Cells and Cell Structure

Structural Organisation

The body is divided into four distinct levels:

Cells - The lowest structural level, they are specialised to carry out specific functions. E.g. muscle cells, red blood cells.

Tissues - Made up of cells with similar specialisations. They group together to carry out common functions.

Organs - Made up of two or more tissues. Group together to carry out a common function.

System - Highest level of organisation. It is made up of a group of organs working together for a common purpose.

Structure of Cells

Cells are the basic structural and functional unit of all living things. This is known as cell theory.

Cells are made up of many different parts:

  • Cell membrane

  • Cytoplasm

  • Cytosol

  • Cytoskeleton

  • Organelles (Vesicles, centrioles, golgi body, mitochondria, nucleus, nucleolus, lysosomes, Endoplasmic reticulum and ribosomes)

Cell Membrane

Structure: Double layered membrane made up of phospholipids and proteins.

Function: Controls movement of substances into and out of the cell, and provides a physical barrier between the inside and outside of the cell.

Cytoplasm

Function: Thick fluid consisting of cytosol and the organelles suspended in it.

Structure: Allows chemical reactions to occur and provides shape to the cell.

Cytosol

Structure: Consists of 75-90% water with some dissolved substances (salts, etc.)

Function: Metabolic reactions occur here and controls osmotic pressure of the cell.

Nucleus

Structure: Spherical/ovoid structure.

Function: Stores the generic material, mostly in the form of DNA.

Nucleolus

Structure: Small structure within the nucleus

Function: Contains genetic material, mostly RNA, helps with protein synthesis. Produces ribosomes.

Lysosomes

Structure: Small spherical structures in the cytoplasm.

Function: Contains enzymes that break down materials/worn out organelles.

Endoplasmic Reticulum

Structure: Parallel membranes connecting cell membrane and nuclear membrane.

Function: Provide surface for chemical reactions. Store/transport materials. May be rough (ribosomes attached) or smooth (no ribosomes).

Ribosomes

Structure: Small spheres, may be free in the cytoplasm or attached to the endoplasmic reticulum.

Function: Joins amino acids together to form proteins.

Vesicles

Structure: Small membrane bound sack.

Function: Transports materials in, out, and within the cell.

Golgi Body

Structure: Stacked, flattened membranes.

Function: Modify and package proteins for secretion.

Centrioles

Structure: Pairs of cylinders located near the nucleus

Function: Involved in cell reproduction.

Mitochondria

Structure: Double membraned elongated structures (looks like nutri-grain)

Function: Release energy for the cell through cellular respiration.

Cytoskeleton

Structure: A framework of protein fibres, consisting of microtubules (long rods), and microfilaments.

Function: Gives the cell its shape and assists cell movement. Microtubules keep organelles in place or move them around the cell, and microfilaments move materials around the cytoplasm or move the whole cell.