Biology 1001
FALL 2004
WEEK 10 LABORATORY
Adaptations for Survival in Terrestrial Environments
In earlier laboratories, you studied certain cellular features that allowed the movement onto land,
including root hairs to absorb water and nutrients, tracheids and vessels to carry them, and epidermal
cells, including guard cells, to restrict water loss. You also studied features of angiosperm
reproduction that have evolved to allow greater reproductive success on land. These include the ovule
and seeds, whereby the eggs and sperm and resultant zygote and embryo are retained on the mother
plant, the carpel and fruit for protecting the developing ovules and seeds from desiccation and
predation, and the pollen grain and pollen tube, for delivering the sperm to the egg.
Angiosperms have become adapted to a wide variety of terrestrial and shallow aquatic environments by
modifying the basic body plan of root and shoot (with stem and leaves) and the type and distribution of
specific cells.
Just as plants have evolved mechanisms for survival on land, animals have adapted in several ways to a
terrestrial environment. These adaptations include modifications to the general body plan that include
the following:
(l) an outer impervious "skin" to prevent desiccation;
(2) mechanisms to conserve body water by excretion of concentrated wastes; and
(3) reproductive changes that provide for internal fertilization and protection of embryonic
development. This last feature results in the amniotic egg, which we will study today.
In this laboratory, you will study changes in the plant vegetative body and the vertebrate egg that allow
survival in terrestrial environments. By comparing the fish embryo with that found in the amniotic
eggs of chicks and pigs, you will have a chance to compare and contrast embryonic development in
three major groups of animals.
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I. Plant Kingdom: Adaptations in leaves for reducing water loss
II. Animal Kingdom: Adaptations for terrestrial reproduction
Appendix: Derivatives of the primary germ layers
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Tobin and Dusheck, 3rd edition: I. pp.637-640; II. pp. 503-510, 860-867
Lab 10-1
I. EVOLUTION IN PLANTS: ADAPTATIONS IN LEAVES FOR MOISTURE LEVEL
Depending on available moisture in their specific habitat, plants may be described as hydrophytes,
mesophytes, or xerophytes. These are only general ecological groupings since there is no hard and
fast division between them. Many species have a wide range of moisture tolerance. Plants have
adapted to extremes in moisture level by altering their vegetative structures. All parts of the plant may
be affected, leaves, stems and roots. Some parts may even be lost or highly modified. For example, in
many cacti, the leaves only grow as spines to protect against being eaten and serve no photosynthetic
function.
In this section, we will study changes in leaf structure that are adaptive for different habitats.
A. HYDROPHYTES
Hydrophytes grow as free-floating or completely submerged fresh water plants. Their leaf
characteristics may include:
1. a cuticle only on the upper epidermis in floating leaves and absent in submerged
leaves
2. thin and ribbon-like leaf shape
3. a well-developed aeration system including enlarged intercellular air chambers
throughout the plant
4. stomata only on the upper epidermis in plants with floating leaves and lacking in
submerged leaves.
B. MESOPHYTES
Mesophytes are plants that have adapted to an environment of moderate moisture. This
moisture is typical of the meadows and forests of temperate climates. Since most vascular
plants are mesophytes, their structure and adaptations are already familiar to us. Their leaf
characteristics include:
1. a thin cuticle covering the epidermis
2. an epidermis that is usually a single cell layer thick
3. stomata often present on both sides of the leaf in vertically held leaves (often only on
the lower side of a horizontally held leaf)
4. a thin leaf due to a moderate amount of mesophyll
Lab 10-2
C. XEROPHYTES
Xerophytes are plants that survive where there is a limited water supply. They are
characteristic of desert or semi-desert regions. Succulents, such as cacti, are generally
regarded as highly specialized xerophytes. Non-succulent xerophytes are mostly grasses and
woody taxa such as the evergreens. Their characteristics include:
1. a thick cuticle and thick epidermal cell walls
2. sunken stomata with an increased mesophyll layer containing large water storage cells
3. thick coats of epidermal hairs on either or both leaf surfaces
4. small leathery leaves
You will be given cross sections of leaves from each type. Record your observations of
morphological features in relation to environmental adaptations in Table 10-1.
In the laboratory you will find examples of these three plant groups. Examine them carefully,
paying particular attention the different types of hydrophytes and xerophytes. Note how some
have evolved different ways to grow so they can prosper in very wet or very dry habitats.
From the examples on display, write two separate short essays on your data sheet comparing two
hydrophytic and two xerophytic plants that differ in their adaptations to an aquatic or a dry habitat.
Lab 10-3
TABLE 10-1. ENVIRONMENTAL ADAPTATIONS IN ANGIOSPERM LEAVES
EXAMPLE
_________________
_________________
_________________
ADAPTATION
Hydrophyte
Mesophyte
Xerophyte
Habitat
Thickness of Cuticle
Number and Location
of Stomates
Number of
Air Spaces
Amount of Mesophyll
Number and Size
of Leaves
Lab 10-4
II. EVOLUTION IN ANIMALS: ADAPTATIONS IN EGGS FOR DRY ENVIRONMENTS
The fertilized eggs or zygotes of all vertebrates undergo a rapid series of mitotic divisions referred to as
cleavage. When you studied mitosis in laboratory 4, the whitefish blastula whose cells you were
observing had undergone cleavage.
