Module 1: Cells as a Basis of Life

Cell Structure

Inquiry Question: What Distinguishes one cell from another?

Cell Theory

  • All living things are made of cells

  • Cells are the basic structural and functional units of organisms

  • All cells come from pre-existing cells

Cell Structure

Classification of cells

  • Prokaryotes (Unicellular Organisms)

    • Primitive cells

    • smaller and simpler than eukaryotic cells

    • abundance compared to eukaryotic cells

    • No membrane bound organelles

    • Divided into two groups → Archaea and Bacteria

    • Small and efficient→ High SA:V ratio

    • Four Main Structures:

      • Cell

      • Cytoplasm

      • Ribosomes

      • Genetic Material → Found in a large loop called the nucleoid.

  • Eukaryotes (Unicellular and Multicellular)

    • More complex and large than prokaryotes

    • 10-100um

    • Multicellular plants and animals are composed of a variety of different types of eukaryotic cells

    • Divided into kingdoms → Amoeba, fungi, Plantae and animalia

    • Contain membrane bound organelles

      • Each organelle has a specific function within the cell

      • Together the organelles carry out all the biochemical processes and reactions like transpiration and photosynthesis.


  • Large prokaryotic cells engulfed smaller prokaryotic cells → Photosynthesising made chloroplasts + cells that used oxygen to produce their own energy made a mitochondria

  • Size of mitochondria and chloroplasts tend to be the same size as bacteria

  • The way mitochondria and chloroplasts divide tend to be the same process as prokaryotes


MitochondriaThe mitochondria is the powerhouse of the cell. They produce the energy for the cell known as ATP through cellular respiration. Responsible for creating more than 90% of the energy needed to sustain life. Animals have more than plants. Plants only use their mitochondria at night.
CytoplasmCytoplasm consists of a liquid based background, in which there are dissolved chemical substances (e.g. ions such as chloride ions). Approximately 90 per cent of the cytoplasm is water.
NucleusThe nucleus is a large spherical oval structure in the cytoplasm. The nucleus is transparent and colourless. There are two main functions for a nucleus including; storing the cell’s DNA and being responsible for the cells growth, reproduction etc. The nucleus produces ribosomes.
ChloroplastsChloroplasts are only found in plant cells. Photosynthesis occurs in this section of the cell. The chloroplast uses the sunlight to convert the energy into sugars to power the plant cells. Inside of the chloroplasts there are little green chlorophylls (molecules).
Endoplasmic ReticulumThe endoplasmic reticulum also known as ER is an organelle found in the cells of eukaryotic organisms. ER occurs in nearly every type of eukaryotic cell except red blood cells and sperm cells. There are two types of endoplasmic reticulum rough endoplasmic reticulum (RER) (have ribosomes attached) and smooth endoplasmic reticulum (SER). It is a form of transportation for materials
VacuolesIs a sac-like structure that stores materials such as water, ions, wastes and proteins. The size of the vacuoles depends on the shape and size of the cell. They are found in both plant and animal cells, but are larger in plants. Has a membrane
RibosomesRibosomes are a cell structure that assists with making protein. Ribosomes are found floating around in the cytoplasm and/or attached to the rough endoplasmic reticulum.
Golgi BodiesThe golgi body is an organelle found in most eukaryotic cells. There are numerous functions of the golgi such as sorting and processing proteins. They are also responsible for determining which proteins are allowed outside of the cell.
LysosomesThe main function of lysosomes is to digest and remove waste from the cell. They contain digestive enzymes. They are the stomach of the cell. Lysosomes are surrounded by a layer of lipids acting as a membrane.
CytoskeletonCytoskeleton are present in all cells. They are a complex network of interlinking filaments and tubules throughout the cytoplasm. They supports, shape and helps facilitate movement.
Cell WallThe cell wall provides support and protection for the cell. They are only found in plant cells. Cell walls lie on the outside of the cell membrane


Light Microscope

  • A light source passes through a condenser lens then through the specimen

  • The beam of light passes through the convex objective lens, the image is magnified and viewed through the ocular lens.

  • Magnification of up to 1500x and maximum resolution of 200nm

Fluorescence Microscope

  • Better resolution than light microscope

  • Sample is labelled with a fluorescent dye that attaches to particular structures

  • Sample is illuminated with a high intensity source of light that causes the fluorescent substance to emit light.

