Unit 2 Organisation of the organism
2.1 Cell structure
OBJECTIVES:
1. Each should be able to describe and compare the structure of a plant cell with an animal
cell, limited to: cell wall, cell membrane, nucleus, cytoplasm, chloroplasts, ribosomes,
mitochondria, vacuoles
2. Describe the structure of a bacterial cell, limited to: cell wall, cell membrane, cytoplasm,
ribosomes, circular DNA, plasmids
3. Identify the cell structures listed in 2.1.1 and 2.1.2 in diagrams and images of plant,
animal and bacterial cells
4. Describe the functions of the structures listed in 2.1.1 and 2.1.2 in plant, animal and
bacterial cells
5. State that new cells are produced by division of existing cells
Organelles are structures in the cytoplasm which have particular functions. In the cytoplasm, a
great number of chemical reactions are taking place which keep the cell alive by providing
energy and making substances that the cell needs.
All living things are made of cells. New cells are produced by division of existing cells
1. Cell Membrane: separates the cell’s contents from its surroundings. It is also a
membrane that controls the entry and exit of dissolved substances. It is living and
selectively permeable.
2. Cytoplasm: is a jelly-like medium, with particles and organelles in it . it contains water
and dissolved substances such as sugars and salts. It is the site for all chemical reactions.
3. Nucleus: is a rounded structure enclosed in a membrane and embedded in the cytoplasm.
It contains the genetic material (DNA). This carries the coded instructions for
controlling the activities and characteristics of the cell. The nucleus also controls cell
division.
4. Ribosomes can also be found free in the cytoplasm. They build up the cell’s proteins by
joining amino acids.
5. Mitochondria: a tiny oval shaped organelle where aerobic respiration happens. They
have an outer membrane and an inner membrane that folds inward to increase the
surface area for respiration.
6. Chloroplast: Small organelle which contains chlorophyll and enzymes necessary for the
production of glucose by photosynthesis. The chlorophyll is a green pigment which
traps light energy for photosynthesis. They have an outer membrane and an inner
membrane that folds inward to increase the surface area for photosynthesis.
7. Large permanent Vacuole: contains water necessary to provide turgor pressure and may
store ions and other molecules such as cell sap, sugar, pigments and tic chemicals.
8. Cellulose cell wall: provides structural support, it is freely permeable for dissolved
substances and water and it is rigid and prevents damage or burstiong when the cell is in
a hypotonic solution i.e. cell can’t explode.
A typical plant cell (e.g. the palisade cell) has all the above things.
Bacteria: Virus:
Viruses and bacteria:
Features Virus Bacteria
Covered by Protein coat Cell wall
Cell No Yes
membrane
Cytoplasm No Yes
Genetic DNA or RNA – only a few DNA – enough for several
material genes hundred genes
Living or Non-living unless in host Living
not?
Specialisation of cells
Most cells, when they have finished dividing and growing, become specialised. When cells are
specialised:
● they do one particular job
● they develop a distinct shape
● special kinds of chemical change take place in their cytoplasm.
The changes in shape and the chemical reactions enable the cell to carry out its special function.
Red blood cells and root hair cells are just two examples of specialised cells.
Diagrams of specialised cells in animals:
Ciliated cell
Nerve cell
Red blood cells
Sperm cell
Egg cell
Root hair cell
Xylem structure
Specialised Cells in Animals Table
Examples of specialised cells in plants:
Stem cells
Stem cells are cells that have the potential to develop into many different types of cells in the
body. They serve as a repair system for the body.
2. Levels of organisation:
Organelle: a specialized part of a cell that has its own function, e.g. the nucleus or the
mitochondrion
Cell: the smallest part of a living organism that can operate as an independent unit e.g. the red
blood cell
Tissue: a group of cells with similar structures, working together to perform a shared function
e.g. muscle tissue
Organ: a structure made up of a group of tissues, working together to perform specific functions
e.g. the heart
Organ system: a group of organs with related functions, working together to perform body
functions e.g. respiratory system
Organism: an individual made of organ systems which work to keep that organism alive e.g. a
Levels of organization
Examples of animal tissues
Examples of plant tissues
