Get ready to dive into the fascinating world of cells!... Show more
AP Biology59 views·Updated May 27, 2026·2 pagesAP Bio Unit 2 Review: Cell Structure and Function (No Organelles)
Mariela Hilario@marielahilario_pkkw
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Cell Structure and Transport
Ever wonder what makes up the tiny building blocks of life? All cells contain a plasma membrane and cytosol, but eukaryotic cells (like yours!) have membrane-bound organelles and a nucleus, while prokaryotic cells don't. Prokaryotes are single-celled organisms that multiply quickly, while eukaryotes can form complex multicellular organisms.
The plasma membrane is made of a phospholipid bilayer - think of it as a security fence around the cell with special gates. It has hydrophilic heads facing outward and hydrophobic tails facing inward, making it selectively permeable. Cholesterol molecules fill gaps in the membrane, maintaining fluidity. Different proteins embedded in the membrane serve as channels, anchors, or communication devices.
Cells move materials in and out through several transport methods. Passive transport requires no energy and moves substances from high to low concentration (like sliding downhill). This includes simple diffusion (O₂, CO₂), facilitated diffusion through protein channels (like water through aquaporins), and osmosis (water movement across membranes). Active transport uses ATP energy to move substances against their concentration gradient (like pushing a boulder uphill).
💡 Water follows solute concentration! In a hypertonic environment (too salty outside), water moves out of the cell. In a hypotonic environment (too watery outside), water moves into the cell. In an isotonic environment, water movement is balanced.
The amount of water in cells affects their pressure and shape. Animal cells can lyse (burst) from too much water, while plant cells become turgid (firm). When cells lose water, animal cells shrivel while plant cells become flaccid (wilted) or plasmolyzed (dead). Bulk transport methods include exocytosis (releasing materials from the cell) and endocytosis (taking materials into the cell).
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Cell Connections and Specialization
Did you know cells don't just float around independently? The extracellular matrix acts like cement between cells, holding tissues together. Made of proteins and polysaccharides, it provides structure outside the plasma membrane.
Cells connect to each other through specialized junctions. Tight junctions create waterproof seals between cells (like in your bladder). Gap junctions are like tiny doorways allowing molecules to pass directly between cells (common in heart muscle). Desmosomes work like rivets, fastening cells into strong sheets (found in skin).
Cell efficiency depends on surface area to volume ratio. A larger ratio means more efficient cells because more surface area compared to volume allows better exchange of materials. As cells grow larger, they often develop compartmentalization - specialized areas for specific functions. You can see this in the different shapes of blood cells, sperm cells, and brain cells.
🔍 The endosymbiont theory explains how eukaryotic cells evolved! It suggests that certain organelles (like mitochondria) were once free-living prokaryotes that were engulfed by larger cells and formed a mutually beneficial relationship.
Cells have specialized structures for movement and storage. Flagella are long, whip-like structures used for movement (like in sperm cells), while cilia are shorter, more numerous hairlike structures (like in your respiratory tract). Plant cells typically have one large vacuole for storage, while animal cells have several smaller ones. When cells make proteins, they follow a specific path: ribosomes or rough ER → Golgi apparatus → vesicles → membrane.
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AP Biology59 views·Updated May 27, 2026·2 pagesAP Bio Unit 2 Review: Cell Structure and Function (No Organelles)
Mariela Hilario@marielahilario_pkkw
Get ready to dive into the fascinating world of cells! This review covers the essential differences between cell types, how cells transport materials, and the specialized structures that help them function efficiently. Understanding these basics is key to mastering AP... Show more
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Cell Structure and Transport
Ever wonder what makes up the tiny building blocks of life? All cells contain a plasma membrane and cytosol, but eukaryotic cells (like yours!) have membrane-bound organelles and a nucleus, while prokaryotic cells don't. Prokaryotes are single-celled organisms that multiply quickly, while eukaryotes can form complex multicellular organisms.
The plasma membrane is made of a phospholipid bilayer - think of it as a security fence around the cell with special gates. It has hydrophilic heads facing outward and hydrophobic tails facing inward, making it selectively permeable. Cholesterol molecules fill gaps in the membrane, maintaining fluidity. Different proteins embedded in the membrane serve as channels, anchors, or communication devices.
Cells move materials in and out through several transport methods. Passive transport requires no energy and moves substances from high to low concentration (like sliding downhill). This includes simple diffusion (O₂, CO₂), facilitated diffusion through protein channels (like water through aquaporins), and osmosis (water movement across membranes). Active transport uses ATP energy to move substances against their concentration gradient (like pushing a boulder uphill).
💡 Water follows solute concentration! In a hypertonic environment (too salty outside), water moves out of the cell. In a hypotonic environment (too watery outside), water moves into the cell. In an isotonic environment, water movement is balanced.
The amount of water in cells affects their pressure and shape. Animal cells can lyse (burst) from too much water, while plant cells become turgid (firm). When cells lose water, animal cells shrivel while plant cells become flaccid (wilted) or plasmolyzed (dead). Bulk transport methods include exocytosis (releasing materials from the cell) and endocytosis (taking materials into the cell).
2
of 2Sign up to see the content. It's free!
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Cell Connections and Specialization
Did you know cells don't just float around independently? The extracellular matrix acts like cement between cells, holding tissues together. Made of proteins and polysaccharides, it provides structure outside the plasma membrane.
Cells connect to each other through specialized junctions. Tight junctions create waterproof seals between cells (like in your bladder). Gap junctions are like tiny doorways allowing molecules to pass directly between cells (common in heart muscle). Desmosomes work like rivets, fastening cells into strong sheets (found in skin).
Cell efficiency depends on surface area to volume ratio. A larger ratio means more efficient cells because more surface area compared to volume allows better exchange of materials. As cells grow larger, they often develop compartmentalization - specialized areas for specific functions. You can see this in the different shapes of blood cells, sperm cells, and brain cells.
🔍 The endosymbiont theory explains how eukaryotic cells evolved! It suggests that certain organelles (like mitochondria) were once free-living prokaryotes that were engulfed by larger cells and formed a mutually beneficial relationship.
Cells have specialized structures for movement and storage. Flagella are long, whip-like structures used for movement (like in sperm cells), while cilia are shorter, more numerous hairlike structures (like in your respiratory tract). Plant cells typically have one large vacuole for storage, while animal cells have several smaller ones. When cells make proteins, they follow a specific path: ribosomes or rough ER → Golgi apparatus → vesicles → membrane.
We thought you’d never ask...
What is the Knowunity AI companion?
Our AI companion is specifically built for the needs of students. Based on the millions of content pieces we have on the platform we can provide truly meaningful and relevant answers to students. But its not only about answers, the companion is even more about guiding students through their daily learning challenges, with personalised study plans, quizzes or content pieces in the chat and 100% personalisation based on the students skills and developments.
Where can I download the Knowunity app?
You can download the app in the Google Play Store and in the Apple App Store.
Is Knowunity really free of charge?
That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.
Most popular content in AP Biology
9Most popular content
9Can't find what you're looking for? Explore other subjects.
Students love us — and so will you.
4.6/5App Store
4.7/5Google Play
The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.
Stefan SiOS user
This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.
Samantha KlichAndroid user
Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.
AnnaiOS user