MCAS Biology: Human Systems Review

Transcription

1 MCAS Biology: Human Systems Review This booklet is designed to introduce or review the human biology concepts tested on the MCAS exam. Since this unit comes at the end of the year, it is often a rushed and sometimes we do not get to a particular topic before you sit the exam. After reading this booklet, you should be capable of excelling at the MCAS exam. Please note, however, that the Honors Biology course expects you to know and understand much more than is found in this simple booklet. In short: mastering this booklet will allow you to master the MCAS, but NOT Honors Biology. 1. The digestive system converts macromolecules into smaller molecules. The purposes of the digestive system are to mechanically digest food into small pieces, to chemically digest food into monomers, and then to absorb the monomers into the blood for use throughout the body. Mechanical digestion starts in the mouth, with chewing. Saliva moistens and lubricates the food, and provides the enzyme salivary amylase to begin the digestion of starch. The chewed food is then pushed down the esophagus by peristalsis (rhythmic contractions of smooth muscle) into the stomach. Here, stomach acid sterilizes the food and the enzyme pepsin begins to break down proteins. From the stomach, food moves into the small intestine, a 20-foot long tube. In the first foot of the small intestine, the pancreas adds many different digestive enzymes to break down all of the biomolecules in your meal. In this first foot, the liver via the gall bladder adds bile, which mechanically breaks down lipids. In the remaining 19 feet of the small intestine, biomolecules are absorbed through little finger-like projections called villi and microvilli (the use of these small structures increases the surface area of the small intestine). Finally, the indigestible remains of the meal enter the large intestine, where liters of water are reclaimed. The nutrients from the food are brought to the liver by the circulatory system. Here, toxins in your blood are neutralized and the biomolecules are processed. Some of the nutrients may be stored in your liver for future use. Others may be released into your blood for immediate use by your body.

2 2. The circulatory system transports nutrients and oxygen, and removes cell wastes. Kidneys and liver remove waste from blood. The main purpose of the circulatory system is to transport oxygen and nutrients throughout the body. The heart pumps oxygen-rich blood through the arteries. The vessels narrow into capillaries, where nutrients and oxygen are ken up by the body cells. The deoxygenated blood then returns to the heart through the veins. The veins return the oxygen poor blood into the right atrium; it then flows into the right ventricle. The blood travels to the lungs through the pulmonary artery, where oxygen diffuses into the blood, and returns to the heart through the pulmonary vein. Finally, it is pumped through the left atrium into the left ventricle and then back out to the body. Arteries are thick-walled blood vessels that carry blood away from the heart remember Artery, Away. Veins are thin-walled blood vessels that contain valves to keep blood from going backwards. Capillaries are smaller blood vessels where diffusion of nutrients and oxygen into surrounding cells occurs. Capillaries are one cell thick. There are three types of blood cells. Red blood cells use the protein hemoglobin to carry oxygen through the circulatory system. White blood cells defend the body from foreign invaders. Platelets are small fragments of cells that clot blood in wounds. Waste products are carried in the blood plasma. Highly toxic wastes are detoxified in the liver, and then the safer forms are deposited into the blood. Wastes in the blood plasma especially nitrogenous wastes from the breakdown of proteins are removed by the kidneys, and collected into urine. The kidneys are also responsible for removing or conserving water to maintain homeostasis in the body. 3. The respiratory system provides exchange of O2 and CO2. The primary purpose of the respiratory system is to supply the body with steady amounts of oxygen (O 2 ), and remove carbon dioxide (CO 2 ) from the body. The respiratory system works closely with the circulatory system. The air enters through the mouth or nose, travels down the pharynx, larynx, trachea, bronchi and finally into the lungs. There, the air enters alveoli small hollow spheres where gas exchange occurs with the bloodstream. Many small alveoli increase the surface area of the lungs, allowing more gas exchange. Cilia line the respiratory surfaces, and help trap and filter out particles that you inhale. The contraction of the diaphragm (a muscle in your thorax) causes the chest cavity to expand, and the increase in volume pulls oxygen-rich air into the lungs. The relaxation of the diaphragm causes a decrease in volume in the lungs and carbon dioxide-rich air is forced out. An increase in activity or need for oxygen by the mitochondria causes an increase in breathing rate in order to maintain homeostasis.

