Brown's Biology AQA GCSE Additional Science-BIOLOGY
2 Revision Notes
Biology Unit B2.2 Tissues, organs and
organ systems Study Notes
for GCSE Additional Science or GCSE Biology
REVISION NOTES GUIDE SUMMARY: What do you need to know
for the examinations? What do you need to able to do in the exams? In AQA GCSE Science
A examinations HT means for higher tier students only.
Sorry, but I don't have much time to answer questions, but if you see any
apparent errors or wish to comment, please
email me. All my notes, learning
objectives, comments for exam revision are based on the official AQA GCSE Science A Key Stage 4
AQA GCSE Science BIOLOGY 2 Unit
B2.2 Tissues, organs and
Know that the cells of multicellular organisms may differentiate and become adapted for
specific functions - specialised cells.
Know that tissues are
aggregations of similar cells and organs are aggregations of tissues performing
specific physiological functions eg heart and liver.
Know that organs are organised into organ systems, which work together to form organisms.
AQA GCSE Science BIOLOGY Unit B2.2.1 Animal organs
a) Know that large multicellular organisms develop systems
for exchanging materials.
Know that during the development
of a multicellular organism, cells differentiate so that they can perform
The specialised cells form
tissues, one or more types of tissue are structured to form organs and two
or more organs can work together in an organ system.
Bigger multicellular systems
e.g. animals like mammals have several different organ systems for absorbing
(e.g. gut), transporting (e.g. blood system) and exchanging materials (e.g.
You should develop an
understanding of size and scale in relation to cells, tissues, organs and
b) Know that a tissue is a group of
specialised cells with similar structure and carry out a particular function.
c) Know that organs are made of
different tissues acting together to perform some particular function.
d) Know that organ systems are
groups of organs that work together to perform a particular function.
Know that the digestive system is one
example of a system in which humans and other mammals exchange substances
with the environment.
The digestion process requires a
variety of enzymes to breakdown food into soluble products we can absorb
from the digestive system, and these enzymes are produced by specialised
cells in the glands and gut system.
Large insoluble molecules like
proteins, starch like carbohydrates and oils/fats cannot pass through the
membranes of the cell walls of the gut system.
However, smaller soluble
molecules like amino acids, sugars and fatty acids can pass through the
walls of the digestive system.
Some examples of the enzymes
responsible for the breakdown of large insoluble molecules into small
soluble absorbable molecules are ...
protease enzymes like pepsin
convert proteins to amino acids,
carbohydrase enzymes like
amylase convert carbohydrates like starch to sugars,
lipase enzymes convert oils/fats
to fatty acids and glycerol
Know that the digestive system includes:
(1) In the mouth,
salivary glands produce the enzyme amylase which can break down
carbohydrates like starch. The saliva also moistens the food and, together
with the chewing action (mastication) of the mouth muscles, balls of food
are formed that are easily swallowed.
(2) The oesophagus
(gullet) is a tube that connects the mouth to the stomach and its lined with
muscles that help move the balls of food along (this action is an example of
(3) In the stomach the food is churned and broken up into
smaller chunks by the muscles of the stomach wall. The protease enzyme
pepsin is secreted which can break down proteins to amino acids. At the same
time hydrochloric acid is produced, killing most of the bacteria present and
creates the right acidic pH conditions (~pH 2) for the protease enzyme,
best in these acid conditions to break down proteins.
(4) The liver produces alkaline bile, which neutralises excess
stomach acid (most enzymes can't work in very acid conditions), and bile helps to emulsify oils/fats.
The emulsification is
essential for the efficient faster digestion of oils/fats, the oils/fats are more
dispersed giving greater surface area (greater surface area - think of the
oil/fat as broken down into smaller droplets/particles).
(5) The gall bladder
stores bile before its released into the small intestine to help with
(6) The pancreas gland produces digestive juices
containing the enzymes (i) protease pepsin (breaks down proteins), (ii)
amylase (breaks down starches) and (iii) lipase (breaks down oils/fats),
which are released into the small intestine.
(7) The small intestine is where
digestion process continues with the release of the enzymes from the
pancreas. Here the absorption of soluble food into the blood stream occurs
from the digestive system eg smaller molecules like amino acids, sugars and
fatty acids - the products of enzyme
breakdown of larger food molecules (x-reference with the enzymes above,
which are released into the small intestine).
(8) In the
large intestine excess water is absorbed from the undigested food, producing
faeces which are initially stored in the rectum before release through the
should be able to recognise the organs of the digestive system on a diagram
and know their function where described in this module (Biology B2).
eg salivary glands, stomach,
gall bladder, liver, large intestine, pancreas, small intestine, rectum
The functions of the components
of the digestion system are described in the section above.
AQA GCSE Science BIOLOGY Unit B2.2.2 Plant organs
a) You should know that plant organs include stems,
roots and leaves.
Details of the internal
structure are only needed for the leaf.
Know the structure and function
of palisade cells and guard cells in plants.
Palisade cells contain
chlorophyll and are adapted for photosynthesis.
Guard cells are adapted to open
and close the pores which allow gas exchange and water evaporation.
b) You should know examples of plant tissues
epidermal tissues, the outer
layers which cover
the whole plant,
mesophyll, between two epidermis
layers, where most photosynthesis happens,
xylem and phloem, which transport substances
around the plant eg sugars like sucrose and glucose, minerals and water.
AQA GCSE Additional
keywords: multicellular organisms differentiated cells
adapted specific functions tissues muscular glandular enzymes hormones
epithelial tissue digestive system stomach small/large intestine liver bile
epidermal mesophyll tissue xylem phloem
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