By the third cleavage in fish (and amphibian) eggs, a distinct animal pole with small cells and a
vegetal pole with larger cells can be seen. The animal pole divides more quickly than the vegetal,
producing many small cells. At the blastula or hollow ball stage, a cavity called a blastocoel forms
near the animal pole.
The next stage of development is termed gastrulation. It is marked by the appearance of a groove,
called the dorsal lip, below the equator of the blastula. Gastrulation in lower vertebrates takes place
by inward migration of cells at the edge of the yolk. Cells move inward and pass through the dorsal
lip, then spread through the interior, forming a second cell layer, the endoderm. As these movements
proceed, a new cavity, the archenteron is formed, obliterating the blastocoel.
By the end of gastrulation, three primary germ layers (ectoderm, mesoderm, and endoderm) have been
formed. The mesoderm is formed from certain cells on the dorsal surface of the endoderm between
the ectoderm and endoderm. In addition, a group of cells in the mesoderm form an anterior- posterior
rod termed notochord. This rod induces formation of the nervous system from the ectoderm above it.
The Appendix at the end of this lab gives the derivatives of the three primary germ layers.
THE AMNIOTIC EGG
The amniotic egg is distinguished by the presence of membranes that form in addition to the
developing embryo (animal) proper. Typically the embryo will develop four membranes. The
innermost, the amnion, functions in protection, the yolk sac for nutrition, the allantois for circulation,
and the chorion (the outermost) for protection.
The amniotic egg is found in reptiles, birds and mammals, but is not seen in the other vertebrate
classes, the amphibians and fishes. In addition, a protective shell may form around the embryo as it
develops, a porous leathery one in reptiles or a calcified shell in birds. Such shells afford protection
while allowing for the exchange of gases. Placental mammals do not have shells and typically retain
the embryo during development.
Lab 10-5
PROCEDURE
1.
Examine the embryos of the Japanese Medaka, a freshwater killifish. These fish embryos
have developed beyond the gastrula stage. They have two-chambered hearts, blood cells,
eyes, limb buds, and a large mass of yolk. Remember, in fish embryos, you will not see
extra-embryonic membranes. Locate a single fish under the scanning lens of your
microscope.
2.
Examine prepared microscope slides of a developing chick at 72-96 hours of incubation.
3.
Examine a gravid pig uterus showing mammalian development.
Contrast the development of the three groups observed: fish, bird and mammal, with respect to the
environment they live, number of offspring produced and the degree of protection offered by the
parents to the developing zygote by completing Table 10-2.
Lab 10-6
TABLE 10-2. DEVELOPMENTAL DIFFERENCES IN FISH, BIRDS AND MAMMALS
Environment
Number of
Offspring
Fish
Birds
Mammals
Lab 10-7
Protection
APPENDIX: DERIVATIVES OF PRIMARY GERM LAYERS
ECTODERM
MESODERM
ENDODERM
Adrenal medulla
Anal canal
Cutaneous glands
Enamel of teeth
Hair
Hypophysis
Lens
Nails
Nasal cavity
Nervous system
Oral glands
Sense organs
Sinuses
Skin (epidermis only)
Adrenal cortex
Blood
Blood vessels
Body cavities
Bone
Cartilage
Genital ducts
Gonads
Heart
Joint cavities
Kidneys
Lymph tissue
Marrow
Muscles
Notochard
Skeletal tissue
Teeth
Ureter
Vagina
Auditory tube
Bladder
Larynx
Lining of digestive tract
Liver
Lungs
Parathyroids
Pancreas
Pharynx
Root of tongue
Thymus
Thyroid
Tonsils
Trachea
Urethra and associated glands
Lab 10-8
BIOLOGY 1001
NAME___________________________________
DATA SHEET: LABORATORY 10--Adaptations for Survival in Terrestrial Environments
I.
Plant Kingdom: Adaptations in Leaves for Moisture Level
Attach Table 10-1.
From the examples on display, write two separate paragraphs comparing two hydrophytic and two
xerophytic plants that differ in their adaptations to an aquatic or a dry habitat.
a. Two hydrophytes and how they differ in their adaptations to an aquatic habitat:
b. Two xerophytes and how they differ in their adaptations to a dry habitat:
Lab 10-9
III.
Animal Kingdom: Adaptations for Terrestrial Reproduction
Attach Table 10-2.
1. Write a short essay summarizing the observations you made in Table 10-2 of egg
development in fish, birds and mammals. If you wish, you can type your essay and attach it
to your worksheets.
Lab 10-10
2.
Eggs of reptiles, birds and some mammals are laid on land, usually away from water and
independent sources of food. How do the following adaptations allow for this type of early
development?
yolk
amnion
hard porous shell
Lab 10-11