3 4. The nervous system mediates communication. The nervous system is a modified endocrine system. Its primary roles are to provide fast communication about stimuli from outside the body, and allow quick response (like movement) to that information. It consists of the central nervous system (the brain and spinal cord) and the peripheral nervous system (nerves in the body and extremities). The basic structural unit is the neuron (nerve cell), which is shown in the adjacent diagram. There are three types of neurons: sensory neurons sense different conditions (e.g., pain, light, or pressure); interneurons (in the brain and spinal cord) interpret stimuli and decide how to respond to them; motor neurons control skeletal muscles and allow precise movement. One of the simplest responses of the nervous system is a reflex. In a reflex, your sensory neurons detect a stimulus, for example, you touch something hot. This stimulus travels down the sensory neuron from your hand to your spine. Interneurons in the spine interpret the stimulus and react to it, which triggers a motor neuron controlling an arm muscle. This new stimulus travels down the motor neuron and causes your arm muscle to contract, pulling away from the hot object. Your brain is one of the most complex collections of interneurons known. Your brain has three general parts: the cerebrum, where memory, thought, and emotion are processed; the cerebellum, which coordinates movement and is the home of athletic muscle memory; and the medulla and brainstem, which integrate the brain and the spine and is the site of basic life-support functions like control of heartbeat, breathing, and body temperature. 5. The muscular/skeletal system supports the body and allows for movement. Bones produce blood cells. The skeletal system provides structure and support. Bones of the body protect internal organs such as the lungs and the heart, and provide a site for muscle attachment, which allows movement. Bone marrow is inside the bone, and it produces blood cells. Bones also store minerals, especially Ca 2+ (calcium ions). Besides bone, other tissues make up the skeletal system. Tough, flexible cartilage acts as a cushion between bones (to avoid bone-to-bone contact), and forms your ears and nose. Ligaments are tough cables that attach bone to bone and tendons are cables that attach bone to muscle. The point at which two bones meet is known as a joint. There are several types of joints: hinge joints are found in your elbows and knees; ball and socket joints make up your shoulder and hips; pivot joints allow rotation of your forearm or to shake your head no ; and immovable joints, such as the joints between the bones of the skull, do not move. Remember the location of these bones: the femur is in your thigh, and your radius and ulna are in your wrist.

4 6. The sexual reproductive system allows organisms to produce offspring that receive half of their genetic information from their mother and half from their father, and that sexually produced offspring resemble, but are not identical to, either of their parents. The reproductive system refers to the production of eggs and sperm, as well as the processes that lead to fertilization. In asexual reproduction, only one mate is needed. The offspring created are identical to the parent, so the offspring o not vary and may have difficulty surviving in times of hardship for the species. We will be focusing on sexual reproduction between two members of the same species, with different sexes. Males produce sperm. Sperm are created through meiosis, and are haploid (n). Spermatogenesis is the meiotic process that produces the sperm cells. Sperm cells have flagella (a whip-like tail) and a head containing the chromosomes. They eventually swim to the egg once introduced into the female. Females produce eggs during their development. They do not develop these eggs further until fertilization, the introduction of sperm and eggs that yield a zygote. The female undergoes a menstrual cycle. This cycle provides for moments of a peak fertilization opportunity. The follicular phase is the creation of the egg, ovulation is the release of the egg, and the luteal phase is the process of estrogen secretion afterwards. When a sperm cell reaches the egg, it fuses with the egg cell. Once one sperm enters the egg, the egg no longer allows entrance of other sperm cells. The two cells will eventually yield a diploid (2n) zygote. This will eventually yield an embryo once development has occurred. The embryo shares DNA from both the father and mother, and the offspring expresses traits from each parent. 7. Communication among cells is required for coordination of body functions. The endocrine system secretes hormones from glands. Hormones are chemical messengers that travel in the bloodstream. They trigger responses in target cells. One hormone can trigger different responses in different types of target cells. Since hormones travel through the bloodstream, endocrine communication is slower than nervous communication. It is also less specific, and can cause a response in more cells and thus more systems than nervous impulses. Hormones must be received by the target cells in order to get a response. There are different classes of hormones, each of which interacts with the target cells in a different manner. Protein hormones like insulin and glucagon bind to the outside of the target cell. Steroid hormones like testosterone and estrogen enter the target cell. An example is adrenaline, produced in the adrenal glands over the kidneys. When a person is scared or under stress, adrenaline is released. It travels through the blood, and has a number of effects at different organs. It increase your respiration rate, increases your heart rate, releases sugar from your liver into your blood stream, and redirects blood away from the skin into the core of the body. Note how the endocrine system interacts with many other systems.

5 8. Body systems interact to maintain homeostasis using physiological feedback loops. Homeostasis is the maintenance of a constant internal environment regardless of changes in the external environment. For example, whether the temperature outside is 0 C or 45 C, your body temperature is kept at 37 C. All of your systems work together to maintain homeostasis. If you are competing in the 100m dash, when the starter pistol fires your adrenal glands (endocrine system) release a flood of adrenaline into your blood stream. In response to the adrenaline, your liver dumps a huge supply of glucose (stored from a previous meal processed by your digestive system) into your blood. Your arteries and capillaries carry the adrenaline and the glucose throughout your body (circulatory system). As your leg muscles (muscular system) pull on your leg bones (skeletal system), they quickly use up the oxygen in your blood and are starving for more. In response, your brain speeds up your breathing (respiratory system) to bring more oxygen to your blood. Your heart (also circulatory) beats faster in order to bring this oxygen to your muscles quicker.