Summary
OCR Biology A level 5.1.1 Communication and homeostasis summary notes
Summary notes for topic 5.1.1 Communication and homeostasis in the OCR Biology A level Module 5. Detailed electronic notes with diagrams.
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5.1.1 Communication and Homeostasis(a) the need for communication systems in multicellular organisms
Responding to change
Living things need to maintain a certain set of conditions inside their cells. Cellular activities rely on the action of
enzymes. Enzymes need a specific set of conditions to work correctly.
These include:
temperature
pH
aqueous environment that keeps substrates and products in solution
freedom from toxins and excess inhibitors
As cells undergo metabolic activities they use up substrates and produce products
The products may be toxic
They diffuse out into tissue fluid
Therefore, the activities of the cells alter their environment.
e.g Carbon dioxide
Builds up changing the pH of the environment around cell
Enzymes may denature
Co-ordination
A good communication system will:
cover the whole body
enable cells to communicate with each other
enable specific communication
enable rapid communication
enable both short-term and long-term responses
(b) the communication between cells by cell signalling
One cell releases a chemical that is detected by another cell. The second cells will respond to the signal released by
the first cell.
(c) the principles of homeostasis
Homeostasis:
Maintenance of the internal environment in a constant state within set limits despite external changes.
Living organisms need to keep a number of conditions constant such as:
Body temperature
o Low temperatures slow down metabolic reactions; high temperatures can cause proteins to
denature
Blood glucose concentration
o A lack of it causes respiration to slow down or halt, as the cells now have no energy source
o Too much glucose in the tissue fluid can cause water to move out of cells by osmosis
Blood salt concentration
Water potential of the blood
o Lack of water in tissue fluid causes water to move out of cells by osmosis; causing metabolic
reactions in cells to slow down/stop
o Too much water in tissue fluid causes water to move into cells by osmosis; cell may swell/burst
Blood pressure
Carbon dioxide concentration
o Enters red blood cells and combines with water forming carbonic acid
o Dissociates to hydrogencarbonate and hydrogen ions
o Makes blood more acidic
o Haemoglobin absorbs the H+ ions to form haemoglobonic acid, causing it to lose oxygen molecules
they are carrying, reducing oxygen transport
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