State the differences between phototropism , gravitropism , hydrotropism , and thigmotropism. ( HELP ITS URGENT DO RIGHT NOW !!! )

Tropisms are curvature movements of plant organs induced by directional environmental stimuli. Phototropism is the curvature of a plant organ induced by an external gradient of light. It manifests itself in seedlings, shoots and reproductive organs. On the other hand, hydrotropism is the growth response of an organism to water or moisture. Gravitropism is a curvature movement of a plant organ with respect to the direction of gravitational acceleration and thigmotropism are plant growth responses to contact, allowing roots to grow around various obstacles.

Explanation:

Plants have certain movements towards certain stimuli, for example, the roots seek the earth; the stem and leaves grow in the direction of the light. These movements are made in the direction of those factors because they are necessary for the survival of the plant. The movements that plants make in favor or not of a stimulus is called tropism. The direction of the different tropisms depends on the direction of the stimulus and they are named according to the stimulus. Phototropism is the orientation of the plant towards the light. The leaves and the stem will grow in the direction of the light (positive phototropism), these responses to stimuli are regulated by substances called plant hormones or phytohormones. The subterranean organs (the roots) show negative phototropism, grow towards the ground in opposition to the stimulus or are insensible to light gradients. On the other hand, gravitropism refers to the curvature response of a plant organ with respect to the direction of gravitational acceleration. The response is also due to a differential growth between opposite parts of the organ and, therefore, it occurs in growth organs or in mature organs that regain the ability to grow, it will be positive because the root goes towards the ground in the roots and negative in the aerial organs. Gravitropism is a threshold phenomenon, that is, it requires a minimal stimulus to trigger the response. The dose of the gravitational stimulus is a function of the direction and magnitude of the acceleration and the presentation time. Hydrotropism is a form of tropism characterized by the growth or movement response of a cell or an organism to moisture or water, that is, directional growth of plant roots in relation to the availability of water. Thigmotropism is growth and movement in response to contact, it allows roots to grow around various obstacles and is responsible for the ability of climbing plant stems to roll over supporting structures. When the aerial parts of a plant tend to grow around a support, they have positive thigmotropism. The roots, on the other hand, have negative thigmotropism, since it allows them to avoid obstacles that appear on the ground, such as rocks.

synovial joints are characterized by the presence of a joint cavity. the walls of this space are formed by the articular capsule, a fibrous connective tissue structure that is attached to each bone just outside the area of the bone’s articulating surface. the bones of the joint articulate with each other within the joint cavity.

friction between the bones at a synovial joint is prevented by the presence of the articular cartilage, a thin layer of hyaline cartilage that covers the entire articulating surface of each bone. however, unlike at a cartilaginous joint, the articular cartilages of each bone are not continuous with each other. instead, the articular cartilage acts like a teflon® coating over the bone surface, allowing the articulating bones to move smoothly against each other without damaging the underlying bone tissue. lining the inner surface of the articular capsule is a thin synovial membrane. the cells of this membrane secrete synovial fluid (synovia = “a thick fluid”), a thick, slimy fluid that provides lubrication to further reduce friction between the bones of the joint. this fluid also provides nourishment to the articular cartilage, which does not contain blood vessels. the ability of the bones to move smoothly against each other within the joint cavity, and the freedom of joint movement this provides, means that each synovial joint is functionally classified as a diarthrosis.

outside of their articulating surfaces, the bones are connected together by ligaments, which are strong bands of fibrous connective tissue. these strengthen and support the joint by anchoring the bones together and preventing their separation. ligaments allow for normal movements at a joint, but limit the range of these motions, thus preventing excessive or abnormal joint movements. ligaments are classified based on their relationship to the fibrous articular capsule. an extrinsic ligament is located outside of the articular capsule, an intrinsic ligament is fused to or incorporated into the wall of the articular capsule, and an intracapsular ligament is located inside of the articular capsule.

at many synovial joints, additional support is provided by the muscles and their tendons that act across the joint. a tendon is the dense connective tissue structure that attaches a muscle to bone. as forces acting on a joint increase, the body will automatically increase the overall strength of contraction of the muscles crossing that joint, thus allowing the muscle and its tendon to serve as a “dynamic ligament” to resist forces and support the joint. this type of indirect support by muscles is very important at the shoulder joint, for example, where the ligaments are relatively weak.

additional structures associated with synovial joints

a few synovial joints of the body have a fibrocartilage structure located between the articulating bones. this is called an articular disc, which is generally small and oval-shaped, or a meniscus, which is larger and c-shaped. these structures can serve several functions, depending on the specific joint. in some places, an articular disc may act to strongly unite the bones of the joint to each other. examples of this include the articular discs found at the sternoclavicular joint or between the distal ends of the radius and ulna bones. at other synovial joints, the disc can provide shock absorption and cushioning between the bones, which is the function of each meniscus within the knee joint. finally, an articular disc can serve to smooth the movements between the articulating bones, as seen at the temporomandibular joint. some synovial joints also have a fat pad, which can serve as a cushion between the bones.

it marks things for degradation via the proteasome. it alters there celluar location.