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.

Endosymbiosis

• 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

Organelles

Technology

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

Cholesterol

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

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

Temperature

• 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

Proteins

• 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

• 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

Anaerobic

■ 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

Aerobic

■ 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