B1 Cells 1
B2 Movement across membranes 3
B3 Cell division and sex determination 4
B4 Inheritance 6
B5 DNA 6
B6 Gene technologies 7
B7 Variation 9
B8 Enzymes 9
B9 Animal physiology 10
B10 Ecosystems 18
,B1 Cells
Structure and function of the main subcellular components of animal/plant eukaryotic cells
Subcellular Structure and description Function
component
Cell membrane A partially permeable layer that forms a Contains the cell contents and
boundary around the cytoplasm of the controls the movement of
cell. substances in and out of the cell. It
allows 𝐻2𝑂, 𝑂2 and nutrients to enter
and allows waste products (e.g. 𝐶𝑂2)
to leave.
Chromosomal One or more linear pieces of Stores the genetic material required
DNA double-stranded DNA. for the various cell processes.
Cytoplasm A jelly-like region, surrounded by cell Is the site of chemical reactions and
membrane. Salt ions and sugar contains enzymes that control these
molecules are dissolved in it. Fat reactions. It holds the cell
molecules and proteins, e.g. enzymes, organelles.
are suspended in it. Also contains food
reserves (e.g. glycogen in AC, starch in
PC) and organelles such as the nucleus
and mitochondria. Chloroplasts in
cytoplasm of photosynthetic plant cells.
Nucleus Usually round or oval, contained by two Regulation of cell functions through
nuclear membranes and containing DNA directing the production of RNA and
in the form of chromosomes. It is found protein required for all cell
inside the cytoplasm. processes, including cell division,
cell differentiation (specialisation)
and cell metabolism (chemical
reactions).
Mitochondrion A small organelle (electron microscope) Controls the production and release
with an inner and outer membrane. Inner of ATP (usable energy) from aerobic
membrane has inward-pointing folds. respiration.
Cell wall (plant A tough, rigid layer surrounding the cell Provides a rigid external coat to
only) membrane made primarily of cellulose. It plant cells, providing mechanical
is freely permeable to water and salts. strength which allows cells to resist
bursting when the cell is turgid.
Chloroplast A small organelle with its own double Traps (absorbs) light energy and
(plant only) membrane, found in the cytoplasm of converts it to chemical energy by the
photosynthetic plants, containing process of photosynthesis.
chlorophyll and other pigments.
1
, Vacuole (plant A fluid-filled space surrounded by a Stores water-soluble chemicals and
only) membrane in plant cells. It is found ions and helps to keep plant cells
inside the cytoplasm. The fluid is called and tissues firm.
sap, which is a watery solution of sugars
and salts. In some cells, e.g. rhubarb, it
is also coloured.
Structure and function of the main subcellular components of prokaryotic cells (bacteria)
Subcellular Structure and description Function
component
Cell membrane A partially permeable layer that forms a Contains the cell contents and
boundary between the cytoplasm and controls the movement of
the cell wall. Functions as a boundary some molecules into and out
to restrict materials moving between of the cell.
the inside and outside of a cell.
Cytoplasm A jelly-like region, surrounded by the Is the site of chemical
cell membrane. It may contain reactions and contains
glycogen granules, fats (lipids) and enzymes that control these
other food molecules. reactions. It holds the cell’s
DNA.
Cell wall A tough, rigid external coat that Provides structural support
surrounds the cell membrane. It is and protection to bacteria. It is
made of a complex mixture of proteins, freely permeable to small
lipids (fats) and sugars. This makes it molecules, so does not control
different from plant cell walls, which the intake or loss of materials.
are made of cellulose. Some bacterial
cells have a slime capsule surrounding
the cell wall.
Chromosomal DNA A large closed circular coiled molecule Carries genetic information
(bacteria) of double-stranded strand DNA located that regulates most bacterial
within the bacterial cytoplasm (no cell processes.
nucleus or enclosing membrane).
Plasmid DNA A small molecule of closed Carries genetic information for
double-stranded circular DNA, usually specialist cell functions (like
present in multiple copies per cell. antibiotic resistance). It can
replicate and operate
independently from the
chromosomal DNA. Can be
readily moved between
different bacterial cells,
including for genetic
engineering (biotechnology)
purposes.
