Pre-lab homework Lab 4: Movement and Support

Lab Section: Pre-lab homework Lab 4: Movement and Support Name: 1. In lab this week we will examine the location of the three main plant tissues. What are these three tissues and what role do they play in a plant? 2. As they age trees and other woody plants increase the girth of their stems by a process called secondary growth. What is the difference between primary and secondary growth? 3. We examine support systems in lab this week. While looking at these systems in animals we will see that there are several different strategies for building support systems. Briefly contrast hydrostatic support systems and other skeletal systems 1

2

Lab 4: Movement and support Lab section Name: Objectives: Upon completion of this activity, you should be able to: Describe the tissues found in plant roots and shoots. Describe secondary growth and how this growth generates the support system of woody plants. Describe the tissues used for support and movement in animals Explain the basics of muscle contraction and why muscles come in antagonistic pairs. Identify the structures seen in human bone. Introduction: Plants and animals both have a need to be able to support an often large, multicellular body. The support systems used have very different structures often due to the fact that animal support systems must also accommodate the movement of an organism while plant support systems do not need to. In addition to comparing the support systems of plants and animals we will examine some of the diversity seen in support systems in animals. As we examine these support systems we will do so at a variety of scales beginning with an examination of support systems at the microscopic level of the tissues used and moving on up to the macroscopic level of examining tree trunks and human bones. By examining the hierarchy of structures responsible for the systems we investigate we should be able to see how structures at all different scales aid an organism. This is a pattern that we will repeat throughout the term. Exercise 1: Plant tissues: Plant cells are generally divided into three different tissue types; dermal tissue that covers the outer surface of the plant, vascular tissue that is responsible for transporting water and minerals or sugars throughout the plant, and ground tissue which makes up the majority of the living tissue in a plant and is where a plants major metabolic activities occur (including photosynthesis and storage of excess energy compounds). Tissues in plant roots: In a typical dicot root all three tissues are easily seen. Epidermal tissue is found surrounding the root. Ground tissue is found in a ring surrounding a central cylinder of vascular tissue. This central vascular cylinder (sometimes called a stele) is made up of vascular tissues. The whole cylinder is surrounded by a ring of cells called the endodermis. Cross section of a typical dicot root (40x) 3

Tissues in plant stems: In a typical dicot stem all three tissues are also easy to see. Epidermal tissue is found surrounding the stem. The vascular tissue is organized into bundles that are organized into a ring. Vascular tissue comes in two types, xylem that transports water and phloem that transports sugars. The ground tissue in the stem is located both within this ring, where it is called the pith, and outside the ring of vascular tissue where it is called the cortex. Cross section of a typical dicot stem Exercise 2: Secondary growth in plants: As plants grow their stems must thicken to support the weight of the growth occurring above. The largest plants, and some trees are very large indeed, must have a very substantial support system that grows from meristematic tissue laid down during primary growth. In a woody stem undifferentiated meristamatic cells are found in a ring in between the xylem and phloem that make up the vascular tissue of the stem. These cells, called collectively the lateral meristem, are capable of dividing through mitosis to produce new xylem toward the center of the stem and new phloem toward the outside. It is the woody xylem that makes up the majority of the support system of woody plants. Examine a cut tree trunk notice distinct rings that allow you to determine the age of the tree, division between bark and wood and two different colors of interior wood (if the tree is older than about 10 years) that show heartwood and sapwood. The wood portion of the tree is the xylem that develops from the lateral meristem. The phloem makes up a substantial part of the bark. Cut tree trunk 4

Now look at a slide of a one year old tree stem and identify the xylem (the center of the stem) and phloem (toward the outside). The group of cells between these two tissues is the vascular cambium, a meristematic region that is responsible for the production of new xylem and phloem cells and therefore is responsible for secondary growth. Slide of a 1 year old tree After you have looked at the 1 year old stem examine a 3-year old stem. During the last two years cells in the lateral meristem have been dividing and generating new vascular tissue. Cells right next to the meristem are the newest while cells farther from this region in any direction are older Now look toward the center of the tree and notice the growth rings apparent in the xylem. Slide of a 3 year old tree 1. Look closely at the cells making up the xylem where rings are visible. What seems to be different about the cells toward the center of the tree vs. those farther out? 2. What do you think could be causing this difference? (remember that it must be something that changes throughout the year to cause the growth rings) 5

Exercise 3: Animal Support systems Bone & Cartilage: The rigid support system of most vertebrates is based on bone a complex type of tissue made up of cells surrounded by an extra-cellular matrix (ECM) of protein and minerals. These proteins and minerals provide the structure that makes bone such a strong support system. Another important component of most vertebrate skeletal systems is cartilage, a much more flexible material that is often used to cushion joints. Like bone the majority of cartilage is an extra-cellular matrix secreted by specialized cells that end up in little chambers surrounded by ECM. Bone cells: Make a sketch of a slide of bone, and label the spaces where cells would normally be found and the extra-cellular matrix. The large central opening in living bone contains blood vessels and sometimes nerves. Bone (magnification ) Cartilage : View the slide labeled hyaline cartilage it at 100x magnification. Here the ECM is made up of proteins and carbohydrates. Once again the open spaces represent the spaces left behind by the cells that secreted the ECM. Notice that cartilage lacks the large open spaces that contains blood vessels and nerves in bone. Cartilage (magnification ) Cut bone : View the cross section of bone on display. Notice that the bone itself is made up of a thick out edge of compact bone surrounding a space full of spongy bone that also includes bone marrow where blood cells form. In the long bones of your body there is also an open cavity called the medullary cavity. Cross section of bone (1x) 6

