Most human cells are like most other
animal cells and contain a nucleus,
cytoplasm, cell membrane, mitochondria
and ribosomes.
Plant and algal cells contain all the structures seen
in animal cells as well as a cell wall. Many plant
cells also contain chloroplasts and a permanent
vacuole filled with sap.
Diffusion
The greater the difference in concentration,
the faster the rate of diffusion.
Diffusion is the net movement of particles from
an area where they are at a high concentration to
an area where they are at a lower concentration.
Dissolved substances and gases such as
oxygen move in and out of cells by diffusion.
Tissues and organs
A tissue is a group of cells with
similar structure and function.
Organs are made of tissues. One organ may
contain several types of tissues.
Specialised cells
Cells may be specialised to carry out a particular function.
Examples of specialised cells
are fat cells, cone cells, toot
hair cells and sperm cells.
Organ systems
Organ systems are groups of organs
that performs a particular function.
Plants organs include stems, roots and leaves.
The digestive system in a mammal is an
example of a system where substances are
exchanged with the environment.
Bacteria and yeast
A bacterial cell contains of cytoplasm and a
membrane surrounded by a cell wall. The genes are
not in a distinct nucleus.
Yeast is a single-celled organism. Each
cell has a nucleus, cytoplasm and a
membrane surrounded by a cell wall.