Support, Movement and Growth

The cheetah is the fastest terrestrial animal on Earth and can move from 0 to 96 km per hour in just three seconds p. 113.

6.1 Support, Movement and Growth in Animals

Skeleton is the support system for all types of animals, and there are three types of support: endoskeleton, exoskeleton and hydrostatic skeleton p. 114. Endoskeleton is the type of support for all vertebrates including humans, made up of internal bones and cartilage p. 114. It supports the body weight, protects the internal organs, maintains the body shape and is the basic attachment for muscles p. 114. Exoskeleton is the type of support for most invertebrates and consists of an outer layer of waxy chitin or shell p. 114. Soft-bodied invertebrates such as worms are supported by a hydrostatic skeleton, a muscular wall that encloses a body cavity filled with fluid p. 115. The fluid exerts pressure on the muscular wall in all directions, causing the animal’s body to be firm p. 115.

Growth can be measured by plotting a graph of growth unit, such as height (cm), volume, wet mass (g) or dry mass (g), against time, called the growth curve p. 115. The growth curve of all organisms basically is sigmoid in shape p. 116. The exoskeleton of animals such as the cockroach and grasshopper is made up of hard chitin and is unable to expand p. 116. These animals shed the exoskeleton repeatedly until they reach adulthood, and the process of shedding the skin is called ecdysis p. 116. During ecdysis, the animal sucks in air to break the old exoskeleton, and rapid growth occurs before the new exoskeleton hardens p. 116. The horizontal part of the curve shows the zero growth stage, called the instar p. 116. This ecdysis stage causes the growth curve graph to be step-shaped, and a hormone controls every stage of the ecdysis p. 117.

The earthworm has a hydrostatic skeleton and moves on land with the aid of chaetae, the bristles at the side of its body p. 118. When the circular muscles contract, the longitudinal muscles relax and the body becomes thin and long; when the longitudinal muscles contract, the body becomes thicker and shorter p. 118. Where the segments shorten and thicken, the chaetae grip the ground, while the other segments lengthen and their chaetae release the grip so the earthworm moves forward p. 119.

Terrestrial vertebrates need a strong and firm skeleton, and their body weight is supported especially by the pectoral girdle and pelvic girdle p. 120. Aquatic vertebrates such as the whale have small and weak girdles, because their weight is supported by the buoyancy force p. 121. A bird has a flat and wide sternum for the attachment of flight muscles, hollow and light bones, and a small skull p. 121.

The human skeleton is made up of 206 bones and is divided into the axial skeleton and the appendicular skeleton p. 122. The axial skeleton consists of the skull, the vertebral column, the sternum and the ribs, while the appendicular skeleton consists of the pectoral girdle, the upper limbs, the pelvic girdle and the lower limbs p. 122. The pectoral girdle consists of the clavicle and the scapula p. 123. The upper limb consists of the humerus, radius, ulna, carpus, metacarpus and phalanx p. 123. The pelvic girdle is formed from a pair of hip bones and supports weight, protects the bladder and the reproductive organs p. 123. The lower limb consists of the femur, tibia, fibula, tarsus, metatarsus and phalanx p. 123.

Elephants have big, compact and strong bones because their whole body weight is supported by the endoskeleton, while birds have hollow bones to enable them to fly p. 124. Hollow bones are light and strong, allow the vertebrates to move more quickly and need less calcium and phosphorus p. 124. Experiment 6.1 tests the hypothesis that the hollow bone is stronger than the compact bone, using paper cylinders that support textbooks p. 124.

Stability is the ability of an object to maintain its original position p. 126. An object with a higher centre of gravity is less stable, and an object with a big base area is more stable p. 126. The giraffe spreads its legs to drink, which increases the base area and lowers the centre of gravity p. 127. The kangaroo uses its tail as a strut to increase the base area when not moving p. 127.

6.2 Human Movement and Growth

The contraction and relaxation of the skeletal muscles produce movement p. 128. Each muscle pair that acts in opposite directions is known as antagonistic muscles p. 128. The joint is the meeting place between two or more bones: a movable joint such as the hinge joint at the elbow, or an immovable joint such as the joint at the skull p. 128. The muscles involved in the hinge joint movement are the biceps and triceps p. 128.

The ligament is an elastic, flexible and strong connective tissue that joins two bones p. 129. The tendon connects muscles to the bone and consists of strong and inelastic fibres, so the muscle contraction force is transferred to the bone through the tendon p. 129. The synovial fluid lubricates the joint and provides nutrients to the cartilage, and the cartilage acts as a cushion and reduces friction p. 129. Common problems related to joints and muscles are injuries caused by physical activities and knee pain among the elderly p. 130. An orthopaedist treats injuries such as bone fractures, backbone defects or osteoporosis p. 130.

Human growth is a permanent and irreversible process that occurs due to the increase in number of cells in the body p. 130. Infancy is from 0-3 years, when male and female infants undergo the same, very high rate of growth p. 131. In childhood the rate is lower, and a male child grows faster than a female child p. 131. At 13-15 years both genders grow rapidly and the female teenager is usually taller and bigger p. 131. Growth decreases and stops for the female at 16-18 years, while the male continues until 18-20 years p. 131. The human growth pattern forms an “S-shape” (sigmoid curve), and growth stops when it reaches maturity p. 132. Body mass, height and the diameter of the head are measured at health clinics to monitor the growth of babies and children p. 133.

6.3 Support, Growth and Stability in Plants

A support system helps plants to stand vertically so the leaves are exposed to sunlight to carry out photosynthesis, and gives strength to withstand wind p. 133. The main support for plants is the stem and root p. 133. Woody plants such as the rambutan tree and angsana tree are supported by hard, strong and tough woody tissue built from lignin p. 134. Non-woody plants obtain their support from the turgidity of the cells and will wilt when they lack water p. 134. Additional supports in woody plants are buttress roots, prop roots and stilt roots, and in non-woody plants tendrils, clasping roots and hollow stems p. 134. Stilt roots support mangrove plants living in swamps, and tendrils are present in cucumber, bitter gourd and pumpkin plants p. 134.

Aquatic plants obtain their main support from the water buoyancy force, aided by air spaces formed by aerenchyma tissue p. 135. Some aquatic plants such as the water hyacinth and lotus have swollen, hollow and big stems to increase the buoyancy force p. 135. The age of a woody plant can be found by cutting the trunk across and counting the growth rings, where one ring represents one year p. 135. In the second method, the tree is bored with a special drill to half the diameter of the tree, which saves the tree from being cut p. 136.

The plant stability is influenced by the centre of gravity and the base area, and the lower the centre of gravity, the more stable the plant p. 136. Tall timber trees such as the chengal tree have buttress roots and a tap root that penetrates deep into the earth p. 136. Experiment 6.2 tests the hypothesis that the growth pattern of a green bean plant is sigmoid-shaped p. 137.