Acid soaked bone: When bones are soaked in a weak acid solution the minerals that make up the ECM are slowly leached out. This leaves the protein component of the ECM behind so that you can examine it more fully. Examine an acid soaked bone and notice the properties that it has. These properties are caused primarily by the protein component of the bone. Describe the acid soaked bone in the space below. Baked bone: When bones are baked the proteins are denatured but the mineral component is left behind relatively unchanged. This allows you to examine the mineral component of the ECM more fully. Examine a baked bone and notice the properties that it has. These properties are caused primarily by the mineral component of the bone. Describe the baked bone in the space below. 1. The ECM in living bone is made up of both the mineral and protein components and is both strong and flexible, based on your observation of baked and acid soaked bone which component (mineral or protein) provides the most ridgid support and which provides the most flexibility. 7

Exercise 3: Animal Support systems Continued: Human Skeletons: The basic structure of bone tissue is the same in all your bones but the organization of the tissue into a larger bone varies greatly from bone to bone. The different shapes and sizes of these bones give them very different properties (emergent properties!) here we will examine several examples of differences in skeletal structure. 1. Vertebrae: Your vertebrae support the weight of your entire upper body while also providing a protective covering for your spinal cord. On your desk are two vertebrae one from high up in the spinal column and one from much lower make a hypothesis about which is which and sketch them in the boxes below be sure to label the space the spinal cord passes through and then note the structural differences that make you think one bone is from lower in the spine than the other. High in the spine vertebrae Lower in the spine vertebrae 2. Male and Female bones: The bones in your body are very similar whether you are a male or a female. The bones that show the greatest difference in structure between the two genders are the bones that make up the pelvic girdle. These bones, which make up the hips, show differences in both the shape of the bones and the angles that they are connected together. Examine the male and female hips and sketch them noting the differences that you notice between the two. Be sure to note the location of the birth canal, the circle of bone through which a baby must pass during birth. Male pelvis Female pelvis 8

Species differences: The basic body plan of all the vertebrates with four limbs (the tetrapods) is very similar. The bones in your body are essentially the same as the bones found in a bat or a cat but different animals have adapted so that the size and shape of the bones is greatly modified. Pick a couple of different bones from three different organisms and sketch them in the space below. Try to pick the bones that show the greatest difference in structure between the different species. Species 1: Species 2: Which bones did you chose? Species 3: How are these bones similar to each other in the different species? How are these bones different in the different species? Why do you think this is? 9

Exercise 4: Alternative Support systems Other support systems: Internal skeletons of bone are not the only support systems found in the animal kingdom several other systems can be found that all have their own advantages and disadvantages. 1. External skeleton - Arthropods: Insects and other arthropods (spiders, millipedes, crustaceans) all have external skeletons made of chitin. Can you think of some advantages and disadvantages of this system of support? Arthropod exoskeleton 2. External skeleton - Molluscs: Other external skeletons found in the molluscs (clams, snails, chitons) are made of much harder/heavier compounds and create a shell that is very difficult to pierce. How would this type of skeleton be better and worse than that found in the arthropods? Mollusc exoskeleton 3. Hydrostatic skeletons: Many organisms forgo a rigid skeletal system and rely on pressurized fluids to maintain their shape. A classic example of this is the earthworm. Each of the segments of an earthworm is a separate pressurized chamber full of fluid. What are some advantages and disadvantages of this system? Hydrostatic skeleton 10

Exercise 5: Muscles Support and Movement: It is the interaction of muscles and the support systems of animals that actually allows for movement. Muscles must be anchored to the skeletal system. 1. Muscle tissue: Specialized tissue that contains cells that can shorten their length by contracting sets of specialized proteins are found throughout the animal kingdom. In vertebrates there are three basic types for this exercise we will examine skeletal muscle. As you sketch your slide try to see the short regions (called sarcomeres) that will pull together during contraction. These make the tissue appear to have stripes (striations). Skeletal muscle tissue ( x) 2. Antagonistic muscles: Because it is only the contraction step that can generate force muscles must work in pairs. Think about the muscles that control the bending of your elbow. To bring your lower arm closer to your upper arm your bicep contracts but to return your arm to a straight position requires a different muscle, the triceps. Throughout your body pairs (or larger groups) of muscles contract against each other to control movement. Pick one simple movement you commonly perform (like bending your elbow but you can t pick that one!) and take a moment to look at the bones that move on the skeleton when you perform this move. Now perform the opposite movement and think about where the antagonistic muscles must be located to accomplish these opposite movements. Sketch these movements in the space below and label the muscles using text books found in the room. Bones involved Muscles and bones 11