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Content Benchmark L.12.B.1
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Life Science
Structure of Life
Organisms and Their Environment
Diversity of Life
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Nature of Science (NOS)
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Physical Science

Students know cell structures and their functions E/S

The smallest thing that exhibits all of the characteristics of life is a single cell. Some organisms are made up of only one cell while complex organisms are made up of trillions. The understanding of the Cell Theory, types of cells, and cellular organelle structure and function is essential to any biology student.

Cell Theory
The Cell Theory is the summation of 150 years of research by many scientists, like Theodor Schwann and Matthias Schleiden. The research groups worked independently on topics of animal cells, plants cells, and cellular reproduction. These pieces contributed to what is now known as the Cell Theory. The Cell Theory has three main components:
1. All living things are composed of at least one cell.
2. Cells are the most basic unit of structure and function.
3. All cells come from preexisting cells.

Prokaryotic vs. Eukaryotic
Cells can be separated into two groups based on the presence or absence of membrane bound organelles. The first group lack organelles and are called Prokaryotic. Bacteria are prokaryotic.

Figure 1. A diagram of a prokaryotic cell.

Eukaryotic cells contain many membrane bound organelles. Each organelle has very specific job to complete, like protein synthesis, trash clean up, or energy production. All organisms except bacteria are eukaryotic.

Figure 2. A diagram of a Eukaryotic cell.

Eukaryotic Cell Organelles

1. Cell membrane
The cell membrane separates the cell from the surrounding environment. It is composed of two layers of lipids with a variety of proteins and carbohydrates embedded in it. The membrane is often described with the Fluid Mosaic Model. It states that the embedded proteins and lipid layers actually move about, thus giving the membrane a fluidity to it. Some proteins form channels to help move material through the cell membrane. Other proteins are chemical receptors that signal the cell to begin or stop some metabolic activities. The carbohydrates bound to the membrane allow the organism’s immune response system to differentiate between its own cells from foreign invaders.

Figure 3. A diagram of the two lipid layers of a cell membrane showing the variety of embedded proteins and carbohydrates.

The membrane is semi permeable. Some things pass freely through the membrane while other substances must be transported across. Transport can be either a passive or active process. Passive transportation across the membrane does not require the expenditure of energy. Substances, like water and gases, can move freely across the membrane into and out of the cell. This process is called diffusion or the random movement of molecules from areas of high concentration to areas of low concentration until equilibrium is reached. A special type of diffusion is osmosis, the diffusion of water through a selectively permeable membrane. Water will also move into and out of a cell from areas of high concentration of water to low areas of concentration of water until an osmotic balance is reached.

Active transport allows a cell to move substances against the concentration gradient but it requires the expenditure of energy. One process uses the embedded membrane proteins to pump ions into or out of the cell. Another process, called endocytosis, actually has the cell membrane making pockets of materials by encircling a substance creating a vesicle. The vesicle then breaks off to the inside of the cell and releases the material to the cell. Endocytosis of a liquid is called pinocytosis and of a solid is called phagocytosis. The movement of materials out of the cell is called exocytosis.

Figure 4. Passive transport of lipid soluble molecules through
a selectively permeable membrane

Figure 5. An example of active transport. Protein channels are being used to move materials opposite the concentration gradient.

Figure 6. An example of active transport by endocytosis.

Figure 7. The structure of a cell wall.

2. Cell wall
The cells of plants, bacteria, and algae are enclosed by a rigid cell wall. The main purpose of the cell wall is to support and protect the cell. The cell wall lies outside of cell membrane and is usually composed of cellulose. The cell wall has large pores which allows all materials to pass (it is completely permeable). Sometimes, strands of membranes pass through the pores connecting neighboring cells. Animal cells do not contain cell walls.

3. Nucleus
This membrane bound organelle houses the control center of the cell. The nucleus protects and maintains the integrity of the DNA, the molecule that contains the coded instructions of the cell. An analogy would be the nucleus is a safe for the original blue prints (DNA) for a large project. Copies of the blue prints can be sent out of the nucleus but the original must stay safe.

Figure 8. The nucleus.
The drawing above is from

Figure 9. Ribosomes located on rough endoplasmic reticulum.

4. Ribosomes
The site of protein synthesis is the ribosomes. The instructions from the DNA are delivered to the ribosomes by mRNA. Once the instructions are read, amino acids are delivered to the ribosome by tRNA and put into proper order to construct the specific protein. Ribosomes located on the rough endoplasmic reticulum usually produce proteins to be exported from the cell and ribosomes floating in the cytoplasm usually produce proteins to be used by the cell.

