Section One
1.1 characteristics of living cells:
Cells are the building blocks of life. Groups of specialised cells could be organised into organs and
tissue found in pants and animals.
Cells carry out the same 7 principles of life, like plants and animals; (MRS. GREN).
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Movement – ability to change the position of organism within environment
Respiration – ability to manufacture energy
Sensitivity – ability to respond to changes in its surroundings (environment)
Growth – ability to increase in size and complexity (development)
Reproduction – ability to produce offspring
Excretion – ability to remove toxic metabolic waste products
Nutrition – ability to feed, acquire food, make use of it.
1.2: Prokaryotic and Eukaryotic cells and the impact viruses have on them.
By definition a prokaryotic cell is a simple form of life and the most primitive form of cell. They
belong to groups such as bacteria and archaea. They can tolerate extremes in environmental
conditions such as higher levels in temperature, salinity and acidity. They have no true nucleus and
their DNA is coiled into a region called the nucleoid. It is not separated from the rest of the cell by a
nuclear membrane. In prokaryotic forms of life, cell division is normally due to a process referred to
as binary fission. This is where the DNA replicates and the original cell then divides to form two
identical daughter cells.
In contrast, a eukaryotic cell is defined as a cell which contains a true nucleus where the DNA is
contained within a nuclear membrane. Overall the eukaryotic cell is more complex in structure than
the prokaryotic cell. In general terms, a eukaryotic cell is approximately ten times larger in diameter
than a prokaryotic cell.
Both prokaryotic and eukaryotic organisms carry out the process of respiration. In eukaryotic forms
the process is mainly aerobic making use of an organelle called the mitochondrion. Prokaryotic cells
can exist more easily by anaerobic respiration which happens in the cell cytoplasm. The difference
between the types of respiration is aerobic uses oxygen and generates a greater quantity of energy
which is needed for more complex organisms and their metabolic demands.
There is a contrast in their mode of reproduction. Eukaryotic cells use two forms of cell division,
mitosis and meiosis. Mitosis occurs when identical copies of cells are required such as in growth of
tissues. The latter, meiosis, occurs within the reproductive organs of the organism during sexual
reproduction. Meiosis results in the male and female gametes containing half of the normal number
of the chromosomes for a cell of that species. This ensures the correct number of chromosomes are
restored when the gametes fuse during fertilisation. In prokaryotic forms of life, cell division
is normally due to a process referred to as binary fission. This is where the DNA replicates and the
original cell then divides to form two identical daughter cells.
Viruses
A virus is described as a sub-microscopic infectious agent unable to grow or reproduce outside of
another living host cell. It is commonly referred to as being an obligate intracellular parasite which is
of an acellular nature, i.e. having no cells. Its genome or genetic makeup consists of a nucleic acid
(either DNA or RNA), enclosed within a protein coat known as a capsid. It uses the host cells
metabolic facilities and ribosomes to manufacture components which assemble into particles called
virions.
Viruses can infect cellular forms of life grouped into animal, plant or bacterial types; it all depends
upon which specific virus it is and the nature of the host cell required. When one refers back to the
characteristics of living cells earlier, it is important to remember what living cells shared in common.
Viruses don't confirm to these rules as they:
Structure of a typical prokaryotic cell
Structure of a typical eukaryotic cell
One way to compare main features in eukaryotic and prokaryotic cells is to consider their overall
structures in the form of a table - see below. The role of these features/organelles will be
discussed in a later section.
Prokaryote
Oldest cell type
Small and simple
Lack nucleus
Lack Organelles
Single-Celled
Single cellular organism
Both
DNA
Ribosomes
Cytoplasm
Plasma membrane
Eukaryote
Evolved from prokaryote
Larger and more complex
Contain nucleus
Contain organelles
Single-celled or multicellular
Multi linear chromosomes
1.3: Eukaryotic sub-cellular structure and organelles.
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Nucleus: is located at the centre of the cell and controls what the cell does. But not all cells
have nuclei, some single cell-organisms such as bacteria do not. Some cells in the body like
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red blood cells don’t have nuclei. Nucleus contains all the organisms genetic information on
strands of DNA or deoxyribonucleic acid.
Cell membrane: The wall around the cell, is selectively permeable allowing beneficial
substances in and excretes waste products.
Cytoplasm: Is the liquid inside the cell, that transforms food molecules into materials
needed for energy and growth
Mitochondria: Converts food into energy
Endoplasmic reticulum: Is a network of channels that moves material within the cell
Ribosome: Are made in the nucleolus and are attached to the endoplasmic reticulum. They
produce proteins
Golgi body: Distributes proteins and other material within the cell.
Lysosomes: Are sacks filled with digestive enzymes, they ingest worn out cell parts, dead
cells and foreign micro-organisms.