Biology Midterm Questions

What molecules make up the cell membrane? Which part of the cell membrane is hydrophobic and the part that is hydrophilic?

A cell membrane is a phospholipid bilayer. The phospholipid bilayer consists of a polar hydrophilic phosphate head and a nonpolar hydrophobic fatty acid tail. Cell membranes also contain protein channels that facilitate the transport of substances across a cell membrane. They do this through the process of either facilitated diffusion or active transport depending on the concentration gradient, or the difference in the concentration of substances inside and outside the cell membrane.

Explain in detail what happens when a cell is placed in a hypertonic solution. Give a reason for your answer.

A hypertonic solution is a solution that has a high solute concentration and low water concentration. Due to osmosis, the process by which a higher concentration of water molecules diffuses across a semipermeable membrane to a lower concentration of water, when a cell is placed in a hypertonic solution, the water from the cell diffuses across the semipermeable membrane to the outside solution due to its low water concentration. When the water leaves the cell, the cell will ultimately shrivel from lack of water.

Describe one way that burning rain forest trees affects nutrient cycling differently than cutting them down and leaving them on the forest floor.

Burning trees instead of leaving them on the ground negatively impacts the nutrients cycle because it releases many hazardous chemicals in smoke that harm the environment. For example, carbon dioxide, which is a greenhouse gas, is released. These gases, when released into the atmosphere, allow sunlight to pass through the earth but trap heat by reflecting and radiating it from Earth's surface. Because of this, temperatures increase or what is called "Global Warming." This could lead to many issues like rising sea levels and an increase in flooding. Leaving a tree on the ground allows the soil to absorb the nutrients in the tree and allow other plants to absorb nutrients in the future, so the nutrient cycle continues.

Define "active transport" and explain an example.

During active transport, substances move against the concentration gradient, from an area of low concentration to an area of high concentration across a cellular membrane. Active transport requires energy, such as ATP, to cross the cellular membrane. An example of active transport is endocytosis. Endocytosis takes large compounds or molecules into the cell that are too large to passively cross the cell membrane. Due to the size of the compounds or molecules, they have to be brought across the membrane using active transport which uses energy.

The teacher told the students that one of the foods is a type of fruit and the other is a type of meat. Identify which food is the fruit and which is the meat. Explain your answer.

Food 2 is a type of fruit because it contains a large amount of carbohydrates. Fruits are high in carbs due to their natural sugars. Food 1 is a type of meat because meat is commonly full of protein. Meat is full of protein because it is the muscle tissue of an animal which is a great source of protein.

Explain why immigration and emigration are not likely to have an effect on the size of the island's moose population.

Immigration is the act of coming to a foreign place to live and emigration is the act of leaving one's native land to settle in another. Both of these processes require a mode of transportation to get from one place to the other. Since the island is in a remote location and the moose have no way to get off or on the island, it would be impossible for them to immigrate to or emigrate. Therefore, the population would not be affected by this. Also, if the island is secluded, new animals, invasive species, or new diseases most likely won't impact the island which means the balance between all the animals stay the same and the food chain does not change.

Identify and EXPLAIN two different natural factors that could have contributed to the change in moose population size you described in part (b).

In the natural world, limiting factors like the availability of food, water, shelter and space can change animal and plant populations. Without food and water the moose would not be able to live and therefore die. If there wasn't enough space the resources would decrease, which could cause the death rate to decrease. Competition for resources can then cause populations to decrease because they directly kill each other to live or indirectly kill each other by stealing others resources to live.

Define "passive transport" and explain an example.

Passive transport is the movement of substances through diffusion across a cell membrane without the expenditure of energy. An example of passive transport is osmosis. Osmosis by definition is the diffusion of a solvent through a semipermeable membrane. During osmosis, the solvent moves from the solution that is lower in solute concentration to the solution that is higher in solute concentration. No energy is needed for osmosis to occur making it a form of passive transport.

Describe what happened to the size of the island's moose population from 1995 to 1997, and describe how the birth rate and the death rate must have compared during this time.

1995 to 1997 decreased. 1995 birth rates were high and death rates were low. 1997 birth rates were low and death rates were high.

