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Chapter 1  Communication a)-c). Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to coordinate the activities of different organs.

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chapter 1 communication a c

Chapter 1  Communication a)-c)

Outline the need for communication systems within multicellular organisms, with reference to the need to respond to changes in the internal and external environment and to coordinate the activities of different organs.

State that cells need to communicate with each other by a process called cell signalling.

State that neuronal and hormonal systems are examples of cell signalling.


Sending the message … some definitions



Cell signalling

A chemical secreted by an endocrine gland which brings about a response in an organ elsewhere in the body

Eg: in plants = plant growth regulators such as auxin

A group of axons and dendrons from many neurones surrounded by a protective covering. Transfers an electrical signal/impulse to the synapse

Communication between one cell and another – it can be by chemical or electrical signal!

reflex actions

Let’s think back …

3. Relay neurone in the spinal chord

2. Sensory neurone

4. Motor neurone

1. Receptor

5. Effector

Reflex actions

What are the receptors?


The binding of extracellular signal molecules to either cell-surface receptors or intracellular receptors.

Most signal molecules are hydrophilic and are therefore unable to cross the plasma membrane directly; instead, they bind to cell-surface receptors, which in turn generate one or more signals inside the target cell.

Some small signal molecules, by contrast, diffuse across the plasma membrane and bind to receptors inside the target cell either in the cytosol or in the nucleus (as shown here). Many of these small signal molecules are hydrophobic and nearly insoluble in aqueous solutions; they are therefore transported in the bloodstream and other extracellular fluids after binding to carrier proteins, from which they dissociate before entering the target cell.

nervous vs hormonal signalling
Nervous Vs Hormonal signalling




Summarising cell signalling

Summarise the main similarities and differences between the two types of cell signalling: hormonal and nervous


Cell signalling in action … some real examples

Flight or fight response:

(or on Youtube)

In single cells – chemotaxis of single cells …


And now for something completely different … really! 

  • Communication in plants depends upon chemicals – plant hormones/growth regulators
  • These are produced in small quantities in a variety of tissues, so difficult to study
  • They move either:
    • From cell to cell (diffusion or active transport)
    • Via the xylem and phloem
    • OR don’t move at all!
  • From information so far, some hormones have differing effects according to concentration! They also have different effects in different species, in different tissues and at different stages of development.
  • They also act together as well as alone – all a bit tricky really!

Plant growth hormones - AUXINS

Eg: Indole 3-acetic acid (IAA; ‘auxin’)

Synthesised in the growing tips of roots and shoots

Transported cell-to-cell (and a small amount in phloem) to the rest of the plant

Involvement in growth upwards of a plant – APICAL DOMINANCE


Plant growth hormones - AUXINS

Auxin is synthesised in the apical bud

When a plant has an active growing point at its apex (top) this tends to stop lateral buds (at the side of the stem) from growing – the plant grows UP rather than OUT

If you cut off the top of a plant is cut off then the lateral buds start to grow – so the apex is DOMINANT (hence apical dominance)

Scientists think that auxin is transported down to the apical buds and is found at a concentration that inhibits their growth. Removal of the apical bud causes auxin concentration to drop – although the evidence is contradictory …

…perhaps other plant growth hormones are also involved!


PLENARY – slime mould!

Read all about Slime mould on Text Book p.1

Slime mould time lapse movie