Electron Microscope

  • Uses an electronic beam instead of light and electromagnetism instead of glass lenses

  • Greater resolution due to shorter wavelengths

  • Many cells were seen for the first time with this invention

Computer Enhanced Technology

  • Microscopic images can be digitally processed to allow cells to be viewed in different ways

  • Cells scan software can provide #D images of cell structures.

Biological Drawings

  • Cell Size (1mm = 1000micrometres)

  • Size of Object/cells = Field of view / Fit Number

  • E.g. FOV is 30mm, 3 cells fill it up → Each cell is 10cm wide

Fluid Mosaic Model

  • Controls the exchange of material between internal and external environments of the cell

  • Selectively permeable → Allows certain molecules and ions into and out of the cell

  • The structure of it allows the concentration to be constant inside and outside of the cell

  • The membrane is not stationary and continuously moving.

Phospholipid Bilayer (Phosphate-Lipid)

  • Phosphate heads are hydrophilic (able to absorb water)

  • Lipid tails are hydrophobic (water avoidant and not able to dissolve in water)

Factors affecting the membrane


  • Gives stability to the cell membrane without affecting the fluidity.

  • Reduces the permeability of the cell membrane to small, water soluble molecules.


  • As temperature increases, fluidity increases.

  • Phospholipids become less tightly packed and move more freely

  • As temperature decreases, cell membranes with a high percentage of saturated fatty acid may solidify


  • Some penetrate the whole way through the membrane, forming channels that allow some materials to pass through the membrane.

  • Receptor proteins cause the cells to respond only to signals from substances.

  • Carrier proteins can assist in facilitated diffusion or active transport (May require energy to go against the concentration gradient)

Cell Function

Inquiry Question: How do cells coordinate activities within their internal and external environments?

  • Movement across cell membrane

○ Chemical properties of the material being moved

○ Physical properties like shape and size

○ Permeability of the cell membrane to the material

○ Concentration gradient → Higher the gradient, faster the movement

○ Surface Area to volume ratio

  • Diffusion

○ Particles move from a high concentration to a low concentration

○ Movement is slow as particles collide

○ Passive movement → Does not require Energy

○ Factors Influencing diffusion → Particle size, Concentration, Temperature

○ Simple Diffusion

■ Solute membranes diffuse across a membrane if the membrane is permeable to them

■ Movement is constant

■ If the concentration is equal on both sides, there is no net movement

○ Facilitated Diffusion

■ Membrane transport proteins are specific for particular particles, so transport is selective.

■ Transport is more rapid than simple diffusion.

■ Transport proteins can become saturated as the concentration of the transported substance increases.

■ No energy is required, movement is with a concentration gradient.

■ Require a channel or carrier protein to assist in transport

  • Osmosis

○ The net movement of water molecules across a semipermeable membrane.

○ If a dilute and concentrated solution are separated by a semipermeable membrane which allows the movement of free water molecules, the water molecules will move from the dilute solution to the concentrated solution. The pressure causing water to move is called osmotic pressure.

  1. Hypotonic - Concentration of solute is higher in the cell, water will be diffused into the cell.

○ Hypertonic - Concentration of solute is higher outside the cell, water will be diffused out of the cell.

  • Active Transport

    1. Movement of molecules from a low concentration to a high concentration→ Against the concentration gradient ○ Requires energy input.

○ Active transport requires a carrier protein that spans the membrane to actively move chemicals from a low to a high concentration, utilising cellular energy

  • Endocytosis

    1. A particle is too large to pass through the membrane, the membrane can change shape to surround and engulf the particle.

○ Form vesicles in the membrane

○ Phagocytosis- Eating

○ Pinocytosis- Drinking

● Exocytosis

○ A process in which substances are transported to the external environment of the cell.

○ Used for secreting proteins, removing waste and breakdown products from the lysosomes.

  • Surface Area to Volume

○ Smaller cells = More efficient

○ The larger the cell becomes, the smaller the SA:V ratio, therefore becomes less efficient to absorb nutrients

○ Smaller cells allow a faster movement of substances between the center and surface of the cell → Less energy required

○ Cells may have elongated extensions to increase SA:V ratio to be more efficient.

○ As the cell size continues to grow it reaches a point where diffusion is not fast enough to sustain the cell, so the cell divides if it’s possible.

○ Increasing SA:V ratio

■ Cell Compartmentalisation

  • Organelles live and work in separate areas.

