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Lab 1 Biology 1002...

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LAB 1 – ADAPTATIONS OF PLANT LEAVES At the end of this lab you should be able to: 1. 2. 3. 4. 5. 6.

Recognize and identify basic leaf structure and its tissues Able to classify a leaf as to its type of habitat Able to describe various leaf modifications Know how to do an epidermal peel How to make a leaf cross section Learn how to do a titled and proportioned tissue plan

Plants adapted to wet environments are called HYDROPHYTES; dry environments are called XEROPHYTES; and moderate environments called MESOPHYTES. TABLE 1: Comparison of leaves of plants adapted to various amounts of water in the environment. HYDROPHYTE • Large amount • Some completely submerged • Some in wet areas • To control amount of water moving into the plant • Some may need to control water loss

MESOPHYTE • Medium amount • Varies from slightly wet to slightly dry

XEROPHYTE • Reduced amount • May be dry all the time or only part of the time

• Depends on the amount of water available • Most have a few restrictions on water loss

• Most have several ways to conserve water or reduce loss • Need extra support to protect against wilting

Thin

Flexibility

Thin Small, narrow, finely divided Large Thick, thin, one-side or absent Flexible

Leaf edge

Irregular

Irregular

Water content

Moist

Moist

Leaf Surface

Smooth

Smooth

Amount of water in the environment

Adaptations needed

FEATURES OF WHOLE LEAF Thickness Size SA/V ratio Cuticle

Medium to large

thick Large; very reduced or absent Small

Thin, not as obvious

Thick obvious

Flexible

Stiff, rigid Smooth, rounded (reduces SA) Wet, juicy Epidermal hairs; spines; leaves reduced or absent

Medium

FEATURES SEEN FROM SECTIONS OF LEAF Thickness of epidermis Cuticle

Stomata

1 layer of cells, thin walls Thick, think, one-sided or absent • May be restricted to upper surface, absent in submerged leaves • On surface of leaf

1 layer, thin walls

May have larger cells, thicker walls, or multiple layers

Thin, not as obvious

Thick obvious

• On both sides of leaf • On surface of leaf

• May be only on lower side/inside of leaf that curls up • May be sunken in small pits of larger crypts 1

Amount of support tissue

Small amt of vascular tissue (veins)

• Medium amount of vascular tissue • Small-medium amount of thick walled support cells around veins

Water storage region

NOT NEEDED

Depends on amount of water available

Air spaces in mesophyll Internal air chambers

Large – for gaseous exchange Throughout spongy mesophyll (large spaces for flotation)

• Larger amount of vascular tissue • Large amount of thick walled support cells around veins or beneath epidermis • In or beneath epidermis • Around veins (large empty, thin-walled cells)

Medium

Small – to conserve water

NOT NEEDED

NOT NEEDED

EXERCISE 1: STRUCTURE of A MESOMORPHIC LEAF SYRINGA CROSS SECTION – Labelled

QUESTIONS (pg. 23) 1. Are epidermal cells photosynthetic? Explain your reasoning. The guard cells contain chloroplasts, so they can manufacture food by photosynthesis (The epidermal cells do not contain chloroplasts). Guard Cells are the only epidermal cells that can make sugar (photosynthesize).

2. What organelles do they contain that makes photosynthesis possible? • Photosynthetic cells contain special pigments that absorb light energy. Different pigments respond to different wavelengths of visible light. • Chlorophyll, the primary pigment used in photosynthesis, reflects green light and absorbs red and blue light most strongly. 2

• In plants, photosynthesis takes place in chloroplasts, which contain the chlorophyll. Chloroplasts are surrounded by a double membrane and contain a third inner membrane, called the thylakoid membrane, that forms long folds within the organelle. • In electron micrographs, thylakoid membranes look like stacks of coins, although the compartments they form are connected like a maze of chambers. • The green pigment chlorophyll is located within the thylakoid membrane, and the space between the thylakoid and the chloroplast membranes is called the stroma.

How are the palisade cells stacked? Palisade mesophyll cells are tall and closely packed to absorb maximum light. They contain many chloroplasts. Most photosynthesis takes place in the palisade cells.

3. Which of these two tissues also functions in gas exchange? Explain your reasoning. Do the cells of the spongy mesophyll contain as many chloroplasts as the palisade mesophyll? Suggest a reason for your answer. • Gases enter the photosynthetic tissue of the leaf through dissolution onto the moist surface of the palisade and spongy mesophyll cells. • The spongy mesophyll cells are loosely packed, allowing for an increased surface area, and subsequently an increased rate of gas-exchange.

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Do the cells of the spongy mesophyll contain as many chloroplasts as the palisade mesophyll? Suggest a reason for your answer. No. Palisade mesophyll cells are closely packed together, whereas spongy mesophyll cells have air spaces between them. Therefore, palisade mesophyll cells contain more chloroplasts than spongy mesophyll. Note: palisade mesophyll cells are tall and closely packed to absorb maximum light. They contain many chloroplasts. Most photosynthesis takes place in the palisade cells. Spongy mesophyll also captures light and makes food. Spongy mesophyll cells have air spaces between them to allow easy gas exchange. Describe the difference, size, shape and associated organelles between the guard cells and the epidermal cells.