Identify the main type of macromolecule found in Food 2. Explain that molecule's structure. Then, list its main function in the cell, and list one example of this molecule that's used by the human body.

The main type of macromolecule found in this is carbohydrates. They're made of sugar and starch molecules and typically hexagonal in shape. It contains the elements carbon, hydrogen, and oxygen. The ratio of these is 1 carbon: 2 hydrogen: 1 oxygen. The main function of carbs is providing energy and storage of energy. Carbohydrates provide the body with glucose, which is converted to energy used to support bodily functions and physical activity.

Describe one role of the trees in the oxygen cycle.

The oxygen cycle is the constant movement of oxygen through the atmosphere, plants and animals, and the earth's crust. Trees go through the process of photosynthesis that produces oxygen. During the light dependent reaction of photosynthesis, ADP is converted to ATP through photophosphorolation, NADP+ is converted to NADPH, and oxygen is produced from the splitting of water. The oxygen produced is then released into the atmosphere from the tree.

Identify and describe one biological process that raises carbon dioxide concentrations by adding carbon dioxide to the atmosphere.

Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. Cellular respiration needs glucose and oxygen to be performed and releases carbon dioxide and water. It is split into three main parts: Glycolysis, Krebs cycle, and electron transport chain. Glycolysis breaks a glucose molecule in half an creates two pyruvic acid molecules. It uses 2 ATP, makes 4 ATP, so has net of 2 ATP. Then, the pyruvic acid is broken down into carbon dioxide in a series of energy extracting reactions. Produces a net of 2 ATP. Finally, ETC uses the high-energy electrons from the Krebs cycle to convert ADP to ATP. The waste products of cellular respiration are carbon dioxide and water that are released. The carbon dioxide released from all the organisms in the forest performing cellular respiration increases carbon dioxide concentration by adding carbon dioxide to the atmosphere.

Describe how nighttime carbon dioxide concentrations near the forest should compare with the midday concentrations near the forest. Explain your answer using two biological processes.

Night time carbon dioxide concentrations are higher that the midday concentrations because in order for photosynthesis to happen (which takes carbon dioxide in as a reactant) sunlight needs to be present. Without sunlight, at nightime, plants cannot undergo photosynthesis which in turn raises carbon dioxide concentrations because the plants can't remove the carbon dioxide from the air. All animals, plants, and fungi, and also in algae and other protists undergo cellular respiration. Cellular respiration is the process that releases energy by breaking down food molecules in the presence of oxygen. Cellular respiration is split into three main parts: Glycolysis, Krebs cycle, and electron transport chain. Glycolysis breaks a glucose molecule in half an creates two pyruvic acid molecules. It uses 2 ATP, makes 4 ATP, so has net of 2 ATP. Then, the pyruvic acid is broken down into carbon dioxide in a series of energy extracting reactions. Produces a net of 2 ATP. Finally, ETC uses the high-energy electrons from the Krebs cycle to convert ADP to ATP. The waste products of cellular respiration are carbon dioxide and water that are released. The constant addition of carbon dioxide being released from the organisms during cellular respiration and the plants unable to perform photosynthesis and take in the carbon dioxide, makes night time have a higher concentration of carbon dioxide.

How is nitrogen removed from the atmosphere and converted into a useable form for plants.

Nitrogen is removed from the atmosphere and converted to a usable form for plants through bacteria and lighting fixation. In lightning fixation, each bolt of lightning carries electrical energy that is powerful enough to break the strong bonds of the nitrogen molecule in the atmosphere. Once split, the nitrogen atoms quickly bond to oxygen in the atmosphere, forming nitrogen dioxide, which dissolves in moisture to form nitrates that are carried to Earth's surface by precipitation. In bacteria fixation, the bacteria in the roots of legumes convert the nitrogen in the atmosphere into a usable form for plants.

Identify and EXPLAIN two carbon cycle processes that add carbon dioxide to the atmosphere.

