Unit Test: Ecosystems, Living Systems, and Cells

Question 1

What is the basic unit of all living things?

Accepted Answer

A cell

Question 2

Which cell structure controls what enters and leaves the cell?

Accepted Answer

The cell membrane

Question 3

A student looks at two cells under a microscope. One cell has a cell wall and chloroplasts. The other cell does not. What conclusion can the student BEST draw?

[FIGURE: Side-by-side labeled diagram of two cells under a microscope: Cell A (plant cell) showing a rectangular shape with visible cell wall, large central vacuole, and green chloroplasts; Cell B (animal cell) showing an irregular round shape with no cell wall, no chloroplasts, and smaller vacuoles. Both cells show a nucleus and cell membrane.]

Accepted Answer

Cell A is a plant cell and Cell B is an animal cell.

Question 4

Which organelle is responsible for producing energy for the cell?

Accepted Answer

Mitochondria

Question 5

A food web in a pond ecosystem is shown below.

[FIGURE: Diagram of a pond food web with labeled arrows showing energy flow. Algae → Water flea → Small fish → Large fish → Osprey. Also: Algae → Tadpole → Snake → Osprey. Arrows point from prey to predator.]

What would MOST LIKELY happen to the small fish population if all the water fleas disappeared?

Accepted Answer

The small fish population would decrease.

Question 6

In a forest ecosystem, which organism is a producer?

Accepted Answer

An oak tree that makes its own food from sunlight

Question 7

The table below shows the population data for four organisms in a meadow ecosystem over three years.

| Organism | Year 1 Population | Year 2 Population | Year 3 Population |
|----------|-------------------|-------------------|-------------------|
| Grass    | 10,000            | 8,500             | 7,200             |
| Rabbits  | 500               | 420               | 350               |
| Foxes    | 80                | 65                | 50                |
| Hawks    | 30                | 25                | 20                |

Based on the data, which statement BEST describes the trend in this ecosystem?

Accepted Answer

All populations are declining, suggesting the ecosystem may be under stress.

Question 8

Which process do plants use to make their own food using sunlight?

Accepted Answer

Photosynthesis

Question 9

A student sets up an experiment with two identical plants. Plant A is placed in sunlight and given water. Plant B is placed in a dark closet and given water. After two weeks, Plant B is wilted and yellow.

[FIGURE: Side-by-side illustration of two identical potted plants after two weeks. Plant A (in sunlight) is tall, green, and healthy. Plant B (in a dark closet) is wilted, pale yellow, and shorter. Both pots are labeled with equal amounts of water given.]

Why did Plant B turn yellow and wilt?

Accepted Answer

Plant B could not perform photosynthesis without light to make food.

Question 10

Which of the following BEST describes the role of decomposers in an ecosystem?

Accepted Answer

They break down dead organisms and return nutrients to the soil.

Question 11

A scientist studied how energy moves through a food chain. The diagram below shows the amount of energy available at each level.

[FIGURE: Energy pyramid diagram with four levels. Bottom level (Producers/Grass) labeled 10,000 units. Second level (Grasshoppers) labeled 1,000 units. Third level (Frogs) labeled 100 units. Top level (Hawks) labeled 10 units. Each level is progressively smaller and shaded darker going up.]

About what percentage of energy is passed from one level to the next level up in the pyramid?

Accepted Answer

10%

Question 12

Which of the following is an example of a biotic factor in an ecosystem?

Accepted Answer

The bacteria living in the soil

Question 13

A student examines a cell and notices it has a large central vacuole, a cell wall, and chloroplasts. Which type of cell is this?

Accepted Answer

A plant cell

Question 14

The graph below shows the population of wolves and elk in a national park over 20 years after wolves were reintroduced.

[FIGURE: Dual-line graph titled 'Wolf and Elk Populations in Yellowstone National Park (Years 1–20).' X-axis: Year (1–20). Y-axis: Population (0–20,000). Blue line (Elk) starts high at ~18,000 in Year 1, decreases to ~8,000 by Year 20. Red line (Wolves) starts low at ~50 in Year 1, increases to ~300 by Year 20. Lines move in opposite directions, crossing around Year 8.]

What relationship do the wolf and elk population trends BEST show?

Accepted Answer

As the wolf population increases, the elk population decreases.

Question 15

Which of the following BEST explains why there are fewer organisms at the top of an energy pyramid than at the bottom?

Accepted Answer

Energy is lost at each level, so less energy is available to support large populations at higher levels.

Question 16

A group of students measured the dissolved oxygen levels in two ponds. Pond A had many aquatic plants. Pond B had very few plants. Their results are shown below.

| Pond | Number of Aquatic Plants | Dissolved Oxygen (mg/L) |
|------|--------------------------|-------------------------|
| A    | High (abundant)          | 9.2                     |
| B    | Low (few)                | 4.1                     |

What is the MOST LIKELY reason Pond A has higher dissolved oxygen levels?

Accepted Answer

Pond A's plants release oxygen during photosynthesis.

Question 17

How are the cells in a multicellular organism organized to carry out life functions?

Accepted Answer

Cells are grouped into tissues, which form organs, which form organ systems.

Question 18

A student is comparing how matter cycles through an ecosystem. Which statement BEST describes the role of decomposers in the carbon cycle?

Accepted Answer

Decomposers release carbon back into the environment by breaking down dead organisms.

Question 19

A scientist observes that a species of frog has disappeared from a wetland ecosystem. She also notices that the mosquito population has dramatically increased and the heron population has declined. Which statement BEST explains these observations?

Accepted Answer

The loss of frogs disrupted the food web, reducing heron food and allowing mosquitoes to multiply.

Question 20

A class is designing a model ecosystem in a closed terrarium. They include soil, rocks, water, plants, small insects, and a decomposer layer of leaf litter with microbes. The terrarium receives sunlight through a glass top.

[FIGURE: Labeled cross-section diagram of a sealed glass terrarium ecosystem. Layers from bottom to top: gravel drainage layer, soil layer with microbes and leaf litter (labeled 'decomposers'), small plants (labeled 'producers'), two small insects (labeled 'consumers'). Arrows show: sunlight entering from above, water cycling as condensation on the glass walls, and nutrient arrows between decomposer layer and soil.]

If the students seal the terrarium completely and observe it for one month, which statement BEST predicts what will happen to the matter inside the terrarium?

Accepted Answer

Matter will cycle continuously among the organisms, soil, water, and air inside the terrarium.

Unit Test: Ecosystems, Living Systems, and Cells

Adaptive Selected Response

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