Examples of specialised cells are ciliated cells, red blood cells, nerve cells (neurones),
sperm cells, root hair cells and palisade mesophyll cells
2
B2 Movement across membranes 3
B3 Cell division and sex determination 4
B4 Inheritance 6
B5 DNA 6
B6 Gene technologies 7
B7 Variation 9
B8 Enzymes 9
B9 Animal physiology 10
B10 Ecosystems 18
,B1 Cells
Structure and function of the main subcellular components of animal/plant eukaryotic cells
Subcellular Structure and description Function
component
Cell membrane A partially permeable layer that forms a Contains the cell contents and
boundary around the cytoplasm of the controls the movement of
cell. substances in and out of the cell. It
allows 𝐻2𝑂, 𝑂2 and nutrients to enter
and allows waste products (e.g. 𝐶𝑂2)
to leave.
Chromosomal One or more linear pieces of Stores the genetic material required
DNA double-stranded DNA. for the various cell processes.
Cytoplasm A jelly-like region, surrounded by cell Is the site of chemical reactions and
membrane. Salt ions and sugar contains enzymes that control these
molecules are dissolved in it. Fat reactions. It holds the cell
molecules and proteins, e.g. enzymes, organelles.
are suspended in it. Also contains food
reserves (e.g. glycogen in AC, starch in
PC) and organelles such as the nucleus
and mitochondria. Chloroplasts in
cytoplasm of photosynthetic plant cells.
Nucleus Usually round or oval, contained by two Regulation of cell functions through
nuclear membranes and containing DNA directing the production of RNA and
in the form of chromosomes. It is found protein required for all cell
inside the cytoplasm. processes, including cell division,
cell differentiation (specialisation)
and cell metabolism (chemical
reactions).
Mitochondrion A small organelle (electron microscope) Controls the production and release
with an inner and outer membrane. Inner of ATP (usable energy) from aerobic
membrane has inward-pointing folds. respiration.
Cell wall (plant A tough, rigid layer surrounding the cell Provides a rigid external coat to
only) membrane made primarily of cellulose. It plant cells, providing mechanical
is freely permeable to water and salts. strength which allows cells to resist
bursting when the cell is turgid.
Chloroplast A small organelle with its own double Traps (absorbs) light energy and
(plant only) membrane, found in the cytoplasm of converts it to chemical energy by the
photosynthetic plants, containing process of photosynthesis.
chlorophyll and other pigments.
1
, Vacuole (plant A fluid-filled space surrounded by a Stores water-soluble chemicals and
only) membrane in plant cells. It is found ions and helps to keep plant cells
inside the cytoplasm. The fluid is called and tissues firm.
sap, which is a watery solution of sugars
and salts. In some cells, e.g. rhubarb, it
is also coloured.
Structure and function of the main subcellular components of prokaryotic cells (bacteria)
Subcellular Structure and description Function
component
Cell membrane A partially permeable layer that forms a Contains the cell contents and
boundary between the cytoplasm and controls the movement of
the cell wall. Functions as a boundary some molecules into and out
to restrict materials moving between of the cell.
the inside and outside of a cell.
Cytoplasm A jelly-like region, surrounded by the Is the site of chemical
cell membrane. It may contain reactions and contains
glycogen granules, fats (lipids) and enzymes that control these
other food molecules. reactions. It holds the cell’s
DNA.
Cell wall A tough, rigid external coat that Provides structural support
surrounds the cell membrane. It is and protection to bacteria. It is
made of a complex mixture of proteins, freely permeable to small
lipids (fats) and sugars. This makes it molecules, so does not control
different from plant cell walls, which the intake or loss of materials.
are made of cellulose. Some bacterial
cells have a slime capsule surrounding
the cell wall.
Chromosomal DNA A large closed circular coiled molecule Carries genetic information
(bacteria) of double-stranded strand DNA located that regulates most bacterial
within the bacterial cytoplasm (no cell processes.
nucleus or enclosing membrane).
Plasmid DNA A small molecule of closed Carries genetic information for
double-stranded circular DNA, usually specialist cell functions (like
present in multiple copies per cell. antibiotic resistance). It can
replicate and operate
independently from the
chromosomal DNA. Can be
readily moved between
different bacterial cells,
including for genetic
engineering (biotechnology)
purposes.
Examples of specialised cells are ciliated cells, red blood cells, nerve cells (neurones),
sperm cells, root hair cells and palisade mesophyll cells
2
