CE

Cells Biology Year 11 T2

Prokaryotes vs Eukaryotes                                  17/3/25 




Cells can be classified into two groups: Prokaryotes and eukaryotes 


  • Prokaryotes (pro = before; karyon = nucleus) are primitive and have a very simple structure e.g. Bacteria


  • Eukaryotes (eu = true karyon = nucleus) are much more complex cells and have membrane - bound internal structures e.g. Paramecium, Amoeba, cells that make up animals and plants



Prokaryotes 



  • Generally smaller, less complicated than Eukaryotic cells 

  • Many - large surface area → to volume ratio. Allows for fast exchange and replication

  • NO membrane bound organelles (e.g. chloroplasts, mitochondria, nucleus) 

  • Have cell membrane and cell wall. 

  • Have ribosomes (to synthesize proteins



Eukaryotes 


  • Much larger and more complex 

  • Contain membrane bound organelles 

  • Both found in unicellular and multicellular organisms 





Organelles 


  • The stuff inside the cell, mitochondria, Nucleus, Vacuoles






Mitochondria, Chloroplast                                    17/3/25 






Mitochondria 

Produce energy in the form of ATP → Respiration


glucose + oxygen → CO2 + Water + energy



Chloroplast 


  • Organelle found in plants where photosynthesis takes place 


  • Found anywhere were there is a green pigment on leaves/trees 


  • Membranes, Stroma, Ribosomes. Thylakoids 


  • Hydrogen, Oxygen, Carbon Bond, Energy is stored









Cell Membrane                                                      1/4/25 



Cell Membranes 


  • For any cell to function it must interact with its surrounding environment and with the cells which surround it. Substances required by cells for their functioning need to move into cells and waste substances need to pass out of cells.



What do Cells need? / What goes into cells?


  • Oxygen 

  • Carbon dioxide 

  • Sugars 

  • Amino acids 

  • Water 



Boundaries 


The movement of chemicals occurs across the cell boundary. 


Both Plant and Animal Cells, the cell membrane is in direct contact with the cytoplasm and it controls the passage of water and other molecules, into or out of the cell


Within the membrane are microscopic pores (Like gates that let things in) 


  • The pores of the membrane are small enough to restrict molecules from entering


  • Larger molecules will need special assistance to enter cells. 


Cell Membrane is too small for any microscopes to see 





Liquid Component 


  • Fluid component of the cell membrane is made of two layers of phospholipids:



Lipid Component 


This layering is termed bilayer and it is not rigid in structure, hence, the term “fluid” mosaic



Protein Component 


  • Protein molecules are scattered throughout the lipid bilayer, suspended in it. Some proteins penetrate all the way through the bilayer forming channels that allow some materials to cross the membrane. 


  • Proteins are described as ‘floating’ in the lipid bilayer 



Other Components 


  • Carbohydrates are attached to the cell membrane and play a role in recognition. 




Phospholipids 


  • Form the cell membrane to protect the cell 


  • The ‘head’ of the phospholipid is called Hydrophilic Head 

  • The tail is called the Hydrophilic Tail 





Cell Organelles                                                     8/4/25 



Definition of a cell: Smallest structural unit (building blocks) of every living organism





Cell membrane = The sack/border of the cell


Cytoplasm = Fluid 


Organelles = The floating things each serving a different purpose



Organelles 



Nucleus 

  • Contains the cells genetic information → needed for growth, repair. 

  • Responsible for telling the cell what to do 



Nucleolus 

  • Makes Ribosomes



Ribosomes 

  • Made of ribosomal RNA and protein 

  • Make proteins 

  • Found attached to the endoplasmic reticulum 


Endoplasmic Reticulum 

  • (ER) is connected to nucleus

  • Network of flattened, interconnected membranes 

  • Rough ER: has ribosomes 

  • Smooth ER: no ribosomes

 

  • Rough ER:  Makes and modifies proteins

 

  • Smooth ER:  Makes lipids (Fat)



Golgi Body 

  • Made of flat membrane sacs stacked on top of each other

  • Job is to process and package substances the cell has made

  • After processing, The membrane pinches off around the substance to form a VESICLE (bubble around the processed substance)


Lysosomes 

  • Digest cell waste

  • Membrane bound sacs that contain digestive enzymes 

  • Needed to break down other substances 










Cell Diffusion                                                     29/4/25 


Molecules move from area of HIGH to LOW concentration



Simple Diffusion 


  • Requires NO energy 

  • Molecules move from area of HIGH to LOW concentration


Diffusion 

  • PASSIVE process which means no energy is used to make the molecules to move 


Diffusion through a membrane 

  • Solute moves DOWN the concentration gradient (HIGH to LOW)


Facilitated Diffusion 

  • Molecules will randomly move through the pores in Channel Proteins 


Types of Transport Proteins 

  • Channel proteins are embedded in the cell membrane and have a pore for materials to cross 

  • Carrier proteins can change shape to move material from one side o f the membrane to the other 


Facilitated diffusion 




Cell Diffusion Prac                                               30/4/25 



Simple Diffusion 

  • Molecules move from HIGH to LOW concentration




  • The potassium iodide (orange fluid) has a higher concentration than inside the bag, the starch is in the bag to show that the molecules are moving




Osmosis                                                               30/4/25 



Diffusion of water across a membrane 

  • Moves from HIGH water concentration to LOW water concentration 

  • WATER IS ATTRACTED TO SOLUTES (like salt) 








Cells In Solution 


  • Isotonic = A solution whose solute concentration is the same as the solute concentration inside the cell


  • Hypotonic (LOW) = A solution whose solute concentration is LOWER than the solute concentration inside a cell 


  • Hypertonic (HIGH) = A solution whose solute concentration is HIGHER than the solute concentration inside a cell  






Concentration Gradient                                        5/5/25 



Concentration Gradient


  • The concentration gradient is the difference in concentration of a substance across a membrane


  • The shorter the distance materials must travel, the faster the rate of movement. Longer distances slow down the process.


