DEF Practice Test

Snowshoe Hare 

The snowshoe hare molts during winter to help protect itself from predators. Molting is a process of shedding fur. In the case of the snowshoe hare, this shedding causes the hare to change coat colors from brown to white. This adaptation helps the hare avoid being preyed upon by predators like the lynx. The image shows the predator-prey relationship between the snowshoe hare and lynx over time. 

Climate change and global warming have continued to alter the time at which winter begins, in certain regions.  This is creating confusion about the molting process for snowshoe hares. Scientists have noticed a mismatch process of snowshoe hares having a brown coat during a snowy, wintry, white season. Such a mismatch makes the snowshoe hare vulnerable to predators. 

After years of brown hares mating with jackrabbits, scientists have discovered that snowshoe hares have inherited a gene called agouti. This borrowed gene is found to make it harder for snowshoe hares to turn white in the winter. 

Question 1: Prior to the recent increase in climate change, how did natural selection contribute to a surge in snowshoe hare population growth?

• They became more skilled at finding new places to forage for food in the winter.

• They mismatched their fur coat colors as seasons changed.

• 
  They were able to hide from predators by camouflaging themselves.

• 
  They ran faster and were more agile when trying to stay away from predators.

Snowshoe Hare 

The snowshoe hare molts during winter to help protect itself from predators. Molting is a process of shedding fur. In the case of the snowshoe hare, this shedding causes the hare to change coat colors from brown to white. This adaptation helps the hare avoid being preyed upon by predators like the lynx. The image shows the predator-prey relationship between the snowshoe hare and lynx over time. 

Climate change and global warming have continued to alter the time at which winter begins, in certain regions.  This is creating confusion about the molting process for snowshoe hares. Scientists have noticed a mismatch process of snowshoe hares having a brown coat during a snowy, wintry, white season. Such a mismatch makes the snowshoe hare vulnerable to predators. 

After years of brown hares mating with jackrabbits, scientists have discovered that snowshoe hares have inherited a gene called agouti. This borrowed gene is found to make it harder for snowshoe hares to turn white in the winter. 

Question 2:
Use evidence from the graph and text to explain how the agouti gene will impact future populations of snowshoe hares over time.

Question 3: Mistakes or changes that occur in the DNA sequence are called —

• adaptations

• Darwinism

• natural selection

• mutations

Huntington's disease: What Causes It?

Huntington's disease is a rare but severe brain disorder. It leads to uncontrolled movements and cognitive problems. Like many diseases, scientists have determined that Huntington's disease is caused by genetics. 

Our DNA makes up sections called genes. Genes are sections of DNA that code for a specific product, usually a protein. This protein then goes on to carry out a specific function in the body. Another way to think of genes is that they are instructions that determine traits. There are genes for eye color, hair texture, freckles, and thousands more.

 

In Huntington's disease, the relevant gene is called HTT. The HTT gene holds the instructions for a protein called huntingtin. A person with Huntington's Disease has many repeats of the CAG nucleotides in the DNA of the huntingtin gene. The number of repeats is important in determining the outcome of the disease. 10 to 35 CAG repeats is a normal amount and does not result in Huntington's Disease. A person with 27 to 35 repeats of CAG does not actually develop the disease themselves, but their children may be at risk. A person with 36-60 repeats will develop Huntington's Disease as an adult. Someone with 60 or more CAG repeats in their DNA will likely start showing symptoms of Huntington's disease as a child. 

 

The reason that the CAG repeats cause such a problem is because the increased length of the huntingtin protein gets cut into smaller fragments which then clump together and disrupt the normal function of neurons in the brain.

Question 4:
An effect of Huntington's disease is a brain disorder. What is the cause of the disease?

• A mistake during protein synthesis

• An environmental factor

• 
  The structure of the DNA sequence

• A pathogen

The model shows the process of protein synthesis.

Question 5: Choose three ways the different types of RNA are used.

• rRNA is the ribosome.

• 
  mRNA is the ribosome.

• 
  tRNA moves the amino acids.

• rRNA moves the amino acids.

• 
  mRNA provides the code in translation.

Plants are large, multicellular organisms that create their own food. The process of creating food involves capturing energy from the sun and carbon atoms from the carbon dioxide found in the air. Plants are able to take carbon, oxygen, and hydrogen atoms and create sugar through the process of photosynthesis.

Plants use the sugars they make in photosynthesis to create all the molecules needed to grow by cell division and carry out essential functions like building amino acids into proteins. Many different large biological molecules are needed to give the plant support, move water and nutrients into different parts of the plant, and to respond to outside stimuli. These large biological molecules are mostly made of carbon, hydrogen, and oxygen. With the help of enzymes that speed up chemical reactions, plants can break down the sugars they make in photosynthesis and rearrange the atoms, add new atoms like nitrogen and phosphorous, and create the large biological molecules needed.

Question 6: How are sugars used to make large molecules in plants?

