Support is the ability of an organism to bear its weight and maintain its body form. Movement on the other hand refers to displacement of parts of the body or the whole organism from one position to another. Plants mainly display localized movement while animals display both localised and locomotory movement.
Animals move from place to place in search of food, territory, mate or escape danger. Plants movements are not locomotory in nature. Their movement is mainly by growth responses. They grow towards useful stimulus or away from injurious ones. All organisms have support structures which enables them to bear their body weight as well as maintain their body forms. Both plants and animals possess a variety of structures that helps in support and movement.
Support and movement in plants
Anatomy of dicotyledonous plants: Structures discussed in the previous chapter (collenchyma, sclerenchyma, xylem and phloem) are important in carrying out the transport functions.
Root anatomy and function: The root is important in absorption, anchorage and storage of food. It is made up of the epidermis, cortex, endodermis and stele (consisting of xylem, phloem and pericycle).
Stem anatomy and function: Stems contain an epidermis, cortex and vascular cylinder (consisting of pericycle, xylem, phloem, cambium and pith). Stems are important for growth, support, storage and transport of water, mineral salts and manufactured sugars.
Secondary growth: Secondary growth is the thickening of the stem or root as new layers of xylem and phloem are formed by mitosis. It is carried out by cambium and results in stems and roots becoming thicker as the plant ages / matures. Secondary thickening results in the annual rings found in trees that can be used to work out the age of a tree.
Transpiration: Transpiration is the loss of water from the stomata of plants. It creates a ‘suction’ or transpirational pull that is important for the movement of water through the plant. Transpiration is affected by environmental conditions e.g wind, temperature, humidity and light intensity. The rate of transpiration is measured using a potometer. In order to prevent excessive transpiration, plants have developed adaptations such as thickened cuticle, position of stomata, hairs on leaves, reduction of leaf size, leaf spines, leaf arrangements and rolling of leaves.
Translocation: Translocation is the transport of food material (sugars), synthesised in the leaves, to other parts of the plant via phloem. This mode of transport is multi-directional but requires energy as it occurs by active transport against a concentration gradient. Phloem vessels consist of sieve-tube elements and companion cells which are connected by plasmodesmata. Companion cells act as the regulators and energy stores of the phloem.
Wilting and guttation are processes of water loss in the plant. Wilting entails excessive loss of water through plasmolysis resulting in excessive cell death, at times resulting into death of the entire plant. Guttation is the release of water via the hydathodes due to high humidity.
Support systems in animals
Movement is one of the essential features of living things. Cellular movement is observed in one-celled amoebas, ciliates, and flagellates. Flagella whip about to produce cellular motion, while cilia beat synchronously to propel a cell.
In animals, movement is essential for locating food, escaping predators, and seeking mates. In many animals, the movement process is centered in the muscle cell, which contracts and relaxes. The contraction yields great force, which is applied against a surface by means of a skeleton.
Skeletal systems provide structure and protection for a variety of organisms. A water-based skeleton provides the structure necessary for movement in worms. The hard external skeleton (exoskeleton) not only provides a protective mechanism for many organisms but also assists in the movement of insects. The internal skeleton (endoskeleton) present in many animals provides the structural network for support, protection, and movement.
Many animals have a water-based skeleton or hydrostatic skeleton. Hydrostatic skeletons do not contain hard structures, such as bone, for muscles to pull against. Rather, the muscles surround a fluid-filled body cavity. In a worm, for example, movement occurs when muscle cells contract and the contractions squeeze internal fluid (the hydrostatic skeleton) against the skin, causing the worm to stiffen and the body to shorten and widen. The squirming motion of a worm also depends on a hydrostatic skeleton.
THE VIDEO EXPLAINS HYDROSTATIC SKELETON
The second type of skeleton, the exoskeleton, exists in arthropods and mollusks. In mollusks, the exoskeleton is a hard, protective outer covering. An example is a clamshell; when a clam’s muscles contract, they close the shell rapidly, creating a spurt of water that propels the clam. In arthropods, the exoskeleton also provides protection and movement. Usually, wings are attached by muscles in the hard body surface, which provides a foundation for the muscle contractions. Muscle contractions raise and lower the wings, allowing flight.
Vertebrates have an internal skeleton called the endoskeleton, a framework of bones and cartilage (see Figure 27-1) that serves as a point of attachment for muscle. The endoskeleton thus transmits the force of muscle contractions. The endoskeleton also provides support for the body (for example, the legs) and protection (the skull).
Bone contains concentric rings of tissue in which bone cells called osteoblasts produce the inorganic materials (fibers and matrix) of bone. Much of this material is calcium phosphate, formed from calcium and phosphorus delivered by the blood. Living, mature bone cells called osteocytes are also located in the bone. Bone-destroying cells called osteoclasts break down bone, thus providing a turnover of bone material needed in other areas. The combination of bone cells and bone tissue comprises a unit called a Haversian system.Blood vessels and nerves also exist within the Haversian system.
Bones come together to form a joint, which may be immovable, such as in the sutures of the skull, or movable, such as in the joints of the elbow and shoulder. In a movable joint, a capsule of synovial fluid provides lubrication. Tough, fibrous tissues, known as ligaments, link bones to one another. Connective tissues, called tendons, attach muscles to bones.