edexcel biology

1. All living things are made
up of cells. They are the
basic building blocks of all
organisms.
The simplest life forms
have only one cell, but
multicellular organisms
can have trillions.

2. During the development of
multicellular organisms, cells
specialise to carry out particular
functions.
Sperm cell Nerve cell
Intestinal cell Muscle cell
Human stem cell

3. Specialised cells form tissues...
tissues form organs...
...and organs form organ systems.

4. Specialised Cells are Organised into Tissues

5. A tissue is a group of similar cells which work together to perform a
function. Examples in mammals include:
1. Muscle tissue which contracts to move
whatever it is attached to e.g. skin or
bones.
2. Glandular tissue which produces and
secretes enzymes and hormones.
3. Epithelial tissue covers the outside of
the body and lines many organs e.g. in
inside of the gut.

6. Tissues can include more than one cell type.
Epithelial cells Epithelial tissue
For example these are all types of
epithelial cell. They are similar but
not identical.

7. Tissues are Organised into Organs

8. An organ is a group of several
different types of tissues working
together to perform a function.
Epithelial
tissue
Muscle tissue Glandular tissue
For example the stomach is an organ which includes:

9. Glandular tissue produces
the digestive juices and
enzymes to break down food
Epithelial tissue lines the
inside and outside of the
stomach
Muscular tissue moves the
stomach wall to churn up
food

10. Organs are Organised into Organ Systems

11. Organ systems are groups
of organs working together
to perform a certain
function, for example the
digestive system.
The organs in the
digestive system work
together to break down
and absorb food.
Salivary glands and
pancreas produce
digestive juices
Liver produces bile
Stomach and small
intestine digest food
Small intestine
absorbs soluble
molecules of broken-
down food
Large intestine
absorbs water from
indigestible food

12. Summary of cell organisation:
Cell
Tissue
Organ
Organ system
Organism
<0.1mm
10cm
Salivary glands
Stomach
Liver
Pancreas
Small
intestine
Large
intestine

13. Extension
• Other organ systems include the respiratory system, the reproductive system and
the nervous system. Some organs can contribute to more than one organ system,
for example the mouth is involved in the digestive and respiratory systems.
• The largest organ in the body is the skin. Most organs are compact but the skin
stretches over the whole body.