Surface Area 


  • A larger surface area allows more material to pass through at a given time, increasing the rate of movement. 


Characteristics of material 


  • Size: Smaller molecules move faster across membranes 

  • Solubility: lipid-soluble substances pass through the lipid bilayer more easily 

  • Polarity: Non-polar molecules diffuse faster than polar molecules 








Surface Area to Volume Ratio                             6/5/25



🦠 Surface Area

  • Surface Area will determine the exchange of materials between the cell and its environment.

  • Bigger cells will metabolise more.

  • They need more surface area to support that metabolism.

  • The sites of metabolism in bigger cells will be further from the surface of the cell.


🔄 Metabolic Activity and Cell Size

  • Smaller cell → does less → produces less waste

  • Larger cell → does more → produces more waste

Cell Membrane + SA:VR

  • Cell Membrane decides what gets in and out of the cell

  • As a cell grows its SA:VR decreases 

  • Each unit of surface area services a limited amount of volume 

  • As cells get larger, they get less efficient and get to a point where they can no longer get any bigger. 


Active Transport                                                    8/5/25



Active Transport

  • Active transport is the movement of molecules form a region of LOW concentration to a region of HIGH concentration 

  • Sometimes in living things, a chemical may need to be moved against the concentration gradient


  • Active transport requires a Carrier Protein that spans the membrane to actively move chemicals from a LOW to HIGH concentration using energy



Transport of Large Molecules 




  • When a large particle has to be moved into a cell, the cell membrane changes its shape to surround the particle and engulf it by the process of endocytosis 


Phagocytosis vs Pinocytosis 


  • Phagocytosis - Solid particle


  • Pinocytosis - Fluid 




Endocytosis: WHEN A SOLID/FLUID IS GOING INTO THE CELL 


Exocytosis: WHEN A SOLID/FLUID IS GOING OUT OF THE CELL






🔬 Types of Microscopes & Key Features

1. Compound Light Microscope

  • Uses light, condenser lens, objective lens, and ocular lens to view specimens.

  • Magnification: Up to 1500x depending on lenses used.

  • Resolution: Maximum of 200 nanometres (nm) – can only distinguish two points if they’re at least 200 nm apart.

  • Can view living and non-living specimens.

  • Commonly used in school labs.

2. Fluorescence Microscope

  • Modified light microscope that uses fluorescent substances to label specific parts of a cell.

  • A high-intensity light source causes fluorescence, and filters isolate only the fluorescing parts.

  • Useful for seeing structures beyond the resolution limit of standard light microscopes.

3. Electron Microscopes

  • Use electron beams and electromagnets instead of light and glass lenses.

  • Allows much higher magnification and greater resolution due to shorter wavelengths of electrons.

  • Can view subcellular structures, even individual atoms.

➤ Transmission Electron Microscope (TEM)

  • Electrons pass through the specimen.

  • Produces 2D images.

  • Magnification: Up to 1,500,000x.

  • Resolution: About 2 nm.

  • Reveals internal structures of cells in great detail.

➤ Scanning Electron Microscope (SEM)

  • Electrons bounce off the surface of a specimen.

  • Produces 3D images of surfaces.

  • Resolution: Around 10 nm.

  • Excellent for examining surface detail.

4. Confocal Laser Scanning Microscope

  • Uses a laser to scan the specimen point by point at different depths.

  • Creates detailed 3D images of intact cells.

  • Useful for studying the structure of cells without damaging them.

⚠ Limitations of Microscopes

  • Electron Microscopes:

    • Cannot view living specimens (require a vacuum).

    • Complex preparation may introduce artefacts (false structures).

    • Expensive and large; require high maintenance.

  • Light Microscopes:

    • Limited resolution (can’t see below 200 nm).

    • Can’t show fine internal details like organelles in depth

Chemicals and Cells                                            12/5/25




🧪Chemicals In Cells 


  • All Cells require chemicals and ions to function 

  • They are split into two major groups - Organic AND Inorganic




🌿Organic 


  • Contain Hydrogen, Oxygen, Carbon are considered Organic 


  • Organic Compounds are derived from living organisms


  • 4 main groups of organic 

  • Carbohydrates 

  • Lipids 

  • Proteins

  • Nucleic acids


Carbohydrates 


  • Monosaccharides: Basic sub unit of Carbohydrates 

  • Disaccharides: 2 Joined together 

  • Polysaccharides: More than 2


Lipids 


  • Energy storage molecules

  • Includes fats and oils


Proteins 


  • Proteins contain nitrogen, carbon, oxygen, hydrogen 

  • More complex than Lipids and Carbohydrates

  • Sub units are amino acids: Joined together with polypeptide bond



Nucleic Acids 


  • Genetic material of all organisms

  • 2 Types: 

  • DNA

  • RNA

  • Sub units are nucleotides



☢ Inorganic


  • Water 

  • Oxygen

  • Carbon Dioxide 

  • Nitrogen