5. Endoplasmic reticulum
The endoplasmic reticulum (ER) is a system of membrane channels throughout the cell. There are two types of ER, rough and smooth. The rough ER is studded with ribosomes giving it a rough appearance while the smooth ER lacks ribosomes. The ER’s primary purpose is to transport materials around the cell. The ER also provides a large membrane surface area on which many biochemical processes take place. It also divides the cell into compartments so more than one biochemical reaction can be completed concurrently.

Figure 9. This is a plant cell with a large central vacuole identified.

6. Vacuoles
Vacuoles are fluid filled membrane organelles and primarily functions as long term storage. In plant cells, a single vacuole can occupy most of the cell space filled mostly with stored water. In animal cells, vacuoles are usually small (relative to the cell) and may contain proteins, fats, or carbohydrates.

Figure 10. The process of Lysosomes engulfing damaged organelles is shown.
7. Lysosomes
Lysosomes are membrane bound sacs that contain digestive enzymes that can collect, breakdown, and recycle worn out organelles. Lysosomes in immune defense cells, like white blood cells, engulf and destroy bacteria and viruses. In some organisms, lysosomes may also be used to digest macromolecules.

8. Chloroplasts
Chloroplasts are only found in plant and certain types of algae. Chloroplasts contain the pigment chlorophyll, giving plants their green color. The chloroplast is where photosynthesis takes place. The process of photosynthesis converts light energy from the sun into chemical energy in the form of glucose.

Figure 11. The chloroplast rendition below is from

9. Mitochondria
Mitochondria are double membraned organelles. The outer membrane forms the boundary of the organelle, while the inner membrane is folded increasing the surface area necessary to produce energy (ATP and NADH) from the breakdown of sugars. The breakdown of macromolecules to release stored chemical energy is called cellular respiration. An average cell may contain 500 mitochondria. Cells that require large amounts of energy, like muscle cells, may contain thousands of mitochondria.

Figure 12. The mitochondria rendition above is from

10. Golgi apparatus
Golgi apparatus (or Golgi bodies) looks like stacks of flattened membrane sacs. The Golgi apparatus is responsible for processing, packaging, and storing products of the cell to be delivered to the cell membrane for release from the cell.

Figure 13. Golgi apparatus. The products of the cell are transferred from the ER to the Golgi and then, through a series of steps for packaging. The package is delivered to the cell membrane for release from the cell.

11. Cytoplasm
Cytoplasm is the watery environment inside the cell and includes everything from the cell membrane to the nuclear membrane. It consists mostly of water with small quantities of salts and dissolved gases. The space outside the various organelles is more specifically called the cytosol. The cytosol also contains structural elements called the cytoskeleton which give the cell structure and may aid in the cellular movement of cilia and flagella.

12. Centrioles
Centrioles are a pair of organelles found in animal cells but not in plant cells.
During cell division, the centrioles move to opposite ends of the cells and form the spindle that pull the chromatids apart and move them to the opposite poles so two daughter cells can form.

Figure 14. This is late prophase showing the centrioles at each pole of the cell and the formation of a spindle between the centrioles.

Plant vs. Animal Cells

Plant and animal cells have many key differences.
1. Plant cells have a cell wall.
2. Plant cells have chloroplasts and are photosynthetic.
3. Plant cells have a large central vacuole that can take up 95% of the cells volume.
4. Animal cells have centrioles
5. Lysosomes are common in animal cells and very rare in plant cells.

Figure 15. A typical animal cell.

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Content Benchmark L.12.B.1

Students know cell structures and their functions E/S

Common misconceptions associated with this benchmark:

1. Cells are resting when they are not dividing

Cells are most metabolically active during interphase, the period between cell divisions. They are typically engaged in biosynthesis and growth during this time.

2. Respiration occurs in the lungs and is solely the process of gas exchange.

Respiration has two stages - gas exchange which occurs in lungs, gills, or stomata, and biochemical changes that occur in the cells (cellular respiration).

3. Cellular respiration is characteristic of animal cells but not plant cells. Plant cells photosynthesize instead.

All eukaryotic cells capture energy from the breakdown of sugars via cellular respiration in the mitochondria.

4. Plant and animal cells obtain their nutrients (food) from the environment.

Plant cells have the unique capacity to synthesize their own nutrient building blocks, 6-carbon sugar molecules, from inorganic substances such as CO2 and H2O. All other organisms and their cells must take in organic molecules derived directly or indirectly from plants.

