the hexapods); most insects possess wings too, but some rarely use them.

Examine the insects available in lab, noting the features listed above. Be sure and keep in mind how insects differ from other arthropods.

Vertebrates

The most familiar of the animals are the vertebrates: animals with an internal, segmented backbone. Vertebrates have been very successful in terms of colonization of numerous habitats, aquatic, terrestrial and aerial. The internal segmented backbone is crucial for the function of legs, wings and to some extent, fins. One way of classifying the vertebrates is to divide the group into four-limbed and non-legged groups. In this approach the vertebrates are subdivided into the fishes and the tetrapods. These groups are further organized as outlined below.

 

Fishes

Chondrichthyes: Cartilaginous fishes such as sharks and rays. Actual bone is restricted to the jaws,

and in the case of the sharks, to tiny skin projections called denticles. The rest of the skeleton is

primarily cartilage.

Osteichthyes: Sometimes called the “ray finned or bony fishes”; and including all the familiar

fishes such as trout, bass, tuna, perch, etc. There is a well developed internal skeleton of bone. The

bony fishes have been very successful, and far outnumber the chondricthians in terms of species.

 

Tetrapods

Amphibians. Frogs, salamanders. Most amphibians have four legs, so they qualify as tetrapods.

Amphibians are rather poorly adapted to life on land, since their eggs do not have shells and will dry

out if they are not in water. Amphibians occupy a transitional world between aquatic and terrestrial

life.

Reptiles. Lizards, snakes, turtles. Superficially similar to amphibians, but much better suited for life

on land for several reasons: waterproof skin, better shoulder/hip bones, shelled (amniotic egg).

Reptiles are a conspicuous part of the natural world today, and were the dominant vertebrates

during the Mesozoic era.

Birds. It is pretty clear these days that birds are descendent from reptiles (dinosaurs); the

relationship goes way back to the Mesozoic era. Obviously, birds are characterized by wings and

the ability to fly (except in certain specialized groups). Like their reptile progenitors, birds have

amniotic eggs. Birds are further distinguished by feathers, and several skeletal features associated

with flight: no jaw bones or teeth, a keeled sternum, many hollow (light) bones. Birds are also

warm blooded, so unlike extant reptiles can remain active during cold temperatures.

Mammals. Mammals are characterized by several features including: hair, many types of glands in

the skin (among them mammary glands from which the group takes its name), and a diaphragm

for more efficient breathing.

Examine the skeletons and other preserved specimens of vertebrates on display in lab and note

those features referred to above.

 

Home | Syllabus | Labratory Guide Links | Valuable Learning Links | Introduction | Lab 1. Tools | Lab 2. Minerals & Rocks | Lab 3. The Nature of Cells | Lab 4. Plant & Animal Diversity | Lab 5. Plate tectonics | Lab 6. Maps | Lab 7. Fossils | Lab 8. Soils & Plant Growth | Lab 9. Lichens & Biological Diversity | Lab 10. Campus Field trip |

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