One process that adds carbon dioxide to the atmosphere is cellular respiration. In cellular respiration, glucose is broken down into pyruvic acid and ATP through glycolysis. This acid is then broken down into carbon dioxide in a series of energy extracting reactions and more ATP is produced, which is called the Krebs cycle. Finally, the electron transport chain uses high-energy electrons from the Krebs cycle to convert ADP to ATP. The carbon dioxide produced from the Krebs cycle releases carbon dioxide into the atmosphere when the organism breathes. Another process is the burning of fossil fuels, like coal and natural gas, adds carbon dioxide to the atmosphere. When it's released, it allows sunlight to pass through the Earth's atmosphere, but traps the heat by radiating and reflecting it back to the Earth's surface. This results in average temperatures increasing. This concept is most commonly known as the greenhouse effect.

Identify and EXPLAIN one carbon cycle process that removes carbon dioxide from the atmosphere.

One process that removes carbon dioxide from the atmosphere is photosynthesis. In the first part of photosynthesis or the light reaction, chlorophyll molecules in the membrane capture light energy. Then, the chloroplasts use the captured energy to split the absorbed water into oxygen and hydrogen ions. The oxygen is a byproduct released through the leaves of the stomata. The chloroplasts then use the hydrogen ions to create a high energy molecule called NADPH and use the captured light energy to create ATP. This occurs in the chloroplasts. In the second part or, the light independent reaction, sugar is made from the atoms in carbon dioxide, the hydrogen ions, and the high-energy electrons carried by NADPH. NADP+ and ADP+P are products of this cycle. This occurs in the stroma of the chloroplasts. Due to carbon dioxide being a reactant of photosynthesis, the carbon dioxide is taken from the atmosphere.

Describe one role of the trees in the water cycle.

One role the trees play in the water cycle is through transpiration. Transpiration in trees is the process by which water is carried through the tree from the roots to small pores on the underside of leaves. There it changes into vapor and is released into the atmosphere. Transpiration is a vital process for the water cycle because it returns water back into the atmosphere.

Describe one action that humans could take to reduce levels of carbon dioxide, and explain how the action would reduce carbon dioxide levels.

One way that humans can decrease the amount of carbon dioxide in the atmosphere is not driving a car anywhere that's walking distance or carpooling. Cars are fueled by gas, a fossil fuel. The engines burn the gas and release carbon dioxide in the form of exhaust. If the usage of cars is limited by walking or carpooling carbon dioxide levels would be reduced.

Describe one role of the trees in the carbon cycle.

The carbon cycle describes the process in which carbon atoms continually travel from the atmosphere to the Earth and then back into the atmosphere. Trees go through photosynthesis. Photosynthesis uses light, carbon dioxide, and water to produce oxygen and glucose. The trees absorb the carbon dioxide from the atmosphere and turn it into oxygen. Trees also go through cellular respiration which releases carbon dioxide into the atmosphere.

Explain why the lowest carbon dioxide concentration occurs closest to the forest. Be sure to include a biological process in your answer.

The lowest carbon dioxide concentration occurs closest to the forest because the forest is filled with plants that undergo photosynthesis. Photosynthesis is a process by which plants and some other organisms use light energy to convert water and carbon dioxide into oxygen and high-energy carbohydrates such as sugars and starches. The reactants of photosynthesis, what goes into the plant, are light, water, and carbon dioxide. The carbon dioxide along with the other reactants are converted into sugars and starches. All the plants take in the carbon dioxide from the air which is why a forest filled with plants have a lower carbon dioxide concentration.

Identify the main type of macromolecule found in Food 1. Explain that molecule's structure. Then, list one of its functions in the cell, and list one example of where this molecule would be found in high concentration in the human body.

The main macromolecule is protein. The structure of a protein is one or two chains of linked amino acids called polypeptides. One of its functions in the cell is to control and speed up chemical reactions in the cell, act as enzymes. Protein is necessary in building and repairing body tissues. One place where this can be found in high concentration is muscle tissue.

Explain the function of the cell membrane.

Their function is to keep a cell organized by regulating the transport of substances across the membrane, only allowing certain substances to pass. Cell membranes enable organisms to maintain homeostasis by regulating the materials that may enter or leave a cell. The cell membrane also protects the cell.