4. Describe the difference in size, shape, and associated organelles between the guard cells and the epidermal cells. Guard Cell vs Epidermal Cell • The difference between guard cell and epidermal cell can be observed in the structure, content, and function of each cell type. Definitions of Guard Cell and Epidermal Cell: • Guard Cell: Guard cells are bean-shaped cells and are found in pairs, creating a mouth-shaped epidermal opening called stoma. • Epidermal Cell: Epidermal cells are the cells of the epidermis that originate from the protoderm and cover the whole body of the plant. Characteristics of Guard Cell and Epidermal Cell: Origin: • Guard Cell: Some of the epidermal cells are modified into guard cells. • Epidermal Cell: Epidermal cells originate from protoderm. Ability of Photosynthesis: • Guard Cell: Guard cells can photosynthesis. • Epidermal Cell: Majority of epidermal cells are not photosynthetically active. Amount: • Guard Cell: Guard cells are found only in some parts of the plant body. • Epidermal Cell: Main cell mass of the epidermis is made up of epidermal cells. Function: • Guard Cell: Guard cells control the rate of gas exchange and water evaporation between plant body and environment. • Epidermal Cell: Epidermal cells form the protective tissue of the plant body. Structure: • Guard Cell: Guard cells are bean-shaped cells and found as pairs in such a way to form an opening called stoma. • Epidermal Cell: Epidermal cells are usually tubular in shape, but that may vary depending on the place they are found in the plant body. Content: • Guard Cell: Guard cells contain chloroplasts. • Epidermal Cell: Epidermal cells contain plastids but very few grana, thus they are deficient in chlorophyll 4

Draw and label a tissue plan of this leaf x.s. include calculations for size, scale and drawing width.

Syringa (lilac) leaf cross section, 100X A = palisade mesophyll; B = upper cuticle; C = xylem; D = phloem; E = upper epidermis; F = (vascular bundle); G = lower epidermis; H = lower cuticle; I = spongy mesophyll; J = guard cell; K = stoma

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EXERCISE 2: ADAPTATIONS OF LEAVES OF XEROPHYTES AND HYDROPHYTES

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Monocot leaf epidermis whole mount slide

Epidermal Peel Prepare a Leaf Epidermal Peel • The cells on the surface of a leaf (epidermal cells) form the barrier between air/water and the inner cells of the leaf. The surface may have a wax coating/hairs as protective structures. • Stomata are specialized structures found on the surface of leaves. • They are formed from two guard cells (bean‐shapes cells) joined at their ends. • Guard cells, which contain chloroplasts, swell or shrink in association with osmotic changes. • When guard cells are turgid (swollen) a space between the cells opens – this is the stoma or stomatal pore through which CO2 enters the plant and O2 and H2O vapour leave the plant. 7

• Plants need to regulate the amount of time the pore is open to maximize CO2 entry for photosynthesis and limit water loss (transpiration). • Between the epidermal layers are the mesophyll cells, which carry most of the chloroplasts and where photosynthesis occurs. This method describes how to prepare a peel of the leaf epidermis for microscopic observation of the epidermal cells, guard cells and leaf hairs if they are present. Plants vary in the shape of epidermal cells and size and number of stomata on each surface. If a good peel is obtained it is possible to estimate density of stomata. In leaves that have pigment in the vacuole, an epidermal peel can also be used to observe osmosis.

Method ‐ Leaf epidermal peel a) b) c) d) e) f) g)

Collect a suitable leaf and all other materials. Label a microscope slide Bend the leaf to break the surface or tear the leaf from the edge Tear off some epidermis, the transparent thin layer of surface cells Cut the epidermal layer from the leaf, place on a microscope slide Add a drop or two of water Place a coverslip on the sample View under the compound light microscope at an appropriate magnification (usually 100x or 400x)

Guard cells that form stomata are identified by the bean‐shaped cells joined at the ends. Guard cells contain chloroplasts (green organelles). The shape of the epidermal cells around stomata varies in different plants. In most plants, the epidermal cells surrounding the stomata lack chloroplasts. Epidermis strip preparation: https://www.youtube.com/watch?v=hqGB9GiGqLs Demonstration of Stomata on leaf peel: https://www.youtube.com/watch?v=UG08SsO8zQA

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EXERCISE 3: DETERMINATION OF HABITAT BASED ON LEAF CHARACTERISTICS Tulipa, tulip, leaf epidermis with stomata whole mount (w.m.), showing large stomata and guard cells for general study prepared microscope slide.

BASED ON THIS CHARACTERISTICS ALONE, CAN YOU DECIDE WHETHER THE LEAF YOU OBSERVED IS FROM A MESOPHYTE, XEROPHYTE, OR A HYDROPHYTE? HYDROPHYTES - the stomata are located only on the part of the plant surface that's exposed to air. Underwater plants will often lack stomata since they no longer need to exchange gases with the atmosphere anymore. Having more stomata on the upper side of the leaf will increase the amount of carbon dioxide entering the leaf for photosynthesis. MESOPHYTES - the stomata are generally found on the underside of the leaf. Since water evaporates upwards, having most stomata on the underside of the leaf will mean water is trapped under the leaf, which reduces water loss.

