Ever wondered how substances get in and out of cells?...
Biology85 views·Updated 26 Aug 2026·9 pagesCCEA AS Biology Unit 1: Comprehensive Cell Physiology Notes
mollie@molliegilmore_xwcx
1 / 9
1
of 9
Cell Transport: The Basics
Your cells are constantly moving substances around, and simple diffusion is the most basic way this happens. Think of it like a crowded room where people naturally spread out - molecules move from areas of high concentration to low concentration without any energy needed.
This passive process relies on the natural kinetic energy of molecules bouncing around. The rate gets faster with higher temperatures, thinner surfaces, and larger surface areas - just like how heat makes molecules move more quickly.
Facilitated diffusion works similarly but uses special proteins as helpers. Channel proteins act like selective doorways for ions, whilst carrier proteins change shape to transport larger molecules across the cell membrane.
Key Point: Both simple and facilitated diffusion are passive - they don't require energy from the cell!
2
of 9
Protein Helpers: Channels and Carriers
Channel proteins are like water-filled tunnels that allow specific ions to pass through the cell membrane. They're highly selective - each channel only allows one type of ion through, and they can be opened or closed like gates when they receive the right signal.
Carrier proteins handle the bigger jobs, transporting larger ions and polar molecules. When a molecule binds to the carrier, the protein changes shape to move it across the membrane - it's like a revolving door that flips the molecule to the other side.
Understanding hypotonic and hypertonic solutions is crucial here. These terms describe the concentration differences that drive all these transport processes.
Remember: Channel proteins are for small ions, carrier proteins are for larger molecules!
3
of 9
Active Transport: Going Against the Flow
Sometimes cells need to move substances uphill, from low concentration to high concentration - that's where active transport comes in. Unlike passive processes, this requires energy in the form of ATP, which means cells need lots of mitochondria to power it.
The process works through specific protein carriers that span the membrane. These proteins accept molecules, change shape to transport them, then react with ATP to get the energy needed for the job.
Anything that increases respiration - like higher temperature or exercise - will boost active transport rates. That's because more respiration means more ATP production, giving cells more energy to power these uphill journeys.
Energy Fact: Active transport is like pushing a boulder uphill - it takes serious cellular energy!
4
of 9
Cytosis: Moving the Big Stuff
When molecules are too large for protein carriers, cells use cytosis - transport via vesicles (tiny membrane bubbles). This process can handle massive molecules or even transport smaller ones in bulk.
There are two main types: endocytosis (bringing material into the cell) and exocytosis (moving material out). During endocytosis, the cell surface membrane invaginates (folds inward), pinches off, and forms a vesicle containing the material.
The process is like the cell's mouth - it can 'eat' particles by wrapping membrane around them and pulling them inside.
Size Matters: When regular transport proteins can't handle the job, cytosis takes over!
5
of 9
Types of Cytosis and Osmosis Basics
Phagocytosis handles solid materials - the cell membrane wraps around particles, forms vesicles, then digests the contents with enzymes. Pinocytosis does the same job but for liquids, creating smaller vesicles.
Exocytosis works in reverse - vesicles move toward the cell surface, fuse with the membrane, open up, and release their contents outside.
Osmosis is the net movement of water from high water potential to low water potential across a selectively permeable membrane. Water moves through specialised aquaporins - protein channels designed specifically for water molecules.
Water Transport: Aquaporins are like express lanes just for water molecules!
6
of 9
Water Potential: Understanding the Driving Force
Water potential measures a solution's tendency to take in water by osmosis, expressed in kilopascals (kPa). Pure water has a water potential of 0 kPa because all water molecules are free to move.
When solutes are added, water potential becomes more negative because some water molecules form hydration shells around the solutes. The more concentrated a solution, the more negative its water potential becomes.
Here's the key: higher water potential means a less negative number, whilst lower water potential means a more negative number. A solution with -600 kPa will take in less water than one with -1000 kPa.
Think Negative: More concentrated = more negative water potential!
7
of 9
Plant Cells and Turgor Pressure
Plant cells have two components affecting water movement: solute potential (Ψs) relates to solute concentration only, whilst pressure potential (Ψp) is the effect of pressure on the solution. The formula is: Ψcell = Ψs + Ψp.
In hypotonic solutions, plant cell vacuoles increase in size, pushing the cell membrane against the cell wall and creating turgor pressure. This turgidity gives plants structural support - it's why plants wilt when they lack water.
Pressure potential should be positive and varies from 0 in fully plasmolysed cells to maximum in turgid cells.
Plant Support: Turgor pressure is what keeps plants standing upright!
8
of 9
Plant Cell Responses to Different Solutions
In hypertonic solutions, plant cell vacuoles shrink, pulling the cell membrane away from the wall - this process is called plasmolysis. The cell loses its structural support and becomes floppy.
Isotonic solutions create equilibrium with equal amounts of water entering and leaving the cell. This state is called incipient plasmolysis, where the membrane begins to lose contact with the cell wall.
You can observe three distinct states: plasmolysed (shrunken), flaccid (limp), and turgid (firm and upright).
Plant Health Check: Turgid = healthy, plasmolysed = dehydrated!
9
of 9
Animal Cells and Osmotic Challenges
Animal cells face greater osmotic challenges because they lack protective cell walls. In hypotonic solutions, water enters animal cells, and if too much gets in, the cells burst - this destructive process is called cell lysis.
In hypertonic solutions, water leaves animal cells, causing them to shrink and shrivel up. This is why maintaining proper fluid balance is crucial for animal survival.
Unlike plant cells that can benefit from some water pressure, animal cells need to maintain careful water balance to avoid damage.
No Protection: Without cell walls, animal cells are more vulnerable to osmotic damage!