• Sugars spontaneously break down into carbon, hydrogen, and oxygen atoms

• Sugars build upon themselves to become other molecules

• Enzymes add other atoms to sugars to make molecules

• Enzymes break down sugars into carbon, hydrogen, and oxygen atoms so they can be built into new molecules.

Plants are large, multicellular organisms that create their own food. The process of creating food involves capturing energy from the sun and carbon atoms from the carbon dioxide found in the air. Plants are able to take carbon, oxygen, and hydrogen atoms and create sugar through the process of photosynthesis.

Plants use the sugars they make in photosynthesis to create all the molecules needed to grow by cell division and carry out essential functions like building amino acids into proteins. Many different large biological molecules are needed to give the plant support, move water and nutrients into different parts of the plant, and to respond to outside stimuli. These large biological molecules are mostly made of carbon, hydrogen, and oxygen. With the help of enzymes that speed up chemical reactions, plants can break down the sugars they make in photosynthesis and rearrange the atoms, add new atoms like nitrogen and phosphorous, and create the large biological molecules needed.

Question 6: Why are sugars used by plants to make other large biological molecules? Choose three correct answers.

• 
  Sugars are always readily available in the plant

• Sugars are components of other macromolecules

• Sugars spontaneously break down

• 
  Plants do not need sugars

• 
  Large biological molecules are made of carbon, oxygen, and hydrogen

How Do Organisms Obtain Energy?

Every organism is an open system, meaning they exchange energy with the environment. To power cell and body functions, organisms have to constantly replenish their energy supplies through cellular respiration, a process that rearranges the bonds of sugars through chemical reactions to release energy. Typically, plants and animals take in sugars and oxygen gas, called aerobic cellular respiration, to produce carbon dioxide, water, and energy. When there is no oxygen available, cells are still able to produce energy by the process called fermentation or anaerobic cellular respiration, also producing carbon dioxide, water, and energy. While plants can create their own sugars through photosynthesis, animals obtain sugars through eating plants (and animals that ate plants).

Question 8: Based on the information in Passage, what conclusions can be drawn?

• The flow of matter and energy into and out of cells is driven by photosynthesis

• All organisms exchange energy with the environment

• Organisms can obtain energy only by taking in food

• All organisms can undergo aerobic and anaerobic cellular respiration

• All organisms produce carbon dioxide, water, and energy

The picture depicts an alligator in an algae bloom. These happen all around the world, but a famous example is in the Gulf of Mexico. The formation of an algae bloom can lead to a dead zone, where aquatic life such as fish cannot survive. What causes this?

 

Algae blooms are usually caused by an overabundance of nutrients in the water, such as from fertilizer running off into a lake, bay, or coastal area. The nutrients in the fertilizer act as a super food for algae, which then grow and reproduce rapidly. This leads to the algae bloom that you see in the image. When the algae form a layer on top of the water, sunlight can no longer penetrate the water to reach the plants below. With no sunlight, the plants cannot do photosynthesis. When the algae die, they are fed on by bacteria, which use up large amounts of oxygen. Between less photosynthesis from the plants, and the heavy oxygen consumption by the bacteria, oxygen levels in the water drop to unhealthy levels.

 

Dead zones are also known as “hypoxic zones”. “Hypoxia” refers to a reduced level of oxygen in the water.

Question 9: In a dead zone, some species may be able to survive after the oxygen disappears. What must these species be utilizing to survive in these conditions?

• 
  Photosynthesis

• 
  Oxygen

• 
  Anaerobic respiration

• 
  Aerobic respiration

How Do Organisms Obtain Energy?

Every organism is an open system, meaning they exchange energy with the environment. To power cell and body functions, organisms have to constantly replenish their energy supplies through cellular respiration, a process that rearranges the bonds of sugars through chemical reactions to release energy. Typically, plants and animals take in sugars and oxygen gas, called aerobic cellular respiration, to produce carbon dioxide, water, and energy. When there is no oxygen available, cells are still able to produce energy by the process called fermentation or anaerobic cellular respiration, also producing carbon dioxide, water, and energy. While plants can create their own sugars through photosynthesis, animals obtain sugars through eating plants (and animals that ate plants).

Question 10:
Scientists have discovered that organisms can survive in more extreme conditions than once thought possible. There are organisms that flourish at the mouths of underwater volcanoes, in high-salt lakes, in sub-zero temperatures, and in extremely low- and high-pH conditions. In the deep sea, no light reaches the many organisms that live there. Even so, they produce the products of cellular respiration.

Based on your knowledge from  Passage, Identify two possible explanations for this phenomenon.

• Organisms at deep-sea vents exchange energy and matter with the environment, but this flow is driven only by anaerobic cellular respiration.

• 
  Organisms at deep-sea vents do not rearrange the bonds of sugars to produce energy

• Organisms at deep-sea vents use chemical compounds rather than light to produce sugars

• Organisms at deep-sea vents use less energy than land organisms