  • Allows for more efficient movement because of more space

  • Reduces the amount of exchange between the membrane

■ Flattened Shape

  • Volume constant but increases surface area

  • Red blood cells

■ Membrane extensions

  • Works well for absorbing cells and secreting cells

  • Microvilli

Simple DiffusionDoes not require energy. Allows smaller molecules to easily move through the membrane
Facilitated DiffusionRequires energy and is assisted by carrier proteins and channel proteins. Allows large molecules to pass through
Solutewhat will be dissolved
Solventthe liquid in which a solute is dissolved in. They will form a solution
Solutionis a mixture of two or more substances mixed together
Concentrated SolutionIs a solution that contains a large amount of solute compared to the amount that could dissolve
Dilute SolutionDilution is decreasing the concentration of a solute in the solution. Occurs when mixing with more solvent.
Concentration Gradientan area where particles move from high concentration to low concentration
Semi Permeableallows certain substances to enter into the cell through the ‘semipermeable membrane’
ImpermeableDoes not allow substances through the membrane
Selectively Permeablethe membrane only lets some materials through, by passive or active transport
Channel Proteinsused in passive transport
Carrier Proteinsused in active transport
OsmosisIs the process in which water moves in and out of the cell, it does not need energy. Goes from high concentration to low concentration. Diffusion of water
Osmotic gradientThe difference in concentration between two solutions on either side of a semipermeable membrane.
Osmotic pressurethe pressure that is applied to a solvent to stop it from passing into a given solution by osmosis.
Isotonic solutionTwo solutions that have the same osmotic pressure across the membrane
Hypertonic solutionWhen the concentration is greater outside the cell than inside
Hypotonic SolutionWhen the concentration isgreater inside the cell than outside
Active TransportMoves from low concentration to high concentration against the gradient ; requires energy
Passive TransportThe movement of substances in and out of the cells without exerting energy
EndocytosisLarge particles that have to be moved into the cell, the membrane changes shape to let the particle in. type of active transport. turns into vesicle once inside the cell.
Exocytosismoves materials out of the cell eg: waste. removes vesicle membrane
Vesiclessmall structure in a cell which consists of fluid enclosed by a lipid bilayer. (membrane bubble)
Phagocytosis‘cell eating’ when solid particles are engulfed
Pinocytosis‘cell drinking’ when fluid is engulfed
Receptor-mediateddetectives specific molecules
  • Cell Requirements

  • Organic Compounds

○ Contain Carbon and Hydrogen → Protein, Vitamins, Carbohydrate

  • Inorganic Compounds ○ Water (H2O)

■ Important solvent and transport medium.

  1. Oxygen (O2)

■ Needed for efficient energy supply from cellular respiration.

■ Taken in as gas or in solution.

○ Carbon Dioxide (CO2)

■ Ultimate source of carbon atoms for organic molecules.

○ Nitrogen (N2)

■ Key atom in the acids that make up proteins.

○ Minerals

■ Important for building enzymes and vitamins.

  • Biochemical Processes

  • Photosynthesis

    1. Stage 1 → Light Stage

■ Photon from the sun enter the chlorophyll

■ The light is used to break down water into oxygen and hydrogen. ■ Oxygen is released into the atmosphere ■ Hydrogen is absorbed.

○ Stage 2 → Light independent Stage

■ Occurs in the stroma

■ ATP energy is used to combine hydrogen and CO2

■ Glucose is produced → Hydrogen + CO2

  • $\ce{C6H12O6}$

  • Factors Affecting Photosynthesis ○ Light intensity

■ More light, faster the rate → Until it reaches optimal rate

  1. CO2

■ Carbon Dioxide is required to make glucose

■ The more abundant the quicker the rate ○ Temperature

■ Temperature affects the rate that the enzymes catalyse at

Cellular Respiration


■ Not a good supply of oxygen

■ Breakdown of Glucose to form ethanol and carbon dioxide

■ This supplies the cell with ATP → adenosine triphosphate

■ Less efficient and lactic acid is created


■ In the presence of oxygen

■ Glucose and oxygen are broken down to create energy - ATP is released in the process

  • Removal Of Waste

    1. Waste are the products that are not used for cellular activity

○ Many of these wastes can be removed by simple diffusion through the cell membrane → CO2 in muscle activity is diffused into the capillaries

○ Other wastes are removed by exocytosis or by the enzymes present in lysosomes

  • Enzymes

    1. Protein molecules that control all metabolic reactions within a cell

○ Biological catalysts that speed up the rate of reactions → Get rid of the activation energy required for a reaction.

○ Specific for unique reactions → Enzymes in stomach differ from enzymes in mouth

○ Factors that Impact enzyme activity

■ Temperature

■ Concentration

■ pH

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