Natural Selection End of Unit Exam

Blue jays are birds that live in the forest. They can have beaks of different thicknesses. Blue jays use their beaks to get to the seeds they eat. Blue jays with thinner beaks can easily reach and eat the seeds inside pinecones. Blue jays with thicker beaks can easily open and eat seeds with hard shells. The diagrams below show three possible blue jay populations. If their environment changes to have only seeds in pinecones, which of the following blue jay populations will most likely survive? (L1)

• Populations 1 and 2 will most likely survive.
• Populations 2 and 3 will most likely survive.
• Only Population 2 will survive because it is the only population with variation.
• All the populations will survive because the blue jays will change the thickness of their beaks if they need to.

Scientists measured the spine size of a population of cactuses found in an area in 1970. They measured the spine size of the cactus population again in 2015. Which of the statements below best describes the difference in the cactuses at the two time points? (SC1)

• The cactuses in 1970 had smaller spines than the cactuses in 2015.
• The cactuses in 1970 had larger spines than the cactuses in 2015.
• There were more cactuses in 1970 than there were in 2015.
• There was more variation in spine size in 1970 than there was in 2015.

Northern foxes can have different fur colors. The foxes hunt squirrels for food. Foxes that have fur the same color as their environment are better at getting closer to squirrels and catching them. The diagram below shows a population of foxes that live in one area. At time 1, the population had the same number of brown and white foxes. At time 2, after many generations, there were many more brown foxes and fewer white foxes in the population. How did the environment change between time 1 and time 2? How did the population change? (L2)

• You cannot tell how the environment changed. With each generation, more foxes passed on the gene for brown fur to their offspring.
• The environment became brown. Brown foxes are more likely to survive, so the white foxes changed to have brown fur.
• The environment became brown. Brown foxes are more likely to survive, so both kinds of foxes passed on the gene for brown fur to their offspring.
• The environment became brown. With each generation, more brown foxes survived long enough to pass on the gene for brown fur to their offspring.

Scientists measured the spot size of all the guppies (small fish) that lived in a river 40 years ago. They measured the spot size of the guppy population again last year. When was there more variation in the spot size of guppies in the river? (SC2)

• These bar graphs do not show the amount of variation in the population.
• There was the same amount of variation in spot size 40 years ago and last year.
• There was more variation 40 years ago.
• There was more variation last year.

The population of hummingbirds once lived in an environment where there were very few long or medium flowers. The image above shows what the population looked like then. The environment changed so that mostly long and medium flowers now grow there. The diagrams below show two predictions for what the population could be like after many generations. Which prediction best shows what the population could look like after many generations? What caused it to change? (L3)

• Prediction 1 is best. Two hummingbirds with short or medium beaks had a baby with a mutation in its genes for the long-beak trait. Because long-beak hummingbirds are more likely to survive, that baby survived long enough generations.
• Prediction 1 is best. Hummingbirds with long beaks are more likely to survive, so hummingbirds with short and medium beaks began to have offspring with a mutation in its genes for the long-beak trait so that their offspring would have a better chance to survive.
• Prediction 2 is best. A hummingbird could have been born with a mutation in its genes for the long-beak trait and lived for a little while. Because long-break hummingbirds are more likely to die, it would have been more likely to die before it had any offspring, so the final population will only have medium or short beak hummingbirds
• Prediction 2 is best. A hummingbird could have been born with a mutation in its genes for the long-beak trait, but having a mutation in its genes would have caused it to die when it was born, so the final population will only have medium or short beak hummingbirds.

Guppies are small fish that live in South American rivers. They can have different sized spots on their bodies. The river bottoms are covered in rocks. Guppies with spots that are the same size as the rocks on the bottom are harder for bigger fish to see and catch. The diagrams below show three possible guppy populations. If their environment changes to have only large rocks, which of the following guppy populations will most likely survive? (L1)

• Only Population 2 will survive because it is the only population with variation.
• All the populations will survive because the guppies will change the size of their spots if they need to.
• Populations 1 and 2 will most likely survive.
• Populations 2 and 3 will most likely survive.

Scientists measured the beak length of a population of birds in a lake in 1960. They measured the beak length of the bird population again in 2010. When was there more variation in the beak lengths of the birds by the lake? (SC2)

• There was the same amount of variation in 1960 and in 2010.
• These bar graphs do not show the amount of variation in the population.
• There was more variation in 2010.
• There was more variation in 1960.

Emerald tree boas are snakes that live in rain forest trees. The snakes have scales on their skin that can be different colors. Eagles hunt the snakes in the trees. Snakes with scales that are the same color as the leaves around them are harder for the eagles to see and catch. The diagram below shows a population of snakes that live in a rain forest. At time 1, the population had the same number of yellow and red snakes. At time 2, after many generations, there were many more red snakes and fewer yellow snakes in the population. How did the environment change between time 1 and time 2? How did the population change? (L2)

• You cannot tell how the environment changed. With each generation, more snakes passed on the gene for red scales to their offspring.
• There were more trees with red leaves. With each generation, more red snakes survived long enough to pass on the gene for red scales to their offspring.
• There were more trees with red leaves. Red snakes are more likely to survive, so the yellow snakes changed to have red scales.
• There were more trees with red leaves. Red snakes are more likely to survive, so both kinds of snakes passed on the gene for red scales to their offspring.

The population of seals once lived in an environment where the water was cold. The image above shows what the population looked like then. The environment changed and now the water is very warm. The diagrams below show two predictions for what the population could be like after many generations. Which prediction best shows what the population could look like after many generations? What caused it to change? (L3)

• Prediction 1 is best. Two seals with thick or medium blubber had a baby with a mutation in its genes for the thin trait. Because thin seals are more likely to survive, that baby survived long enough to pass on its mutation, so the thin trait became more common over generations.
• Prediction 1 is best. Seals with thin blubber are more likely to survive, so seals with thick and medium blubber began to have offspring with a mutation in its genes for the thin trait, so that their offspring would have a better chance to survive.
• Prediction 2 is best. A seal could have been born with a mutation in its genes for the thin trait and lived for a little while, but it would have been more likely to die before it had any offspring, so the final population will only have seals with thick or medium blubber.
• Prediction 2 is best. A seal could have been born with a mutation in its genes for the thin trait, but having a mutation in its genes would have caused it to die when it was born, so the final population will only have seals with thick or medium blubber.

Scientists measured the height of giraffes in two populations—one in the wild and one in a nature preserve. Which statement best describes the difference between the two populations? (SC1)

• There is more variation in height of the giraffes found in the wild.
• There is more variation in height of the giraffes found in the nature preserve.
• The giraffes in the wild are mostly shorter than the giraffes found in the nature preserve.
• The giraffes in the wild are mostly taller than the giraffes found in the nature preserve.