Comparing Different Types of Cells

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	Unicellular Algae and Fungi	Colonial Parasites	Multicellular Birds and Humans
Cellular Features	Single-cell	Many cells	Many cells
Cellular Classifications	Mostly prokaryotes; some eukaryotes	Eukaryotes	Eykaryotes
Cellular Structure	One cell carries out all the functions to sustain life	Individual animals; e.g. zooids work together to sustain the colony	Functions are carried out at cellular, tissue, organ and system level
Cellular Function	Functions are carried out within the cell	Functions are carried out by individuals with specific roles in the colony	Functions are carried out at a cellular, tissue, organ and system level
Microscopic or Macroscopic	Microscopic – SA:V limits the size of the cell	Usually macroscopic	Macroscopic; increasing the number of cells allows for an increase in body size
Life Span	Short lifespan due to high energy output	Long lifespan	Long lifespan
Asexual or Sexual	Mostly asexual: budding, mitosis, reproduction	Mostly asexual: mitosis, colonial reproduction	Mostly sexual
Reproductive Success	The whole organism is involved	Usually, specific zooids are responsible for reproduction	Only cells specialised for reproduction (gametes) will reproduce

Relating Structure and Specialisation to Function

Organelle	Membrane-bound compartment or structure in a cell that performs a special function. e.g. mitochondria, vacuole
Specialised cell	Cells that have a specific function e.g. root hair cell, lead guard cell
Tissue	A group of similar cells working together to carry out a specific function in multicellular organisms e.g. muscle tissue, root tissue
Organ	Two or more tissues that work together to perform one or more specialised tasks e.g. heart, liver, flowers, leaves
System	A group of organs that work together to perform a vital task

Cell Specialisation and Differentiation

Specialisation is a specialised function for cell. Differentiation is the process where a cell changes from one type to another, typically an unspecialised cell becoming specialised.

Structure and Function of Specific Cells – Examples

Cell	Structure Related to Function
Red blood cell	– Carry oxygen around the body – Thin outer membrane allows oxygen to diffuse – Shape increases SA:V which allows the oxygen to be absorbed more efficiently – No nucleus, leaving room for haemoglobin – Shape allows it to squeeze through vesicles and thin capillaries
Epidermal cell	– Has 2 layers to keep external and internal environments separate
Xylem cell	– Transports water and nutrients from the soil to stems and leaves – Provides mechanical support and storage – Internal hydrophobic surface facilitating water transport – Tracheids are hollow and connect to each other to improve transport efficiency – Think lignin coated cell walls provide shape and structure
Phloem cell	– Transport of sugars around the plant – Next to xylem for osmosis of water – Has a source and sink as transport for substance
Guard cell	– Multiple large vacuoles to absorb water – Multiple chloroplasts for photosynthesis – One thicker wall for stability and a thinner wall for differentiation – Close stomata when they lose potassium ions
Palisade mesophyll cells	– Found in the mesophyll of the leaf – The main function is light absorption – Multiple chloroplasts for photosynthesis
Root hair cell	– Extremely narrow tubes – Have thin hairs which protrude outwards, allowing an increase in SA: V for osmosis – Long and thin to penetrate between soil particles and prevent harmful organisms from entering the plant

Cohesion is where water molecules stick together because they are attracted to each other due to their charges. Adhesion is where water molecules stick to a surface. Capillarity is where water molecules move up thin tubes (xylem).