Which of the following statements is true about folate?

Folate

Folate is a B-vitamin that is naturally present in many foods. A form of folate, called folic acid, is used in dietary supplements and fortified foods. Humans need folate to make DNA and other genetic material. Folate is also needed for the body’s cells to divide.

The recommended amount of folate varies, depending on age and life stage. Average daily recommended amounts are listed in the table in micrograms (mcg) of dietary folate equivalents (DFEs). All women and teen girls who could become pregnant should consume 400

400

mcg of folic acid daily from supplements, fortified foods, or both in addition to the folate they get naturally from foods.

Folate is naturally present in many foods and food companies sometimes add folic acid to other foods, including bread, cereal, and pasta. The best way to get enough folate is to eat a variety of foods, including vegetables, fruits, nuts, beans, grains, and grain-based foods like flour. Only small amounts of folate are found in most animal foods like meats, poultry, seafood, eggs, and dairy products.

Folic acid is available in multivitamins and prenatal vitamins. It is also available in B-complex dietary supplements and supplements containing only folic acid.

Most people in the United States get enough folate, but some people get barely enough. Getting too little folate can result in megaloblastic anemia, which causes weakness, fatigue, trouble concentrating, irritability, headache, heart palpitations, and shortness of breath. Folate deficiency can also cause open sores on the tongue and inside the mouth as well as changes in the color of the skin, hair, or fingernails.

Women who don’t get enough folate are at risk of having babies with neural tube defects, such as spina bifida. Folate deficiency can also increase the likelihood of having a premature or low-birth-weight baby.

Choose the set of words that best completes the following sentence:

When a person’s blood glucose level becomes too low, _____ cells in the pancreas will release _____.

Homeostatic Regulation of Blood Glucose

Homeostasis refers to an organism’s ability to maintain a nearly constant internal environment within a narrow range that supports life. Examples of homeostasis in humans and other mammals include regulation of: body temperature, blood pH, and concentrations of ions and glucose in the blood. These homeostatic mechanisms actively maintain a stable internal environment even while there are changes constantly taking place in the organism’s external environment.

One example of homeostasis in humans involves regulation of the blood glucose concentration. After a meal, glucose levels in the blood may rise above the normal set point of about 90 milligrams per 100 milliliters of blood plasma. Beta cells within the pancreas detect the rise in blood glucose and respond by secreting insulin into the bloodstream. The insulin acts as a signal to certain cells, mainly liver, fat, and muscle cells, to increase uptake of glucose. The increased uptake of glucose from the blood lowers the blood glucose level back to the normal set point. The glucose that has been taken up by cells will be used for energy or converted to glycogen, a storage polysaccharide.

If the level of blood glucose drops too low, such as between meals, pancreatic alpha cells are stimulated to secrete glucagon into the blood. Glucagon is a hormone that signals cells in the liver to convert glycogen to glucose, which is released back into the bloodstream to return the blood glucose level to the normal set point.

Based on the results of the experiment, should doctors prescribe a low-carbohydrate diet to patients that need to reduce their LDL cholesterol levels?

Does a Low-Carbohydrate Diet Reduce LDL Cholesterol?

Scientists are conducting an experiment to determine whether eating a low-carbohydrate diet will reduce LDL cholesterol in patients. For 30 days, five men are placed on a low-carbohydrate diet, and five men are told to eat their normal diet. At the end of the experiment, LDL cholesterol is measured in all ten men. Results are shown in the table.

Copying DNA Sequence

The polymerase chain reaction (PCR) copies a sequence of DNA. In order to do this, a strand of DNA is mixed with nucleotides (DNA precursors). Nucleotides target a spe- cific piece of DNA, as well as polymerase, an enzyme that helps to assemble DNA. Heat is applied until the temperature reaches 200°F. The energy from the heating sep- arates the DNA strands. The mixture is then cooled to 140°F. At this temperature, the primers attach themselves to the DNA strands. Raising the temperature to 160°F causes the nucleotides to begin to attach to the DNA strands. After all this, two copies of the DNA are created.

In order to clone an organism, you require an identical DNA blueprint. Why is the PCR something a scientist who is interested in cloning would want to study?

Heredity, Then and Now

How often have you seen a young child and said, “She takes after her parents.” Many traits in a child do come from her parents. Physical and other characteristics, such as hair color and nose shape, are transmitted from one generation to the next. These characteristics, passed from one generation to the next, exist because of genetic code.

The first scientist to experiment with heredity was Gregor Mendel during the 19th century. Mendel experimented with pea plants and noted that characteristics appear- ing in “child” plants were similar to the “parent” plants. Mendel hypothesized that these characteristics were carried from generation to generation by “factors.” It took many years of research to understand why children often look like their parents, but genetic code is now the basis of the study of heredity. 10. According to the passage, what is a pri mary determinant for characteristics of the next generation?

Why Do Birds Fly South for the Winter?

Every fall, the sky is full of birds flying south for the winter. However, you can still see a few birds in the northern part of the country during the winter. Scientists have advanced theories about this phenomenon.

Some birds eat insects for food. In winter, many species of birds fly south, because that’s where the food exists. In southern states, insects are available all year long, providing a banquet for the birds, whereas in the northern parts of the country, insects (as well as other food sources, such as seeds and berries) are scarce or even nonexistent during the winter. The birds fly south for winter to follow the food. In the spring, as insects once again become plentiful in the northern states, the birds still follow the food, this time to the north.

Why do migratory birds return to the northern states in the spring?

The process of metabolism is an essential process in every living cell. Metabolism allows the cell to obtain and distribute energy, which is necessary for survival. Light from the sun is absorbed and converted into chemical energy by photosynthesis, and it is this chemical energy that is necessary for animals to survive.

One of the primary carbohydrates derived from plants is glucose. Through a process called glycolysis, energy is obtained from glucose. This reaction takes place in mito- chondria and the glucose molecule is broken down into pyruvic acids, which are fur- ther broken down into molecules, such as ethanol and lactic acid. This process is cyclical as the energy produced keeps the fermentation going.

Pyruvic acids are broken down to carbon dioxide and water by respiration, which releases far more energy. What started out as sunlight has become energy that keeps animals alive.

How do animals depend on plants to stay alive?

One of the creatures living in all the world’s oceans is the jellyfish. Although it lives in the ocean, it is not a fish. The jellyfish is an invertebrate; that is, an animal lacking a backbone. Not only does it lack a backbone, but the jellyfish has no heart, blood, brain, or gills and is over 95-percent water.

The jellyfish has a body and tentacles. These tentacles are the long tendrils around the bell-like structure that contain stinging cells, which are used to capture prey. The movement of the prey triggers the sensory hair in the stinging cell, and the prey is then in trouble.

Unfortunately, people are also in trouble if they get too close to the tentacles of a jel- lyfish. The stings are not fatal to humans but can cause a great deal of discomfort.

Why is a jellyfish considered an invertebrate?