XEROPHYTES - the stomata can often be found in sunken pits. Having the stomata in pits shields them from the wind. When wind blows on the stomata, the water is immediately blown away resulting in transpiration occurring faster, therefore meaning protection from the wind will reduce water loss in the plant.

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EXERCISE 4: SPECIALIZED LEAVES EXAMINE PLANT AND DETERMINE TYPE OF LEAF SPECIALIZATION (TENDRILS, BUD SCALES, SHOWY BRACKETS, ETC.) AND ITS FUNCTION FOR EACH SPECIMEN A. Specialized Leaves - The purpose of the leaf is to make food for the plant. Sometimes the leaf is specialized to perform a different function. 10

B. Leaf Tendrils - A leaf tendril is a specialized leaf. A leaf tendril coils around an object to help the plant to climb. Peas and squash are examples of plants with leaf tendrils.

C. Spines - Spines are specialized leaves. Spines are hard, sharp leaves that are specialized to defend the plant from being eaten by animals. Spines do not make food for the plant. The stem makes food for the plant. Cactus and ocotillo are examples of plants with spines. Showy bracts – a modified leaf or scale, typically small, with a flower or flower cluster in its axil. Bracts are sometimes larger and more brightly colored than the true flower, as in a poinsettia.

D. Water Storage or Succulent Leaves - Water storage or succulent leaves are specialized leaves. Succulent leaves are leaves that are specialized to store water for the plant. The jade plant is an example of a plant with succulent leaves.

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E. Food Storage Leaves of Bulbs - Food storage leaves are specialized leaves. Food storage leaves are leaves that are specialized to store food for the plant. Food storage leaves are underground leaves in bulbs. Food storage leaves do not make food for the plant. The onion is an example of a plant with food storage leaves.

F. Leaves that Reproduce - Leaves that reproduce are specialized leaves. Leaves that reproduce are leaves that are specialized to grow roots to make a new plant.

H. Bud Scales - Bud scales are specialized leaves. Bud scales are leaves that are specialized to protect the buds of deciduous plants during the winter. Bud scales prevent the buds from drying out. The cottonwood plant is an example of a plant with bud scales.

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I. Conifer Needles - Conifer needles are specialized leaves. Conifer needles are leaves that are specialized to store water. Conifer needles are needle-shaped and have a thick cuticle to prevent water loss. Conifer needles contain resins to protect them from freezing and to prevent insects from eating them. Pine trees are examples of plants with conifer needles.

EXERCISE 5: SPECIALIZED LEAVES OF INSECTIVOROUS PLANTS Insect-Trapping Leaves - Insect-trapping leaves are specialized leaves. Insect-trapping leaves are leaves that are specialized to trap insects. Insect-trapping leaves may be sticky to trap the insect, they may form containers to trap the insects, or they may snap shut when the insect lands on the leaves. The plant uses the nutrients, such as nitrogen, from the decaying insect to supplement the low nutrient supply in its environment. The sundews, the pitcher plant, and the Venus flytrap are examples of the three types of plants with insect-trapping leaves.

Pitcher Plant - have modified leaves known as pitfall traps—a prey-trapping mechanism featuring a deep cavity filled with digestive liquid. The traps of what are "true" pitcher plants are formed by specialized leaves. The plants attract and drown their prey with nectar.

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Pitchers of the carnivorous plant Nepenthes have evolved specialized organs serving the purpose of attracting, capturing, retaining and digesting small animals, mostly insects. They consist of several well distinguishable zones, including a leaflike lid, a collar-like peristome, a slippery zone and a digestive zone, differing in morphology, microstructure, chemical composition and physical properties. Discriminating zones display different functions, and the combined effects of several zones result in great trapping efficiency. They consist of the pitcher lid, the peristome, the waxy zone (slippery zone) and the digestive zone (glandular zone). The smooth transitional zone has some isolated scale-like wax crystals. Both the external and the inner surface of the pitcher is coated with scale-shaped crystalloids or platelets, and the waxy zone contains more wax crystals than other zones.

Pitcher lid and peristome - The leaf-like lid acts as a disc and prevents the inner pitcher from being contaminated by dust, rainwater and other contaminants, as well as reduces the evaporation of pitch fluid. The peristome bears a very regular, smooth and glassy microstructure consisting of radial ridges. Each epidermal cell of the ridges overlaps the cell adjacent to the pitcher inside, so that the surface contains a series of steps toward the pitcher inside and exhibits the property of anisotropy.

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The extraordinarily regular cell surface structure is completely wetted by nectar secreted at its inner margin. Only under wet conditions do homogeneous liquid films form on the surface of the peristome, making it extremely slippery for insects and causing the prey to slide into the lower part of the pitcher. WAXY ZONE - Located below the peristome, is crucial for successful trapping and preventing the escape of prey. DIGESTIVE ZONE - Is believed to contribute solely to the utilization of prey and has been studied mostly for its microstructure and chemical function in digestion, absorption and transport of the insect-derived nitrogen compounds.

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