All animal and plant cells have a nucleus,
cytoplasm and a cell membrane. Plant cells
also have a cell wall, chloroplasts and a
vacuole. Different parts of the cell are
adapted to perform different functions.
Unspecialised stem cells can differentiate –
develop into any other type of cell. Stem
cells are found in animal zygotes (very
young embryos), and in plants of all ages.
Plants and animals grow and differentiate
their tissues in different ways.
Plant cells
All animals and plants are made of cells. Remember that
animal cells and plant cells have features in common,
including: A nucleus Cytoplasm A cell membrane
Mitochondria Ribosomes
In addition, plant cells also have chloroplasts, where
photosynthesis happens. They also have a vacuole
and a cell wall:
Bacteria cells
Bacterial cells a salmonella bacterium cell
Structure of a salmonella bacterium cell Bacterial
cells are smaller and simpler than plant and
animal cells. Bacterial cells do not contain
chloroplasts (like animal cells but unlike plant
cells). In addition, unlike animal and plant cells,
bacterial cells lack: A 'true' nucleus Mitochondria
Instead of a cell nucleus containing
chromosomes, the DNA in bacterial cells is
arranged in a single circular strand in the
cytoplasm.
Growth curves
Growth involves cell division followed by cells becoming
specialised. Growth can be measured as an increase in:
Height Wet mass Dry mass Height and wet mass can be
measured when an organism is alive, but dry mass can only be
measured when an organism has had all its water removed
and is dead. However,dry mass is the best measure of growth
Differentiation
Differentiation is the process of
cells becoming specialised. Most
types of animal cells differentiate at
an early stage. They become
specialised for a particular function
and cannot change into different
types of cells. In mature animals,
cell division is mainly restricted to
replacement and repair. On the
other hand, many plant cells keep
the ability to differentiate.
Stem cells
Stem cells can be made to differentiate to form different types
of cell, such as nerve cells. Human stem cells can come from:
Human embryos (embryonic stem cells) Adult bone marrow
(adult stem cells) Stem cells can develop into any kind of human
cell.