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Biology85 views·Updated 26 Aug 2026·9 pagesCCEA AS Biology Unit 1: Comprehensive Cell Physiology Notes
mollie@molliegilmore_xwcx
Ever wondered how substances get in and out of cells? Cell physiology is all about the different transport methods that keep your cells alive and functioning. From simple diffusion to complex active transport, these processes are happening in your body...
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Cell Transport: The Basics
Your cells are constantly moving substances around, and simple diffusion is the most basic way this happens. Think of it like a crowded room where people naturally spread out - molecules move from areas of high concentration to low concentration without any energy needed.
This passive process relies on the natural kinetic energy of molecules bouncing around. The rate gets faster with higher temperatures, thinner surfaces, and larger surface areas - just like how heat makes molecules move more quickly.
Facilitated diffusion works similarly but uses special proteins as helpers. Channel proteins act like selective doorways for ions, whilst carrier proteins change shape to transport larger molecules across the cell membrane.
Key Point: Both simple and facilitated diffusion are passive - they don't require energy from the cell!
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Protein Helpers: Channels and Carriers
Channel proteins are like water-filled tunnels that allow specific ions to pass through the cell membrane. They're highly selective - each channel only allows one type of ion through, and they can be opened or closed like gates when they receive the right signal.
Carrier proteins handle the bigger jobs, transporting larger ions and polar molecules. When a molecule binds to the carrier, the protein changes shape to move it across the membrane - it's like a revolving door that flips the molecule to the other side.
Understanding hypotonic and hypertonic solutions is crucial here. These terms describe the concentration differences that drive all these transport processes.
Remember: Channel proteins are for small ions, carrier proteins are for larger molecules!
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Active Transport: Going Against the Flow
Sometimes cells need to move substances uphill, from low concentration to high concentration - that's where active transport comes in. Unlike passive processes, this requires energy in the form of ATP, which means cells need lots of mitochondria to power it.
The process works through specific protein carriers that span the membrane. These proteins accept molecules, change shape to transport them, then react with ATP to get the energy needed for the job.
Anything that increases respiration - like higher temperature or exercise - will boost active transport rates. That's because more respiration means more ATP production, giving cells more energy to power these uphill journeys.
Energy Fact: Active transport is like pushing a boulder uphill - it takes serious cellular energy!
4
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Cytosis: Moving the Big Stuff
When molecules are too large for protein carriers, cells use cytosis - transport via vesicles (tiny membrane bubbles). This process can handle massive molecules or even transport smaller ones in bulk.
There are two main types: endocytosis (bringing material into the cell) and exocytosis (moving material out). During endocytosis, the cell surface membrane invaginates (folds inward), pinches off, and forms a vesicle containing the material.
The process is like the cell's mouth - it can 'eat' particles by wrapping membrane around them and pulling them inside.
Size Matters: When regular transport proteins can't handle the job, cytosis takes over!
5
of 9Sign up to see the content. It's free!
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Types of Cytosis and Osmosis Basics
Phagocytosis handles solid materials - the cell membrane wraps around particles, forms vesicles, then digests the contents with enzymes. Pinocytosis does the same job but for liquids, creating smaller vesicles.
Exocytosis works in reverse - vesicles move toward the cell surface, fuse with the membrane, open up, and release their contents outside.
Osmosis is the net movement of water from high water potential to low water potential across a selectively permeable membrane. Water moves through specialised aquaporins - protein channels designed specifically for water molecules.
Water Transport: Aquaporins are like express lanes just for water molecules!
6
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Water Potential: Understanding the Driving Force
Water potential measures a solution's tendency to take in water by osmosis, expressed in kilopascals (kPa). Pure water has a water potential of 0 kPa because all water molecules are free to move.
When solutes are added, water potential becomes more negative because some water molecules form hydration shells around the solutes. The more concentrated a solution, the more negative its water potential becomes.
Here's the key: higher water potential means a less negative number, whilst lower water potential means a more negative number. A solution with -600 kPa will take in less water than one with -1000 kPa.
Think Negative: More concentrated = more negative water potential!
7
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Plant Cells and Turgor Pressure
Plant cells have two components affecting water movement: solute potential (Ψs) relates to solute concentration only, whilst pressure potential (Ψp) is the effect of pressure on the solution. The formula is: Ψcell = Ψs + Ψp.
In hypotonic solutions, plant cell vacuoles increase in size, pushing the cell membrane against the cell wall and creating turgor pressure. This turgidity gives plants structural support - it's why plants wilt when they lack water.
Pressure potential should be positive and varies from 0 in fully plasmolysed cells to maximum in turgid cells.
Plant Support: Turgor pressure is what keeps plants standing upright!
8
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Plant Cell Responses to Different Solutions
In hypertonic solutions, plant cell vacuoles shrink, pulling the cell membrane away from the wall - this process is called plasmolysis. The cell loses its structural support and becomes floppy.
Isotonic solutions create equilibrium with equal amounts of water entering and leaving the cell. This state is called incipient plasmolysis, where the membrane begins to lose contact with the cell wall.
You can observe three distinct states: plasmolysed (shrunken), flaccid (limp), and turgid (firm and upright).
Plant Health Check: Turgid = healthy, plasmolysed = dehydrated!
9
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Animal Cells and Osmotic Challenges
Animal cells face greater osmotic challenges because they lack protective cell walls. In hypotonic solutions, water enters animal cells, and if too much gets in, the cells burst - this destructive process is called cell lysis.
In hypertonic solutions, water leaves animal cells, causing them to shrink and shrivel up. This is why maintaining proper fluid balance is crucial for animal survival.
Unlike plant cells that can benefit from some water pressure, animal cells need to maintain careful water balance to avoid damage.
No Protection: Without cell walls, animal cells are more vulnerable to osmotic damage!
We thought you’d never ask...
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