These A-Level Biology notes are designed for students aiming for top grades and a future in medicine. They are both aesthetic and detailed, offering comprehensive coverage of the syllabus while being visually engaging.
Comprehensive Coverage: Every topic is fully covered, directly aligned with t...
5.1 Communica-on and homeostasis
5.1.1 The Need for Homeostasis
Need for Communica-on Systems in Organisms
- Organisms need to respond to changes in internal/external environment, and coordinate different organs
- Control + communica;on systems ensure internal condi;ons are rela;vely constant for the organism to
func;on effec;vely
- Homeostasis = physiologically controlling systems to maintain internal environment within restricted
limits, cri;cally important to ensure maintenance of op;mal condi;ons for enzyme ac;on and cell func;on
- Physiological factors controlled by homeostasis: core body temperature, metabolic waste, blood pH, conc.
of blood glucose, water poten;al of blood, conc. of respiratory gases in blood
- Homeostasis requires informa;on to be transferred between parts of the body using 2 communica;on
systems: 1. The nervous system, 2. The endocrine system
The nervous system
- Human nervous system consists of: 1. CNS (central nervous system) – brain and spinal cord, 2. PNS
(peripheral nervous system) – all of the nerves in the body
- Allows humans to make sense of and respond to surroundings, coordinate and regulate body func;ons
- Informa;on is sent as nerve impulses – electrical signals that pass along nerve cells called neurones that
form bundles called nerves
- Neurones coordinate the ac;vity of sensory receptors, decision making centres in the CNS and effectors
e.g. muscles/glands
The endocrine system
- Hormone = a chemical substance produced by an endocrine gland and carried by the blood to transmit
informa;on from one part of an organism to another and bring about a change by altering the ac;vity of
one or mul;ple specific target organs
- Used to control func;ons that don’t need instant responses
- Gland = a group of cells that produces and releases one or mul;ple substances during secre;on – all
endocrine glands together form the endocrine system
The importance of homeostasis
- Homeosta;c mechanisms help organisms to keep their internal body condi;ons within restricted limits
- 3 key factors to control: temperature, pH, blood glucose conc.
- Stable core temperature and blood pH are vital for enzyme ac;vity – if either are too high or too low it can
nega;vely affect the rate of vital enzyme-controlled reac;ons
, pH
- All enzymes have an op;mum pH and are denatured at pH extremes
- Hydrogen and ionic bonds in the ter;ary structure are broken by excess of H+ or OH- ions in acidic/alkaline
solu;ons -> alters the shape of the ac;ve site -> enzyme-substate complexes form less easily un;l they
cannot form at all -> complete denatura;on of the enzyme
- Op;mal pH of each enzyme is influenced by where it operates in the body
Blood glucose concentra-on
- Conc. of blood glucose is vital as it affects the water poten;al of the blood and the availability of
respiratory substrate for cells
- Normal blood glucose conc. is 90mg per 100cm3 of blood
- Sufficient amount of circula;ng glucose is essen;al for cellular respira;on, brain cells can become rapidly
damaged or die without this, but too much drama;cally affects water poten;al
Stomata
- Plants carry out homeostasis to maintain a constant internal environment e.g. supply of carbon dioxide
- Stomata (especially guard cells) control the diffusion of gases in and out of leaves
- Stomata opening during the day is: 1. Good as carbon dioxide can be gained for photosynthesis, 2. Bad as
leaves lose lots of water through transpira;on
- Stomata closing at night is: 1. Good as water is retained (good during water stress), 2. Bad as supply of
carbon dioxide is reduced so rate of photosynthesis decreases
5.1.2 Principles of Homeostasis
Nega-ve Feedback
- Majority of homeosta;c control mechanisms use nega;ve feedback to maintain homeosta;c balance –
keeping certain physiological factors within specific limits
- Nega;ve feedback control loops involve: 1. A receptor to detect a s;mulus, 2. Coordina;on system
(nervous or endocrine) to transfer informa;on between parts of body, 3. Effector to carry out a response
- The factor/s;mulus is con;nuously monitored, so if it increases the body responds to make it decrease
and vice versa
The benefits of buying summaries with Stuvia:
Guaranteed quality through customer reviews
Stuvia customers have reviewed more than 700,000 summaries. This how you know that you are buying the best documents.
Quick and easy check-out
You can quickly pay through credit card for the summaries. There is no membership needed.
Focus on what matters
Your fellow students write the study notes themselves, which is why the documents are always reliable and up-to-date. This ensures you quickly get to the core!
Frequently asked questions
What do I get when I buy this document?
You get a PDF, available immediately after your purchase. The purchased document is accessible anytime, anywhere and indefinitely through your profile.
Satisfaction guarantee: how does it work?
Our satisfaction guarantee ensures that you always find a study document that suits you well. You fill out a form, and our customer service team takes care of the rest.
Who am I buying these notes from?
Stuvia is a marketplace, so you are not buying this document from us, but from seller alevelrevisionresources. Stuvia facilitates payment to the seller.
Will I be stuck with a subscription?
No, you only buy these notes for £6.99. You're not tied to anything after your purchase.
