Connection for AP® Courses
Eukaryotic cells possess many features that prokaryotic cells lack, including a nucleus with a double membrane that encloses DNA. In addition, eukaryotic cells tend to be larger and have a variety of membrane-bound organelles that perform specific, compartmentalized functions. Evidence supports the hypothesis that eukaryotic cells likely evolved from prokaryotic ancestors; for example, mitochondria and chloroplasts feature characteristics of independently-living prokaryotes. Eukaryotic cells come in all shapes, sizes, and types; (for example, animal cells, plant cells, and different types of cells in the body.) Hint—This a rare instance where you should create a list of organelles and their respective functions because later you will focus on how various organelles work together, similar to how your body’s organs work together to keep you healthy. Like prokaryotes, all eukaryotic cells have a plasma membrane, cytoplasm, ribosomes, and DNA. Many organelles are bound by membranes composed of phospholipid bilayers embedded with proteins to compartmentalize functions such as the storage of hydrolytic enzymes and the synthesis of proteins. The nucleus houses DNA, and the nucleolus within the nucleus is the site of ribosome assembly. Functional ribosomes are found either free in the cytoplasm or attached to the rough endoplasmic reticulum where they perform protein synthesis. The Golgi apparatus receives, modifies, and packages small molecules like lipids and proteins for distribution. Mitochondria and chloroplasts participate in free energy capture and transfer through the processes of cellular respiration and photosynthesis, respectively. Peroxisomes oxidize fatty acids and amino acids, and they are equipped to break down hydrogen peroxide formed from these reactions without letting it into the cytoplasm where it can cause damage. Vesicles and vacuoles store substances, and in plant cells, the central vacuole stores pigments, salts, minerals, nutrients, proteins, and degradation enzymes, and helps maintain rigidity. In contrast, animal cells have centrosomes and lysosomes but lack cell walls.
Information presented and the examples highlighted in the section support concepts and Learning Objectives outlined in Big Idea 1, Big Idea 2, and Big Idea 4 of the AP® Biology Curriculum Framework. The Learning Objectives listed in the Curriculum Framework provide a transparent foundation for the AP® Biology course, an inquiry-based laboratory experience, instructional activities, and AP® exam questions. A Learning Objective merges required content with one or more of the seven Science Practices.
Big Idea 1 |
The process of evolution drives the diversity and unity of life. |
Enduring Understanding 1.B |
Organisms are linked by lines of descent from common ancestry. |
Essential Knowledge
|
1.B.1
Organisms share many conserved core processes and features that evolved and are widely distributed among organisms today.
|
Science Practice |
7.2
The student can connect concepts in and across domains to generalize or extrapolate in and/or across enduring understandings.
|
Learning Objective
|
1.15
The student is able to describe specific examples of conserved core biological processes and features shared by all domains or within one domain of life, and how these shared, conserved core processes and features support the concept of common ancestry for all organisms.
|
Big Idea 2 |
Biological systems utilize free energy and molecular building blocks to grow, to reproduce and to maintain dynamic homeostasis. |
Enduring Understanding 2.B |
Growth, reproduction and dynamic homeostasis require that cells create and maintain internal environments that are different from their external environments. |
Essential Knowledge
|
2.B.3
Eukaryotic cells maintain internal membranes that partition the cell into specialized regions.
|
Science Practice |
6.2
The student can construct explanations of phenomena based on evidence produced through scientific practices.
|
Learning Objective
|
2.13
The student is able to explain how internal membranes and organelles contribute to cell functions.
|
Science Practice |
1.4
The student can use representations and models to analyze situations or solve problems qualitatively and quantitatively.
|
Learning Objective
|
2.14
The student is able to use representations and models to describe differences in prokaryotic and eukaryotic cells.
|
Big Idea 4 |
Biological systems interact, and these systems and their interactions possess complex properties. |
Enduring Understanding 4.A |
Interactions within biological systems lead to complex properties. |
Essential Knowledge
|
4.A.2
The structure and function of subcellular components, and their interactions, provide essential cellular processes.
|
Learning Objective
|
4.5
The student is able to construct explanations based on scientific evidence as to how interactions of subcellular structures provide essential functions.
|
The Science Practices Assessment Ancillary contains additional test questions for this section that will help you prepare for the AP exam. These questions address the following standards:
- [APLO 1.15]
- [APLO 2.5]
- [APLO 2.25]
- [APLO 1.16]
Have you ever heard the phrase form follows function? It is a philosophy practiced in many industries. In architecture, this means that buildings should be constructed to support the activities that will be carried out inside them. For example, a skyscraper should be built with several elevator banks; a hospital should be built so that its emergency room is easily accessible.
Our natural world also utilizes the principle of form following function, especially in cell biology, and this will become clear as we explore eukaryotic cells (Figure 4.8). Unlike prokaryotic cells, eukaryotic cells have: (1) a membrane-bound nucleus; (2) numerous membrane-bound organelles such as the endoplasmic reticulum, Golgi apparatus, chloroplasts, mitochondria, and others; and (3) several rod-shaped chromosomes. Because a eukaryotic cell’s nucleus is surrounded by a membrane, it is often said to have a true nucleus. The word organelle means little organ, and, as already mentioned, organelles have specialized cellular functions, just as the organs of your body have specialized functions.
At this point, it should be clear to you that eukaryotic cells have a more complex structure than prokaryotic cells. Organelles allow different functions to be compartmentalized in different areas of the cell. Before turning to organelles, let’s first examine two important components of the cell: the plasma membrane and the cytoplasm.
Visual Connection
If the nucleolus were not able to carry out its function, what other cellular organelles would be affected?
- The structure of endoplasmic reticulum would not form.
- The function of lysosomes would be hindered, as hydrolases are formed by the nucleolus.
- The free ribosomes and the rough endoplasmic reticulum, which contains ribosomes, would not form.
- The Golgi apparatus will not be able to sort proteins properly.