5. Everything a cell needs gets into it by diffusion.

Only the smallest molecules such as H2O, CO2, and O2 can diffuse freely into and out of cells. Larger more charged molecules such as sugar and salt ions require active transport across the membrane.

The misconceptions listed in this section came from the website listed below.

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Content Benchmark L.12.B.1

Students know cell structures and their functions. E/S

Sample Test Questions

1st Item Specification: Identify major cell structures and their functions.

Depth of Knowledge Level 1

  1. Which organelles are most directly involved in transporting materials out of the cell?
    1. Nucleus and Ribosomes
    2. Chloroplast and Mitochondria
    3. Cell Membrane and Cell wall
    4. Golgi apparatus and Cell Membrane
  1. Which organelle is the site of cellular respiration in both animal AND plant cells?
    1. Nucleus
    2. Chloroplasts
    3. Mitochondria
    4. Vacuole
  1. Which statement BEST describes the cell membrane in a typical plant cell? The membrane
    1. selectively controls what enters and exits the cell.
    2. is composed of protein and carbohydrates only.
    3. has the same permeability to all substances moving in and out the cell.
    4. is a composed of two protein layers with lipids floating inside.
  1. Which organelle is responsible for photosynthesis?
    1. Nucleus
    2. Chloroplasts
    3. Mitochondria
    4. Vacuole

Depth of Knowledge Level 2

  1. In the diagram below, Cell I and II represent typical cells.

(Diagram from Examgen 4.3)

In both cells, organelle 5 is the site of

  1. photosynthesis .
  2. cellular respiration.
  3. resource storage.
  4. protein synthesis.
  1. If the ribosomes stop working in a cell, which cellular process would be most directly affected?
    1. Photosynthesis
    2. Aerobic respiration
    3. Protein synthesis
    4. Excretion of cellular wastes

2ndItem Specification: Identify the differences between plant and animal cells based on their structures and functions.

Depth of Knowledge Level 1

  1. Which of the following is present in a typical plant cell but NOT in an animal cell?
    1. Mitochondria
    2. Cell Wall
    3. Ribosome
    4. Golgi Apparatus
  1. Which organelle functions in the storage of water and biomolecules?
    1. Vacuole
    2. Cell Wall
    3. Endoplasmic Reticulum
    4. Chloroplast

Depth of Knowledge Level 2

  1. Use the following diagram to answer the next question.

(Diagram modified from Examgen 4.3)

This cell is most likely a plant cell because it contains

  1. Structure 1.
  2. Structure 2.
  3. Structure 3.
  4. Structure 4.
  1. Plants are unable to move to a new location in response to changes in their environment. Which of the following organelles plays a role in maintaining homeostasis in a plant?
    1. Cell Wall
    2. Chloroplast
    3. Vacuole
    4. Nucleus

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Content Benchmark L.12.B.1

Students know cell structures and their functions. E/S

Answers to Sample Test Questions

  1. D, DOK Level 1
  2. C, DOK Level 1
  3. A, DOK Level 1
  4. B, DOK Level 1
  5. B, DOK Level 2
  6. C, DOK Level 2
  7. B, DOK Level 1
  8. A, DOK Level 1
  9. D, DOK Level 2
  10. C, DOK Level 2

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Content Benchmark L.12.B.1

Students know cell structures and their functions E/S

Intervention Strategies and Resources

The following is a list of intervention strategies and resources that will facilitate student understanding of this benchmark.

1. Interactive models
This website has interactive animated plant and animal models. Students can click on the organelles and get a description of its structure and function. It is a good resource for visual learners. It also has many links for students under “homework links”. It even has links to puzzles and self quizzes.

You can access these models at:

2. On-line cell biology and quizzes
This site is very interactive. Its goals are for students to:
1. Recognize the differences between prokaryotic and eukaryotic cells
2. Recognize the differences between plant and animal cells
3. Understand the function of the major organelles in these cells

The site allows students to examine each cell, “zoom in” for more information, and even has “Pop up questions” to self quiz. At the conclusion, it has a “Construct a Cell” self quiz. Students are asked to construct a plant, animal, or prokaryotic cell and check their accuracy.

You can access the quizzes here:

3. On-line quizzes and concept maps
This is a good site for computer savvy students. “Organize-It is a new kind of self –testing system. It’s designed to practice your knowledge of how ideas fit together.” It has student arrange a list of terms into a “concept map” like list. It treats the organization as a quiz and students can check their answers.

You can access this site at:

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