A baby's bones begin to grow in the womb. At birth, the skeleton is partially formed. Many bones are still in "parts." The ends (epiphyses) and bony shafts (diaphyses) of long bones form separately in the womb. At birth, the ends of the long bones are mainly cartilage, with centers of bone beginning to form inside. As a child grows, the shafts get longer, and bone gradually replaces the cartilage epiphyses. Through the growing years, a layer of cartilage (the growth plate) separates each epiphyses from the bone shaft.
Clavicle. Image courtesy of: Smithsonian InstitutionBetween 17 and 25 years, normal growth stops. The development and union of separate bone parts is complete. At this point, you and your skeleton are as tall as you are going to get - with many fewer bone parts than you started with!
Facts:The clavicle (collar bone), pictured above, is the last bone to complete growth, at about age 25.Measuring the length of long bones can give an estimate of age for children, but this technique is useful only until bones have stopped growing.The tibia completes growth at about age 16 or 17 in girls, and 18 or 19 in boys.For toddlers to teenagers up to age 21, teeth are the most accurate age indicators. Learn more here!In AdultsSkeletons record an adult's age in several ways. The surfaces of the cranium, pubic bones, and rib ends hold clues. At the microscopic level, investigators can see the bone "remodeling" that takes place throughout life, as well as age-related bone breakdown.
Bone "Remodeling"Femur cross sections of adults ages 24 (left) and 77 (right). Images courtesy of: Smithsonian InstitutionEven after childhood growth stops, bone "remodeling" continues. Throughout a lifetime, bone makes new osteons — minute tubes containing blood vessels. Microscopic exams show these changes, which can indicate adult age to within 5 to 10 years. Younger adults have fewer and larger osteons. Older adults have smaller osteons and more osteon fragments, as new ones form and disrupt older ones.
Clues in the CraniumCraniums of a 20 year-old (left) and a 70 year-old (right). Images courtesy of: Smithsonian InstitutionThe bones that enclose the brain grow together during childhood along lines called cranial sutures. During adulthood, bone "remodeling" may gradually erase these lines, at variable rates. Closure of cranial sutures gives general information about a person's age. It is best used with additional indicators to estimate age, or when other age indicators are unavailable.
Other Age-Related ChangesArthritis on the spine as evidenced by "lipping" of the vertebrae. Image courtesy of: Smithsonian InstitutionWear and tear on a body throughout a lifetime affects the skeleton. Arthritis of the spine and joints can reflect increasing age. Scientists also recognize many other clues to aging, such as the appearance of the rib ends and the cartilage that joins them to the sternum. In a young adult, the rib end walls are thick and smooth, with a scalloped or rounded edge. In an older adult, the walls are thin, with sharp edges, and the rim often has bony, irregular projections.
Photosynthesis primarily happens in the chloroplasts of plant cells, especially in the leaves. However any green part of the plant containing chloroplasts can participate in photosynthesis.
Photosynthesis generally occurs in the chloroplasts of plant cells. These are the organelles where light energy is converted into chemical energy, the process we know as photosynthesis. The chlorophyll molecules, which give plants their green color, are located within the thylakoids of the chloroplasts and play a crucial role in capturing sunlight for photosynthesis.
Chloroplasts are typically found in high concentrations in the plant's leaves, which are themselves organized to maximize light absorption. This is why the leaves are usually the main site for photosynthesis in a plant, but photosynthesis can also occur in any green parts of the plant, including stems and un ripened fruit, meaning any parts where there are cells containing chloroplasts.
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A.
worms
B.
frogs
C.
clams
D.
fish
Any of a subphylum (Vertebrata) of chordates consisting of animals (such as mammals, birds, reptiles, amphibians, and fishes) with a bony or cartilaginous spinal column that replaces the notochord.
The vertebrates are frogs and fish.
Thus, we can conclude that Options B and D are correct.
You can learn more about vertebrates here:
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